光纤通信复习题英文
光纤通信英文版答案
n1 - n2 , since n1 =1.4692, Δ =0.36%, we can (n1 + n2 ) / 2
1.4639 ,
easily derive that n2 =
Байду номын сангаас
2- Δ 2 - 0.0036 n1 = ? 1.4692 2+ Δ 2 + 0.0036
b.
Pth ( SRS ) ≈
16 Aeff g R Leff
=
16 × 72 µm 2 = 576mw 1 × 10 −13 m / w × 20km
Pth ( SBS ) ≈
21Aeff g B Leff
=
21 × 72 µm 2 = 1.5mw 5 × 10 −11 m / w × 20km
6.7 Solution: a. Because the demands for the speed and quality of communications is insatiable, and any type fiber, including DSF, will never be an end for eliminating dispersion, so we need to cope with dispersion by better means. b. dispersion-shift, dispersion-flatten fibers, chirp grating and so on. 6.9 Solution: Chirped-grating can reflect a set of wavelengths. When the input light beam incidents into the grating, the reflected light will include not only one wavelength. According to the chirped grating design, it includes a various period grating aligned along the fiber axile. The shorter the period of grating, the longer the wavelength it reflects. This effect can be used to compensate the time delays for different wavelengths. 6.16 Solution: a. SPM which stems from the fact that different parts of a propagating pulse have different levels of power is a limitation in a single-channel system while XPM is in a multichannel system whose modulation is induced by the power of the adjacent channel. b. Soliton is a pulse which is able to keep its shape and width steady as a result of mutual compensation of dispersion-broadening and self-phase-modulated
光纤通信系统Optical_Fiber_Communications_英文资料及中文翻译
光纤通信系统Optical Fiber Communications英文资料及中文翻译Communication may be broadly defined as the transfer of information from one point to another .When the information is to be conveyed over any distance a communication system is usually required .Within a communication system the information transfer is frequently achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal .This modulated carrier is then transmitted to the required destination where it is received and the original information signal is obtained by demodulation .Sophisticated techniques have been developed for this process by using electromagnetic carrier waves operating at radio requites as well as microwave and millimeter wave frequencies.The carrier maybe modulated by using either optical an analog digital information signal.. Analog modulation involves the variation of the light emitted from the optical source in a continuous manner. With digital modulation, however, discrete changes in the length intensity are obtained (i.e. on-off pulses). Although often simpler to implement, analog modulation with an optical fiber communication system is less efficient, requiring a far higher signal to noise ratio at the receiver than digital modulation. Also, the linearity needed for analog modulation is mot always provided by semiconductor optical source, especially at high modulation frequencies .For these reasons ,analog optical fiber communications link are generally limited to shorter distances and lower bandwidths than digital links .Initially, the input digital signal from the information source is suitably encoded for optical transmission .The laser drive circuit directly modulates the intensity of the semiconductor last with the encoded digital signal. Hence a digital optical signal is launched into the optical fiber cable .The avalanche photodiode detector (APD) is followed by a front-end amplifier and equalizer or filter to provide gain as well as linear signal processing and noise bandwidth reduction. Finally ,the signal obtained isdecoded to give the original digital information .Generating a Serial SignalAlthough a parallel input-output scheme can provide fast data transfer and is simple in operation, it has the disadvantage of requiring a large number of interconnections. As an example typical 8 bit parallel data port uses 8 data lines, plus one or two handshake lines and one or more ground return lines. It is fairly common practice to provide a separate ground return line for each signal line, so an 8 bit port could typically use a 20 core interconnection cable. Whilst such a multi way cable is quite acceptable for short distance links, up to perhaps a few meters, it becomes too expensive for long distance links where, in addition to the cost of the multiword cable, separate driver and receiver circuits may be required on each of the 10 signal lines. Where part of the link is to be made via a radio link, perhaps through a space satellite, separate radio frequency channels would be required for each data bit and this becomes unacceptable.An alternative to the parallel transfer of data is a serial in which the states of the individual data bits are transmitted in sequence over a single wire link. Each bit is allocated a fixed time slot. At the receiving end the individual bit states are detected and stored in separate flip-flop stages, so that the data may be reassembled to produce a parallel data word. The advantage of this serial method of transmission is that it requires only one signal wire and a ground return, irrespective of the number of bits in the data word being transmitted. The main disadvantage is that the rate at which data can be transferred is reduced in comparison with a parallel data transfer, since the bits are dealt with in sequence and the larger the number of bits in the word, the slower the maximum transfer speed becomes. For most applications however, a serial data stream can provide a perfectly adequate data transfer rate . This type of communication system is well suited for radio or telephone line links, since only one communication channel is required to carry the data.We have seen that in the CPU system data is normally transferred in parallel across the main data bus, so if the input -output data is to be in serial form, then a parallel to serial data conversion process is required between the CPU data bus andthe external I/O line. The conversion from parallel data to the serial form could be achieved by simply using a multiplexed switch, which selects each data bit in turn and connects it to the output line for a fixed time period. A more practical technique makes use of a shift register to convert the parallel data into serial form.A shift register consists of a series of D type flip-flops connected in a chain, with the Q output of one flip-flop driving the D input of the next in the chain. All of the flip-flops ate clocked simultaneously by a common clock pulse, when the clock pulse occurs the data stored in each flip-flop is transferred to the next flip-flop to the right in the chain. Thus for each clock pulse the data word is effectively stepped along the shift register by one stage, At the end of the chain the state of the output flip-flop will sequence through the states of the data bits originally stored in the register. The result is a serial stream of data pulses from the end of the shift register.In a typical parallel to serial conversion arrangement the flip-flops making up the shift register have their D input switchable. Initially the D inputs are set up in a way so that data can be transferred in parallel from the CPU data bus into the register stages. Once the data word has been loaded into the register the D inputs are switched so that the flip-flops from a shift register .Now for each successive clock pulse the data pattern is shifted through the register and comes out in serial form at the right hand end of the register.At the receiving end the serial data will usually have to be converted back into the parallel form before it can be used. The serial to parallel conversion process can also be achieved by using a shift register .In this case the serial signal is applied to the D input of the stage at the left hand end of the register. As each serial bit is clocked into the register the data word again moves step by step to the right, and after the last bit has been shifted in the complete data word will be assembled within the register .At this point the parallel data may be retrieved by simply reading out the data from individual register stages in parallel It is important that the number of stages in the shift register should match the number of bits in the data word, if the data is to be properly converted into parallel form.To achieve proper operation of the receiving end of a serial data link, it isimportant that the clock pulse is applied to the receive shift register at a time when the data level on the serial line is stable. It is possible to have the clock generated at either end of the link, but a convenient scheme is to generate the clock signal at the transmitting end (parallel-serial conversion )as the master timing signal. To allow for settling time and delays along the line, the active edge of the clock pulse at the receive end is delayed relative to that which operates the transmit register. If the clock is a square wave the simples approach might be to arrange that the transmit register operates on the rising edge of the clock wave, and the receive register on the falling edge, so that the receiver operates half a clock period behind the transmitter .If both registers operate on arising edge, the clock signal from the transmitter could be inverted before being used to drive the receive shifty register.For an 8 bit system a sequence of 8 clock pulses would be needed to send the serial data word .At the receiving end the clock pulses could be counted and when the eighth pulse is reached it might be assumed that the data in the receive register is correctly positioned, and may be read out as parallel data word .One problem here is that, if for some reason the receive register missed a clock pulse ,its data pattern would get out of step with the transmitted data and errors would result. To overcome this problem a further signal is required which defines the time at which the received word is correctly positioned in the receive shift register and ready for parallel transfer from the register .One possibility is to add a further signal wire along which a pulse is sent when the last data bit is being transmitted, so that the receiver knows when the data word is correctly set up in its shift register. Another scheme might be to send clock pulses only when data bits are being sent and to leave a timing gap between the groups of bits for successive data words. The lack of the clock signal could then be detected and used to reset the bit counter, so that it always starts at zero at the beginning of each new data word.Serial and Parallel Data lion is processed. Serial indicates that the information is handled sequentially, similar to a group of soldiers marching in single file. In parallel transmission the info The terms serial and parallel are often used in descriptions of data transmission techniques. Both refer to the method by which information isdivided in to characters, words, or blocks which are transmitted simultaneously. This could be compared to a platoon of soldiers marching in ranks.The output of a common type of business machine is on eight—level punched paper tape, or eight bits of data at a time on eight separate outputs. Each parallel set of eight bits comprises a character, and the output is referred to as parallel by bit, serial by character. The choice of cither serial or parallel data transmission speed requirements.Business machines with parallel outputs, how—ever, can use either parallel outputs, how—ever, can use either direct parallel data trans—mission or serial transmission, with the addition of a parallel—to—serial converter at the interface point of the business machine and the serial data transmitter. Similarly, another converter at the receiving terminal must change the serial data back to the parallel format.Both serial and parallel data transmission systems have inherent advantages which are some—what different. Parallel transmission requires that parts of the available bandwidth be used as guard bands for separating each of the parallel channels, whereas serial transmission systems can use the entire linear portion of the available band to transmit data, On the other hand, parallel systems are convenient to use because many business machines have parallel inputs and outputs. Though a serial data set has the added converters for parallel interface, the parallel transmitter re—quires several oscillators and filters to generate the frequencies for multiplexing each of the side—by—side channels and, hence, is more susceptible to frequency error.StandardsBecause of the wide variety of data communications and computer equipment available, industrial standards have been established to provide operating compatibility. These standards have evolved as a result of the coordination between manufacturers of communication equipment and the manufacturers of data processing equipment. Of course, it is to a manufacturer’s advantage to provide equipment that isuniversally acceptable. It is also certainly apparent that without standardization intersystem compatibility would be al—most impossible.Organizations currently involved in uniting the data communications and computer fields are the CCITT, Electronic Industries Association (EIA), American Standards Association (ASA), and IEEE.A generally accepted standard issued by the EIA, RS—232—B, defines the characteristics of binary data signals, and provides a standard inter—face for control signals between data processing terminal equipment and data communications equipment. As more and more data communications systems are developed, and additional ways are found to use them, the importance ways are found to use them, the importance of standards will become even more significant.Of the most important considerations in transmitting data over communication systems is accuracy. Data signals consist of a train of pulses arranged in some sort of code. In a typical binary system, for example, digits 1 and 0 are represented by two different pulse amplitudes. If the amplitude of a pulse changes beyond certain limits during transmission, the detector at the receiving end may produce the wrong digit, thus causing an error.It is very difficult in most transmission systems to completely avoid. This is especially true when transmission system designed for speech signals. Many of the inherent electrical characteristics of telephone circuits have an adverse effect on digital signals.Making the circuits unsatisfactory for data transmission—especially treated before they can be used to handle data at speeds above 2000 bits per second.V oice channels on the switched (dial—up) telephone network exhibit certain characteristics which tend to distort typical data signal waveforms. Since there is random selection of a particular route for the data signal with each dialed connection, transmission parameters will generally change, sometimes upsetting the effect of built—in compensationNetworks. In addition, the switched network cannot be used of for large multipleaddress data systems using time sharing. Because of these considerations, specially treated voice bandwidth circuits are made available for data use. The characteristics and costs of these point—to—point private lines are published in document called tariffs, which are merely regulatory agreements reached by the FCC, state public utilities commissions, and operating telephone companies regarding charges for particular types of telephone circuits. The main advantage of private or dedicated facilities is that transmission characteristics are fixed and remain so for all data communications operations.Correlative TechniqueCorrelative data transmission techniques, particularly the Duobinary principle, have aroused considerable interest because of the method of converting a binary signal into three equidistant levels. This correlative scheme is accomplished in such a manner that the predetermined level depends on past signal history, forming the signal so that it never goes from one level extreme to another in one bit interval.The most significant property of the Duobinary process is that it affords a two—to—one bandwidth compression relative to binary signaling, or equivalently twice the speed capability in bits per second for a fixed bandwidth. The same speed capability for a multilevel code would normally require four levels, each of which would represent two binary digits.The FutureIt is universally recognized that communication is essential at every level of organization. The United States Government utilizes vast communications network for voice as well as data transmission. Likewise, business need communications to carry on their daily operations.The communications industry has been hard at work to develop systems that will transmit data economically and reliably over both private—line and dial up telephone circuits. The most ardent trend in data transmission today is toward higher speeds over voice—grade telephone channels. New transmission and equalization techniques now being investigated will soon permit transmitting digital data over telephone channels at speeds of 4800 bits per second or higher.To summarize: The major demand placed on telecommunications systems is for more information-carrying capacity because the volume of information produced increases rapidly. In addition, we have to use digital technology for the high reliability and high quality it provides in the signal transmission. However, this technology carries a price: the need for higher information-carrying capacity.The Need for Fiber-Optic Communications Systems The major characteristic of a telecommunications system is unquestionably its information-carrying capacity, but there are many other important characteristics. For instance, for a bank network, security is probably more important than capacity. For a brokerage house, speed of transmission is the most crucial feature of a network. In general, though, capacity is priority one for most system users. And there’s the rub. We cannot increase link capacity as much as we would like. The major limit is shown by the Shannon-Hartley theorem,Where C is the information-carrying capacity(bits/sec), BW is the link bandwidth (Hz=cycles/sec), and SNR is the signal-to-noise power ratio.Formula 1.1 reveals a limit to capacity C; thus, it is often referred to as the “ Shannon limit.” The formula, which comes from information theory, is true regardless of specific technology. It was first promulgated in 1948 by Claude Shannon, a scientist who worked at Bell Laboratories. R. V. L. Hartley, who also worked at Bell Laboratories, published a fundamental paper 20 years earlier, a paper that laid important groundwork in information theory, which is why his name is associated with Shannon’s formula.The Shannon-Hartley theorem states that information-carrying capacity is proportional to channel bandwidth, the range of frequencies within which the signals can be transmitted without substantial attenuation.What limits channel bandwidth? The frequency of the signal carrier. The higher the carrier’s frequency, the greater the channel bandwidth and the higher the information-carrying capacity of the system. The rule of thumb for estimating possible order of values is this: Bandwidth is approximately 10 percent of the carrier-signal frequency. Hence, if a microwave channel uses a 10-GHz carrier signal.Then its bandwidth is about 100 MHz.A copper wire can carry a signal up to 1 MHz over a short distance. A coaxial cable can propagate a signal up to 100 MHz. Radio frequencies are in the range of 500 KHz to 100 MHz. Microwaves, including satellite channels, operate up to 100 GHz. Fiber-optic communications systems use light as the signal carrier; light frequency is between 100 and 1000 THz; therefore, one can expect much more capacity from optical systems. Using the rule of thumb mentioned above, we can estimate the bandwidth of a single fiber-optic communication link as 50 THz.To illustrate this point, consider these transmission media in terms of their capacity to carry, simultaneously, a specific number of one-way voice channels. Keep in mind that the following precise value. A single coaxial cable can carry up to 13,000 channels, a microwave terrestrial link up to 20,000 channels, and a satellite link up to 100,000 channels. However, one fiber-optic communications link, such as the transatlantic cable TAT-13, can carry 300,000 two-way voice channels simultaneously. That’s impressive and explains why fiber-optic communications systems form the backbone of modern telecommunications and will most certainly shape its future.To summarize: The information-carrying capacity of a telecommunications system is proportional to its bandwidth, which in turn is proportional to the frequency of the carrier. Fiber-optic communications systems use light-a carrier with the highest frequency among all the practical signals. This is why fiber-optic communications systems have the highest information-carrying capacity and this is what makes these systems the linchpin of modern telecommunications.To put into perspective just how important a role fiber-optic communications will be playing in information delivery in the years ahead, consider the following statement from a leading telecommunications provider: “ The explosive growth of Internet traffic, deregulation and the increasing demand of users are putting pressure on our customers to increase the capacity of their network. Only optical networks can deliver the required capacity, and bandwidth-on-demand is now synonymous with wavelength-on-demand.” Th is statement is true not only for a specific telecommunications company. With a word change here and there perhaps, but withthe same exact meaning, you will find telecommunications companies throughout the world voicing the same refrain.A modern fiber-optic communications system consists of many components whose functions and technological implementations vary. This is overall topic of this book. In this section we introduce the main idea underlying a fiber-optic communications system.Basic Block DiagramA fiber-optic communications system is a particular type of telecommunications system. The features of a fiber-optic communications system can be seen in Figure 1.4, which displays its basic block diagram.Information to be conveyed enters an electronic transmitter, where it is prepared for transmission very much in the conventional manner-that is, it is converted into electrical form, modulated, and multiplexed. The signal then moves to the optical transmitter, where it is converted into optical detector converts the light back into an electrical signal, which is processed by the electronic receiver to extract the information and present it in a usable form (audio, video, or data output).Let’s take a simple example that involves Figures 1.1, 1.3, and 1.4 Suppose we need to transmit a voice signal. The acoustic signal (the information) is converted into electrical form by a microphone and the analog signal is converted into binary formby the PCM circuitry. This electrical digital signal modulates a light source and the latter transmits the signal as a series of light pulses over optical fiber. If we were able to look into an optical fiber, we would see light vary between off and on in accordance with the binary number to be transmitted. The optical detector converts the optical signal it receives into a set of electrical pulses that are processed by an electronic receiver. Finally, a speaker converts the analog electrical signal into acoustic waves and we can hear sound-delivered information.Figure 1.4 shows that this telecommunications system includes electronic components and optical devices. The electronic components deal with information in its original and electrical forms. The optical devices prepare and transmit the light signal. The optical devices constitute a fiber-optic communications system.TransmitterThe heart of the transmitter is a light source. The major function of a light source is to convert an information signal from its electrical form into light. Today’sfiber-optic communications systems use, as a light source, either light-emitting diodes (LEDs) or laser diodes (LDs). Both are miniature semiconductor devices that effectively convert electrical signals are usually fabricated in one integrated package. In Figure 1.4, this package is denoted as an optical transmitter. Figure 1.5 displays the physical make-up of an LED, an LD, and integrated packages.Optical fiberThe transmission medium in fiber-optic communications systems is an optical fiber. The optical fiber is the transparent flexible filament that guides light from a transmitter to a receiver. An optical information signal entered at the transmitter end of a fiber-optic communications system is delivered to the receiver end by the optical fiber. So, as with any communication link, the optical fiber provides the connection between a transmitter and a receiver and, very much the way copper wire and coaxial cable conduct an electrical signal, optical fiber “ conducts” light.The optical fiber is generally made from a type of glass called silica or, less commonly nowadays, from plastic. It is about a human hair in thickness. To protect very fragile optical fiber from hostile environments and mechanical damage, it is usually enclosed in a specific structure. Bare optical fiber, shielded by its protective coating, is encapsulated use in a host of applications, many of which will be covered in subsequent chaptersReceiver The key component of an optical receiver is its photodetector. The major function of a photodetector is to convert an optical information signal back into an electrical signal (photocurrent). The photodetector in today's fiver-optic communications systems is a semiconductor photodiode (PD). This miniature device is usually fabricated together with its electrical circyitry to form an integrated package that provides power-supply connections and signal amplification. Such an integrated package is shown in Figure 1.4 as an optical receiver. Figure 1.7 shows samples of a photodiode and an integrated package.The basic diagram shown in Figure 1.4 gives us the first idea of what a fiber-optic communications system is and how it works. All the components of this point-to-point system are discussed in detail in this book. Particular attention is given to the study of networks based on fiber-optic communications systems.The role of Fiber-Optic Communications Technology has not only already changed the landscape of telecommunications but it is still doing so and at a mind-boggling pace. In fact, because of the telecommunications industry's insatiable appetite for capacity, in recent years the bandwidth of commercial systems has increased more than a hundredfold. The potential information-carrying capacity of a single fiber-optic channel is estimated at 50 terabits a second (Tbit/s) but, from apractical standpoint, commercial links have transmitted far fewer than 100 Gbps, an astoundingamount of data in itself that cannot be achieved with any other transmission medium. Researchers and engineers are working feverishly to develop new techniques that approach the potential capacity limit.Two recent major technological advances--wavelength-division multiplexing (WDM) anderbium-doped optical-fiber amplifiers (EDFA)--have boosted the capacity of existing system sand have brought about dramatic improvements in the capacity of systems now in development. In fact,' WDM is fast becoming the technology of choice in achieving smooth, manageable capacity expansion.The point to bear in mind is this: Telecommunications is growing at a furious pace, and fiber-optic communications is one of its most dynamically moving sectors. While this book refleets the current situation in fiber-optic communications technology, to keep yourself updated, you have to follow the latest news in this field by reading the industry's trade journals, attending technical conferences and expositions, and finding the time to evaluate the reams of literature that cross your desk every day from companies in the field.光纤通信系统一般的通信系统由下列部分组成：(1) 信息源。
光纤通信英文版常见中英对照单词表
AAbsorption coefficient 吸收系数ac alternating current 交变电流交流Acoustic phonon 声学声子Active component 有源器件AM amplitude modulation 幅度调制AM，FM，PM：幅度/频率/相位调制AON all-optical network 全光网络AOTF acoustic optic tunable filter 声光调制器APD avalanche photodiode 雪崩二极管AR coatings antireflection coatings 抗反膜ASE amplified spontaneous emission 放大自发辐射ASK amplitude shift keying 幅移键控ASK/FSK/PSK 幅/频/相移键控ATM asynchronous transfer mode 异步转移模式Attenuation coefficient 衰减系数Attenuator 衰减器Auger recombination：俄歇复合AWG arrayed-waveguide grating 阵列波导光栅BBand gap：带隙Band pass filter 带通滤波器Beam divergence 光束发散BER bit error rate 误码率BER：误码率BH buried heterojunction 掩埋异质结Binary representation 二进制表示方法Binary 二进制Birefringence 双折射Birefringence双折射Bitrate-distance product 比特距离的乘积Block diagram 原理图Boltzman statistics：玻尔兹曼统计分布BPF band pass filter 带通滤波器Bragg condition 布拉格条件Bragg diffraction 布拉格衍射Brillouin scattering 布里渊散射Brillouin shift 布里渊频移Broad area 宽面Buried heterostructure 掩埋异质结CC3 cleaved-coupled cavity 解理耦合腔Carrier lifetime：载流子寿命CATV common antenna cable television 有线电视CDM code division multiplexing 码分复用Characteristics temperature 特征温度Chirp 啁啾Chirped Gaussian pulse 啁啾高斯脉冲Chromatic dispersion 色度色散Chromatic dispersion 色度色散Cladding layer：包层Cladding 包层CNR carrier to noise ratio 载噪比Conduction band：导带Confinement factor 限制因子Connector 连接头Core cladding interface 纤芯包层界面Core-cladding interface 芯层和包层界面Coupled cavity 耦合腔CPFSK continuous-phase frequency-shift keying 连续相位频移键控Cross-phase modulation 交叉相位调制Cross-talk 串音CSO Composite second order 复合二阶CSRZ：载波抑制归零码Cutoff condition 截止条件CVD chemical vapour deposition 化学汽相沉积CW continuous wave 连续波Cylindrical preform：预制棒DDBR distributed Bragg reflector 分布布拉格反射DBR: distributed Bragg reflector 分布式布拉格反射器dc direct current 直流DCF dispersion compensating fiber 色散补偿光纤Depressed-cladding fiber: 凹陷包层光纤DFB distributed feedback 分布反馈DFB: Distributed Feedback 分布式反馈Differential gain 微分增益Differential quantum efficiency 微分量子效率Differential-dispersion parameter：微分色散参数Diffusion 扩散Digital hierarchy 数字体系DIP dual in line package 双列直插Direct bandgap：直接带隙Directional coupler 定向耦合器Dispersion compensation fiber：色散补偿光纤Dispersion decreasing fiber：色散渐减光纤Dispersion parameter：色散参数Dispersion shifted fiber 色散位移光纤Dispersion slope 色散斜率Dispersion slope：色散斜率Dispersion-flatten fiber：色散平坦光纤Dispersion-shifted fiber：色散位移光纤Double heterojunction 双异质结Double heterostructure：双异质结Doubly clad：双包层DPSK differential phase-shift keying 差分相移键控Driving circuit 驱动电路Dry fiber 无水光纤DSF dispersion shift fiber 色散位移光纤DWDM dense wavelength divisionmultiplexing/multiplexer密集波分复用/器DWDM: dense wavelength division multiplexing密集波分复用E~GEDFA erbium doped fiber amplifier 掺铒光纤激光器Edge emitting LED 边发射LEDEdge-emitting 边发射Effective index 有效折射率Eigenvalue equation 本征值方程Elastic scattering 弹性散射Electron-hole pairs 电子空穴对Electron-hole recombination 电子空穴复合Electron-hole recombination：电子空穴复合Electrostriction 电致伸缩效应Ethernet 以太网External cavity 外腔External quantum efficiency 外量子效率Extinction ratio 消光比Eye diagram 眼图FBG fiber-bragg grating 光纤布拉格光栅FDDI fiber distributed data interface 光纤数据分配接口FDM frequency division multiplexing频分复用FDM：频分复用Fermi level 费米能级Fermi level：费米能级Fermi-Dirac distribution：费米狄拉克分布FET field effect transistor 场效应管Fiber Manufacturing：光纤制作Field radius 模场半径Filter 滤波器Flame hydrolysis 火焰裂解FM frequency modulation 频率调制Forward-biased ：正向偏置FP Fabry Perot 法布里-珀落Free spectral range 自由光谱范围Free－space communication 自由空间光通信系统Fresnel transmissivity 菲涅耳透射率Front end 前端Furnace 熔炉FWHM full width at half maximum 半高全宽FWHM: 半高全宽FWM four-wave mixing 四波混频Gain coefficient 增益系数Gain coupled 增益耦合Gain-guided semiconductor laser 增益波导半导体激光器Germania 锗GIOF graded index optical fiber 渐变折射率分布Graded-index fiber 渐变折射率光纤Group index 群折射率GVD group-velocity dispersion 群速度色散GVD: 群速度色散H~LHBT heterojunction-bipolar transistor异质结双极晶体管HDTV high definition television 高清晰度电视Heavy doping：重掺杂Heavy-duty cable 重型光缆Heterodyne 外差Heterojunction：异质结HFC hybrid fiber-coaxial 混合光纤/电缆Higher-order dispersion 高阶色散Highpass filter 高通滤波器Homodyne 零差Homojunction：同质结IC integrated circuit 集成电路IM/DD intensity modulation with direct detection 强度调制直接探测IM/DD: 强度调制/直接探测IMD intermodulation distortion 交互调制失真Impulse 冲激Impurity 杂质Index-guided 折射率导引Indirect bandgap：非直接带隙Inelastic scattering 非弹性散射Inhomogeneous非均匀的Inline amplifier 在线放大器Intensity noise 强度噪声Intermodal dispersion：模间色散Intermode dispersion 模间色散Internal quantum efficiency：内量子效率Intramodal dispersion: 模内色散Intramode dispersion 模内色散Intrinsic absorption 本征吸收ISDN integrated services digital network 综合业务数字网ISI intersymbol interference 码间干扰Isotropic 各向同性Jacket 涂层Jitter 抖动Junction：结Kinetic energy：动能Lambertian source 朗伯光源LAN local-area network 局域网Large effective-area fiber 大有效面积发光Laser threshold 激光阈值Laser 激光器Lateral mode 侧模Lateral 侧向Lattice constant：晶格常数Launched power 发射功率LD laser diode 激光二极管LD：激光二极管LED light emitting diode 发光二极管LED: 发光二极管L-I light current 光电关系Light-duty cable 轻型光缆Linewidth enhancement factor 线宽加强因子Linewidth enhancement factor 线宽增强因子Linewidth 线宽Longitudinal mode 纵模Longitudinal model 纵模Lowpass filter 低通滤波器LPE liquid phase epitaxy 液相外延LPE：液相外延M~NMacrobending 宏弯MAN metropolitan-area network 城域网Material dispersion 材料色散Material dispersion：材料色散Maxwell’s equations 麦克斯韦方程组MBE molecular beam epitaxy 分子束外延MBE：分子束外延MCVD Modified chemical vapor deposition改进的化学汽相沉积MCVD：改进的化学汽相沉积Meridional rays 子午光线Microbending 微弯Mie scattering 米氏散射MOCVD metal-organic chemical vapor deposition金属有机物化学汽相沉积MOCVD：改进的化学汽相沉积Modal dispersion 模式色散Mode index 模式折射率Modulation format 调制格式Modulator 调制器MONET Multiwavelength optical network 多波长光网络MPEG motion-picture entertainment group视频动画专家小组MPN mode-partition noise 模式分配噪声MQW multiquantum well 多量子阱MQW: 多量子阱MSK minimum-shift keying 最小频偏键控MSR mode-suppression ratio 模式分配噪声MSR: Mode suppression ratio 模式抑制比Multimode fiber 多模光纤MZ mach-Zehnder 马赫泽德NA numerical aperture 数值孔径Near infrared 近红外NEP noise-equivalent power 等效噪声功率NF noise figure 噪声指数Nonradiative recombination 非辐射复合Nonradiative recombination：非辐射复合Normalized frequency 归一化频率NRZ non-return to zero 非归零NRZ：非归零码NSE nonlinear Schrodinger equation 非线性薛定额方程Numerical aperture 数值孔径Nyquist criterion 奈奎斯特准则O P QOC optical carrier 光载波OEIC opto-electronic integrated circuit 光电集成电路OOK on-off keying 开关键控OOK：通断键控OPC optical phase conjugation 光相位共轭Optical mode 光模式Optical phase conjugation 光相位共轭Optical soliton 光孤子Optical switch 光开关Optical transmitter 光发射机Optical transmitter：光发射机OTDM optical time-division multiplexing 光时分复用OVD outside-vapor deposition 轴外汽相沉积OVD：轴外汽相沉积OXC optical cross-connect 光交叉连接Packaging 封装Packet switch 分组交换Parabolic-index fiber 抛物线折射率分布光纤Passive component 无源器件PCM pulse-code modulation 脉冲编码调制PCM：脉冲编码调制PCVD：等离子体化学汽相沉积PDF probability density function 概率密度函数PDM polarization-division multiplexing 偏振复用PDM：脉冲宽度调制Phase-matching condition 相位匹配条件Phase-shifted DFB laser 相移DFB激光器Photon lifetime 光子寿命PMD 偏振模色散Polarization controller 偏振控制器Polarization mode dispersion：偏振模色散Polarization 偏振PON passive optical network 无源接入网Population inversion：粒子数反转Power amplifier 功率放大器Power-conversion efficiency 功率转换效率PPM：脉冲位置调制Preamplifer 前置放大器PSK phase-shift keying 相移键控Pulse broadening 脉冲展宽Quantization noise 量化噪声Quantum efficiency 量子效率Quantum limit 量子极限Quantum limited 量子极限Quantum noise 量子噪声RRA raman amplifier 喇曼放大器Raman scattering 喇曼散射Rate equation 速率方程Rayleigh scattering 瑞丽散射Rayleigh scattering 瑞利散射Receiver sensitivity 接收机灵敏度Receiver 接收机Refractive index 折射率Regenerator 再生器Repeater spacing 中继距离Resonant cavity 谐振腔Responsibility 响应度Responsivity 响应度Ridge waveguide laser 脊波导激光器Ridge waveguide 脊波导RIN relative intensity noise 相对强度噪声RMS root-mean-square 均方根RZ return-to-zero 归零RZ: 归零码SSAGCM separate absorption, grading, charge, and multiplication吸收渐变电荷倍增区分离APD的一种SAGM separate absorption and multiplication吸收渐变倍增区分离APD的一种SAM separate absorption and multiplication吸收倍增区分离APD的一种Sampling theorem 抽样定理SBS 受激布里渊散射SBS stimulated Brillouin scattering 受激布里渊散射SCM subcarrier multiplexing 副载波复用SDH synchronous digital hierarchy 同步数字体系SDH：同步数字体系Self-phase modulation 自相位调制Sellmeier equation：塞米尔方程Sensitivity degradation 灵敏度劣化Sensitivity 灵敏度Shot noise 散粒噪声Shot noise 散粒噪声Single-mode condition 单模条件Sintering ：烧结SIOF step index optical fiber 阶跃折射率分布SLA/SOA semiconductor laser/optical amplifier 半导体光放大器SLM single longitudinal mode 单纵模SLM: Single Longitudinal mode单纵模Slope efficiency 斜率效率SNR signal-to-noise ratio 信噪比Soliton 孤子SONET synchronized optical network 同步光网络SONET：同步光网络Spectral density：光谱密度Spontaneous emission：自发辐射Spontaneous-emission factor 自发辐射因子SRS 受激喇曼散射SRS stimulated Raman scattering 受激喇曼散射Step-index fiber 阶跃折射率光纤Stimulated absorption：受激吸收Stimulated emission：受激发射STM synchronous transport module 同步转移模块STM：同步转移模块Stripe geometry semiconductor laser 条形激光器Stripe geometry 条形STS synchronous transport signal 同步转移信号Submarine transmission system 海底传输系统Substrate:衬底Superstructure grating 超结构光栅Surface emitting LED 表面发射LEDSurface recombination：表面复合Surface-emitting 表面发射TTCP/IP transmission control protocol/internet protocol传输控制协议/互联网协议TDM time-division multiplexing 时分复用TDM：时分复用TE transverse electric 横电模Ternary and quaternary compound：三元系和四元系化合物Thermal equilibrium：热平衡Thermal noise 热噪声Thermal noise 热噪声Threshold current 阈值电流Timing jitter 时间抖动TM transverse magnetic 横磁Total internal reflection 全内反射Transceiver module 收发模块Transmitter 发射机Transverse 横向Transverse mode 横模TW traveling wave 行波U ~ ZVAD vapor-axial epitaxy 轴向汽相沉积VAD：轴向沉积Valence band：价带VCSEL vertical-cavity surface-emitting laser垂直腔表面发射激光器VCSEL: vertical cavity surface-emitting lasers 垂直腔表面发射激光器VPE vapor-phase epitaxy 汽相沉积VPE：汽相外延VSB vestigial sideband 残留边带Wall-plug efficiency 电光转换效率WAN wide-area network 广域网Waveguide dispersion 波导色散Waveguide dispersion：波导色散Waveguide imperfection 波导不完善WDMA wavelength-division multiple access 波分复用接入系统WGA waveguide-grating router 波导光栅路由器White noise 白噪声XPM cross-phase modulation 交叉相位调制YIG yttrium iron garnet 钇铁石榴石晶体Zero-dispersion wavelength 零色散波长Zero-dispersion wavelength：零色散波长。
通信工程专业英语习题
第一课1.将下述句子译成英文。
(1) An analog information source produces messages that are defined on a continuum, whilea digital information source produces a finite set of possible messages.(2) The beacon-fire tower in ancient China was a communications system.(3) Show that the entropy is a maximum when the probability of sending a binary 1 is equalto the probability of sending a binary 0 .(4) Information capacity is a measure of how much information can be transferred through acommunications system in a given period of time .(5) The wider the bandwidth and the longer the time of transmission, the more informationcan be conveyed through the system .2.Answer the following questions :(1) Samuel Morse developed the first electronic communications system in 1837 .(2) Y es.(3) The vacuum-tube triode .(4) Hartley’s law simply states that the wider the bandwidth and the longer the transmissiontime, the more information that can be conveyed through the system . The Shannon’s formula is I=B log2(1+S/N) , where I=information capacity(bps), B=bandwidth(Hz), S/N=signal-to-noise power ratio(unitless) .(5) (a) VLF, (b) MF, (c) SHF第二章信息源1.根据课文回答下列问题。
武汉理工大学光纤通信2015年试题
一 Consider a multimode silica fiber that has core refractive index 1 1.480n =and a cladding index 2 1.478n =. Find (a) the critical angel, (b) the numerical aperture, and (c) the acceptance angel.解：（a ）由式21sin c n n ϕ=可以求得临界角 （b ）由式122212sin ()2A NA n n n n θ==-≈可以计算出数值孔径（c ）由式12220,max 112sin sin sin ()A c n n n n n θθθ===-可以求得出空气中的接受角为二、Consider a multimode step-index fiber with a 62.5- m μcore diameter and a core-cladding index difference of 1.5 percent. If the core refractive index is 1.480, estimate the the total number of modes supported in the fiber at a wavelength of 850nm.Solution ： the normalized frequency is 2aV n πλ≈, the total number of modesis 22V M =三suppose we have a multimode step-index optical fiber that has a core radius of 25m μ,a core index of 1.480 and an index difference 0.01∆=.What are the number of modes in the fiber at wavelengths 860, 1310, and 1550nm. 解：首先由22a V n πλ=计算出V 值，再利用212M V =可以计算出总模数。
光纤通信必考填空题、计算题及答案知识点
光纤通信必考填空题、计算题及其答案知识点一、填空题1The main constituents of an optical fiber communications link . The key sections are a transmitter consisting of a light source and its associated drive circuitry, a cable offering mechanical and environmental protection to the optical fibers contained inside, and a receiver consisting of a photodector plus amplification and signal-restoring circuitry.光纤通信链路的主要成分。
的关键部分是一个发射机包括一个光源及其相关的驱动电路，一个电缆提供机械和环境保护于光纤内部包含，和一个接收器包括一个光电探测器加放大和信号复原电路。
2Attenuation of a light signal as it propagates along a fiber is an important consideration in the design of an optical communication system, the basic attenuation mechanisms in a fiber are absorption, scattering, and radiative losses of the optical energy.因为它传播沿纤维是在光通信系统的设计中的重要考虑因素的光信号的衰减，在一个光纤中的基本衰减机制是吸收，散射，以及光学能量的辐射损失。
3Intermodal dispersion or modal delay appears only in multimode fibers. This signal-distorting mechanism is a result of each mode having a different value of the group velocity at a single frequency.模间色散或模延迟只出现在多模光纤。
通信英语综合练习题.doc
《通信英语》综合练习题（即课后练习题）（第一章）•请将下述词组译成英文：抽样量化与编码话路幅值抽样频率抽样速率脉冲流重复率编码过程模拟信号传输质量数字通信数字传输含噪声的环境传输路由信噪比信号电平地面系统噪声功率二进制传输反向操作8位码序列接收端帧格式同步宁二•请将下述词组译成中文：1.the schemes for performing these three functions2.the series of amplitude values3.the speech channel of telephone quality4.the sequence of 8~binary digits5.the minimum theoretical sampling frequency6.the voice channel occupying the range 300 Hz to 3. 4 kHz7.the 8~digits per sample value8.the sparking of a car ignition system9.the stream of the pulses with a repetition rate of 64 kHz10.the relationship of the true signal to the noise signal11.the signal received from a satellite12.the complete information about a particular message13.the shape of the transmitted signal14.the a/ttenuation introduced by transmission path15.the unit that converts sampled amplitude value to a set of pulses16.the sequence relating to channel 1, 2 and so on17.the unique sequence of pulses called synchronization word18.the terrestrial system19.the presence or absence of the pulse20.the high-speed electronic switch21.the time division multiplexer22.the Time Division Multiplexing五.请将下述短文译成中文：1.If we consider binary transmission, the complete information about aparticular message will always be obtained by simply detecting the presence or absence of the pulse. By comparison, most other forms of transmission systems convey the message information using the shape, or level of the transmittedsignal; parameters that are most easily affected by the noise and attenuation introduced by the transmission path. Consequently there is an inherentadvantage for overcoming noisy environments by choosing digital transmission.2.The reader may ask, how does the demultiplexer know which group of 8~digitsrelates to channel 1, 2, and so on? Clearly this is important! The problem is easily overcome by specifying a frame format, where at the start of each framea unique sequence of pulses called the frame code, or synchronization word, isplaced so as to identify the start of the frame. A circuit of thedemultiplexer is arranged to detect the synchronization word, and thereby itknows that the next group of 8~digits corresponds to channel 1.3.Noise can be introduced into transmission path in many different ways; perhapsvia a nearby lightning strike, the sparking of a car ignition system, or thethermal low-level noise within the communication equipment it self. It is the rela tio nship of the t rue signal to the noise signal, known as the signal一to-noise ratio, which is of most interest to the communication engineer・4.Basically, if the signal is very large compared to the noise level, then aperfect message can take place; however, this is not always the case. Forexample, the signal received from a satellite, located in far outer space, is very week and is at a level only slightly above that of the noise・Alternative examples may be found within terrestrial systems where, althoughthe message signal is strong, so is the noise power・5.So far we have assumed that each voice channel has a separate coder, the unitthat converts sampled amplitude values to a set of pulses; and decoder, theunit that performs the reverse operation. This need not be so, and systems are in operation where a single codec is shared between 24, 30, or even 120separate channels.6.A high-speed electronic switch is used to present the analog informationsignal of each channel, taken in tern, to the codec. The codec is thenarranged to sequentially sample the amplitude value, and code this value into the 8 - dig it sequence. Thus the output to the codec may be seen as asequence of 8 pulses relating to channel 1, then channel 2, and so on. Thisunit is called a time division multiplexer.（第九章）一.请将下述词组译成英文：个人通信通信标准固定电话业务网络容量移动交换中心国际漫游宽带业务接口转换频谱分配模拟方式蜂窝通信原理拥塞蜂窝裂变基站移动交换中心寄存器收费功能接入方法突发脉冲传输方式开销信息切换算法短消息服务技术规范二.请将下述词组译成中文：1.the total access communication system2.the global mobile communication system3.the time division multipie access4.the facsimile and short message service5.the fixed communication networks6.the more personalized system7.the cost and quality of the link8.the market growth9.the fixed telephone service10.the coaxial cable11.the interface conversion12.the cellular communication principle13.the frequency reuse and cell splitting14.the cochannel interference15.the theoretical spectral capability16.the micro-cellular system17.the base station transceiver18.the subscriber register19.the burst transmission mode20.the overhead information21.the advanced handover algorithms22.the facsimile and short message service23.the GSM technical specifications五.请将下述短文译成中文：1.The success of mobile systems across the world is a sign that communication ismoving to wards a more personalized, convenie nt sys tem. People who have to use a mobile phone on business soon begin to realize that the ability to phone any time, any place in one' s personal life rapidly becomes a necessity, not a convenience.2.The fixed telephone service is global and the interconnection varies fromcoaxial cable to optical fiber and satellite. The national standards aredifferent, but with common interfaces and interface conversion,interconnection can take place. For mobi 1 e the problem is far more complex, with the need to roam creating a need for complex networks and systems. Thus in mobile the question of standards is far more crucial to success than fixed systems.3.The GSM system is based on a cellular communications principle which was firstproposed as a concept in the 1940s by Bell System engineers in the US. Theidea came out of the need to increase net work capac ity and got round thefact that broadcast mobile networks, operating in densely populated areas,could be jammed by a very small number of simuItaneous calls. The power of the cellular system was that it allowed frequency reuse.4.The cellular concept is defined by two features, frequency reuse and cellsplitting. Frequency reuse comes into play by using radio channels on the same frequency in coverage areas tha/t are far enough apart not to cause cochannel interference. This allows handling of simuItaneous calls that exceed thetheoretical spectral capacity. Cell splitting is necessary when the trafficdemand on a cell has reached the maximum and the cell is then derived into amicro-cellular system.5.The cell coverage area is cont rolled by a base station which is it self madeup of two elements. The first element is the transmission system whichcommunicates out to the mobile and also receives information from it to set upand maintain calls when actually in operation. The base station transceiver iscontrolled by the base station controller, which communicates with the mobileswitching center --------------------------------- the essential link to thelocal public swit ched t elephone net work, and to the subscriber data whichis stored in registers within the system.6.The GSM system operates in a burst transmission mode with 124 radio channels inthe 900 MHz band, and these bursts can carry different types of information.The first type of information is speech, which is coded at 6. 5 kbit/s or 13kbit/s. The second type is data, which can be sent a/t 3. 6 kbit/s, 6 kbit/s or12.6 kbit/s. These two forms of information are the useful part of thetransmission, but have to be supported by overhead information which is sent incontrol channels.7.The use of dig ital radio t ransmission and the advanced handover algor it hmsbetween radio cells in GSM networks allows for significantly better frequentlyusage than in analogue cellular systems, thus increasing the number ofsubscribers that can be served. Since GSM provides common standard, cellularsubscribers will also be able to use their telephones over the entire GSMservice area. Roaming is fully autoina/tic bet ween and wit hin all countriescovered by GSM system.8.In addition to international roaming, GSM provides new user services, such ashigh speed data communication, Facsimile and short message service. The GSMtechnical specifications are designed to work in concert with other standards,e. g. ISDN. Interworking between the standards is in this way assured. In thelong term perspective cellular systems, using a digital technology, will becomethe universal method of telecommunication.《通信英语》综合练习题答案说明：山于《通信英语》的综合练习题全部选自教材中第一、九单元的课后练习，而这些练习又都出自课文，所以可在课文中查找答案，这里就不再给出答案。
通信专业英语之光纤通信
Translation of Text 1-2
第8课 光纤通信 广义地说，把信息从一点传送到另一点就称 为通信。当信息跨越一段距离被传送时，就需要 一个通信系统。在通信系统中，信息传送是通过 把信息叠加在电磁波上或对电磁波进行调制来实 现的，电磁波起着载送信号的作用。
Translation of Text 2-1
Translation of Text 1-1
Lesson 8 Optical Fiber Communications
Communication may be broadly defined as the transfer of information from one point to another. When the information is to be conveyed over any distance a communication system is usually required. Within a communication system the information transfer is frequently achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal.
Typical optical fiber communications system is shown in Fig.13-1. In this case the information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give modulation of the lightwave carrier. The optical source which provides the electrical-optical conversion may be either a semiconductor laser or light emitting diode (LED).
武汉理工大学光纤通信复习题(答案版)
一、画图Drawing1.Please draw out the basic setup for an automatic-repeat-request(ARQ) error-correctionscheme2.Please draw out the fundamental concept of a coherent lightwave system相干光系统的基本原理图3.Please draw out the general heterodyne receiver configurations.(a)Synchronous detection uses a carrier-recovery circuit(b)Asynchronous detection uses a one-bit delay line一般的外差接收机结构(a)使用载波恢复电路的同步检测(b)使用1比特延迟线的异步检测4.Please draw out the basic constituents of a generic RF--over--fiber link光载射频系统的基本框图5.Please draw out the configurations of an EDFA:(a)codirectionalpumping,(b)counterdirectional pumping(c)dual pumpingEDFA 三种结构(a)前向泵浦(b)后向泵浦(c)双向泵浦6.Please draw out a simple 4*4 optical crossconnect architecture using optical space switchesand wavelength converters使用光空分交换和波长交换的4*4光交叉连接结构7.Please draw out the components of a typical WDM link典型WDM链路的构成8.Please draw out the components of the intensity modulated digital optical receiver强度调制数字光接收机的方框图9.Please draw out the generic configuration of a large SONET or SDH network consisting oflinear chains and various types of interconnected rings10. Please draw out the schematic diagram of NNI position in the SDH network二、计算题1、2利用NA 、归一化频率求总模数 3、4求耦合损耗 5求信噪比 6求入射光功率 7求SOA 的泵浦功率和零信号增益 8 EDFA 的功率 9/10 求其模式色散τ∆及传输容量BL 11、12带宽距离积 13、14系统设计1. Suppose we have a multimode step--index optical fiber that has a core radius of 25um ，a coreindex of 1.48，and an index difference △ = 0.01. What are the number of modes in the fiber at wavelengths 860，1310，and1550m μ ? Solution ：(a)First, from and at an operating wavelength of 860nm the value of V is =38.2Using the total number of modes at 860nm is(b)Similarly,at 1310nm we have V = 25.1 and M = 315.()2221222212V n n a M =-⎪⎭⎫ ⎝⎛=λπ∆≈-==2sin 1212221A n n n n NA ）（θ01.0286.048.1252221⨯⨯⨯=∆≈mm n aV μμπλπ()2221222212V n n a M =-⎪⎭⎫ ⎝⎛=λπ72922=≈V M 72922=≈V M(c)Finally at 1550nm we have V = 21.2 and M = 224.2. Suppose we have three multimode step--index optical fibers each of which has a core indexof 1.48，and an index difference △ = 0.01. Assume the three fibers have core diameters of 50,62.5 and 100m μ.What are the number of modes in these fibers at wavelength of 1550m μ ? Solution ：(a)First, from and at 50mμ diameter the value of V isUsing the total number of modes at 50m μ core diameter fiber is(b)Similarly,at 62.5m μ we have V = 26.5 and M = 351.(c)Finally at 100m μ we have V = 42.4 and M = 898.3. A GaAs optical source with a refractive index of 3.6 is coupled to a silica fiber that has arefractive index of 1.48. What is the power loss between the source and the fiber? Solution ：If the fiber end and the source are in close physical contact,then,from , the Fresnel reflection at the interface isThis value of R corresponds to a reflection of 17.4 percent of the emitted optical power backinto the source.Given that()emittedcoupled P R P -=1the power loss L in decibels is found from:This number can be reduced by having an index-matching material between the source andthe fiber end.4. An InGaAsP optical source that has a refractive index of 3.540 is closely coupled to astep-index fiber that has a core refractive index of 1.480.Assume that the source size is smaller than the fiber core and that the small gap between the source and the fiber is filled211⎪⎪⎭⎫⎝⎛+-=n n n n R 174.048.160.348.160.32211=⎪⎭⎫⎝⎛+-=⎪⎪⎭⎫ ⎝⎛+-=n n n n R ()()dBR P P L emitted coupled 83.0826.0log 101log 10log 10=-=--=⎪⎪⎭⎫⎝⎛-=∆≈-==2sin 1212221A n n n n NA ）（θ()2221222212V n n a M =-⎪⎭⎫⎝⎛=λπ2.2101.0255.148.1252221=⨯⨯⨯=∆≈mm n aV μμπλπ()2221222212V n n a M =-⎪⎭⎫ ⎝⎛=λπ22422=≈V Mwith a gel that has a refractive index of 1.520 .(a)What is the power loss in decibels from the source into the fiber? (b)What is the power loss if no gel is used? Solution ：(a)Here we need to consider the reflectivity at two interfaces.First, using we have that the reflectivity sg R at the source-to-gel interface isSimilarly,usingwe have that the reflectivity gfR at the gel-to-fiber interface isThe total reflectivity then is()()0064.0040.0159.0=⨯=⨯=gf sg R R R .The power loss in decibels is ()()dB R L 0028.0994.0log 101log 10=-=--= (b)If no index-matching gel is used, and if we assume there is no gap between the source and the fiber, then fromwe have that the reflectivity isIn this case the power loss in decibels is()()dB R L 799.0832.0log 101log 10=-=--=5. Consider a Si APD operating at 300o K and with a load resistor R L = 1000Ω.For thisAPD assume the responsivityW A65.0=ℜ and let x = 0.3 (a)If dark current isneglected and 100nW of optical power falls on the photodetector , what is the optimum avalanche gain? (b)What is the SNR if B e = 100MHz? (c)How does the SNR of this APD compare with the corresponding SNR of a Si pin photodiode? Assume the leakage current is negligible. Solution ：(a)Neglecting dark current and withPI p ℜ= , we have()()()()()()421010065.010001060.13.03001038.1443.2191923=⎥⎦⎤⎢⎣⎡⨯⨯⨯=⎪⎪⎭⎫ ⎝⎛ℜ=---P xqR T k M L B opt211⎪⎪⎭⎫ ⎝⎛+-=n n n n R 159.0520.1540.3520.1540.32=⎪⎭⎫⎝⎛+-=sg R 211⎪⎪⎭⎫⎝⎛+-=n n n n R 040.0520.1480.1520.1480.12=⎪⎭⎫ ⎝⎛+-=gf R 211⎪⎪⎭⎫⎝⎛+-=n n n n R 168.0480.1540.3480.1540.32=⎪⎭⎫⎝⎛+-=R(b)Neglecting dark current and with ()()3.042==xM M F , we have()()()()[]()()()()()()()6591010010003001038.14421010065.0106.12421010065.0426233.2919293.22=⨯⎥⎦⎤⎢⎣⎡⎪⎪⎭⎫ ⎝⎛⨯+⨯⨯⨯=⎥⎦⎤⎢⎣⎡⎪⎪⎭⎫ ⎝⎛+ℜℜ=----e L B B R T k PM q PM SNRor in decibels , SNR = 10log659 = 28.2dB(c)For a pin photodiode with M = 1, the above equation yields SNR(pin) = 2.3 = 3.5dB. Thus, compared to a pin photodiode, the APD improves the SNR by 24.7dB.6. Consider an analog optical fiber system operating at 1550nm, which has an effective receivernoise bandwidth of 5MHz. Assuming that the received signal is quantum noise limited, what is the incident optical power necessary to have a signal-to-noise ratio of 50dB at the receiver?Assume the responsivity is 0.9A/W and that m = 0.5. Solution ：First we note that a 50dB SNR means that S/N = 105 . Then, solving ere p qB P m qB I m N S 4422ℜ=≈for P r yields()()()()()()mWnW m qB N S P er32619521042.1142090.05.0105106.141014--⨯==⨯⨯⨯=ℜ=or in dBm()dBm P dBm P r r 5.281042.1log 10log 103-=⨯==-7. Consider the following parameters for a 1300nm InGaAsP SOA:System Parameter Value w Active area width 3um d Active area thickness 0.3um L Amplifier length 500um Γ Confinement factor 0.3 τr Time constant 1nsa Gain coefficient 2×10-20m 2 n th Threshold density 1.0×10-24m -3 (a)What is the pumping rate for the SOA? (b)What is the zero-signal gain? Solution ：(a)If a 100mA bias current is applied to the device, then, from ()()qd t J t R p =, the pumpingrate is()()()()()s m electrons m m m C A qdwL qd J R p 333191039.150033.0106.11.01⨯=⨯===-μμμ (b)From ⎪⎪⎭⎫⎝⎛-Γ=r th r n qd J a g ττ0 , the zero-signal gain is ()()11324133322004.2323400.1100.11039.11102.03.0------==⎪⎪⎭⎫ ⎝⎛⨯-⨯⨯⨯=cm m ns m s m ns m g8. Consider an EDFA being pumped at 980nm with a 30mW pump power. If the gain at 1550nmis 20dB, what are the maximum input and output powers? Solution ：From1,,-⎪⎭⎫ ⎝⎛≤G P P inp s p ins λλ , the maximum input power is()()WmW P ins μ1901100301550980,=-≤Fromin p spin s out s P P P ,,,λλ+≤ , the maximum output power is()()()dBm mW mW W P P P in p spin s out s 8.121.193063.0190max max ,,,==+=+=μλλ9. 一根突变型多模光纤的长度km L 1=，纤芯的折射率5.11=n ，相对折射率差01.0=∆，求其模式色散τ∆及传输容量BL 。
通信专业英语之光纤通信英语拓展
Exercises
b. Photodiodes (p-n, p-i-n or avalanche)
and
phototransistoare utilized for the
detection of the optical signal and the
optical-electrical conversion.
Exercises
a. Within a communication system the information transfer is achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier.
Exercises
d. There is a requirement for electrical interfacing at either end of the optical link and at present the signal processing is usually performed electrically.
b. Sophisticated techniques have been developed for this process by using magnetic carrier waves operating at radio frequencies as well as microwave and millimeter wave frequencies. (F)
Exercises
c. The information source provides an electrical signal to a transmitter comprising an electrical stage which drives an optical source to give modulation of the light wave carrier. (T)
通信工程专业英语考试试卷
XXXXXX大学2015-2016学年第一学期《English for Telecommunication Engineering》期末考试试卷（A卷）考核形式（开卷）第一题、通信工程专业英语常用词组翻译。
（每小题1.5分，共30分）1.将下列英文词组翻译为汉语。
（1）Mobile telephone 移动电话（2）retrieval 检索（3）bandwidth 频带宽度（4）second moment 二阶矩（5）hypermedia 超媒体（6）interface 界面（7）d iscrete media离散介质（8）（8）database 数据库（9）e-commerce 电子商务（10）communication 通信2.将下列汉语词组翻译为英语。
（1）模拟器simulator（2）铸造标记语言Foundry Markup Language（3）投资报酬率return-on-investment（4）纯文本plain text（5）连续介质continuous media（6）语音识别speech recognition（7）万维网World Wide Web（8）虚拟现实virtual reality（9）蓝牙技术bluetooth technology（10）信息技术information technology第二题、英文和汉语词组正确搭配。
（每小组1分，共10分）（a）S tandard Generalized Markup Language 数据信道 f （b）I ntegrated Services Digital Network 网络公司e （c）analog system 全球电子商务联盟g （d）T erminal Adapter 载波信道j （e）d ot-com 模拟系统c （f）data channel 终端适配器 d （g）t he Global E-commerce Consortium 端到端数字连接i （h）b rand commoditization 标准通用标记语言a （i）end-to-end digital connectivity 综合业务数字网 b （j）Bearer channel 品牌商品化 h（每小题5分，共15分）1.Wi-Fi is the trademark for the popular wireless technology used in home networks, mobile phones, video games and other electronic devices that require some form of wireless networking capability.Wifi是流行无线技术的标志，用在家庭网络、移动电话、电子游戏等其他需要某种形式的无线网络容量的电子设备上。
光纤通信(双语)总复习课件 科大
scattering
geometric effects
total loss
18
fiber attenuation
2.5
Attenuation (dB/km)
Rayleigh scattering
Glass absorption In infrared
0.2 850 1300 glass absorption In ultraviolet 1550
3
1.2 The Basic Communications System
Transmitter
Information ChannelReceຫໍສະໝຸດ verBL product
4
1.2.10 computing power levels in decibels
decibel (dB)： the relative power level.
Wavelength (nm)
19
attenuation coefficient
Pin
L
Pout
⎛ Pout 10 α (dB / km) = − log10 ⎜ ⎜P L ⎝ in
⎞ ⎟ ⎟ ⎠
20
Q4
A fiber system operates at the wavelength 1300nm, where the fiber loss is 0.5dB/km. The LED light source emits 1.59mW and couples into the fiber with a 16-dB loss. Connectors and splices in the system contribute a total loss of 6dB. The receiver sensitivity (the power required for the receiver to detect the message with a specified error rate or signal-to-noise ratio) is given as -30dBm. A 4-dB margin is specified to account for system degradations (such as aging of the LED). What is the maximum length of fiber that can be used?
光纤通信系统Optical Fiber Communications 英文资料及中文翻译
光纤通信系统Optical Fiber Communications英文资料及中文翻译Communication may be broadly defined as the transfer of information from one point to another .When the information is to be conveyed over any distance a communication system is usually required .Within a communication system the information transfer is frequently achieved by superimposing or modulating the information on to an electromagnetic wave which acts as a carrier for the information signal .This modulated carrier is then transmitted to the required destination where it is received and the original information signal is obtained by demodulation .Sophisticated techniques have been developed for this process by using electromagnetic carrier waves operating at radio requites as well as microwave and millimeter wave frequencies.The carrier maybe modulated by using either optical an analog digital information signal.. Analog modulation involves the variation of the light emitted from the optical source in a continuous manner. With digital modulation, however, discrete changes in the length intensity are obtained (i.e. on-off pulses). Although often simpler to implement, analog modulation with an optical fiber communication system is less efficient, requiring a far higher signal to noise ratio at the receiver than digital modulation. Also, the linearity needed for analog modulation is mot always provided by semiconductor optical source, especially at high modulation frequencies .For these reasons ,analog optical fiber communications link are generally limited to shorter distances and lower bandwidths than digital links .Initially, the input digital signal from the information source is suitably encoded for optical transmission .The laser drive circuit directly modulates the intensity of the semiconductor last with the encoded digital signal. Hence a digital optical signal is launched into the optical fiber cable .The avalanche photodiode detector (APD) is followed by a front-end amplifier and equalizer or filter to provide gain as well as linear signal processing and noise bandwidth reduction. Finally ,the signal obtained isdecoded to give the original digital information .Generating a Serial SignalAlthough a parallel input-output scheme can provide fast data transfer and is simple in operation, it has the disadvantage of requiring a large number of interconnections. As an example typical 8 bit parallel data port uses 8 data lines, plus one or two handshake lines and one or more ground return lines. It is fairly common practice to provide a separate ground return line for each signal line, so an 8 bit port could typically use a 20 core interconnection cable. Whilst such a multi way cable is quite acceptable for short distance links, up to perhaps a few meters, it becomes too expensive for long distance links where, in addition to the cost of the multiword cable, separate driver and receiver circuits may be required on each of the 10 signal lines. Where part of the link is to be made via a radio link, perhaps through a space satellite, separate radio frequency channels would be required for each data bit and this becomes unacceptable.An alternative to the parallel transfer of data is a serial in which the states of the individual data bits are transmitted in sequence over a single wire link. Each bit is allocated a fixed time slot. At the receiving end the individual bit states are detected and stored in separate flip-flop stages, so that the data may be reassembled to produce a parallel data word. The advantage of this serial method of transmission is that it requires only one signal wire and a ground return, irrespective of the number of bits in the data word being transmitted. The main disadvantage is that the rate at which data can be transferred is reduced in comparison with a parallel data transfer, since the bits are dealt with in sequence and the larger the number of bits in the word, the slower the maximum transfer speed becomes. For most applications however, a serial data stream can provide a perfectly adequate data transfer rate . This type of communication system is well suited for radio or telephone line links, since only one communication channel is required to carry the data.We have seen that in the CPU system data is normally transferred in parallel across the main data bus, so if the input -output data is to be in serial form, then a parallel to serial data conversion process is required between the CPU data bus andthe external I/O line. The conversion from parallel data to the serial form could be achieved by simply using a multiplexed switch, which selects each data bit in turn and connects it to the output line for a fixed time period. A more practical technique makes use of a shift register to convert the parallel data into serial form.A shift register consists of a series of D type flip-flops connected in a chain, with the Q output of one flip-flop driving the D input of the next in the chain. All of the flip-flops ate clocked simultaneously by a common clock pulse, when the clock pulse occurs the data stored in each flip-flop is transferred to the next flip-flop to the right in the chain. Thus for each clock pulse the data word is effectively stepped along the shift register by one stage, At the end of the chain the state of the output flip-flop will sequence through the states of the data bits originally stored in the register. The result is a serial stream of data pulses from the end of the shift register.In a typical parallel to serial conversion arrangement the flip-flops making up the shift register have their D input switchable. Initially the D inputs are set up in a way so that data can be transferred in parallel from the CPU data bus into the register stages. Once the data word has been loaded into the register the D inputs are switched so that the flip-flops from a shift register .Now for each successive clock pulse the data pattern is shifted through the register and comes out in serial form at the right hand end of the register.At the receiving end the serial data will usually have to be converted back into the parallel form before it can be used. The serial to parallel conversion process can also be achieved by using a shift register .In this case the serial signal is applied to the D input of the stage at the left hand end of the register. As each serial bit is clocked into the register the data word again moves step by step to the right, and after the last bit has been shifted in the complete data word will be assembled within the register .At this point the parallel data may be retrieved by simply reading out the data from individual register stages in parallel It is important that the number of stages in the shift register should match the number of bits in the data word, if the data is to be properly converted into parallel form.To achieve proper operation of the receiving end of a serial data link, it isimportant that the clock pulse is applied to the receive shift register at a time when the data level on the serial line is stable. It is possible to have the clock generated at either end of the link, but a convenient scheme is to generate the clock signal at the transmitting end (parallel-serial conversion )as the master timing signal. To allow for settling time and delays along the line, the active edge of the clock pulse at the receive end is delayed relative to that which operates the transmit register. If the clock is a square wave the simples approach might be to arrange that the transmit register operates on the rising edge of the clock wave, and the receive register on the falling edge, so that the receiver operates half a clock period behind the transmitter .If both registers operate on arising edge, the clock signal from the transmitter could be inverted before being used to drive the receive shifty register.For an 8 bit system a sequence of 8 clock pulses would be needed to send the serial data word .At the receiving end the clock pulses could be counted and when the eighth pulse is reached it might be assumed that the data in the receive register is correctly positioned, and may be read out as parallel data word .One problem here is that, if for some reason the receive register missed a clock pulse ,its data pattern would get out of step with the transmitted data and errors would result. To overcome this problem a further signal is required which defines the time at which the received word is correctly positioned in the receive shift register and ready for parallel transfer from the register .One possibility is to add a further signal wire along which a pulse is sent when the last data bit is being transmitted, so that the receiver knows when the data word is correctly set up in its shift register. Another scheme might be to send clock pulses only when data bits are being sent and to leave a timing gap between the groups of bits for successive data words. The lack of the clock signal could then be detected and used to reset the bit counter, so that it always starts at zero at the beginning of each new data word.Serial and Parallel Data lion is processed. Serial indicates that the information is handled sequentially, similar to a group of soldiers marching in single file. In parallel transmission the info The terms serial and parallel are often used in descriptions of data transmission techniques. Both refer to the method by which information isdivided in to characters, words, or blocks which are transmitted simultaneously. This could be compared to a platoon of soldiers marching in ranks.The output of a common type of business machine is on eight—level punched paper tape, or eight bits of data at a time on eight separate outputs. Each parallel set of eight bits comprises a character, and the output is referred to as parallel by bit, serial by character. The choice of cither serial or parallel data transmission speed requirements.Business machines with parallel outputs, how—ever, can use either parallel outputs, how—ever, can use either direct parallel data trans—mission or serial transmission, with the addition of a parallel—to—serial converter at the interface point of the business machine and the serial data transmitter. Similarly, another converter at the receiving terminal must change the serial data back to the parallel format.Both serial and parallel data transmission systems have inherent advantages which are some—what different. Parallel transmission requires that parts of the available bandwidth be used as guard bands for separating each of the parallel channels, whereas serial transmission systems can use the entire linear portion of the available band to transmit data, On the other hand, parallel systems are convenient to use because many business machines have parallel inputs and outputs. Though a serial data set has the added converters for parallel interface, the parallel transmitter re—quires several oscillators and filters to generate the frequencies for multiplexing each of the side—by—side channels and, hence, is more susceptible to frequency error.StandardsBecause of the wide variety of data communications and computer equipment available, industrial standards have been established to provide operating compatibility. These standards have evolved as a result of the coordination between manufacturers of communication equipment and the manufacturers of data processing equipment. Of course, it is to a manufacturer’s advantage to provide equipment that isuniversally acceptable. It is also certainly apparent that without standardization intersystem compatibility would be al—most impossible.Organizations currently involved in uniting the data communications and computer fields are the CCITT, Electronic Industries Association (EIA), American Standards Association (ASA), and IEEE.A generally accepted standard issued by the EIA, RS—232—B, defines the characteristics of binary data signals, and provides a standard inter—face for control signals between data processing terminal equipment and data communications equipment. As more and more data communications systems are developed, and additional ways are found to use them, the importance ways are found to use them, the importance of standards will become even more significant.Of the most important considerations in transmitting data over communication systems is accuracy. Data signals consist of a train of pulses arranged in some sort of code. In a typical binary system, for example, digits 1 and 0 are represented by two different pulse amplitudes. If the amplitude of a pulse changes beyond certain limits during transmission, the detector at the receiving end may produce the wrong digit, thus causing an error.It is very difficult in most transmission systems to completely avoid. This is especially true when transmission system designed for speech signals. Many of the inherent electrical characteristics of telephone circuits have an adverse effect on digital signals.Making the circuits unsatisfactory for data transmission—especially treated before they can be used to handle data at speeds above 2000 bits per second.V oice channels on the switched (dial—up) telephone network exhibit certain characteristics which tend to distort typical data signal waveforms. Since there is random selection of a particular route for the data signal with each dialed connection, transmission parameters will generally change, sometimes upsetting the effect of built—in compensationNetworks. In addition, the switched network cannot be used of for large multipleaddress data systems using time sharing. Because of these considerations, specially treated voice bandwidth circuits are made available for data use. The characteristics and costs of these point—to—point private lines are published in document called tariffs, which are merely regulatory agreements reached by the FCC, state public utilities commissions, and operating telephone companies regarding charges for particular types of telephone circuits. The main advantage of private or dedicated facilities is that transmission characteristics are fixed and remain so for all data communications operations.Correlative TechniqueCorrelative data transmission techniques, particularly the Duobinary principle, have aroused considerable interest because of the method of converting a binary signal into three equidistant levels. This correlative scheme is accomplished in such a manner that the predetermined level depends on past signal history, forming the signal so that it never goes from one level extreme to another in one bit interval.The most significant property of the Duobinary process is that it affords a two—to—one bandwidth compression relative to binary signaling, or equivalently twice the speed capability in bits per second for a fixed bandwidth. The same speed capability for a multilevel code would normally require four levels, each of which would represent two binary digits.The FutureIt is universally recognized that communication is essential at every level of organization. The United States Government utilizes vast communications network for voice as well as data transmission. Likewise, business need communications to carry on their daily operations.The communications industry has been hard at work to develop systems that will transmit data economically and reliably over both private—line and dial up telephone circuits. The most ardent trend in data transmission today is toward higher speeds over voice—grade telephone channels. New transmission and equalization techniques now being investigated will soon permit transmitting digital data over telephone channels at speeds of 4800 bits per second or higher.To summarize: The major demand placed on telecommunications systems is for more information-carrying capacity because the volume of information produced increases rapidly. In addition, we have to use digital technology for the high reliability and high quality it provides in the signal transmission. However, this technology carries a price: the need for higher information-carrying capacity.The Need for Fiber-Optic Communications Systems The major characteristic of a telecommunications system is unquestionably its information-carrying capacity, but there are many other important characteristics. For instance, for a bank network, security is probably more important than capacity. For a brokerage house, speed of transmission is the most crucial feature of a network. In general, though, capacity is priority one for most system users. And there’s the rub. We cannot increase link capacity as much as we would like. The major limit is shown by the Shannon-Hartley theorem,Where C is the information-carrying capacity(bits/sec), BW is the link bandwidth (Hz=cycles/sec), and SNR is the signal-to-noise power ratio.Formula 1.1 reveals a limit to capacity C; thus, it is often referred to as the “ Shannon limit.” The formula, which comes from information theory, is true regardless of specific technology. It was first promulgated in 1948 by Claude Shannon, a scientist who worked at Bell Laboratories. R. V. L. Hartley, who also worked at Bell Laboratories, published a fundamental paper 20 years earlier, a paper that laid important groundwork in information theory, which is why his name is associated with Shannon’s formula.The Shannon-Hartley theorem states that information-carrying capacity is proportional to channel bandwidth, the range of frequencies within which the signals can be transmitted without substantial attenuation.What limits channel bandwidth? The frequency of the signal carrier. The higher the carrier’s frequency, the greater the channel bandwidth and the higher the information-carrying capacity of the system. The rule of thumb for estimating possible order of values is this: Bandwidth is approximately 10 percent of the carrier-signal frequency. Hence, if a microwave channel uses a 10-GHz carrier signal.Then its bandwidth is about 100 MHz.A copper wire can carry a signal up to 1 MHz over a short distance. A coaxial cable can propagate a signal up to 100 MHz. Radio frequencies are in the range of 500 KHz to 100 MHz. Microwaves, including satellite channels, operate up to 100 GHz. Fiber-optic communications systems use light as the signal carrier; light frequency is between 100 and 1000 THz; therefore, one can expect much more capacity from optical systems. Using the rule of thumb mentioned above, we can estimate the bandwidth of a single fiber-optic communication link as 50 THz.To illustrate this point, consider these transmission media in terms of their capacity to carry, simultaneously, a specific number of one-way voice channels. Keep in mind that the following precise value. A single coaxial cable can carry up to 13,000 channels, a microwave terrestrial link up to 20,000 channels, and a satellite link up to 100,000 channels. However, one fiber-optic communications link, such as the transatlantic cable TAT-13, can carry 300,000 two-way voice channels simultaneously. That’s impressive and explains why fiber-optic communications systems form the backbone of modern telecommunications and will most certainly shape its future.To summarize: The information-carrying capacity of a telecommunications system is proportional to its bandwidth, which in turn is proportional to the frequency of the carrier. Fiber-optic communications systems use light-a carrier with the highest frequency among all the practical signals. This is why fiber-optic communications systems have the highest information-carrying capacity and this is what makes these systems the linchpin of modern telecommunications.To put into perspective just how important a role fiber-optic communications will be playing in information delivery in the years ahead, consider the following statement from a leading telecommunications provider: “ The explosive growth of Internet traffic, deregulation and the increasing demand of users are putting pressure on our customers to increase the capacity of their network. Only optical networks can deliver the required capacity, and bandwidth-on-demand is now synonymous with wavelength-on-demand.” Th is statement is true not only for a specific telecommunications company. With a word change here and there perhaps, but withthe same exact meaning, you will find telecommunications companies throughout the world voicing the same refrain.A modern fiber-optic communications system consists of many components whose functions and technological implementations vary. This is overall topic of this book. In this section we introduce the main idea underlying a fiber-optic communications system.Basic Block DiagramA fiber-optic communications system is a particular type of telecommunications system. The features of a fiber-optic communications system can be seen in Figure 1.4, which displays its basic block diagram.Information to be conveyed enters an electronic transmitter, where it is prepared for transmission very much in the conventional manner-that is, it is converted into electrical form, modulated, and multiplexed. The signal then moves to the optical transmitter, where it is converted into optical detector converts the light back into an electrical signal, which is processed by the electronic receiver to extract the information and present it in a usable form (audio, video, or data output).Let’s take a simple example that involves Figures 1.1, 1.3, and 1.4 Suppose we need to transmit a voice signal. The acoustic signal (the information) is converted into electrical form by a microphone and the analog signal is converted into binary formby the PCM circuitry. This electrical digital signal modulates a light source and the latter transmits the signal as a series of light pulses over optical fiber. If we were able to look into an optical fiber, we would see light vary between off and on in accordance with the binary number to be transmitted. The optical detector converts the optical signal it receives into a set of electrical pulses that are processed by an electronic receiver. Finally, a speaker converts the analog electrical signal into acoustic waves and we can hear sound-delivered information.Figure 1.4 shows that this telecommunications system includes electronic components and optical devices. The electronic components deal with information in its original and electrical forms. The optical devices prepare and transmit the light signal. The optical devices constitute a fiber-optic communications system.TransmitterThe heart of the transmitter is a light source. The major function of a light source is to convert an information signal from its electrical form into light. Today’sfiber-optic communications systems use, as a light source, either light-emitting diodes (LEDs) or laser diodes (LDs). Both are miniature semiconductor devices that effectively convert electrical signals are usually fabricated in one integrated package. In Figure 1.4, this package is denoted as an optical transmitter. Figure 1.5 displays the physical make-up of an LED, an LD, and integrated packages.Optical fiberThe transmission medium in fiber-optic communications systems is an optical fiber. The optical fiber is the transparent flexible filament that guides light from a transmitter to a receiver. An optical information signal entered at the transmitter end of a fiber-optic communications system is delivered to the receiver end by the optical fiber. So, as with any communication link, the optical fiber provides the connection between a transmitter and a receiver and, very much the way copper wire and coaxial cable conduct an electrical signal, optical fiber “ conducts” light.The optical fiber is generally made from a type of glass called silica or, less commonly nowadays, from plastic. It is about a human hair in thickness. To protect very fragile optical fiber from hostile environments and mechanical damage, it is usually enclosed in a specific structure. Bare optical fiber, shielded by its protective coating, is encapsulated use in a host of applications, many of which will be covered in subsequent chaptersReceiver The key component of an optical receiver is its photodetector. The major function of a photodetector is to convert an optical information signal back into an electrical signal (photocurrent). The photodetector in today's fiver-optic communications systems is a semiconductor photodiode (PD). This miniature device is usually fabricated together with its electrical circyitry to form an integrated package that provides power-supply connections and signal amplification. Such an integrated package is shown in Figure 1.4 as an optical receiver. Figure 1.7 shows samples of a photodiode and an integrated package.The basic diagram shown in Figure 1.4 gives us the first idea of what a fiber-optic communications system is and how it works. All the components of this point-to-point system are discussed in detail in this book. Particular attention is given to the study of networks based on fiber-optic communications systems.The role of Fiber-Optic Communications Technology has not only already changed the landscape of telecommunications but it is still doing so and at a mind-boggling pace. In fact, because of the telecommunications industry's insatiable appetite for capacity, in recent years the bandwidth of commercial systems has increased more than a hundredfold. The potential information-carrying capacity of a single fiber-optic channel is estimated at 50 terabits a second (Tbit/s) but, from apractical standpoint, commercial links have transmitted far fewer than 100 Gbps, an astoundingamount of data in itself that cannot be achieved with any other transmission medium. Researchers and engineers are working feverishly to develop new techniques that approach the potential capacity limit.Two recent major technological advances--wavelength-division multiplexing (WDM) anderbium-doped optical-fiber amplifiers (EDFA)--have boosted the capacity of existing system sand have brought about dramatic improvements in the capacity of systems now in development. In fact,' WDM is fast becoming the technology of choice in achieving smooth, manageable capacity expansion.The point to bear in mind is this: Telecommunications is growing at a furious pace, and fiber-optic communications is one of its most dynamically moving sectors. While this book refleets the current situation in fiber-optic communications technology, to keep yourself updated, you have to follow the latest news in this field by reading the industry's trade journals, attending technical conferences and expositions, and finding the time to evaluate the reams of literature that cross your desk every day from companies in the field.光纤通信系统一般的通信系统由下列部分组成：(1) 信息源。
光纤通信简介专业英语要点
Optical Fiber Communication-introduction ForewordThe use of light to send messages is not new .Fires were used for signaling in biblical times, smoke signals have been used for thousands of years and flashing lights have been used to communicate between warships at sea since the days of Lord Nelson.The idea of using glass fiber to carry an optical communication signal originated with Alexander Graham Bell. However this idea had to wait some 80 years for better glasses and low-cost electronics for it to become useful in practical situations.The predominant use of optical technology is for transmission of data at high speed. Optical fibers replace electric wire in communications systems and nothing much else changes. Perhaps this is not quite fair. The very speed and quality of optical communications systems has itself predicated the development of a new type of electronic communications itself designed to be run on optical connections. ATM (Asynchronous Transfer Mode) and SDH (Synchronous Digital Hierarchy) technologies are good examples of the new type of systems.It is important to realize that optical communications is not likeelectronic communications. While it seems that light travels in a fiber much like electricity does in a wire this is very misleading. Light is an electromagnetic wave and optical fiber is a waveguide. Everything to do with transport of the signal even to simple things like coupling (joining) two fibers into one is very different from what happens in the electronic world. The two fields (electronics and optics) while closely related employ different principles in different ways.Some people look ahead to “true”optical networks. These will be networks where routing is done optically from one end-user to another without the signal ever becoming electronic. Indeed some experimental local area (LAN) and metropolitan area (MAN) networks like this have been built. In 1998 optically routed nodal wide area networks are imminently feasible and the necessary components to build them are available. However, no such networks have been deployed operationally yet.In 1998 the “happening”area in optical communications was Wavelength Division Multiplexing (WDM). This is the ability to send many (perhaps up to 1000) independent optical channels on a single fiber. The first fully commercial WDM products appeared on the market in 1996. WDM is a major step toward fully optical networking.1. Transmitting Light on a FiberAn optical fiber is a very thin strand of silica glass in geometry quite like a human hair. In reality it is a very narrow, very long glass cylinder with special characteristics. When light enters one end of the fiber, it travels (confined within the fiber) until it leaves the fiber at the other end. Two critical factors stand out:Very little light is lost in its journey along the fiber.Fiber can bend around corners and the light will stay within it and be guided around the corners.An optical fiber consists of two parts: the core and the cladding. The core is a narrow cylindrical strand of glass and the cladding is a tubular jacket surrounding it. The core has a (slightly) higher refractive index than the cladding. This means that the boundary (interface) between the core and the cladding acts as a perfect mirror. Light traveling along the core is confined by the mirror to stay within it-even when the fiber bends around a corner.When light is transmitted on a fiber, the most important consideration is “what kind of light?”The electromagnetic radiation that we call light exists at many wavelengths. These wavelengths go from invisible infrared through all the colours of the visible spectrum to invisible ultraviolet. Because of the attenuation characteristics of fiber, we are only interested in infrared “light”for communication applications. This light is usuallyinvisible, since the wavelengths used are usually longer than the visible limit of around 750 nanometers ( nm ) .If a short pulse of light from a source such as a laser or an LED is sent down a narrow fiber, it will be changed (degraded) by its passage down the fiber. It will emerge (depending on the distance) much weaker, lengthened in time (“smeared out”), and distorted in other ways.2. Optical Transmission System ConceptsThe basic components of an optical communication system are optical transmitter and receiver,Fiber jumpers,Optical,fiber splice tray Optical fiber.A serial bit stream in electrical from is presented to a modulator, which encodes the data appropriately for fiber transmission.A light source (laser or Light Emitting Diode—LED) is driven by the modulator and the light focused into the fiber. The light travels down the fiber (during which time it may experience dispersion and loss of strength).At the receiver end the light is fed to a detector and converted to electrical form. The signal is then amplified and fed to another detector, which isolates the individual state changes and their timing. It then decodes the sequence of state changes and reconstructs the original bit stream.The timed bit stream so received may then be fed to a using device. Optical communication has many well-known advantages.Weight and SizeFiber cable is significantly smaller and lighter than electrical cables to do the same job. In the wide area environment a large coaxial cable system can easily involve a cable of several inches in diameter and weighing many pounds per foot. A fiber cable to do the same job could be less than one half an inch in diameter and weigh a few ounces per foot. This means that the cost of laying the cable is dramatically reduced. Material CostFiber cable costs significantly less than copper cable for the same transmission capacity.Information CapacityThe idea rate of system in 1998 was generally 150 or 620Mbps on a single (unidirectional) fiber. This is because these systems were installed in past years. The usual rate for new systems is 2.4Gbps or even 10Gbps. This is very high in digital transmission terms.In telephone transmission terms the very best coaxial cable systems give about 2,000 analog voice circuits. A 150Mbps fiber connection gives just over 2,000 digital telephone (64kbps) connections. But the 150Mbpsfiber is at a very early stage in the development of fiber optical systems. The coaxial cable system with which it is being compared is much more costly and has been developed to its fullest extent.Fiber technology is still in its infancy. Using just a single channel per fiber, researchers have trial systems in operation that communicate at speeds of 100Gbps.By sending many (“wavelength division multiplexed ”) channels on a single fiber, we can increase this capacity a hundred and perhaps a thousand times. Recently researchers at NEC reported a successful experiment where 132 optical channels of 20Gbps each were carried over 120km. This is 2.64 terabits per second! This is enough capacity to carry about 30 million uncompressed telephone calls (at 64kbps per channel). Thirty million calls is about the maximum number of calls in progress in the world at any particular moment in time. That is to say, we could carry the world’s peak telephone traffic over one pair of fibers. Most practical fiber systems don’t attempt to do this because it costs less to put multiple fibers in a cable than to use sophisticated multiplexing technology.No Electrical ConnectionThis is an obvious point but nevertheless a very important one . Electrical connections have problems. In electrical systems there is always the possibility of “ground loops” causing a serious problem,especially in theLAN or computer channel environment . When you communicate electrically you often have to connect the grounds to one another or at least go to a lot of trouble to avoid making this connection. One little known problem is that there is often a voltage potential difference between “ground”at different locations. The author has observed as much as 3 volts difference in ground potential between adjacent buildings (this was a freak situation). It is normal to observe 1or 2 volt differences over distance of a kilometer or so.With shielded cable there can be a problem if you earth the shields at both ends of the connection. Optical connection is very safe. Electrical connections always have to be protected from high voltages because of the danger to people touching the wire . In some tropical regions of the world, lightning poses a severe hazard even to buried telephone cables! Of cause, optical fiber isn’t subject to lightning problems but it must be remembered that sometimes optical cables carry wires within them for strengthening or to power repeaters . These wires can be a target for lightning.No Electromagnetic InterferenceBecause the connection is not electrical, you can neither pick up nor create electrical interference (the major source of noise). This is one reason that optical communication has so few errors. There are very few source of things that can distort or interfere with the signal. In a buildingthis means that fiber cables can be placed almost anywhere electrical cables would have problems, (foe example near a lift motor or in a cable duct with heavy power cables). In an industrial plant such as a steel mill, this gives much greater flexibility in cabling than previously available.In the wide area networking environment there is much greater flexibility in route selection. Cables may be located near water or power lines without risk to people or equipment.Distances between RegeneratorsAs a signal travels along a communication line it loses strength (is attenuated) and picks up noise. The traditional way to regenerate the signal, restoring its power and removing the noise, is to use either a repeater or an amplifier. Indeed it is the use of repeaters to remove noise that gives digital transmission its high quality.In long-line optical transmission cables now in use by the telephone companies, the repeater spacing is typically 40 kilometers. This compares with 12 km for the previous coaxial cable electrical technology. The number of required repeaters and their spacing is a major factor in system cost.Open Ended CapacityThe maximum theoretical capacity of installed fiber is very great (almostinfinite). This means that additional capacity can be had on existing fibers as new technology becomes available. All that must be done is change the equipment at either end and change or upgrade the regenerators.Better SecurityIt is possible to tap fiber optical cable. But it is very difficult to do and the additional loss caused by the tap is relatively easy to detect.There is an interruption to service while the tap is interested and this can alert operational staff to the situation. In addition, there are fewer access points where an intruder can gain the kind of access to a fiber cable necessary to insert a tap.3. Wavelength Division MultiplexingWavelength Division Multiplexing (WDM) is the basic technology of optical networking. It is a technique for using a fiber (or optical device) to carry many separate and independent optical channels. The principle is identical to that used when we tune our television receiver to one of many TV channels. Each channel is transmitted at a different radio frequency and we select between them using a “tuner” which is just a resonant circuit within the TV set. Of course wavelength in the optical world is just the way we choose to refer to frequency and optical WDM isquite identical to radio FDM.There are many varieties of WDM. A simple form can be constructed using 1310nm as one wavelength and 1550 as the other or 850 and 1310. This type of WDM can be built using relatively simple and inexpensive components and some applications have been in operation for a number of years using this principle.Wavelength selective couplers are used both to mix (multiplex) and to separate (de-multiplex) the signals. The distinguishing characteristic here is the very wide separation of wavelengths used (different bands rather than different wavelengths in the same band).Th ere are many variations around on this very simple theme. Some systems use a signal fiber bidirectionally while others use separate fibers for each direction . Other systems use different wavelength bands from those illustrated in the figure (1310and 1550 for example). The most common systems run at very low data rates. Common application areas are in video transport for security monitoring and in plant process control.Dense WDM however is another thing.Dense WDM refers to the close spacing of channels.Sadly，＂dense＂is a qualitative measure and just what dense means is largely in the mind of the description.Others use the term to distinguish systems where the wavelength spacing is 1nm per channel or less.Each optical channel is allocated its own wavelength —or rather range of wavelengths.A typical optical channel might be 1nm wide. This channel is really a wavelength range within which the signal must stay. It is normally much wider than the signal itself. The width of a channel depends on many things such as the modulated line width of the transmitter,its stability and the tolerances of the other components in the system. In practical terms the transmitter is always a laser.It must have a line width which (after modulation) fits easily within its allocated band. It must not go outside the allocated band so it should have chirp and drift characteristics that ensure this. Depending on the width of the allocated band,these characteristics don't need to be the most perfect obtainable.However they do have to be such that the signal stays where it is supposed to be. The receiver is relatively straightforward and is generally the same as a non-WDM receiver .This is because the signal has been de-multiplexed before it arrives at the detector.光纤通信简介前言使用光来传送信息并不新鲜。
光纤通信_A卷英文解析
1. Multiple choice (10P each 1P)1) Which of the following codes cannot be transmitted in fiber ______.A. CMIB. HDB3C. 5B6BD. 8B1H2) A single mode fiber usually has a core diameter of ______.A. 10mB. 62. 5nmC. 125nmD. 50mm3) Dispersion-shifted fiber (DSF) is a type of single-mode fiber designed to have zero dispersion near _____ nm.A.1550B.850C.1310D.15104) To make sure that the APD photo-detector works properly, a sufficiently ______ is applied across the p-n junction.A. high forward-bias voltageB. low forward-bias voltageC. low reverse-bias voltageD. high reverse-bias voltage5) It is well known that the total dispersion in the single-mode regime is composed of two components, ______ and ______ .A. mode-partition noise , inter- symbol InterferenceB. frequency chirp , modal dispersionC. material dispersion , waveguide dispersionD. modal dispersion , waveguide dispersion6) The mode has no cut off and ceases to exist only when the core diameter is zero.A. HE11B. TE01C. TM01D. EH117) In graded-index optical fiber, the numerical aperture NA can be expressed as ______.A.21n n -B.∆2aC.∆2n 1D.21n n a -8) Which of the following doesn’t belong to passive optical components ______.A. Directional couplerB. Semiconductor laserC. Optical fiber connectorD. Optical attenuator2. Write the full name of the following acronym （10P each 1P）1)IMD2)SCM3)AOTF4)RA5)SPM6)HFC7)OTDM8)TW9)SCM10) DBR3. Filling blanks (20P each 1P)1) The main cause of intrinsic absorption in the infrared region is ( ).22) STM-1 frames provide a transmission bit rate of ( ).3) The sensitivity of a photo detector in an optical fiber communication system is describable in terms of( ).4) According to whether there is electric or magnetic field in the direction of propagation or not,transverse modes of light waves are classified into different types: ( ), ( ), ( ) and ( ).5) Please list three steps of SDH Multiplexing: ( )，( )，( ).6)The principal noises associated with photo detectors that have no internal gain are quantum noise,dark-current noise generated in the bulk material of the photodiode, and ( ).7)Largely due to ( ) and ( ), the optical signals undergo waveform distortion anddecreased amplitude.8)The STM-1 frame is the basic transmission format for SDH. The frame lasts for ( )microseconds; therefore there are ( ) frames per second.9) A laser consists of a ( ) inside a highly reflective ( ) as well as a means to supplyenergy to the gain medium.10)( ) performance and jitter are two important indicators in a optical digital communicationsystem.11)Optical transmitter consists of ( ), a modulator and a channel coupler.12)List two classes of transmission medium: ( ), ( ).4. Give a brief description of following terms and questions (10P each 2P)1) Stimulated Emissions2) What are the advantages and disadvantages of SDH system as compared to PDH system?3) Gain saturation4) The disadvantage of Raman amplifier5) Dynamic range:5. Draw a block diagram of a typical optical digital communication system and briefly describe the functions of each part. (10P)6. A GaAs laser operating at 800nm has a 500-µm length and a refractive index n=3.7.What are the frequency and wavelength spacing? (10P)7. In a 100-ns pulse, 6×106 photons at a wavelength of 1300nm fall on an In GaAs photo detector. On the average, 5.4×106 electron-hole (e-h) pairs are generated.Please calculate the quantum efficiency. (10P)8. (20P) Consider a graded-index optical fiber, core index n1=1.50 and the core cladding index difference Δ=0.01.Try to calculate:1) The cladding index n22) The numerical aperture NA1．Multiple choice (10P each 1P)1) B 2) A 3) A 4) D 5) C 6) A 7) C 8) B2.Write the full name of the following acronym （10P each 1P）1)IMD (intermodulation disortion)2)SCM (subcarrier multiplexing)3)AOTF (acousto-optic tunable filter)4)RA (raman amplifier)5)SPM (self-phase modulation)6)HFC (hybrid fiber-coaxial)7)OTDM (optical time-division multiplexing)8)TW (traveling wave)9) SCM (subcarrier multiplexing)10) DBR (distributed Bragg reflector)3. Filling blanks (20P each 1P)1)the characteristic vibration frequency of atomic bonds2)155 Mbit/s3)the minimum detectable optical power4)TEM modes; TE modes; TM modes; hybrid modes5)mapping; aligning; multiplexing6)surface leakage current noise7)attenuation; dispersion8)125 ; 80009)gain medium ; optical cavityforward10)BER (The bit error rate)11) absorption losses; scattering losses; and bending losses12) Optical Add Drop Multiplexer(OADM)4. Give a brief description of following questions (10P each 2P)1) Stimulated Emissions: If a photon of energy hv12 impinges on the system while the electron is still in its excited state, the electron is immediately stimulated to drop to the ground state and give off a photon of energy hv12.2) The main limitations of PDH are:Inability to identify individual channels in a higher-order bit stream;Insufficient capacity for network management;Most PDH network management is proprietary;There is no standardized definition of PDH bit rates greater than 140 Mbit/s; and,There are different hierarchies in use around the world. Specialized interface equipment is required to interwork the two hierarchies.3)Gain saturation: when near saturation, the gain is nonlinear; saturation, the signal cannot be amplified.4) The disadvantage of Raman amplifier:Need large output power pump laser. As Raman Scattering, the energy is transferred from high frequency to low frequency. Cross talk will affect signal.5) Dynamic range: System dynamic range is the maximum optical power range to which any detector must be able to respond.5. (10P)6. (10P) From 2c Ln ν∆=，22Lnλλ∆= obtain: 86310812250010 3.7c GHz Ln ν-⨯∆===⨯⨯⨯， (5P).17.07.3105002)10800(26292nm Ln =⨯⨯⨯⨯==∆--λλ7. (10P)The quantum efficiencyNumber of e-h pairs generated= ----------------------------------------- (6P)Number of incident photons =665.410610⨯⨯0.90= (4P)8. (20P)According to(2P)(1) (3P)(2) (3P)From （1）:2 n 12∆= n 12- n 22n 22= n 12（1-2∆）n 2= n 1∆-21 (4P) And: n 1 =1.50，∆=0.01， Obtain: n 2==1.5002.01-=1.5098.0⨯=1.50⨯0.98995=1.48491 (4P)NA = n 1∆2=1.5002.0=1.50⨯0.14142=0.21213 (4P)。
光纤通信复习题(含答案)
1.Make a choice （共十题 每题1分）10p(1).Which of the following dispersion (色散)dose not exist in single-mode optical fiber? （ D ）A .material （材料）dispersion B.waveguide （波导） dispersionC.polarization-mode （偏振）dispersionD.intermodal （联合） dispersion(2).The unit （单位）of the fiber attenuation coefficient （衰减系数）is (C)A. dBB. dBmC. dB/kmD. dBm/km(3).the bands of Optical fiber communication is (B)A.0.01um-0.39umB. 0.8um-2.0umC.0.39um-0.79umD.100um-1000um(4).If the optical input power of a Optical amplifier is 10mW ，and the optical output power is 100mW as well ,then its output gain level is (A)A.10dBB.20dBC.30dBD.40dB(5)In order to make sure of the system BER （比特误差率） conditions , if the minimum optical input power of the receiver is 1 uW, the sensitivity of the receiver must be (A)A.－30dBmB.－40dBmC.－20dBmD.－43dBm(6)The principal （主要）light sources used for fiber optical communications applications are ：（D ）A.OA 、LDB.PIN 、APDC.PD 、LEDD.LD 、LED(7)laser （激光） action is the result of three key process ，which one of the following is not be included ？（D ）A.photon absorption （光子吸收）B.spontaneous emission （自发发射）C.stimulated emission （受激发射）pound radiation （复合发射）(8) A single mode fiber usually has a core diameter （芯径）of A.A. 10mB. 62.5nmC. 125nmD. 50mm (9)To make sure that the APD photo-detector works properly, a sufficiently D is applied across the p-n junction.A. high forward-bias voltage （高的前置偏压）B. low forward-bias voltageC. low reverse-bias voltage （低的反相偏压）D. high reverse-bias voltage(10) When DFA fiber amplifier uses as light Repeaters （中继器）, its main effect is B.A. amplifying and regenerating the signalB. regenerating the signalC. amplifying the signalD. reducing the signal noise(11) In graded-index optical fiber, the numerical aperture （数值孔径） NA can be expressed as C. A. 21n n - B. ∆2a C. ∆2n 1 D. 21n n a -(12) In practical SMFs, the core diameter is just below the cutoff （截止） of the first higher-order （高阶）mode; that is, for V slightly A.A. <2.4B. > 2.4C. =3D. =3.5(13) It is well known that the total dispersion in the single-mode regime is composed of two components: C.A. mode-partition noise （电流分配噪声）, inter- symbol InterferenceB. frequency chirp, modal dispersionC. material dispersion, waveguide dispersionD. modal dispersion, waveguide dispersion(14)At present, erbium doped （涂饵的）fiber amplifier’s maximum small signal gain （小信号增益）is around A.A. 40 dBB. 30 dBC. 20 dBD. 10 dB(15)Which of the following doesn’t belong to passive optical components （无源光学组件）BA. Directional coupler（定向耦合器）B. Semiconductor laser（半导体激光）C. Optical fiber connector（光纤连接器）D. Optical attenuator（光学衰减器）(16) The A mode has no cut off（截止）and ceases（停止）to exist only when the core diameter （芯径）is zero.A. HE11B. TE01C. TM01D. EH11(17)When the phase difference（相位差）is an integral multiple（整数倍）of A, the two modeswill beat and the input polarization（偏振）state will be reproduced.A. 2πB. πC. 1800D. π/2(18)which one of the following model can transmit in the single-mode optical fiber ?(A)A.HE11B. TE01C. TM01D. EH112. Write the full name of the following acronym（共十题每题1分）10p(1)DCF: dispersion compensating fiber（色散补偿光纤）(2)CNR: carrier to noise ratio（载噪比）(3)SRS: Stimulated Raman Scattering（受激的拉曼色散）(4)SOA: Semiconductor optical amplifier（半导体激光放大器）(5)NA: numerical aperture（数值孔径）(6)PON: passive optical network（无源光网络）(7)SLM: single longitudinal mode（单纵向模式）(8)NEP: noise-equivalent power(噪声等效功率)(9)DSF: dispersion shift fiber（色散转移光纤）(10)SONET: synchronous optical network（同步光网络）(11)A TM: asynchronous transfer mode（异步传输模式）(12)ISDN: integrated services digital network（综合业务数字网）(13)WDM: wavelength-division multiplexing(波分多路复用)(14)SDH: Synchronous digital hierarchy(同步数据系列)(15)TLLM: transmission-line laser model(传输线激光模式)(16)ONSL: optical network simulation layer（光网络模拟层）(17)OVPO: outside vapor-phase oxidation（外气相沉积法）(18)V AD: vapor-phase axial deposition(汽相轴向沉积)(19)CDMA: code-division multiple access(码分多址)(20)FDM: frequency-division multiplexing（频分复用）(21)DSP: digital signal processing（数字信号处理）(22)MCVD: modified chemical vapor deposition（修正的化学汽相沉积）(23)EDFA: erbium-doped fiber amplifier(惨饵光纤放大器)(24)FDDI: fiber distributed data interface(光纤分布式数据接口)(25)SIOF: step index optical fiber(阶跃指数光纤)(26)GIOF: graded index optical fiber(渐变性光纤)(27)SQW: single quantum-well（单量子井）(28)ARQ: automatic reapt request(自动重发请求)(29)FEC: forward error correction（前向纠错）3. Filling blanks(共20空每空1分) 20p(1) According the mode which propagate（传播）in the fiber, the fiber can be divided into (single mode) fiber) and (multimode) fiber.(2) The most common misalignment（非线性）occurring in practice, which also causes the greatest power loss, is (axial displacement轴向移位).(3) The electromagnetic energy（电磁能）of a guided mode is carried partly in the (core) and partly in the (cladding包层).(4)The basic attenuation mechanisms（衰减机制）in a fiber are (absorption吸收), (scattering散射) and (radiative losses辐射损耗) of the optical waveguide.(5) The two main optical amplifier types can be classified as (SOAs半导体激光放大器) and (DFAs).(6) Networks are traditionally divided into: (LANs局域网), (MANs城域网),(W ANs广域网).(7)The principal light sources used for fiber optic communications applications are (ILDs注入型激光二极管) and (LEDs发光二级管) .(8) The dominant noise generated in an optical amplifier is (ASE).(9) The two most common samples of these spontaneous fluctuations（波动）are (shot noise) and (thermal noise热噪声).(10)According to the refractive index（折射率）of the core, the fiber can be divided into (step-index) fiber and (graded-index) fiber .(11)The total dispersion in single-mode fibers consists mainly of (material) and (waveguide) dispersion.(12) The most meaningful criterion（标准）for measuring the performance of a digital communication system is the (average error probability平均概率误差). In an analog system the fidelity criterion is usually specified in terms of a (peak signal-to-noise ratio).(13) The simplest transmission link is a (point-to-point line) that has a transmitter on one end an a receiver on the other.(14)The commonly used materials for fiber lasers are (erbium) and (neodymium).(15)Absorption is related to the fiber material, whereas scattering is associated both with the (fiber material) and with (structural imperfections) in the optical waveguide.(16)The two basic LED configurations being used for fiber optics are (surface emitters) and (edge emitters).(17) The basic schemes for improving the reliability are (ARQ自动重发请求) and (FEC前向纠错).4. Give a brief description of following terms and questions（共5题每题3分）15p (1) Briefly describe the key system features of WDM.波分复用1) capacity upgrade（容量升级）2) transparency （透明度）3) wavelength routing（波长选路）4) wavelength switching（波长转换）5) the connectors used to join individual fiber cables to each other and to the source anddetector(2) Briefly describe there major goals of SDH.同步数据系列1) Avoid the problems of PDH2) Achieve higher bit rates3) Better means for operation, administration and Maintenance(3) List at least three advantages of SOA半导体激光放大器.1) Small size, and easy to be integrated with semiconductor circuits.2) Fabrication（制造）is simple and with low power consumption（功耗）, long life-span and low cost.3) Gain response is very quick and well suited for switching and signal processing in optical networks application.4) Can amplify optical signal and process signal in the same time such as switch, so can be used in wavelength converting and optical switch.(4) List more than three disadvantages of SOA.1) The coupling loss with optical fiber is too large2) Sensitive to polarization3) Noise figure is high(~8 dB)4) crosstalk串音干扰5) Easy to be affected by temperature, low stability(5) Stimulated Emissions受激发射If a photon（光子）of energy hv12 impinges on（撞击）the system while the electron is still in its excited state, the electron is immediately stimulated to drop to the ground state and give off a photon of energy hv12.(6)Dynamic rangeSystem dynamic range is the maximum optical power range to which any detector must be able to respond.(7) What conditions should be met to achieve a high signal-to-noise ratio?1) The photodetector（光电探测器）must have a high quantum efficiency（量子效率）to generate a large signal power.2) The photodetector and amplifier noises should be kept as low as possible.(8) Please write the three basic categories（类别）of degradation of light sources1) internal damage2) ohmic contact degradation3) damage to the facets of laser diodes（激光二极管）(9)List the three factors largely determining the frequency response of an LED1) the doping level（掺杂度）in the active region2) the injected carrier lifetime Ti in the recombination region3) the parasitic capacitance(寄生电容) of the LED.(10)Write the three basic types of two-level binary line codes that can be used for optical fiber transmission links.1) non-return-to-zero (NRZ) format2) return-to-zero (RZ) format3) phase-encoded (PE) format(11) Please write the three different mechanisms causing absorption briefly1) Absorption by atomic defects （原子缺陷） in the glass composition.2) Extrinsic （非固有的） absorption by impurity atoms in the glass material.3) Intrinsic absorption by the basic constituent atoms of the fiber material.(12) The disadvantage of Raman amplifierNeed large output power pump laser. As Raman Scattering, the energy is transferred from high frequency to low frequency. Cross talk will affect signal.5. Figure （共1题 每题5分）5p（1）Please draw the basic step for an automatic-repeat-request (ARQ) error-correction scheme. Solution:（ARQ纠错机制）(2)Please draw out the basic elements of the optical receiver.(5p)（光接收器）Solution:(3)Please draw out the basic elements of an analog link and the major noise contributions. Solution:（模拟链路及噪声源）光发送机电模拟输入信号谐波失真互调失真RIN激光削波光纤信道模式失真损耗GVD 光放大器ASE 噪声光检测器散弹噪声热噪声放大器噪声APD 倍增噪声电模拟输出到RF 接收机(3) consider the encoder shown in Fig.1that changes NRZ data into a PSK ing this encoder,draw the NRZ and PSK waveforms for the data sequence 0001011101001101.clock/2PSK dataNRZ datafrequency Afrequency BFig.1Solution:6. Calculation Problems(共3-4题，统计40分) 40p(1) A wave is specified by 8cos 2(20.8)y t z π=-,where y is expressed in micrometers and the propagation constant （传播常数） is given in 1m μ-.Find (a) the amplitude,(b) the wavelength,(c) the angular frequency （角频率）, and (d) the displacement at time 0t = and 4z m μ=. Solution:The general form is:y = (amplitude) cos()cos[2(/)]t kz A vt z ωπλ-=-.Therefore(a) amplitude 8m μ=(b) wavelength: 11/0.8m λμ-= so that 1.25m λμ=(c) 22(2)4v ωπππ===(d) At 0t = and 4z m μ= we have 18cos[2(0.8)(4)]8cos[2( 3.2)] 2.472y m m πμμπ-=-=-=(2) A certain optical fiber has an attenuation of 0.6dB/km at 1300nm and 0.3dB/km at 1550nm.Suppose the following two optical signals are launched simultaneously into the fiber: an optical power of 150W μ at 1300nm and an optical power of 100W μ at 1550nm. What are the Solution:power levels in W μof these two signals at (a) 8km and (b) 20km?Since the attenuations are given in dB/km, first find the power levels in dBm for100W μ and 150W μ. These are, respectively,P(100W μ) = 10 log (100 W μ/1.0 mW) = 10 log (0.10) = - 10.0 dBmP(150W μ) = 10 log (150 W μ/1.0 mW) = 10 log (0.15) = - 8.24 dBm(a) At 8 km we have the following power levels:P 1300(8 km) = - 8.2 dBm – (0.6 dB/km)(8 km) = - 13.0 dBm = 50W μP 1550(8 km) = - 10.0 dBm – (0.3 dB/km)(8 km) = - 12.4 dBm = 57.5W μ(b) At 20 km we have the following power levels:P 1300(20 km) = - 8.2 dBm – (0.6 dB/km)(20 km) = - 20.2 dBm = 9.55W μP 1550(20 km) = - 10.0 dBm – (0.3 dB/km)(20 km) = - 16.0 dBm = 25.1W μ(3) A double-heterojunction （异质结） InGaAsP LED emitting at a peak wavelength of 1310nm has radiative and nonradiative recombination times of 25 and 90ns, respectively. The drive current is 35mA.(a) Find the internal quantum efficiency and the internal power level.(b) If the refractive index （折射率） of the light source material is n=3.5, find the power emitted from the device.Solution: (a) From Eq. int 11/r nr rτητττ==+, the internal quantum efficiency is int 10.783125/90η==+， and from Eq.int intint I hcI p hv q q ηηλ== the internal power level is int (35)(0.783)26(1310)hc mA p mW q nm ==(b) From Eq.int e int 2p (1)n t p P n n η==+, 21260.373.5(3.51)P mW mW ==+ (4) An LED with a circular emitting area of radius 20m μ has a lambertian emission pattern with a 1002()W cm sr ∙axial radiance at a 100mA drive current. How much optical power can be coupled into a step-index fiber having a 100m μ core diameter and NA=0.22? How much optical power can be coupled from this source into a 50m μ core-diameter graded-index fiber having 12.0, 1.48n α== and 0.01∆=?Solution:The source radius （半径） is less than the fiber radius,so Eq. 222222,1()2LED step s o s o P r B NA r B n ππ==∆ holds: 22223222,()(210)(100/)(0.22)191LED step s o P r B NA cm W cm W ππμ-==⨯= From Eq. 222,122[1()]2s LED graded s o r P r B n απαα=∆-+ 232222,122(210)(100/)(1.48)(0.01)[1()]15925LED graded P cm W cm W πμ-=⨯-=(5)Suppose an avalanche photodiode hasthe following parameters ：1/231,1,0.85,,10L D L I nA I nA F M R η=====Ω, and 1B kHz=.Consider a sinusoidally(正弦） varying 850nm signal, which has a modulation index m=0.85 and an average power level 050P dBm =-, to fall on the detector at room temperature. At what value of M does the maximum signal-to-noise ratio occur?Solution: Using Eq.2222()()24/p P D L B Li M S N q I I M F M B qI B k TB R <>=+++ we have 22005/2001()22()24/D L B LR P m M S N qB R P I M qI B k TB R =+++ 162235/2191.215102.17610 1.65610M M ---⨯=⨯+⨯ The value of M for maximum S/N is found from Eq.224/()x L B L opt P D qI k T R M xq I I ++=+, with x = 0.5:Moptimum = 62.1.(6)An LED operating at 1300 nm injects 25W μ of optical power into a fiber. If the attenuation （衰减） between the LED and the photodetector （光电探测器） is 40 dB and the photodetector quantum efficiency （量子效率） is 0.65, what is the probability that fewer than 5 electronhole pairs （电子空穴对） will be generated at the detector in a 1-ns interval ?Solution: From ⎰==τηη0)(hvN hv E dt t P ,the average number of electron-hole pairs generated in a time t is 6.10)/103)(106256.6()103.1)(101)(1025(65.0/8346910=⨯⨯⨯⨯⨯===----s m Js m s W hc Pt h E N ληνη Then,from Eq.(7-2)%505.0120133822!5)6.10(!)(6.106.105=====---e e n e N n P N n(7) An engineer has the following components available:(a) GaAlAs laser diode operating at 850 nm and capable of coupling 1 mW (0 dBm) into a fiber. (b) Ten sections of cable each of which is 500 m long, as a 4-dB/km attenuation, and hasconnectors on both ends.(c) Connector loss of 2dB/connector.(d) A pin photodiode receiver.(e) An avalanche photodiode receiver.Using these components, the engineer wishes to construct a 5-km link operating at 20 Mb/s. If the sensitivities of the pin and APD receivers are -45 and -56 dBm, respectively, which receiver should be used if a 6-dB system operating margin is required?Solution:(a)Use margin 2system L l P P P f C R S T ++=-=α，to analyze the link power budget.(a) For the pin photodiode,with 11 jointsdB L km dB dB dBm dBm insystemm L l P P P f C R S T 6)/4()2(11)45(0arg )(11++=--=++=-=αWhich gives L=4.25km. the teansmission distance cannot be met with these components. (b)For the APDdB L km dB dB dBm dBm 6)/4()2(11)56(0++=--Which gives L=7.0km. the transmission distance can be met with these components.(8) Suppose we want to frequency-division multiplex 60 FM signals. If 30 of these signals have a per-channel modulation index i m =3 percent and the other 30 signals have i m =4 percent, find the optical modulation index （调制指数） of the laser.Solution:The total optical modulation index is%4.27])04(.30)03(.30[][2/1222/12=+==∑ii m m(9) An optical transmission system is constrained to have 500-GHz channel spacings. How many wavelength channels can be utilized in the 1536-to-1556-nm spectral band （频谱带）? Solution: In terms of wavelength,at acentral wavelength of 1546nm a 500-GHz channel spacing isnm s sm nm f c 410500/103)1546(19822=⨯⨯=∆=∆-λλ The number of wavelength channels fitting into the 1536-to-1556 spectral band then is 54/)15361556(=-=nm nm N(10) The output saturation （饱和） power sat out P , is defined as the amplifier output power for which the amplifier gain G is reduced by 3 dB (a factor of 2) from its unsaturated value 0G . Assuming 0G >>1, show that in terms of the amplifier saturation power sat amp P ,, the output saturation power issat amp sat out P G G P ,00,)1(2ln -=Solution: Let 2/0G G = and 0,/22/G P P P sat out out in ==.then Eq.(11-15) yields2ln 212,,00satout sat amp P P G G += Solving for s a t out P , and with 10>>G ,we havesat amp sat amp sat amp sat out P P P G G P ,..00,693.0)2(ln 22ln =≈-=。
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一 Make a choice1) In graded-index optical fiber, the numerical aperture NA can be expressed as C. A.21n n - B.∆2a C.∆2n 1D.21n n a-2) In practical SMFs, the core diameter is just below the cutoff of the first higher-order mode; that is, for V slightly A.A. <2.4B. > 2.4C. =3D. =3.53) When the phase difference is an integral multiple of ______, the two modes will beat and the input polarization state will be reproduced. A. 2π B. π C. 1800 D. π/2 4) It is well known that the total dispersion in the single-mode regime is composed of two components: C.A. mode-partition noise, inter- symbol InterferenceB. frequency chirp , modal dispersionC. material dispersion , waveguide dispersionD. modal dispersion , waveguide dispersion 5) Which of the following codes cannot be transmitted in fibers B.A. CMIB. HDB3C. 5B6BD. 8B1H6) Dispersion-shifted fiber (DSF) is a type of single-mode fiber designed to have zero dispersion near A nm.A. 1550B. 850C. 1310D. 15107) To make sure that the APD photo detector works properly, a sufficiently D is applied across the p-n junction.A. high forward-bias voltageB. low forward-bias voltageC. low reverse-bias voltageD. high reverse-bias voltage 8) A single mode fiber usually has a core diameter of A.A. 10mB. 62.5nmC. 125nmD. 50mm二Blank filling1) Each SDH frame comprising three areas: a section overhead area （SOH ）, a pointer area, a payload area including the data to be transmitted.2) List three applications of FBG(fiber Bragg grating): filter 、Optical Add Drop Multiplexer(OADM) and dispersion compensator.3)According to whether there is electric or magnetic field in the direction of propagation or not, transverse modes of light waves are classified into different types: TEM modes, TE modes, TM modes and hybrid modes.4) Transmission of information in an optical format is carried out not by frequency modulation of the carrier, but by varying the intensity of the optical power.5) Largely due to attenuation and dispersion, the optical signals undergo waveform distortion and decreased amplitude.6) Material dispersion occurs because the index of refraction varies as a function of the optical wavelength.7) ZDSF is a dispersion shifted single mode fiber that has the zero dispersion wavelength near the 1550 nm window, but outside the window actually used to transmit signals.8)A laser is constructed from three principal parts: a pump source, a gain medium, and an optical resonator.9)An optical fiber comprises at least two layers, a core and a cladding.10)Optical transmitter consists of optical source, a modulator and a channel coupler.11)Fiber refractive index profiles classify fibers as step-index fibers and graded-index fibers.12)BER (The bit error rate) performance and jitter are two important indicators in a opticaldigital communication system.13)LASER is a mechanism for emitting light within the electromagnetic radiation region of thespectrum, via the process of stimulated emission.14)There are two kinds of SOA：Fabry-Perot Amplifier (FPA) and Traveling-Wave Amplifier(TWA) .15)The principal noises associated with photo detectors that have no internal gain are quantumnoise, dark-current noise generated in the bulk material of the photodiode, and surface leakage current noise.16)In a step-index fiber, the refractive index of the core is uniform and undergoes an abruptchange at the core-cladding boundary. In graded-index fibers, the refractive index of the core varies gradually as a function of radial distance from the fiber center.17)If the input pulse excites both polarization components, it becomes broader as the twocomponents disperse along the fiber because of their different group velocities. This phenomenon is called the PMD.18)The most common semiconductor photo detector is the pin photodiode.19)The main cause of intrinsic absorption in the infrared region is the characteristic vibrationfrequency of atomic bonds.20)In SDH transmission structures, a TU (Tributary Unit) includes a low level VC and a TUPTR.21)Extrinsic absorption is caused by impurities introduced into the fiber material.22)Intramodal dispersion is a result of the group velocity being a function of the wavelength.23)The optical amplifiers is divided into 3 groups: semiconductor optical amplifier (SOA),optical fiber amplifier (OPA) and Raman amplifier (FRA).24)There are two kinds of directional couplers: a prism-fibre and a fibre-fibre lapped coupler.25)EDFA has three pumping structures: ①the forward pumping structure; ②the backwardpumping structure; ③ the double pumping structure.26) A laser consists of a gain medium inside a highly reflective optical cavity, as well as a meansto supply energy to the gain medium.27)Attenuation in an optical fiber is caused by absorption losses, scattering losses, and bendinglosses.28)STM-1 frames provide a transmission bit rate of 155 Mbit/s.29)From the point of view of the wave theory, light wave could be described as anelectromagnetic wave.30)Intermodal dispersion is a result of each mode having a different value of the group velocityat a single frequency.31) A typical optical digital communication system usually comprises three parts: transmitter,optical fiber channel, and receiver.32)The pin Photo detector structure consists of p and n regions separated by a very lightlyn-doped intrinsic (i) region.33)Please list three steps of SDH Multiplexing: mapping，aligning ，multiplexing.34) There are three variations of WDM that are commonly used: Broad WDM, Coarse WDM, and Dense WDM.35) The STM-1 frame is the basic transmission format for SDH. The frame lasts for 125 microseconds; therefore there are 8000 frames per second.36) In SDH frame structure, the SOH is made up of a regenerator section overhead (RSOH) and a multiplexing section overhead (MSOH).37) The sensitivity of a photo detector in an optical fiber communication system is describable in terms of the minimum detectable optical power.38) Please list three applications of EDFA in optical fiber communication system: as preamplifier of receiver 、as power amplifier of transmitter and as the optical repeater.39)An optical isolator (optical diode), is an optical component which allows the transmission of light in only one direction.三Interpretation of terms and phrases1) AON (all-optical network) 2) DBR (distributed Bragg reflector) 3）FDDI (fiber distributed data interface) 4）HFC (hybrid fiber-coaxial) 5）ISDN (integrated services digital network) 6）RA (raman amplifier) 7）OC (optical carrier) 8）OTDM (optical time-division multiplexing) 9）PON (passive optical network) 10）SCM (subcarrier multiplexing) 11）SDH (synchronous digital hierarchy) 12）SPM (self-phase modulation) 13）STS (synchronous transpor signal) 14）TW (traveling wave)15）WGA (waveguide-grating router) 16）IMD (intermodulation disortion) 17）AWG (arrayed-waveguide grating) 18）AOTF (acousto-optic tunable filter) 四 画图题1) Draw the element block of a Distributed forward Raman amplifier2) Draw an element diagram of a Double pump EDFA3) Draw a block diagram of a typical optical digital communication system and briefly describe the functions of each part.OutputInputEDFWDMIsolatorPump LaserIsolatorPump LaserWDMPump LaseroutputfiberinputAn optical communication system consists of a transmitter, which encodes a message into an optical signal, a channel, which carries the signal to its destination, and a receiver, which reproduces the message from the received optical signal. The optical repeater is to extend the transmission distance of optical signal.4) Draw the element diagram of the application of optical amplifier.四 简答题1) Dispersion: Any phenomenon in which the velocity of propagation of any electromagnetic wave is wavelength dependent. 2) Stimulated EmissionsIf a photon of energy hv 12 impinges on the system while the electron is still in its excited state, the electron is immediately stimulated to drop to the ground state and give off a photon of energy hv 12.3) There are 3 dispersion types in the optical fibers in general: 1- Material Dispersion 2- Waveguide Dispersion3- Polarization-Mode Dispersion4) Polarization mode dispersion (PMD) is due to slightly different velocity for each polarization mode because of the lack of perfectly symmetric & anisotropic of the fiber5) Laser is an optical oscillator. It comprises a resonant optical amplifier whose output is fed back into its input with matching phase. Any oscillator contains: 1. An amplifier with a gain-saturated mechanism 2. A feedback system3. A frequency selection mechanism4. An output coupling schemeOptical transmitterRepeaterOptical receiverfiberfiber6) In thermal equilibrium the stimulated emission is essentially negligible, since the density of electrons in the excited state is very small, and optical emission is mainly because of the spontaneous emission. Stimulated emission will exceed absorption only if the population of the excited states is greater than that of the ground state. This condition is known as Population Inversion. Population inversion is achieved by various pumping techniques.7) Turn on DelayWhen the driving current suddenly jumps from low (I1 < Ith) to high (I2 > Ith) , (step input), there is a finite time before the laser will turn on8) The Quantum LimitFor an ideal photo-detector having unity quantum efficiency and producing no dark current, it is possible to find the minimum received optical power required for a specific BER performance in a digital system. This minimum received power level is known as the quantum limit.9) Gain flatness: The difference between the biggest gain and the smallest gain of the different frequency signal.10) The advantage of Raman amplifier: Simple fabricationLow noise, because amplifying action take place inside the ordinarily fiber.The wavelength can be selected in the low loss waveband.Very wide gain bandwidth.11) Micro bending Loss: microscopic bends of the fiber axis that can arise when the fibers are incorporated into cables. The power is dissipated through the micro bended fiber, because of the repetitive coupling of energy between guided modes & the leaky or radiation modes in the fiber.12) Gain saturation: when near saturation, the gain is nonlinear; saturation, the signal cannot be amplified.13) The disadvantage of Raman amplifier:Need large output power pump laser. As Raman Scattering, the energy is transferred from high frequency to low frequency. Cross talk will affect signal.14) The principal noises associated with photo detectors are:1- Quantum (Shot) noise: arises from statistical nature of the production and collection of photo-generated electrons upon optical illumination. It has been shown that the statistics follow a Poisson process.2- Dark current noise: is the current that continues to flow through the bias circuit in the absence of the light. This is the combination of bulk dark current, which is due to thermally generated e and h in the pn junction, and the surface dark current, due to surface defects, bias voltage and surface area.15) List the advantages of fiber-optic communications over other types of communication technologies.The advantage of optical fiber communication:1. Weight and Size2. Material cost (SiO2 is plentiful)3. Information Capacity4. No electromagnetic interference5. No electrical connection6. Distance between repeaters7. Better security 8. Low crosstalk16) The fabrication of amplifierOptical isolator ，Optical multiplexer, EDF, Pump laser17) What are the advantages and disadvantages of SDH system as compared to PDH system? The main limitations of PDH are:Inability to identify individual channels in a higher-order bit stream; Insufficient capacity for network management; Most PDH network management is proprietary;There is no standardized definition of PDH bit rates greater than 140 Mbit/s; and,There are different hierarchies in use around the world. Specialized interface equipment is required to interwork the two hierarchies.18) List the types of fiber attenuation and dispersion. Absorbing\scattering and bending loss Material/ mode/ waveguide dispersion. 19) The avalanche effect.The created carriers are accelerated by the high electric field, gaining enough energy to cause further impact ionization. 20) Dynamic range:System dynamic range is the maximum optical power range to which any detector must be able to respond.21) Differentiate between step index and graded index optical fiber.Step index fiber has a core of one index of refraction; graded index fiber has a core in which the outside edge starts with a low index of refraction that gradually increases towards the center. 五 计算题1) Suppose two graded index fibers are misaligned with an axial offset of d=0.3a. Try to calculate the fraction of optical power coupled from the first fiber into the second fiber. （Parameter a is the core radius ）The fraction of optical power coupled in the fiber ：122222arcco s()152262T P d d d d P a a a a π⎧⎫⎡⎤⎛⎫⎪⎪⎛⎫=---⎢⎥⎨⎬ ⎪ ⎪⎝⎭⎢⎥⎝⎭⎪⎪⎣⎦⎩⎭()()21220.320.15arcco s(0.15)10.15532π⎧⎫⎛⎫⎪⎪⎡⎤=--- ⎪⎨⎬⎣⎦ ⎪⎪⎪⎝⎭⎩⎭0.748=Turn it into d B , obtain 10lo g1.27T P d B P=-2) A GaAs laser operating at800nm has a 500-µm length and a refractive index n=3.7.What arethe frequency and wavelength spacing?From 2c L nν∆=，22L nλλ∆=obtain:863108122500103.7c G H z L nν-⨯∆===⨯⨯⨯，3) In a 100-ns pulse, 6×106 photons at a wavelength of 1300nm fall on an In GaAs photo detector. On the average, 5.4×106 electron-hole (e-h) pairs are generated.Please calculate the quantum efficiency. The quantum efficiencyNumber of e-h pairs generated = ----------------------------------------- Number of incident photons =665.410610⨯⨯0.90=4) Consider a graded-index optical fiber, core index n1=1.50 and the core cladding index difference Δ=0.01.Try to calculate: 1. The cladding index n22. The numerical aperture NA解：已知：n 1 =1.50，∆=0.01， 根据(1)(2)由（1）式，可知2 n 12∆= n 12- n 22 n 22= n 12（1-2∆） n 2= n 1∆-21 将n 1、∆代入上式，可得n 2==1.5002.01-=1.5098.0⨯=1.50⨯0.98995=1.48491将n 1、∆代入（2）式，可得NA = n 1∆2=1.5002.0=1.50⨯0.14142=0.21213 5) The numerical aperture NA is NA=∆21n =22.001.02560.1=⨯⨯6) The normalized frequencyV=∆221λπna =01.0231.15056.11416.3⨯⨯⨯=26.454>V C =2.4057) Consider a 30-km long optical fiber that has an attenuation of 0.8dB/km at 1300 nm. If 200µW of optical power is launched into the fiber, try to calculate the optical output power P out .First we turn the input signal power unit from mW into dBm63()20010()10lo g 10lo g 7.01110in in P W W P d B m d B m m W W --⎡⎤⨯⎡⎤===-⎢⎥⎢⎥⨯⎣⎦⎣⎦From()10(0)l g()P d Bo kmzP z α=, as z=30k,the output power is ： ()()()10lo g10lo g 11o u t in P WP W Pd B m z o u tm W m W α⎡⎤⎡⎤==-⎢⎥⎢⎥⎣⎦⎣⎦7.0(0.8/)(30)31.0d B m d B km km d B m=--=-Also31.0/103(30)10(1)0.79100.79P km m W m W W μ--==⨯=8) A photodiode is constructed of GaAs, which has a band-gap energy of 1.43eV at 300K.What is the cutoff wavelength? The cutoff wavelength is ()()()()348196.62510310/8691.43 1.610/c gJ s m s h c n m E eV J eVλ--⨯⋅⨯===⨯。