光通讯基础课件1教学材料

Prof. Yang, The college of Optic and Electronic Information Engineering, USST 7
A Photon
What happens if an atom jumps from an upper level to a lower level, say, from level E3 to level E2? There is an energy gap between these two levels, ΔE = E3 – E2 , and this difference will be released as a quantum of energy , which is called a photon .
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 5
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 6
Light :
1. Electromagnetic (EM) . A ray or beam ----In the geometric optics view 3. A stream of photons ---- In the quantum view
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 2
6.Interference
There is interference between light waves of both arms. If light waves of both arms have the same phase, they will interfere constructively and destructively if they are reverse.
7.diffraction
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 3
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 4
1.l ELECTROMAGNETIC WAVES
1. Wavelength:λ 2. Velocity: c 3. Frequency:
= 1/T
4. The period: T
λ =c
(1.l)
5. Spectrum : Visible :λ=400 nm----700 nm
Prof. Yang, The college of Optic and Electronic Information Engineering, USST 1
The incident angle at which the angle of refraction equals 900 is called the critical incident angle, θ1C.
Total internal reflection is a necessary condition to make optical fiber work as a communications link.
A photon as a particle, an elementary particle that carries a quantum of energy, EP, and that travels with the speed of light, c A photon's energy, EP, is defined as follows:
1.3 A STREAM OF PHOTONS An energy-Level Diagram
Bohr's model assumes that electrons rotate on stationary orbits and therefore possess a stationary value of energy. An atom can be at any of these levels, or other words, it can change its energy states, and it can change its energy only by jumping from one level to another; In level only discretely
EP = h (1.4) Where h is Planck's constant (h = 6.626 10-34 J . s) and is the photon's frequency The higher the photon's frequency, the more energy it carries. Light is a stream of photons.
Snell's law :
θ1 =θ3
n1 sinθ1 = n2 sinθ2
(1.3)
Total internal reflection : When light travels from a medium with a higher refractive index to a medium with a lower refractive index and it strikes the boundary at more than the critical incident angle, (θ1 >θ1C )all light will be reflected back to the incident medium, meaning it will not penetrate the second medium.