OFC-2014-Tu2F.6

Tu2F.6.pdf
OFC 2014 © OSA 2014
Master-to-slave injection-locked WRC-FPLD pair with 16 DWDM-PON channels for 16-QAM OFDM transmission
1
Min-Chi Cheng, Cheng-Ting Tsai, and Gong-Ru Lin*
Tu2F.6.pdf
OFC 2014 © OSA 2014
The slave WRC-FPLD is biased at 45 mA (about 2.5 times of the I th) temperature controlled at 24.5oC to match the modal wavelength of the master WRC-FPLD, which is then injection-locked by the one of the modes from master WRC-FPLD filtered by the DeMux. The polarization controller (PC) is used to adjust the polarization injected into the slave WRC-FPLD. After passing through the DeMux in this DWDM-PON architecture, the partially coherent WRC-FPLD master can simultaneously support multiple single-mode channels for the injection-locked slave WRC-FPLD by properly fitting the channel wavelength of the DeMux with a precise temperature control. The 20-Gbit/s large 16-QAM OFDM data stream with 214 OFDM subcarriers occupying a bandwidth of 5 GHz is generated by a 12 GSa/s arbitrary waveform generator (AWG, 7122B) to directly modulate the master-to-slave injection-locked WRC-FPLD. The optical OFDM data is received by a photodiode with amplifier after propagating over a 25-km single mode fiber (SMF). The amplified analog OFDM data-stream was sampled by a real-time oscilloscope (Tektronix, DSO 71254) with a sampling rate of 100 GS/s, and then resolved with homemade MATLAB decoder. 3. Results and Discussions The packages and injection-locking spectra of the master-to-slave WRC-FPLD pair are shown in Fig. 2. Both the wavelength range of master and slave WRC-FPLDs are between 1570 and 1590 nm (L-band). The optical spectrum of the master WRC-FPLD with mode spacing of 0.4-0.5 nm (tunable by varying the cavity length) is shown in Fig. 2(i), the slave WRC-FPLD exhibits a similar mode spacing with the master so as to easily match their wavelength for performing injection-locking at each corresponding mode.
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Fig. 1. Schematic diagram of a master-to-slave injection-locked WRC-FPLD pair for 16-QAM OFDM transmission at bit rate of 20 Gbit/s. AWG: arbitrary waveform generator, PD: photodetector, Amp: amplifier, DSO: digital signal oscilloscope, OSA: optical spectrum analyzer.
OCIS codes: (140.3520) Lasers, injection-locked; (140.5960) Frequency modulation; (140.2020) Diode lasers; (060.2330) Fiber optics communication.
1. Introduction The self-controlled universal transmitter is a mandatory solution for implementing cost-effective dense wavelength division multiplexing passive optical network (DWDM-PON), while the development of most injection-locked colorless transmitters considered to be employed in either the central office (CO) or the optical network units (ONUs) [1] are still under progress. Recently, we have proposed the direct modulation of a long weak resonant cavity Fabry-Perot laser diode (WRC-FPLD) under coherently wavelength injection-locking for 16-QAM OFDM at 12 Gbit/s [2]. However, the coherent single-mode tunable laser or distribute feedback laser diode is not a cost-effective solution to serve as the master for injection-locking the slave transmitters in a DWDM-PON as each channel requires one single-mode source for remote wavelength control. The non-universal and high cost features restricts the real application of aforementioned architecture in DWDM-PON. To further reduce the cost of the injection-locking master source, the non-coherent broadband light source based on amplified spontaneous emission (ASE) was proposed [3], which inevitably limits the transmission performance due to the relative intensity noise added into the injection-locked mode. Therefore, partially coherent multi-mode laser diode is recently considered as the new class of broadband master to function as a remote multi-channel wavelength controller in the DWDM-PON link. In addition, the optical orthogonal frequency division multiplexing (OFDM) data format has been applied particularly for the DWDM-PON transmitters with finite modulation bandwidth, which is capable of transmitting large bit-rate data with high spectral usage efficiency in frequency domain [4]. In this work, we successfully demonstrated a partially coherent master-to-slave injection-locked WRC-FPLD pair for delivering the 16-QAM OFDM data at up to 20 Gbit/s transmission over 25-km long single-mode fiber. Such a master-to-slave injection-locked WRC-FPLD pair not only promotes its 16-QAM-OFDM transmission performance to be comparable with the purely coherent injection-locked WRC-FPLD [5], but also provides multiple injection-locked channels concurrently to meet the demand of an universal colorless transmitter required for the DWDM-PON. 2. Experimental Setup Figure 1 illustrates the DWDM-PON architecture based on the partially coherent master-to-slave injection-locked WRC-FPLD pair with a limited bandwidth of 5 GHz for the 16-QAM OFDM transmission at total bit rate of 20-Gbit/s. The master WRC-FPLD is biased at 56 mA (nearly third the threshold condition) at a controlled temperature of 23oC to ensure the constant power of each laser mode is higher than -4 dBm after passing through a circulator and a AWG based DeMux in the DWDM-PON.