100Gb/s归零码信号的2R再生

本文提出了基于半导体光放大器(SOA)中的瞬态交叉相位调制(T-XPM)效应与交叉增益压缩(XGC)效应的全光2R再生方法, 同时研究了SOA中的T-XPM效应获得反逻辑码信号以及XGC 效应光开关门的特性, 实现了100 Gb/s归零码(RZ)信号的2R再生, 接收机灵敏度提高了1.7-2 dB; 对该方案中的反逻辑码对于再生效果的影响进行了量化研究, 并在C波段范围内研究了该再生方案的再生效果, 实现了覆盖1535-1555 nm的全光2R再生.

A study of 100 Gb/s 2R regeneration for return-to-zero code signal

Quality of optical signal can be severely degraded after a long distance optical fiber transmission, therefore all-optical 2R (re-amplification, re-shaping) regeneration is required for its low power consumption and good potential of high-speed operation. Semiconductor optical amplifier (SOA) is a very promising candidate for regeneration due to its relatively low nonlinear switching power threshold and possibility of integration. However, speeds of the existing 2R schemes based on SOAs are limited by pattern effects introduced by the long carrier recovery time. So far, most of experimental results for SOA-based regeneration schemes have been limited to 40 Gb/s, only a few demonstrations at 80 Gb/s are available. An effective method to cope with the pattern effects in the SOA is to employ cross gain compression (XGC) effect. Simultaneously injecting two signals of different wavelengths with complementary logics and balanced powers into the SOA leads to an almost constant ability to make the XGC effect intrinsically immune to the pattern effects. Previously, 2R experimental results were demonstrated at 10 Gb/s and 40 Gb/s with XGC respectively, but no further results of higher speed have been presented to date. In this study, we improve the previous two-stage configuration for XGC-based regeneration by introducing a transient cross phase modulation (T-XPM) in the first SOA for generating the high-quality logic-inverted signal, which, as we find, is essential to facilitating the high-speed XGC operation in the next SOA. Firstly, a numerical model of the photon-electron dynamics in an SOA is built with considering the ultrafast intra-band processes, amplified spontaneous emission (ASE) noise at multiple wavelengths, and device segmentation along propagation direction. The quality of the logic-inverted signal with different offsets of the filter wavelength for T-XPM is studied with the model. It is found that the appropriate blue-shift detuning of the filter wavelength greatly helps to improve the quality of the logic-inverted signal. In experiment, the influence of the filter offset on the quality of the logic-inverted signal is also investigated systematically and the best quality and the largest eye-opening of the logic-inverted signal are achieved with a blue-shift of 0.72 nm, which are consistent with the simulation result. With the best logic-inverted signal, XGC effect is deployed in the second SOA. Effective reduction of the amplitude fluctuation can be observed by comparing the eye diagrams of the input degraded with output regenerative signals. Bit error rates (BERs) are also measured for all four tributaries of the degraded and the regenerated signals and the receiving sensitivity at a BER of 10^-9 is improved by 1.7-2 dB. Such results show that the XGC-based 2R regeneration scheme is effective even at a speed of as high as 100 Gb/s with the help of high-quality logic-inverted signal. Degraded signals at different wavelengths (from 1535 nm to 1555 nm) are successfully regenerated with Q-factor improvement, demonstrating the wavelength-independent regeneration capability of the XGC-based 2R regenerator.