利用光锁相环路实现40Gb/s时钟恢复

40 Gb/s Clock Recovery Based on Optical Phase-Locked Loop

提出并建立了一种新型的基于光纤四波混频效应和压控光脉冲源的光锁相环路(OPLL),用于光时分复用系统(OTDM)中的时钟恢复过程。从理论上分析了其工作原理,及各模块结构和功能。利用高非线性光纤中的四波混频效应实现全光鉴相器,有效缩短了光纤长度,减小了光纤色散引起的脉冲走离,鉴相器消光比超过30 dB。采用再生锁模光纤激光器实现压控光脉冲源,在保证脉冲质量的前提下,重复频率调节范围达到380 kHz。在40 Gb/s时钟恢复实验中,获得脉宽为7.2 ps、接近变换极限的时钟脉冲,时间抖动(RMS)为152 fs,超模抑制比大于60 dB。实验证明,输入信号幅度波动和码型效应对环路影响很小。

A novel optical phase-locked loop （OPLL） based on four-wave-mixing in optical fibers and optical voltagecontrolled oscillator （OVCO） is proposed and built to perform clock recovery in optical time-division multiplexed systems. The operation principle of the optical phase-locked loop and the configurations and functions of modules in optical phase-locked loop are analyzed theoretically. With the use of highly-nonlinear fibers in all-optical phase detector, the fiber length is shortened sufficiently, which reduces the walk-off between two pulse trains induced by dispersion. The phase detector has an extinction ratio beyond 30 dB. The optical voltage-controlled oscillator based on regenerative mode-locked fiber laser provides high-quality pulses over a repetition frequency range of 380 kHz. In the clock recovery experiment, a transform-limited pulse train is recovered from a 40 Gb/s signal, with pulse width of 7. 2 ps, timing jitter （root-mean-square） of 152 fs, and super-mode suppression ratio over 60 dB. The loop is robust against pattern effect and amplitude fluctuation of input signal.