为减少全光时钟提取中的码型效应,设计了混码器对注入数据脉冲进行预处理。理论分析表明,在时域上,混码器可以改变注入数据信号脉冲幅度的概率分布,减少零码；在频域上,混码器可以减少连续谱分量。实验证明混码器能使注入数据信号的脉冲幅度集中于最大值的二分之一处,并减少零码。理论计算和实验同时证明,使用路数更多的混码器,或将几个混码器级联使用,提取的时钟能得到更大的改善。实验中使用基于半导体光放大器(SOA)的注入锁模光纤激光器进行40 GHz全光时钟提取,由码型效应导致的时钟信号的幅度波动和定时抖动得到了明显的抑制,使用混码器后提取的时钟信号的定时抖动均方根(Jitter RMS)小于2.4 ps。

To reduce the pattern effect in all-optical clock recovery, a novel device termed as code mixer was designed to preprocess the injected data signals. In the time domain, the code mixer can change the probability distribution of the amplitude of the data pulses and reduce the amount of code “0”. In the power spectrum, the code mixer can reduce the continuous spectral component. It was demonstrated in the experiment that the code mixer can concentrate the probability distribution of the amplitude of the pulses to half of the maximum amplitude. It was also demonstrated theoretically and experimentally that using a code mixer of more ways or several cascade code mixers the clock signal recovered can be further improved. In the experiments of 40 GHz all-optical clock recovery using an injection mode-locked ring laser based on a semiconductor optical amplifier, the amplitude fluctuation and timing jitter of the clock pulses recovered caused by the pattern effect were reduced obviously. The timing jitter root mean square (RMS) of the clock pulses recovered using code mixers was less than 2.4 ps.