Mitigation of sampling clock drift in asynchronously under-sampled optical bit pattern monitoring

Asynchronous optical under-sampling in combination with subsequent digital signal processing is an economical approach for characterization of ultrahigh speed optical data signals. In this paper, we propose a digital signal processing technique for bit pattern monitoring of ASK signals, which effectively mitigates the random walk clock drift between the data signal and the sampling source in such asynchronously under-sampling systems. The method is verified by measurements on 40 Gb/s NRZ and 160 Gb/s RZ data signals. A quantitative analysis of the displayed timing jitter is performed.