Optical Performance Monitoring Based On Delay-Tap Sampling

Optical performance monitoring(OPM) has been a widespread research topic in the field of high rate and capacity optical fiber communications. It becomes increasingly important to evaluate the performance of optical networks. Performance parameters mainly include optical signal-to-noise ratio(OSNR), chromatic dispersion(CD), polarization mode dispersion( PMD), and Q-factor. Those impairments degrade the quality of the network, and it seems significant to realize the monitoring of all the impairments.We are dedicated to the research of OPM performance parameters monitoring based on delay-tap sampling. The following novel contributions to the field of optical performance monitoring are made in the course of this research:(1) A novel CD monitoring technique of OOK signal based on delay tap sampling is proposed. This method can differentiate the polarity of CD and has the advantage of independent of OSNR and PMD. The existing models of CD monitoring need introducing other signals, such as pilot tone, RF modulated ASE, and frequency-modulated signal.Method of spectrum needs no extra signal but it is affected by OSNR and PMD. We modeled a CD monitoring method for 10/40-Gb/s NRZ-OOK signals based on delay-tap sampling scheme by evaluating the distance ratio of delay-tap plots. We analyzed plots with 1B delay for CD monitoring. Then the distance ratio is defined which displays one-to-one relationship with CD and CD monitoring range is confirmed. With an ODI, we can also differentiate positive and negative CD. The measuring range was around ±900 ps/nm for 10-Gb/s NRZ-OOK link and ±60 ps/nm for 40 G link, the monitoring error is smaller than 2 ps/nm.(2) An original OSNR monitoring method of OOK signal based on delay tap sampling is proposed. A majority of techniques are sampling points distributed along the diagonal of two tap plots, and then histogram Gaussian fitting is used to analyze further. Our proposed model is an improvement of the basic ones. For 10-Gb/s NRZ-OOK signals, we analyzed the histogram plots by fitting samples located not only along the delay-tap plots diagonal but also with an appropriate angle(α=1°) to enhance the accuracy. Then the OSNR monitoring factor FOSNR was defined which displayed the one-to-one relationship with actual OSNR. To analyze the impacts of CD and PMD, the polynomial coefficients were calculated based on the OSNR monitoring data for CD and PMD free case(CD=0ps/nm, PMD=0ps)which is regarded as standard equations. In different CD and PMD cases, the OSNR was calculated by using the standard equations. After 3 order polynomial fitting, the estimation error is acquired. This scheme shows advantage of robust to CD and PMD effects with low OSNRs for 1d B error.