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Optical performance monitoring (OPM) becomes an attractive topic as the rapid growth of data rate in optical
communication networks. It provides improved operation of the high capacity optical transmission systems. Among the
various impairments, chromatic dispersion (CD) is one of major factors limiting the transmission distance in high-speed
communication systems. Polarization-mode dispersion (PMD) also becomes a degrading effect in the system with data
rate larger than 40 Gbit/s. In this paper, we summarize several CD and PMD monitoring methods based on RF spectrum
analysis and delay-tap sampling. By using a narrow band fiber Bragg grating (FBG) notch filter, centered at 10 GHz
away from the optical carrier, 10-GHz RF power can be used as a CD-insensitive PMD monitoring signal. By taking the
10-GHz RF power ratio of non-filtered and filtered signal, PMD-insensitive CD monitoring can be achieved. If the FBG
notch filter is placed at optical carrier, the RF clock power ratio between non-filtered and filtered signal is also a PMDinsensitive
CD monitoring parameter, which has larger RF power dynamic range and better measurement resolution.
Both simulation and experiment results show that the proposed methods are efficient on measuring CD and PMD values
in 57-Gbit/s D8PSK systems. Delay-tap sampling is another efficient method of measuring residual CD. Amplitude ratio
of asynchronous delay-tap sampling plot decreases with CD monotonously, and the amplitude ratio can be obtained by
using low bandwidth balanced receiver. The simulated results show that our method is efficient on residual CD
measurement in 50-Gbit/s 50% RZ DQPSK systems with a 12-GHz balanced receiver. Since no modification on the
transmitter or receiver is required, the proposed scheme is simple and cost effective.
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