Experimental Investigation of Delay-Tap Sampling Technique for Online Monitoring of RZ-DQPSK Signals

We experimentally demonstrate optical performance monitoring of 20-Gb/s return-to-zero differential quadrature phase-shift keying signals using an asynchronous delay-tap sampling technique. This method allows online monitoring of accumulated chromatic dispersion in the range from $-$600 to $+$600 ps/nm. We also show evaluation of optical signal-to-noise ratio at a level of 6.7 dB and monitor operation at input power of $-$ 16 dBm.