Chromatic dispersion monitoring of DQPSK and D8PSK signals based on delay-tap sampling technique

We demonstrate a simple chromatic dispersion (CD) monitoring method using amplitude ratio of asynchronous delay-tap sampling plot. By utilizing amplitude ratio in the delay-tap sampling plot, the residual CD values in the range of 0∼75 ps/nm can be measured for 40-Gbit/s 67% carrier-suppressed return-to-zero (CSRZ) differential quadrature phase-shift keying (DQPSK), 50% return-to-zero (RZ) DQPSK and 60-Gbit/s 50% RZ differential eight phase-shift keying (D8PSK) signals. The simulated results in VPItransmission 7.0 show that the amplitude ratio of delay-tap sampling plot decreases monotonously with residual CD in 67% CSRZ DQPSK, 50% RZ DQPSK and 50% RZ D8PSK systems. Since no synchronization or modification on transmitter/receiver is required, the proposed scheme is simple and cost effective.