In-service chromatic dispersion monitoring based on imperfect phase tuned delay interferometer for NRZ-DPSK systems

Differential phase-shift keying (DPSK) modulation format has been widely employed in high speed long haul transmission systems. The DPSK modulation format is a promising technique to increase the system performance, for example: extending the transmission distance, reducing the OSNR requirement and suppressing the nonlinearity. So the optical signal performance monitoring is quite necessary and indispensible for this modulation format. In this paper, a chromatic dispersion (CD) monitoring method for DPSK signals has been demonstrated using an optical delay interferometer with imperfect phase adjustment. We found the eye diagrams shown inclination with the combination effect of phase error and residual CD. This method can not only be used for CD monitoring but also can discriminate dispersion polarity. The CD monitoring range could cover from −425 to +425ps/nm of 10 GHz NRZ-DPSK system.