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Chromatic dispersion and polarization mode dispersion insensitive optical signal to noise ratio monitoring based on electronic variable optical attenuators and optical bandpass filter

In this paper, an optical signal to noise ratio (OSNR) monitoring method based on radio frequency (RF) power of two signals in parallel connection. The test optical signal was split equally into two signals in parallel connection. One removed out-of-band noise by optical bandpass filter, the other kept output power constant by electronic variable optical attenuators (EVOA) with power-locking control loop. One radio frequency power of the two signals treated by different ways increased with the increase of OSNR when the two signals are at the same place. The other decreased. The difference of radio frequency power of the two signals at the same place was used to monitor OSNR. The simulation results showed that the proposed technique can implement OSNR monitoring between 2dB and 30dB for 40Gb/s NRZDQPSK optical signal. Monitoring error was within 1.5dB and the proposed technique was insensitive to chromatic dispersion (CD) and polarization mode dispersion (PMD).