Optical signal-to-noise ratio monitoring of an 80 Gbits/s polarization-multiplexed return-to-zero differential phase-shift keying channel.

We propose and experimentally demonstrate an optical signal-to-noise ratio (OSNR) monitoring technique for an 80 Gbits/s polarization-multiplexed return-to-zero differential phase-shift keying channel utilizing a narrowband optical filter and a low-speed detector. A maximum power increment of 19.7 dB is measured at a radio frequency (rf) of 250 MHz for monitoring of OSNR up to 27 dB, insensitive to chromatic dispersion of 0-300 ps/nm and polarization-mode dispersion (PMD) of 0-50 ps.