OSNR Monitoring Method for OOK and DPSK Using Tunable Filter with Periodic Passband

We describe a simple method to measure the optical signal-to-noise ratio (OSNR) of OOK and DPSK signals by using an optical filter with a periodic and tunable passband. This OSNR monitoring method is independent of chromatic dispersion, polarization-mode dispersion, and noise polarization. We show experimentally that accurate OSNR measurements are made for a 10-Gb/s OOK signal by using a 1-bit optical delay interferometer (ODI) and a 40-Gb/s DPSK signal by using a partial- bit ODI with the OSNR ranging from 5 dB to 25 dB.