OSNR monitoring technique using polarization-nulling method

We report on the simple technique for monitoring the optical signal-to-nois e ratios (OSNRs) of wavelength-division-multiplexed (WDM) signals. This tec hnique, based on the polarization-nulling method, was implemented simply by using a rotating quarter-wave plate and rotating linear polarizer, However , the performance of this technique could be affected by nonlinear birefrin gence and polarization-mode dispersion (PMD), The result shows that this te chnique is suitable for monitoring the OSNRs of highspeed (>10-Gb/s) WDM si gnals transported over the fiber link with low PMD.