OSNR monitoring technique using polarization-nulling method

摘要

We demonstrated a simple technique that can be used to monitor the OSNR's of WDM signals automatically. This technique, based on polarization-nulling method, was implemented by using a rotating quarter-wave plate and a rotating linear polarizer. The accuracy of the proposed technique was better than 0.6 dB, regardless of bit rates. However, the main disadvantage of this technique was found to be its sensitivity to the PMD. When we used DCF's for the transmission of 10-Gb/s signals over 640 km of SMF (total PMD of DCF's was ～6.4 ps), the measurement error was increased up to 3 dB. Thus, for the use of this technique, it is essential for the transmission fiber to have low PMD.