Sensitivity Issues Of Optical Performance Monitoring

The sensitivity of the optical performance monitoring with an optical preamplifier is analyzed. It is found that while the optical pre-amplification mitigates the received intrinsic noise limitations in the similar way as it does for the optically preamplified receiver cases, the requirement of the noise performance for the preamplifier is much more stringent for monitoring cases than that for the receiver cases. This is mainly due to the different requirements on the receiving SNR for receiver cases and the highest detectable SNR for the monitoring cases. The requirement for the gain is found to be moderate, similar to that of the optically preamplified receiver cases. About 15 dB gain would be sufficient and the higher gain will not improve the sensitivity further. At sufficient gain, the sensitivity is found to be roughly that of the shot-noise limit plus the penalty of the noise figure of the optical preamplifier. Given a specified noise performance of available front ends, the noise spec of the preamplifier that allows for the preamplified schemes to outperform non-preamplified schemes is also provided.