Impact of Out-of-Band Noise on OSNR Measurement Using Brillouin Optical Spectrum Analyzer and Its Mitigation Method

Brillouin optical spectrum analyzer (BOSA) based on stimulated Brillouin scattering (SBS) can provide ultra-high resolution, which in theory can greatly improve the optical signal-to-noise ratio (OSNR) measurement accuracy, especially for systems with close channel spacing and cascaded filtering effect (CFE). BOSA utilizes narrow bandwidth SBS as an active optical band-pass filter (A-OBPF); thus, the unwanted out-of-band spectral components are actually not completely suppressed and may account for an unneglectable proportion of the spectral power filtered out, especially for broadband multi-channel signals. Such out-of-band noise (OBN) will degrade the OSNR measurement accuracy. In this paper, the OBN impact on both interpolation and reference optical spectrum (ROS) based OSNR measurement methods are investigated theoretically and experimentally. An effective mitigation method of OBN impact is then proposed and verified by experiments.