Optical signal-to-noise ratio monitoring using uncorrelated signal-spontaneous beat noise

Abstract—We propose and experimentally demonstrate a new technique for monitoring optical signal-to-noise ratio (OSNR). The noisy signal to be measured is split into two paths. With offset optical bandpass filters and balanced radio-frequency subtraction after detection, the signal is separated from the beat noise. OSNR can then be monitored by analyzing this beat noise. An experi-ment for a 10-Gb/s system shows that for OSNR in the range of 10–30 dB, the proposed OSNR monitoring scheme produces errors of less than 0.5 dB. Index Terms—Amplified spontaneous emission (ASE) noise, beat noise, optical signal-to-noise ratio (OSNR) monitoring, wave-length-division multiplexing (WDM). I