Method for optical signal-to-noise ratio monitoring based on modulation spectrum assessment

A novel method for optical signal-to-noise ratio monitoring is presented. The method is based on two-filter narrowband filtering which, combined with the knowledge of the modulation format, allows the determination of the amount of amplified spontaneous emission noise in the channel spectrum. The major advantage of the method is simplified experimental setup. The robustness of the method against various signal impairments is discussed and assessed through simulation. It is shown that the method provides sufficient accuracy for most practical applications and is remarkably resilient against other physical phenomena reducing signal quality. In particular, the method is inherently insensitive to chromatic dispersion and polarisation-related impairments. All results are presented for 10 Gb/s return-to-zero format.