Device and method for monitoring optical signal quality, and optical transmission device

摘要

A device for monitoring optical signal includes: an optical filter configured to allow part of a spectrum of an optical signal on which a frequency or phase modulated signal is superimposed to pass; and a detection unit configured to detect signal quality of the optical signal, based on a power ratio of a signal component to a noise component of the modulated signal, the power ratio being obtained based on a power change in accordance with the modulated signal of light that has been caused to pass through the optical filter.