APPARATUS AND A METHOD FOR MEASURING A OPTICAL SIGNAL-TO-NOISE RATIO, PARTICULARLY FOR MINIMIZING THE INFLUENCE OF A CHANGE IN AN EXTERNAL ENVIRONMENT AND SIMPLY AND ACCURATELY MEASURING AN OPTICAL SIGNAL-TO-NOISE RATIO

摘要

PURPOSE: An apparatus and method for measuring an optical signal-to-noise ratio are provided to stably measure an optical signal-to-noise ratio by using an interference phenomenon difference between a signal component of an optical signal and an ASE(Amplified Spontaneous Emission) noise. CONSTITUTION: A polarization controller(31) inputs an optical signal toward a specific direction of an optical fiber. An optical signal interfering unit divides the optical signal inputted by the polarization controller(31) into two vertical polarization states, provides two optical paths different from each other for them, and causes a phase-change in one of the two optical path. A polarization coupler(34) couples the optical signals which have passed through the two vertical optical paths, to interfere them. An optical detector(35) converts the interfered optical signal into an electric signal. A signal processor(30) measures a signal component and a noise component of the electric signal outputted from the optical detector(35) in order to measure an optical signal-to-noise ratio of the optical signal.