DEVICE AND METHOD FOR MONITORING OPTICAL TRANSMISSION, AND OPTICAL FIBER TRANSMISSION SYSTEM

摘要

PROBLEM TO BE SOLVED: To easily and practically monitor optical transmission without using any complicated expensive circuit device by making luminous flux which needs to be monitored incident on an optical-pathdifference modulated interferometer and detecting desired signal abnormality with correlation output between its light waves. SOLUTION: Part of light signal luminous flux which is propagated in an optical fiber transmission line 100 is demultiplexed by an optical coupler 101 and inputted to a variable optical-path-difference interferometer 102. Optical differences among optical paths that the interferometer 102 has inside are modulated by a modulator 103. At this time, an intensity-modulated signal depending upon the modulation frequency and amplitude of the optical path difference of the interferometer 102 by the modulator 103 and signal intensity propagated in the optical transmission line 100 appears in the electric signal output of a light intensity detector 104 which receives the output of the interferometer 102. A filter 106 extracts an intensity-modulated component from the electric signal output of the light intensity detector 104 and a decision unit 107 makes a threshold decision on the intensity of the intensity-modulated component to monitor whether or not a signal is present.