OPTICAL SIGNAL MONITOR CIRCUIT AND OPTICAL AMPLIFIER

摘要

PROBLEM TO BE SOLVED: To detect whether a dummy light is below the level of a signal light or cut off and send the dummy light to a rare earth element-added fiber of an optical amplifier by providing an optical coupler for applying the dummy light sent from a dummy optical source to this fiber after branching a signal light to be fed to the optical amplifier and detecting the signal light. SOLUTION: The optical signal monitor circuit has an optical brancher 11 at the signal light input which is connected to an optical detector O/E 12 for detecting a branched signal light. An electric signal output of the detector is coupled to a signal light detector circuit 13 to which a dummy optical source drive circuit 14 is connected to drive or stop a dummy optical source according to the signal level. The dummy source 15 is connected to an optical coupler 17 through an optical isolator 16. An optical multiplexer 16 is disposed to send the dummy light to an Er-added optical fiber reverse to the signal light whereby the monitor circuit detects whether the dummy light is below the level of the signal light or cut off and sends the dummy light to the rare earth element- added fiber.