ACTIVE TYPE HETERODYNE/HOMODYNE DETECTION SYSTEM

摘要

PURPOSE:To increase the photodetection sensitivity and SN ratio by providing a transmission line to which a rare earth metal is added and an exciting optical coupler which couples and transmits exciting light in the transmission line between a directional coupler and a photodetecting element. CONSTITUTION:The transmission line 5 to which the rare earth element is added and a wavelength selection type multiplexer 6 are provided between the directional coupler 4 which mixes signal light 1 with wavelength lambdas and local oscillation light 2 with wavelength lambdaL and the photodetecting element 7. Then, the exciting light 3 with wavelength lambdaP is inputted to the wavelength selection type multiplexer 5 and propagated in the transmission lien 5 to which the rare earth element is added. The exciting light 3(lambdaP) is propagated in this transmission line 5 and then the signal light lambdas inputted to the photodetecting element 7 and the local oscillation light 2(lambdaL) inputted to the photodetecting element 7 are both amplified. Consequently, the photodetection sensitivity and SN ratio are increased.