| 摘要 |
PURPOSE:To lower a noise level below some reference value and to cope with the variation in noise level due to a secular change by controlling the temperature of a semiconductor laser module on an optical transmission line made of a single-mode fiber. CONSTITUTION:An optical transmission system 20 is coupled with the semiconductor module 202 and part of transmitted light of the optical transmission system 201 is extracted by a branching device 203 and converted by a photodetector 204 into an electric signal, which is passed through an amplifier 205, band-pass filter 206, and detector 207 to detect its noise level. Further, the detector 207 is equipped with an averaging function and the current of a heat absorbing and generating device 209 is varied by a control part 208 to control the temperature of the semiconductor laser 202 so that the noise level drops below some reference value. Further, an output control part 212 detects rear output light of the semiconductor laser in the module 202 by a photodetector 211 and controls the bias current of the semiconductor laser so that the mean light output to the transmission line is constant. |
