INJECTION CURRENT SETTING CIRCUIT OF SEMICONDUCTOR LASER

摘要

PURPOSE:To facilitate keeping the gain of optical amplification always constant even if the intensity of applied light or an ambient temperature is changed by controlling the injection current of a semiconductor laser by feedback to make the minimum value of the optical output of the semiconductor laser the same intensity of the optical output by the oscillation threshold value of the semiconductor laser when light is not applied or less value. CONSTITUTION:The means of externally applying modulated light (input light) L3 in a semiconductor laser 13 and a photodetector 14 which receives optically amplified output light (amplified light) L4 from the above-mentioned semiconductor laser 13 and converts to an electric signal are provided. The means of controlling the input current of the semiconductor laser 13 by feedback are also provided to make the minimum value of the output current (optical current) I1 of the photodetector 14 equal to the value of the output current of the photo detector 14 when the quantity of emitted light near the oscillation threshold value of the semiconductor laser 13 when no light is applied or less quantity is received. Or further, the optically amplified output light L4 from the above- mentioned semiconductor laser 13 is divided into two, one is given to the photodetector 14 and the means of sending out the other externally are provided.