| 摘要 |
PURPOSE:To maintain the light output at a constant value, by detecting the lowest value of the light output of a laser diode which has been shifted as a result of a temperature change, comparing this lowest value with a reference voltage, and controlling the bias current supplied to the laser diode. CONSTITUTION:The transmission signal input to an input terminal 8 is passed through a driver circuit 7 and input to a laser diode 1 having a temperature t1. The light output from the laser diode 1 is passed through a light-receiving element 2 and input to a lowest value detecting circuit 10 where the lowest value P01 of the waveform of the light output is detected, and the detected lowest value is input to a comparator circuit 11. A reference voltage 12 based on the light output corresponding to the threshold current supplied to the laser diode 1 is set in the comparator circuit 11. The lowest value P01 is compared with the reference voltage 12, and a resultant error signal is input to a bias circuit 13 where the bias current is shaped so that the error signal is made coincident with 0 by by control effected by the loop [B] of the APC circuit. With this bias current, the laser diode 1 is operated, and a beam of constant level is thereby output from the laser diode 1 at all times. |
