| 摘要 |
PURPOSE:To prevent the destruction of a semiconductor laser element by adjusting the current in one element of a differential couple which constitutes a direct current bias current adjusting circuit according to the output from a photodetector. CONSTITUTION:A d.c. bias current adjusting circuit of a semiconductor laser element 1 consists of a differential pair of transistors Tr4, Tr5 and a constant current power source 15, and the output of a photodetector 2 is supplied to the base of one transistor Tr5 via a voltage follower including an operational amplifier 11, an operational amplifier 12 and a subtraction circuit which includes resistances R3, R4, R5, R6. The negative phase input terminal of the operational amplifier 12 receives reference voltage Vref from the collector of one transistor Tr1 of the differential pair which supplies the signal component of the semiconductor laser element 1. The subtraction circuit controls the transistor Tr5 in accordance to the difference between Vref and the output from the photodetector 2, so that the d.c. component of the element 1 can be controlled according to an optical output and the optical output can be maintained constant irrespective of temperature. |
