| 摘要 |
PURPOSE:To prevent the deterioration of a laser diode (LD) in an electro-optical converter circuit which control (APC-control) so that the light output of the LD always becomes constant value by providing a current compensator and an APC alarm circuit. CONSTITUTION:An LD bias alarm circuit 2 outputs an alarm AL1 when an LD bias current exceeds a limited value. A light output decrease alarm circuit 3 outputs an alarm AL2 when the light output of the LD13 is decreased to a value not higher than the lower limit value. An LC light output monitor signal which is obtained by a photodiode 16 for photodetecting part of the light output of the LD13 and a light output detecting resistor 17 is inputted to a current compensating and APC alarm circuit 4, thereby branching the LD bias current and outputting an APC alarm AL3 when the monitor signal exceeds the upper limit value, i.e., when the LD light output exceeds not lower than the specified value. Since the light output of the LD is limited to the prescribed value, the deterioration of the LD can be prevented. |
