LASER DIODE DRIVE CIRCUIT

摘要

PURPOSE:To contrive the reduction of the deterioration of extinction coefficient and that of light output a high-velocity operation by taking out an average value signal from a light accepting element output by means of a d.c. monitor circuit and compar ing it with an average value of the input signal and controlling a d.c. bias current value of laser diode corresponding to the differential quantity. CONSTITUTION:The output of a level recognition circuit 5 is input in a rising delay detecting circuit 6 and a lowering delay detecting circuit 7 together with an input signal 1. An addition device 8 applies a constant offset voltage VB to the output of the rising delay detecting circuit 6 in order to give a contant delay time tX to a rising of the wave of light output. The signal of the output of the rising delay detecting circuit 6 added with the offset voltage VB and the output of the lowering delay detecting circuit 7 are input in a differential amplifier 9. The bias current source 11 for controlling the magnitude of a modulation current IP through a filter 10 is supplied. Meanwhile, the output of the light accepting element 3 is detected its average value by a d.c. monitor circuit and it is input in a differential amplifier 15 together with the output of a low-pass filter 14. It is input in a bias power source 17 for supply ing a d.c. bias current IB through a filter 16, thereby controlling the d.c. bias current IB.