JPS6439839A - Semiconductor laser driving circuit - Google Patents

Abstract

PURPOSE:To automatically execute a duty adjustment of an optical pulse by controlling a threshold level of a discriminating circuit by a result of comparison of an output of an average value detecting circuit. CONSTITUTION:A 1B2B-encoded digital signal which is inputted to a signal input terminal 11 is allowed to pass through a low-pass filter circuit 8 and a discriminating circuit 10 whose threshold level is variable, and by a signal driving circuit 1, a semiconductor laser 2 is allowed to emit a light beam. Subsequently, an output light which is emitted from the semiconductor laser 2 is photodetected by a photodetector 3, and a peak value and an average value are detected by a peak value detecting circuit 6 and an average value detecting circuit 4. Next, in accordance with these detection value, a threshold voltage generating circuit 7 outputs a signal so that the average value goes to, for instance, 1/2 of the peak value, and by its output, the threshold level of the discriminating circuit 10 is controlled. In such a way, the duty of an optical pulse can be adjusted automatically to an optimum value.