JPS6484769A - Semiconductor laser drive circuit - Google Patents

Abstract

PURPOSE:To output a stable optical signal of a definite pulse width by a method wherein the optical signal is monitored and converted into an electric signal, the pulse width is detected and compared with a reference pulse width and the pulse width of an input signal to a semiconductor laser is controlled in such a way that both pulse widths coincide with each other. CONSTITUTION:An optical signal which is output by a semiconductor laser 6 is monitored by an optical-signal-to-electric-signal conversion circuit 8, is converted, by means of a pulse width detection circuit 9, into a voltage V corresponding to a pulse width of the optical signal; this voltage V is compared with a reference voltage Vref by means of a pulse width comparator 10, and a difference is output to a pulse width control circuit. The pulse width control circuit 1 controls a pulse width of an input signal in such a way that an output level of the pulse width comparator 10 becomes '0', and outputs this pulse width to a level-shifting circuit 2. Accordingly, a rate occupied by a pulse of the optical signal which is output by the semiconductor laser 6 becomes definite; accordingly, the eye of a waveform on the reception side is not deteriorated; an S/N ratio of a received signal can be enhanced.