SEMICONDUCTOR LASER DRIVING CIRCUIT

A semiconductor laser driving circuit that ensures the satisfied extinction ratio, the accuracy of the light output, and enables the light output dynamically to change based on a modulation signal. The semiconductor laser driving circuit includes a semiconductor laser LD of which the laser light is modulated by the analog modulation signal v_MOD, the differential pair circuit having impedance elements 11, 12 and transistors Q1, Q2, a power source 13, a differential driver 22 that generates a differential voltage to switch on-and-off the transistors Q1, Q2 by an analog modulation signal, a threshold electric current generation element that generates the threshold electric current to flow the threshold that the semiconductor laser emits, a slope signal generation element 32 that generates a slope signal V_SLOPE by executing a level conversion by a predetermined slope coefficient relative to the analog modulation signal, and an adder 35 that adds a slope signal, which the slope generation element generates and the threshold electric current that the threshold electric current generation element and controls the electric current or the power source by the addition output.