Semiconductor laser control circuit capable of setting all output power levels of a semiconductor laser by means of setting only one level

摘要

In response to the output of an operational amplifier, a CPU sets via an R-D/A converter an R-constant current circuit for supplying a read power current Ir to a semiconductor laser thereby driving it, and also sets via a W0-D/A converter an W0-constant current circuit for supplying a first write power current Iw0 to the semiconductor laser thereby driving it. The output of the W0-D/A converter is applied to two voltage- controlled amplifiers so that W1-constant current circuit and W2- constant current circuit provide second and third write power currents Iw1 and Iw2, respectively, to the semiconductor laser in accordance with the outputs of the respective voltage-controlled amplifiers. The gains of these two voltage-controlled amplifiers are set by the CPU such that the gains corresponds to the ratios of Iw1 and Iw2 relative to Iw0. Thus a semiconductor laser control circuit for controlling the operation of driving a semiconductor laser at a plurality of power levels can be realized using a single low-speed semiconductor laser monitor without having to use three high-speed APC circuits. This allows a reduction in the cost of the semiconductor laser control circuit. A plurality of constant current circuits are set to have an equal gain so that the output power of the semiconductor laser control circuit may be easily set using the optimized optical output power setting value which has been already determined. This allows the test light emission for setting the power to be performed in a simple manner and thus resulting in a reduction in time required to perform the test light emission for setting the power level.