THERMAL TIME CONSTANT MEASURING METHOD AND APPARATUS FOR SEMICONDUCTOR LASER

摘要

PURPOSE:To accurately evaluate the thermal time constant of many elements in a short time by modulating a semiconductor laser applied with a constant current bias to measure the value when the phase difference in the transmitting characteristic from the current input to the light output becomes maximum and the modulating frequency of the case. CONSTITUTION:A laser drive power source 2 applies a drive current Id+i0sinomegat modulated by the voltage output V0sinomegat of ultrafine sinusoidal wave of a voltage-controlled variable frequency oscillator 1 to a semiconductor laser 3. The modulating light output of the laser 3 is detected by a photodetector 3 applied with a constant bias voltage by a bias power source 7. A phase difference detector 5 outputs a drive current of the laser 3 and a photoinduced current of the detector 4 and a phase difference. The frequency omega and the phase difference beta are indicated on indicators 6 and 8, respectively. The frequency of the oscillator 1 is automatically set to the frequency omegam becoming maximum in the phase difference beta after the prescribed time, thereby obtaining the maximum value betam of the phase difference and the frequency omegam at that time. These values are calculated by an equation (1) to obtain the thermal time constant.