Power Supply and Current Modulation Circuits for Semiconductor Lasers

Design and construction of a stable current supply with protection circuits are described. The reported circuit provides a high-stable and high-level current variable from 0.5-1.2 A with the protect ion circuits to prevent over load current, voltage and off-range temperature operation. A detailed analysis of the circuit parameters is given and the time behaviors of the load voltage/current and shut-off voltage/current are presented. Theoretical analysis shows a turn-on time of about 20 ns for the load current and a shut-off time of about 150 ns. The proposed scheme is verified both by simulation and by constructing a prototype. The prototype version of this circuit shows a good stability in load current, and the laser diode temperature can be monitored with an accuracy of about 1 degree. In addition, design and analysis of the current modulator and switching circuit s for laser diodes are reported. Modulation process and different modulation techniques are explained in detail. Drive circuits for positive and negative intensity modulation are presented. Transient analysis for the proposed drivers is performed by using PSPICE software and the results are reported here. Evaluation of the results indicates that the reported modulators can be used successfully for direct current modulations.