Power control system for a semiconductor laser

Abstract

In an optical recording system employing a semiconductor diode laser and having both read and write capabilities, the laser power must be carefully controlled at both the appropriate level for reading and at a different level for writing. Typically, a continuous read beam is emitted by the laser while pulses at the higher write power level are generated. The laser power control loop of the present disclosure maintains both the read and write output power of the laser within predetermined limits. A light sensing diode is used to determine laser output power, which is then used to operate the control circuit by adjusting the read and write current supplied to the laser. The output of the sensing diode voltage is passed through a read/write switch which is controlled by write pulses, which also control the laser. In read mode a DC signal is sent to a quad comparator circuit for read power control. In write mode a pulsed signal is sent to a sample and hold circuit which output goes through an amplifier to another quad comparator circuit for write power control.