Patent ID: 6504857
Filing Date: 2003-01-07
Classification: H01S

Abstract:
A laser diode deterioration detection circuit for a laser beam emitting device employing a laser diode, the laser beam emitting device including a drive current supply circuit that supplies a driving current to said laser diode, a laser power detection circuit that detects an optical output power of said laser diode and outputs a laser power detection signal representing the detected optical output power, a first differential amplifier that outputs a first differential signal corresponding to a difference between the laser power detection signal and a reference value, said drive current supply circuit varying the driving current based on the output of said first differential amplifier, said laser diode deterioration detection circuit comprising:a biasing circuit that modifies the laser power detection signal upon issuance of a deterioration detection command; a sample-hold circuit that samples and holds a value of the first differential signal output by said first differential amplifier before the deterioration detection command is issued; a second differential amplifier that outputs a second differential signal corresponding to a difference between said first differential signal after the deterioration detection command is issued and the value held by said sample-hold circuit; and a deterioration determining circuit that compares the second differential signal and a deterioration detection reference value, said deterioration determining circuit determining whether the laser diode is deteriorated based on the comparison result.