Optical EngineeringDynamic laser feedback noise measurement for the optical information storage system
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The conventional measuring system of laser feedback noise for an optical pickup was specifically implemented only for laser diodes by using a static optical system. With no closed-loop servo control, it is impossible to measure the genuine laser noise distribution of a pickup while operating in an optical drive. By modifying the optical system of a commercial pickup, this study built up a system that was integrated with precision mechanical design, optical design, servo control design, and opto-electronic signal inspection for providing dynamic real-time laser feedback noise measurement. Using this system, some experimental results have been observed. The laser feedback noise is responsible to the focusing point within the linear range of an optical pickup head. It has the maximum value while the lens is on the best focus. The higher the environmental temperature, the noisier the laser output will be. Besides, the central frequency of noise is dependent on the disk rotation speed, and the noise level is reducible by increasing the disk rotation speed.