Optical information reading method for reducing laser noise using a semiconductor laser and a driving device for the semiconductor laser

TLDR: In this article, a method for optically reading recorded information by radiating laser light emitted from a semiconductor laser which oscillates in a single longitudinal mode to an information recording medium and by detecting laser light reflected from a recording face of the information record medium is disclosed.

Abstract: A method for optically reading recorded information by radiating laser light emitted from a semiconductor laser which oscillates in a single longitudinal mode to an information recording medium and by detecting laser light reflected from a recording face of the information recording medium is disclosed. In the method, the optical frequency of the laser light is modulated in order that the modulated optical frequency is a periodic function dependent on time, and the absolute value of a time differential coefficient R (Hz/s) of the periodic function, a spectral line width δ ν (Hz) of the laser light, and a time period τ (s) from the time when the laser light is emitted to the time when the laser light reflected from the recording face of the information recording medium reaches the semiconductor laser satisfy the condition of R≧δ ν/τ. The periodic function varies to have a sawtooth waveform or a triangular waveform.