Diode laser noise at control frequencies in optical videodisc players

Abstract

Video frequency noise in diode laser output and its influence on reproduced picture quality have been studied in an optical videodisc player. It was found that laser noise is related to an instability of oscillating longitudinal modes and has a strong correlation with picture quality. A single-mode laser easily oscillates in two or more modes by temperature change and optical feedback, which causes mode-hopping noise and results in white dots randomly appearing on a picture. A multimode laser has a consistently high noise level, and this results in a rough picture quality. Using high frequency superimposed current to power a single-mode laser enables multimode oscillation to be maintained at a steady level. This produces a relatively low noise level resulting in good picture quality. With regard to the video frequency laser noise specifications, it is determined that relative intensity noise should be <6 × 10−14 (Hz−1) in a practical player and <3 × 10−14 (Hz−1) in a pickup simulating noise measuring system.