Optical disk reproducer

TL;DR: In this article, the authors presented a method to reproduce an optical disk which is recorded with high density by applying laser light to a nonlinear optical crystal matter from a semiconductor laser to produce an optical higher harmonic wave containing a 2omega component and then reading the pit information out of the optical disk with the light containing the 2OMEga component.

Abstract: PURPOSE:To reproduce an optical disk which is recorded with high density by applying laser light to a nonlinear optical crystal matter from a semiconductor laser to produce an optical higher harmonic wave containing a 2omega component and then reading the pit information out of the optical disk with the light containing the 2omega component. CONSTITUTION:The type and the direction are selected for a crystal which can have 90 deg. phase matching with a frequency omega. Thus the light of wavelength omega is converted into the light of double frequency, i.e., the 2nd higher harmonic wave. The light of 2omega condensed on an optical lens 10 passes through again an objective lens 11 and 1/4lambda plate 10 to be reflected by 90 deg. by the 2nd polarized beam splitter 9 with modulation and dispersion done by the pit information and is made incident on a photodetecting element 13 via a BPF12 which transmits only the light of 2omega. The element 13 uses a PIN diode or an avalanche diode and produces an RF signal corresponding to the bit information read out by the light of 2omega. Thus it is possible to reproduce an optical disk which is recorded with high density.