Patent ID: 6091690
Filing Date: 2000-07-18
Classification: G11B

Abstract:
An optical head apparatus comprising:a light source for emitting light;a front-end converging optical system for converging the light emitted from said light source onto a multi-layer information storage medium;a back-end converging optical system for reconverging the light reflected from a layer on said multi-layer information storage medium;wavefront converting means for accepting said reconverged light, and for forming a wavefront to enable detection of a focus error signal and a tracking error signal; anda photodetector for receiving the light from said wavefront converting means, and for outputting a signal proportional to the amount of said received light,wherein h is greater than two times the product of tmax and .beta., where tmax is an optical distance between two information layers located farthest apart on said multi-layer information storage medium, .beta. is a longitudinal magnification of optics leading from said multi-layer information storage medium to said photodetector, K is a point to which the light reflected from a desired information layer on said multi-layer information storage medium is reconverged by said back-end converging optical system when said light emitted from said light source is focused on said desired information layer by said front-end converging optical system, and h is an optical distance between said wavefront converting means and said point K.