Patent ID: 8391120
Filing Date: 2013-03-05
Classification: G11B

Abstract:
1. An optical head for recording or reproducing information on or from a first information recording medium including at least three information recording surfaces having different light transmitting layer thicknesses, comprising: a first light source for emitting first laser light having a first wavelength; a first mirror for reflecting the first laser light; a first objective lens for focusing the first laser light reflected by the first mirror on a specified information recording surface of the first information recording medium; a coupling lens arranged between the first light source and the first mirror; a second mirror in the form of a parallel plate arranged between the coupling lens and the first mirror; a spherical aberration corrector for correcting a third-order spherical aberration created according to the light transmitting layer thickness of the first information recording medium by moving the coupling lens in an optical axis direction; and a photodetector for receiving reflected light from the information recording surface of the first information recording medium; wherein the first objective lens is so designed as to be tilted in a radial direction of the first information recording medium, and satisfy a relationship of tc>(t