Patent ID: 7120107

Claim:
An optical head, comprising: (a) a light source for emitting a light beam to be irradiated to an optical recording medium as an incident light beam; (b) a hologram element for receiving a reflected light beam generated by reflection of said incident light beam on said medium to generate at least two diffracted light beams for focusing error detection and at least two diffracted light beams for tracking error detection; and (c) an optical detector for detecting the at least two diffracted light beams for focusing error detection and the at least two diffracted light beams for tracking error detection; said detector including a first receiving surface for receiving the at least two diffracted light beams for focusing error detection and a second receiving surface for receiving the at least two diffracted light beams for tracking error detection; each of said first and second receiving surfaces being divided into receiving regions; the at least two diffracted light beams for focusing error detection being received at said receiving regions of said first receiving surface; the at least two diffracted light beams for tracking error detection being received at said receiving regions of said second receiving surface; wherein said hologram element has diffraction gratings, said gratings having different grating patterns and at least one of said grating patterns being non-linear and having an offset center with respect to another of said grating patterns, and wherein the at least two diffracted light beams for focusing error detection and the at least two diffracted light beams for tracking error detection are generated by said gratings of said element, and wherein said hologram element has a property of selectively exhibiting a diffraction grating function according to a polarization direction of said reflected light beam, and wherein the hologram element has a refractive index that varies according to the polarization direction, and wherein said hologram element has a first diffraction grating on a surface of said element and a second diffraction grating on an opposite surface thereof.