Patent ID: 7835251
Filing Date: 2010-11-16
Classification: G11B

Abstract:
1. An optical device for an optical pickup apparatus for recording or reproducing information with respect to a first information recording medium having a plurality of recording layers and a second information recording medium having a single recording layer, the optical device comprising: a substrate; a hologram element to diffract a first main beam of a first wavelength that is reflected by a first one of the plurality of recording layers that is a recording or reproducing object in the plurality of recording layers of the first information recording medium, and first and second sub-beams of the first wavelength that are reflected by the first one of the plurality of recording layers of the first information recording medium so as to reach different positions, respectively, during recording or reproducing information to or from the first information recording medium, and a second main beam of a second wavelength that is reflected by the single recording layer of the second information recording medium, and third and fourth sub-beams of the second wavelength that are reflected by the single recording layer of the second information recording medium so as to reach different positions, respectively, during recording or reproducing information to or from the second information recording medium; a plurality of first light receiving regions arranged on the substrate to receive first and second diffracted beams that are diffracted from the first and second sub-beams respectively by the hologram element; a plurality of second light receiving regions arranged on the substrate to receive third and fourth diffracted beams that are diffracted from the third and fourth sub-beams respectively by the hologram element; and an operation unit, wherein: the wavelength of an incident beam to the hologram element is one wavelength of either the first or second wavelengths, the operation unit performs a subtraction operation between a signal that is photoelectrically converted from the light received by the plurality of first light receiving regions that receives the first and second diffracted beams and unnecessary light reflected by one or more of the plurality of first information medium recording layers other than the recording layer that is a recording or reproducing object and a signal that is photoelectrically converted from the light received by the plurality of second light receiving regions that receive the unnecessary light scattering over the substrate including the plurality of first and second light receiving regions reflected by one or more of the plurality of first information medium recording layers other than the recording layer that is the recording or reproducing object, the operation unit removes a component representative of the unnecessary light from the signal that is photoelectrically converted from the light received by the plurality of first light receiving regions, and the operation unit outputs a detection signal representative of the first light wavelength, when the one wavelength is the first wavelength, and wherein the operation unit: performs a subtraction operation between a signal that is photoelectrically converted from the light received by the plurality of second light receiving regions that receive the third and fourth diffracted beams and unnecessary light reflected by the single recording layer of the second information recording medium and a signal that is photoelectrically converted from the light received by the plurality of first light receiving regions that receive unnecessary light scattering over the substrate including the plurality of first and second light receiving regions reflected by the single recording layer of the second information recording medium, removes a component representative of the unnecessary light from the signal that is photoelectrically converted from the light received by the plurality of second light receiving regions, and outputs a detection signal representative of the second light wavelength, when the one wavelength is the second wavelength.