Patent ID: 7821899

Claim:
An optical pickup device for emitting a light beam to an optical recording medium to perform at least one of reading of data recorded on the optical recording medium and recording of data to the optical recording medium, comprising: a light source for emitting a light beam at the time of performing at least one of reading of data recorded on the optical recording medium and recording of data to the optical recording medium; a diffraction grating for diffracting the light beam emitted from the light source to apply at least a zeroth-order diffraction ray, a + first-order diffraction ray, and a − first-order diffraction ray to the optical recording medium; a light focusing device which focuses the diffraction rays to the optical recording medium; a light receiving device which receives the diffraction rays reflected from the optical recording medium and outputs light modulated signals; and a control device which controls a position on the optical recording medium of the light focusing device on the basis of the light modulated signals, wherein in the diffraction grating, when pitch of grooves formed in a recording surface of the optical recording medium in the radial direction of the optical recording medium is GP, effective diameter of a light beam in the light focusing device is D, wavelength of the light beam is λ, numerical aperture is NA, and n is a natural number, first and second lattice grooves are arranged at the pitch P satisfying the following equation in a direction perpendicular to a track direction in which data is recorded in the optical recording medium, P = λ · D ( 2 ⁢ n + 1 ) · GP · NA ( Equation ⁢ ⁢ 1 ) each of the first and second lattice grooves has grooves formed in predetermined cycle in the track direction in which data is recorded on the optical recording medium, and the grooves in the track direction of one of the first and second lattice grooves are shifted from the grooves in the other lattice groove by ½ of the cycle.