Patent ID: 8064315
Filing Date: 2011-11-22
Classification: G11B

Abstract:
1. An optical pickup comprising: a first emission unit emitting a first optical beam with a first wavelength corresponding to a first optical disc; a second emission unit emitting a second optical beam with a second wavelength, which is longer than the first wavelength, corresponding to a second optical disc different from the first optical disc; a third emission unit emitting a third optical beam with a third wavelength, which is longer than the second wavelength, corresponding to a third optical disc different from the first and second optical discs; a condensing optical device condensing, on a signal recording surface of a corresponding optical disc, the first optical beam emitted from the first emission unit, the second optical beam emitted from the second emission unit, and the third optical beam emitted from the third emission unit; and a diffraction unit provided in the condensing optical device, which is disposed on an optical path of the first optical beam with the first wavelength, the second optical beam with the second wavelength, and the third optical beam with the third wavelength, wherein the diffraction unit has a substantially circular first diffraction region provided on an innermost portion, a ring zone-shaped second diffraction region provided outside the first diffraction region, and a ring zone-shaped third diffraction region provided outside the second diffraction region, the first diffraction region has a first diffraction structure formed in a ring zone shape to have a predetermined depth, and is configured to emit first diffracted light of an order of the first optical beam with the first wavelength, which passes therethrough and is condensed on the signal recording surface of the first optical disc through the condensing optical device, to emit second diffracted light of an order of the second optical beam with the second wavelength, which passes therethrough and is condensed on the signal recording surface of the second optical disc through the condensing optical device, and to emit third diffracted light of an order of the third optical beam with the third wavelength, which passes therethrough and is condensed on the signal recording surface of the third optical disc through the condensing optical device, the second diffraction region has a second diffraction structure, different from the first diffraction structure, formed in the ring zone shape of the second diffraction region to have a predetermined depth, and is configured to emit fourth diffracted light of an order of the first optical beam with the first wavelength, which passes therethrough and is condensed on the signal recording surface of the first optical disc through the condensing optical device, to emit fifth diffracted light of an order of the second optical beam with the second wavelength, which passes therethrough and is condensed on the signal recording surface of the second optical disc through the condensing optical device, and to emit sixth diffracted light such that diffracted light of an order other than the order of the third optical beam with the third wavelength which passes therethrough and is condensed on the signal recording surface of the third optical disc through the condensing optical device is dominant, the third diffraction region has a third diffraction structure, different from the first and second diffraction structures, formed in the ring zone shape of the third diffraction region to have a predetermined depth, and is configured to emit seventh diffracted light of an order of the first optical beam with the first wavelength, which passes therethrough and is condensed on the signal recording surface of the first optical disc through the condensing optical device, to emit eighth diffracted light such that diffracted light of an order other than the order of the second optical beam with the second wavelength which passes therethrough and is condensed on the signal recording surface of the second optical disc through the condensing optical device is dominant, and to emit ninth diffracted light such that diffracted light of an order other than the order of the third optical beam with the third wavelength which passes therethrough and is condensed on the signal recording surface of the third optical disc through the condensing optical device is dominant, and the first and second diffraction structures are cyclical structures in which unit cyclical structures having a concavo-convex shape are successively formed in a radial direction of each ring zone, and satisfy Expressions (1) and (2), respectively: wherein, N N