Patent ID: 6333906
Filing Date: 2001-12-25
Classification: G11B

Abstract:
An optical pickup for reading information recorded on a plurality of information tracks of a recording medium by using at least a main light beam and a subsidiary light beam, the main light beam being applied to a reading track which is one of the plurality of information tracks on which the information to be read is recorded, the subsidiary light beam being applied to an adjacent track which is different one of the plurality of information tracks adjacent to the reading track, the optical pickup comprising:a light source for emitting an original light beam;a diffraction device for diffracting the original light beam to divide the original light beam into the main light beam and the subsidiary light beam, so that the main light beam and the subsidiary light beam are applied to the reading track and the adjacent track, respectively; anda receiving device for receiving the main light beam and the subsidiary light beam reflected by the recording medium and generating a main signal corresponding to the received main light beam and a subsidiary signal corresponding to the received subsidiary light beam,wherein the diffracting device is made of an optical material having coefficient of linear expansion .beta., which is determined as follows:.alpha.-.DELTA..alpha..sub.1.ltoreq..beta..ltoreq..alpha.+.DELTA..alpha.. sub.2,.alpha.=.DELTA..lambda./.lambda..sub.0,.DELTA..alpha..sub.1 ={(1+.alpha..times..DELTA.t.sub.max).times..DELTA.L.sub.max }/{(L.sub.0 +.DELTA.L.sub.max).times..DELTA.t.sub.max },.DELTA..alpha..sub.2 ={(1+.alpha..times..DELTA.t.sub.max).times..DELTA.L.sub.max }/{(L.sub.0 -.DELTA.L.sub.max).times..DELTA.t.sub.max },where .lambda..sub.0 is a wavelength of the original light beam at a design temperature of the optical pickup, .DELTA..lambda. is an amount of a change of the wavelength of the original light beam per unit temperature, .DELTA.t.sub.max is a predetermined permissible amount of a change of an ambient temperature at which the optical pickup is used, L.sub.0 is a spacing between an irradiation position of the subsidiary light beam and an irradiation position of the main light beam at the design temperature, and .DELTA.L.sub.max is a predetermined permissible amount of a change of the spacing between the irradiation position of the subsidiary light beam and the irradiation position of the main light beam.