Patent ID: 6285645
Filing Date: 2001-09-04
Classification: G11B

Abstract:
An optical device for recording or reading data in a data recording surface of an optical disk by collecting light from a light source providing light incident to the data recording surface through an objective lens, collected light being reflected from the data recording surface and received by a light receiving element through the objective lens, the optical device comprising:a first light source and a second light source as the light source;an auxiliary lens arranged such that said second light source, said auxiliary lens and said objective lens are arranged in the optical device so that the optical axis of said second light source, the optical axis of said auxiliary lens and the optical axis of said objective lens are fixed in a line; anda first optical disk and a second optical disk as the optical disk wherein the thickness of a transparent substrate of the first optical disk is different from the thickness of a transparent substrate of the second optical disk,wherein when data in respective data recording surfaces of the first and second optical disks are to be recorded or read, the data in the data recording surface of the first optical disk is recorded or read by collecting light from the first light source through the objective lens and the transparent substrate of the first optical disk in this order, and the data in the data recording surface of the second optical disk is recorded or read by collecting light from the second light source through the auxiliary lens, the objective lens and the transparent substrate of the second optical disk in this order,in response to recording or reading of the data in the data recording surface of the first optical disk, specifications of the objective lens are determined so that the absolute value in RMS value of a spherical aberration of the third order is 0.03 .lambda..sub.1 or less and an off-axial coma aberration in an image height of 0.1 mm is 0.03 .lambda..sub.1 or less, andin response to recording or reading of the data in the data recording surface of the second optical disk, specifications in a combination of the auxiliary lens and the objective lens are determined so that the absolute value in RMS value of a spherical aberration of the third order is 0.03 .lambda..sub.2 or less and an off-axial coma aberration in an image height of 0.1 mm is 0.03 .lambda..sub.2 or less where .lambda..sub.1 represents a wavelength of the light from the first light source and .lambda..sub.2 represents a wavelength of the light from the second light source.