Optical head, objective lens, optical disc device, computer, optical disc player, and optical disc recorder

摘要

An objective lens (101) is configured to converge laser light of a first wavelength λ1 (390 [nm]≦λ1≦430 [nm]), laser light of a second wavelength λ2 (630 [nm]≦λ2≦680 [nm]), and laser light of a third wavelength λ3 (750 [nm]≦λ3≦810 [nm]) on an information recording surface of a first information recording medium, an information recording surface of a second information recording medium, and an information recording surface of a third information recording medium, and is configured such that the distance from a convergent point of normal diffracted order light, to a virtual collecting point formed by virtual diffracted order light between the convergent point of normal diffracted order light and a collecting point of unwanted diffracted order light is twice or more of the pull-in range of a focus error signal to be obtained in recording or reproducing information with respect to the third information recording medium.

主权项

1. An optical head for recording or reproducing information with respect to an information recording surface of a first information recording medium, an information recording surface of a second information recording medium, and an information recording surface of a third information recording medium, the first information recording medium, the second information recording medium, and the third information recording medium having protective substrate thicknesses different from each other, the optical head comprising:
a light source configured to output laser light of a first wavelength λ1, laser light of a second wavelength λ2, and laser light of a third wavelength λ3, the first wavelength λ1, the second wavelength λ2, and the third wavelength λ3 being different from each other; and an objective lens configured to converge the laser light of the first wavelength λ1, the laser light of the second wavelength λ2, and the laser light of the third wavelength λ3 on the information recording surface of the first information recording medium, the information recording surface of the second information recording medium, and the information recording surface of the third information recording medium, wherein the first wavelength λ1 satisfies a condition: 390 [nm]≦λ1≦430 [nm], the second wavelength λ2 satisfies a condition: 630 [nm]≦λ2≦680 [nm], the third wavelength λ3 satisfies a condition: 750 [nm]≦λ3≦810 [nm], at least one surface of the objective lens is provided with a diffraction structure having a step for giving an optical path length difference with respect to the laser light to be incident on the objective lens,
the diffraction structure is configured to generate normal diffracted order light which is converged on the information recording surface of the third information recording medium, and unwanted diffracted order light which is collected at a position away from the information recording surface of the third information recording medium, from laser light of the third wavelength λ3 transmitted through the objective lens, and a distance from a convergent point of the normal diffracted order light, to a virtual collecting point formed by virtual diffracted order light between the convergent point of the normal diffracted order light and a collecting point of the unwanted diffracted order light is twice or more of a pull-in range of a focus error signal to be obtained in recording or reproducing information with respect to the third information recording medium, a third focus error signal to be detected based on the virtual diffracted order light is generated between a first focus error signal to be detected based on the normal diffracted order light and a second focus error signal to be detected based on the unwanted diffracted order light, the diffraction structure forms a plurality of virtual collecting points respectively formed by a plurality of virtual diffracted order lights between the convergent point of the normal diffracted order light and the collecting point of the unwanted diffracted order light, the third focus error signal includes a plurality of third focus error signals to be detected based on the virtual diffracted order light, and a distance between a zero-cross point of the third focus error signal closest to the first focus error signal, out of the plurality of the third focus error signals, and a zero-cross point of the first focus error signal is twice or more of the pull-in range of the first focus error signal to be obtained in recording or reproducing information with respect to the third information recording medium.