US 2002/0159342 A1Published application

Optical pickup apparatus and focusing control method

AssigneePioneer Corporation

InventorsMasakazu Ogasawara, Ikuya Kikuchi

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Abstract

An optical pickup apparatus having an irradiation optical system for condensing a light beam on a track of a recording plane and a photodetection optical system for guiding return light to a photodetector to detect a focal error includes a holographic lens provided in the optical path of the return light for outputting 0-th and ±1st order diffracted lights based on the return light; an optical element provided in front of or behind the holographic lens for providing astigmatism; photodetectors for receiving the 0-th and ±1st order diffracted lights; and servo-signal generating operation circuits connected to the photodetectors for generating a first and second focus error signals having a first and second capture ranges based on the output signal of the photodetector.

Claims22

Dependent claims

An optical pickup apparatus having an irradiation optical system for condensing a light beam into a spot on a track on a recording plane of an optical recording medium and a photodetection optical system for guiding return light reflected back from said spot to a photodetector, said optical pickup apparatus detecting the focal error of said light beam, said optical pickup apparatus comprising:

a holographic lens provided in the optical path of said return light in said photodetection optical system for outputting 0-th order diffracted light and ±1st order diffracted light based on said return light;
an optical element provided in one of two positions, a first position in front of and a second position behind said holographic lens in the optical path of said return light in said photodetection optical system for providing astigmatism
a photodetector for receiving the 0-th order diffracted light output from said holographic lens;
a photodetector for receiving the ±1st order diffracted light output from said holographic lens;
a servo-signal generating operation circuit for the 0-th order diffracted light connected to said photodetector for the 0-th order diffracted light for generating a first focus error signal having a first capture range based on the output signal of the photodetector;
and
a servo-signal generating operation circuit for the ±1st order diffracted light connected to the photodetector for said ±1st order diffracted light for generating a second focus error signal having a second capture range different from said first capture range based on the output signal of the photodetector.

4 more elements

A focus control method for an optical pickup, said optical pickup having an irradiation optical system for condensing a light beam into a spot on a track on a recording layer of an optical recording medium having at least two recording layers placed on one another with an intermediate layer therebetween;

and a photodetection optical system for guiding return light reflected back from said spot to a photodetector, said optical pickup detecting a focus error of said light beam, said focus control method comprising the steps of:
a first focus error signal detection step of generating a first focus error signal having a first capture range smaller than the smallest distance between adjacent recording layers of the optical recording medium;
and
a second focus error signal detection step of generating a second focus error signal having a second capture range larger than said first capture range.

1 more element

Dependencies are inferred from the claim text.