Converging optical apparatus, optical pickup and optical disc apparatus

Abstract

A converging optical apparatus reduces the diffraction loss and realizes compatibility with three different wavelengths by means of a hologram element. The present invention provides an optical pickup for recording signals on and / or reproducing signals from a plurality of optical discs having respective protection substrates of different thicknesses for protecting the recording surfaces thereof by means of light beams of different wavelengths, the optical pickup including a first emission section that emits a light beam of a first wavelength, a second emission section that emits a light beam of a second wavelength, a third emission section that emits a light beam of a third wavelength, an objective lens for converging the light beams of the first through third wavelengths emitted respectively from the first through third emission sections on the signal recording surfaces of the optical discs, and a hologram element arranged between the first through third emission sections and the objective lens, the hologram element having two major surfaces, wherein the hologram element is provided with a reference curved surface on one of the major surfaces thereof, the reference curved surface being an aspherical shape, and a hologram section is formed on the reference curved surface.

Description

technical field [0001] The present invention relates to a converging optical device and an optical pickup capable of recording and reproducing information signals on and from any one of three different types of disc-shaped recording media through a single objective lens, and also relates to the use of the converging optical device and optical pickup head of the disc drive. Background technique [0002] Optical discs suitable for high-density recording and reproduction of signals by light beams having a wavelength of about 405 nm from blue-violet semiconductor lasers (hereinafter referred to as high-density recording optical discs) have been proposed. In addition, high-density recording optical discs having a cover layer for protecting a signal recording layer having a thickness as small as 0.1 mm have also been proposed. [0003] From the standpoint of providing an optical pickup for such high density recording discs, it may be desirable that the optical pickup be compatibl...

AI Technical Summary

Problems solved by technology

[0009] Although an optical pickup having such a diffraction element and an objective lens can correct aberrations attributable to the thickness of the disc by the diffraction element, there may be a problem of light quantity reduction due to the diffraction efficiency at both surfaces of the diffraction element

[0010] Therefore, it is very difficult to achieve compatibility with high-density recording optical discs using different wavelengths, DVDs and CDs, and to achieve recording / reproduction performance relative to optical discs due to various problems including the problem of reduction in the amount of light due to diffraction loss. Excellent optical pickup head

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