Diffraction optical element and optical pickup device

Abstract

A simply-structured optical pickup device in which the diffracted lights of three laser beams can be made efficiently to enter a single optical sensor, and proper focus control can be carried out according to the detection signal from the optical sensor, and a diffraction optical element used for such an optical pickup device are provided. The optical pickup device comprises a laser light source (10) capable of emitting three different laser beams, a diffraction optical element (42) for diffracting the reflected laser beams from an optical disk (31), and an optical sensor (43) for sensing thediffracted lights outputted from the diffraction optical element (42). The diffraction optical element (42) is composed of an optical member fabricated so that the zero-order diffracted light produced from each of the two laser beams whose wavelengths is close to each other (the difference between the wavelengths is small) may be the component having the greatest intensity, and the +1 order diffracted light or -1 order diffracted light produced from the other laser beam may be the component having the greatest intensity.

Description

technical field [0001] The present invention relates to an optical pickup device capable of supporting three types of optical disc standards, and a diffractive optical element mountable on the optical pickup device. Background technique [0002] As optical discs, there are CDs (compact discs) that record or reproduce information using infrared laser light with a center wavelength of 0.78 μm, and DVDs that use red laser light with a center wavelength of 0.65 μm to record or reproduce information. (Digital Versatile Disc: digitalversatile disc). In addition, HD-DVD and Blu-ray discs (hereinafter collectively referred to as "blue laser discs" or "Blu-ray discs") that record or reproduce information using a blue laser with a center wavelength of 0.405 μm have also begun to be obtained. practical application. [0003] Generally, a recording / reproducing device for a blue laser disc is configured to be capable of recording or reproducing information also on conventional DVDs and ...

AI Technical Summary

Problems solved by technology

[0009] However, when the linear range of the focus error signal is reduced, focus control for CDs that allow a large disc surface wobble in the focus direction (that is, have a large focus shift allowable value) becomes difficult

[0010] Conversely, when the linear range of the focus error signal is increased, focus control for CD becomes easy, but the accuracy of focus control for Blu-ray discs and DVDs decreases, and each signal recording surface of a dual-layer disc cannot be recognized

[0011] In this way, since the depth of focus of the CD standard is about 7 times that of the Blu-ray standard, it is very difficult to set the linear range of the focus error signal that satisfies both standards

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