Optical pickup device and birefringence correction plate

Abstract

An optical pickup device is provided with a light source; an objective lens for focusing an optical beam emitted from the light source on a recording plane; a polarizing beam splitter arranged on an optical path between the light source and the objective lens; and a birefringence correction plate arranged on an optical path between the objective lens and the polarizing beam splitter for giving a phase difference between two polarization components of the entered optical beam which are orthogonally intersecting each other. In the optical pickup device, the phase difference generated by the birefringence correction plate differs, depending on a position within the plane of the birefringence correction plate. Thus, influence of birefringence is more effectively reduced by using the simpler optical element, and a margin for birefringence fluctuation of an information recording medium is widened.

Description

Optical pickup device and birefringence compensation plate technical field The present invention relates to an optical pickup device for irradiating light onto a recording surface of an information recording medium having a light-transmitting medium, and receiving reflected light from the recording surface, a playback device, and birefringence compensation used in these devices plate. Background technique In the field of information recording medium technology, the improvement of recording density has become an increasingly important technical issue. In the past, recording was realized from the improvement of the line recording medium along the information channel and the improvement of the surface recording density by narrowing the channel pitch. Increased density. For DVD, which is one of the information recording media, by setting the laser wavelength at 650 nm and setting the numerical aperture NA of the objective lens at 0.6, an areal density of 4.7 GB in CD size ca...

AI Technical Summary

Problems solved by technology

As a result of examining the influence of birefringence in HDDVD, the inventors of the present invention have found that, in the HDDVD standard, the areal density has been improved by shortening the laser wavelength and increasing the numerical aperture (0.60→0.65), but On the contrary, the light transmission property of the information recording medium that exists between the information recording surface of the information recording medium and the objective lens of the optical pickup device, that is, the influence of the birefringence of the transparent substrate becomes larger, and the signal modulation degree is relatively transparent on the surface of the substrate. The fluctuation of the fluctuation of the amount of internal birefringence increases

That is, it is known that for HDDVD, the influence of the birefringence of the transparent substrate becomes larger, and the allowable range of the in-plane birefringence amount (relative to the fluctuation range of the in-plane birefringence amount) becomes narrower.

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