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Optical information detecting method, optical head, and optical disc apparatus

A detection method and optical information technology, which are applied in the recording/reproducing, information storage, recording information storage and other directions by optical methods, can solve the problems of high S/N, practical difficulties, etc., and achieve the effect of high signal amplification effect.

Inactive Publication Date: 2008-03-19
HITACHI CONSUMER ELECTRONICS CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Furthermore, as another problem, there is no particular explanation on how to adjust the optical path difference of the two beams, and it is difficult in practical use.
In Patent Document 2, although it is explained that the reference mirror for obtaining interference light is provided on the disk and separated from the recording film, this problem is not achieved by making the existing disk high S. / N

Method used

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  • Optical information detecting method, optical head, and optical disc apparatus
  • Optical information detecting method, optical head, and optical disc apparatus
  • Optical information detecting method, optical head, and optical disc apparatus

Examples

Experimental program
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Effect test

Embodiment 1

[0127]FIG. 1 is a block diagram showing an optical system for realizing the optical signal detection method of the present invention. The light emitted from the laser 301 is transmitted through the first λ / 2 plate 321, so that the polarization direction is rotated by 45 degrees. The polarization-rotated light is split into two orthogonal linearly polarized lights by the first polarization beam splitter 341, and the light of one polarized light (reproduction light) is reflected and transmitted through the first λ / 4 plate 322, thereby being transformed into a circular polarized light. The polarized light is then condensed by the objective lens 311 and irradiated on the optical disk 4 . The reflected light (hereinafter referred to as signal light) from the optical disc 4 rotated by the spindle motor 77 is changed back to parallel light with the objective lens 311, and is changed back to linearly polarized light on the first λ / 4 plate 322, but due to the Reflection, the direction...

Embodiment 2

[0159] In Embodiment 1, it is assumed that the signal light and the reference light are completely coherent, but in general semiconductor lasers, the resonator length is short and the coherence length (light-interferable distance) is not too long. 8 is a graph showing changes in reproduction signal intensity when a normal blue light semiconductor laser (LD) is used in the configuration of the first embodiment. In order to track and focus against disc shake, the objective lens 311 moves up and down, and the optical path length of the signal light changes. However, since the optical path length of the reference light does not change, a difference in optical path length occurs between the reference light and the signal light. If the difference in the optical path length is larger than the coherent distance of the LD, the output of the formula (7) cannot be obtained. Usually, the output in the incompletely coherent state is multiplied by the degree of coherence (interferability) ...

Embodiment 3

[0163] In Examples 1 and 2, the reproduced signal was obtained by the calculation of Equation (7), but the reproduced signal can also be obtained without performing the square root calculation.

[0164] That is, put (Sig1) 2 +(Sig2) 2 =|Esig| 2·|Eref| 2 Used as a signal. In this calculation, since the square root calculation is not required, the circuit configuration is simplified, and there is an advantage that the energy of the signal light is proportional to the reproduction output. In the conventional optical signal detection method, the reproduced signal output is also the same as |Esig| 2 Therefore, in the method of this embodiment, there is an advantage that it is easy to use the same signal processing method as in the past.

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Abstract

In multilayer optical discs and high-speed optical discs, the amount of reproduction light per unit time greatly decreases and the reproduction signal quality (S / N) significantly drops due to the low effective reflectivity and the short read time of the medium. These problems are solved by causing reflected signal light from the optical disc and reference light, which is separated from the same light source and introduced into a detector without being shone onto the optical disc, to interference with each other on the detector. Detector outputs having four different interference states are simultaneously obtained, the interference states being displaced at intervals of 90 DEG in terms of the phase relationship between the reference light and the signal. Based on a operation of the four detector outputs, a reproduction signal can be obtained that is stable at all times and amplified with high quality, even when there is an optical path length variation due to disc undulations.

Description

technical field [0001] The present invention relates to a higher S / N of a reproduced signal of an optical disc device. Background technique [0002] The commercialization of Blu-ray Disc (BD) using blue semiconductor lasers and high NA objective lenses has been realized. The resolution of the optical system of the optical disc has almost reached the limit. In the face of further large capacity, multilayer is considered It will be useful in the future. In a multi-layer optical disc, the reflectance from a specific layer has to be reduced because the amount of detection light from each layer must be substantially the same. However, the increase in the capacity of the optical disk is accompanied by the need for an increase in the reproduction speed of video and the like, and the increase in the transfer rate is also continued. In this state, the S / N ratio of the reproduced signal cannot be sufficiently ensured. Therefore, in order to advance both multilayer and high speed in ...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G11B7/13
CPCG11B2007/0013G11B7/005G11B7/1356G11B7/13
Inventor 宮本治一三上秀治岛野健
Owner HITACHI CONSUMER ELECTRONICS CORP
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