Optics: measuring and testing – By light interference – For dimensional measurement
Reexamination Certificate
2002-05-29
2004-10-19
Turner, Samuel A. (Department: 2877)
Optics: measuring and testing
By light interference
For dimensional measurement
C356S521000
Reexamination Certificate
active
06806964
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical recording and/or reproduction apparatus which optically performs recording and reproduction of information on an optical recording medium, such as an optical disc, optical card, etc.
2. Description of the Related Art
In recent years, as our society has become more information-intensive, an external storage device having a larger capacity has been in increasing demand. In an optical recording of information, a recording density cannot be infinitely increased by reducing the size of a recording pit because of a diffraction limit which is defined by the wavelength of light and the numerical aperture of an objective lens. In order to address such a problem, an optical recording medium having a three-dimensional structure where information is recorded not only on one two-dimensional recording plane but on multiple recording layers superimposed along a direction perpendicular to the two-dimensional plane (optical axis direction), and an optical recording and/or reproduction apparatus have been proposed (Japanese Laid-Open Publication No. 6-28672).
FIG. 12
shows an example of a conventional optical recording and/or reproduction apparatus for recording information on/reproducing information from an optical recording medium having a three-dimensional structure.
The optical recording and/or reproduction apparatus
1200
shown in
FIG. 12
includes: a light source
101
; a beam splitter
360
; an objective lens
103
; a three-axes stage
761
on which a photosensitive material
760
A for recording information is mounted; and a detection section
130
. In the photosensitive material
760
A, information is three-dimensionally recorded.
As shown in
FIG. 12
, a laser beam emitted by the light source
101
, which is a semiconductor laser, is converged on the photosensitive material
760
A by the objective lens
103
. In this example, a LiNbO
3
crystal, which is a photorefractive crystal, is used as the photosensitive material
760
A. The refractive index of the LiNbO
3
crystal is changed in relation to a differential value of the intensity distribution of light. The light intensity on the optical axis is proportional to the square root of D (D
1/2
), where D denotes the distance from the focal point. Accordingly, a variation of the refractive index in the crystal, which occurs when the laser beam is converged on the photosensitive material
760
A, is proportional to the cube root of D (D
1/3
), where D denotes the distance from the focal point. As a result, a variation of the refractive index in the crystal occurs only in the vicinity of a point where the laser beam is converged. With such a variation in the refractive index, information can be three-dimensionally recorded in the photosensitive material (crystal)
760
A.
In reproduction of information recorded three-dimensionally in the photosensitive material
760
A, a laser beam emitted by the light source
101
is converged at a portion where the refractive index has been varied, and light reflected from that portion is detected by the detection section
130
, whereby the three-dimensionally recorded information is reproduced. The three-axes stage
761
is used to move the entire photosensitive material
760
A such that the laser beam is converged at a portion in the entire photosensitive material
760
A where a desired information is to be recorded.
However, in the above technique, since the three-axes stage
761
is used for positional control in order to achieve three-dimensional recording of information in the photosensitive material
760
A, the following problems occur. Firstly, the information recording density in the photosensitive material
760
A is limited due to the mechanical precision of the three-axes stage
761
. Secondly, moving the entire photosensitive material
760
A by using the three-axes stage
761
cannot be achieved speedily, and accordingly, recording/reproduction times become long. Thirdly, when the photosensitive material
760
A is replaced with another, the relative positions of the photosensitive material
760
A and the three-axes stage
761
are shifted, so that three-dimensionally recorded in formation cannot be read out.
In an optical recording and/or reproduction apparatus for recording information on/reproducing information from an optical recording medium, such as an optical disc or the like, the recording or reproduction time can be shortened by rotating the optical recording medium at a high speed, for example. In order to control a recording position, the position of a guiding groove, which is formed in the optical recording medium at the time of production thereof, is detected by using a push-pull method, a three-beam method, or the like. An objective lens is driven according to the position of the detected guiding groove, whereby the recording position is controlled. The recording position on the optical recording medium and the position of the guiding groove formed on the optical recording medium do not shift even when the recording medium is replaced with another. Thus, replacement of recording media is possible.
However, in such a conventional method for controlling a recording position employed for an optical recording medium, information cannot be recorded in a portion where no guiding groove is formed, although information can be recorded in a portion where a guiding groove is formed.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided an optical recording and/or reproduction apparatus for use with an optical recording medium, the optical recording medium including a recording layer and a substrate which has a guiding portion where concave portions and convex portions are periodically formed along a predetermined direction, the optical recording and/or reproduction apparatus comprising: a light source for emitting a first light beam; an optical system for diffracting a portion of the first light beam so as to output a first diffracted light beam and a second diffracted light beam, and for converging the other portion of the first light beam, thereby outputting a second light beam so as to be converged at a predetermined convergence point; and a controlling section for controlling the optical system, wherein the first and second diffracted light beams interfere with each other to generate interference fringes which extend in a direction substantially perpendicular to the recording layer, the interference fringes include bright portions and dark portions which occur alternately along the predetermined direction, the optical system outputs the first and second diffracted light beams and the second light beam such that the bright portions of the interference fringes form light spots on the guiding portion when the predetermined convergence point of the second light beam is present within the recording layer, the optical recording and/or reproduction apparatus further includes a detection section for detecting the interference fringes reflected by the guiding portion so as to output a detection signal, and the control section controls the optical system based on the detection signal such that the optical spots follow at least either of the concave portions and the convex portions.
In one embodiment of the present invention, the recording layer includes a plurality of recording planes; and the control section controls the optical system such that the predetermined convergence point of the second light beam is positioned on one of the plurality of recording planes.
In another embodiment of the present invention, the frequency of the interference fringes is equal to the frequency at which the concave portions and convex portions are formed.
In still another embodiment of the present invention, the frequency of the interference fringes is a half of the frequency at which the concave portions and convex portions are formed.
In still another embodiment of the present invention, the optical system is positioned at an opposite side to the recording layer with respec
Saimi Tetsuo
Shiono Teruhiro
Yamamoto Hiroaki
Matsushita Electric - Industrial Co., Ltd.
Renner , Otto, Boisselle & Sklar, LLP
Turner Samuel A.
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