JP2003185837A - Bisected optical rotating plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bisected optical rotating plate. <P>SOLUTION: The bisected optical rotating plate 1 has a rotating plate 12R disposed in the right side of the optical axis and a rotating plate 12L disposed in the left side of the optical axis. The polarization direction of the incident light L entering the bisected optical rotating plate 1 is rotated by -45 degrees by the plate 12R and rotated by +45 degrees by the plate 12L and the light exits as exiting light LR, LL. The rotating plate 12R and the rotating plate 12L are stuck by direct bonding, and reflective coating films 2a, 2b each comprising a dielectric single layer film or a dielectric multilayer film are formed on the exit face and the entrance face, respectively. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-part optical rotation plate, and more particularly to a two-part optical rotation plate for hologram recording using a direct bonding technique. 2. Description of the Related Art Holographic recording, in which information is recorded on a recording medium using holography, generally involves superimposing an information beam having image information and a reference beam inside the recording medium, This is performed by writing the interference fringes generated in the recording medium. When reproducing the recorded information, the recording medium is irradiated with reference light, whereby the image information is reproduced by diffraction due to interference fringes. In recent years, volume holography, particularly digital volume holography, has been developed in the practical range for ultra-high-density optical recording and has attracted attention. Volume holography is a method of writing interference fringes three-dimensionally by actively utilizing the thickness direction of the recording medium. Increasing the thickness increases the diffraction efficiency, and increasing the recording capacity by using multiplex recording. There is a feature that can be achieved. And
The digital volume holography is a computer-oriented hologram recording method in which the recording image information is limited to a binary digital pattern while using the same recording medium and recording method as the volume holography. In this digital volume holography, for example, image information such as an analog picture is once digitized, developed into two-dimensional digital pattern information, and recorded as image information. At the time of reproduction, this digital pattern information is read out and decoded, thereby returning to the original image information and displaying it. Thus, even if the SN ratio (signal-to-noise ratio) is somewhat poor during reproduction, differential detection can be performed,
By coding the coded data and performing error correction, it is possible to reproduce the original information very faithfully. The recording / reproducing system in the conventional digital volume holography includes a spatial light modulator for generating information light based on two-dimensional digital pattern information, and hologram recording by condensing the information light from the spatial light modulator. A lens for irradiating the medium, reference light irradiating means for irradiating the hologram recording medium with reference light in a direction substantially orthogonal to the information light, and a CCD (charge) for detecting reproduced two-dimensional digital pattern information Coupling element) CCD that condenses the reproduction light emitted from the hologram recording medium
A lens for irradiating the array. Note that a hologram recording material such as a crystal such as LiNbO ₃ or a photopolymer is used for the hologram recording medium. In the above-described configuration, information can be multiplex-recorded on the same hologram recording medium. However, in order to record information at an extremely high density, positioning of the information light and the reference light with respect to the hologram recording medium is important. . However, in the above configuration, since there is no information for positioning in the hologram recording medium itself, the positioning of the information light and the reference light with respect to the hologram recording medium has to be performed mechanically, and it is difficult to perform highly accurate positioning. Therefore, the removability (easiness of transferring the hologram recording medium from one recording / reproducing apparatus to another recording / reproducing apparatus and performing the same recording / reproducing) is poor, and random access is difficult and high-density recording is difficult. There is a problem that is. Furthermore, since the optical axes of the information light, the reference light, and the reproduction light are spatially arranged at mutually different positions, the optical system for recording or reproduction becomes large, and the information light, the reference light, and the reproduction light Each optical axis must be aligned, which is difficult. FIG. 3 shows, as a means for solving the above-mentioned problems, for example, a pickup configuration in "Optical Information Recording Apparatus and Method and Optical Information Reproducing Apparatus and Method" disclosed in JP-A-11-31937. FIG. The pickup 111 according to this embodiment includes a light source device 11 that emits coherent linearly polarized laser light.
2, a collimator lens 113 arranged in order from the light source device 112 side in the traveling direction of light emitted from the light source device 112, and a neutral density filter (neutral density filter).
er; hereinafter, referred to as an ND filter. ) 114, an optical rotation element 115, a polarizing beam splitter (hereinafter abbreviated as PBS) 116, a phase spatial light modulator 117, a beam splitter (hereinafter abbreviated as BS) 118, and a photodetector 119. The light source device 112 emits S-polarized light or P-polarized linearly polarized light.
The collimator lens 113 converts the light emitted from the light source device 112 into a parallel light beam and emits the light. The ND filter 114 has characteristics such that the intensity distribution of the light emitted from the collimator lens 113 is made uniform. Note that S-polarized light is linearly polarized light whose polarization direction is perpendicular to the plane of incidence, and P-polarized light is linearly polarized light whose polarization direction is parallel to the plane of incidence, and will be used in the same sense below. The optical element for optical rotation 115 is an ND filter 1
The emitted light of 14 is rotated to emit light including an S-polarized component and a P-polarized component. Optical element for optical rotation 1
As 15, for example, a half-wave plate or an optical rotation plate is used. The PBS 116 has a PBS surface 116a that reflects the S-polarized light component and transmits the P-polarized light component of the light emitted from the optical rotation optical element 115. [0008] The BS 118 has a beam splitter surface 118.
a. This beam splitter surface 118a
For example, a P-polarized component is transmitted by 20% and reflected by 80%. The photodetector 119 is used for monitoring the light amount of the reference light and performing automatic light amount adjustment of the reference light. The pickup 111 further includes a light source device 1
12 from the beam splitter surface 118 of the BS 118
A PBS 120, a two-part optical rotation plate 121, and a rising mirror 122 are sequentially arranged from the BS 118 side in the direction in which the light is reflected by a and travels. The PBS 120 has a PBS surface 120a that reflects an S-polarized component of the incident light and transmits a P-polarized component. As shown in FIG. 4, the two-part optical rotation plate 121 has an optical rotation plate 121R arranged on the right side of the optical axis and an optical rotation plate 121L arranged on the left side of the optical axis. The optical rotation plate 121R rotates the polarization direction by -45 degrees, and the optical rotation plate 121L rotates the polarization direction by +45 degrees. The optical rotation plate 121R and the optical rotation plate 121L are bonded to each other with an adhesive (optical adhesive) 121B and fixed to each other, and one surface of which is provided with an antireflection coating MNR of a dielectric multilayer film. Plates 121U and 1
The surfaces of the 21D, on which the antireflection coating MNR is not applied, are bonded to the upper and lower sides of the optical rotation plate 121R and the optical rotation plate 121L with an adhesive 121A. The rising mirror 122 is a two-part optical rotation plate 1
It has a reflecting surface that is inclined at 45 degrees with respect to the optical axis of the light from 21 and reflects the light from the two-part optical rotation plate 121 in a direction perpendicular to the plane of FIG. The pickup 111 is further arranged in a direction in which light from the two-part optical rotation plate 121 is reflected by the rising surface of the rising mirror 122 and travels, and when the optical information recording medium is fixed to the spindle, An objective lens 123 facing the transparent substrate side of the optical information recording medium;
23 is provided with an actuator (not shown) movable in the thickness direction and the track direction of the optical information recording medium. [0013] In the invention according to the present invention,
Since the optical axes of the information light, the reference light, and the reproduction light are spatially identical to each other by using the two-part optical rotation plate 121, the optical system for recording or reproduction can be downsized. But,
The two-divided optical rotation plate 121 is composed of an optical rotation plate 121R arranged on the right side of the optical axis and an optical rotation plate 1 arranged on the left side of the optical axis.
21L and glass plates 121U and 121D on which an anti-reflection coating MNR is formed. The optical rotation plates 121R, 121L, and glass plates 121U and 121D on which the anti-reflection coating MNR is formed.
Are bonded and fixed to each other with adhesives 121B and 121A. As a result, the optical rotation plate 121R and the optical rotation plate 1
There is a problem that an invalid area exists at the boundary of the bonding with 21L by the thickness of the adhesive, and the larger the thickness is, the more the influence of Fresnel diffraction occurs, and the phenomenon of blurring the image occurs.
Furthermore, since the boundary is joined by using a resin-based adhesive, heat resistance is insufficient, and an anti-reflection coating process using a dielectric multilayer film or the like cannot be performed on the entrance surface and the exit surface. For this purpose, measures have been taken such as pasting the glass material which has been subjected to the anti-reflection coating process on both sides of the entrance surface and the exit surface. In such a manufacturing method, a glass plate coated with an anti-reflection coating is required in addition to the optical rotatory plate. In addition to an increase in cost, the size of the element is increased due to an increase in the dimension in the thickness direction. In addition, the right and left portions are not parallel due to variations in the thickness of the adhesive, and the two-part optical rotation plate 12
Light from 1 is not focused on the same point on the hologram recording medium. Further, there is a problem that an operation of bonding a glass plate having been subjected to an anti-reflection coating treatment to a rotation plate is required. The present invention solves the above problem and provides a two-piece optical rotation plate used for hologram recording and the like in which the boundary between the right and left portions of the two-piece optical rotation plate is extremely thin. It was done for the purpose of doing. According to a first aspect of the present invention, there is provided a two-divided optical rotation plate according to the first aspect of the present invention, wherein a right optical rotation plate disposed on a right portion of the optical axis and a left optical rotation plate disposed on the right side of the optical axis. In a two-part light-rotating plate having a left-handed optical rotation plate disposed in a part, the right-handed optical rotation plate is a light-rotating material that rotates the polarization direction by +/− 45 degrees, and the left-handed light rotation plate is a polarization optical material that rotates the polarization direction by − / + 45 degrees. The right and left rotatory plates are bonded by direct bonding, and a non-reflective coating film made of a dielectric multilayer film is formed on an incident surface and an exit surface thereof. FIG. 1 is a view showing a two-part optical rotation plate 1 according to an embodiment of the present invention. The direct bonding is a technique which is conventionally performed mainly on a semiconductor as a technique for integrating two substrates without using an adhesive. Such direct bonding is realized by subjecting two materials to a predetermined surface treatment and then bonding the two materials, and performing a heat treatment on the two bonded materials at a predetermined temperature. The surface treatment and the heat treatment differ depending on the material and are determined as appropriate. Here, S-polarized light, P-polarized light, A-polarized light, and B-polarized light used in the following description are defined as follows. That is, S-polarized light is linearly polarized light whose polarization direction is parallel to the Y direction in FIG. 1, and P-polarized light is linearly polarized light whose polarization direction is parallel to the X direction. The A-polarized light is obtained by subtracting the S-polarized light by -4.
This is linearly polarized light obtained by rotating the polarization direction by 5 degrees or P polarization by +45 degrees. B-polarized light is S-polarized light at +45 degrees or P-polarized light at -45 degrees, and linearly polarized light whose polarization direction is rotated. A
The polarization directions of the polarized light and the B-polarized light are orthogonal to each other. In FIG. 1, the two-part optical rotation plate 1 has an optical rotation plate 12R arranged on the right side of the optical axis and an optical rotation plate 12L arranged on the left side of the optical axis. For simplification of the description below, the incident light L incident on the two-part optical rotation plate 1
Is the S-polarized light, the optical rotation plate 12R rotates the polarization direction by −45 degrees to A-polarized light, and the optical rotation plate 12L changes the polarization direction to +4.
Rotate 5 degrees to make B-polarized light, and output light LR, LL,
Description will be made assuming that each is emitted. The incident light, the optical rotation plate 12R and the optical rotation plate 1
The relationship with 2L may be other than this. That is, the incident light L may be the P-polarized light, and the optical rotation plate 12R rotates the polarization direction by +45 degrees to be B-polarized light, and the optical rotation plate 12L.
May be A-polarized light by rotating the polarization direction by -45 degrees. In such a case, it is used in consideration of the optical rotation of the material forming the two-part optical rotation plate 1. In FIG. 1, the optical rotation plate 12R and the optical rotation plate 12
The material used for L is quartz, which is a kind of optical rotation material.
The quartz has optically birefringence and optical rotation, and has a wavelength of 0.1 mm.
It has high transmittance between 3 and 1.5 μm. As shown in FIG. 2, optical rotatory power K (degree / mm)
Varies depending on the wavelength λ (nm) and the thickness CD (mm) of the crystal, and the optical rotation power K is generally obtained by the following equation. K = 7.19 × 10 ⁶ × λ ² / (λ ² −92.6 ² )
² (degrees / mm) For example, if the wavelength of the incident light L is λ = 532 nm
Then, K = 27.016 (degrees / mm). Therefore, in order to rotate the incident light by 45 degrees as described above, the thickness CD of the crystal becomes 1.66 mm. The size of the vertical CH and the horizontal CW of the crystal is determined as necessary. For example, when the CD is 1.66 mm, CH = 6 m each.
m, CW = 10 mm. When quartz is used as a polarizing material such as an optical rotator, the homogeneity of the birefringence of the quartz is important. As is well known, the homogeneity is best in the Z region of the crystal lattice.
Use as 2L. The optical rotation plate 12R cut out of the crystal,
12L is bonded by well-known direct bonding. For example, IEICE Technical Report, TECHNICAL
The direct bonding technique disclosed in REPORT OF IEICE OPE99-12 (1999-05) is used. That is, the optical rotation plate 1
2R determines the crystal plane so that the polarization direction is rotated by -45 degrees to be A polarized light, and the optical rotation plate 12L rotates the polarization direction by +45 degrees to be B polarized light. Optical rotation plate 12R, bonded after surface treatment the bonding surface of the 12L heat treatment in a H ₂ atmosphere in the crystal surface. The temperature of the heat treatment is appropriately determined depending on the material of the optical rotation plates 12R and 12L, and is, for example, 110 to 330 degrees Celsius. Since there is no ineffective area due to the thickness of the adhesive at the boundary between the optical rotation plates 12R and 12L bonded by direct bonding, the image is not blurred due to the influence of Fresnel diffraction. Further, the right and left portions do not become parallel due to the variation in the thickness of the adhesive, so that the light from the two-part optical rotation plate 1 is not focused on the same point on the hologram recording medium. Further, there is no need to bond the glass plate having been subjected to the anti-reflection coating treatment to the optical rotation plates 12R and 12L. Non-reflective coating films 2a and 2b each composed of a dielectric single-layer film or a dielectric multilayer film are formed on the output surface and the incident surface of the optical rotation plates 12R and 12L bonded by direct bonding, respectively, by a known method. I do. As a result, in addition to the optical rotation plates 12R and 12L, a glass plate subjected to an anti-reflection coating process becomes unnecessary, and the cost is reduced, and the element is not increased due to an increase in the dimension in the thickness direction. According to the two-part optical rotation plate according to the first aspect,
The right-handed and left-handed light-rotating plates made of optically-rotating material are bonded together by direct bonding, and the anti-reflection coating film is formed on the entrance and exit surfaces, thereby blurring the image due to the influence of Fresnel diffraction. It is possible to realize a small, high-performance two-piece optical rotation plate that has been eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram of a two-part optical rotation plate according to an embodiment of the present invention. FIG. 2 is a diagram showing a relationship between the optical rotation power (degree / mm) of a quartz crystal and a wavelength λ (nm). FIG. 3 is an explanatory diagram showing a configuration of a pickup in a conventional “optical information recording apparatus and method and optical information reproducing apparatus and method”. FIG. 4 is a diagram of a conventional two-part optical rotation plate. [Description of Signs] 1 2 split optical rotation plates 2a, 2b Non-reflective coating films 12R, 12L Optical rotation plate L Incident light LL, LR Outgoing light

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Claims (1)

Claims: 1. A two-piece optical rotation plate having a right rotation plate disposed on a right portion of an optical axis and a left rotation plate disposed on a left portion of an optical axis, wherein the right rotation plate is provided. Is +/- 45 for the polarization direction
The left rotatory plate is formed of a rotatory material that rotates the polarization direction by-/ + 45 degrees, respectively, and the right rotatory plate and the left rotatory plate are bonded by direct bonding, and there is no reflection on the entrance surface and the exit surface. A two-part optical rotation plate, wherein a coating film is formed.