JP2004078091A - Method for manufacturing optical element, optical element, optical pickup, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element which can be easily manufactured, can contribute to dwonsizing and cost reduction, and can eliminate problems, such as deterioration of films. <P>SOLUTION: Periodic structures sufficiently smaller than the wavelength of a light source are formed on a substrate and thereafter the refractive index of the substrate is changed. For example, an EB resist 5 is applied on the substrate 3 made of quartz glass (a). Patterns are drawn by an EB lithographic system and are developed (b). Metallic films 6 of Cr, etc., are deposited by vacuum vapor deposition and the metallic film patterns are formed by a lift-off method using a resist stripper (c). The substrate 3 formed with the metallic patterns is subjected to dry etching using gaseous fluorocarbon, such as CH<SB>3</SB>, C<SB>4</SB>F<SB>8</SB>, and CHF<SB>3</SB>, (d) to form the fine periodic structures and to remove the metallic films (e). Finally, a quarter wave plate is completed by doping boron B to the periodic structures 4. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing an optical element, and particularly relates to an optical element used for an optical pickup for recording and reproducing information on and from an optical recording medium, a method for manufacturing the optical element, and a configuration using the optical element. And an optical disk device having the optical pickup.
[0002]
[Prior art]
Polarizing optical elements are elements that change the polarization state of light, and are indispensable as elements that compose an optical system, like lenses, prisms and mirrors, and are used in optical communication devices, optical pickups, liquid crystal display devices, etc. ing.
As the polarizing optical element, an element using a birefringent crystal such as quartz or calcite, or an element having a dichroic molecule in a polymer film are often used.
It is known that a fine periodic structure (concavo-convex diffraction structure) in which flat plates having different refractive indices that do not originally have birefringence characteristics are arranged at a period sufficiently smaller than the wavelength of light exhibits birefringence characteristics (Principle). of Optics, Max Born and Emil Wolf, PERGAMON PRESS LTD.), and a polarizing optical element using this structural birefringence have been proposed.
[0003]
On the other hand, in recent years, mobile recording / reproducing apparatuses and information technology apparatuses for music and images have become more mobile, and there has been a demand for smaller and lighter optical disc apparatuses mounted in these recording / reproducing apparatuses and information technology apparatuses and lower cost.
Further, there is a demand for an increase in the capacity (higher recording density) of the optical disk device, and an optical disk device using a blue-violet LD (wavelength: 405 nm) as a light source has been actively developed.
Conventionally, an optical pickup mounted on an optical disk device often uses a relatively large optical element such as a polarization beam splitter as a polarization splitting element. At present, however, a polarization hologram (a polarization hologram element) as shown in FIG. ) 100 (Japanese Patent Application Laid-Open No. 2000-11443) and a polarization hologram 111 as shown in FIG. 8 (Japanese Patent Application Laid-Open No. 2000-155974) have been used to reduce the size, weight, and cost. . 7, reference numeral 101 denotes a quarter-wave plate, 102 denotes a cover, 103 denotes a semiconductor laser chip, 104 denotes a heat sink, 105 denotes an incident surface, 106 denotes a housing, 107 denotes a light receiving element, and 108 denotes a light receiving element. Denotes a light receiving surface, 109 denotes a bottom surface, and 110 denotes an opening.
8, reference numeral 112 denotes an optical recording medium, 113 denotes an objective lens, 114 denotes a quarter-wave plate, 115 denotes a prism mirror, 116 and 121 denote detectors, 117 and 120 denote semiconductor lasers, and 118 Reference numeral 119 denotes a collimating lens.
[0004]
[Problems to be solved by the invention]
In the device described in JP-A-2000-11443, a hologram pattern is formed by proton exchange on a lithium niobate substrate to produce a polarization hologram. However, since the pitch of the diffraction pattern is relatively large, the diffraction angle is small. Therefore, it is difficult to further reduce the size because the distance to the divided photodiode must be increased. Further, the lithium niobate substrate is expensive and disadvantageous for cost reduction.
In Japanese Patent Application Laid-Open No. 2000-155974, the polarization hologram is formed using a birefringent organic thin film, so that the pitch of the diffraction pattern can be narrowed and the diffraction angle can be increased. The distance to the photodiode can be shortened, and further miniaturization is easy. In addition, since it can be manufactured at low cost, cost reduction can be performed.
However, the organic thin film has problems such as a decrease in transmittance and a deterioration of the film with respect to light having a short wavelength, and thus cannot be used as a component of an optical disk device using a blue-violet LD as a light source. was there.
[0005]
Japanese Patent No. 3106047 describes a technique for forming a polarization hologram by forming a fine periodic structure smaller than a wavelength called a structure birefringence on a glass substrate, as shown in FIG. In FIG. 9, reference symbol A indicates a grating pitch, and reference symbol B indicates a period shorter than the wavelength.
According to this, the pitch of the diffraction pattern can be narrowed to increase the diffraction angle, and the optical pickup can be miniaturized, without using an expensive birefringent crystal, and for light having a short wavelength of about 400 nm. Can also be used.
However, in Japanese Patent No. 3106047, although the type of glass is not particularly specified, when quartz glass which is relatively easy to be processed by dry etching is used, the period is less than the wavelength and the height is about 1.2 μm. It is necessary to form a structure, and it is very difficult to manufacture. That is, when such a fine periodic structure is manufactured, the difficulty of the manufacturing increases as the depth (height) increases.
If BK7, which has a higher refractive index than quartz glass, is used as the glass to be used, it is possible to reduce the height of the fine periodic structure. There was a problem that fabrication was difficult.
[0006]
Therefore, the present invention provides an optical element manufacturing method, an optical element, an optical pickup using the optical element, an optical pickup, which can be easily manufactured, contribute to downsizing and cost reduction, and can also solve problems such as film deterioration. The main object is to provide an optical disk device having a pickup.
[0007]
[Means for Solving the Problems]
The purpose of the present invention is to configure a polarizing optical element such as a wave plate or a polarization hologram with a birefringent structure, and in the manufacturing method, after forming a fine periodic structure on the substrate, change the refractive index of the substrate itself. is there. In other words, instead of using the refractive index of the substrate such as glass as the structure birefringence as it is, on condition that the refractive index of the substrate is changed by a method such as doping, by adjusting the depth of the periodic structure according to this. It is intended to facilitate the fabrication.
[0008]
Specifically, according to the first aspect of the present invention, after forming the periodic structure on the substrate, in the optical element having a birefringent property by forming a periodic structure sufficiently smaller than the wavelength of the light source on the substrate, The refractive index of the substrate was changed.
[0009]
According to the invention as set forth in claim 2, in the optical element having a periodic structure sufficiently smaller than the wavelength of the light source formed on the substrate and imparting birefringence characteristics, the refractive index of the substrate after the periodic structure is formed on the substrate Was changed.
[0010]
According to a third aspect of the present invention, in the method of manufacturing an optical element according to the first aspect, changing the refractive index of the substrate is to give an impurity to the substrate.
[0011]
According to a fourth aspect of the present invention, in the optical element according to the second aspect, changing the refractive index of the substrate is to give impurities to the substrate.
[0012]
According to a fifth aspect of the present invention, in the method of manufacturing an optical element according to the first or third aspect, the substrate is made of quartz glass.
[0013]
In the invention according to claim 6, in the optical element according to claim 2 or 4, the substrate is made of quartz glass.
[0014]
According to a seventh aspect of the present invention, in the optical element of the second, fourth or sixth aspect, the periodic structure having the same shape is uniformly formed.
[0015]
According to an eighth aspect of the present invention, in the optical element according to the second, fourth or sixth aspect, at least two or more regions having different shapes of the periodic structure are provided.
[0016]
In the ninth aspect of the present invention, in the optical element according to the second, fourth or sixth aspect, there are at least two portions where the same periodic structure is uniformly formed and at least two regions where the periodic structures have different shapes. Both of the parts are formed integrally.
[0017]
According to a tenth aspect of the present invention, in the optical pickup having an optical element, the optical element is the optical element according to the second, fourth, sixth, seventh, eighth, or ninth aspect.
[0018]
According to an eleventh aspect of the present invention, an optical disc device includes the optical pickup according to the tenth aspect.
[0019]
According to a twelfth aspect of the present invention, in the optical disk device of the eleventh aspect, it is possible to perform additional writing or rewriting.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a perspective view of a quarter-wave plate (λ / 4 plate) as an optical element in the present embodiment. A region 2 indicated by hatching of the 波長 wavelength plate 1 is a portion that functions as a wavelength plate. FIG. 2 is an enlarged view of a region 2 functioning as a wave plate of a cross section taken along line AA ′ in FIG. As shown in FIG. 2, a fine periodic structure 4 is formed on a quartz glass substrate 3, and a portion including the periodic structure 4 is doped (diffused) with boron B as an impurity as shown by hatching. .
[0021]
A method for manufacturing the quarter-wave plate 1 in the present embodiment will be described with reference to FIG. First, an EB resist 5 is applied on the substrate 3 as shown in FIG. Thereafter, as shown in (b), a pattern is drawn by an EB drawing apparatus and developed. Next, as shown in (c), a metal film 6 of Cr or the like is formed by vacuum evaporation, and a metal film pattern is formed by a lift-off method using a resist stripper.
Next, as shown in (d), the substrate 3 on which the metal film pattern is formed is dry-etched using a fluorocarbon gas such as CF ₄ , C ₄ F ₈ , or CHF ₃ to form a fine periodic structure 4. Then, the metal film is removed (e). Finally, the periodic structure 4 is doped with boron B to complete a quarter-wave plate (f).
[0022]
Although the ECR etching apparatus is used as the dry etching apparatus, another etching apparatus such as an ICP etching apparatus may be used. Although the liquid source BBr ₃ was used for doping boron B, a gas source B ₂ H ₆ or solid source B ₂ O ₃ may be used, or doping may be performed by ion implantation.
The pattern formation with the resist may be performed not only by EB drawing but also by a method using a stepper.
In order to function as a quarter-wave plate with respect to light having a wavelength of 405 nm, the height of the structural birefringence must be about 1.1 μm in the case where the quartz glass is used as it is. When boron B is doped to make the refractive index 1.53, the height of the structural birefringence may be 0.9 μm, which is about 80%, and the formation of the fine periodic structure 4 becomes easy.
The material to be doped may be other than boron. When the refractive index is set to 1.6, the height of the structural birefringence is 0.7 μm, which is about 60%, and the fine periodic structure 4 can be easily formed.
[0023]
Next, a second embodiment will be described with reference to FIG. FIG. 4 is an enlarged view of a part of a polarization hologram as an optical element.
In the region I on the substrate 3, a fine periodic structure 4A is formed, and in the region II, a fine periodic structure 4B whose direction is different by 90 ° is formed. That is, there are at least two or more regions having different shapes of the periodic structure.
When the duty ratio of the periodic structure 4 in the region I is 0.44 and the duty ratio in the region II is 0.67, and boron is doped so that the refractive index of the glass is 1.6, the polarization direction of x is obtained. (Wavelength: 405 nm), the refractive index of both regions is 1.30, and the light is transmitted as it is. However, for the light whose polarization direction changes by 90 ° and the polarization direction is y, the region I Since the refractive index in the area II is 1.17 and the refractive index in the area II is 1.43, a hologram pattern is formed in the area I and the area II, and light is diffracted.
[0024]
When trying to obtain the maximum diffraction efficiency while keeping the refractive index of quartz glass, the height of the periodic structure 4 is required to be 1.2 μm, whereas the height of the periodic structure 4 is The maximum diffraction efficiency is obtained at 0.78 μm, and the formation of the periodic structure 4 is facilitated.
The polarization hologram of the present embodiment can be manufactured in exactly the same manner as the quarter-wave plate of the above embodiment, and only needs to change the drawing pattern at the time of EB drawing.
The quarter-wave plate according to the first embodiment and the polarization hologram according to the second embodiment can be easily manufactured integrally on one glass substrate (a quarter-wave plate is provided on one surface and the other is provided). (A polarization hologram is formed on each surface), so that the number of components of the optical pickup can be reduced, and furthermore, the optical pickup can be reduced in size and weight and cost can be reduced.
[0025]
Next, a third embodiment will be described with reference to FIGS. An object of the present embodiment is to provide an inexpensive, compact and lightweight optical pickup module. FIG. 5 is a configuration diagram of the optical pickup module according to the present embodiment. The optical pickup module 7 has a light source unit 8 using a GaN laser as a light source, an objective lens 9, and an actuator 11 as moving means for moving the objective lens 9 via a lens holder 10. In FIG. 5, reference numeral 12 denotes an optical disk as an optical recording medium.
[0026]
The light source unit 8 includes an illumination optical system for guiding light from the light source to the objective lens 9, and as shown in FIG. 6, a semiconductor laser 13 as a light source, a split photodiode 14 as a signal detecting means, and a heat sink 15 And a 1/4 wavelength plate / polarization hologram integrated optical element 16 described in the second embodiment.
The laser light emitted from the semiconductor laser 13 is converted from linearly polarized light to circularly polarized light by a quarter-wave plate arranged so that the optical axis forms an angle of 45 ° with respect to the polarization plane, and the recording surface of the optical disk 12 is recorded by the objective lens 9. Focus on The condensed laser light is reflected by the recording surface, is again converted from circularly polarized light into linearly polarized light by a quarter-wave plate through the objective lens 9, and is subjected to a diffraction pattern on the divided photodiode 14 by a diffraction grating formed in a polarization hologram. Is formed, a signal recorded on the recording surface of the optical disc 12 can be detected.
[0027]
Next, a fourth embodiment will be described. An object of the present embodiment is to provide an inexpensive, compact, lightweight, and large-capacity optical disk device.
Although not shown, the configuration is based on the optical pickup module 7 shown in the third embodiment, a driving unit for driving the LD, a rotation mechanism for rotating the optical recording medium, and a focus signal detected by the detection system. A focus control unit that drives a focus actuator, a track control unit that drives a track actuator based on a track signal detected by a detection system, and a signal reproduction unit that reproduces data recorded on an optical recording medium.
In the fourth embodiment, if a signal processing unit for converting a signal to be recorded on a write-once optical recording medium or a rewritable optical recording medium based on externally input data is provided, it is inexpensive, small, and lightweight. In addition, a large-capacity write-once or rewritable optical disk device can be realized (fifth embodiment).
[0028]
【The invention's effect】
According to the first aspect of the present invention, in the optical element having a periodic structure sufficiently smaller than the wavelength of the light source formed on the substrate and imparting birefringence characteristics, after forming the periodic structure on the substrate, Since the refractive index is changed, the fine periodic structure can be formed in a relatively easy-to-process state, and the optical element can be easily manufactured.
[0029]
According to the invention as set forth in claim 2, in the optical element having a periodic structure sufficiently smaller than the wavelength of the light source formed on the substrate and imparting birefringence characteristics, after forming the periodic structure on the substrate, Since it is manufactured by changing the refractive index, the fine periodic structure can be formed in a state that is relatively easy to process, and the optical element can be easily manufactured.
[0030]
According to the third aspect of the present invention, in the method of manufacturing an optical element according to the first aspect, changing the refractive index of the substrate is to give an impurity to the substrate (for example, to diffuse). The refractive index can be easily changed.
[0031]
According to the fourth aspect of the present invention, in the optical element according to the second aspect, changing the refractive index of the substrate is to give an impurity to the substrate (for example, diffusion). Can be easily changed.
[0032]
According to the fifth aspect of the present invention, in the method of manufacturing an optical element according to the first or third aspect, since the substrate is made of quartz glass, good workability can be obtained at low cost.
[0033]
According to the sixth aspect of the present invention, in the optical element of the second or fourth aspect, since the substrate is made of quartz glass, it is possible to obtain good workability at low cost.
[0034]
According to the seventh aspect of the present invention, in the optical element according to the second, fourth or sixth aspect, the periodic structure having the same shape is formed uniformly, so that the optical element capable of converting the polarization state of light is provided. (Wave plate) can be easily manufactured.
[0035]
According to the eighth aspect of the present invention, in the optical element according to the second, fourth or sixth aspect, at least two or more regions having different shapes of the periodic structure are provided. An optical element (polarization hologram) capable of preventing diffraction can be easily manufactured.
[0036]
According to the ninth aspect of the present invention, in the optical element according to the second, fourth or sixth aspect, there are at least two portions where the same periodic structure is uniformly formed, and at least two regions having different periodic structures. Since both of the above parts are formed integrally, it is possible to reduce the size, weight, and cost of the optical element.
[0037]
According to the tenth aspect of the present invention, in the optical pickup having the optical element, the optical element is the optical element according to the second, fourth, sixth, seventh, eighth or ninth aspect. A low-cost optical pickup (apparatus) can be easily realized.
[0038]
According to the eleventh aspect of the present invention, since the optical disk device includes the optical pickup according to the tenth aspect, it is possible to easily realize a small, lightweight and low-cost optical disk device.
[0039]
According to the twelfth aspect of the present invention, in the optical disk device according to the eleventh aspect, it is possible to perform write-once or rewrite, so that a compact, lightweight, low-cost write-once or rewritable optical disk device can be easily realized. be able to.
[Brief description of the drawings]
FIG. 1 is a perspective view of a quarter-wave plate as an optical element according to a first embodiment of the present invention.
FIG. 2 is an enlarged view of a cross section taken along line AA ′ of FIG.
FIG. 3 is a diagram illustrating a manufacturing process of a quarter-wave plate.
FIG. 4 is an enlarged perspective view of a part of a polarization hologram as an optical element according to a second embodiment.
FIG. 5 is a schematic configuration diagram of an optical pickup according to a third embodiment.
FIG. 6 is a detailed view of a light source unit in the optical pickup.
FIG. 7 is a schematic diagram of an optical pickup in a conventional example.
FIG. 8 is a schematic view of an optical pickup in another conventional example.
FIG. 9 is a perspective view of structural birefringence in still another conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 1/4 wavelength plate 3 as optical element 3 Substrate 4 Periodic structure 7 Optical pickup 13 Semiconductor laser B as light source B as impurity

Claims (12)

In an optical element formed by forming a periodic structure sufficiently smaller than the wavelength of the light source on the substrate to impart birefringence characteristics,
After forming the periodic structure on the substrate, the refractive index of the substrate is changed. In an optical element formed by forming a periodic structure sufficiently smaller than the wavelength of the light source on the substrate to impart birefringence characteristics,
An optical element manufactured by forming the periodic structure on the substrate and changing the refractive index of the substrate. The method for manufacturing an optical element according to claim 1,
A method of manufacturing an optical element, wherein changing the refractive index of the substrate is to add an impurity to the substrate. The optical element according to claim 2,
An optical element, wherein changing the refractive index of the substrate is to give an impurity to the substrate. The method for manufacturing an optical element according to claim 1, wherein
A method for manufacturing an optical element, wherein the substrate is quartz glass. The optical element according to claim 2 or 4,
An optical element, wherein the substrate is quartz glass. The optical element according to claim 2, 4 or 6,
An optical element wherein a periodic structure having the same shape is formed uniformly. The optical element according to claim 2, 4 or 6,
An optical element comprising at least two or more regions having different shapes of the periodic structure. The optical element according to claim 2, 4 or 6,
An optical element, wherein both a portion in which a periodic structure having the same shape is uniformly formed and a portion in which at least two or more regions having different shapes of the periodic structure are integrally formed. In an optical pickup having an optical element,
10. An optical pickup, wherein the optical element is the optical element according to claim 2, 4, 6, 7, 8, or 9. An optical disc device comprising the optical pickup according to claim 10. The optical disk device according to claim 11,
An optical disc device capable of being added or rewritten.

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