JPH0990130A - Optical head device - Google Patents

Abstract

(57) Abstract: Optical wavefront aberration caused by fine irregularities on the surface of a hologram element is reduced. SOLUTION: A volume hologram 2 and an optical retardation element 3 are laminated on a glass substrate 1, and on top of that, it has a refractive index almost the same as that of the optical retardation element 3 and is polymerized by ultraviolet rays to generate visible light. A UV-curable acrylic adhesive 4 which is optically transparent in the wavelength region was coated to a thickness of 20 μm. Wavefront aberration is 0.0
It was improved to 15λ _rms .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing apparatus for reproducing information on an optical recording medium such as an optical disk and / or an optical head apparatus usable for an information recording apparatus.

[0002]

2. Description of the Related Art Conventionally, as an optical head device for writing optical information on an optical recording medium such as an optical disk and a magneto-optical disk, and reading the optical information from the optical recording medium, a volume hologram or a volume hologram and an optical head are used. There has been proposed an optical head device using a hologram element obtained by adhering a laminate of retardation elements on a glass substrate or a plastic substrate.

However, according to this structure, optical wavefront aberration is generated due to fine irregularities on the surface of the volume hologram or the hologram element in which the volume hologram and the optical phase difference element are laminated, and the aspherical lens of the objective lens or the like causes the light source. There is a problem that it becomes difficult to collect the light from the light spot into a fine spot of a desired size.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head device capable of reducing the above-mentioned problems of the prior art, that is, optical wavefront aberration caused by fine irregularities on the surface of a hologram element.

[0005]

The present invention is directed to a light source for irradiating an optical recording medium with light, a photodetector for detecting reflected light reflected by the optical recording medium, the light source and optical recording. In an optical head device including a hologram element provided between a hologram element and a medium, the hologram element includes a volume hologram, and at least one surface of the hologram element is covered with a transparent organic resin. Provide a device.

In the present invention, the hologram element is
It is preferable to include a laminate of a volume hologram and an optical retardation element such as a λ / 4 plate because the optical retardation element is packaged and a highly efficient optical head device utilizing polarized light can be provided. .

It is preferable that the entire surface of the hologram element is covered with a transparent organic resin because the flatness can be further improved.

When a transparent substrate having a high flatness such as a glass substrate or a plastic substrate is laminated on the surface of the hologram element covered with the transparent organic resin, the flatness can be further increased.
This is preferable because the wavefront aberration can be further reduced and the reliability is improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the drawings.

The hologram element in the present invention is manufactured by laminating the volume hologram 2 on the glass substrate 1 or a transparent plastic substrate made of acrylic resin, polyolefin or the like. Alternatively, the volume hologram 2 and the optical retardation element 3 made of polyvinyl alcohol, polycarbonate, or the like are laminated on the glass substrate 1 or the plastic substrate to be manufactured.

In this case, even if the flatness of the glass substrate 1 or the plastic substrate is ensured, the hologram element is formed by the minute irregularities on the surface of the volume hologram 2 or the optical phase difference element 3 or the minute irregularities of the adhesive layer. Wavefront aberration occurs in the incident and transmitted laser light.

Generally, when the aberration exceeds 0.07λ _rms (λ: wavelength of light, rms: root mean square value), the transmitted light is condensed by an aspherical lens to a minute spot (diffraction limit) on the optical disk. It is said that it is difficult to do so (Marshall's condition), which poses a serious problem in practical use.

In the optical recording / reproducing system, the factors causing the aberration are the astigmatic difference of the semiconductor laser of the light source, the inclination of the optical disc, the uneven thickness, and the optical parts (lens etc.). The wavefront aberration of the hologram element in which the element 3 is laminated is preferably 0.015λ _rms or less.

In order to suppress the occurrence of aberration, as shown in FIG. 1, the surface of the volume hologram 2 or the layered structure of the volume hologram 2 and the optical phase difference element 3 is refracted to have almost the same refraction as the volume hologram 2 or the optical phase difference element 3. Coated with an organic resin that has a refractive index, is photopolymerizable or thermopolymerizable, and is optically transparent at the desired wavelength. As a result, the surface of the hologram element can be made optically flat, the irregularities on the surface can be compensated, and as a result, a desired suppressed wavefront aberration can be obtained.

Further, as shown in FIG. 2, a flat glass substrate 5 having a refractive index substantially the same as that of the organic resin or a transparent substrate such as a plastic substrate is adhered to the surface of the organic resin of the hologram element so that the flatness can be improved. It is possible to increase the wavefront aberration and reduce the wavefront aberration.

Further, as shown in FIG. 3, the reliability is improved by coating and sealing one surface and the side surface of the volume hologram 2 or the laminated volume hologram 2 and the optical phase difference element 3 with the organic resin. Also, the cuttability when a large number of hologram elements are formed and cut on one glass substrate 1 is improved.

In the present invention, when the glass substrate 1 is used, it is preferable that the incident surface of the light from the light source is also flattened. When the light source side of the volume hologram 2 is directly coated with the organic resin without using the glass substrate 1,
It is preferable that the incident surface of light from the light source of the organic resin is also flattened. Therefore, the flattening as described above flattens the light input / output surface of the hologram element as a whole, and as a result, a desired wavefront aberration is obtained.

A diffraction grating for tracking error detection or a diffraction grating for focus error detection by three beams can be formed on the glass substrate 1 by a dry etching method, a plastic injection molding method, a plastic injection molding method or the like.

As the light source in the present invention, a semiconductor laser, various solid-state lasers and the like can be used, and the semiconductor laser is preferable in terms of downsizing and weight reduction, continuous oscillation and the like. Further, as the optical recording medium, a recording medium capable of optically recording / reproducing such as an optical disk and a magneto-optical disk is preferable.

As the photodetector in the present invention, a semiconductor photodetector such as a photodiode or CCD is preferable because it is small and lightweight and can be driven at a low voltage.

The volume hologram has a size of several hundred μm ² to several tens m.
An area of about m ^{2 and} a thickness of about several μm to several tens of μm are preferable, and as a material thereof, a photosensitive material such as polyvinylcarbazole, dichromated gelatin, photoresist, photopolymer, silver salt and the like is preferable.

The optical retardation element preferably has a birefringence, and a desired optical retardation element can be obtained by controlling the birefringence amount and the thickness thereof. As the material, organic compounds such as stretched polycarbonate, polyvinyl alcohol, polyvinyl butyral, polyethylene terephthalate and polypropylene are preferable.

As the transparent organic resin, UV (ultraviolet) is used.
A curable acrylic photopolymer, a thermosetting epoxy resin, a UV curable epoxy resin and the like can be preferably used.

[0024]

【Example】

[Example 1] The configuration of Example 1 is shown in FIG. 100 mm x 100
mm on the glass substrate 1 of thickness 0.7 mm, 100 mm
× 100 mm × 20 μm thick volume holograms 2 and 10
An optical retardation element 3 having a thickness of 0 mm × 100 mm × thickness of 80 μm is laminated, and has a refractive index almost the same as that of the optical retardation element 3, and is superposed by ultraviolet rays to optically generate in the wavelength region of visible light. A transparent UV-curable acrylic adhesive 4 was coated to a thickness of 20 μm.

The volume hologram 2 is formed into a substrate or a film having a refractive index distribution formed by exposing two lights in a photopolymer so that they are exposed to each other, and is adhered onto the glass substrate 1 with a transparent adhesive. . The optical retardation element 3 is a film made of polycarbonate, the thickness of which is adjusted according to the amount of birefringence so as to function as a λ / 4 plate,
It adhered on the volume hologram 2 with a transparent adhesive.

Next, a UV-curable acrylic adhesive (trade name: 3013B, manufactured by ThreeBond Co., Ltd.) 4 is uniformly applied on the optical retardation element 3 in an uncured state, and polymerized and cured by ultraviolet rays in a nitrogen atmosphere. Adhesion was performed to produce a hologram element.

A semiconductor laser (not shown) as a light source is installed on the glass substrate 1 side of this hologram element, and an objective lens and an optical disk (not shown) are arranged on the UV-curable acrylic adhesive 4 side, so that light is emitted. It is configured as a head device.

Example 2 The configuration of Example 2 is shown in FIG. The glass substrate 1, the volume hologram 2 and the optical phase difference element 3 were produced in the same manner as in Example 1. Further, on the surface of the optical retardation element 3, a flat glass substrate 5 having a refractive index substantially the same as that of the glass substrate 1, the volume hologram 2 and the optical retardation element 3 (0.006λ _rms or less within a circle having a diameter of 2 mm at the central portion) Wavefront aberration)
UV curable acrylic adhesive 4 having almost the same refractive index as the glass substrate 1, the volume hologram 2 and the optical phase difference element 3.
Then, the hologram element was manufactured by bonding.

In this case, the glass substrate 5 is placed on the UV-curable acrylic adhesive 4 with the UV-curable acrylic adhesive 4 in an uncured state, and the UV-curable acrylic adhesive 4 is pressed while pressing. Was polymerized and cured by ultraviolet rays. In addition, in this case, in order to prevent bubbles from being generated between the glass substrate 5 and the UV-curable acrylic adhesive 4, the hologram element may be placed in a decompression chamber for manufacturing.

In Example 2, the UV curable acrylic adhesive 4
The flatness was remarkably improved as compared with the case where only the surface was covered, and as a result, the wave aberration was able to be made smaller. An optical head device was constructed in the same manner as in Example 1.

Example 3 The configuration of Example 3 is shown in FIG. The glass substrate 1, the volume hologram 2, the optical phase difference element 3, and the UV curable acrylic adhesive 4 were prepared in the same manner as in Example 1. However, the volume hologram 2 and the optical retardation element 3 are the glass substrate 1
The area is smaller than that of the optical phase difference element 3, and one side (the upper surface in FIG. 3) of the optical phase difference element 3 and the side end surface of the volume hologram 2 and the side end surface of the optical phase difference element 3 are covered with the UV curable acrylic adhesive 4. . Further, a glass substrate 5 is laminated on the upper surface of the UV curable acrylic adhesive 4. An optical head device was constructed in the same manner as in Example 1.

In Example 3, the volume hologram 2 and the optical phase difference element 3 are sealed by the UV-curable acrylic adhesive 4, and the volume hologram 2 and the optical phase difference element 3 are in the air. It is possible to suppress swelling and white turbidity due to the influence of humidity and deterioration of reliability.

Example 4 The configuration of Example 4 is shown in FIG. First, the uncured UV-curable acrylic adhesive 4 on the glass substrate 1
Then, the same volume hologram 2 and optical phase difference element 3 as in Example 1 were laminated on the UV-curable acrylic adhesive 4, and then uncured UV-curable acrylic was applied. The system adhesive 4 was applied, and the volume hologram 2 and the optical phase difference element 3 were completely covered and sealed with the UV curable acrylic adhesive 4. The glass substrate 5 was placed thereon, and the UV-curable acrylic adhesive 4 was polymerized and cured by ultraviolet rays and bonded to produce a hologram element. An optical head device was constructed in the same manner as in Example 1.

Also in Example 4, the volume hologram 2 and the optical phase difference element 3 are sealed by the UV-curable acrylic adhesive 4, and the volume hologram 2 and the optical phase difference element 3 are in the air. It is possible to prevent swelling and turbidity due to the influence of humidity and deterioration of reliability.

Example 5 The structure of Example 5 is shown in FIG. As the glass substrate 11, 100 mm × 100 mm × thickness 1 mm
A soda lime glass (blue plate) that had been polished was used. The transmitted wavefront aberration due to the glass substrate 11 was about 0.006λ _rms within a circle having a diameter of 2 mm near the center (effective area actually used).

A transmissive volume hologram 2 having a size of 100 mm × 100 mm × thickness of about 20 μm was laminated thereon by using an epoxy-based transparent adhesive. 10 more on it
An optical retardation film (λ / 4 plate) 13 made of polycarbonate and having a thickness of 0 mm × 100 mm × a thickness of 80 μm was laminated using an acrylic transparent adhesive. A UV-curable acrylic adhesive 4 was coated on it to produce a hologram element. An optical head device was constructed in the same manner as in Example 1.

[Example 6 (Comparative Example)] A hologram element was prepared in the same manner as in Example 5 except that the UV-curable acrylic adhesive 4 was not used, and an optical head device was constructed in the same manner as in Example 1.

Using the hologram elements of Examples 1 to 6, He
-The wavefront aberration was measured by a measuring device (trade name Mark4 manufactured by Zygo Co., Ltd.) using interference of Ne laser light.
The measurement was performed on the inside of a circle having a diameter of 2 mm at the center, which is the effective area (the area actually used) of the hologram element. Table 1 shows the measured wavefront aberration.

When configured as an optical head device, the one subjected to the coating treatment (Examples 1 and 5) has the effect of reducing the wavefront aberration and reducing the cost, and further the glass substrate 5 or the glass substrate 11 is laminated. Things (Examples 2-4)
Has the effect of reducing wavefront aberration and high reliability.

[0040]

[Table 1]

[0041]

According to the present invention, the optical wavefront aberration of the hologram element is improved, the environment resistance against high temperature and high humidity, thermal shock, etc. is also improved, and the reliability is also improved. 1
When many hologram elements are manufactured and cut on one glass substrate, damage to the volume hologram and the phase difference element at the time of cutting can be reduced, and the manufacturing yield is improved. Further, when configured as an optical head device, there is also an effect that the light from the light source can be accurately focused on a fine spot having a desired size.

[Brief description of drawings]

FIG. 1 is a side sectional view of a hologram element of Example 1.

FIG. 2 is a side sectional view of the hologram element of Example 2.

FIG. 3 is a side sectional view of the hologram element of Example 3.

FIG. 4 is a side sectional view of the hologram element of Example 4.

FIG. 5 is a side sectional view of the hologram element of Example 5.

[Explanation of symbols]

 1: Glass substrate 2: Volume hologram 3: Optical retardation element 4: UV curable acrylic adhesive 5: Glass substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yosuke Fujino 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Central Research Laboratory, Asahi Glass Co., Ltd.

Claims (4)

[Claims] 1. A light source for irradiating an optical recording medium with light,
In an optical head device including a photodetector for detecting reflected light reflected by the optical recording medium, and a hologram element provided between the light source and the optical recording medium, the hologram element is a volume hologram. An optical head device including a hologram element, at least one surface of which is coated with a transparent organic resin. 2. The optical head device according to claim 1, wherein the hologram element includes one in which a volume hologram and an optical phase difference element are laminated. 3. The optical head device according to claim 1, wherein the entire surface of the hologram element is covered with a transparent organic resin. 4. The optical head device according to claim 1, wherein a transparent substrate is laminated on a surface of the hologram element covered with a transparent organic resin.