JP2004178773A - Optical head device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical head device which has reduced aberration and is small-sized and light-weighted, and which is compatible with different kinds of optical disks. <P>SOLUTION: A liquid crystal element mounted in an optical head device is constituted so that a liquid crystal is sandwiched between two transparent substrates. At the periphery of an area decided by a numerical aperture to outgoing light having a maximum wavelength between at least two usable wavelength on a surface of one transparent substrate, the element is formed so that concentric electrodes about an optical axis are formed and a wave aberration of the outgoing light having the maximum wave length is compensated. The liquid crystal device 10 is located in an optical path between a synthesis prism 7 of the optical head device, and an optical recording medium 5. <P>COPYRIGHT: (C)2004,JPO

Description

【００３６】
【発明の効果】
以上説明したように、本発明の異なる２波長以上の光（例えばＨＤ／ＤＶＤ／ＣＤ用では３波長）で再生または記録する互換光ヘッド装置において、その収差を低減させるために組み込んだ液晶素子にＨＤ／ＤＶＤ光ディスク用の収差補正機能、およびＣＤ光ディスク用収差補正機能を組み合わせて一体化することにより良好な再生または記録特性が得られ、さらに装置を小型化できた。また、ＣＤ光ディスクの収差補正機能に関しては、開口数により決定される領域の周辺部に形成された光軸を中心とする同心円状の電極により収差を低減する位相差を発生させることにより収差補正機能を付与し、別の開口制限素子を組み込む必要がなくなり、装置の小型軽量化およびコスト低減が実現できた。
【図面の簡単な説明】
【図１】本発明の光ヘッド装置の原理構成の一例を示す概念的断面図。
【図２】液晶素子の構成の一例を示す概念的断面図。
【図３】ＨＤ／ＤＶＤ光ディスクの収差を補正する、本発明における液晶素子に形成された電極および給電部材パターンを示す模式的平面図。
【図４】ＣＤ光ディスクの収差を低減する、本発明における液晶素子に形成された電極および給電部材パターンを示す模式的平面図。
【図５】球面収差を補正する本発明における液晶素子に形成された分割電極パターンを示す模式的平面図。
【図６】コマ収差を補正する本発明における液晶素子の電極分割パターンを示す模式的平面図。
【図７】ＣＤ光ディスクの収差を低減する、本発明における液晶素子に形成された電極および給電部材パターンを示す模式的平面図。
【符号の説明】
１Ａ、１Ｂ、１Ｃ：半導体レーザ
２：ビームスプリッタ
３、７：合波プリズム
４：コリメートレンズ
５：対物レンズ
６：光ディスク
８、８Ａ、８Ｂ：光検出器
９、９Ｂ、９Ｃ：ホログラム素子
１０：液晶素子
２１、２１Ａ、２１Ｂ：ガラス基板
２２：シール材
２３：液晶
２４、２４Ａ、２４Ｂ：電極
２５：絶縁膜
２６：配向膜
２８：液晶分子
３０〜３２：給電部材
４０、５０〜５３：透明電極
６０：引出配線
１０１：アクチュエータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head device, and more particularly to an optical head device that records and / or reproduces an optical recording medium such as an optical disk using three different wavelengths.
[0002]
[Prior art]
A DVD, which is an optical disk, records digital information at a higher density than a CD, which is also an optical disk, and an optical head device for reproducing a DVD has a light source wavelength of 650 nm, which is shorter than the 780 nm of the CD. The numerical aperture (hereinafter referred to as NA) of the objective lens is set to 0.6 or 0.65, which is larger than 0.45 or 0.5 of CD, to reduce the spot diameter focused on the optical disk surface.
[0003]
Further, in the next generation optical recording, it has been proposed to obtain a higher recording density by setting the wavelength of the light source to around 400 nm and NA of 0.6 or more (hereinafter, the high recording density is referred to as HD). ). However, due to the shortening of the wavelength of the light source and the increase of the NA of the objective lens, the allowable amount of tilt in which the optical disk surface is tilted from the right angle with respect to the optical axis and the allowable amount of uneven thickness of the optical disk are reduced. The reason why these tolerances are reduced is that coma aberration occurs when the optical disc is tilted, and spherical aberration occurs when the optical disc is uneven in thickness. This makes it difficult to read signals. In high-density recording, several methods have been proposed to increase the allowable amount of the optical head device by coping with tilt and thickness unevenness of the optical disk.
[0004]
As one method, there is a method in which an axis for tilting is added to an objective lens actuator that normally moves in the biaxial direction of the tangential direction and the radial direction of the optical disc so that the objective lens is tilted according to the detected tilt angle. is there. However, this additional axis method has problems such that spherical aberration cannot be corrected and the structure of the actuator is complicated.
[0005]
As another method, there is a method in which wavefront aberration is corrected by a phase correction element provided between the objective lens and the light source. In this correction method, the allowable amount of tilt of the optical disk and the allowable amount of thickness unevenness can be increased only by incorporating an element into the optical head device without significantly modifying the actuator.
[0006]
For example, the above correction method for correcting the tilt of the optical disk using a phase correction element is described in JP-A-10-20263. This is because the voltage is applied to the divided electrodes formed by dividing the electrodes on each of the pair of substrates sandwiching the birefringent material such as liquid crystal constituting the phase correction element, and the birefringence is achieved. In this method, the substantial refractive index of the material is changed in accordance with the tilt angle of the optical disk, and the coma aberration generated by the tilt of the optical disk is corrected by the wavefront change of transmitted light generated by the change of the refractive index.
[0007]
Further, in the HD / DVD / CD optical disc, the disc thickness and the operating wavelength are different from each other. Therefore, when an objective lens designed for any one type of disc thickness is used, a large spherical surface is obtained for other disc thicknesses. There is a problem that pit information cannot be recorded / reproduced due to aberration. Various methods have been proposed to reduce spherical aberration that occurs when information is recorded / reproduced on different optical discs using the same objective lens. Among them, an aperture limiting element is proposed in which an optical multilayer film is patterned on a substrate in a donut shape, for example, one of two wavelengths of light is transmitted and the other wavelength is reflected at the same time to switch the NA. Yes.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2001-143303
[Problems to be solved by the invention]
However, when the above aperture limiting element and liquid crystal phase correction element are used in combination, each of them is composed of individual components, and an optical multilayer film is patterned on the substrate of the liquid crystal phase correction element and integrated with the aperture limitation. It is done. However, the former has problems such as an increase in weight and an increase in cost, and the latter has a problem in connection with an increase in cost. This is the same when using light of two wavelengths or when using light of three wavelengths.
[0010]
[Means for Solving the Problems]
The present invention has been made in order to solve the above-described problems. The light source, the objective lens for condensing the light emitted from the light source onto the optical recording medium, and the light collected and reflected on the optical recording medium. In an optical head device comprising a photodetector for receiving emitted light, and a liquid crystal element disposed in an optical path between the light source and the optical recording medium, and using the emitted light of at least two different wavelengths, the liquid crystal element is A liquid crystal is sandwiched between two transparent substrates, and a concentric electrode centered on the optical axis is formed at the periphery of a region determined by the numerical aperture for the emitted light having the maximum wavelength on the surface of one transparent substrate. Provided is an optical head device in which the wavefront aberration of emitted light having a maximum wavelength is corrected.
[0011]
Further, the emitted light used in the optical head device is light of three wavelengths λ ₁ , λ ₂ , λ ₃ (λ ₁ <λ ₂ <λ ₃ ), and the surface of the one transparent substrate of the liquid crystal element in the provided electrodes for correcting the further wavefront aberration within a region determined by the numerical aperture is formed, and the surface of the other transparent substrate correcting the wavefront aberration of the light emitted from the wavelength lambda ₁ and wavelength lambda ₂ There is provided the above-described optical head device in which an electrode is formed.
[0012]
Furthermore, the above-mentioned optical head device in which the liquid crystal element is integrated with a phase plate is provided.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to an optical head device that records and / or reproduces information using emitted light of at least two different wavelengths. In this optical head device, the light source and the emitted light from the light source are collected on an optical recording medium. An objective lens for causing light to illuminate, a photodetector for receiving outgoing light collected and reflected by the optical recording medium, and a liquid crystal element disposed in an optical path between the light source and the optical recording medium .
[0014]
In the liquid crystal element of the present invention, the liquid crystal is sandwiched between two transparent substrates, and the peripheral portion of the region determined by the numerical aperture for the emitted light having the maximum wavelength of two or more wavelengths on the surface of one transparent substrate In this case, a concentric transparent electrode centered on the optical axis is formed to correct the wavefront aberration of the emitted light having the maximum wavelength. This concentric circle is centered on the intersection of the optical axis and the surface on which the electrodes of the transparent substrate are formed. The application of a voltage to the concentric electrodes has an effect of reducing the wavefront aberration, particularly spherical aberration, of the emitted light having the maximum wavelength by giving a phase difference to the emitted light having the maximum wavelength. Also, it serves as an aperture limiting element for outgoing light with the maximum wavelength. Outgoing light having two or more wavelengths has two wavelengths when using a DVD and a CD optical disk, and has three wavelengths when using an HD, DVD, and CD optical disk.
[0015]
Hereinafter, it demonstrates in detail based on drawing. FIG. 1 is a conceptual sectional view showing an example of the principle configuration of the optical head device of the present invention. This example relates to an optical disc apparatus that records and / or reproduces information on an optical disc such as a CD, DVD, or HD. This optical head device is a semiconductor laser 1A, 1B, 1C (for example, 1A is an HD semiconductor laser, 1B is a DVD semiconductor laser, and 1C is a CD semiconductor laser), a beam splitter 2, and a multiplexing light source. It has an actuator 101 on which prisms 3 and 7, a collimating lens 4, an optical disk 6, photodetectors 8A, 8B and 8C, hologram elements 9B and 9C, and an objective lens 5 are mounted.
[0016]
Furthermore, the liquid crystal element 10 that changes the wavefront of the light emitted from the semiconductor laser 1A, 1B, or 1C is disposed. The liquid crystal element 10 has a liquid crystal sandwiched between two transparent substrates, and has an electrode for applying a voltage to the liquid crystal on the surface of the transparent substrate.
[0017]
The structure of the liquid crystal element shown in FIG. 2 will be described. Glass substrates 21A and 21B, which are transparent substrates, are bonded by a sealing material 22 to form a liquid crystal cell. On the inner surface of the glass substrate 21A, an electrode 24A from the inner surface side, an insulating film 25 mainly composed of silica and the alignment film 26 are arranged in this order, and on the inner surface of the glass substrate 21B, the electrode 24B from the inner surface side. The insulating film 25 and the alignment film 26 are coated in this order.
[0018]
The electrode 24A is provided with an electrode lead portion 27. The liquid crystal cell is filled with liquid crystal to form a liquid crystal layer 23, and the liquid crystal molecules 28 shown in FIG. 2 are in a homogeneous alignment state aligned in one direction. The aberration correction function of this liquid crystal element in the optical head device will be described with reference to FIG.
[0019]
When the alignment direction of the liquid crystal molecules in the liquid crystal layer matches the polarization direction of the incident light, the effective refractive index changes by applying a voltage to the liquid crystal layer, and the polarization state of the light is hardly changed. The wavefront of light can be changed. As a result, the outgoing light can change the wavefront of the light by applying a voltage to the liquid crystal layer with almost no change in the polarization state when passing through the liquid crystal element.
[0020]
That is, assuming that three lights are now used and the wavelengths are λ ₁ , λ ₂ , and λ ₃ (λ ₁ <λ ₂ <λ ₃ ), the numerical aperture of the wavelength λ _{3 on} the surface of one transparent substrate of the liquid crystal element. In addition to an external concentric electrode, an electrode for correcting wavefront aberration is further formed inside the region determined by, and the outgoing light of wavelength λ ₁ and wavelength λ ₂ is formed on the surface of the other transparent substrate. It is preferable that an electrode for correcting the wavefront aberration is formed.
[0021]
That is, of the two transparent substrates sandwiching the liquid crystal layer 23, the other transparent substrate includes, for example, a thickness deviation of an optical disc substrate for HD (using wavelength λ ₁ ) or DVD (using wavelength λ ₂ ), reproduction of a multilayer optical disc, Alternatively, for example, an electrode as shown in FIG. 3 divided for correcting spherical aberration generated due to a difference in wavelength is provided.
[0022]
Further, the one of the substrates, CD in order to reduce the aberration by the phase difference arranged outside the determined area by the optical disc substrate of thickness correction and NA (wavelength lambda ₃ using) for, for example, as shown in FIG. 4 Provide a suitable electrode. When reproducing or recording an optical disk of each wavelength, a voltage is applied to each electrode so as to correct the aberration signal obtained by the photodetector. The electrodes on the unused side have the same voltage.
[0023]
The number of concentric transparent electrodes 50, 51, 52 outside the area determined by NA is three here, but any number of concentric transparent electrodes 50, 51, 52 may be used as long as it is one or more. However, about eight are preferable from the viewpoint of ease of production and further effects. For correction of spherical aberration, the region determined by NA may be corrected by providing divided electrodes (concentric circles indicate dividing lines) as shown in FIG.
[0024]
Further, the electrode shown in FIG. 6 (the line in the figure indicates the dividing line) divided for correcting the coma generated by the tilt of the optical disk is combined with the electrode shown in FIG. 3 or FIG. It may be provided. 3 and 4, in order to generate a continuous voltage distribution, a thin film electrode 40 is formed on the surface of the substrate inside the region determined by NA2, so that the desired voltage distribution is obtained. On the electrode 40 that is not divided, a plurality of power supply members 30, 31, and 32 having shapes that can cope with the respective aberrations are provided. Reference numeral 60 denotes a lead wiring for the power supply member. By applying an appropriate voltage to each power supply member, the voltage drop in the electrode surface between the power supply members is used to generate a continuous voltage distribution in the electrode surface between the power supply members to correct aberrations. You may let them. Furthermore, the continuous voltage distribution may be applied to the transparent electrodes 50, 51, and 52 outside the region determined by the NA of the CD.
[0025]
The liquid crystal element is preferably an optical head device integrated with a phase plate. That is, the number of components can be reduced by laminating a phase plate such as a quarter wave plate on the liquid crystal element. Furthermore, by mounting the liquid crystal element on the actuator mounted with the objective lens, the objective lens and the liquid crystal element move together during tracking, and deterioration of the aberration correction performance due to the positional deviation of these two parts can be suppressed.
[0026]
The liquid crystal material used for the liquid crystal element is preferably a nematic liquid crystal used for display or the like, and may be twisted by adding a chiral agent.
Moreover, as a material of the transparent substrate to be used, glass, polycarbonate resin, acrylic resin, epoxy resin, vinyl chloride resin, and the like can be used, but a glass transparent substrate is preferable from the viewpoint of durability.
[0027]
As the quarter-wave plate, a plate having a phase difference that is an odd multiple of the quarter-wavelength, such as a quarter-wave plate or a quarter-wave plate, may be used. As a material for the quarter-wave plate, a birefringent single crystal such as quartz or LiNbO ₃ may be used, or an organic film such as a polymer liquid crystal or polycarbonate may be used.
[0028]
A voltage is output by a liquid crystal element control circuit, which is a control voltage generation means, toward the liquid crystal element 10 shown in FIG. 1 so that, for example, the intensity of the reproduction signal of the optical disk obtained from the photodetector is optimized. The voltage output from the liquid crystal element control circuit is a voltage corresponding to the thickness deviation amount and tilt amount of the optical disk, the positional deviation between the liquid crystal element and the objective lens, and the substantially changing voltage applied to the electrodes of the liquid crystal element. Become.
[0029]
【Example】
The optical head device of the present embodiment has an HD / DVD / CD optical disk compatibility function. HD and DVD optical discs are used with NA of 0.65, and CD optical discs with NA of 0.50. The wavelength used was λ ₁ = 405 nm for the HD optical disc, λ ₂ = 660 nm for the DVD optical disc, and λ ₃ = 780 nm for the CD optical disc. The objective lens used was optimized for a single-layer HD optical disc.
[0030]
Therefore, in the case of HD double-layer optical disc playback or recording, DVD optical disc playback or recording, or CD optical disc playback or recording, spherical aberration occurs and signal reading accuracy decreases. In order to correct the aberration, the phase correcting liquid crystal element shown in FIG. 2 was incorporated in the optical head device.
[0031]
The substrate thickness of the optical disk was 0.6 mm for HD / DVD and 1.2 mm for CD, and the HD optical disk was used with a distance between two layers of 40 μm. In this phase correcting liquid crystal element (see FIG. 2), the orientation direction of the liquid crystal molecules 28 is changed to the polarization direction of the outgoing light when passing through the liquid crystal layer 23 so as to change the wavefront of the outgoing light from the semiconductor laser. Parallel.
[0032]
As shown in FIG. 2, the liquid crystal layer 23 is surrounded by a sealing material 22 and sandwiched between the alignment film 26, the intermediate film 25, the transparent electrode films 24A and 24B, and the glass substrates 21A and 21B. In this embodiment, a glass substrate, which is two transparent substrates sandwiching a liquid crystal layer, has a continuous voltage distribution for correcting spherical aberration as shown in FIG. 3 for HD and DVD optical disks so that a voltage can be applied to the liquid crystal layer. Was formed on the glass substrate 21B on the upper surface, and the electrode shown in FIG. 7 was formed on the lower glass substrate 21A as a spherical aberration correction electrode for CD.
[0033]
For the purpose of reducing the size of the element, a wide-band quarter-wave plate for HD / DVD / CD optical disc was laminated on the objective lens side of the liquid crystal element 10. When recording and reproducing an HD double-layer optical disc or a DVD optical disc, the signals A to D shown in FIG. 7 applied to the glass substrate 21A are set to zero potential, and the aberration generated from the aberration signal obtained from the photodetector is corrected. Thus, good recording and reproduction characteristics could be obtained by applying an optimum AC voltage to the electrodes of signals 1 to 3 shown in FIG. 3 of the glass substrate 21B. Further, since it is not necessary to incorporate an aperture limiting element for wavelength λ ₃ = 780 nm, the apparatus can be reduced in size and weight.
[0034]
Further, when recording and reproducing a CD optical disk, the signals 1 to 3 shown in FIG. 3 of the glass substrate 21B are set to zero potential, and an optimum AC voltage for correcting the aberration generated by the obtained aberration signal is set to the glass substrate 21A. The recording and reproducing characteristics can be obtained by adding to the electrode signals A to D (FIG. 7). Note that the values of the outer diameters D1 to D2 of the concentric electrodes in FIG. 7 are the values shown in Table 1, the voltage of the signal D in FIG. 7 is the same voltage as the signal C, and the voltage of the signal A is the voltage of the signals C and D. A voltage that generates a phase difference 0.366 μm larger than the generated phase difference was applied.
[0035]
[Table 1]

[0036]
【The invention's effect】
As described above, in the compatible optical head device that reproduces or records with light of two or more wavelengths (for example, three wavelengths for HD / DVD / CD) according to the present invention, the liquid crystal element incorporated to reduce the aberration is used. By combining and integrating the aberration correction function for HD / DVD optical disc and the aberration correction function for CD optical disc, good reproduction or recording characteristics can be obtained, and the apparatus can be further downsized. As for the aberration correction function of the CD optical disc, the aberration correction function is achieved by generating a phase difference that reduces aberration by concentric electrodes centered on the optical axis formed in the periphery of the region determined by the numerical aperture. Therefore, it is not necessary to incorporate another aperture limiting element, and the apparatus can be reduced in size and weight and cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a conceptual cross-sectional view showing an example of the principle configuration of an optical head device of the present invention.
FIG. 2 is a conceptual cross-sectional view illustrating an example of a structure of a liquid crystal element.
FIG. 3 is a schematic plan view showing electrodes and a power supply member pattern formed on a liquid crystal element according to the present invention for correcting aberrations of an HD / DVD optical disc.
FIG. 4 is a schematic plan view showing electrodes and power supply member patterns formed on a liquid crystal element according to the present invention for reducing aberration of a CD optical disk.
FIG. 5 is a schematic plan view showing a divided electrode pattern formed on a liquid crystal element according to the present invention for correcting spherical aberration.
FIG. 6 is a schematic plan view showing an electrode division pattern of a liquid crystal element according to the present invention for correcting coma aberration.
FIG. 7 is a schematic plan view showing electrodes and power supply member patterns formed on a liquid crystal element according to the present invention for reducing aberration of a CD optical disk.
[Explanation of symbols]
1A, 1B, 1C: Semiconductor laser 2: Beam splitter 3, 7: Combined prism 4: Collimator lens 5: Objective lens 6: Optical disc 8, 8A, 8B: Photo detectors 9, 9B, 9C: Hologram element 10: Liquid crystal Element 21, 21A, 21B: Glass substrate 22: Sealing material 23: Liquid crystal 24, 24A, 24B: Electrode 25: Insulating film 26: Alignment film 28: Liquid crystal molecules 30-32: Power supply members 40, 50-53: Transparent electrode 60 : Lead wire 101: Actuator

Claims (3)

A light source, an objective lens for condensing the light emitted from the light source on the optical recording medium, a photodetector for receiving the emitted light collected and reflected by the optical recording medium, and between the light source and the optical recording medium A liquid crystal element disposed in the optical path of the optical head device, wherein the liquid crystal element includes a liquid crystal sandwiched between two transparent substrates, and uses one of the transparent substrates. A concentric electrode centered on the optical axis is formed in the periphery of the surface determined by the numerical aperture for the emitted light with the maximum wavelength on the surface of the surface to correct the wavefront aberration of the emitted light with the maximum wavelength. An optical head device. The emitted light used in the optical head device is light of three different wavelengths λ ₁ , λ ₂ , λ ₃ (λ ₁ <λ ₂ <λ ₃ ), and on the surface of the one transparent substrate of the liquid crystal element, An electrode for correcting wavefront aberration is further formed in the region determined by the numerical aperture, and the wavefront aberration of the emitted light having the wavelengths λ ₁ and λ ₂ is corrected on the surface of the other transparent substrate. The optical head device according to claim 1, wherein the electrode is formed. The optical head device according to claim 1, wherein the liquid crystal element is integrated with a phase plate.

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