JP2002319172A - Optical head device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical head device wherein light condensing characteristics on an optical recording medium and an optical detector are enhanced. SOLUTION: A first liquid crystal layer 100 interposed between transparent substrates having electrodes formed on the surfaces thereof and changing the wave front of the outgoing light from a light source 1 to the optical recording medium 8 and a second liquid crystal layer 101 interposed between transparent substrates having electrodes formed on the surfaces thereof and changing the wave front of reflection light reflected on the optical recording medium 8 and going from the optical recording medium 8 to the optical detector 9 are disposed on the optical recording medium 8 side or the light source 1 side to a quarter wave plate 5 provided in the optical head device in the optical path, while respective liquid crystal molecules of the liquid crystal layers are made to be aligned in the directions orthogonal to each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device, and more particularly to an optical head device having a liquid crystal layer sandwiched between a transparent substrate having electrodes formed on the surface thereof.

[0002]

2. Description of the Related Art A DVD, which is an optical disk, stores digital information at a higher density than a CD, which is also an optical disk.
The wavelength of the light source is set to 650 nm or 635 nm shorter than 780 nm of CD, or the numerical aperture (NA) of the objective lens.
Is set to 0.6 which is larger than 0.45 of the CD to reduce the spot diameter condensed on the optical disk surface.

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 about 400 nm and the NA to 0.6 or more.
However, due to the shorter wavelength of the light source and the higher NA of the objective lens, the allowable amount of tilt of the optical disk surface inclined from a right angle to the optical axis and the allowable amount of uneven thickness of the optical disk are reduced.

[0004] The reason why these allowances are small is that coma aberration occurs when the optical disk is tilted, and spherical aberration occurs when the thickness of the optical disk is uneven. This is due to the fact that signal reading becomes difficult due to deterioration. In high-density recording, several methods have been proposed to increase the tolerance of the optical head device for tilt and thickness unevenness of the optical disk.

As one method, a tilting axis is added to an actuator of an objective lens which normally moves in two axial directions, that is, a tangential direction and a radial direction of an optical disk, so as to tilt the objective lens according to the detected tilt angle. There is a method to do. However, this additional method has problems that spherical aberration cannot be corrected and the structure of the actuator becomes complicated.

As another system, there is a system in which a wavefront aberration is corrected by a phase correction element provided between an objective lens and a light source. In this correction method, the allowable amount of tilt of the optical disk and the allowable amount of unevenness in thickness can be increased only by incorporating an element into the optical head device without making significant modifications to the actuator.

For example, Japanese Patent Laid-Open No. 10-20 discloses a correction method for correcting the tilt of an optical disk using a phase correction element.
263. This is because a voltage is applied to a divided electrode formed by dividing an electrode on each of a pair of substrates sandwiching a birefringent material such as a liquid crystal which constitutes a phase correction element, and a birefringent material is formed. 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 generated by the tilt of the optical disk is corrected by the change in the wavefront of the transmitted light generated by the change in the refractive index.

[0008]

However, in a conventional phase correction element using a liquid crystal, the polarization direction acts only on linearly polarized light having a specific direction. However, in order to increase the light use efficiency, in a polarization type optical head device in which the polarization direction of the light emitted from the light source and the polarization direction of the reflected light traveling from the optical disk toward the photodetector by reflection are different, the phase correction element is not provided. There has been a problem that it only affects either the emitted light or the reflected light.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has a light source, an objective lens for condensing light emitted from the light source on an optical recording medium, and A photodetector that receives the emitted light that is collected and reflected from the optical recording medium;
In an optical head device including a four-wavelength plate, a two-wavelength plate sandwiched between transparent substrates with electrodes for changing the wavefront of emitted light is provided.
One liquid crystal layer is disposed in the optical path on the light source side with respect to the quarter wavelength plate or on the optical recording medium side with respect to the quarter wavelength plate, and the voltage of the liquid crystal molecules constituting the two liquid crystal layers is not applied. Provided is an optical head device, wherein respective orientation directions at the time of application are orthogonal.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a light source, an objective lens for condensing light emitted from the light source on an optical recording medium,
An optical head device includes a photodetector that receives emitted light that is collected and reflected from an optical recording medium, and a quarter-wave plate in an optical path between a light source and an objective lens. Further, in the optical head device of the present invention, the wavefront of the emitted light is changed.
Two liquid crystal layers sandwiched between the electrode-attached transparent substrates are arranged in an optical path on the light source side with respect to the quarter wavelength plate or on the optical recording medium side with respect to the quarter wavelength plate. That is, two liquid crystal layers sandwiched between transparent substrates are arranged in the light path on the light source side with respect to the quarter-wave plate. Alternatively, two liquid crystal layers sandwiched between transparent substrates are arranged in the optical path on the optical recording medium side with respect to the quarter-wave plate. The liquid crystal molecules constituting each liquid crystal layer are arranged in a fixed direction when no voltage is applied, and the orientation of the liquid crystal molecules is orthogonal to each other. However, the alignment direction of the liquid crystal molecules may deviate from the orthogonal state (90 degrees) as long as the effects of the present invention can be realized, and may be a deviation of about ± 10 degrees.

According to this structure, the two liquid crystal layers act on the outgoing light from the light source toward the optical recording medium to change the wavefront, thereby improving the light condensing characteristics on the optical recording medium. It also acts on the outgoing light reflected from the optical recording medium and traveling from the optical recording medium to the photodetector, changing the wavefront and improving the light condensing characteristics on the photodetector, and improving the light use efficiency. it can.

The two liquid crystal layers are arranged in an optical path on the light source side with respect to the quarter wavelength plate, and can change the wavefront with respect to the outgoing light from the light source toward the optical recording medium. Outgoing light reflected from the optical recording medium toward the photodetector (hereinafter referred to as reflected light)
And a second liquid crystal layer capable of changing the wavefront. In this case, it is preferable that the polarization direction of the linearly polarized light incident on each liquid crystal layer coincides with the alignment direction of the liquid crystal molecules, but both directions may form an angle of about ± 10 degrees. With this configuration, there is no restriction on the thickness of the two liquid crystal layers, and the degree of freedom in design is increased, which is preferable.

FIG. 1 shows an example of an optical head device according to the present invention. First liquid crystal layer 100 for changing the wavefront of light emitted from semiconductor laser 1 as a light source, and second liquid crystal layer 1 for changing the wavefront of light reflected from optical disk 8 as an optical recording medium.
01 was arranged. The two liquid crystal layers 100 and 101 are each sandwiched between transparent substrates having electrodes formed on the surface so that a voltage can be applied to the liquid crystal.

The outgoing light, which is linearly polarized light from the semiconductor laser 1, becomes parallel light by the collimator lens 30, and after passing through the beam splitter 2 and the liquid crystal layers 100 and 101, becomes 1/4.
The light passes through the wave plate 5 to become circularly polarized light, and is condensed on the optical disk 8 by the objective lens 6 installed on the actuator 7. When transmitting through the liquid crystal layer 100, the wavefront of the emitted light changes.

The circularly polarized outgoing light reflected by the optical disk 8 becomes reflected light, and the reflected light passes through the objective lens 6 and the quarter-wave plate 5 again, and the direction of polarization is substantially orthogonal to the outgoing light from the light source. It becomes linearly polarized light. When transmitted through the liquid crystal layer 101, the wavefront of the reflected light changes, and the beam splitter 2
And is condensed on the photodetector through the condenser lens 31.

As shown in FIG. 7, for example, as shown in FIG. 7, the liquid crystal layer which changes the wavefront of light is made of transparent substrates 21a and 21b on which electrodes 24a and 24b are formed and liquid crystal molecules 28 are oriented parallel to the paper surface.
And the periphery thereof is sealed by the sealing material 22. Here, 25 is an insulating film, and 26 is an alignment film. When the alignment direction of the liquid crystal molecules 28 matches the polarization direction of the incident light, the electrode 2
By applying a voltage using 4a and 24b, the substantial refractive index of the liquid crystal layer changes, and the wavefront of the transmitted light can be changed without substantially changing the polarization state of the light.

Here, the polarization direction and the wavefront of the light having a polarization direction substantially orthogonal to the alignment direction of the liquid crystal molecules in the liquid crystal layer are not substantially changed. That is, the second liquid crystal layer 101 having an alignment direction substantially orthogonal to the polarization direction of the light emitted from the semiconductor laser does not affect the wavefront of the emitted light, and has an alignment substantially orthogonal to the polarization direction of the light reflected from the optical disk. The first liquid crystal layer 100 having a direction does not affect the wavefront of the reflected light.

Here, the first liquid crystal layer 100 and the second
For example, concentrically divided electrodes as shown in FIG. 8 for correcting the thickness deviation of the optical disk substrate and the spherical aberration generated by the reproduction of the multilayer optical disk, or the inclination of the optical disk ( The electrodes (51 to 55) divided as shown in FIG. 9 may be provided for correcting the coma generated by the tilt. Further, these electrodes may be combined.

Further, for example, an electrode shown in FIG. 10 for generating a continuously changing voltage distribution may be formed on a transparent substrate. As shown in FIG. 10, a thin transparent electrode 80 is first formed over the entire surface of the transparent substrate. A plurality of power supply members 81, 82, and 83 are provided on the transparent electrode 80 as a voltage application electrode having a shape capable of coping with the respective aberrations that occur next. Then, an appropriate voltage having a desired voltage distribution for coping with the above-mentioned spherical aberration is applied as a signal 1, a signal 2 and a signal 3 to the respective power supply members through the lead-out wiring 84, thereby providing a continuous voltage. Generate a distribution.

That is, a power supply member having a shape in which a plurality of power supply members are adjusted to the shape of the aberration is provided on the electrode so as to correct the generated aberration. Then, for example, it is assumed that the power supply member shown in FIG. 10 is formed on one substrate, and a uniform thin-film electrode is provided on the other opposing substrate surface. Power supply member 81
And a voltage V81 between the power supply member 82 and the thin film electrode of the other substrate.
2 is applied. It is assumed that the voltage V81 is different from the voltage V82.

Here, the resistance values of the power supply members 81 to 83 are made smaller than the resistance value of the electrode 80. That is, when a voltage is applied to the power supply members, the power supply members have the same potential, and the respective resistance values are selected such that a potential difference (voltage distribution) occurs on the electrode surface between the power supply members.

By generating this continuous voltage distribution, the refractive index distribution of the liquid crystal layer can be made continuous, and the wavefront change of the transmitted light from the liquid crystal layer can be made continuous. This wavefront change is preferably a continuous wavefront change closer to the actually generated aberration than the discrete wavefront change obtained from the concentric divided electrodes shown in FIG. In particular, in the case of correcting spherical aberration, since the amount of change in aberration in a peripheral portion far from the optical axis is large, a power supply member is formed as compared with a method in which the electrodes are divided to generate a discrete wavefront change. It is more preferable that a continuous wavefront change be made, which can cope with a change in aberration. Furthermore, a pattern for generating such a continuous wavefront change and a discrete wavefront change by the split electrode may be combined, or a voltage application distribution to the liquid crystal layer may be combined so as to correct a plurality of aberrations. .

As described above, the aberration of the light emitted from the semiconductor laser toward the optical disk is corrected by the first liquid crystal layer 100, so that good light focusing characteristics can be obtained on the optical disk. Further, in the conventional method using only one liquid crystal layer, this liquid crystal layer does not have an aberration correcting function for reflected light from an optical disk. However, by adding the second liquid crystal layer and using this liquid crystal layer as in the present invention, the aberration of the light reflected from the optical disk can also be corrected. Further, good light-collecting characteristics can be exhibited on the photodetector, and deterioration of focus servo and tracking servo characteristics can be prevented.

In the optical head device of the present invention shown in FIG. 1, two liquid crystal layers are laminated (described in detail later with reference to FIGS. 2 and 3). Further, the number of components can be reduced by further laminating the quarter-wave plate 5 on the two liquid crystal layers. Hereinafter, since the liquid crystal layer has a function of correcting the aberration by changing the wavefront of the transmitted light, the two liquid crystal layers sandwiching the liquid crystal layer between two transparent substrates and laminating them are also referred to as a liquid crystal aberration correction element.

By mounting the liquid crystal aberration correcting element on the actuator holding the objective lens, if the objective lens and the liquid crystal aberration correcting element move together during tracking, the positional deviation between the optical axis of the objective lens and the liquid crystal aberration correcting element will increase. Does not occur, and the aberration correction performance is not deteriorated.

In another example of the optical head device of the present invention shown in FIG. 4, the first liquid crystal layer 100 of the two liquid crystal layers is held (mounted) on the actuator 7 together with the quarter-wave plate 5, and The second liquid crystal layer 101 is not held (mounted) on the actuator 7. The liquid crystal layer 100 mainly generates a wavefront change of the light emitted from the semiconductor laser 1, and the liquid crystal layer 10
In FIG. 4, elements denoted by the same reference numerals as those in FIG. 1 mean the same as those in FIG. Causes a wavefront change.

Since the liquid crystal layer 100 is mounted on the actuator, no displacement occurs with respect to the objective lens 6 and the weight can be further reduced and the power consumption can be suppressed. The liquid crystal layer 101 that generates the wavefront change of the reflected light is
Since the aberration correction function required as compared with the liquid crystal layer 100 may be lower, it can function sufficiently even if it is separately provided from the objective lens.

The liquid crystal layer 101 may be provided in both the optical path of the emitted light and the reflected light as shown in FIG. 4, or the light after the reflected light from the optical disc is split by the beam splitter 2. It may be before the detector. As another example of the optical head device of the present invention, as shown in FIG. 6, an objective lens is provided without mounting a liquid crystal aberration correction element in which a liquid crystal layer 100 and a liquid crystal layer 101 sandwiched between transparent substrates are stacked on an actuator 7. 6 and the beam splitter 2. In FIG. 6, the elements having the same reference numerals as those in FIG. 1 mean the same as those in FIG.

In the example of the optical head device of the present invention shown in FIGS. 1, 4 and 6, the two liquid crystal layers are arranged in the optical path on the light source side with respect to the quarter wavelength plate. Both the light emitted from the semiconductor laser and the light reflected from the optical disk are linearly polarized when they pass through the liquid crystal layer.

On the other hand, in the example of the optical head device of the present invention shown in FIG. 5, two liquid crystal layers are arranged in the optical path on the optical disk side with respect to the quarter wavelength plate. The outgoing light, which is linearly polarized light from the semiconductor laser 1, passes through the quarter-wave plate 5 and becomes substantially circularly polarized light, and passes through a liquid crystal aberration correction element (two liquid crystal layers 100 and 101 are laminated). At this time, the liquid crystal aberration correcting elements are stacked so that the alignment directions of the liquid crystal molecules of the respective liquid crystal layers are orthogonal to each other. The layers can change their respective wavefronts.

Also, the wavefront can be similarly changed with respect to the circularly polarized reflected light from the optical disk 8. Moreover, the combination of the two liquid crystal layers and the quarter-wave plate 5 allows the reflected light from the optical disk 8 to pass through the quarter-wave plate 5 and then be polarized orthogonal to the polarization direction of the light emitted from the semiconductor laser 1. The direction can be obtained, and the reflected light can be guided to the photodetector 9 with high efficiency by the polarization beam splitter 2. In FIG. 5, elements having the same reference numerals as those in FIG. 1 mean the same elements as those in FIG. In the example of the optical head device shown in FIG. 5, the liquid crystal aberration correcting element (two liquid crystal layers) and the quarter-wave plate are separated, but these may be integrated and mounted on the actuator, or mounted on the actuator. There is no significant difference in optical functions.

As a method of producing a liquid crystal aberration correction element,
Glass substrate 2 on which electrode 24j is formed as shown in FIG.
After sealing the periphery of the glass substrate 21d on which the electrode 1c and the electrode 24c (and the electrode 24d) are formed with the sealing material 22, a liquid crystal layer 23a is formed by injecting a liquid crystal between the two glass substrates. Similarly, after sealing the periphery of the glass substrate 21d and the glass substrate 21e on which the electrode 24k is formed with the sealing material 22, the liquid crystal layer 23b may be formed by injecting liquid crystal between the two glass substrates.

As another method of producing a liquid crystal aberration correcting element, as shown in FIG. 3, a peripheral portion of a glass substrate 21g on which an electrode 24h is formed and a glass substrate 21h on which an electrode 24e is formed are sealed. After sealing with the material 22, the liquid crystal layer 2 is formed by injecting liquid crystal between both glass substrates.
3c is formed. Similarly, the periphery of the glass substrate 21j on which the electrode 24f is formed and the electrode 24g is formed and the periphery of the glass substrate 21k is sealed with the sealing material 22, and then a liquid crystal is injected between the two glass substrates to form a liquid crystal layer 23d. May be. 2 and 3, reference numeral 5 denotes a 波長 wavelength plate, and reference numerals 21f and 21m denote glass substrates. 2 and 3, a glass substrate is used as the transparent substrate.

The liquid crystal material used is, for example, a nematic liquid crystal used for a display purpose. In addition, as a material of the transparent substrate to be used, glass, polycarbonate resin, acrylic resin, epoxy resin,
A substrate such as a vinyl chloride resin can be used, but a glass substrate is preferable in terms of durability and the like.

As the quarter wavelength plate, a 3/4 wavelength plate,
It may have a phase difference of an odd multiple of a quarter wavelength such as a 5/4 wavelength plate. As the material of the wave plate, a birefringent optical single crystal such as quartz or lithium niobate may be used, or an organic thin film such as a polymer liquid crystal or polycarbonate may be used.

The voltage is controlled by a correction element control circuit, which is control voltage generation means for the electrodes of the liquid crystal aberration correction element (or liquid crystal layer), so that the intensity of, for example, a reproduction signal of the optical disk obtained by the photodetector is optimized. Is output. The voltage output from the correction element control circuit is a voltage corresponding to the thickness deviation amount and the tilt amount of the optical disc, the positional deviation between the liquid crystal aberration correction element and the objective lens, and is substantially applied to the electrodes of the liquid crystal aberration correction element. The voltage changes to

[0037]

EXAMPLE 1 The optical head device of this example is provided with a liquid crystal aberration correcting element for correcting a spherical aberration caused by a thickness deviation of an optical disk. When the thickness of the optical disc deviates from the design value, the objective lens generates spherical aberration, and the signal reading accuracy is reduced. A liquid crystal aberration correcting element for correcting the spherical aberration was incorporated as a liquid crystal aberration correcting element (a laminate of a first liquid crystal layer and a second liquid crystal layer) of the optical head device of FIG. FIG. 3 shows a conceptual diagram of this element. This liquid crystal aberration correction element has two liquid crystal layers, that is, a first liquid crystal layer 100 (23c) and a second liquid crystal layer 101 (23d).

The orientation direction of the liquid crystal molecules in the liquid crystal layer 100 is changed so as to change the wavefront of the light emitted from the semiconductor laser 1.
The light was emitted from the semiconductor laser 1 in a direction parallel to the polarization direction.
The orientation direction of the second liquid crystal layer 101 is
The reflected light from the liquid crystal layer 101 was substantially parallel to the polarization direction when entering the liquid crystal layer 101 (that is, the alignment directions of the liquid crystal molecules of the liquid crystal layer 100 and the liquid crystal molecules of the liquid crystal layer 101 were orthogonal). Here, the quarter-wave plate 5 was laminated below the objective lens 6 so that the polarization direction of the reflected light from the optical disk 8 was rotated by 90 degrees.

In this embodiment, two glass substrates as transparent substrates sandwiching two liquid crystal layers are divided from concentric ITO films as shown in FIG. 8 so as to give the same voltage distribution to the liquid crystal layers. A transparent electrode having the same shape was formed. An appropriate voltage was applied to each of the divided transparent electrodes so as to correct spherical aberration due to thickness deviation of the optical disk.

The NA of the objective lens is 0.85, the thickness of the cover layer up to the reflection surface of the optical disk is about 0.10 mm,
The reproduction characteristics of three types of optical disks of 0.11 mm and 0.12 mm were examined. The optical head device used was adjusted so that spherical aberration was minimized when the cover layer of the optical disk had a thickness of 0.10 mm. With this optical disk (cover layer thickness 0.10 mm), good reproduction characteristics were obtained without applying a voltage to the two liquid crystal layers.

On the other hand, when an optical disk having a cover layer of 0.11 mm was used, the reproduction characteristics deteriorated due to the influence of spherical aberration. The voltage distribution applied to the liquid crystal layer 100 is adjusted,
By generating a spherical aberration having a sign opposite to that of the spherical aberration caused by the thickness deviation of the cover layer, the light on the optical disc exhibited good light-collecting characteristics, and the reproduction characteristics were improved. At this time, the liquid crystal layer 101 had a reproduction characteristic that could be used practically without applying a voltage.

On the other hand, the thickness of the cover layer was 0.12 m.
When it was set to m, the light-collecting characteristics on the optical disk were improved by adjusting the distribution of the voltage applied to the liquid crystal layer 100.
However, simply applying a voltage only to the liquid crystal layer 100 results in
Since the aberration cannot be corrected for the reflected light from the optical disk, an offset occurs in the focus error signal for performing the focus servo. Then, the S-shaped curve of the focus servo signal was distorted, and it was difficult to sufficiently execute the focus servo, and the reproduction characteristics deteriorated. Therefore, by applying the same voltage distribution to the liquid crystal layer 101 as that of the liquid crystal layer 100, the spherical aberration of the reflected light from the optical disk is also improved, and the offset of the focus error signal and the distortion of the S-shaped curve are eliminated, which is favorable. Reproduction characteristics were obtained.

Example 2 The optical head device of this example has a configuration as shown in FIG. 2 in the optical head device of this example
First liquid crystal layer 1 capable of changing a wavefront with respect to linearly polarized light emitted from a semiconductor laser in one liquid crystal layer 1
00 and a quarter-wave plate 5 are stacked and mounted on an actuator 7 fixing an objective lens 6 as shown in FIG.
Further, the second liquid crystal layer 101 capable of changing the wavefront of the reflected light from the optical disk 8 was used without being mounted on the actuator. The alignment directions of the liquid crystal molecules of the liquid crystal layer 100 and the liquid crystal layer 101 are orthogonal to each other. These two liquid crystal layers 1
Samples 00 and 101 were sandwiched between glass substrates on which electrodes having the same shape as in Example 1 were formed. Here, as a result of performing a reproduction test using the same optical disk as in Example 1, reproduction characteristics almost equivalent to those in Example 1 were obtained. Further, the liquid crystal layer 100 mounted on the actuator 7 can be reduced in weight to about 60% as compared with the liquid crystal aberration correction element of Example 1, and the load on the actuator 7 is reduced, which is effective in increasing the speed and reducing power consumption. Was.

Example 3 The optical head device of this example has a configuration as shown in FIG. In this example, the two liquid crystal layers are divided by 1 /
It was arranged on the optical recording medium side with respect to the four-wavelength plate 5. Output light of linearly polarized light from the semiconductor laser 1 passes through the quarter-wave plate 5 and becomes circularly polarized light, and then the first liquid crystal layer 100 and the second liquid crystal layer 101 having liquid crystal molecules oriented in mutually orthogonal directions. And is condensed on the optical disk 8 by the objective lens 6. The light condensed and reflected by the optical disk 8 again passes through the liquid crystal aberration correction element, passes through the quarter-wave plate 5, becomes a polarization orthogonal to the polarization direction of the emitted light, and is reflected by the beam splitter 2 and collected. The light passed through the optical lens 31 and was guided to the photodetector 9.

The two substantially equal retardation values R _d of the liquid crystal layer, by passing through the two liquid crystal layers with alignment direction of liquid crystal molecules are orthogonal to each other, can the polarization state of light passing through the element unchanged Was. R _d of these two liquid crystal layers
Although the voltage applied to each liquid crystal layer may be adjusted in order to make the same, it is preferable to use a liquid crystal layer of the same type of liquid crystal and the same thickness so that the polarization state can be maintained,
The liquid crystal layers had the same thickness. Thus it was performed the regeneration test equivalent optical disk and the examples 1 and 2 using the liquid crystal aberration correcting element having uniform R _d.

When transmitted through the two liquid crystal layers, only the polarization component of light parallel to the alignment direction of the liquid crystal molecules of each liquid crystal layer can change the wavefront. When light is incident, the same voltage was applied to each of the two liquid crystal layers, whereby the wavefront of light could be changed, and good reproduction characteristics were obtained.

As described above, in this example, the actuator equipped with the objective lens is equipped with the liquid crystal aberration correcting element having two liquid crystal layers, and the quarter wavelength plate is not mounted on the actuator. The weight of the element was reduced to 80% as compared with the case of Example 1 and the weight was reduced. In some cases, it may not be necessary to mount it on the actuator.

[0048]

As described above, in the optical head device of the present invention, the two liquid crystal layers are stacked so that the alignment directions of the liquid crystal molecules are orthogonal to each other. By changing the wavefront of the outgoing light toward the optical recording medium and improving the light condensing characteristics on the optical recording medium, the liquid crystal layer changes the wavefront of the reflected light from the optical recording medium toward the photodetector. As a result, it is possible to improve the light collecting characteristics of the light on the photodetector, and to improve the light use efficiency.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional view showing an example of an optical head device in which two liquid crystal layers in the present invention are on the light source side with respect to a quarter-wave plate.

FIG. 2 is a cross-sectional view illustrating an example of a liquid crystal aberration correction element according to the present invention.

FIG. 3 is a cross-sectional view showing another example of the liquid crystal aberration correction element according to the present invention.

FIG. 4 is a conceptual cross-sectional view showing another example of the optical head device in which two liquid crystal layers in the present invention are on the light source side with respect to the quarter wavelength plate.

FIG. 5 is a conceptual cross-sectional view showing an example of an optical head device in which two liquid crystal layers in the present invention are on the optical recording medium side with respect to a quarter wavelength plate.

FIG. 6 is a conceptual cross-sectional view showing another example of the optical head device in which two liquid crystal layers in the present invention are on the light source side with respect to the quarter wavelength plate.

FIG. 7 is a conceptual cross-sectional view illustrating an example of a configuration of a liquid crystal layer.

FIG. 8 is a schematic plan view showing a divided electrode shape of a liquid crystal layer in the present invention for correcting spherical aberration.

FIG. 9 is a schematic plan view showing a shape of a divided electrode of a liquid crystal layer in the present invention for correcting coma aberration.

FIG. 10 is a schematic plan view showing the shape of a transparent electrode and a power supply member of a liquid crystal layer in the present invention for correcting spherical aberration.

[Explanation of symbols]

 1: Semiconductor laser 2: Beam splitter 30: Collimating lens 5: 1/4 wavelength plate 6: Objective lens 7: Actuator 8: Optical disk 9: Photodetector 100, 101: Liquid crystal layer 21a, 21b: Glass substrate 22: Sealing material 23: Liquid crystal layer 24a, 24b: Electrode 25: Insulating film 26: Alignment film 28: Liquid crystal molecule 80: Transparent electrode 81-83: Power supply member 84: Lead wiring

Claims (4)

[Claims] A light source, an objective lens for condensing light emitted from the light source on an optical recording medium, a photodetector for receiving condensed light emitted from the optical recording medium, and a light source. In an optical head device including a quarter-wave plate in an optical path between the objective lens and the objective lens, the optical head device changes a wavefront of emitted light.
Two liquid crystal layers sandwiched between transparent substrates with electrodes are disposed in an optical path on the light source side with respect to the 波長 wavelength plate or on the optical recording medium side with respect to the 波長 wavelength plate. An optical head device, wherein the orientation directions of liquid crystal molecules constituting a layer when voltage is not applied are orthogonal to each other. 2. The liquid crystal device according to claim 1, wherein the two liquid crystal layers are arranged in an optical path on a light source side with respect to a quarter wavelength plate, and change a wavefront with respect to light emitted from the light source toward the optical recording medium. 2. The optical head device according to claim 1, comprising: a first liquid crystal layer that can be formed; and a second liquid crystal layer that can change a wavefront with respect to light emitted from the optical recording medium toward the photodetector. 3. The optical head device according to claim 2, wherein the first liquid crystal layer is held by an actuator holding the objective lens, and the second liquid crystal layer is not held by the actuator. 4. The optical head device according to claim 1, wherein the two liquid crystal layers are arranged in an optical path on the optical recording medium side with respect to the quarter wavelength plate.