JP3885251B2 - Optical anisotropic diffraction grating, driving method thereof, and optical head device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical anisotropic diffraction grating, a driving method thereof, and an optical recording medium such as a CD (compact disk), a CD-ROM, a video disk, a DVD (digital video disk), and a magneto-optical disk. The present invention relates to an optical head device for writing optical information and reading optical information.
[0002]
[Prior 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, signal light reflected from the recording surface of the optical recording medium is guided to a photodetector. It is known to use an optical anisotropic diffraction grating using liquid crystal as an optical component for (beam splitting).
[0003]
A typical example of the optical anisotropic diffraction grating is one in which liquid crystal is sandwiched between a first substrate having a grating-like uneven portion on the inner surface and a flat second substrate. This optically anisotropic diffraction grating exhibits anisotropy in which light is simply transmitted or diffracted depending on the polarization direction of incident light. Using this, and straight ahead when the light emitted from the light source toward the optical recording medium, when that return either et optical recording medium is diffracted, as possible out to reach the photodetector.
[0004]
[Problems to be solved by the invention]
Since the optical head device using such an optical anisotropic diffraction grating exhibits the above anisotropy, a highly efficient optical head device can be configured without using an expensive beam splitter, etc. Also suitable for.
[0005]
In recent years, new optical recording media such as DVDs have appeared, and it has been desired that CDs and DVDs can be used together in a single device. For this reason, there is a demand for an optical head device to read both optical recording media with one optical head device or to read two surfaces of a DVD.
[0006]
To solve this, or moves the optical head device itself and the condenser lens, it has been proposed to change the focal position. However, if rise to such mechanical movement is reduced reading speed is time consuming, reliability was a problem you decrease because of the adjustment of its position is movable unit becomes complicated.
[0007]
[Means for Solving the Problems]
The present invention has been made to solve such a problem, and is an optically anisotropic film in which a liquid crystal is sandwiched between a first substrate having a grid-like uneven portion on its inner surface and a second substrate. The optically anisotropic diffraction grating is characterized in that a striped electrode group is provided on the inner surface of a second substrate except for its central portion.
[0008]
In addition, a nematic liquid crystal having positive dielectric anisotropy is used as the liquid crystal, and the liquid crystal molecules are aligned along the longitudinal direction of the lattice-shaped uneven portions on the first substrate and the second substrate, stripe electrodes of the second substrate provides an upper SL optically anisotropic diffraction grating that is so that its longitudinal direction coincides with the longitudinal direction of the lattice-shaped uneven portion of the first substrate.
[0009]
In addition, using these optical anisotropic diffraction gratings, a voltage that causes a potential difference between adjacent electrodes is applied to the electrodes of the second substrate so that the alignment state of the liquid crystal molecules changes, thereby providing by the driving method of the optical anisotropic diffraction grating so that the aperture diameter is changed.
[0010]
Further, light that irradiates light from the light source onto the optical recording medium and passes the return light from the optical recording medium through a phase difference element and an optical anisotropic diffraction grating, thereby diffracting the light and detecting it with a photodetector. in the head apparatus, the optical anisotropy diffraction grating to provide an optical head device Ru Ah in the optically anisotropic grating.
[0011]
Furthermore, a voltage that causes a potential difference between adjacent electrodes is applied to the electrode of the second substrate of the optical anisotropic diffraction grating so that the alignment state of the liquid crystal molecules is changed, whereby the aperture diameter is changed. There is provided an optical head device adapted to change.
[0012]
By having such a configuration, the optical head device of the present invention can electrically change its aperture ratio by the optical anisotropic diffraction grating itself, and can focus on different optical recording media or different positions. .
[0013]
Since this action is performed by the optical anisotropic diffraction grating itself, separate aperture ratio changing means and a variable focus mechanism are not required, and the optical head device can be miniaturized and adjusted easily. Furthermore, since the aperture ratio can be electrically switched, switching is extremely fast and the reading speed is hardly adversely affected.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
The optically anisotropic diffraction grating according to the present invention has a liquid crystal sandwiched between a first substrate having a grating-like uneven portion formed on the surface of a transparent substrate and a second substrate, and an inner surface of the second substrate. A striped electrode group is provided except for the central portion.
[0015]
FIG. 1 is a plan view showing the state of the electrodes of the second substrate of the optically anisotropic diffraction grating of the present invention. FIG. 2 is a cross-sectional view of the optically anisotropic diffraction grating of the present invention. 1 and 2, 1 is a second substrate, 2A, 2B, 2C, 2D, 2E, 2F, and 2G are striped electrodes, and 3 is a sealing material that joins the first substrate and the second substrate. 4 is a central portion where no electrode is provided, 5 is a first substrate having a grid-like uneven portion, 6 is a concave portion, 7 is a convex portion, and 8 is between the first substrate and the second substrate. The sandwiched liquid crystal is shown.
[0016]
In the present invention, the optically anisotropic diffraction grating constitutes the diffraction grating by the difference in refractive index between the convex portion of the substrate and the liquid crystal. Since the liquid crystal has a refractive index anisotropy, the liquid crystal can be aligned in a specific direction by performing an alignment treatment on the substrate surface. Using this, the polarized light incident on the optical anisotropic diffraction grating, kill Ride or did let to diffraction.
[0017]
As the substrate of the present invention, a transparent substrate such as glass or plastic can be used, and a transparent substrate having a refractive index of about 1.4 or more and 1.6 or less, such as glass or polyolefin, is used. Since it is easy to match 1.5, it is preferable.
[0018]
In order to form the concavo-convex portion on the first substrate, the substrate itself may be processed into such a shape by etching or mechanical cutting, and a transparent film having a refractive index substantially equal to the refractive index of any of the liquid crystals May be laminated on the surface of the transparent substrate. At the time of forming the transparent film, a mask may be provided, and the uneven portion may be formed simultaneously with the formation of the transparent film, or the transparent film may be formed on the entire surface, and the uneven portion may be formed by a photolithography process.
[0019]
What is necessary is just to set this uneven | corrugated | grooved part so that a desired diffraction characteristic may be acquired with a height of about 0.5-5 micrometers and a pitch of about 2-50 micrometers. In this case, the width of the concave portion and the width of the convex portion may be usually the same, but a difference may be given. These parameters may be determined experimentally so that desired diffraction characteristics can be obtained.
[0020]
In general, the second substrate may be a flat substrate, but an uneven portion may be formed on the second substrate as necessary.
[0021]
In the present invention, striped electrodes 2A, 2B, 2C, 2D, 2E, 2F, and 2G are formed on the second substrate. Although seven striped electrodes are shown in the figure, the necessary number may be formed depending on the aperture diameter and electrode pitch of the optical anisotropic diffraction grating. The electrode may have an electrode gap of about 4 to 30 μm with respect to the adjacent electrode, and it is only necessary that the alignment state of the liquid crystal is changed between the adjacent electrodes when a voltage is applied between the adjacent electrodes.
[0022]
The pitch of the electrodes of the second substrate and the pitch of the concavo-convex portions of the first substrate may or may not match.
[0023]
This electrode is preferably a transparent electrode such as In ₂ O ₃ —SnO ₂ (ITO) or SnO ₂ , but if the width of the electrode is narrowed, a metal electrode such as chromium or aluminum can be used.
[0024]
In the present invention, the electrode is provided only on the second substrate. For this reason, productivity is good compared with forming an electrode in both board | substrates. In particular, since the second substrate is cut at a flat substrate, it is easy to form a high-precision electrodes.
[0025]
In the present invention, no electrode is provided at the center of the striped electrode. Therefore, when a voltage is applied between the electrodes, the alignment of the liquid crystals changes in the portion where the electrodes are present, and the alignment of the liquid crystals does not change in the central portion where there is no electrode. Thereby, the function as a diffraction grating can be eliminated or reduced in the peripheral part where the electrode is provided, and only the central part can function as a diffraction grating, that is, the aperture ratio of the diffraction grating can be made electrically variable.
[0026]
The shape of the central portion where the electrode is not provided may be generally circular as shown in FIG. This is also because it is sufficient to provide the desired diffraction characteristics are obtained, it remote was elliptical or a square shape as needed.
[0027]
Further, if necessary, a thin film of polyimide, polyamide, SiO ₂ or the like may be provided on the surface of the substrate or the substrate with electrodes for the purpose of insulation, suppression of electrode appearance, and improvement of orientation. Further, the substrate itself or the surface of this thin film is rubbed, or oblique deposition is performed for orientation treatment.
[0028]
The second substrate is usually subjected to an alignment process along the direction of the stripe of the electrode. Since the first substrate has a lattice-shaped uneven portion and the liquid crystal molecules have a tendency to be aligned along the grooves, the alignment treatment may not be performed.
[0029]
As the liquid crystal used in the optically anisotropic diffraction grating of the present invention, a known liquid crystal, a liquid crystal composition, or a polymer liquid crystal used in a liquid crystal display device such as a nematic liquid crystal or a smectic liquid crystal can be preferably used. However, the use of nematic liquid crystals is preferred, and the use of nematic liquid crystals with positive dielectric anisotropy is particularly preferred.
[0030]
Further, it is preferable that the liquid crystal itself is slightly twisted by mixing an optically active substance, cholesteric liquid crystal, or the like with nematic liquid crystal. Specifically, the twist may be such that the liquid crystal is twisted by 90 ° or less in the gap between the substrates. More specifically, it is preferably 30 ° or more and less than 90 °.
[0031]
This is because when the voltage is applied to the electrodes, the alignment of the liquid crystal molecules changes, but if the liquid crystal itself is slightly twisted, in which case the direction of the change will be constant and optically stable. Because.
[0032]
A specific example will be described based on an example using a nematic liquid crystal having positive dielectric anisotropy. In this case, in a state where no voltage is applied, the liquid crystal molecules are arranged so that the longitudinal direction of the liquid crystal molecules is parallel to the longitudinal direction of the striped electrodes of the second substrate. Here, when a voltage is applied so as to generate a potential difference between adjacent electrodes, the liquid crystal molecules are arranged in a direction orthogonal to the longitudinal direction of the stripe-like electrode and parallel to the substrate surface.
[0033]
In the present invention, the voltage applied to the electrodes of the second substrate is set such that a potential difference that changes the alignment state of the liquid crystal occurs between the electrodes. Specifically, an example in the case of applying a voltage to the electrodes in FIGS. 1 and 2 will be described. First, when the aperture is used with a wide opening, the electrodes 2A to 2G are in a floating state or the same voltage is applied, and there is no potential difference between the electrodes. A potential difference that does not substantially change the aperture ratio of the liquid crystal may be applied between the electrodes in terms of circuit characteristics and the response speed of the liquid crystal.
[0034]
When it is desired to change the aperture ratio, a voltage is applied so as to generate a potential difference that changes the alignment of the liquid crystal between the adjacent electrodes of the electrodes 2A to 2G. In this case, a high voltage may be sequentially applied to the electrodes 2A, 2B, 2C, 2D, 2E, 2F, and 2G. For example, the electrode 2A may be 0V, the electrode 2B may be 5V, the electrode 2C may be 10V, the electrode 2D may be 15V, the electrode 2E may be 20V, the electrode 2F may be 25V, and the electrode 2G may be 30V.
[0035]
Note that it is preferable to apply a voltage of opposite polarity alternately to the electrodes 2A, 2B, 2C, 2D, 2E, 2F, and 2G because the driving circuit and the power source are simplified. For example, 0V may be used for the electrodes 2A, 2C, 2E, and 2G, and 5V may be set for the electrodes 2B, 2D, and 2F.
[0036]
In any of these cases, it is preferable to drive with alternating current rather than with direct current. That is, in the latter example, after setting the electrodes 2A, 2C, 2E, and 2G to 0V, and the electrodes 2B, 2D, and 2F to 5V, the electrodes 2A, 2C, 2E, and 2G have 5V, and the electrodes 2B, 2D, and 2G, It may be set to 0 V for 2F.
[0037]
When the liquid crystal molecules are arranged in a direction perpendicular to the longitudinal direction of the striped electrode, there is a problem of which one twists by 90 °. Even if the liquid crystal is oriented horizontally, it is tilted and arranged at an angle of about several degrees or less. For example, in FIG. 1, assuming that the liquid crystal molecules are arranged in the vertical direction in contact with the substrate surface on the upper side, when a voltage is applied between the adjacent electrodes, the liquid crystal molecules are arranged left and right. At this time, when the end in contact with the substrate is fixed, two types of movements are considered, that is, whether the liquid crystal molecules are twisted to the right or twisted to the left.
[0038]
If the liquid crystal itself does not have a function of twisting itself, the liquid crystal molecules are twisted in a direction that is easily twisted on the substrate surface in the vicinity of the liquid crystal molecules and other states. This results in partially different twist directions. For this reason, since two types of arrangement | sequences coexist and the interface exists, a non-uniform arrangement | sequence state will arise and diffraction efficiency will fall easily. For this reason, it is preferable that the liquid crystal itself is twisted so that the liquid crystal molecules are twisted in a specific direction so as to have a uniform alignment state.
[0039]
Among these substrates, the inner surface of the substrate on the flat side is subjected to orientation treatment. In particular, it is preferable to form an alignment film by providing an alignment film made of a polyimide film or the like and rubbing the alignment film. Since it is difficult to perform the alignment process on the substrate side provided with the uneven portion, the alignment process may be omitted.
[0040]
FIG. 3 is a schematic diagram showing a typical configuration of the optical head device of the present invention. In FIG. 3, 11 is a light source such as a semiconductor laser, 12 is an optical anisotropic diffraction grating, 13 is a phase difference element such as a quarter-wave plate, 14 is a condenser lens, 15 and 16 are optical recording media, and 17 is 1 shows a photodetector.
[0041]
The light emitted from the light source 11 has linearly polarized light, for example, P-polarized light, but the optically anisotropic diffraction grating 12 does not act as a diffraction grating and is transmitted as it is. Then, the light passes through the phase difference element 13, is condensed by the condenser lens 14 which is an aspherical lens, reflected by the recording surface of the optical recording medium 15 or 16, and again passes through the condenser lens 14 and the phase difference element 13. Then, it becomes S-polarized light and enters the optical anisotropic diffraction grating 12. Then, since the polarization direction is shifted by 90 ° from the forward path, the optical anisotropic diffraction grating 12 works as a diffraction grating, and the light is diffracted and reaches the photodetector 17.
[0042]
In the present invention, an electrode is provided on the optical anisotropic diffraction grating 12, and the arrangement of liquid crystals is changed depending on the state of voltage application to the electrode to change the aperture ratio of the optical anisotropic diffraction grating. If the aperture ratio changes, the aberration changes.
[0043]
For example, in DVD, the distance to the focal point in the disc is short (0.6 mm), so the lens is designed accordingly. In that case, when reading a CD having a long distance to the focal point in the disk (1.2 mm), the aberration of light increases. By using the optical head device of the present invention and reducing the aperture ratio by applying a voltage, the aberration of the light can be reduced by eliminating the peripheral large aberration portion.
[0044]
By placing a retardation element such as a retardation plate or retardation film functioning as a λ / 2 plate, λ / 4 plate, or the like on the optical recording medium side with respect to the optical anisotropic diffraction grating, light travels. The direction of polarization and the direction of return of light are orthogonal to each other, so that it can function as an optically anisotropic diffraction grating. Wherein the phase difference element, polycarbonate having a thickness of about several tens to several hundreds of 100 [mu] m, polyvinyl alcohol or polyarylate materials can be preferably used.
[0045]
At least one surface of the retardation element is covered with an optically transparent organic resin such as a photopolymer or a thermosetting epoxy resin, or a flat substrate such as a glass substrate or a plastic substrate is laminated through the organic resin. Adhesion is preferred because of the advantages of reducing wavefront aberration and improving reliability.
[0046]
In this diffraction element, a second diffraction grating may be formed on the surface of the substrate on the light source side, and in this case, tracking error detection by the three-beam method can be performed. The second diffraction grating is preferably formed by applying a photopolymer, a photoresist or the like and exposing it to a predetermined pattern, or by directly processing a transparent substrate by a dry etching method.
[0047]
When the optical head device of the present invention is used for reading, a light detector for detecting reflected light from the optical recording medium is usually provided on the light source side, and the reflected light is desired on the light receiving surface of the detector. An in-plane curvature may be imparted to the pattern of the optical anisotropic diffraction grating, or a distribution may be imparted to the lattice spacing so that the light beam (spot) is condensed.
[0048]
Pattern of optically anisotropic grating, curvature distribution designed by a computer system, the lattice spacing distribution, cut with the optimum pattern SSD focus error detection method such as (spot size Detection) method. As the photodetector, one using a semiconductor element such as a photodiode or a CCD element is preferable because of its small size and light weight and low power consumption.
[0049]
The semiconductor laser as the light source of the present invention, the solid-state laser such as YAG laser, can be used gas lasers such as the He-Ne, a semiconductor laser is smaller and lighter, continuous wave, preferred in terms of maintenance and inspection. Further, when a harmonic generator (SHG) in which a semiconductor laser or the like and a nonlinear optical element are incorporated in a light source unit and a short wavelength laser such as a blue laser is used, high-density optical recording and reading can be performed.
[0050]
The optical recording medium of the present invention is a medium capable of recording and / or reading information by light. For example, optical disks such as CD (compact disk), CD-ROM, video disk, DVD (digital video disk), magneto-optical disk, phase change optical disk, and the like can be used.
[0051]
By providing an antireflection film on the light incident / exit surface of the diffractive element, light loss can be prevented. In that case, it is preferable to use an amorphous fluororesin as the antireflection film because the film can be formed at a low cost without using an expensive and large film forming apparatus such as a vapor deposition apparatus.
[0052]
The basic operation of this optical head device will be described. For example, the alignment treatment is performed so that the liquid crystal is aligned in a direction substantially parallel to the longitudinal direction of the lattice-shaped uneven portions (in FIG. 3, a direction perpendicular to the paper surface). In this case, for the P wave incident from the semiconductor laser of the light source 11 (in FIG. 3, the polarization component whose polarization direction is parallel to the paper surface), the liquid crystal and the convex portion have the same refractive index, that is, the optical anisotropic diffraction grating is Transparent to P waves. Therefore, the P wave does not receive any change and enters the quarter wave plate as the phase difference element 13 as it is, changes to circularly polarized light, passes through the aspherical lens as the condensing lens, and is almost 100% light. Reaches the recording surface of the optical recording medium 15.
[0053]
That is, the return light to the semiconductor laser is very small, which is advantageous in terms of return light noise. Further, the high transmission rate of the forward path is excellent in terms of cost in that the writing type optical disk apparatus can be written with a semiconductor laser having a relatively low output during writing.
[0054]
The reflected light reflected from the recording surface of the optical recording medium 15 and returned again through the aspherical lens passes through the quarter-wave plate again and changes to S waves whose polarization directions are different by 90 °. When the S wave is incident on the optical anisotropic diffraction grating, this time, it functions as a diffraction grating because the refractive index of the liquid crystal and the convex portion is different, and is about 40% at the maximum as + 1st order diffracted light and about 40% at the maximum as -1st order diffracted light Diffraction efficiency is obtained. When the detectors for detecting the + 1st order diffracted light and the −1st order diffracted light are arranged in only one of them, the reciprocating efficiency of 40% can be obtained.
[0055]
Further, when the concave and convex portion is formed into a slope shape (sawtooth shape), a reciprocation efficiency of about 81% is obtained when it is formed in a shape of approximately 70 to 90% and three steps.
[0056]
Here, when the optical recording medium is replaced and the optical recording medium 16 is used, a voltage is applied to the electrode of the optical anisotropic diffraction grating 12 to reduce its aperture ratio, and the recording surface of the optical recording medium 16 is reduced. Can be read with less aberration.
[0057]
【Example】
A SiO _x N _y film having a thickness of 1.4 μm was formed by plasma CVD on one surface of a glass substrate having a thickness of 1 mm, 10 mm × 10 mm, and a refractive index of 1.52. At this time, x and y were about 1.8 and 0.17, respectively. Next, a first substrate on which a concavo-convex portion for a diffraction grating having a depth of 1.4 μm and a pitch of 6 μm having a rectangular shape was formed by a photolithography method and a dry etching method.
[0058]
An ITO electrode having a thickness of 20 nm was formed on the surface of another glass substrate, and this ITO electrode was patterned in a stripe shape with an electrode width of 20 μm and an electrode pitch of 60 μm, except for a central portion having a diameter of 2.5 mm. This electrode was connected at every other end to form a second substrate in the shape of a comb.
[0059]
On the second substrate, a polyimide film having a thickness of 60 nm was formed as an alignment film for liquid crystal alignment, and a rubbing treatment was performed along the longitudinal direction of the electrodes for alignment. The surface of the first substrate on which the concavo-convex portion is formed is made to face the surface on which the alignment film of the second substrate is formed, and the rubbing direction of the alignment film is the same as the stripe direction of the concavo-convex portion. In this way, two glass substrates were laminated.
[0060]
At that time, except for the liquid crystal injection port, the periphery of the two glass substrates was sealed with an epoxy resin sealing material including a spherical spacer. Liquid crystal (Merck's product name BL002, nematic liquid crystal, ordinary light refractive index 1.525, extraordinary light refractive index 1.771) was vacuum injected from the liquid crystal injection port.
[0061]
A quarter-wave plate is laminated and adhered to the surface of the second substrate opposite to the alignment film with a transparent adhesive, and a photopolymer for improving wavefront aberration and a third glass substrate are laminated and adhered thereon. Thus, a diffraction element was produced. A light-reflecting film made of a dielectric multilayer film was applied to the light incident part and light-emitting part from the light source of the diffraction element.
[0062]
When a semiconductor laser was used as the light source and a P wave having a wavelength of 678 nm (a polarization component parallel to the paper surface of FIG. 3) was incident, the transmittance of the P wave was about 83%. Also, the reflected light (circularly polarized light) from the optical disk is changed to S wave (polarized component perpendicular to the paper surface) by the quarter wavelength film, and this S wave is diffracted by the optical anisotropic diffraction grating, The diffraction efficiency was 25%, and the diffraction efficiency of -1st order diffracted light was 26%.
[0063]
As a result, the forward path efficiency was about 83% and the round-trip efficiency was about 42% (± first-order diffracted light detection). On the other hand, when an AC voltage of 5 V was applied between adjacent electrodes by switching to an optical recording medium having a different thickness, the light that passed through the central portion had almost the same efficiency. The light passing through the peripheral part provided had a diffraction efficiency of 2% for the + 1st order diffracted light of the returning S wave and 2% for the -1st order diffracted light. As a result, it was possible to obtain return light with less aberration in any of the optical recording media having different thicknesses.
[0064]
【The invention's effect】
The present invention makes it possible to read and write to different optical recording media by diffracting return light and changing its aperture ratio using an optical anisotropic diffraction grating using liquid crystal provided with specific electrodes. sell. For this reason, it is not necessary to provide a lens moving mechanism or an aperture ratio variable mechanism or a focal length variable mechanism in which a liquid crystal diaphragm or a liquid crystal lens is arranged, and the optical head device can be downsized. Moreover, since it is not necessary to provide an electrode on the substrate side provided with the concavo-convex portion, manufacturing is also easy. Furthermore, the present invention can be applied in various ways as long as the effect is not impaired.
[Brief description of the drawings]
FIG. 1 is a plan view showing an electrode state of a second substrate of an optically anisotropic diffraction grating according to the present invention.
FIG. 2 is a cross-sectional view of an optical anisotropic diffraction grating according to the present invention.
FIG. 3 is a schematic diagram showing a typical configuration of an optical head device of the present invention.
[Explanation of symbols]
1: 2nd board | substrate 2A-2G: Electrode 3: Sealing material 4: Center part 5: 1st board | substrate 6: Concave part 7: Convex part 8: Liquid crystal

Claims (5)

In an optical anisotropic diffraction grating in which a liquid crystal is sandwiched between a first substrate having a lattice-like uneven portion on the inner surface and a second substrate, the central portion is removed from the inner surface of the second substrate. An optically anisotropic diffraction grating provided with a striped electrode group. A nematic liquid crystal having a positive dielectric anisotropy is used as the liquid crystal, and the liquid crystal molecules are aligned along the longitudinal direction of the lattice-shaped irregularities on the first substrate and the second substrate, and the second substrate optically anisotropic grating of stripe electrodes whose longitudinal direction matches manner has been請 Motomeko 1 wherein the longitudinal direction of the lattice-shaped uneven portion of the first substrate. The optical anisotropic diffraction grating according to claim 1 or 2, wherein a voltage that causes a potential difference between adjacent electrodes is applied to the electrodes of the second substrate so that the alignment state of the liquid crystal molecules is changed. thereby adapted aperture diameter is changed the driving method of the optical anisotropic diffraction grating. An optical head device that irradiates light from a light source onto an optical recording medium, diffracts the light by passing the return light from the optical recording medium through a phase difference element and an optical anisotropic diffraction grating, and detects the light with a photodetector. in optically anisotropic grating Oh Ru optical head device in an optical anisotropic diffraction grating according to claim 1, wherein. A voltage that causes a potential difference between adjacent electrodes is applied to the electrodes of the second substrate of the optically anisotropic diffraction grating so that the alignment state of the liquid crystal molecules changes, thereby changing the aperture diameter. optical head device 請 Motomeko 4, wherein is in.

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