JP3947828B2 - Optical head device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head device for writing optical information on an optical disk such as a CD (compact disk), a CD-ROM, a video disk, and a magneto-optical disk, and for reading the optical information.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an optical head device that writes optical information on an optical disk, a magneto-optical disk, or the like, or reads optical information, an optical component that guides (beam splits) signal light reflected from the recording surface of the disk to a detection unit In particular, the one using a prism type beam splitter and the one using a diffraction grating or a hologram element are known.
[0003]
Conventionally, a diffraction grating or hologram element for the optical head device, a glass or plastic substrate, a rectangular grating (relief type) formed by Doraie' Jin grayed method or injection molding method having a rectangular cross-section, thereby diffraction light The beam split function was added.
[0004]
In addition, it is conceivable to use polarized light when trying to increase the light utilization efficiency as compared with an isotropic diffraction grating having a light utilization efficiency of about 10%. When using polarized light, a prism beam splitter is combined with a λ / 4 plate to increase the efficiency of reciprocation (direction from the light source to the recording surface) and return (direction from the recording surface to the detection unit) to increase the reciprocal efficiency. There was a way to raise.
[0005]
However, prismatic polarization beam splitters are expensive, and other methods have been sought. Using a plate of birefringent crystal such as LiNbO ₃ as a method, to methods et forming an anisotropic diffraction grating having polarization selectivity is known to the surface. However, the birefringent crystal itself is expensive and difficult to apply to the consumer field.
[0006]
As described above, the use efficiency of the isotropic diffraction grating is about 50% in the forward direction (direction from the light source to the recording surface), and the utilization efficiency in the return direction (direction from the recording surface to the detection unit) is about 20%. Therefore, about 10% is the limit in the round trip.
[0007]
[Problems to be solved by the invention]
It is an object of the present invention to provide an optical head device that can solve the above-described problems, increase the light utilization efficiency, and can be manufactured at low cost.
[0008]
[Means for Solving the Problems]
The present invention relates to an optical head device for writing information and / or reading information by irradiating light from a light source onto an optical recording medium through a diffraction element, wherein the diffraction element has a lattice-like shape on the surface of a transparent substrate. An uneven portion is formed, the uneven portion is made of an optically isotropic material, the uneven portion has optical anisotropy, and a difference Δn between an ordinary light refractive index and an extraordinary light refractive index is 0.05 or more and 0.35. The following liquid crystal is filled, and the refractive index of the concavo-convex portion is an optical anisotropic diffraction grating substantially equal to the ordinary light refractive index or the extraordinary light refractive index of the liquid crystal, and the refractive index of the concavo-convex portion is n, Depth is D, liquid crystal's ordinary refractive index is _ng , liquid crystal's extraordinary refractive index is n _e , | n−n _g | and | n−n _e |, whichever is larger, ΔN, when the wavelength in vacuum and _{λ 0, DΔN = λ 0/} 2 the relationship 30 By so filled at a higher temperature, the temperature characteristic in the temperature range of 0 to 60 ° C. to provide an optical head apparatus characterized by enhanced reciprocating efficiency due to diffraction so as to optimize.
Further, the diffraction element uses two transparent substrates having a lattice-like uneven portion formed on the surface thereof, faces each other where the uneven portions are formed, or the uneven portions formed on the two transparent substrates. However, it is laminated so as to be asymmetric with respect to the laminating surface, the liquid crystal is filled in the concavo-convex portion, and two transparent substrates are laminated, and the cross-sectional shape of the lattice-like concavo-convex portion Provides an optical head device that is asymmetrical.
[0009]
Further, an optical head device for reading the write and / or information of the information by irradiating on the optical recording medium through the diffraction element to the light from the light source, the diffraction element is lattice-shaped uneven portion on the surface And a liquid crystal filled in the concavo-convex portion and having an optical anisotropy and having a difference Δn between ordinary light refractive index and extraordinary light refractive index of 0.05 to 0.35. The refractive index of the concavo-convex part is n, the depth is D, the ordinary light refractive index of the liquid crystal is _ng , and the extraordinary light refractive index of the liquid crystal is n _e , | n−n. _{g |} a _| n-n e |, whichever is larger the .DELTA.N, when a wavelength in vacuum of the light from the light source and _{λ 0, DΔN = λ 0/} 2 the relationship is satisfied at a temperature above 30 ° C. by way, so the temperature characteristic is optimum in the temperature range of 0 to 60 ° C. In the method for manufacturing an optical head device characterized by enhanced reciprocating efficiency due to diffraction, the optical anisotropic diffraction grating, to cover the transparent thin film having a refractive index substantially equal to the refractive index of the transparent substrate on the transparent substrate A method of manufacturing an optical head device comprising: a step; and a step of processing the transparent thin film by a photolithography method to form a lattice-shaped uneven portion; and Provided is a method for manufacturing an optical head device in which the transparent thin film is a SiO _x film (1 <x <2).
[0010]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, if the concavo-convex portion is made of an optically isotropic material and its refractive index is substantially equal to the ordinary or extraordinary refractive index of the liquid crystal, it functions as an optically anisotropic diffraction grating utilizing the polarization of light. However, in particular, when the refractive index is almost equal to the ordinary light refractive index, the selection range of the transparent substrate material having the concavo-convex portion is widened, which is preferable because a low-cost and high-quality diffraction element can be produced. Further, when the refractive index of the concavo-convex portion is made substantially equal to the extraordinary light refractive index of the liquid crystal, a transparent substrate material having a high refractive index such as polycarbonate (refractive index 1.58) can be used effectively.
[0015]
Using two transparent substrates with a grid-like concavo-convex portion formed on the surface, the surfaces with the concavo-convex portions facing each other, filling the concavo-convex portions with the liquid crystal, and laminating the two transparent substrates An optical anisotropic diffraction grating may be formed. In that case, each concavo-convex portion may be shallow, which is preferable because it is easy to manufacture. Moreover, it is preferable also in the point which the orientation of a liquid crystal improves by the two uneven | corrugated | grooved part which faces.
[0016]
When the concavo-convex portions formed on the two transparent substrates are laminated so as to be asymmetric with respect to the laminated surface, a diffraction grating having an asymmetric cross-sectional shape can be easily produced, and any of ± first-order diffracted light One of the diffraction efficiencies is increased, and light having a higher diffraction efficiency can be detected by one detector, which is preferable.
[0017]
As the liquid crystal used in the present invention, known liquid crystals used for liquid crystal display devices such as nematic liquid crystals and smectic liquid crystals can be used.
[0018]
In the present invention, it is assumed that the difference Δn between the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal is 0.05 or more and 0.35 or less. The reason is that if it is less than 0.05, it is necessary to deepen the concavo-convex portion, which makes it difficult to produce and easily increases the cost, and if it exceeds 0.35, the liquid crystal tends to deteriorate due to ultraviolet rays or the like.
[0019]
As the transparent substrate, a glass, polyolefin, polycarbonate or the like having a refractive index of about 1.4 or more and 1.6 or less is preferable because it easily matches the ordinary refractive index of liquid crystal of about 1.5.
[0020]
The concavo-convex portion is made of an optically isotropic material, the refractive index is n, the depth of the concavo-convex portion is D, the ordinary refractive index of the liquid crystal is _ng , the extraordinary refractive index is _ne , | n−n _{g |} a _| n-n e |, whichever is larger the .DELTA.N, when a wavelength in vacuum of the light from the light source and lambda _0, so that the temperature at which DΔN = λ _0/2 is at a temperature higher than 30 ° C. To be . That, DΔN = λ _0/2 of but reciprocating efficiency is highest due to diffraction when, .DELTA.N in order to optimize the temperature characteristic in the range of 0 to 60 ° C. with the changes with temperature, over 30 ° C. a temperature is in the depth of the uneven portion such as to satisfy the above relationship.
[0022]
On the optically anisotropic diffraction grating of the transparent substrate, a second transparent substrate made of glass or plastic such as acrylic resin, polyolefin, polycarbonate or the like is laminated to sandwich a liquid crystal layer. It is preferable because it can be fixed. The liquid crystal is not only filled in the concavo-convex portion, but a thin layer of liquid crystal may be formed between the transparent substrate and the second transparent substrate in the portion overflowing from the concavo-convex portion. If the distance between the flat portion of the surface on which the concavo-convex portion of the transparent substrate is formed and the second transparent substrate is too large, the alignment force of the liquid crystal by the alignment film formed on the second transparent substrate is reduced, and is preferably 10 μm or less. 5 μm or less is more preferable.
[0023]
When a second transparent substrate is laminated on the optically anisotropic diffraction grating of the transparent substrate, and a polyimide film (alignment film) for liquid crystal alignment is formed on the liquid crystal side of the second transparent substrate, the transparent substrate Compared with the case where a polyimide film is formed on the substrate, the rubbing cloth is less damaged at the time of rubbing, which is preferable because the manufacturing cost is reduced.
[0024]
A transparent substrate having a lattice-shaped uneven portion has an alignment function similar to that of an alignment film in which the uneven portion itself is rubbed, and even if it does not provide an alignment film on the second transparent substrate, it is sufficient as a diffraction element. It was found that the characteristics of can be obtained. In that case, substantially the same characteristics as those obtained when the alignment film is provided can be obtained, and there is an advantage that the alignment film can be provided at a low cost because the alignment film need not be provided.
[0025]
Further, when the polyimide film is formed on the second transparent substrate, the rubbing direction for alignment and the stripe direction of the uneven portions (longitudinal direction of the lattice-shaped uneven portions) are made the same to align the liquid crystal. It is preferable in that the stability and reproducibility can be improved, ΔN can be increased, and a decrease in the orientation rate due to the surrounding environment such as temperature can be prevented.
[0026]
When the cross-sectional shape of the lattice-like uneven part is asymmetrical in a plane perpendicular to the longitudinal direction (stripe direction) of the uneven part, the diffraction efficiency of either the + 1st order diffracted light or the −1st order diffracted light is increased, If only the one having higher diffraction efficiency is used, it is preferable that a large round trip efficiency can be obtained with only one detector. The left-right asymmetric shape is a step shape, a slope shape (sawtooth shape) or the like.
[0027]
Also, the distribution of the uneven portions is made to have a distribution, a part of the uneven portion is left-right asymmetric and the other is left-right symmetrical, a portion of the uneven portion is a convex portion and the others are concave portions, Such a change may be made.
[0028]
When a retardation plate and retardation film functioning as a λ / 2 plate, λ / 4 plate, etc. are laminated on the optically anisotropic diffraction grating of the transparent substrate, the light forward direction (from the light source side to the optical recording medium) The direction of polarization) is orthogonal to the direction of light return (the direction from the optical recording medium side to the light source side), and can function as an optically anisotropic diffraction grating. For the retardation plate and retardation film, materials such as polycarbonate or polyvinyl alcohol having a thickness of about several tens to several hundreds of μm can be preferably used.
[0029]
At least one surface of the retardation plate or retardation film is covered with an organic resin such as a photopolymer or a thermosetting epoxy resin, or a third glass substrate, a plastic substrate or the like having good flatness through the organic resin. Adhering a transparent substrate is preferable because of the advantages of reducing wavefront aberration and improving reliability.
[0030]
By sealing the peripheral portion between the transparent substrate and the second transparent substrate, or the peripheral portion of the entire diffractive element with a sealing material such as an epoxy resin, not only leakage of liquid crystal is prevented, but also the humidity of the external environment It is preferable because undesirable physical or chemical changes such as liquid crystals and organic resins due to temperature changes can be prevented.
[0031]
A second diffraction grating that generates three beams for tracking error detection may be provided on the surface (light source side surface) opposite to the surface on which the uneven portion of the transparent substrate is provided. It is easy and preferable. The second diffraction grating is formed by applying a photopolymer, a photoresist, or the like and exposing it to a predetermined pattern, or by directly processing the second substrate by a dry etching method.
[0032]
When the optical head device of the present invention is used for reading, a 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 optical anisotropic diffraction grating pattern of the diffraction element, or a distribution may be imparted to the grating spacing so as to condense into a beam shape. The lattice pattern can be a curvature distribution and a lattice interval distribution designed by a computer, and can be an optimum pattern for a focus error detection method such as a spot size detection method. As the detector, one using a semiconductor element such as a photodiode or a CCD element is preferable because it is small and light and has low power consumption.
[0033]
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.
[0034]
If the light source, diffractive element, detector, objective lens, and the like are accommodated in the same package, it is preferable that a small-sized optical head device that can easily adjust the optical axis is provided.
[0035]
The light source of the present invention preferably uses a semiconductor element such as a semiconductor laser (LD) or LED, and is preferable because the LD is small and light, has low power consumption, and has coherence. Optical recording media include optical discs such as CDs, CD-ROMs, DVDs (digital video discs), magneto-optical discs, phase change optical discs, optical cards, and other light that writes and / or reads information with light. Recording media for the system can be used.
[0036]
Further, in the present invention, when the transparent thin film is a SiO _x film (1 <x <2), it is preferable that an uneven portion substantially matching the ordinary light refractive index of the liquid crystal can be easily produced. Moreover, you may make it form an uneven | corrugated | grooved part using 2P method (photopolymerization method) or selective photopolymerization method by using the said transparent thin film as organic resins, such as an acrylic resin.
[0037]
Specifically, the uneven portion is formed as follows. A photoresist is coated on the surface of a polished transparent substrate such as a glass substrate by a spin coat method or the like. A photomask having a predetermined pattern is brought into close contact with the photoresist film, exposed to ultraviolet rays, and subjected to a photoresist development process to form a photoresist lattice pattern on the surface of the transparent substrate. By using the photoresist lattice pattern as a mask and dry etching using a gas such as CF ₄ , a lattice-like uneven portion for an optical anisotropic diffraction grating having a depth of 1 to 2 μm and a pitch of 2 to 20 μm is formed. Form.
[0038]
Alternatively, a transparent substrate created by the above method is used as a master substrate to inject and mold acrylic resin or the like, or a mold is created based on the transparent substrate, and materials such as acrylic resin, polyolefin, polycarbonate, and polyether sulfone are used. A transparent substrate having a lattice-shaped uneven portion can be produced by an injection molding method, a 2P method, or the like.
[0039]
Here, for example, the glass substrate can be directly dry-etched, but the etching rate is slow, it is difficult to form a constant depth with good reproducibility, and it is difficult to reduce the depth distribution, etc. There's a problem.
[0040]
Therefore, a film having a refractive index close to the refractive index of a transparent substrate such as a glass substrate, such as a SiO ₂ film, is formed to a thickness such that a desired uneven portion depth can be obtained by vapor deposition or the like. By utilizing the difference in etching rate between the _two films, dry etching can be performed with good reproducibility and small surface distribution. The difference between the refractive index of the transparent substrate and the refractive index of the transparent thin film such as the SiO ₂ film is preferably within 0.1 in order to prevent undesired reflection or the like by the interface.
[0041]
The refractive index of the SiO ₂ film is usually about 1.46, and it is not easy to obtain good characteristics lower than the ordinary refractive index of liquid crystal. Also, the ordinary light refractive index of liquid crystals is usually lower than the extraordinary light refractive index. Therefore, it is possible to easily manufacture a concavo-convex portion that substantially matches the ordinary refractive index of liquid crystal by the following method.
[0042]
That is, an SiO _x film (1 <x <2) can be formed by forming a mixture of SiO having a high refractive index and SiO ₂ having a low refractive index by an evaporation method or the like. Alternatively, when the SiO film is formed by vapor deposition, the SiO _x film (1 <x <2) can be formed by gradually increasing the oxygen partial pressure of the atmospheric gas in the vapor deposition apparatus. Since this SiO _x film is an oxide of Si, for example, when CF ₄ is used as an etching gas, the dry etching rate is higher than the high volatility of CF ₄ and the etching selectivity with the glass substrate is also good. .
[0043]
Although a single diffraction element has been described above, for example, a diffraction element in which a plurality of liquid crystals are filled in a transparent substrate having a width of 120 × 120 mm can be formed and finally cut individually.
[0044]
The liquid crystal is oriented in a direction substantially parallel to the longitudinal direction of the lattice-shaped irregularities (in FIG. 1, the direction perpendicular to the paper surface), but is incident on a P wave (polarized in FIG. 1) from a light source (downward in FIG. 1). For the polarization component whose direction is parallel to the plane of the paper, the liquid crystal and the concavo-convex portion have the same refractive index, that is, the optical anisotropic diffraction grating is transparent to the P wave. Therefore, the P wave is not affected by any change and enters the λ / 4 plate as it is, changes to circularly polarized light, passes through an aspheric lens as an objective lens, and almost 100% of the light is incident on the recording surface of the optical recording medium. To reach.
[0045]
The reflected light reflected on the recording surface and returned through the aspherical lens again passes through the λ / 4 plate again and changes to an S wave whose polarization direction is different by 90 degrees. 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 is different from that of the concavo-convex portion, and is about 40% at the maximum as + 1st order light and about 40% at the maximum as -1st order light. Diffraction efficiency is obtained. When the detectors for detecting the + 1st order light and the −1st order light are arranged in only one of them, the reciprocating efficiency of 40% can be obtained.
[0046]
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.
[0047]
【Example】
[Example 1]
The configuration of Example 1 is shown in FIG. A cross section having a depth of 1.55 μm and a pitch of 9 μm is formed on one surface of a glass substrate 1 having a thickness of 1 mm, a width of 10 × 10 mm, and a refractive index of 1.54 and a relatively low alkali component by photolithography and dry etching. A rectangular lattice-shaped uneven portion 2 was formed.
[0048]
Specifically, a photoresist is coated on one surface of the glass substrate 1 whose both surfaces have been polished by spin coating. Next, a photomask having a predetermined pattern is brought into close contact with the photoresist film, exposed to ultraviolet rays, and subjected to photoresist development to form a photoresist lattice pattern on the surface of the transparent substrate. Using the photoresist lattice pattern as a mask, it was formed by dry etching using CF ₄ gas.
[0049]
A polyimide film 4 was formed as an alignment film for liquid crystal alignment on one surface of the second glass substrate 3 having relatively little alkali component, and a rubbing treatment for alignment was performed. The surface of the glass substrate 1 on which the concavo-convex portion 2 is formed faces the surface of the second glass substrate 3 on which the polyimide film 4 is formed, and the rubbing direction of the polyimide film 4 and the stripe direction of the concavo-convex portion 2 are the same. Then, two glass substrates were laminated, and the periphery of the two glass substrates was sealed with an epoxy resin 5 including a spherical spacer having a diameter of about 4 μm except for the liquid crystal injection port.
[0050]
Liquid crystal 6 (nematic liquid crystal, product name P-008 manufactured by Merck & Co., Inc., ordinary light refractive index 1.525, extraordinary light refractive index 1.771) was vacuum-injected from the liquid crystal injection port. In this case, ΔN = 0.23, a D = 1.55 (μm), λ 0 = 678 (nm), satisfy the DΔN = λ _0/2 was set to D to be 35 ° C..
[0051]
A λ / 4 film 7 is laminated and adhered to the surface of the second glass substrate 3 opposite to the polyimide film 4 with a transparent adhesive, and further a photopolymer 8 for improving wavefront aberration, a third A diffractive element 10 was produced by laminating and bonding the glass substrate 9. The light incident portion 11 and the light emitting portion 12 from the light source of the diffractive element 10 are provided with an antireflection film made of a dielectric multilayer film.
[0052]
When a semiconductor laser (provided below the diffractive element 10 in FIG. 1 but not shown) is used as a light source and a P-wave having a wavelength of 678 nm (a polarization component parallel to the paper surface) is incident, the transmittance of the P-wave Was about 97%. In addition, the reflected light (circularly polarized light) from the optical disk (provided above the diffraction element 10 in FIG. 1 but not shown) is changed to an S wave (polarized component perpendicular to the paper surface) by the λ / 4 film 7. The S wave was diffracted by the optically anisotropic diffraction grating. The diffraction efficiency of the + 1st order diffracted light was 33%, and the diffraction efficiency of the −1st order diffracted light was 33%. As a result, the forward path efficiency was about 97% and the round trip efficiency was about 64% (± first-order diffracted light detection).
[0053]
[Example 2]
It was produced in the same manner as in Example 1 except that the cross-sectional shape of the concavo-convex portion formed on the glass substrate 1 was changed to a saw shape as shown in FIG. In Example 2, the transmittance of the P wave was about 97%, the diffraction efficiency of the + 1st order diffracted light of the S wave was about 75%, and the diffraction efficiency of the −1st order diffracted light was about 2%. As a result, the forward path efficiency was about 97% and the round trip efficiency was about 73% (+ 1st order diffracted light detection).
[0054]
[Example 3]
It was produced in the same manner as in Example 1 except that the cross-sectional shape of the concavo-convex portion formed on the glass substrate 1 was changed to a three-step shape as shown in FIG. In Example 3, the transmittance of the P wave was about 97%, the diffraction efficiency of the + 1st order diffracted light of the S wave was about 70%, and the diffraction efficiency of the −1st order diffracted light was about 2%. As a result, the forward path efficiency was about 97% and the round trip efficiency was about 68% (+ 1st order diffracted light detection).
[0055]
[Example 4]
The configuration was the same as in Example 1 except that the polyimide film 4 was not formed. In this case, the liquid crystal 6 was aligned only by the alignment force of the uneven portion 2. In Example 4, the transmittance of the P wave was about 97%, the diffraction efficiency of the + 1st order diffracted light of the S wave was about 31%, and the diffraction efficiency of the −1st order diffracted light was about 30%. As a result, the forward path efficiency was about 97% and the round trip efficiency was about 59% (± first-order diffracted light detection).
[0056]
【The invention's effect】
The present invention is capable of mass production with a larger substrate area than a birefringent crystal without using an expensive material such as a birefringent crystal, and is higher than an isotropic grating such as a relief type diffraction grating. Light utilization efficiency can be obtained.
[0057]
Since the basic structure such as the pitch of the optically anisotropic diffraction grating is defined not by the liquid crystal itself but by the transparent substrate, it has excellent temperature characteristics and environmental resistance. Further, the liquid crystal can be aligned without providing a liquid crystal alignment film such as a polyimide film. As for the grating pattern of the optical anisotropic diffraction grating, a complex grating pattern can be easily formed with high productivity by the CGH (Computer Generated Hologram) method using an exposure mask or the like.
[0058]
The lambda / 4 plate or the like retardation plate, if laminated to the retardation film in the diffraction element can overall excellent compact highly productive.
[Brief description of the drawings]
FIG. 1 is a side view of a basic configuration of an optical head device using an optically anisotropic diffraction grating made of liquid crystal, showing Example 1. FIG.
2 is a side view of a transparent substrate for an optical head device of Example 2. FIG.
3 is a side view of a transparent substrate for the optical head device of Example 3. FIG.
[Explanation of symbols]
1: glass substrate 2: concavo-convex part 3: second glass substrate 4: polyimide film 5: epoxy resin 6: liquid crystal 7: λ / 4 film 8: photopolymer 9: third glass substrate 10: diffraction element 11: light Incident part 12: light emitting part

Claims (6)

In an optical head device that writes information and / or reads information by irradiating light from a light source on the optical recording medium through the diffraction element, the diffraction element has a lattice-shaped uneven portion formed on the surface of the transparent substrate. A liquid crystal in which the concavo-convex portion is made of an optically isotropic material, the concavo-convex portion has optical anisotropy, and a difference Δn between an ordinary light refractive index and an extraordinary light refractive index is 0.05 or more and 0.35 or less. In which the refractive index of the uneven portion is substantially equal to the ordinary light refractive index or the extraordinary light refractive index of the liquid crystal, and the refractive index of the uneven portion is n and the depth is D. , The normal light refractive index of the liquid crystal is _ng , the extraordinary light refractive index of the liquid crystal is n _e , | n−n _g | or | n−n _e |, whichever is larger, ΔN, and the wavelength of light from the light source in vacuum when the a _{λ 0, DΔN = λ 0/} 2 the relationship is greater than 30 ° C. By so filled in degrees, the optical head device, wherein the temperature characteristic is enhanced reciprocating efficiency due to diffraction so as to optimize the temperature range of 0 to 60 ° C..   Using two transparent substrates with a grid-like concavo-convex portion formed on the surface, the surfaces with the concavo-convex portions facing each other, filling the concavo-convex portions with the liquid crystal, and laminating the two transparent substrates The optical head device according to claim 1.   The optical head device according to claim 2, wherein the uneven portions formed on the two transparent substrates are laminated so as to be asymmetric with respect to the laminated surface.   2. The optical head device according to claim 1, wherein a cross-sectional shape of the lattice-shaped concavo-convex portion is asymmetrical in a plane perpendicular to a longitudinal direction (stripe direction) of the concavo-convex portion. An optical head device for writing information and / or reading information by irradiating light from a light source onto an optical recording medium through a diffraction element, wherein the diffraction element has a lattice-shaped uneven portion formed on a surface thereof. A transparent substrate and a liquid crystal filled in the concavo-convex portion and having optical anisotropy and having a difference Δn between ordinary light refractive index and extraordinary light refractive index of 0.05 to 0.35. An optically anisotropic diffraction grating, wherein the uneven portion has a refractive index n, a depth D, a liquid crystal normal light refractive index _ng , and a liquid crystal extraordinary light refractive index _ne , | n−n _g | _| n-n e |, whichever is larger the .DELTA.N, when a wavelength in vacuum of the light from the light source and lambda _0, so that DΔN = λ _0/2 the relationship is satisfied at a temperature above 30 ° C. by diffraction as the temperature characteristic is optimum in the temperature range of 0 to 60 ° C. In the method of manufacturing an optical head device, wherein the optical anisotropic diffraction grating has a refractive index substantially equal to the refractive index of the transparent substrate, the transparent thin film is coated on the transparent substrate. And then manufacturing the optical thin-film device by a method of processing the transparent thin film by a photolithography method to form a lattice-shaped uneven portion. The manufacturing method according to claim 5, wherein the transparent thin film is a SiO _x film (1 <x <2).

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