JP3550905B2 - Manufacturing method of diffraction element used for optical head device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head device for writing and reading optical information on optical disks such as CDs (compact disks), CD-ROMs, video disks, and magneto-optical disks, and a method of manufacturing the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an optical head device for writing optical information on an optical disk or a magneto-optical disk or reading optical information, an optical component for guiding (beam splitting) signal light reflected from a recording surface of the disk to a detection unit. And those using a prism type beam splitter and those using a diffraction grating or a hologram element have been known.
[0003]
A diffraction grating or a hologram element for an optical head device forms a rectangular grating (relief type) having a rectangular cross section on a glass or plastic substrate by a dry etching method or an injection molding method. Function was given.
[0004]
In addition, when trying to increase the light use efficiency over an isotropic diffraction grating having a light use efficiency of about 10%, it is conceivable to use polarized light. When trying to use polarized light, a prism type beam splitter is combined with a λ / 4 plate to increase the efficiency of the forward path (the direction from the light source to the recording surface) and the return path (the direction from the recording surface to the detection unit) to reduce the reciprocation efficiency. There was a way to raise it.
[0005]
However, the prism type polarizing beam splitter is expensive, and other methods have been sought. As one method, a method of using a flat plate of birefringent crystal such as LiNbO ₃ and forming an anisotropic diffraction grating on the surface to have polarization selectivity is known. However, since the birefringent crystal itself is expensive and the productivity is poor, it has been difficult to apply it to the consumer field. Also, when a lattice is formed on LiNbO ₃ by the proton exchange method, there is a problem that it is difficult to form a lattice having a fine pitch because protons in the proton exchange solution are easily diffused into the substrate.
[0006]
[Problems to be solved by the invention]
In order to solve this problem, it is also known to form an uneven shape on a substrate and form an anisotropic diffraction grating by combining this with a liquid crystal. This can be considered that the substrate is usually etched or cut to form an uneven shape on the substrate.
[0007]
However, it is difficult to precisely process unevenness of a glass substrate by wet etching, and dry etching is not easy. For this reason, the present inventors have also proposed a method of forming a SiO ₂ film or a SiON film on a glass substrate and dry-etching the SiO ₂ film or SiON film in order to facilitate the production.
[0008]
Even in the case where such a transparent film is formed and etched, it is necessary to perform dry etching, so that a manufacturing method that has higher productivity and can easily create a precise uneven shape has been desired. .
[0009]
[Means for Solving the Problems]
The present invention has been made to solve the above-described problem, and is a diffraction element used for an optical head device in which a diffraction element is arranged between a light source and an optical recording medium, wherein the diffraction element is provided between two substrates. it is filled with an optically anisotropic material, that is the two least one surface of the substrate of the substrate is glass protrusions of the grid-shaped formation, the refractive index of the convex portions, optically anisotropic material In the method for producing a diffractive element having optical anisotropy, which has a refractive index substantially equal to either the ordinary refractive index or the extraordinary refractive index, the method of forming the glass convex portion includes forming a glass frit on a glass substrate. A method for producing a diffraction element, comprising a step of forming a film, firing the film, and then press-molding the film .
[0010]
Further, the method of forming a glass convex portion of the substrate of the diffractive element of the optical head device, a glassy film formed by the sol-gel method on the glass substrate, and press molding the glass membrane in the gel state, then Provided is a method for manufacturing a diffraction element , comprising a step of firing.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic diagram showing a basic configuration of an optical head device using the diffraction grating of the present invention. In FIG. 1, reference numeral 1 denotes a light source such as a semiconductor laser, 2 denotes an optically anisotropic diffraction grating, and 3 denotes a phase difference element such as a λ / 4 plate. Reference numeral 4 denotes a diffraction element, which includes the optically anisotropic diffraction grating 2 and the retardation element 3. 5 is a condenser lens for condensing light, 6 is an optical recording medium, and 7 is a detector.
[0012]
Figure 2 is a cross-sectional view of a reference example of the optical anisotropic diffraction grating, illustrating an example of forming a convex portion in the glass substrate itself. In FIG. 2, reference numeral 11 denotes a first substrate provided with a convex portion, 12 denotes a flat second substrate, 13 denotes a convex portion, 14 denotes a sealing material for sealing the periphery, and 15 denotes an optically anisotropic member disposed therebetween. It is a liquid crystal which is a conductive material. In the present invention, the convex portion of the substrate is formed by molding using a mold of a transparent material film formed on the glass substrate, but in the reference example of FIG. 2, the convex portion is formed of the material of the first substrate 11 itself which is a glass substrate. A part 13 is formed.
[0013]
FIG. 3 is a cross-sectional view of another example of the optically anisotropic diffraction grating used in the present invention, showing an example in which a projection made of a transparent material film is formed on a glass substrate. In FIG. 3, reference numeral 21 denotes a first substrate provided with a convex portion, 22 denotes a flat second substrate, 23 denotes a convex portion thereof, 24 denotes a sealing material for sealing the periphery, and 25 denotes an optically anisotropic member disposed therebetween. It is a liquid crystal which is a conductive material. In the present invention, the convex portion of the substrate is formed by molding with a mold, and in the example of FIG. 3, the convex portion 23 is formed of a transparent material layer of glass laminated on a glass substrate.
[0014]
4 and 5 are cross-sectional views of another reference example and another example of the optically anisotropic diffraction grating used in the present invention, and show an example in which a convex portion is formed in a blazed shape. FIG. 4 shows a reference example in which a convex portion is formed on a glass substrate itself, and FIG. 5 shows an example in which a convex portion made of a transparent material film is formed on a glass substrate.
[0015]
4 and 5, reference numerals 31 and 41 denote a first substrate provided with projections, 32 and 42 denote flat second substrates, 33 and 43 denote projections thereof, and 34 and 44 denote sealing materials for sealing the periphery. , 35 and 45 are liquid crystals which are optically anisotropic materials disposed therebetween. In the reference example of FIG. 4, the blazed convex portion 33 is formed of the material of the first substrate 31 itself, which is a glass substrate. In the example of FIG. 5, a blazed convex portion 43 is formed of a transparent material layer made of glass laminated on a glass substrate.
[0016]
In the present invention, the convex portion is formed of glass, and the convex portion is formed by molding with a mold. Specifically, press molding is performed. This press molding may be a batch press or a continuous press.
[0017]
The convex portion of the glass in the first substrate, the surface of the substrate, by forming a glass transparent material film to form it into a convex portion. In the present invention, as an optically anisotropic material used in combination with this substrate, liquid crystal is used as a typical material.
[0018]
Transparent material film formed on the base plate, the refractive index of the substrate of this is nearly equal refractive index is of about 1.5 is used. Also, the refractive index of the convex portion can be made to match the extraordinary light refractive index of the liquid crystal. Usually, the extraordinary light refractive index of the liquid crystal is about 1.6 to 1.8, so the material is selected so that the refractive indices of the substrate and the transparent material film match the extraordinary light refractive index.
[0019]
The optically anisotropic grating of the present invention, a transparent material film formed on the surface of the base plate, and processed into a predetermined shape to form a grid-shaped convex portions. In this case, the depth, pitch, and shape of the projections may be determined according to the desired diffraction shape. The projection is formed by molding with a mold. The following is mentioned as a molding method using a mold.
[0020]
On a glass board to form a glass transparent material film, to press forming the projections on the transparent material layer. Transparency material film, a frit paste method, Ru is formed on a substrate by a sol-gel method.
[0021]
Compared with the method of directly press-molding a glass substrate, the frit paste method facilitates press-forming at a low temperature, and is advantageous in terms of mold life and thermal deformation. That is, in the frit paste method, since a glass frit film is formed and baked to form a glass transparent material film, a transparent material film having a relatively low softening point can be easily formed, and low-temperature pressing becomes possible. .
[0022]
In the sol-gel method, a vitreous film is formed on a glass substrate by a sol-gel method, and the vitreous film is press-molded in a gel state and then fired. In this method, by pressing the vitreous film in a gel state, press molding can be performed at a lower temperature than the glass frit film, which is advantageous.
[0023]
In the present invention, the convex part adjusts the refractive index to the ordinary light refractive index or the extraordinary light refractive index of the liquid crystal . When shaped by direct the glass substrate is subjected to two constraints that can be molded by and relatively low temperatures refractive index of the glass substrate are matched to it. And since glass is melted in a kiln in mass production and the composition cannot be easily changed, conversely, liquid crystals must be selected and used.
[0024]
On the other hand, in the manufacturing method using the glass frit film or the sol-gel method, it is relatively easy to change the refractive index. Therefore, it is easy to match the refractive index with the liquid crystal. In this case, as the base glass substrate, a glass substrate used in a normal liquid crystal display element can be used. For this reason, a substrate with projections can be obtained at low cost.
[0025]
The optically anisotropic diffraction grating of the present invention is manufactured as follows.
For first first glass substrate (first substrate), forming a protrusion in the transparent material film laminated on the I Rimoto plate molding method using such type as described above. The cross-sectional shape of the uneven portion in a plane perpendicular to the longitudinal direction may be a symmetrical rectangular shape such as a rectangle or a square, or an asymmetrical shape such as a step shape or a saw shape.
[0026]
In the case where the convex portion has an asymmetric shape, the diffraction efficiency of one of the ± 1st-order diffracted lights by the optically anisotropic diffraction grating is increased, and if only the diffracted light having the higher diffraction efficiency is detected. Often, a single detector can provide high light use efficiency.
[0027]
In the present invention, usually, an alignment film such as polyimide is formed on the surface of the first substrate in contact with the liquid crystal, and the liquid crystal alignment direction of the alignment film is aligned with the longitudinal direction of the projection. The alignment of the liquid crystal may be performed by rubbing or another method such as oblique evaporation, but the rubbing method has good productivity.
[0028]
Next, a second glass substrate (a second substrate) is prepared, and a polyimide alignment film is also formed on the surface in contact with the liquid crystal, and the rubbing direction of the alignment film is the same as the rubbing direction of the first substrate. Rub in the direction.
[0029]
As described above, the second glass substrate is laminated and bonded to the first glass substrate with the liquid crystal alignment directions being the same. At that time, a sealing material is applied to and adhered to the peripheral portions of the first glass substrate and the second glass substrate in portions other than the opening for liquid crystal injection. The sealing material may be a resin such as an epoxy resin or a glass frit mixed with a spacer as necessary. Then, liquid crystal is injected from the opening in a vacuum, and the opening is closed with a sealing resin.
[0030]
Note that the sealing step, the liquid crystal injection step, and the opening sealing step are not limited to the above steps, and may be steps in which liquid crystal injection and seal pressure bonding are performed simultaneously.
[0031]
As the liquid crystal used in the present invention, a polymer liquid crystal, a liquid crystal monomer, a liquid crystal composition and the like can be appropriately used. In the case of a normal liquid crystal composition, a nematic liquid crystal used in a normal TN type liquid crystal may be used. It is preferable to use a liquid crystal having a large refractive index anisotropy since a large diffraction angle can be obtained. Specifically, Δn ≧ 0.2, particularly Δn ≧ 0.25 is preferable.
[0032]
When a high-molecular liquid crystal is used as the liquid crystal, after the liquid crystal monomer is injected, the liquid crystal monomer may be polymerized by irradiating ultraviolet rays or heating in an aligned state. In that case, the polymer liquid crystal can be oriented only by the convex portion, and therefore, the orientation film may be omitted if the liquid crystal is oriented in a specific direction. In the case of using the polymer liquid crystal, it is only necessary to maintain the orientation of the liquid crystal monomer and polymerize the polymer liquid crystal. Therefore, it is not necessary to change the orientation after the polymer liquid crystal is formed.
[0033]
A retardation element typified by a λ / 4 plate is laminated on the optically anisotropic diffraction grating manufactured as described above to produce a diffraction element. This phase difference element converts light passing through the optically anisotropic diffraction grating into circularly polarized light. This phase difference element is arranged on the side opposite to the light source, that is, on the optical recording medium side. As the retardation element, a known retardation film made of a material such as polycarbonate and polyvinyl alcohol can be used.
[0034]
In this case, in the present invention, the optically anisotropic diffraction grating is configured such that the first glass substrate having the convex portion is on the opposite side to the light source, and the phase difference element is laminated on the first glass substrate. I do.
[0035]
As described above, it is assumed that the lattice-shaped protrusions (the longitudinal direction is the depth direction in FIG. 1) are opposite to the light source, and a positive dielectric anisotropic nematic liquid crystal is used, and the lattice-shaped protrusions of the first substrate are refracted. The operation in the case where the refractive index is made substantially equal to the ordinary light refractive index of the liquid crystal and a P-wave (having a polarization in a direction parallel to the paper surface) from the semiconductor laser is incident thereon will be described with reference to FIG.
[0036]
On the outward path, for the P-wave incident from the semiconductor laser, the anisotropic diffraction grating does not function as a diffraction grating because the refractive index of the lattice-shaped convex portion is substantially equal to the refractive index of the liquid crystal portion. Is transmitted.
[0037]
On the return path, the polarization direction is changed by the retardation film, and the S-wave is incident on the anisotropic diffraction grating. At this time, since the refractive index of the liquid crystal corresponding to the S-wave corresponds to the extraordinary light refractive index, unlike the refractive index of the lattice-like convex portion (substantially equal to the ordinary light refractive index), the liquid crystal functions as a diffraction grating and diffracts light. Occur.
[0038]
Another embodiment of the present invention, are those substantially equal a grid refractive index of the convex portion of the first substrate to the abnormal light refractive index of the liquid crystal. Also in this case, since the diffracted light must reach the photodetector, the longitudinal direction of the lattice-shaped protrusions in FIG. 1 is the depth direction on the paper of FIG. Thereby, it can be applied to an S-wave input element from a semiconductor laser.
[0039]
Also in this case, in the present invention, the optically anisotropic diffraction grating is configured such that the first glass substrate on which the convex portion is formed comes to the opposite side to the light source, and the phase difference element is laminated on the first glass substrate. To
[0040]
As described above, it is assumed that the lattice-shaped protrusions (the longitudinal direction is the depth direction in FIG. 1) are opposite to the light source, and a positive dielectric anisotropic nematic liquid crystal is used, and the lattice-shaped protrusions of the first substrate are refracted. The operation in the case where the refractive index is made substantially equal to the extraordinary light refractive index of the liquid crystal and an S-wave (having a deflection in a direction perpendicular to the paper surface) from the semiconductor laser is incident on the liquid crystal will be described with reference to FIG.
[0041]
On the outward path, the S-wave incident from the semiconductor laser does not function as a diffraction grating because the anisotropic diffraction grating does not function as a diffraction grating because the refractive index of the lattice-shaped convex portion and the refractive index of the liquid crystal portion are almost equal. Is transmitted.
[0042]
On the return path, the polarization direction changes due to the retardation film, and the P-wave is incident on the anisotropic diffraction grating. At this time, since the refractive index of the liquid crystal corresponding to the P wave corresponds to the ordinary light refractive index, unlike the refractive index of the lattice-shaped convex portion (substantially equal to the extraordinary light refractive index), the liquid crystal functions as a diffraction grating and diffracts light. Occur.
[0043]
In the diffraction element of the present invention, another diffraction grating may be formed on the substrate surface on the light source side, that is, on the second substrate side. In this case, diffraction to the photodetector and tracking error detection by the three-beam method are performed. Diffraction can be realized by one element.
[0044]
The pattern of the convex portions of the optically anisotropic diffraction grating according to the present invention may have a curvature in the diffraction grating plane or a distribution of the grating interval so that the beam shape of the return light from the optical recording medium has a desired shape. You can also.
[0045]
In the above description, an example in which the liquid crystal is not twisted has been described, but in the present invention, the liquid crystal may be twisted. In order to twist the liquid crystal, the alignment treatment direction of the alignment film is arranged according to the twist, and a component that causes the liquid crystal to twist is added as necessary. In this case, the longitudinal direction of the convex portion forming the grating is arranged in accordance with the twisted and propagated polarized light so that it does not cause diffraction on the outward path but causes diffraction on the return path.
[0046]
In the present invention, when a coating such as a UV-curable acrylic resin is provided on the surface of the diffraction element on the light source side and / or the surface on the optical recording medium side, the wavefront caused by the unevenness of the surface of the λ / 4 plate or the glass substrate This is preferable because aberration can be reduced. Further, by laminating a glass substrate, a plastic substrate, or the like with good flatness on the coating of the UV-curable acrylic resin or the like, the wavefront aberration can be remarkably reduced, which is preferable. Therefore, since the light entrance / exit surface of the diffraction element is flattened, the wavefront aberration is consequently reduced.
[0047]
As the light source in the present invention, a solid-state laser such as a semiconductor laser or a YAG laser, or a gas laser such as He-Ne can be used, and a semiconductor laser is preferable in terms of reduction in size and weight, continuous oscillation, maintenance and inspection, and the like. Using a harmonic generator (SHG) in which a semiconductor laser or the like and a non-linear optical element are incorporated in the light source section and using a short wavelength laser such as a blue laser enables high-density optical recording and reading.
[0048]
The optical recording medium of the present invention is a medium on which information can be recorded and / or read by light. Examples thereof include optical disks such as CDs, CD-ROMs, DVDs (digital video disks), magneto-optical disks, and phase-change optical disks.
[0049]
【Example】
"Example 1"
A mixed solution containing methyltrimethoxysilane as a main component and containing glacial acetic acid, colloidal silica and tetraisopropyl titanate is stirred at room temperature for 8 hours, and placed on a glass substrate having a size of 10 mm × 10 mm × 0.5 mm and a refractive index of 1.52. Applied. After standing at room temperature and gelling, it was press-molded at 400 ° C and baked at 450 ° C for 30 minutes.
[0050]
As a result, a lattice-shaped projection 13 having a refractive index of 1.52 and a rectangular cross section in a plane perpendicular to the longitudinal direction was formed. The pitch of the projections at this time was 13 μm, and the depth was 1.4 μm. A polyimide alignment film was formed on the surface in contact with the liquid crystal. The rubbing direction was set along the longitudinal direction of the convex portion (the direction perpendicular to the drawing of FIG. 2).
[0051]
A second glass substrate having a length of 10 mm, a width of 10 mm, a thickness of 0.5 mm, and a refractive index of 1.52 was prepared, and a polyimide alignment film was formed on a surface in contact with the liquid crystal. The rubbing direction was the same as the longitudinal direction of the projection. Next, the first glass substrate and the second glass substrate were overlapped with each other in a state where their orientation directions were parallel to each other, and the peripheral portion was sealed except for an opening for injecting liquid crystal.
[0052]
Specifically, it was as follows. An epoxy resin containing an 8 μm spherical spacer was applied to the periphery of the second glass substrate, and the first glass substrate was mounted thereon. Thereafter, a mixed liquid crystal composition (trade name “BL009” manufactured by Merck, nematic liquid crystal, Δn = 0.28, refractive index of ordinary light = 1.52, refractive index of extraordinary light = 1.80, solid liquid crystal) Phase transition temperature to phase ≦ −20 ° C., phase transition temperature to isotropic phase = 108 ° C.). The opening was closed with a sealing resin to produce an optically anisotropic diffraction grating.
[0053]
Next, a retardation film made of polycarbonate was bonded to the outer surface of the first glass substrate (the surface opposite to the surface provided with the convex portions) using a transparent adhesive. Further, a UV curable acrylic resin was applied thereon. Further, a third glass substrate was placed thereon, and the third glass substrate was laminated and bonded by irradiating ultraviolet rays. Further, with respect to the entire device, an anti-reflection film was formed on a light incident surface and a light output surface to produce a diffraction device.
[0054]
This diffractive element had a transmittance of 90% with respect to a P-wave having a wavelength of 650 nm from a semiconductor laser (light in a polarization direction parallel to the paper surface in FIG. 1). With respect to the S-wave (light in the polarization direction perpendicular to the paper surface) from the optical disk, the diffraction efficiency of the first-order diffracted light was 25% and the diffraction efficiency of the -1st-order diffracted light was 26%.
[0055]
Therefore, the reciprocating efficiency was 45.9% when calculated by 0.90 × 0.51, and a practically high efficiency was obtained. The wavefront aberration of the transmitted light was 0.015λ _rms (root mean square) or less at the center of the light entrance / exit surface of the diffractive element (circular range having a diameter of 2 mm).
[0056]
"Example 2"
A glass frit containing a large amount of PbO and having a refractive index of 1.79, a glass transition point of 380 ° C., and a sag point of 460 ° C. is kneaded with a binder obtained by dissolving ethyl cellulose in α-terpineol to form a paste, which is 10 mm long × 10 mm wide × thick. After printing on a glass substrate having a thickness of 0.5 mm and a refractive index of 1.80, the resultant was baked at 550 ° C. under reduced pressure to form a transparent thin film having a thickness of 20 μm.
[0057]
This was press-formed at 400 ° C., and as a result, a lattice-shaped convex portion 43 having a blazed cross-sectional shape in a plane perpendicular to the longitudinal direction was formed. The pitch of the projections at this time was 13 μm, and the depth was 2 μm. A polyimide alignment film was formed on the surface in contact with the liquid crystal. The rubbing direction was set to be along the longitudinal direction of the projection (the direction perpendicular to the drawing of FIG. 5).
[0058]
An alignment film was formed in the same manner as in Example 1 except that a second glass substrate having a length of 10 mm, a width of 10 mm, a thickness of 0.5 mm, and a refractive index of 1.80 was used, and was overlaid and sealed with the first glass substrate. Then, the same liquid crystal was injected to produce an optically anisotropic diffraction grating. Further, a retardation film is adhered in the same manner as in Example 1, a third glass substrate is laminated and adhered with a UV-curable acrylic resin, and an anti-reflection film is formed on a light incident surface and a light exit surface to produce a diffraction element. did.
[0059]
This diffractive element had a transmittance of 90% with respect to an S-wave (light having a polarization direction perpendicular to the paper surface in FIG. 1) having a wavelength of 678 nm from a semiconductor laser. For a P wave (light in a polarization direction parallel to the paper surface) from the optical disc, the diffraction efficiency of the first-order diffracted light was 65% and the diffraction efficiency of the -1st-order diffracted light was 5%.
[0060]
Therefore, the reciprocating efficiency was 58% when calculated with 0.90 × 0.65 for only the first-order diffracted light, and a sufficiently high efficiency for practical use was obtained. The wavefront aberration of the transmitted light was 0.015λ _rms (root mean square) or less at the center of the light entrance / exit surface of the diffractive element (circular range having a diameter of 2 mm).
[0061]
"Example 3 (Reference example) "
Optical glass ("SF6" manufactured by Ohara) having a length of 10 mm, a width of 10 mm, a thickness of 0.5 mm, a refractive index of 1.79, a glass transition point of 455 ° C, and a deformation point of 475 ° C is press-molded at 480 ° C. A lattice-shaped convex portion 33 having a blazed cross section in a plane perpendicular to the longitudinal direction was formed. The pitch of the projections at this time was 13 μm, and the depth was 2 μm. A polyimide alignment film was formed on the surface in contact with the liquid crystal. The rubbing direction was set along the longitudinal direction of the convex portion (the direction perpendicular to the drawing of FIG. 4).
[0062]
An alignment film was formed in the same manner as in Example 1 except that a second glass substrate having a length of 10 mm, a width of 10 mm, a thickness of 0.5 mm, and a refractive index of 1.79 was used, and was overlaid and sealed with the first glass substrate. Then, the same liquid crystal was injected to produce an optically anisotropic diffraction grating. Further, a retardation film is adhered in the same manner as in Example 1, a third glass substrate is laminated and adhered with a UV-curable acrylic resin, and an anti-reflection film is formed on a light incident surface and a light exit surface to produce a diffraction element. did.
[0063]
This diffractive element had a transmittance of 90% with respect to an S-wave (light having a polarization direction perpendicular to the paper surface in FIG. 1) having a wavelength of 678 nm from a semiconductor laser. For a P-wave (light in a polarization direction parallel to the paper surface) from the optical disk, the diffraction efficiency of the first-order diffracted light was 63% and the diffraction efficiency of the -1st-order diffracted light was 5%.
[0064]
Therefore, the reciprocating efficiency was 56.7% when calculated with 0.90 × 0.63 for only the first-order diffracted light, and a sufficiently high efficiency for practical use was obtained. The wavefront aberration of the transmitted light was 0.016λ _rms (root mean square) or less at the center of the light entrance / exit surface of the diffraction element (circular range having a diameter of 2 mm).
[0065]
【The invention's effect】
In the present invention, since the optically anisotropic diffraction grating is formed using the optically anisotropic material and the substrate having the lattice-shaped glass convex portions formed on the surface by molding with a mold, the precise diffraction grating shape is obtained. Can be easily obtained. In addition, productivity is extremely high because of molding by a mold. Furthermore, a blaze shape that is difficult to obtain by dry etching can be easily obtained.
[0066]
In particular, by forming the glass convex portion of the substrate of the diffraction element by forming a glass frit film on a glass substrate, baking, and then press forming, molding can be performed at a low temperature, and wear of the mold is reduced. .
[0067]
Also, by forming a vitreous film on a glass substrate by a sol-gel method, press-forming the vitreous film in a gel state, and then sintering it, it is possible to form at a lower temperature, and wear of the mold is reduced. Decrease.
[0068]
The present invention can be applied to various applications within a range that does not impair the effects of the present invention.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a basic configuration of an optical head device according to the present invention.
2 is a cross-sectional view of a reference example of the optical anisotropic diffraction grating.
FIG. 3 is a sectional view of another example of the optically anisotropic diffraction grating used in the present invention.
4 is a cross-sectional view of another reference example of the optical anisotropic diffraction grating.
FIG. 5 is a sectional view of another example of the optically anisotropic diffraction grating used in the present invention.
[Explanation of symbols]
1: light source 2: optically anisotropic diffraction grating 3: phase difference element 4: diffraction element 5: condenser lens 6: optical recording medium 7: photodetector 11: first substrate 12: second substrate 13: convex Part 14: sealing material 15: liquid crystal

Claims (2)

A diffraction element used in an optical head device in which a diffraction element is arranged between a light source and an optical recording medium,
An optically anisotropic material is filled between two substrates, and at least one of the two substrates has a lattice-shaped glass projection formed on a surface thereof, and the refractive index of the projection is reduced. In the method for manufacturing a diffraction element having optical anisotropy, which has a refractive index substantially equal to either the ordinary refractive index or the extraordinary refractive index of the optically anisotropic material ,
The method of manufacturing a diffraction element, wherein the method of forming the glass protrusion includes a step of forming a glass frit film on a glass substrate, firing the glass frit film, and then press-molding the glass frit film . A diffraction element used in an optical head device in which a diffraction element is arranged between a light source and an optical recording medium,
An optically anisotropic material is filled between two substrates, and at least one of the two substrates has a lattice-shaped glass projection formed on a surface thereof, and the refractive index of the projection is reduced. In the method for manufacturing a diffraction element having optical anisotropy, which has a refractive index substantially equal to either the ordinary refractive index or the extraordinary refractive index of the optically anisotropic material,
The method of forming the glass convex portion includes a step of forming a vitreous film on a glass substrate by a sol-gel method, pressing the vitreous film in a gel state, and then firing. A method for manufacturing a diffraction element .

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