JP4364083B2 - Optical head device - Google Patents

Description

  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.

  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.

  Conventionally, a diffraction grating or hologram element for an optical head device is formed by forming 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, thereby diffracting light. The beam split function was added.

  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%. In order to use polarized light, a prism type 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.

However, prismatic polarization beam splitters are expensive, and other methods have been sought. As one method, a method of using a birefringent crystal flat plate such as LiNbO ₃ and forming an anisotropic diffraction grating on the surface to provide deflection selectivity is known. However, the birefringent crystal itself is expensive and difficult to apply to the consumer field.

  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.

  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.

The present invention performs writing of optical information on an optical recording medium and / or reading of optical information on an optical recording medium by irradiating a recording surface on the optical recording medium with a light beam from a light source through a diffraction element. In the optical head device, the diffractive element is formed of an optically anisotropic polymer obtained by polymerizing a polymerizable liquid crystal monomer, and has an optical anisotropy including a plurality of convex portions spaced apart from each other on the substrate. Ri Oh diffraction element having a diffraction grating, to provide an optical head apparatus characterized that you have provided lambda / 4 plate on the optical recording medium side of the diffraction element.

The present invention provides the above-described optical head device, wherein the difference between the ordinary light refractive index and the extraordinary light refractive index of the optically anisotropic polymer is 0.02 to 0.30. The optical head according to the above, wherein the uneven portion of the optical anisotropic diffraction grating is filled with an isotropic transparent material having a refractive index substantially equal to the ordinary light refractive index or the extraordinary light refractive index of the optical anisotropic polymer. Providing equipment .

The present invention, on the surface of the light source side and / or the recording surface side of the front Symbol diffraction element, to provide an optical head device according to formed by coating a transparent resin above.

  The optical head device using the optically anisotropic diffraction grating of the present invention does not use an expensive material such as a birefringent crystal having optical anisotropy, and has a larger substrate area and higher mass productivity than a birefringent crystal. Can be produced. In addition, compared with the conventional isotropic diffraction grating, there is an excellent effect that high light utilization efficiency can be obtained.

  By using a photomask or the like for the diffraction grating pattern, a complicated grating shape based on CGH (Computer Generated Hologram) can be easily formed with high productivity. In addition, since the λ / 4 plate can be laminated and integrated, it is extremely excellent in productivity and can be made compact as a whole.

  In addition, the diffraction efficiency of either one of the ± first-order diffracted lights is increased, and only the diffracted light having the higher diffraction efficiency can be detected by one detector with high light reciprocation efficiency.

  Furthermore, because it uses an optically anisotropic polymer obtained by polymerizing a polymerizable liquid crystal monomer, it has excellent temperature characteristics, does not require a sealing material such as an epoxy resin, has excellent reliability, has excellent mass productivity, etc. It also has the effect of.

  The optically anisotropic polymer in the present invention does not need to exhibit normal liquid crystallinity (property indicating a known liquid crystal phase such as nematic, smectic, cholesteric). The optically anisotropic polymer is preferably produced by polymerizing a polymerizable liquid crystal monomer with light or heat. In particular, a polymerizable liquid crystal monomer that can be polymerized with ultraviolet light or visible light is preferable because an optically anisotropic polymer can be produced on-site (directly on a substrate) by a photolithography process.

  The polymerizable liquid crystal monomer refers to a monomer exhibiting liquid crystallinity at room temperature or a temperature during photopolymerization. “Liquid crystallinity” means a known liquid crystal phase such as nematic, smectic, cholesteric. In the present invention, nematic and smectic are more preferable than the case where the pitch of the molecular arrangement (regular repeating unit in the direction of the helical axis) is short like cholesteric. The liquid crystal monomer is preferably selected from esters of acrylic acid or methacrylic acid. It is preferable that one or more, particularly 2 to 3 phenyl groups are contained in the alcohol residue constituting the ester. Furthermore, one cyclohexyl group may be contained in the alcohol residue forming the ester.

  In the present invention, the difference between the ordinary light refractive index and the extraordinary light refractive index of the optically anisotropic polymer is preferably 0.02 to 0.30, more preferably 0.05 to 0.25. If it is smaller than 0.02, the depth of the diffraction grating becomes deep, which makes it difficult to manufacture, and if it is larger than 0.30, an optically anisotropic polymer having a high extraordinary refractive index must be used. An optically anisotropic polymer having a high rate is unfavorable because it has poor environmental properties in that it is easily colored by ultraviolet rays.

  Specifically, the diffraction element is made of a transparent substrate having an optical anisotropic diffraction grating on the recording surface side surface A, and the optical anisotropic diffraction grating is provided on the surface A for liquid crystal alignment. An alignment film and an optically anisotropic polymer formed in a diffraction grating pattern on the alignment film are configured. A polyimide film or the like can be preferably used as the alignment film.

  The uneven portion of the diffraction grating pattern is filled with an isotropic transparent material having a refractive index substantially equal to the ordinary light refractive index or extraordinary light refractive index of the optically anisotropic polymer. In this case, an isotropic polymer having a low refractive index is easier to obtain and has a higher reliability with respect to ultraviolet rays. Therefore, it is better to match the refractive index of the isotropic polymer to an ordinary refractive index lower than the extraordinary refractive index. preferable.

  The isotropic transparent material may be an optically isotropic polymer and an amorphous polymer. The polymer layer is preferably one that can be easily formed on an optically anisotropic diffraction grating of an optically anisotropic polymer. As the formation method, a casting method in which a solution of an amorphous polymer is cast and then the solvent is volatilized, or a photopolymerization method in which a monomer is cast and then photopolymerized is applicable. In particular, the photopolymerization method is simple and preferable.

  Examples of the monomer include styrene and derivatives thereof, acrylic acid esters and derivatives thereof, and methacrylic acid esters and derivatives thereof. In addition, an oligomer having a polymerizable group at both ends of the molecule, such as acrylic polyether, acrylic urethane, and acrylic epoxy, may be used alone or in combination.

  The refractive index of the isotropic transparent material is preferably approximately equal to the ordinary refractive index of the optically anisotropic polymer, and the value is, for example, about 1.5.

  A retardation film such as a λ / 4 plate provided on the surface A of the diffraction element converts light from a light source (linearly polarized P wave) into circularly polarized light, and reflects light from an optical recording medium (signal light). Has a function of diffracting the light into an S wave and diffracting it to the detector with high efficiency. It is preferable to laminate the λ / 4 plate on the surface A of the diffractive element while degassing under reduced pressure so that a highly efficient packaged diffractive element can be manufactured.

  The concavo-convex portion of the diffraction grating pattern is filled with an anisotropic transparent material, and the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer is the ordinary light refraction of the optically anisotropic polymer. Even when it is approximately equal to the rate, it functions as an optically anisotropic diffraction grating utilizing the polarization of light. The refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal is a direction indicating the ordinary light refractive index and the extraordinary light refractive index of the liquid crystal (direction corresponding to the light incident direction and the polarization direction). Means the refractive index in the same direction.

  At this time, the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer is greater than the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer. If it is small, the difference between the extraordinary light refractive index of the optically anisotropic polymer and the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer becomes larger. It is preferable that the obtained diffraction grating has a shallow depth.

  The uneven portion of the diffraction grating pattern is filled with an anisotropic transparent material, and the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer is anomalous of the optically anisotropic polymer. Even when it is substantially equal to the optical refractive index, it functions as an optical anisotropic diffraction grating utilizing the polarization of light.

  At this time, the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer is higher than the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer. If it is large, the difference between the ordinary refractive index of the optically anisotropic polymer and the refractive index of the anisotropic transparent material corresponding to the ordinary refractive index of the optically anisotropic polymer becomes larger, so that a desired diffraction efficiency can be obtained. The depth of the diffraction grating is shallow and preferable.

  As another specific example, the diffraction element comprises a transparent substrate having an optical anisotropic diffraction grating on the recording surface side surface A, and the optical anisotropic diffraction grating is formed on the surface A in a diffraction grating pattern. It is comprised from the uneven | corrugated | grooved part made and the optically anisotropic polymer with which the said uneven | corrugated | grooved part was filled.

  In this case, if the alignment film for aligning liquid crystals is configured to be interposed between the concavo-convex portion and the optically anisotropic polymer (configuration A), the alignment film can be formed by a normal casting method, spin coating method, or the like. It is preferable because an operation such as bonding another transparent substrate on which an alignment film is formed in a vacuum is unnecessary. As another configuration, a configuration in which another transparent substrate on which an alignment film is formed is provided on the optically anisotropic polymer (configuration B), or a configuration in which the above two configurations A and B are simultaneously used (configuration C) can be employed. Configuration A is most preferred for the reasons described above.

  The concavo-convex portion may have a left-right symmetric rectangular shape such as a rectangle or a square, or a left-right asymmetric shape such as a step shape or a saw shape in a plane perpendicular to the longitudinal direction. In the case of a left-right asymmetric shape, either one of the ± 1st-order diffracted lights by the optical anisotropic diffraction grating has a higher diffraction efficiency, and it is only necessary to detect the diffracted light having the higher diffraction efficiency, and one detector. It is preferable because high light utilization efficiency can be obtained.

  Furthermore, the uneven portion may be changed such as providing a distribution in the interval between the uneven portion, the left-right symmetric portion and the left-right asymmetric portion, and the uneven portion and the convex portion being mixed. .

  The diffraction element may further be formed with another diffraction grating on the light source side surface B. In this case, tracking error detection by the three-beam method is preferable.

  The diffraction grating pattern of the present invention may be provided with a curvature within the diffraction grating surface or a distribution of grating intervals so that the beam shape of the return light from the optical recording medium becomes a desired shape.

  As the transparent substrate, a substrate made of a transparent material such as glass or plastic can be used, and a transparent material having a refractive index substantially equal to that of glass or plastic is more preferable.

  The optically anisotropic diffraction grating has two transparent substrates each having a concavo-convex part formed in a diffraction grating pattern on the surface, and the concavo-convex part is filled with an optically anisotropic polymer in a state where the concavo-convex part faces, You may form by laminating. In that case, the depth of each concavo-convex portion may be shallow, which is preferable because the fabrication becomes easy. Moreover, it is preferable also in the point which the orientation of a liquid crystal improves by two uneven | corrugated | grooved parts which face each other.

  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.

  The uneven portion is made of an anisotropic transparent material, and the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer is substantially equal to the ordinary light refractive index of the optically anisotropic polymer. Functions as an optically anisotropic diffraction grating. At this time, the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer is greater than the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer. If it is small, the difference between the extraordinary light refractive index of the optically anisotropic polymer and the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer becomes larger. It is preferable that the obtained diffraction grating has a shallow depth.

  The uneven portion is made of an anisotropic transparent material, and the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer is substantially equal to the extraordinary light refractive index of the optically anisotropic polymer. It also functions as an optically anisotropic diffraction grating. At this time, the refractive index of the anisotropic transparent material corresponding to the ordinary light refractive index of the optically anisotropic polymer is higher than the refractive index of the anisotropic transparent material corresponding to the extraordinary light refractive index of the optically anisotropic polymer. If it is large, the difference between the ordinary refractive index of the optically anisotropic polymer and the refractive index of the anisotropic transparent material corresponding to the ordinary refractive index of the optically anisotropic polymer becomes larger, so that a desired diffraction efficiency can be obtained. The depth of the diffraction grating is shallow and preferable.

  In the present invention, at least one of the light source side surface and the recording surface side surface of the diffraction element is coated with a transparent resin such as a UV curable acrylic photopolymer, a thermosetting epoxy resin, or a UV curable epoxy resin. In this case, wavefront aberration due to irregularities on the surface of the λ / 4 plate or glass substrate can be reduced, which is preferable. Further, it is preferable that a wavefront aberration can be remarkably reduced by laminating a glass substrate or a plastic substrate having a good flatness on the coating film of the UV curable acrylic resin or the like. Accordingly, since the light incident / exit surface of the diffraction element is flattened, the wavefront aberration is reduced as a result.

  In the second invention, specifically, the optical head device of the present invention is manufactured by the following method.

  A polyimide film (alignment film) of about 100 nm or less is formed on the surface of a glass substrate having a thickness of about 1 to 3 mm by spin coating or the like. On a polyimide resin film rubbed for orientation, a photopolymerization initiator added to a polymerizable liquid crystal monomer such as an acrylate is applied by spin coating or casting at a thickness of about 2 to 4 μm, Orient.

  A mask on which a diffraction grating pattern is drawn is brought close to the polymerizable liquid crystal monomer and exposed to ultraviolet rays or the like. The pitch of the grating is about 2 to 3 μm. Thereafter, the unpolymerized polymerizable liquid crystal monomer is eluted and removed with a solvent such as alcohol to form a surface relief type lattice.

  The formed optically anisotropic grating has different refractive indexes between light polarized in the alignment direction and light polarized in the vertical direction, and the refractive index difference is about 0.02 to 0.15. Up to about .25 is possible. The refractive index (abnormal light refractive index) for light polarized in the alignment direction of the liquid crystal is relatively higher than the refractive index (ordinary light refractive index) for light polarized perpendicular to the alignment direction.

The grating irregularities are filled with an isotropic photopolymer having a refractive index substantially equal to one of the two refractive indexes. In that case, an isotropic polymer having a low refractive index is more easily obtained and has a higher reliability with respect to ultraviolet rays. Therefore, it is preferable to make the refractive index of the isotropic polymer coincide with the ordinary refractive index.
Further, a λ / 4 plate formed of polycarbonate resin, polyvinyl alcohol resin or the like is laminated thereon.

When tracking error detection by the three-beam method is performed, another diffraction grating is formed on the surface B on the light source side of the glass substrate at a position facing the optical anisotropic grating of the surface A by a dry etching method or the like.
The above process may be performed on the entire glass substrate having a size of, for example, about 120 mm square, and then an element having a size of several mm square may be formed by cutting.

  In the third invention, specifically, the optical head device of the present invention is manufactured by the following method.

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.

  Alternatively, an acrylic resin is injected and molded using the transparent substrate prepared by the above method as a master substrate, or a mold is prepared based on the transparent substrate, and a material such as acrylic resin, polyolefin, polycarbonate, or polyethersulfone is used for injection. A transparent substrate having a lattice-shaped uneven portion can be produced by a molding method, a 2P (photopolymerization) method, or the like.

  The 2P method is a method of pressing a mold made of a material such as glass or metal, on which a lattice-shaped uneven pattern is formed, against a liquid or gel-like polymerizable liquid crystal and curing it as it is with ultraviolet rays or the like. This is a method for producing an optically anisotropic diffraction grating made of a polymerizable liquid crystal by molding. Moreover, the said metal mold | die can be made into roll shape and can also be manufactured continuously. Therefore, a complicated and fine lattice shape can be preferably manufactured with high productivity.

  As the light source of the present invention, solid lasers such as semiconductor lasers and YAG lasers, various solids such as gas lasers such as He-Ne, and gas lasers can be used. Is preferable. 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.

  The molecule of the optically anisotropic polymer of the present invention has an elongated ellipsoidal shape and has one major axis and two minor axes. It is considered that the major axes are aligned in the rubbing direction. Therefore, when light is incident from the light source side of the diffractive element as in the present invention, the refractive index of the optically anisotropic polymer with respect to light having an electric vector along the major axis direction of the liquid crystal becomes an extraordinary light refractive index, and The refractive index of the optically anisotropic polymer with respect to light having an electric vector along the orthogonal direction (short axis direction) is the ordinary light refractive index.

  Here, for example, when the refractive index of the isotropic polymer matches the ordinary refractive index, linearly polarized light (referred to as a P wave) having an electric vector along the direction orthogonal to the grating is applied to the optical anisotropic diffraction grating. Consider the case of incidence. The incident P wave is separated into three beams by the diffraction grating on the surface B on the light source side of the glass substrate. For the sake of simplicity, the following discussion will show only the strongest central beam (0th order light) of the three beams.

  This 0th-order light is incident on the optically anisotropic diffraction grating, but the grating is uniform with respect to the P-polarized light, so that no change is received, and the light enters the λ / 4 plate as it is and changes into circularly polarized light. In principle, almost 100% of the light passes through the aspheric lens (objective lens) and reaches the disk surface.

The light reflected from the optical disk surface and returned again through the aspherical lens passes through the λ / 4 plate again and changes to light having a polarization direction different by 90 ° (referred to as S-polarized light).
When this S-polarized light is incident on the optically anisotropic diffraction grating, it functions as a diffraction grating because the refractive index of the grating portion and the isotropic polymer portion are different from each other. Theoretically, the maximum is about 40% as primary light, − A maximum of about 40% of diffracted light is obtained as the primary light. When the light receiving element of the detection unit is arranged only in one of the primary light and the −1st order light, a light use efficiency of 80% is obtained when arranged in both directions.

[Example 1]
As shown in FIG. 1, a polyimide film 4 having a thickness of about 100 nm is formed by spin coating on the surface A of the glass substrate 3 having a thickness of 3 mm and a square of 120 mm on the optical disc 9 side. On the polyimide film 4 rubbed for alignment, a nematic liquid crystal monomer mainly composed of acrylate ester added with benzoin methyl ether as a photopolymerization initiator is spin-coated with a thickness of 3.9 μm, Orient.

  A photomask on which a diffraction grating pattern was drawn was brought close to the liquid crystal monomer film, exposed to ultraviolet light having a wavelength of 320 to 395 μm for 1 minute, and photocured into a diffraction grating pattern to form a cured optically anisotropic polymer film. The pitch (period) of the grating is set to 3.5 μm. Thereafter, the unpolymerized optically anisotropic polymer is eluted with ethyl alcohol to form an optically anisotropic diffraction grating by the surface relief type optically anisotropic polymer 5.

  The formed optically anisotropic diffraction grating has a refractive index difference between the refractive index for light deflected in the alignment direction (abnormal light refractive index) and the refractive index for light deflected in the vertical direction (ordinary light refractive index). Was about 0.10. The lattice irregularities are filled with an isotropic photopolymer 6 (about 1 μm) substantially equal to the refractive index of ordinary light refractive index. The material of the isotropic photopolymer 6 is an acrylic urethane-based oligomer. Further, a λ / 4 plate 7 (about 50 μm) formed of polycarbonate resin was laminated thereon while degassing under reduced pressure, and packaged as one diffraction element.

  A laser beam (linearly polarized P wave) from a semiconductor laser 1 having a wavelength of 780 nm as a light source is used as the light source, the diffraction grating 2 provided on the surface B of the glass substrate 3, an optical anisotropic diffraction grating, and an aspherical surface. The optical disk 9 was irradiated through the lens 8 (objective lens), and the diffraction efficiency of 0th-order light in that case was measured. A light transmittance of about 80% with respect to the P-wave incident light is obtained, and ± first-order light (S wave) when reflected light (circularly polarized light) from the optical disk 9 is diffracted back to the light receiving element 10 of the detection unit. The diffraction efficiency of each was about 30%.

[Example 2] Reference Example As shown in FIG. 2, an uneven part for a diffraction grating is formed in advance on the surface A side of a plastic substrate 12 by a dry etching method or a molding method, and an alignment polyimide film 13 is formed. The coating is formed by spin coating or dipping. On top of that, the same liquid crystal monomer as in Example 1 is filled, and the liquid crystal monomer is photopolymerized with ultraviolet rays and cured as in Example 1 to form a film of the optically anisotropic polymer 14. Further, a λ / 4 plate 15 made of polycarbonate resin was laminated thereon while degassing under reduced pressure, and packaged as one diffraction element.
The thicknesses of the polyimide film 13, the photopolymerizable optically anisotropic polymer 14, and the λ / 4 plate 15 are substantially the same as those in Example 1.

  In the same manner as in Example 1, a P wave was incident through the diffraction grating 11 and the diffraction efficiency was measured. The transmittance of the zero-order light was about 80%, and the diffraction efficiency of the S wave of the signal light was about 30%. Since Example 2 does not use a vacuum apparatus, the productivity and workability are superior to those of Example 3 below.

[Example 3] Reference Example As shown in FIG. 3, a polyimide film 13 is formed on another glass substrate 16 by spin coating or the like, and the glass substrate 16 is attached to the plastic substrate 12 in a vacuum using a vacuum apparatus. Match. A UV curable acrylic photopolymer (trade name 30113B, manufactured by ThreeBond Co., Ltd.) 30 is applied on the λ / 4 plate 15, and a glass substrate 31 is laminated thereon and cured by irradiating with ultraviolet rays while being pressed. Glued. Others were the same as Example 2.
In this case, the 0th-order light transmittance is similar to that of Example 2, and the wavefront aberration of the diffraction element is 0.0.
It was improved from 8λ _rms (rms: root mean square) to 0.015λ _rms .

[Example 4] Reference Example As shown in FIG. 4, it is a type in which the ones in FIG. 2 and FIG. 3 are combined (except for the UV curable acrylic photopolymer 30 and the glass substrate 31 in Example 3). The 0th-order light transmittance was the same as in FIG.

[Example 5] Reference Example As shown in FIGS. 5 and 6, the surface of a glass substrate 21 having a thickness of 1 mm and a width of 10 × 10 mm was formed into a step shape that is asymmetrical in the cross section perpendicular to the longitudinal direction of the uneven portion. An uneven portion was formed. The shape is 3.1 μm at the deepest point, 2.07 μm at the next deepest point, 1.0 μm at the next deepest point, and a three-step shape with a step pitch of 12 μm.

Specifically, it was formed as follows. Photoresist was coated on the surface of the polished glass substrate 21 by spin coating or the like. A photomask having a predetermined pattern was brought into close contact with the photoresist film, exposed to ultraviolet light, 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, dry etching is performed using a gas such as CF ₄ . A step was formed by repeating the above process a plurality of times.

  Another glass substrate having a rubbed polyimide film for liquid crystal alignment is set so that the rubbing direction is substantially parallel to the stripe direction (longitudinal direction) of the concavo-convex portion, and the concavo-convex portion and the polyimide film are faced to each other. And the other glass substrate were laminated and adhered. At that time, a polymerizable liquid crystal monomer was vacuum-injected into the concave and convex portions, filled and sealed, and then exposed to ultraviolet rays, and polymerized while maintaining the orientation to form an optically anisotropic diffraction grating as an optically anisotropic polymer. .

As the polymerizable liquid crystal monomer, a nematic liquid crystal monomer composition in which a three-component acrylic ester liquid crystal monomer was mixed was used. The refractive index anisotropy (difference between ordinary light refractive index and extraordinary light refractive index) was 0.19. As a photopolymerization initiator, 1% benzoin methyl ether 1 was added to the liquid crystal monomer composition to obtain an ultraviolet curable liquid crystal monomer composition.
Further, a λ / 4 plate similar to that in Example 1 was laminated on the optical disk side of the other glass substrate to produce a diffraction element.

  Using the diffractive element of Example 5 and entering a P wave in the same manner as in Example 1, the light transmittance for the P wave is about 90%, and the diffraction efficiency for the S wave reflected from the optical disk is + 1st order diffracted light. About 50% and -1st order diffracted light was about 1%. The diffraction efficiency of the + 1st order diffracted light exceeded 40% of the theoretical limit value in the isotropic diffraction grating.

  The present invention is used in 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.

FIG. 3 is a side view of the basic configuration of an optical head device using Example 1 and using an optically anisotropic diffraction grating made of an optically anisotropic polymer. FIG. 6 is a side view of a basic configuration of an optical head device according to a second example. FIG. 10 is a side view of a basic configuration of an optical head device according to a third example. FIG. 6 is a side view of a basic configuration of an optical head device according to a fourth example. FIG. 10 is a side view of a basic configuration of a diffraction element for an optical head device, showing Example 5. 10 is a partially enlarged side view of the basic configuration of the diffraction element of Example 5. FIG.

Explanation of symbols

1: Semiconductor laser 3: Glass substrate 4: Polyimide film 5: Optically anisotropic polymer 6: Isotropic photopolymer 7: λ / 4 plate

Claims (5)

In an optical head apparatus for writing optical information on an optical recording medium and / or reading optical information on an optical recording medium by irradiating a recording surface on the optical recording medium with a light beam from a light source through a diffraction element The diffraction element is formed of an optically anisotropic polymer obtained by polymerizing a polymerizable liquid crystal monomer, and has an optically anisotropic diffraction grating composed of a plurality of convex portions spaced apart from each other on the substrate. Ri Oh diffraction element, wherein the optical recording medium side of the diffraction element provided is lambda / 4 plate optical head device according to claim Rukoto.   2. The optical head device according to claim 1, wherein a difference between an ordinary light refractive index and an extraordinary light refractive index of the optically anisotropic polymer is 0.02 to 0.30.   3. An isotropic transparent material having a refractive index substantially equal to an ordinary light refractive index or an extraordinary light refractive index of an optical anisotropic polymer is filled in the concavo-convex portion of the optical anisotropic diffraction grating. The optical head device described. The diffraction element, an optical head apparatus according to any one of claims 1 to 3 having a diffraction grating on a surface of the light source side. Wherein the surface on the light source side and / or the recording surface of the diffraction element, an optical head apparatus according to formed by coating a transparent resin according to claim 1-4 any one.

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