JP2011112831A - Laminated grating element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a grating element and a manufacturing method thereof, using a high molecular liquid crystal by a simple and easy process, wherein the flexibility of the element constitution is improved by stabilizing the alignment of the liquid crystal without depending on an alignment layer requiring high temperature treatment. <P>SOLUTION: Because the liquid crystal molecules are spontaneously aligned along the longitudinal direction of a groove by filling a groove part of a mold having prescribed recessed and projecting parts, with a polymerizable liquid crystal to cause molecule mutual action between the groove surface and the liquid crystal, the polarizing diffraction grating 2 is structured to align the liquid crystal in the groove longitudinal direction without particularly applying alignment treatment on the surface of the substrate, and a separation element having optical anisotropy is stably formed when the polymerizable liquid crystal is cured by the light irradiation in this state. The formed high molecular liquid crystal grating 2 is next peeled off and transferred on a resin sheet 1 through an adhesive layer 4 composed of a photocurable liquid resin and non-polarized light diffraction grating 3 comprising the photocurable resin is formed in a surface thereof using such a mold having preliminarily formed prescribed projecting and recessed parts. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a grating element and a manufacturing method thereof. The present invention also relates to an optical pickup device provided with the grating element.

  Polarization diffraction gratings are diffractive optical elements that make the diffraction efficiency dependent on the direction of incident polarization, and are used to make optical systems smaller and more functional in optical pickup devices that are complicated to meet various disc standards including DVD. . For example, as disclosed in Japanese Patent No. 3978821, conventionally, a polarizing diffraction grating using a polymer liquid crystal is applied with a polyimide resin on a high heat-resistant transparent substrate such as a glass substrate and thermally cured, followed by an alignment treatment by buffing. To form a liquid crystal alignment film, a polymerizable liquid crystal material is applied to the substrate surface, and the polymerizable liquid crystal is exposed to light at a temperature in a liquid crystal state to form a flat film having a predetermined phase difference. A diffraction grating having optical anisotropy made of a polymerizable liquid crystal was formed by etching.

Japanese Patent No. 3978821

  However, with this method, it is difficult to stably manage the alignment state of the polymerizable liquid crystal by the formed alignment film, and the process such as alignment treatment and cleaning after buffing becomes complicated, and it is difficult to reduce the cost. was there.

  In addition, it is an alignment film when considering integration with organic functional optical layers such as wave plates and diffraction gratings, which are necessary for making plastics the most effective in terms of weight reduction and further miniaturization and high functionality. Since the temperature required for polyimide baking is 180 ° C. or higher, which is much higher than the heat resistance temperature of other organic materials, it is also a big problem that a large restriction is imposed on the structure of the element.

  As countermeasures against this problem, oblique vapor deposition of inorganic oxide films and photo-alignment films using photo-anisotropic materials have been proposed. All of these techniques are applied to the surface of inorganic materials such as glass. Since it is a premise, it was insufficient for application to an organic material which is one of the objects of the present invention.

  In view of the above problems, an object of the present invention is to provide a grating element using a polymer liquid crystal by a simple and easy process and a method for manufacturing the same. Furthermore, it aims at improving the freedom degree of element structure by stabilizing a liquid crystal alignment, without using the alignment film which requires a high temperature process.

  The present invention relates to a polarization beam splitting element characterized in that a uniaxial polymer liquid crystal layer is formed in an isotropic medium in a lattice shape so that the orientation direction thereof coincides with the longitudinal direction of the lattice without using a liquid crystal alignment layer I will provide a.

  Further, the above-mentioned polarization separation element is manufactured by filling a polymerizable liquid crystal in a lattice groove formed in a predetermined dimension in advance, and curing the polymerizable liquid crystal there, and then filling the lattice gap with an isotropic medium. Provide a method.

  By adopting the structure and manufacturing method of the separation element of the present invention, it is possible to satisfactorily and stably align the polymer liquid crystal without using a special alignment film, and it becomes easy to adjust the film thickness. A polarized light separation element having high separation efficiency and good separation efficiency uniformity can be obtained stably.

  In the present invention, a polymerizable liquid crystal is filled in a groove formed in a predetermined shape in advance, and the polymerizable liquid crystal is spontaneously aligned in the longitudinal direction of the groove without any special alignment treatment by the interaction between the groove wall surface and liquid crystal molecules. After that, in this state, the polymerizable liquid crystal was polymerized to obtain a polymer liquid crystal while maintaining the alignment. Thereby, the polymer liquid crystal alignment orientation can be controlled with high accuracy in the longitudinal direction of the groove without using the liquid crystal alignment layer, and the liquid crystal layer thickness can also be controlled by the groove depth formed in advance.

  The polymerizable liquid crystal for forming the polymer liquid crystal thin film used in the present invention is a composition such as a monomer, oligomer or other reactive compound exhibiting liquid crystallinity.

  As a means for curing the polymerizable liquid crystal, there are methods such as irradiation with light such as visible light and UV (ultraviolet) light, and heating. However, the curing method for irradiating light is limited by the phase transition temperature of the polymerizable liquid crystal. Because it is hard to receive, it is preferable. Therefore, here, it is assumed that the polymerizable liquid crystal is polymerized and cured by light irradiation. In this patent, for the sake of convenience, the unpolymerized state of the liquid crystal is called a polymerizable liquid crystal and the polymerized state is called a polymer liquid crystal.

  An example of a grating element according to the present invention is shown in FIG.

  FIG. 1A shows a cross-sectional view of an example of the structure of the present invention. In the figure, 1 is a resin-made transparent sheet, 2 is a polarizing diffraction grating made of uniaxial polymer liquid crystal, and 3 is a photocurable resin. 4 is an adhesive layer made of a photo-curing resin that integrates the transparent flat plate and the polarizing diffraction grating. With this configuration, the polarizing diffraction grating 2 is filled with polymerizable liquid crystal in a groove such as a mold having a predetermined unevenness in advance, so that the liquid crystal molecules spontaneously grow in the longitudinal direction by the molecular interaction between the groove surface and the liquid crystal. Since the liquid crystal is aligned along the direction, the liquid crystal can be aligned in the longitudinal direction of the groove without any special alignment treatment on the substrate surface. In this state, when the polymerizable liquid crystal is cured by light irradiation, it is optically anisotropic. The separation element having the property can be stably formed. In addition, a polymerizable liquid crystal having a mesogenic group that exhibits a liquid crystal state and a functional group having a polymerizable property such as acrylic or epoxy is suitable, and the liquid crystal state before polymerization has the nematic state most. Is suitable.

  The formed polymer liquid crystal lattice 2 is then peeled and transferred onto the resin sheet 1 through an adhesive layer 4 made of a photo-curable liquid resin, and further light is emitted by a mold or the like with predetermined irregularities on the surface. A non-polarizing diffraction grating 3 made of a cured resin is formed.

  Although it is technically possible to form the polarizing diffraction grating 2 directly on the resin sheet 1, the residual liquid crystal layer inevitably formed between the groove gap of the diffraction grating and the resin sheet is thick in the process. This may cause light scattering and deteriorate the device characteristics.

  As the resin sheet 1 used in the present configuration, polycarbonate, thermoplastic plastic typified by polyolefin, epoxy thermosetting material cured product, thermosetting plastic typified by cured acrylic photopolymerizable material, or the like can be used. . It is also possible to use a retardation plate or retardation film such as a λ / 4 plate or a λ / 2 plate that changes the polarization state of incident light. In this case, a polarization conversion function can be added to the element. It is preferable because it is possible.

  Moreover, the process for strengthening adhesive force can also be given to the interface of each layer including a resin sheet as needed. For this strengthening treatment, silane coupling agent treatment, surface plasma treatment, UV ozone treatment, and the like can be applied.

  As the adhesive 4 used for bonding the resin sheet 1 and the polarizing diffraction grating 2, a photo-curing resin is most preferable. In particular, when an acrylic modified type is used for the polymerizable liquid crystal forming the polymer liquid crystal, strong adhesion can be obtained between the polymer liquid crystal layer and the ultraviolet curable resin by using an acrylic ultraviolet curable resin as an adhesive.

Non polarizing diffraction grating 3, the linear polarization direction of close to the ordinary refractive index of the polymer liquid crystal having a refractive index constituting a polarizing diffraction grating 2 (n _o) or the extraordinary refractive index (n _e) is the incident light It is desirable to improve the polarization separation performance by the. As this material, for example, a photopolymerizable acrylic resin or epoxy resin can be used.

  Further, for the convenience of explanation, it has been described that the polarizing diffraction grating gap is filled with a non-polarizing diffraction grating material. However, after filling the polarizing diffraction grating gap with a transparent isotropic material, a further isotropic material is used. A non-polarizing diffraction grating can also be laminated.

  It is also easy to form an antireflection film, a color filter or the like on the surface of the non-polarizing diffraction grating.

  FIG. 1B shows a cross-sectional view of an example of another structure of the present invention. In order to cope with the problem that the resin film has a low rigidity and is easily deformed, A transparent flat plate with high rigidity is laminated and integrated. In the figure, 1 is a resin-made transparent sheet, 2 is a polarizing diffraction grating made of uniaxial polymer liquid crystal, 3 is a non-polarizing diffraction grating made of a photo-curing resin, and 4 is a transparent flat plate and a polarizing diffraction grating. It is an adhesive layer made of a photo-curing resin, and has a configuration in which a transparent flat plate 6 is bonded to the back surface of this laminate through an adhesive layer 5, and a diffraction grating 7 is formed on the back surface of the transparent flat plate 6 as necessary. A double-sided configuration is possible.

  In the configuration of the present invention, a description has been given of a structure in which a polarizing diffraction grating and a non-polarization diffraction grating are sequentially formed on the resin sheet surface. However, the present invention is not limited to this, and for example, the polarization separation element is replaced with another transparent member. It is also possible to adopt a configuration in which the optical member is sandwiched between the optical members and a configuration in which the optical member is laminated with another optical member.

  Some organic materials have high heat resistance, but this heat resistance is (1) the material has crystallinity and partial orientation (biaxially stretched PET, liquid crystal plastic, etc.), and (2) the molecular skeleton has high heat resistance. (Polyimide, polysulfone, etc.). However, (1) has problems such as light scattering and optical anisotropy control, and (2) has transparency problems. In our study, the heat resistance of organic resins that can be used in practical optical elements is thermosetting plastics. 180 ° C, 140 ° C is low for thermoplastics, and it does not endure polyimide alignment film formation, which requires a high-temperature process of 200 ° C or higher. The heat resistance is comprehensively determined from items such as thermal deformation, material thermal decomposition, and light absorption in the use range.

  In the configuration of the present invention described above, the liquid crystal molecules are spontaneously arranged in a direction parallel to the groove by interaction with the groove wall surface, so that the optical axis of the polymer liquid crystal layer is parallel to the longitudinal direction of the groove.

  This effect is exhibited regardless of whether the cross-sectional shape of the groove is rectangular, triangular, semicircular, etc., so that an appropriate shape can be selected depending on the application. However, when used for a diffraction grating, a rectangular shape or a triangular shape is desirable.

  In this configuration, since the alignment of the liquid crystal layer is generated by the interaction between the liquid crystal molecules and the groove wall surface, the optical axis of the resulting polymer liquid crystal is limited only to the longitudinal direction of the groove, but this is used as a polarization separation element. In this case, there is no restriction at all, and conversely, for example, there is an advantage that it is easy to provide a plurality of regions having different orientation directions in one element. However, with respect to the determined incident polarized light, the grating direction in which the polarization diffraction grating of the present invention does not act and the grating direction in which it completely acts are limited.

  Further, although the present invention has been described as a light transmission type element, it is needless to say that this technique can also be applied to a reflection type polarizing element.

  FIG. 2 is a schematic configuration example of the optical pickup device according to the present embodiment. 2 includes a semiconductor laser 101, a grating element 102 of the present invention, a polarizing beam splitter 103, a coupling lens 104, a mirror 105, a quarter wavelength plate 106, an objective lens optical 107, an optical disk 108, and a detection. The lens 109 and the photodetector 110 are included.

  Laser light emitted from the semiconductor laser 101 is incident on the grating element 102 as linearly polarized light. The laser light is diffracted by the isotropic diffraction grating portion of the grating element 102, and three beams for tracking control are generated. Here, if the grating element 102 is arranged so that the grating longitudinal direction of the polarizing diffraction grating portion and the polarization direction of the laser light are orthogonal to each other, the laser light is transmitted through the polarization diffraction grating portion with almost no diffraction. Here, for example, by forming a transparent flat plate with a half-wave plate, the polarization direction of the incident laser light can be rotated by 90 degrees. The laser light that has passed through the polarization beam splitter 103 becomes parallel light by the coupling lens 104, is reflected by the mirror 105, and enters the quarter-wave plate 106. The laser light becomes circularly polarized light by the quarter wavelength plate 106 and is condensed on the information recording surface of the optical disk 108 through the objective lens 107 to form a light spot. The laser light reflected by the optical disk 108 passes through the objective lens 107 again, and becomes linearly polarized light rotated 90 degrees from the forward polarization direction by the action of the quarter wavelength plate 106. The laser beam reflected by the mirror 105 is transmitted through the coupling lens 104, is incident on and reflected by the polarization beam splitter 103, and is detected by the photodetector 110 through the detection lens 109. Here, there is a possibility that the laser light that has not been reflected by the polarization beam splitter 103 returns to the semiconductor laser 101 (hereinafter referred to as return laser light), causing laser noise. However, since the polarization direction of the return laser beam is a direction rotated by 90 degrees with respect to the forward laser beam, it is diffracted by the polarizing diffraction grating portion of the grating element 102. As a result, the return laser beam to the semiconductor laser 101 is cut. As described above, the optical pickup device using the grating element according to the present invention is capable of generating three beams for tracking and suppressing laser noise that can be generated by the semiconductor laser. When the semiconductor laser 101 is a two-wavelength laser in which two lasers are integrated into one package, the grating element 102 may be configured to support two wavelengths.

  Side views of each process of the first manufacturing method of the grating element are shown in FIGS.

  In this example, first, as shown in FIG. 3A, RMS03-001C (polymerizable liquid crystal 10 is formed on a mold 20 having grooves having a groove width of 1.5 μm, a groove pitch of 3 μm, and a depth of 3 μm formed on the surface. (Merck) is dropped on the uneven surface of the mold, the solvent is heated and dried, and after returning to room temperature, the substrate surface is leveled with a squeegee to remove the polymerizable liquid crystal protruding from the substrate groove and flatten the surface. It was. In this mold, grooves are formed by machining on the Ni-P electroless plating surface.

  In this state, as shown in FIG. 3B, the polymerizable liquid crystal was reacted and cured by irradiation with ultraviolet light mainly having a wavelength of 365 nm.

  Next, as shown in FIG. 3C, a liquid ultraviolet curable resin is applied onto a mold 20 filled with the polymer liquid crystal 1, and the resin sheet 1 is laminated thereon, with a wavelength of 365 nm as the main component. The adhesive layer 4 was formed by reacting and curing the ultraviolet curable resin by irradiation with ultraviolet rays. The resin sheet 1 was a 0.2 mm thick polycarbonate broadband λ / 2 wavelength retardation plate (trade name PolarCorrect, manufactured by Color Link Japan Co., Ltd.). The liquid UV curable resin constituting the adhesive layer 4 is 20 parts by weight of dicyclopentadienyl hexaacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), isobornyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) and phenoxy acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) as a refractive index adjuster. ), 80 parts by weight, 3 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a polymerization initiator, and 1 part by weight of silane coupling agent KBM503 (manufactured by Shin-Etsu Chemical) as an adhesion enhancer are mixed, and the refractive index of the cured product is determined. What was 1.53 was used. At this time, the angle formed by the mold groove direction and the optical axis of the broadband wavelength phase difference plate was 45 °.

  At this stage, the transparent isotropic medium 3 made of the cured ultraviolet curable resin is firmly bonded to the polymer liquid crystal, so that the polymer liquid crystal lattice can be transferred to the substrate side.

  After that, the polymer liquid crystal lattice integrated with the phase difference plate through the ultraviolet curable resin is peeled off as shown in FIG. 3 (d), and then the polymer of the resin sheet 1 as shown in FIG. 3 (e). The liquid crystal transfer side surface is coated with another liquid ultraviolet curable resin 11, and a mold 21 having a groove width of 10 μm, a groove pitch of 20 μm, and a depth of 1.5 μm is used. After the diffraction gratings are further laminated so as to be orthogonal to the longitudinal direction of the diffraction grating grooves, ultraviolet light mainly having a wavelength of 365 nm is irradiated (FIG. 3 (f)) to form a non-polarizing diffraction grating 3 made of a transparent resin. Thus, a polarization separation element as shown in FIG. This UV curable resin is composed of 20 parts by weight of 1,6 hexyl diacrylate (manufactured by Kyoeisha Chemical), hydroxybutyl methacrylate (manufactured by Kyoeisha Chemical) and 2-hydroxy-3-phenoxypropyl acrylate (manufactured by Kyoeisha Chemical) as a refractive index adjusting agent. A mixture of 80 parts by weight and 3 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a polymerization initiator was used.

  When the alignment state of the polymer liquid crystal was observed with a polarizing microscope, it was observed that the molecular axes of the polymer liquid crystal lattice were aligned in the groove direction, and it was confirmed that the polymer liquid crystal was in a good alignment state.

  In addition, when the obtained grating was irradiated with polarized red laser light, when the polarization direction was set perpendicular to the groove longitudinal direction, it was visually observed that the diffracted light intensity greatly increased in the parallel direction. It can be confirmed that the polarization direction rotation by the λ / 2 phase difference plate and the good polarization diffracted light by the polarization diffraction grating can be obtained by the present invention.

Table 1 shows the intensity of transmitted light of the diffraction grating measured by changing the refractive index of the cured product of the ultraviolet curable resin forming the non-polarizing diffraction grating.

  The refractive index of the cured product was measured with an Atago Abbe refractometer. Since it is difficult to measure the refractive index of the polarization diffraction grating as it is, the measurement was performed on the prepared polarization diffraction grating gap filled with a polymerizable liquid crystal and cured to form a sheet.

  The measurement is performed with a polarization plane orthogonal to the polarization diffraction grating that is most easily affected by the refractive index difference (because it is integrated with the λ / 2 wavelength plate, so that the incident light is parallel to the longitudinal direction of the diffraction grating). It is standardized by the measured value at a refractive index of 1.53 of the UV cured product having a high transmitted light intensity.

  As the difference between the refractive index of the cured product and the ordinary light refractive index of the polymer liquid crystal increases, diffraction from the polarizing diffraction grating occurs due to the difference in refractive index, resulting in a loss.

  When the standard of loss was 10%, the allowable refractive index difference was 0.02.

  Side views of each process of the first manufacturing method of the grating element are shown in FIGS.

  As shown in FIG. 4A, a liquid ultraviolet curable resin 12 is applied to the surface of a mold 20 in which grooves having a groove width of 1.5 μm, a groove pitch of 3 μm, and a depth of 3 μm are formed by machining in an electroless Ni—P plating mold. After coating, a resin sheet 1 made of Color Link Japan Co., Ltd. wide-band half-wave plate (trade name PolarCorrect) is laminated, and after being irradiated with ultraviolet rays as shown in FIG. 4 (c)), the resin layer 13 having the mold groove structure transferred to the surface of the resin sheet 2 was formed. As UV curable resin 12, 20 parts by weight of dicyclopentadienyl hexaacrylate (manufactured by Kyoeisha Chemical Co., Ltd.), isobornyl acrylate (manufactured by Kyoeisha Chemical Co., Ltd.), and phenoxy acrylate (manufactured by Kyoeisha Chemical Co., Ltd.) as a refractive index adjusting agent are combined and 80 weights. Part, 3 parts by weight of Irgacure 184 (manufactured by Ciba Specialty Chemicals) as a polymerization initiator was mixed, and a cured product having a refractive index of 1.525 was used.

  Next, as shown in FIG. 4 (d), RMS03-001C (manufactured by Merck) is dropped as a liquid polymerizable liquid crystal 10 on the uneven surface of the film, the solvent is heated and dried, and then returned to room temperature. The surface was flattened by removing the polymerizable liquid crystal protruding from the substrate groove.

  In this state, as shown in FIG. 4 (e), ultraviolet light mainly having a wavelength of 365 nm was irradiated to react and cure the polymerizable liquid crystal to form a polymer liquid crystal 2 to obtain a polarization separation element.

  When the alignment state of the polymer liquid crystal was observed with a polarizing microscope, it was observed that the molecular axes of the polymer liquid crystal lattice were aligned in the groove direction, and it was confirmed that the polymer liquid crystal was in a good alignment state.

  Liquid UV curable resin 14 is dropped on the obtained substrate with a polarizing diffraction grating, and the longitudinal direction of the grating groove is polarized and diffracted on a mold 21 having grooves with a groove width of 10 μm, a groove pitch of 20 μm, and a depth of 1.5 μm. The resin sheet was sandwiched between the polarizing diffraction grating side surfaces so as to be orthogonal to the longitudinal direction of the grating grooves, and then irradiated with ultraviolet rays.

  Further, a 1 mm thick glass substrate 6 on which a titanium dioxide layer 7 having grooves with a groove width of 4 μm, a groove pitch of 8 μm, and a groove depth of 0.5 μm is formed is bonded via an adhesive layer 5 made of a photocurable adhesive. Together (FIG. 4 (g)), the entire substrate including the glass substrate after UV irradiation was peeled off from the mold to form a composite diffraction grating (FIG. 4 (h)).

  When the obtained grating is irradiated with polarized red laser light, the diffraction spot caused by the isotropic material on the surface, the diffraction spot caused by the lower polarization diffraction grating, and titanium dioxide on the glass substrate surface are irradiated. When the resulting diffraction spot is observed at the same time and the polarization direction is aligned with the longitudinal direction of the polarization grating groove, it can be visually confirmed that the diffracted light intensity greatly changes in the orthogonal direction. It was confirmed that a laminated body of diffraction gratings can be easily prepared, and that good polarized diffracted light can be obtained without an alignment film such as polyimide.

  In the present embodiment, the polarization diffraction grating direction and the normal diffraction grating direction are orthogonal to each other. However, the present invention is not limited to this, and may be arbitrarily formed in any direction required for design. Is possible.

  The polycarbonate retardation plate used in Examples 1 and 2 is relatively inexpensive and has characteristics in a wide wavelength range, but has low heat resistance and cannot withstand the polyimide alignment film forming process. Therefore, a polarization diffraction grating can be formed on such a material, and the degree of freedom in design is greatly increased.

In the present embodiment, the angle formed by the mold groove direction and the optical axis of the broadband wavelength phase difference plate is 45 °. However, the present invention is not limited to this, and is arbitrary in any direction required for design. Can be formed. Moreover, although the polycarbonate wide wavelength phase difference plate was used for the phase difference plate, it is applicable also to phase difference plates using other materials, for example, polymer liquid crystal.
[Comparative Example 1]
In order to form a polarizing diffraction grating using the same polyimide alignment film as before, after forming silicon dioxide with a thickness of 0.1 μm on the broadband 1/2 wavelength plate (trade name PolarCorrect) manufactured by Color Link Japan Co., Ltd. for surface protection After applying polyimide for alignment film (trade name Sunever manufactured by Nissan Chemical Co., Ltd.) and gradually raising the temperature to 200 ° C. for firing, the wavelength plate birefringence was greatly reduced at 120 ° C., and the softening of the polycarbonate at 150 ° C. It was generated and could not be heated up to the firing temperature, resulting in sample preparation.
[Comparative Example 2]
After coating and rubbing polyimide on the glass plate surface, spin coating and polymerization of polymerizable liquid crystal RMS03-001C (manufactured by Merck) to a thickness of 2 μm, a birefringent organic film is formed on the alignment film polyimide (manufactured by Nissan Chemical Co., Ltd.) When the temperature was gradually raised to 200 ° C. for firing, the film was colored at 180 ° C., cracks were generated at 200 ° C., and sample preparation was not achieved. The cause of coloring and cracking is presumed to be due to thermal oxidation and thermal decomposition of the material.

The side view which shows an example of the grating element in this invention. 1 is a schematic configuration diagram of an optical pickup device of the present invention. The side view which shows an example of the manufacturing process of the grating element by this invention. The side view which shows another example of the manufacturing process of the grating element by this invention.

DESCRIPTION OF SYMBOLS 1 Resin sheet 2 Polarizing diffraction grating 3 Non-polarizing diffraction grating 4, 5 Adhesive layer 6 Transparent flat plate 7 Diffraction grating 10 Polymerizable liquid crystal 11, 14 UV curable resin 13 Resin layer 20, 21 Mold 101 Semiconductor laser 102 Grating element 103 Polarizing beam splitter 104 Coupling lens 105 Mirror 106 1/4 wavelength plate 107 Objective lens 108 Optical disc

Claims (11)

  A grating element in which a plurality of diffraction gratings are laminated on at least one resin sheet, and at least one of the laminated diffraction gratings is a polarizing diffraction grating made of uniaxial polymer liquid crystal And at least one of the stacked diffraction gratings is a non-polarizing diffraction grating made of a photo-curing resin.   2. The grating element according to claim 1, wherein the non-polarizing diffraction grating is a diffraction grating of a layer farthest from the resin sheet among the laminated diffraction gratings.   The polarizing diffraction grating is directly formed on the surface of an acrylic photo-curing resin layer having no optical anisotropy without a polyimide and an inorganic oxide film, and constitutes the polarizing diffraction grating. The grating element according to claim 1, wherein the direction of the extraordinary light refractive index of the uniaxial polymer liquid crystal is the same as the longitudinal direction of the grooves of the diffraction grating.   The uniaxial polymer liquid crystal constituting the polarizing diffraction grating is polymerized by irradiating ultraviolet light onto a photopolymerized liquid crystal mainly composed of a nematic liquid crystal having a polymerizable functional group in the molecule, The difference between the ordinary ray refractive index of the uniaxial polymer liquid crystal polymer constituting the polarizing diffraction grating and the refractive index of the cured acrylic photocurable resin constituting the non-polarizing diffraction grating is 0.02 or less. The grating element according to claim 1, wherein:   The grating element according to claim 1, wherein the heat resistant temperature of the resin sheet is 180 ° C. or less.   The grating element according to claim 1, wherein the resin sheet is composed of a wavelength retardation plate made of a uniaxial polymer material that changes a polarization state of incident light.   The grating element according to claim 1, wherein the resin sheet is fixed to a transparent substrate having higher rigidity than the resin sheet.   8. The grating element according to claim 1, wherein at least one diffraction grating is formed on a surface of the transparent substrate opposite to a surface to which the resin sheet is fixed. 9. .   The groove portion of the transfer mold in which the groove having a predetermined shape is formed is filled with a polymerizable liquid crystal and then cured to obtain a polymer liquid crystal, and the polymer liquid crystal is transferred onto a transparent flat plate through an adhesive layer. And a grating element filling the grating gap of the first diffraction grating with an isotropic medium, wherein a second diffraction grating is formed on the isotropic medium with a transfer mold. A method for manufacturing a grating element, wherein the adhesive layer and the isotropic medium are made of an acrylic photo-curing resin.   A method of manufacturing a grating element, comprising filling a groove portion of a resin layer having a predetermined shape with a polymerizable liquid crystal and then curing to form a polymer liquid crystal, and further filling a lattice gap with an isotropic medium, A diffraction grating structure is transferred to an isotropic medium using a transfer mold, and the resin layer formed with the groove having the predetermined shape and the diffraction grating formed by transfer using the mold are acrylic light. A method of manufacturing a grating element, comprising a cured resin.   9. An optical pickup device for recording / reproducing information by condensing a laser beam on an information recording surface of an optical information recording medium by an objective lens, wherein the optical pickup device is any one of claims 1 to 8. An optical pickup device comprising a grating element.

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