Optical elements

Abstract

Provided is an optical element having a retardation layer that realizes a uniform retardation even in an optical element having a non-flat optical surface, and that does not require a complicated manufacturing process. [Solution] An optical element 10 includes a substrate 11 having a non-planar optical surface 11a, and a retardation layer 12 formed on the optical surface 11a and consisting of a single layer, the retardation layer having a uniform retardation value throughout the layer. The optical element 10 may not have a molecular orientation mechanism for generating retardation in the retardation layer 12.

Description

[Technical Field]

[0001] The present invention relates to an optical element having a retardation layer on a non-planar optical surface. [Background technology]

[0002] In recent years, in addition to conventional liquid crystal displays (LCDs) and organic light-emitting diodes (OLEDs) as devices for displaying computer-generated images, head-mounted displays (HMDs) have been developed and are becoming increasingly popular for virtual reality (VR) and augmented reality (AR) applications. These new display devices, worn on the user's head and displaying images in the user's field of view through eyepieces, are becoming increasingly popular. As with conventional display devices, these new display devices require a wide viewing angle and high contrast to improve display quality. In head-mounted displays, the optical system between the user's eyes and the image display unit of the display device includes elements for improving display quality, such as lenses, polarizers, and retardation films.

[0003] To achieve smaller and lighter head-mounted displays, thinner and more space-saving optical systems are required. To meet this demand, head-mounted displays employ a type of optical system called a pancake optical system, which can increase the optical path length by overlapping reflections between multiple optical elements. The optical system uses optical elements with non-flat optical surfaces, such as convex lenses and aspherical lenses.

[0004] Patent Document 1 discloses an optical element having a retardation layer in which the variation in retardation is reduced by providing a retardation layer consisting of an alignment layer and a liquid crystal layer on a curved lens, aligning the molecules of the liquid crystal layer using the alignment layer, and coating the retardation layer so as to satisfy a predetermined condition that can be achieved by changing the thickness of the retardation layer depending on the position on the lens. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-020360 Summary of the Invention [Problem to be solved by the invention]

[0006] When attempting to realize a retardation layer to be placed on a non-planar lens using a retardation film, if the retardation film is shaped to fit the lens, there is a problem that the retardation of the retardation film disappears or changes significantly due to deformation and stress distortion caused by heating and molding at that time. As a result, the retardation value of the retardation film undesirably deviates from the target value, and a uniform retardation cannot be achieved within the plane.

[0007] In the method of Patent Document 1, an alignment layer and a liquid crystal layer are laminated on a curved lens, and the orientation of the liquid crystal molecules in the liquid crystal layer is aligned by the alignment layer containing molecules with alignment regulating power, thereby forming a two-layer retardation layer consisting of the alignment layer and the liquid crystal layer. The liquid crystal layer is formed so that the thickness of the liquid crystal layer at a predetermined position on the curved lens, which is determined by the directions of the slow axis and fast axis of the liquid crystal layer, satisfies a predetermined condition. However, this method requires complicated processes to form a desired retardation layer, such as a process of forming an alignment film, a process of imparting alignment regulating power to the alignment film, a process of applying and drying a liquid crystal composition to form a liquid crystal layer, and a process of adjusting the thickness of the liquid crystal layer by a dry etching method or the like according to the position on the curved lens. Therefore, optical elements having such retardation layers are expensive to manufacture, and further, since the retardation layer is necessarily composed of multiple layers, it is difficult to make it thin.

[0008] An object of the present invention is to provide an optical element having a retardation layer that can be easily produced and that realizes a uniform retardation by a single layer. [Means for solving the problem]

[0009] In order to achieve the above object, the optical element according to the present invention includes a substrate having a non-planar optical surface, and a retardation layer formed on the optical surface and consisting of a single layer, the retardation layer having a uniform retardation value throughout the layer.

[0010] According to this configuration, an optical element in which a retardation layer having a uniform retardation value is formed on a non-planar optical surface can be realized with a simple structure, and image display quality such as viewing angle, brightness, contrast, etc. can be optimized in a display device using the optical element.

[0011] The optical element may have a configuration that does not have a molecular orientation mechanism for generating a phase difference in the retardation layer.

[0012] According to this configuration, the molecular orientation that generates the phase difference in the retardation layer can be realized without any additional configuration to the optical element, thereby making it possible to realize a non-planar optical element having a uniform retardation layer without requiring any complicated processes.

[0013] In the optical element, the retardation layer may have a thickness of 100 nm to 20,000 nm.

[0014] This configuration allows a desired thickness to be achieved, and a sufficiently thin retardation layer can be provided on the lens surface as required. Note that the thickness of the retardation layer here refers to the thickness in the normal direction of the optical surface on which the retardation layer is disposed.

[0015] In the optical element, the retardation value of the retardation layer may be 100 nm to 400 nm.

[0016] According to this configuration, an ideal phase difference (such as λ / 4; λ is the wavelength of light) can be realized for wavelengths of light in the visible region, thereby further improving the display quality of images displayed via the optical element.

[0017] The optical element may further include a second retardation layer laminated on the retardation layer, and the second retardation layer may be made of a single layer having a uniform retardation value throughout the layer.

[0018] According to this configuration, the optical element includes two retardation layers, namely, a retardation layer formed on the optical surface of the optical element and a second retardation layer formed on the retardation layer, thereby making it possible to more suitably control the retardation properties that the optical element may have.

[0019] In the optical element, the optical axis of the retardation layer and the optical axis of the second retardation layer may not be parallel to each other.

[0020] According to this configuration, by setting the relative angles of the optical axes of the retardation layer and the second retardation layer so as not to be parallel, it is possible to provide the optical element with suitable retardation characteristics, such as reverse wavelength dispersion.

[0021] In the optical element, the substrate may be a resin lens or a glass lens.

[0022] According to this configuration, not only when the substrate is a glass lens, but also when the substrate is a resin lens that has limitations in solvent resistance and processing temperature, a uniform retardation layer can be realized by coating the optical alignment material.

[0023] In the optical element, the optical surface may be convex or concave.

[0024] According to this configuration, the retardation layer can be formed on a non-flat surface regardless of whether the optical element having the retardation layer is a convex lens or a concave lens, and therefore the present invention can be applied to a variety of display devices.

[0025] In the optical element, the substrate may be made of a polymer having no optical anisotropy.

[0026] According to this configuration, even if the substrate itself is made of a material that is not anisotropic, a uniform phase difference can be generated by the phase difference layer. [Effects of the Invention]

[0027] According to the present invention, a retardation layer having a uniform retardation can be provided to an optical element having a non-flat optical surface. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a longitudinal sectional view of an optical element according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a longitudinal sectional view of an optical element according to a second embodiment of the present invention. [Figure 3] 1 is a parallel Nicol image of the optical element produced in Example 1, taken by a polarizing microscope. [Figure 4] 1 is a graph showing the wavelength dependence of in-plane retardation in the optical elements fabricated in Examples 1 and 2. DETAILED DESCRIPTION OF THE INVENTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding components are denoted by the same reference numerals, and their description may be omitted. Furthermore, in the specification, the symbol "to" indicating a range of values ​​means that the values ​​before and after it are included as the lower and upper limits.

[0030] (First embodiment)

[0031] Fig. 1 shows an optical element 10 according to a first embodiment of the present invention. The optical element 10 includes a substrate 11 having a non-planar optical surface 11a, and a retardation layer 12 provided on the optical surface 11a. Note that in Fig. 1 and other figures, the thickness of each layer does not reflect the actual thickness.

[0032] In this embodiment, the substrate 11 is a glass lens having a non-flat, concave optical surface. The material of the substrate 11 is not particularly limited as long as it is a transparent material, and may be inorganic materials such as various types of glass and quartz, or organic materials such as polymethyl methacrylate, polycarbonate, norbornene-based polymers, cellulose-based polymers, or polyester-based polymers. The substrate 11 may also be made of a polymer material that does not have optical anisotropy.

[0033] The optical surface 11a of the substrate 11 is not limited to a concave surface and may be a convex surface. That is, the substrate 11 may be a convex lens. Furthermore, the optical surface 11a may be a non-planar surface, and the substrate 11 is not limited to a concave lens or a convex lens.

[0034] A retardation layer 12 made of a photo-alignable material is provided on the optical surface 11a of the substrate 11 of the optical element 10. By irradiating the retardation layer 12 with polarized light for generating a retardation, molecular orientation of the photo-alignable material can be induced. This allows the retardation layer 12 to have a retardation function, and in particular, to have a substantially uniform retardation function within the layer.

[0035] In the present invention, a photo-alignable material refers to a material that can induce molecular motion by light irradiation (preferably light irradiation and heating / cooling treatment), thereby inducing molecular orientation. Such a photo-alignable material can induce axially selective birefringence in addition to the induction of molecular orientation. Based on this property, the photo-alignable material is also referred to as a birefringence-inducing material hereinafter.

[0036] For example, the birefringence-inducing material may include a liquid crystalline polymer having a photosensitive group and a side chain structure capable of forming a liquid crystal structure, and may have a property in which molecular orientation is induced by a photoreaction of the photosensitive group in the side chain. Examples of the photoreaction include a photodimerization reaction, a photoisomerization reaction, and a photo-Fries rearrangement reaction.

[0037] When a liquid crystalline polymer is capable of forming a liquid crystalline structure, it may exhibit liquid crystalline properties by having a mesogenic group, which is a rigid moiety that exhibits liquid crystalline properties, in its side chain structure, or it may exhibit liquid crystalline properties by having a structure that can form a dimer through hydrogen bonding with another polymer or another side chain of the same polymer, and by forming a mesogenic structure through this dimerization.

[0038] The mesogenic group or mesogenic structure is composed of two or more aromatic or aliphatic rings and a linking group connecting them, and the linking group may be a covalent bond or a hydrogen bond. Examples of aromatic rings include a benzene ring, a naphthalene ring, and heterocycles (for example, oxygen-containing heterocycles such as a furan ring and a pyran ring; nitrogen-containing heterocycles such as a pyrrole ring and an imidazole ring). Examples of aliphatic rings include a cyclohexane ring. These aromatic rings or aliphatic rings may have a substituent, and the substituent may be an alkyl group (for example, C 1-6 Alkyl groups, preferably C 1-4 alkyl groups), alkyloxy groups (e.g., C 1-6 Alkyloxy groups, preferably C 1-4 alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C 1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl groups), halogen atoms, etc. Examples of the linking group, in the case of a covalent bond, include a single bond, -O-, -COO-, -OCO-, -N=N-, -NO=N-, -C=C-, -C≡C-, -CO-C=C-, -CH=N-, an alkylene group, etc. In the case of a hydrogen bond, examples include a side chain structure having a carboxy group at the end, in which case a hydrogen bond is formed between the carboxy groups.

[0039] The photosensitive group is not particularly limited as long as it is a functional group capable of undergoing a photoreaction by light energy, and examples thereof include a chalcone group, a coumarin group, a cinnamoyl group, a cinnamic acid group, a cinnamylidene acetate group, a biphenylacryloyl group, a furyl acryloyl group, a naphthylacryloyl group, an azobenzene group, a benzylideneaniline group, or derivatives thereof, and preferably a cinnamoyl group.

[0040] A liquid crystalline polymer has at least a side chain structure in a repeating unit that has both a photosensitive group and a structure capable of forming a liquid crystal structure, and the photosensitive group may exist independently of the mesogenic group or mesogenic structure in the side chain structure, or may exist in a composite manner by sharing a chemical structure.

[0041] The birefringence inducing material of the present invention may contain a liquid crystalline polymer having at least one structure selected from the group consisting of side chain structures represented by the following formulas (1) and (2).

[0042] [ka]

[0043] (wherein t is an integer of 1 to 3, and R1 is a hydrogen atom, an alkyl group (e.g., C 1-6 Alkyl groups, preferably C 1-4 alkyl groups), alkyloxy groups (e.g., C 1-6 Alkyloxy groups, preferably C 1-4 alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C 1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl groups), and halogen atoms.

[0044] [ka]

[0045] (wherein k is 0 or 1, and when k is 0, l is 0, and when k is 1, l is an integer of 1 to 12; X is a single bond, C 1-3 an alkylene group, -C=C-, -C≡C-, -O-, -N=N-, -COO-, or -OCO-; W is a coumarin group, a cinnamoyl group, a cinnamylidene acetic acid group, a biphenylacryloyl group, a furylacryloyl group, a naphthylacryloyl group, or a derivative group thereof; R2 and R3 are the same or different and each is a hydrogen atom, an alkyl group (e.g., C 1-6 Alkyl groups, preferably C 1-4 alkyl groups), alkyloxy groups (e.g., C 1-6 Alkyloxy groups, preferably C 1-4 alkyloxy groups), alkenyl groups (e.g., C 1-6 Alkenyl groups, preferably C 1-4 alkenyl groups), alkynyl groups (e.g., C 1-6 Alkynyl groups, preferably C 1-4 alkynyl group), a carboxy group, and a halogen atom.

[0046] The side chain structures represented by the above formulas (1) and (2) represent the chemical structures at the ends of the side chains in the repeating units, and various chemical structures may be included between these side chain structures and the main chain structure as long as the effects of the present invention are not impaired.

[0047] The liquid crystalline polymer may be a homopolymer consisting of the same repeating units having the above side chain structure, or a copolymer containing repeating units having a different side chain structure in addition to the repeating units having the above side chain structure. Examples of the main chain structure include structures formed by polymerization of hydrocarbons, acrylates, methacrylates, siloxanes, maleimides, N-phenylmaleimides, etc.

[0048] When the liquid crystalline polymer is a copolymer, it may have a repeating unit that does not have a photosensitive group and / or a structure capable of forming a liquid crystal structure.

[0049] The birefringence-inducing material of the present invention may contain a low-molecular-weight compound together with the liquid-crystalline polymer to promote the alignment of the side chains of the liquid-crystalline polymer. The low-molecular-weight compound preferably has a substituent known as a mesogenic component, such as biphenyl, terphenyl, phenylbenzoate, or azobenzene, and is liquid-crystalline, having such a substituent and a functional group, such as allyl, acrylate, methacrylate, or cinnamic acid group (or a derivative thereof), bonded via a spacer (e.g., an (oxy)alkylene group having 1 to 15 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 5 carbon atoms)). These low-molecular-weight compounds may be used alone or in combination.

[0050] The retardation layer 12 is formed by coating the substrate 11. In this case, the birefringence-inducing material described above is dissolved in a solvent to form a solution, and this solution is then coated onto the substrate. The solvent can be appropriately selected depending on the type of birefringence-inducing material, and examples thereof include dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol derivatives (e.g., ethylene glycol monoethyl ether, diethylene glycol monoethyl ether, etc.), and propylene glycol derivatives (e.g., propylene glycol monomethyl ether, propylene glycol 1-monomethyl ether 2-acetate, etc.). These solvents may be used alone or in combination. The concentration of the solvent is not particularly limited, but may be, for example, 5 to 50 wt % of the birefringence-inducing material, preferably 8 to 40 wt %, and more preferably 10 to 25 wt %. The solution can be applied to the substrate by a known coating method, such as spin coating or roll coating.

[0051] After coating, the coating film may be dried by heating as necessary. To make the coating film uniform in thickness, the concentration of the coating solution may be adjusted, and the orientation or posture of the substrate may be changed over time during the drying process depending on the viscosity of the solution whose concentration has been adjusted.

[0052] Next, polarized light for expressing retardation is irradiated onto the retardation layer 12. This causes a selective photoreaction of molecules on the surface and inside of the retardation layer 12, inducing molecular orientation. In the optical element 10 according to this embodiment, polarized light can be directly irradiated onto the retardation layer 12 without passing through another layer, and therefore the irradiated polarized light can induce molecular orientation so as to have an intended retardation value.

[0053] The polarized light irradiated onto the retardation layer 12 is not particularly limited as long as it is light of a wavelength that causes a photoreaction of the photosensitive group of the liquid crystalline polymer, such as infrared light, visible light, ultraviolet light (e.g., near ultraviolet light, far ultraviolet light, etc.), X-rays, or charged particle beams (e.g., electron beams, etc.), and although it varies depending on the type of side chain structure of the liquid crystalline polymer, the wavelength of the light may be 200 to 500 nm. The polarized light irradiated may be, for example, linearly polarized ultraviolet light, and in this case, for example, the light may be converted into linearly polarized light via a Glan-Taylor prism using an ultraviolet irradiation device such as a high-pressure mercury lamp as a light source. The amount of irradiation of polarized light is set to, for example, 10 mJ / cm from the viewpoint of aligning not only the surface but also the interior of the retardation layer. 2 ~10J / cm 2 and preferably 50 mJ / cm 2 ~1J / cm 2 , more preferably 100 mJ / cm 2 ~500mJ / cm 2 may be.

[0054] The polarized light irradiated onto the retardation layer 12 may have a parallel propagation direction, i.e., a vertical propagation direction in FIG. 1. Alternatively, the direction of the light path of such parallel irradiation light may be changed by a lens arranged on the irradiation light path so that the irradiation direction differs at each position on the non-planar optical surface 11a. When the retardation layer 12 is formed on the concavely curved optical surface 11a as shown in FIG. 1, by arranging an upwardly convex lens on the light-incident side of the retardation layer 12 in FIG. 1, polarized light having a propagation direction approximately parallel to the normal direction can be irradiated at each position on the optical surface 11a. This makes it possible to achieve a retardation layer 12 with a more uniform in-plane retardation value.

[0055] The process of forming the retardation layer 12 may, if necessary, include a heating step of heating the formed retardation layer after the polarized light irradiation step. Molecular orientation is induced depending on the irradiation direction and vibration direction of the polarized light irradiated in the polarized light irradiation step, and unoriented molecules are also oriented according to the oriented molecules. Subsequent heating allows the liquid crystalline polymer to undergo molecular motion, thereby promoting the orientation of the unoriented molecules. After heating, the liquid crystalline polymer may be cooled to about room temperature, for example, by leaving it to stand.

[0056] The heating temperature in the heating step is not particularly limited as long as the orientation of unoriented molecules is induced along the side chains that have undergone a photoreaction due to molecular motion of the liquid crystalline polymer, but it is preferably set to a temperature equal to or higher than the liquid crystal phase transition temperature and lower than the isotropic phase transition temperature of the birefringence-inducing material. For example, the temperature may be 100 to 200°C, preferably 110 to 180°C, and more preferably 120 to 160°C.

[0057] The heating time is not particularly limited as long as the orientation of unoriented molecules is induced along the side chains that have undergone a photoreaction due to molecular motion of the liquid crystalline polymer, but can be appropriately set depending on the type of liquid crystalline polymer, heating temperature, etc. For example, the heating time may be 1 minute or more, preferably 3 minutes or more, and more preferably 5 minutes or more. The upper limit is not particularly limited, but from an economical viewpoint, it may be about 60 minutes (preferably about 40 minutes, more preferably about 30 minutes).

[0058] The retardation layer 12 formed in this manner has a substantially uniform intralayer retardation, and the retardation value Re (550 nm) can be 100 nm to 440 nm. Furthermore, the optical element 10 having the retardation layer 12 does not have a separate alignment layer for inducing molecular alignment in the liquid crystal molecules to exhibit retardation, and the retardation function can be achieved by the single layer retardation layer 12. Such a single retardation layer formed by coating can have a thickness of 100 nm to 20,000 nm, thereby enabling a thin optical system. Furthermore, compared to optical elements in which a retardation layer is formed by providing a liquid crystal layer made of, for example, a polymerizable liquid crystal on an alignment layer such as an alignment film and then aligning the liquid crystal molecules, the optical element can be manufactured easily and at low manufacturing costs because it does not require complicated processes. Furthermore, according to the optical element 10 of this embodiment, the retardation layer 12 is formed directly on the substrate 11, and therefore an adhesive layer is not required, as compared to when a retardation film is attached. Therefore, optical design can be performed without considering an adhesive layer, and this can also contribute to thinner devices.

[0059] (Second embodiment) FIG. 2 shows an optical element 20 according to a second embodiment of the present invention. The optical element 20 includes a substrate 21 having a non-planar optical surface 21a, a retardation layer 22 provided on the optical surface 21a, and a second retardation layer 24 provided on the retardation layer 22. The optical element 20 of this embodiment differs from the optical element 10 of the first embodiment in that it includes the second retardation layer 24. The optical element 20 of this embodiment can also be realized by further forming the second retardation layer 24 on the retardation layer 12 of the optical element 10 of the first embodiment. Hereinafter, the retardation layer 22 on which the second retardation layer 24 is laminated will also be referred to as the first retardation layer 22 to clearly distinguish it from the second retardation layer 24.

[0060] The materials and steps for forming the first retardation layer 22 are the same as those for the retardation layer 12 in the first embodiment. In this embodiment, when a crosslinking agent is contained in the polymerizable liquid crystal material, the birefringence-inducing material used to prepare the first retardation layer 22 may contain a liquid crystalline polymer having a side chain structure with a crosslinkable functional group, from the viewpoint of improving adhesion between the first retardation layer 22 and the second retardation layer 24. The crosslinkable functional group is not particularly limited as long as it is a functional group that undergoes a crosslinking reaction with the crosslinking agent described below, and examples thereof include a hydroxyl group, a carboxyl group, an amino group, and a thiol group. The side chain structure with the crosslinkable functional group may be contained in a repeating unit that has the above-mentioned photosensitive group and a side chain structure capable of forming a liquid crystal structure, or the crosslinkable functional group may be contained in a repeating unit other than the repeating unit.

[0061] For example, a hydroxyl group or a carboxyl group is preferable as the crosslinkable functional group, and the liquid crystalline polymer has a side chain structure having a crosslinkable functional group, such as -(CH2) n It may have at least one structure selected from the group consisting of -OH (wherein n is an integer of 1 to 6) and -Ph-COOH (wherein Ph is a divalent phenyl group). These side chain structures represent at least a part of the chemical structure of the side chain in the repeating unit, and various chemical structures may be included between these side chain structures and the main chain structure as long as the effects of the present invention are not impaired.

[0062] The second retardation layer 24 is formed using generally the same materials and processes as the first retardation layer 22. The thickness of the second retardation layer 24 may be the same as or different from the thickness of the first retardation layer 22. In the polarized light irradiation step for forming the second retardation layer 24, the first retardation layer 22 and the second retardation layer 24 may have optical axes in different directions, i.e., non-parallel directions, by irradiating the first retardation layer 22 with polarized light having a polarization direction different from that of the polarized light irradiated on the first retardation layer 22. This allows the combination of the first retardation layer 22 and the second retardation layer 24 to have reverse wavelength dispersion retardation characteristics for incident light having a wide wavelength range. [Example]

[0063] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0064] (Monomer 1) 4-(6-hydroxyhexyloxy)cinnamic acid was synthesized by heating p-coumaric acid and 6-chloro-1-hexanol under alkaline conditions. This product was esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize Monomer 1, shown in the following chemical formula.

[0065] [ka]

[0066] (Monomer 2) 4-Hydroxybenzoic acid and 6-chloro-1-hexanol were heated under alkaline conditions to synthesize 4-(6-hydroxyhexyloxy)benzoic acid. Next, this product was esterified with a large excess of methacrylic acid in the presence of p-toluenesulfonic acid to synthesize Monomer 2, which is shown in the following chemical formula.

[0067] [ka]

[0068] (Copolymer 1) Monomer 1 and monomer 2 were dissolved in dioxane so that the molar ratio of monomer 1 to monomer 2 was 3:7, and AIBN (azobisisobutyronitrile) was added as a reaction initiator. The mixture was polymerized at 70°C for 24 hours to obtain copolymer 1. This copolymer 1 exhibited liquid crystallinity.

[0069] In the following examples and comparative examples, the optical properties (retardation value Re, etc.) of the obtained optical laminates were measured using a birefringence measuring device (AxoScan, manufactured by AXOMETRICS), and the thickness was measured using a film thickness meter (F20, manufactured by FILMETRICS).

[0070] Example 1 Copolymer 1 was dissolved at 25 wt % in a solvent of diglyme:dimethoxyethane = 2.5:1. This solution was applied to the concave optical surface of a concave lens using a spin coater to a thickness of 4.3 μm and dried at 25 °C. After drying, the coating film was irradiated with polarized light, which was obtained by converting ultraviolet light from a high-pressure mercury lamp into linearly polarized light using a Glan-Taylor prism, at a dose of 500 mJ / cm from a direction parallel to the normal direction at the center of gravity of the concave optical surface. 2 The layer was irradiated with light, then heated at 130°C for 15 minutes, and cooled to room temperature to induce orientation, thereby forming a retardation layer by developing a retardation in the layer made of the coating film. By this method, the optical element of the present invention was obtained.

[0071] The retardation layer of the obtained optical element had an in-plane retardation value of 140.5 nm @ 550 nm. Figure 3 shows a parallel Nicol image of the above optical element taken by a polarizing microscope. As shown in Figure 3, it was confirmed that the transmitted light intensity was approximately uniform over the entire optical surface, and this confirmed that the retardation layer formed on the optical element produced in this example had a uniform retardation over the entire non-planar optical surface.

[0072] Example 2 Further, a solution prepared by dissolving Copolymer 1 at 25 wt % in a solvent of diglyme:dimethoxyethane=2.5:1 was applied to the optical element obtained by the method of Example 1 onto the retardation layer (first retardation layer) formed on the optical element using a spin coater to a thickness of 8.7 μm, and then dried at 25° C. The dried coating film was irradiated with ultraviolet light from a high-pressure mercury lamp using a Glan-Taylor prism into linearly polarized light whose polarization axis direction was 30° different from the polarization axis direction of the polarized light irradiated in Example 1 at an irradiation dose of 500 mJ / cm from a direction parallel to the normal direction at the center of gravity of the concave optical surface. 2The layer was irradiated with polarized light, then heated at 130°C for 15 minutes and cooled to room temperature to induce orientation, thereby forming a second retardation layer. This method resulted in the optical element of the present invention. Since the polarized light irradiated when forming the first retardation layer and the second retardation layer had different polarization axis directions, these retardation layers have non-parallel optical axes.

[0073] FIG. 4 shows the in-plane retardation for each wavelength in the visible light range (450 to 650 nm) for Examples 1 and 2. Here, the incident light is polarized light having a polarization axis that forms a 45° angle with the optical axis direction of the retardation layer for the sample of Example 1, and polarized light having a polarization axis that forms a 20° angle with the optical axis direction of the second retardation layer for the sample of Example 2. While the sample of Example 1 exhibits forward wavelength dispersion at the measurement wavelength, the sample of Example 2 exhibits a smaller retardation value for the light at shorter measurement wavelengths, confirming that it has reverse wavelength dispersion. Furthermore, it was confirmed that the sample has retardation characteristics that are close to λ / 4.

[0074] (Third embodiment) The optical element according to the present invention is not limited in its application to the pancake optical system of a head-mounted display, which was exemplified above as background art, but can be widely used in optical elements having non-flat optical surfaces.

[0075] For example, in an optical element used in a projector that projects an image, a retardation layer may be provided on the surface of a lens, and a retardation may be set so as to cancel the polarization of light from the lens.

[0076] In projectors that use a polarized laser as a light source, bias in the light quantity distribution of the projected image can occur in the light source unit that excites the phosphor and in the illumination optical system, resulting in uneven brightness and color. In conventional technology, the use of a depolarizing element can improve this bias in the light quantity distribution and color unevenness. By applying the optical element of the present invention to a curved lens for such a projector, a separate depolarizing element is no longer necessary, allowing for device miniaturization and reduced manufacturing costs.

[0077] To realize such an optical element, the retardation layer may have a lattice-like optical structure in which substantially linear portions whose optical axes are in a fixed direction are periodically arranged at equal intervals, and the optical axes in the portions between the linear portions are continuously rotated toward the direction of the lattice vector of the lattice-like structure. Specifically, in the step of irradiating the retardation layer with polarized ultraviolet light to induce orientation, the ultraviolet light is irradiated with right-handed circularly polarized light and left-handed circularly polarized light, and the orientation generated by the interference exposure of the two beams is fixed, so that the retardation layer has an optical anisotropy structure in which the optical axis of the retardation layer continuously rotates toward the lattice vector direction, and also has a uniform magnitude of birefringence.

[0078] A specific method for realizing such a retardation layer will be described below. Copolymer 1 and cinnamic acid were dissolved in tetrahydrofuran (THF) in a weight ratio of 95:5 to prepare a solution. This solution was applied to the substrate of an optical element using a spin coater to a thickness of 3 μm and dried at 25°C. After drying, the coating film was subjected to interference exposure (irradiation dose 200 mJ / cm) using an interference exposure optical system with 360 nm ultraviolet laser light emitted from a DPSS laser used as a light source, as left-circularly polarized light and right-circularly polarized light. 2) was then heated at 130°C for 3 minutes and cooled to room temperature to induce alignment. This alignment occurs when axially selective photoreacted side chains are generated in the coating film in accordance with the polarization direction of the light exposed to each region by interference exposure, and the unreacted side chains are aligned along the reacted side chains due to subsequent molecular motion caused by heating. The coating film thus obtained is aligned so that the optical axis continuously rotates toward the lattice vector direction. This method resulted in the production of the optical element of the present invention.

[0079] It should be noted that any method other than those described above can be used as long as it is a method for imparting periodic alignment to a liquid crystalline material exhibiting photoalignment.

[0080] The retardation layer formed on the non-planar optical surface of the substrate may be formed by molding an annealed retardation film onto the optical surface instead of by irradiating a photo-alignment material with polarized ultraviolet light.

[0081] As described above, when a retardation layer is to be formed on a non-planar lens using a retardation film, if a stretched retardation film is formed to fit the lens and attached, the retardation of the retardation film disappears or changes significantly due to deformation and stress distortion caused by heating and forming at that time. This causes an undesirable deviation of the retardation value of the retardation film from a target value, and there is a problem that a uniform retardation cannot be achieved within the plane.

[0082] To address this issue, we investigated the use of retardation films for molding, such as films with fixed molecular orientation of polymerizable liquid crystals or films with fixed orientation of photosensitive birefringence-inducing materials. Although these molding films did not eliminate the retardation, they did not solve the problem of decreased retardation. Furthermore, we attempted to prevent the decrease in retardation that occurs during molding and heating by subjecting the retardation film to heat treatment after it was formed on a glass substrate or PET film base. However, the decrease in retardation was still observed during film molding.

[0083] As a method for solving this problem, the applicant has found that by annealing a retardation film having a retardation at a predetermined temperature and time before shaping and molding it onto a non-flat optical surface, the retardation is not lost or reduced when the retardation film is subsequently shaped and molded to form a retardation layer on the optical surface.

[0084] (Example of Annealing Treatment of Retardation Film) A specific example of the annealing treatment of the retardation film will be described below. 1. Preparation of retardation film First, a retardation film having a phase difference is produced. This retardation film is produced by applying a PGM (propylene glycol monomethyl ether) solution containing 3 wt% of a photoalignment agent (manufactured by Hayashi Telempu: 750025) onto a glass substrate and irradiating it with polarized ultraviolet light (20 mJ / cm). 2 ), and then a PGMEA (propylene glycol 1-monomethyl ether 2-acetate) solution containing 19 wt% of a polymerizable liquid crystal compound (BASF Japan's "Paliocolor LC242") and 1 wt% of a photopolymerization initiator (Ciba Specialty Chemicals' "Irgacure 907") was applied thereon, heated to 90°C and cooled to room temperature to induce alignment, and then irradiated with unpolarized ultraviolet light (200 mJ / cm 2 ) to cause a crosslinking reaction of a polymerizable liquid crystal compound. The in-plane retardation value of the retardation film thus prepared was 150 nm@550 nm.

[0085] 2. Preparation of retardation film Next, the retardation film was transferred onto a triacetyl cellulose film (TAC film). Furthermore, an adhesive with a separator was attached to the retardation film, and the film was sandwiched between the adhesive and the TAC film.

[0086] 3. Annealing Annealing was carried out by heating for 10 minutes in this thermostatic bath at 120° C. In this state, the retardation value of the film was measured and found to be 136 nm@550 nm.

[0087] 4. Molding onto non-planar optical surfaces After removing the separator from the retardation film prepared as described above, it was formed onto an R50 spherical lens by pressure forming and attached to it. The retardation value of the retardation film formed onto the lens was approximately 136 nm @ 550 nm at any point within the formed surface, and it was confirmed that the retardation before forming and molding was maintained.

[0088] (Comparative Example) A film was produced that differed from the above-mentioned example of the annealing treatment of the retardation film by excluding the annealing treatment. When this film was formed onto an R50 spherical lens by pressure molding and attached to the lens, a decrease in retardation was observed and there was also a large in-plane variation. This shows that, in order to realize the formation of a uniform retardation layer on the non-flat optical surface of the optical element, it is important to perform the annealing treatment among the steps included in the examples.

[0089] In the above examples, a liquid crystal alignment film in which molecular alignment was induced by ultraviolet irradiation was used, but molecular alignment may also be induced in the molecules constituting the film by other methods, for example, an alignment film may be formed by rubbing.

[0090] Although the embodiments of the present invention have been described above, the disclosed embodiments are illustrative in all respects and are not limiting. The scope of the present invention is defined by the claims rather than the above description, and it is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0091] 10,20 Optical elements 11,21 Base material 12,22 Retardation layer (first retardation layer) 24 Second retardation layer

Claims

1. a substrate having a non-planar optical surface; a retardation layer formed on the optical surface and having a uniform retardation value throughout the layer, the retardation layer being composed of a single layer; An optical element having

2. 2. The optical element according to claim 1, The optical element does not have a molecular orientation mechanism for generating a phase difference in the retardation layer.

3. 2. The optical element according to claim 1, The optical element has a thickness of the retardation layer of 100 nm to 20,000 nm.

4. 2. The optical element according to claim 1, The optical element has a retardation value of the retardation layer of 100 nm to 400 nm.

5. The optical element according to claim 1 , further comprising: An optical element comprising a second retardation layer laminated on the retardation layer, the second retardation layer being a single layer having a uniform retardation value throughout the layer.

6. 6. The optical element according to claim 5, an optical axis of the retardation layer and an optical axis of the second retardation layer are not parallel to each other.

7. 2. The optical element according to claim 1, wherein the substrate is a resin lens or a glass lens.

8. 2. The optical element according to claim 1, The optical element, wherein the optical surface is convex or concave.

9. 2. The optical element according to claim 1, The optical element, wherein the substrate is made of a polymer having no optical anisotropy.

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