Holographic optical element, and production method therefor

Abstract

To provide a holographic optical element and production method for the holographic optical element that use a retardation layer to prevent an unwanted interference pattern.SOLUTION: The present invention relates to a holographic optical element, and a production method for the holographic optical element, and, particularly, to a holographic optical element, and a production method for the holographic optical element that use a retardation layer so as to prevent an unwanted interference pattern from being formed in the process of recording the interference pattern in a photopolymer resin layer.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention claims the benefit of the filing date of Korean Patent Application No. 10-2020-0117902, filed with the Korean Intellectual Property Office on September 14, 2020, the entire contents of which are incorporated herein by reference. The present invention relates to a holographic optical element and a manufacturing method thereof, and more particularly to a holographic optical element using a retardation layer to prevent the formation of an undesired interference pattern that occurs in the process of recording an interference pattern in a photopolymer resin layer, and a manufacturing method thereof. [Background technology]

[0002] Generally, hologram is a technology that records an interference pattern between an object wave containing image information and a reference wave on a photosensitive material using a coherent light source, and reproduces the image information recorded on the photosensitive material by irradiating the reference wave used for recording on the photosensitive material with the interference pattern recorded. Since the photosensitive material with the interference pattern reproduces image information using diffraction instead of reflection or refraction, such photosensitive material is classified as a type of diffraction optical elements (DOEs).

[0003] Fig. 1 is a schematic diagram of an interference pattern recording of a holographic optical element according to the prior art. It is common to irradiate a holographic optical element with a reference beam, which is a first parallel laser beam L1, and an object beam, which is a second parallel laser beam L2, and record an interference pattern P realized by the interference phenomenon between the reference beam and the object beam. However, in order to enhance the interference phenomenon between the reference beam and the object beam, it is preferable to change the light into linearly polarized light to enhance the interference phenomenon.

[0004] Specifically, by changing all of the reference light and all of the object light to P waves (horizontally polarized light) or all of the reference light and all of the object light to S waves (vertically polarized light), the constructive interference caused by the mutual interference phenomenon is realized more strongly, and the destructive interference pattern is realized weaker, resulting in a clear interference pattern.

[0005] However, when the reference light or object light travels from a photopolymer resin layer with a high refractive index toward an air layer with a low refractive index, a problem of total reflection occurs. As described above, the totally reflected light and other light cause interference again, resulting in an undesired interference pattern. This reduces the diffraction efficiency of the holographic optical element, and at the same time, when a reproducing light is irradiated and diffracted, it is reproduced at an angle that was not recorded.

[0006] 2 is a schematic diagram showing a process of recording an undesired interference pattern P' in a holographic optical element according to the prior art. Referring to FIG. 2, a reference light, which is a first parallel laser light L1 polarized to an S wave, is irradiated to a holographic optical element through a prism 13 having a refractive index of 1.5, and the reference light is incident on a photopolymer resin layer 11 having a refractive index of 1.5. At the same time, an object light, which is a second parallel laser light L2 polarized to an S wave, is irradiated to record an interference pattern P between the reference light and the object light. When the reference light, which is the first parallel laser light L1 polarized to an S wave, travels from the photopolymer resin layer 11 having a refractive index of 1.5 to the air layer having a refractive index of 1, total reflection occurs at the interface between the photopolymer resin layer 11 and the air, and the totally reflected reference light causes an interference phenomenon with the object light again, forming an undesired interference pattern P'.

[0007] As described above, the unwanted interference pattern P' reduces the diffraction efficiency of the holographic optical element, and at the same time, when a reproducing light is irradiated, there is a problem that the pattern is reproduced at an angle that was not recorded. Therefore, there is an urgent need for technological development to solve these problems. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem to be solved by the present invention is to provide a holographic optical element that uses a retardation layer to eliminate undesired interference patterns, and a method for manufacturing the same.

[0009] However, the problems to be solved by the present invention are not limited to those mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the following description. [Means for solving the problem]

[0010] One embodiment of the present invention provides a method for manufacturing a holographic optical element, the method including the steps of providing a retardation layer on one side of a photopolymer resin layer containing a photopolymer resin, and irradiating another side of the photopolymer resin layer, which is the side not provided with the retardation layer, with a first parallel laser light and irradiating the one side of the photopolymer resin layer with a second parallel laser light to record an interference pattern due to an interference phenomenon between the first parallel laser light and the second parallel laser light in the photopolymer resin layer.

[0011] According to an embodiment of the present invention, an incident angle of the first parallel laser beam irradiated onto the photopolymer resin layer may be greater than 42° and less than 90°.

[0012] According to one embodiment of the present invention, the first collimated laser light may be linearly polarized, and the second collimated laser light may be circularly polarized or elliptically polarized.

[0013] According to one embodiment of the present invention, the retardation layer may have a λ / 4 wavelength phase retardation characteristic.

[0014] According to one embodiment of the present invention, a prism may be further provided on the other surface of the photopolymer resin layer.

[0015] According to one embodiment of the present invention, the retardation layer may have a light transmittance of more than 90% and not more than 100%, and the retardation layer may have a haze of more than 0% and less than 1%.

[0016] According to one embodiment of the present invention, the retardation layer may convert circularly polarized light or elliptically polarized light into linearly polarized light.

[0017] According to one embodiment of the present invention, the method may further include a step of removing the retardation layer from the photopolymer resin layer on which the interference pattern is recorded.

[0018] According to an embodiment of the present invention, the method may further include a step of bleaching the photopolymer resin layer on which the interference pattern is recorded by irradiating the photopolymer resin layer with light having a wavelength in the visible to ultraviolet region.

[0019] One embodiment of the present invention provides a holographic optical element comprising a photopolymer resin layer containing a photopolymer resin and a retardation layer provided on one side of the photopolymer resin layer, the photopolymer resin layer having an interference pattern recorded thereon due to an optical interference phenomenon, the photopolymer resin layer having a transmittance of more than 0% and not more than 70%, or more than 90% and not more than 100%, for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to another side of the photopolymer resin layer, which is a side not provided with the retardation layer.

[0020] According to one embodiment of the present invention, the retardation layer may have a λ / 4 wavelength phase retardation characteristic.

[0021] According to one embodiment of the present invention, the retardation layer may have a light transmittance of more than 90% and not more than 100%, and the retardation layer may have a haze of more than 0% and less than 1%.

[0022] According to one embodiment of the present invention, the interference pattern may be caused by an interference phenomenon between the first parallel laser light irradiated onto another surface of the photopolymer resin layer and the second parallel laser light irradiated onto one surface of the photopolymer resin layer. Effect of the Invention

[0023] The method for producing a holographic optical element according to one embodiment of the present invention can eliminate undesired interference patterns in a simple manner.

[0024] A holographic optical element, which is an embodiment of the present invention, can minimize unwanted interference patterns, clarify the recorded interference patterns, and at the same time improve diffraction efficiency.

[0025] The effects of the present invention are not limited to those described above, and effects not mentioned will be clearly understood by those skilled in the art from the present specification and the accompanying drawings. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic diagram of an interference pattern recording in a holographic optical element according to the prior art. [Diagram 2] 1 is a schematic diagram illustrating how an unwanted interference pattern is recorded in a holographic optical element according to the prior art; [Diagram 3] FIG. 2 is a schematic diagram of an interference pattern recording in a holographic optical element according to one embodiment of the present invention. [Figure 4] 2 is a schematic diagram illustrating a process for removing unwanted interference patterns in a holographic optical element according to one embodiment of the present invention. FIG. [Diagram 5] 1 is a graph showing the light transmittance of Reference Examples 1 and 2 for light having a wavelength of 400 nm to 1600 nm. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Throughout this specification, when a part is described as "comprising" a certain element, this means that it can further include other elements, but not to the exclusion of other elements, unless specifically stated to the contrary.

[0028] Throughout this specification, when an element is said to be "on" another element, this includes not only when the element is in contact with the other element, but also when there is another element between the two elements.

[0029] Throughout this specification, the unit "parts by weight" can refer to the weight ratio between each component.

[0030] Throughout this specification, "(meth)acrylate" is used generically to refer to acrylate and methacrylate.

[0031] Throughout this specification, "A and / or B" means "A and B, or A or B."

[0032] Throughout this specification, the term "monomer unit" may refer to a form in which a monomer is reacted within a polymer, specifically, a form in which the monomer undergoes a polymerization reaction to form the backbone of the polymer, for example, the main chain or a side chain.

[0033] Throughout this specification, "interference pattern" refers to a pattern formed by the phenomenon of interference between two or more beams of light.

[0034] Throughout this specification, the term "incidence angle" means the angle between an imaginary perpendicular line to the plane on which light is incident and an imaginary straight line in the direction in which light travels at the moment the light enters the incident surface, i.e., the angle between the normal to the incident plane and an imaginary straight line in the direction in which light travels at the moment the light enters the incident plane.

[0035] Throughout this specification, the term "illumination angle" refers to the angle between an imaginary line in the direction in which light is irradiated and travels and an imaginary line perpendicular to the illuminated surface.

[0036] The present invention will now be described in further detail.

[0037] One embodiment of the present invention provides a method for manufacturing a holographic optical element, the method including the steps of providing a retardation layer on one side of a photopolymer resin layer containing a photopolymer resin, and irradiating another side of the photopolymer resin layer, which is the side not provided with the retardation layer, with a first parallel laser light and irradiating the one side of the photopolymer resin layer with a second parallel laser light to record an interference pattern due to an interference phenomenon between the first parallel laser light and the second parallel laser light in the photopolymer resin layer.

[0038] The method for producing a holographic optical element according to one embodiment of the present invention can eliminate undesired interference patterns in a simple manner.

[0039] According to one embodiment of the present invention, the method includes providing a retardation layer on one side of the photopolymer resin layer containing the photopolymer resin. As described above, by providing a retardation layer on one side of the photopolymer resin layer containing the photopolymer resin, it is possible to minimize the occurrence of undesired interference patterns occurring during the process of recording the interference pattern and improve the diffraction efficiency.

[0040] According to one embodiment of the present invention, the photopolymer resin layer includes a photopolymer resin. As described above, the photopolymer resin layer includes a photopolymer resin, so that an interference pattern generated by an interference phenomenon between the first parallel laser beam and the second parallel laser beam can be effectively recorded.

[0041] According to one embodiment of the present invention, the photopolymer resin can include a polymer of a photopolymer composition including a photoreactive monomer and a photoinitiator. As described above, the photopolymer composition including a photoreactive monomer and a photoinitiator can be used to realize the basic physical properties of a photopolymer resin, and at the same time, a pattern can be formed in the photopolymer resin layer by irradiating light.

[0042] According to one embodiment of the present invention, the photoreactive monomer may include a polyfunctional (meth)acrylate monomer or a monofunctional (meth)acrylate monomer. As described above, the monomer is polymerized during the photopolymerization process of the photopolymer composition, and the refractive index becomes high in the area where the polymer is relatively abundant, and the refractive index becomes relatively low in the other area, resulting in a refractive index modulation, which generates a diffraction grating, i.e., an interference pattern.

[0043] According to one embodiment of the present invention, the photoreactive monomer may be a (meth)acrylate-based α,β-unsaturated carboxylic acid derivative, more specifically, (meth)acrylate, (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid, or a compound containing a vinyl group or a thiol group.

[0044] According to one embodiment of the present invention, the photoreactive monomer may be a multifunctional (meth)acrylate monomer having a refractive index of 1.5 or more, and the multifunctional (meth)acrylate monomer having a refractive index of 1.5 or more may include a halogen atom (bromine, iodine, etc.), sulfur (S), phosphorus (P), or an aromatic ring.

[0045] According to one embodiment of the present invention, the polyfunctional (meth)acrylate monomer having a refractive index of 1.5 or more may be a bisphenol A modified diacrylate, a fluorene acrylate, a bisphenol fluorene epoxy acrylate (HR6100, HR6060, HR6042, etc., manufactured by Miwon), or a halogenated epoxy acrylate (HR1139, HR3362, etc., manufactured by Miwon).

[0046] According to one embodiment of the present invention, the photoreactive monomer may be a monofunctional (meth)acrylate monomer. The monofunctional (meth)acrylate monomer may contain an ether bond and a fluorene functional group inside the molecule, and specific examples of such a monofunctional (meth)acrylate monomer include phenoxybenzyl (meth)acrylate, o-phenylphenol ethylene oxide (meth)acrylate, benzyl (meth)acrylate, 2-(phenylthio)ethyl (meth)acrylate, or biphenyl methyl (meth)acrylate.

[0047] According to one embodiment of the present invention, the photoreactive monomer may have a molecular weight of 50 g / mol to 1000 g / mol, or 200 g / mol to 600 g / mol.

[0048] According to one embodiment of the invention, the photopolymer composition includes a photoinitiator, which is a compound that is activated by light or actinic radiation as described above, to initiate polymerization of compounds that include photoreactive functional groups, such as the photoreactive monomers.

[0049] According to one embodiment of the present invention, the photoinitiator includes a photoradical polymerization initiator and a photocationic polymerization initiator.

[0050] According to one embodiment of the present invention, the photoradical polymerization initiator may be an imidazole derivative, a bisimidazole derivative, an N-arylglycine derivative, an organic azide compound, a titanocene, an aluminate complex, an organic peroxide, an N-alkoxypyridinium salt, a thioxanthone derivative, etc. Specifically, the photoradical polymerization initiator may be 1,3-di(t-butyldioxycarbonyl)benzophenone, 3,3',4,4'-tetrakis(t-butyldioxycarbonyl)benzophenone, 3-phenyl-5-isoxazolone, 2-mercapto These include benzimidazole, bis(2,4,5-triphenyl)imidazole, 2,2-dimethoxy-1,2-diphenylethane-1-one (product name: Irgacure 651 / manufacturer: BASF), 1-hydroxy-cyclohexyl-phenyl-ketone (product name: Irgacure 184 / manufacturer: BASF), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 (product name: Irgacure 369 / manufacturer: BASF), and bis(η5-2,4-cyclopentadiene-1-yl)-bis(2,6-difluoro-3-(1H-pyrrole-1-yl)-phenyl)titanium (product name: Irgacure 784 / manufacturer: BASF).

[0051] According to one embodiment of the present invention, the photocationic polymerization initiator may be a diazonium salt, a sulfonium salt, or an iodonium salt, such as a sulfonic acid ester, an imide sulfonate, a dialkyl-4-hydroxysulfonium salt, an arylsulfonic acid-p-nitrobenzyl ester, a silanol-aluminum complex, (η6-benzene)(η5-cyclopentadienyl)iron(II), etc. In addition, benzoin tosylate, 2,5-dinitrobenzyl tosylate, N-tosylphthalimide, etc. may also be used. Further specific examples of the photocationic polymerization initiator include commercially available products such as Cyracure UVI-6970, Cyracure UVI-6974 and Cyracure UVI-6990 (manufacturer: Dow Chemical Co. in USA), Irgacure 264 and Irgacure 250 (manufacturer: BASF), or CIT-1682 (manufacturer: Nippon Soda).

[0052] According to one embodiment of the present invention, the photopolymer composition may use unimolecular (type I) or bimolecular (type II) initiators. The unimolecular (type I) initiators for the free radical photopolymerization are aromatic ketone compounds in combination with tertiary amines, such as benzophenone, alkylbenzophenones, 4,4'-bis(dimethylamino)benzophenone (Michler's ketone), anthrone and halogenated benzophenones, or mixtures of the above types. The bimolecular (type II) initiators include benzoin and its derivatives, benzil ketals, acylphosphine oxides, such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bisacylphosphine oxides, phenylglyoxyl esters, camphorquinone, alpha-aminoalkylphenones, alpha-, alpha-dialkoxyacetophenones, 1-[4-(phenylthio)phenyl]octane-1,2-dione 2-(O-benzoyloxime), and alpha-hydroxyalkylphenones.

[0053] According to one embodiment of the present invention, the photopolymer composition may contain 10% by weight or more and 70% by weight or less of the photoreactive monomer and 0.1% by weight or more and 15% by weight or less of a photoinitiator, or may contain 20% by weight or more and 60% by weight or less of the photoreactive monomer and 0.1% by weight or more and 10% by weight or less of a photoinitiator. As described below, when the photopolymer composition further contains an organic solvent, the content of the above-mentioned components is based on the sum of these components (the sum of the components excluding the organic solvent).

[0054] According to one embodiment of the present invention, the photopolymer composition may further include a light-sensitive dye. The light-sensitive dye serves as a sensitizing dye that sensitizes the photoinitiator. Specifically, the light-sensitive dye may also serve as an initiator that is stimulated by light irradiated to the photopolymer composition to initiate polymerization of the monomer and the crosslinking monomer. The photopolymer composition may include the light-sensitive dye in an amount of 0.01% by weight to 30% by weight or 0.05% by weight to 20% by weight.

[0055] According to one embodiment of the present invention, the photosensitive dye is selected from the group consisting of sulfonium derivatives of ceramidonin, new methylene blue, thioerythrosine triethylammonium, 6-acetylamino-2-methylceramidonin, eosin, erythrosine, rose bengal, thionine, basic yellow, pinacyanol chloride, rhodamine 6G, gallocyanine, ethyl violet, Victoria blue R, Celestine blue, Quinaldine Red, crystal violet, Brilliant Green, Astrazon Orange G, and the like. Examples of suitable dyes include fluorescein orange G, darrow red, pyronin Y, basic red 29, pyrylium iodide, safranin O, cyanine, methylene blue, azure A, or a combination of two or more of these.

[0056] According to one embodiment of the present invention, the photopolymer composition may further comprise an organic solvent, non-limiting examples of which include ketones, alcohols, acetates, and ethers, or a mixture of two or more thereof.

[0057] According to one embodiment of the invention, the organic solvent may be a ketone, such as methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, or isobutyl ketone; an alcohol, such as methanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, or t-butanol; an acetate, such as ethyl acetate, i-propyl acetate, or polyethylene glycol monomethyl ether acetate; an ether, such as tetrahydrofuran or propylene glycol monomethyl ether; or a mixture of two or more thereof.

[0058] According to one embodiment of the present invention, the organic solvent is added when each component contained in the photopolymer composition is mixed, or each component is added in a dispersed or mixed state in the organic solvent and then added to the photopolymer composition. If the content of the organic solvent in the photopolymer composition is too small, the flowability of the photopolymer composition may decrease, and defects such as stripes may occur in the final film. In addition, when the organic solvent is added in excess, the solid content may be low, coating and film formation may not be performed sufficiently, and the physical properties and surface characteristics of the film may decrease, resulting in defects during drying and curing. Thus, the photopolymer composition may contain an organic solvent such that the total solid concentration of the components contained is 1 wt% to 70 wt% or 2 wt% to 50 wt%.

[0059] According to an embodiment of the present invention, the photopolymer composition may further include other additives, catalysts, etc. The photopolymer composition may include a commonly known catalyst to promote polymerization of the photoreactive monomer. Examples of the catalyst include tin octanoate, zinc octanoate, dibutyltin dilaurate, dimethyl bis[(1-oxoneodecyl)oxy]stannane, dimethyl tin dicarboxylate, zirconium bis(ethylhexanoate), zirconium acetylacetonate, or tertiary amines such as 1,4-diazabicyclo[2.2.2]octane, diazabicyclononane, diazabicycloundecane, 1,1,3,3-tetramethylguanidine, 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido(1,2-a)pyrimidine, etc.

[0060] According to one embodiment of the present invention, the method for manufacturing a holographic optical element uses a retardation layer. By using the retardation layer as described above, the phase of the first collimated laser beam and / or the second collimated laser beam can be changed.

[0061] According to one embodiment of the present invention, the retardation layer may have a single-layer structure or a multi-layer structure in which two or more layers are stacked. When the retardation layer has a multi-layer structure, each layer may be attached via a pressure-sensitive adhesive or adhesive, or may be directly laminated to each other by coating. As described above, the retardation layer may have a single-layer structure or a multi-layer structure in which two or more layers are stacked, thereby effectively changing the phase of the first parallel laser light and / or the second parallel laser light.

[0062] According to one embodiment of the present invention, the retardation layer may be a liquid crystal film or a polymer film. Specifically, the retardation layer may be formed by using a film obtained by stretching a light-transmitting polymer film that can be given optical anisotropy by stretching in an appropriate manner, or by using a liquid crystal film formed by orienting a liquid crystal compound. In addition, a non-stretched polymer film may also be used as long as it has optical anisotropy. As described above, the retardation layer may effectively change the phase of the first parallel laser light and / or the second parallel laser light by using a liquid crystal film and / or a polymer film.

[0063] According to one embodiment of the present invention, the method includes a step of irradiating the other surface of the photopolymer resin layer, which is the surface where the retardation layer is not provided, with a first parallel laser light, and irradiating the one surface of the photopolymer resin layer with a second parallel laser light, thereby recording an interference pattern due to the interference phenomenon of the first parallel laser light and the second parallel laser light in the photopolymer resin layer. As described above, the first parallel laser light is irradiated to the other surface of the photopolymer resin layer, which is the surface where the retardation layer is not provided, and the second parallel laser light is irradiated to the one surface of the photopolymer resin layer, thereby recording an interference pattern due to the interference phenomenon of the first parallel laser light and the second parallel laser light in the photopolymer resin layer, thereby eliminating the occurrence of an undesired interference pattern in the photopolymer resin layer.

[0064] According to one embodiment of the present invention, a first parallel laser beam is incident on one side of a photopolymer resin layer at a predetermined incident angle, and a second parallel laser beam is incident on the other side of the photopolymer resin layer to record an interference pattern. As described above, by incidenting the first parallel laser beam and the second parallel laser beam on the photopolymer resin layer, the interference pattern in the photopolymer resin layer can be efficiently improved.

[0065] According to one embodiment of the present invention, the holographic optical element records an interference pattern due to an interference phenomenon between a first parallel laser beam incident at a predetermined incident angle on one side of a photopolymer resin layer and a second parallel laser beam incident on the other side of the photopolymer resin layer. In this specification, a pattern formed by the interference phenomenon between the first parallel laser beam and the second parallel laser beam is defined as an interference pattern. Specifically, when the first parallel laser beam is incident on one side of the photopolymer resin layer and then the second parallel laser beam is incident on the other side forming an angle with the one side, an interference phenomenon occurs between the parallel laser beams in the photopolymer resin layer. Thereafter, in the overlapping portion formed in the photopolymer resin layer (the portion where constructive interference occurs), the components in the photopolymer resin layer undergo an additional polymerization reaction, and the refractive index changes. In addition, in the non-overlapping portion (the portion where destructive interference occurs), the additional polymerization reaction occurs weakly, and the refractive index changes weakly, and an interference pattern in which the constructive interference portion and the destructive interference portion due to the interference phenomenon are repeated is recorded. Therefore, when light is incident on the photopolymer layer, the light is refracted uniformly due to the pattern of different refractive indices recorded on the photopolymer layer.

[0066] According to one embodiment of the present invention, the wavelengths of the first and second parallel laser beams are not particularly limited and can be appropriately selected in consideration of the application of the holographic optical element to be manufactured. Specifically, the parallel laser beams can be a single laser having any one wavelength, or two or more lasers having different wavelengths. More specifically, to realize a full-color hologram, a combination of lasers having three wavelengths corresponding to red (R), green (G), and blue (B) regions can be used.

[0067] According to one embodiment of the present invention, the first and / or second parallel laser beam may be a continuous wave (CW) laser. A continuous wave laser has a more stable output than a pulsed laser, and therefore can record an interference pattern with uniform optical characteristics in an exposed area of ​​a photosensitive material.

[0068] According to one embodiment of the present invention, the first and / or second parallel laser light may be a single longitudinal mode laser, because when a multi-mode laser is used, the coherency between the light passing through the retardation layer and the diffracted light may decrease.

[0069] According to one embodiment of the present invention, the parallel laser light can be adjusted to have the same intensity in the entire area of ​​the photopolymer resin layer where the parallel laser light is irradiated. As described above, the optical properties realized in the photopolymer resin layer can be adjusted.

[0070] According to one embodiment of the present invention, the first and second parallel laser beams are irradiated to a photopolymer resin layer at a predetermined irradiation angle. Specifically, the first and second parallel laser beams are irradiated to the photopolymer resin layer at a predetermined irradiation angle, and then enter the photopolymer resin layer at a predetermined incident angle. The irradiation angles of the first and second parallel laser beams are not particularly limited and can be determined in consideration of the characteristics of the hologram to be recorded in the photopolymer resin layer and the characteristics of the holographic optical element to be manufactured.

[0071] According to an embodiment of the present invention, the incident angle of the first parallel laser light irradiated and incident on the photopolymer resin layer may be more than 42° and less than 90°. Specifically, the irradiation angle of the first parallel laser light may be 43° or more and less than 90°, 44° or more and less than 90°, less than 45°, less than 90°, 46° or more and less than 90°, 47° or more and less than 90°, 48° or more and less than 90°, 49° or more and less than 90°, 50° or more and less than 90°, 55° or more and less than 90°, 60° or more and less than 90°, 65° or more and less than 90°, 70° or more and less than 90°, 75° or more and less than 90°, or 80° or more and less than 90°. More specifically, the incident angle of the first parallel laser light may be an incident angle at which total reflection occurs at the interface between the photopolymer layer and the air layer. By adjusting the incident angle of the first parallel laser light within the above-mentioned range, an undesired interference pattern occurring due to total reflection at the boundary surface between the photopolymer layer and the air layer is converted into light that undergoes destructive interference by the phase difference layer, thereby preventing the occurrence of an undesired interference pattern.

[0072] According to one embodiment of the present invention, the first and second parallel laser beams are irradiated so as to cause interference inside the photosensitive layer of the photosensitive sheet. In the field of manufacturing holographic optical elements, in order to record a hologram in a photosensitive material, coherent object beam and reference beam must be used, and the object beam and reference beam must be irradiated to a photopolymer resin so that the object beam and reference beam interfere with each other inside the photopolymer resin to record an interference pattern in the photopolymer resin.

[0073] According to one embodiment of the present invention, the two parallel laser beams are irradiated so that the linear regions of the photopolymer resin layer irradiated with the two parallel laser beams coincide with each other on the same or opposite sides.

[0074] According to one embodiment of the present invention, when a first parallel laser beam is irradiated onto one surface of a photopolymer resin layer and a second parallel laser beam is irradiated onto the opposite surface of the first parallel laser beam, the region irradiated with the first parallel laser beam and the region irradiated with the second parallel laser beam are located at positions corresponding to each other on each surface, although they are on different opposite surfaces. As a result, the optical paths of the first parallel laser beam and the second parallel laser beam may overlap each other inside the photopolymer resin contained in the photopolymer resin layer, causing interference.

[0075] According to an embodiment of the present invention, when the first and second parallel laser beams are irradiated onto the same surface of the photopolymer resin layer, the first and second parallel laser beams irradiate the same area on the same surface, so that the optical paths of the first and second parallel laser beams may overlap each other inside the photopolymer resin contained in the photopolymer resin layer, causing interference.

[0076] According to one embodiment of the present invention, the first parallel laser light may be linearly polarized. Specifically, the first parallel laser light may be an S wave or a P wave. As described above, by selecting the first parallel laser light as an S wave or a P wave, the interference pattern can be clearly realized.

[0077] According to one embodiment of the present invention, the second parallel laser light may be circularly polarized or elliptically polarized. Specifically, when the first parallel laser light is an S wave, the second parallel laser light is preferably changed to an S wave when the second parallel laser light passes through a phase difference layer. Also, when the first parallel laser light is a P wave, the second parallel laser light is preferably changed to a P wave when the second parallel laser light passes through a phase difference layer. As described above, the second parallel laser light is circularly polarized or elliptically polarized, and by adjusting the light that changes when it passes through a phase difference layer, an undesired interference pattern occurring in a photopolymer resin layer can be removed.

[0078] According to one embodiment of the present invention, the retardation layer may have a λ / 4 wavelength phase retardation characteristic. In this specification, the term "λ / n wavelength phase retardation characteristic" means a characteristic that can retard the phase of incident light by n times the wavelength of the incident light at least within a certain wavelength range. The λ / n wavelength phase retardation characteristic is a characteristic that converts incident linearly polarized light into elliptically polarized light or circularly polarized light, and conversely, converts incident elliptically polarized light or circularly polarized light into linearly polarized light. As described above, by adjusting the retardation layer to have a λ / 4 wavelength phase retardation characteristic, it is possible to remove undesired interference patterns occurring in the photopolymer resin layer.

[0079] According to an embodiment of the present invention, a prism may be further provided on the other surface of the photopolymer resin layer. Specifically, by providing a prism on the other surface of the photopolymer resin layer, it is possible to prevent the first parallel laser light from passing through the prism and being irradiated onto the photopolymer resin layer, thereby preventing total reflection from occurring. As a result, by providing a prism on the other surface of the photopolymer resin layer, it is possible to manufacture a holographic optical element in which a laser irradiated with a specific wavelength can operate at a predetermined angle or wavelength.

[0080] According to one embodiment of the present invention, the light transmittance of the retardation layer may be more than 90% and less than 100%. Specifically, the light transmittance of the retardation layer may be 91% to 99%, 92% to 98%, 93% to 97%, or 94% to 96%. By adjusting the light transmittance of the retardation layer within the above range, the light efficiency of the irradiated parallel laser light can be improved.

[0081] According to one embodiment of the present invention, the haze of the retardation layer may be more than 0% and less than 1%. By adjusting the haze of the retardation layer within the above-mentioned range, it is possible to prevent the parallel laser light passing through the retardation layer from being scattered.

[0082] According to one embodiment of the present invention, the retardation layer may convert circularly polarized light or elliptically polarized light into linearly polarized light. As described above, by selecting the retardation layer as a layer that converts circularly polarized light or elliptically polarized light into linearly polarized light, it is possible to eliminate undesired interference patterns occurring in the photopolymer resin layer.

[0083] According to one embodiment of the present invention, the method may further include a step of removing the retardation layer from the photopolymer resin layer in which the interference pattern is recorded. As described above, by further including a step of removing the retardation layer, the holographic optical element can be made smaller.

[0084] According to an embodiment of the present invention, the method may further include a step of bleaching the photopolymer resin layer on which the interference pattern is recorded by irradiating light having a wavelength in the visible light to ultraviolet light range. As described above, by including a step of bleaching the photopolymer resin layer on which the pattern is recorded, the reaction of the photoreactive monomer that has not reacted in the photopolymer resin contained in the photopolymer resin layer can be completed.

[0085] According to one embodiment of the present invention, the wavelength of the light irradiated in the bleaching step may be in the visible light region or the ultraviolet light region. As described above, by adjusting the wavelength of the light irradiated in the bleaching step, the reaction of the unreacted photoreactive monomer in the photopolymer resin can be effectively completed.

[0086] According to an embodiment of the present invention, after the bleaching step, a step of additionally curing the photopolymer resin layer may be included. The curing may be thermal curing or photocuring. As described above, by additionally curing the photopolymer resin, the interference pattern recorded in the photopolymer resin layer can be further fixed and high temperature durability can be improved.

[0087] One embodiment of the present invention provides a holographic optical element comprising a photopolymer resin layer containing a photopolymer resin and a retardation layer provided on one side of the photopolymer resin layer, the photopolymer resin layer having an interference pattern recorded thereon due to an optical interference phenomenon, the photopolymer resin layer having a transmittance of more than 0% and not more than 70%, or more than 90% and not more than 100%, for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to another side of the photopolymer resin layer, which is a side not provided with the retardation layer.

[0088] A holographic optical element, which is an embodiment of the present invention, can minimize unwanted interference patterns, clarify the recorded interference patterns, and at the same time improve diffraction efficiency.

[0089] Throughout this specification, the contents overlapping with the manufacturing method of the holographic optical element will not be described.

[0090] According to one embodiment of the present invention, the holographic optical element has a transmittance of more than 0% and 70% or less, or more than 90% and 100% or less, for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to the other surface of the photopolymer resin layer, which is the surface on which the retardation layer is not provided. Throughout this specification, the term "light transmittance" may mean the ratio of the amount of light that is transmitted through an object to the amount of light irradiated when a specific object is irradiated with light. Specifically, the holographic optical element may not have a transmittance of more than 70% and 90% or less for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to the other surface of the photopolymer resin layer, which is the surface on which the retardation layer is not provided. More specifically, the holographic optical element may have a transmittance of more than 90% and not more than 100% for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to the other surface of the photopolymer resin layer, which is the surface not provided with the retardation layer, and may have a transmittance of more than 0% and not more than 70% for the other surface. By checking the light transmittance of the holographic optical element at a specific wavelength within the above-mentioned range, it is possible to check for the presence or absence of an undesired interference pattern, and the diffraction efficiency of the holographic optical element can be improved.

[0091] According to one embodiment of the present invention, the wavelength of the light irradiated to check the light transmittance may be 400 nm or more and 1600 nm or less. Specifically, the wavelength of the light irradiated to check the light transmittance may be 450 nm or more and 1550 nm or less, 500 nm or more and 1500 nm or less, 550 nm or more and 1450 nm or less, 600 nm or more and 1400 nm or less, 650 nm or more and 1350 nm or less, 700 nm or more and 1300 nm or less, 750 nm or more and 1250 nm or less, 800 nm or more and 1200 nm or less, 850 nm or more and 1150 nm or less, 900 nm or more and 1100 nm or less, or 950 nm or more and 1050 nm or less. By adjusting the wavelength of the light irradiated to check the light transmittance within the above-mentioned range, the accuracy of checking the presence or absence of the undesired interference pattern can be improved.

[0092] According to one embodiment of the present invention, the retardation layer may have λ / 4 wavelength phase retardation characteristics.As described above, by adjusting the retardation layer to have λ / 4 wavelength phase retardation characteristics, it is possible to eliminate undesired interference patterns occurring in the photopolymer resin layer.

[0093] According to one embodiment of the present invention, the light transmittance of the retardation layer may be more than 90% and less than 100%. Specifically, the light transmittance of the retardation layer may be 91% to 99%, 92% to 98%, 93% to 97%, or 94% to 96%. By adjusting the light transmittance of the retardation layer within the above range, the light efficiency of the irradiated parallel laser light can be improved.

[0094] According to one embodiment of the present invention, the haze of the retardation layer may be more than 0% and less than 1%. By adjusting the haze of the retardation layer within the above-mentioned range, it is possible to prevent the parallel laser light passing through the retardation layer from being scattered.

[0095] According to one embodiment of the present invention, the interference pattern may be an interference pattern caused by an interference phenomenon between the first parallel laser light and the second parallel laser light, by irradiating the other surface of the photopolymer resin layer, which is the surface not provided with the retardation layer, with a first parallel laser light, and irradiating the one surface of the photopolymer resin layer with a second parallel laser light. As described above, by forming an interference pattern, a desired interference pattern can be formed. EXAMPLES

[0096] Hereinafter, the present invention will be described in detail with reference to examples in order to specifically explain the present invention. However, the examples according to the present invention can be modified into various different forms, and the scope of the present invention is not to be construed as being limited to the examples described below. The examples in the present specification are provided to more completely explain the present invention to those having average knowledge in the art.

[0097] 3 is a schematic diagram of an embodiment of the present invention, in which a holographic optical element records an interference pattern P. Generally, a holographic optical element is irradiated with a first parallel laser beam L1 and a second parallel laser beam L2 to record an interference pattern P realized by the interference phenomenon between the first parallel laser beam L1 and the second parallel laser beam L2.

[0098] Specifically, in order to enhance the interference phenomenon between the first parallel laser light L1 and the second parallel laser light L2, it is preferable to change the light into linearly polarized light to enhance the interference phenomenon. More specifically, by changing the first parallel laser light L1 into an S wave (vertical linear polarization) and changing the second parallel laser light L2, which is circularly polarized or elliptically polarized, into an S wave (vertical linear polarization) by passing through a phase difference layer, the constructive interference generated by the mutual interference phenomenon is realized more strongly, and the destructive interference realizes a pattern more weakly, thereby clearly realizing the interference pattern.

[0099] On the other hand, by changing the first parallel laser light L1 into a P wave (horizontally polarized light) and the second parallel laser light L2, which is circularly polarized or elliptically polarized light, passing through the phase difference layer and being changed into a P wave (horizontally polarized light), the constructive interference generated by the mutual interference phenomenon is realized even stronger, and the destructive interference realizes the pattern even weaker, thereby clearly realizing the interference pattern.

[0100] 4 is a schematic diagram showing a process of removing an undesired interference pattern of a holographic optical element according to an embodiment of the present invention. Specifically, FIG. 4 is a schematic diagram showing a process of minimizing an undesired interference pattern of a holographic optical element according to an embodiment of the present invention. Referring to FIG. 4, as described above, when the first parallel laser light L1 is changed to an S wave (vertical linear polarization), total reflection occurs at the interface between the retardation layer and air, and the first parallel laser light L1 is changed from an S wave to a P wave. At the same time, the P wave, which is the first parallel laser light L1, causes destructive interference with the S wave, which is the second parallel laser light L2, which is changed by passing through the retardation layer, and thus no interference pattern is formed, and therefore no undesired interference pattern is formed.

[0101] Similarly, as described above, when the first parallel laser light L1 changes to a P wave (horizontally linearly polarized light), total reflection occurs at the interface between the retardation layer and air, and the first parallel laser light L1 changes from a P wave to an S wave. At the same time, the S wave, which is the first parallel laser light L1, causes destructive interference with the P wave, which is the second parallel laser light L2, which has changed after passing through the retardation layer, and thus no interference pattern is formed, and no undesired interference pattern is formed.

[0102] <Reference example 1>

[0103] A surface of the holographic optical element having only the photopolymer resin layer was irradiated vertically with light having a wavelength of 400 nm to 1600 nm, and the light transmittance was measured and shown in FIG. 5 below.

[0104] <Reference example 2>

[0105] A holographic optical element having only a photopolymer resin layer was provided with no phase difference layer on one side thereof, and a second parallel laser beam was irradiated onto one side of the photopolymer resin layer, and a first parallel laser beam was irradiated onto the other side of the photopolymer resin layer, thereby recording an interference pattern due to the interference phenomenon of the first parallel laser beam and the second parallel laser beam in the photopolymer resin layer. Then, a light having a wavelength of 400 nm to 1600 nm was irradiated perpendicularly onto one side of the holographic optical element, and the light transmittance was measured, as shown in FIG. 5 below.

[0106] FIG. 5 is a graph showing the light transmittance for light having a wavelength of 400 nm to 1600 nm for each of Reference Example 1 and Reference Example 2. Referring to FIG. 5, it was confirmed that, since there was no interference pattern in Reference Example 1, a peak exceeding 90% appeared for the entire range of light having a wavelength of 400 nm to 1600 nm. In contrast, it was confirmed that, since an interference pattern was recorded in the absence of a retardation layer, an undesired interference pattern was recorded, and a peak appeared at more than 0% to 70% or more than 90% to 100%. Specifically, it was confirmed that, since a peak occurred in the range where the light transmittance was more than 70% to 90%, an undesired interference pattern was recorded in Reference Example 2.

[0107] Therefore, in the present invention, by using the retardation layer in the process of recording an interference pattern, it is possible to eliminate undesired interference patterns and improve the diffraction efficiency.

[0108] Although the present invention has been described above using limited examples, the present invention is not limited thereto, and it goes without saying that various modifications and variations can be made by those having ordinary skill in the art to which the present invention pertains within the technical spirit of the present invention and the equivalent scope of the claims set forth below. [Explanation of symbols]

[0109] 101: Photopolymer resin layer 103: Prism 105: Retardation layer L1: First parallel laser beam L2: Second parallel laser beam P: Interference pattern P': Unwanted interference pattern

Claims

1. Providing a retardation layer on one side of a photopolymer resin layer containing a photopolymer resin; irradiating a first parallel laser light onto another surface of the photopolymer resin layer, which is a surface not provided with the phase difference layer, and irradiating a second parallel laser light onto the one surface of the photopolymer resin layer, thereby recording an interference pattern due to an interference phenomenon between the first parallel laser light and the second parallel laser light in the photopolymer resin layer.

2. 2. The method of claim 1, wherein the incident angle of the first parallel laser beam incident on the photopolymer resin layer is greater than 42[deg.] and less than 90[deg.].

3. the first collimated laser light is linearly polarized, The method for producing a holographic optical element according to claim 1 or 2, wherein the second collimated laser light is circularly polarized or elliptically polarized light.

4. 4. The method for producing a holographic optical element according to claim 1, wherein the retardation layer has a λ / 4 wavelength phase retardation characteristic.

5. The method for producing a holographic optical element according to any one of claims 1 to 4, further comprising providing a prism on the other surface of the photopolymer resin layer.

6. The optical transmittance of the retardation layer is more than 90% and not more than 100%, 6. The method for producing a holographic optical element according to claim 1, wherein the retardation layer has a haze of more than 0% and less than 1%.

7. 7. The method for producing a holographic optical element according to claim 1, wherein the retardation layer converts circularly polarized light or elliptically polarized light into linearly polarized light.

8. The method for producing a holographic optical element according to any one of claims 1 to 7, further comprising the step of removing the retardation layer from the photopolymer resin layer in which the interference pattern is recorded.

9. The method for manufacturing a holographic optical element according to any one of claims 1 to 8, further comprising a step of bleaching the photopolymer resin layer in which the interference pattern is recorded by irradiating the photopolymer resin layer with light having a wavelength in the visible light range to the ultraviolet light range.

10. a photopolymer resin layer including a photopolymer resin; A retardation layer provided on one surface of the photopolymer resin layer, the photopolymer resin layer has an interference pattern recorded thereon due to a light interference phenomenon; A holographic optical element having a transmittance of more than 0% and not more than 70%, or more than 90% and not more than 100%, for light having a wavelength of 400 nm to 1600 nm irradiated perpendicularly to another surface of the photopolymer resin layer, which is a surface on which the retardation layer is not provided.

11. The holographic optical element according to claim 10 , wherein the retardation layer has a λ / 4 wavelength phase retardation characteristic.

12. The optical transmittance of the retardation layer is more than 90% and not more than 100%, 12. The holographic optical element according to claim 10, wherein the haze of the retardation layer is more than 0% and less than 1%.

13. The holographic optical element according to any one of claims 10 to 12, wherein the interference pattern is due to an interference phenomenon between one parallel laser light irradiated onto the other surface of the photopolymer resin layer and a second parallel laser light irradiated onto the one surface of the photopolymer resin layer.

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