Optical element, polarization conversion element, image display device, and method for manufacturing optical element

Abstract

To provide an optical element excellent in heat resistance, light resistance and light transmittance, a polarization conversion element and an image display device equipped with the same, and a method for manufacturing the optical element.SOLUTION: According to an embodiment of the present disclosure, there is provided an optical element including a first glass substrate, a second glass substrate, an optical functional film, and an inorganic bonding layer. The first glass substrate has a first bonding surface. The second glass substrate has a second bonding surface. The optical function film covers the first bonding surface. The inorganic bonding layer is provided between the optical function film and the second bonding surface, and is made of a silicon compound bonded to the second bonding surface by direct bonding.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present technology relates to an optical element having an optically functional film, a polarization conversion element, an image display device including the same, and a method for manufacturing the optical element. [Background technology]

[0002] A polarization conversion element is used in a projection-type image display device (projector) to improve the efficiency of light utilization. For example, Patent Document 1 discloses this type of polarization conversion element, which has a first substrate and a second substrate made of optical glass such as BK7, a polarization separation film disposed between the first substrate and the second substrate, and a bonding layer made of an organic film such as polyorganosiloxane disposed between the polarization separation film and the second substrate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-113056 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in order to achieve higher image brightness in projection-type image display devices, efforts have been made to increase the output of light sources or the density of optical energy. Therefore, polarization separation elements are required to have further improved heat resistance, light resistance, and light transmittance. However, conventional polarization separation elements use organic adhesives at the joint between the glass substrate and the polarization separation film, which results in low heat resistance and unavoidable degradation due to light. Furthermore, light transmission loss is likely to occur due to the difference in refractive index at the joint interface.

[0005] In view of the above circumstances, an object of the present technology is to provide an optical element, a polarization conversion element, and an image display device including the same, which are excellent in heat resistance, light resistance, and light transmittance, as well as a method for manufacturing the optical element. [Means for solving the problem]

[0006] An optical element according to an embodiment of the present technology includes a first glass substrate, a second glass substrate, an optically functional film, and an inorganic bonding layer. The first glass substrate has a first bonding surface. The second glass substrate has a second bonding surface. The optical function film covers the first bonding surface. The inorganic bonding layer is provided between the optical function film and the second bonding surface, and is made of a silicon compound and bonded to the second bonding surface by direct bonding.

[0007] The optical element has excellent heat resistance and light resistance because the bonding portion between the optical function film and the second bonding surface is made of an inorganic bonding layer made of a silicon compound. Furthermore, because the bonding layer is directly bonded to the second bonding surface, the refractive index difference at the interface is small, thereby improving the transmittance.

[0008] The silicon compound may be a silicon oxide.

[0009] The direct bonding may be plasma bonding.

[0010] In this case, the inorganic bonding layer and the second bonding surface may have a surface roughness (Ra) of 2 nm or less.

[0011] The inorganic bonding layer may have a thickness of 200 nm or more and 1000 nm or less.

[0012] The optical functional film may be an optical multilayer film in which a first dielectric having a first refractive index and a second dielectric having a second refractive index different from the first refractive index are alternately stacked.

[0013] The optical multilayer film may be a polarization separation film.

[0014] The refractive index (n d ) can be greater than or equal to 1.6 and less than or equal to 1.8.

[0015] A polarization conversion element according to an embodiment of the present technology includes a polarization separation element, an inorganic wavelength plate, and a support. The polarization separation element includes a first glass substrate having a first bonding surface, a second glass substrate having a second bonding surface, an optically functional film provided on the first bonding surface, and an inorganic bonding layer made of a silicon compound provided between the optically functional film and the second bonding surface and directly bonded to the second bonding surface. The inorganic wave plate converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light that is orthogonal to the first polarized light. The support member commonly supports the polarization separation element and the inorganic wave plate such that the inorganic wave plate faces the polarization separation element with a gap therebetween.

[0016] An image display device according to an embodiment of the present technology includes a polarization conversion element. The polarization conversion element includes a polarization separation element, an inorganic wavelength plate, and a support. The polarization separation element includes a first glass substrate having a first bonding surface, a second glass substrate having a second bonding surface, an optically functional film provided on the first bonding surface, and an inorganic bonding layer made of a silicon compound provided between the optically functional film and the second bonding surface and directly bonded to the second bonding surface. The inorganic wave plate converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light that is orthogonal to the first polarized light. The support member commonly supports the polarization separation element and the inorganic wave plate such that the inorganic wave plate faces the polarization separation element with a gap therebetween.

[0017] A method for manufacturing an optical element according to an embodiment of the present disclosure includes: forming an optically functional film on the surface of a first glass substrate; forming an inorganic bonding layer made of a silicon compound on the optical functional film; A second glass substrate is bonded to the inorganic bonding layer by plasma bonding.

[0018] The method for manufacturing an optical element may further include polishing bonding surfaces of the inorganic bonding layer and the second glass substrate after forming the inorganic bonding layer and before bonding the second glass substrate.

[0019] Alternatively, the method for manufacturing an optical element may include polishing the surface of the first glass substrate before forming the optical functional film, and polishing the bonding surface of the second glass substrate before bonding the second glass substrate to the inorganic bonding layer.

[0020] The optically functional film may be formed by ion beam sputtering or bias sputtering. [Effects of the Invention]

[0021] As described above, according to the present technology, an optical element having excellent heat resistance, light resistance, and light transmittance can be obtained. The effects described here are not necessarily limited to those described herein, and may be any of the effects described in this disclosure. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is an exploded perspective view showing a configuration of a polarization conversion element according to an embodiment of the present technology; [Figure 2] 2 is a schematic cross-sectional view showing the configuration of the polarization conversion element. FIG. [Figure 3] 3 is a schematic cross-sectional view of a main part showing the configuration of a polarization separation element in the polarization conversion element. FIG. [Figure 4] 3A to 3C are diagrams illustrating a method for producing the polarization separation element. [Figure 5] 3A to 3C are diagrams illustrating a method for producing the polarization separation element. [Figure 6] 3A to 3C are schematic process diagrams illustrating an example of a method for manufacturing the polarization separation element. [Figure 7]3 is a schematic diagram showing an example of a layer structure of a polarization separation film in the polarization separation element. FIG. [Figure 8] 5A to 5C are schematic process diagrams showing another example of the method for manufacturing the polarization separation element. [Figure 9] 3A and 3B are diagrams illustrating an example of optical characteristics of the polarization separation element. [Figure 10] 1 is a schematic configuration diagram illustrating an image display device according to an embodiment of the present technology. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present technology will be described with reference to the drawings.

[0024] First Embodiment Fig. 1 is an exploded perspective view showing a configuration of a polarization conversion element 100 according to an embodiment of the present technology, and Fig. 2 is a schematic cross-sectional view of a main part of the polarization conversion element 100. The polarization conversion element 100 includes a polarization separation element 10, an inorganic wave plate 20, and a support 30 that supports these elements. The polarization conversion element 100 is an optical element that converts unpolarized incident light L into a predetermined polarized light (P-polarized light in this example).

[0025] [Polarization separation element] The polarization separation element 10 has a light incident surface 101 and a light exit surface 102. The polarization separation element 10 is an optical element (polarization beam splitter) that transmits or reflects incident light L depending on the polarization direction of the incident light L.

[0026] The polarization separation element 10 is formed, for example, by bonding a plurality of parallelepiped prisms together in the Z-axis direction. In this embodiment, the plurality of prisms include a first glass substrate 11 and a second glass substrate 12. Between the first glass substrate 11 and the second glass substrate 12, polarization separation layers 13 that reflect S-polarized light and transmit P-polarized light and reflective layers 14 that reflect the S-polarized light reflected by the polarization separation layer 13 again are alternately arranged.

[0027] 3 is a schematic cross-sectional view of a main part showing the configuration of the polarization separation element 10. As shown in the figure, the polarization separation layer 13 is made up of a laminate of a polarization separation film 131 and an inorganic bonding layer 132.

[0028] The polarization separation film 131 is an optically functional film that reflects S-polarized light Ls and transmits P-polarized light Lp, and is made of a dielectric multilayer film that covers the bonding surface 11a (first bonding surface) of the first glass substrate 11. The angle between the bonding surface 11a and the incident surface 101 is typically 45°. The polarization separation film 131 is an optical multilayer film in which first dielectrics having a first refractive index and second dielectrics having a second refractive index different from the first refractive index are alternately stacked.

[0029] The first dielectric is made of a material having a smaller refractive index (nd) than the second dielectric. The refractive indexes of the first and second dielectrics are selected depending on the refractive indexes of the first and second glass substrates 11 and 12. For example, when the refractive index (nd) of the first and second glass substrates 11 and 12 is 1.6 to 1.8, the first dielectric is SiO2 (nd: 1.46) and the second dielectric is Ta2O5 (nd: 2.16). An example of a glass material having a refractive index (nd) of 1.6 to 1.8 is OHARA's glass material S-TIH (nd: 1.72).

[0030] The inorganic bonding layer 132 is provided between the polarization separation film 131 and the bonding surface 12a (second bonding surface) of the second glass substrate 12. The bonding surface 12a is a plane parallel to the bonding surface 11a. The inorganic bonding layer 132 is made of a silicon compound and is directly bonded to the bonding surface 12a of the second glass substrate 12. The surface of the inorganic bonding layer 132 facing the bonding surface 12a forms a bonding interface that is directly bonded to the second glass substrate 12. In other words, the inorganic bonding layer 132 functions as a buffer layer for forming the bonding interface. The buffer layer constitutes part of the polarization separation layer 13 and, when stacked on the polarization separation film 131, performs a predetermined polarization separation function.

[0031] Examples of silicon compounds that form inorganic bonding layer 132 include silicon oxides (SiO, SiO), silicon nitrides (SiN), silicon oxynitrides (SiON), silicon oxide carbides (SiOC), etc. Inorganic bonding layer 132 is directly bonded to bonding surface 12a of second glass substrate 12, and therefore inorganic bonding layer 132 can be integrally bonded to bonding surface 12a without the need for an adhesive at the interface.

[0032] An example of direct bonding is plasma bonding. In plasma bonding, a silicon-oxygen covalent bond or a silicon-silicon covalent bond is formed between the inorganic bonding layer 132 and the bonding surface 12a, thereby firmly fixing the inorganic bonding layer 132 to the bonding surface 12a. In addition to plasma bonding, a solid-state bonding method such as diffusion bonding may also be used for direct bonding.

[0033] In this embodiment, inorganic bonding layer 132 is made of silicon oxide, particularly silicon dioxide, which provides a refractive index close to that of a glass material primarily composed of SiO. Although there is a refractive index difference at the bonding interface between inorganic bonding layer 132 and second glass substrate 12, the thickness of the bonding interface is 1 nm or less, which is sufficiently small compared to the wavelength, and therefore reflection due to the refractive index difference can be eliminated.

[0034] The surface roughness (Ra) of the inorganic bonding layer 132 and the bonding surface 12a is 2 nm or less, which allows stable direct bonding of the inorganic bonding layer 132 to the second glass substrate 12 by plasma bonding. The surface roughness (Ra) of the inorganic bonding layer 132 and the bonding surface 12a is preferably 1 nm or less, and more preferably 0.5 nm or less.

[0035] The inorganic bonding layer 132 may have a thickness sufficient to form the bonding interface, for example, 200 nm to 1000 nm. This reduces the bonding thickness between the first and second glass substrates 11, 12, thereby enabling the polarization separation element 10 and the polarization conversion element 100 to be miniaturized and suppressing the amount of gas generated by heating during bonding to the second glass substrate 12. By making the inorganic bonding layer 132 thicker than 200 nm, the inorganic bonding layer 132 can function as part of the polarization separation layer 13 (low refractive index material layer). The thickness of the inorganic bonding layer 132 may be less than 200 nm, and is not particularly limited as long as it is possible to form a bonding interface.

[0036] On the other hand, the reflective layer 14 is an optically functional film that reflects the S-polarized light Ls reflected by the polarization separation layer 13 back toward the light exit surface 102, and is disposed between the first glass substrate 11 and the second glass substrate 12 in parallel to the polarization separation layer 13. The reflective layer 14 is made of, for example, a dielectric multilayer film. An example of a dielectric multilayer film is a multilayer film in which silicon oxide and titanium oxide are alternately stacked. The reflective layer 14 may also be made of a dielectric multilayer film.

[0037] After the dielectric multilayer film is formed on the surface of the first glass substrate 11 (the surface opposite to the bonding surface 11a), the reflective layer 14 is bonded to the surface of the second glass substrate 12 (the surface opposite to the bonding surface 12a). The bonding method is not particularly limited, and may be direct bonding or bonding using an adhesive. In the case of direct bonding, a silicon dioxide film is formed on the surface of the dielectric multilayer film, and the silicon oxide film is bonded to the first glass substrate 11 by plasma bonding.

[0038] 4, the polarization separation element 10 is formed by cutting an element assembly 10M, in which a second glass substrate 12 is bonded to both sides of a first glass substrate 11, on which a polarization separation layer 13 and a reflective layer 14 are respectively formed, along cutting lines C. As shown in FIGS. 5A to 5C, each of the separated polarization separation elements 10p has both longitudinal ends lapped and polished, and antireflection films 101m and 102m are formed on the light incident surface 101 and the light exit surface 102, and then the ends are bonded together in the longitudinal direction.

[0039] [Inorganic wave plate] The inorganic wave plate 20 is an optical element (half wave plate) that converts the S-polarized light Ls reflected by the reflective layer 14 into P-polarized light Lp. The inorganic wave plate 20 is typically made of a rectangular quartz plate elongated in the X-axis direction, and is disposed at a predetermined distance from the light exit surface 102 of the polarization separation element 10.

[0040] An antireflection film 21 is formed on each of the light incident and light emitting surfaces of the inorganic wave plate 20. The antireflection film 21 is a dielectric multilayer film, and is made of, for example, magnesium fluoride (MgF), silicon dioxide (SiO), TiO, TaO, or the like.

[0041] 1, a plurality of inorganic wave plates 20 are arranged at intervals on the optical path of the reflected light (S-polarized light Ls) from the reflective layer 14. Each inorganic wave plate 20 is supported in common by a second support frame 120.

[0042] [Support] The support 30 is composed of a bonded body of a first support frame 110 and a second support frame 120. The first support frame 110 is composed of a metal plate having a plurality of apertures 111, and is arranged on the light incident surface 101 side of the polarization separation element 10. The second frame 120 is composed of a frame-shaped metal plate arranged on the light exit surface 102 side of the polarization separation element 10. The first support frame 110 and the second support frame 120 are bonded to each other via an adhesive layer 130 or an appropriate connecting mechanism, with the polarization separation element 10 and the inorganic wave plate 20 sandwiched between them.

[0043] The support 30 commonly supports the polarization separation element 10 and the inorganic wave plate 20 so that the inorganic wave plate 20 faces a predetermined position on the light exit surface 102 of the polarization separation element 10. This maintains the relative positional relationship between the polarization separation element 10 and the inorganic wave plate 20 without bonding them to each other with an adhesive or the like. This makes it possible to avoid deterioration in heat resistance, light resistance, and light transmittance due to the presence of an adhesive between the polarization separation element 10 and the inorganic wave plate 20.

[0044] The first support frame 110 has a frame shape and contacts the light incident surface 101 of the polarization separation element 10. The second support frame 120 has a plate shape with an opening formed in its surface to support the inorganic wave plate 20. The first and second support frames 110, 120 are reinforced at their peripheries to ensure their mutual bonding strength. The constituent materials of the first and second support frames 110, 120 are not particularly limited, but are typically made of metal materials. The adhesive layer 130 is made of an organic material such as ultraviolet curing resin, bonds the second support frame 120 to the inorganic wave plate 20 and the polarization separation element 10, and is arranged in an area that is not irradiated with incident light L. This makes it possible to prevent deterioration of the adhesive layer 130 due to light irradiation.

[0045] [Method of manufacturing the polarization separation element] Next, a method for manufacturing the polarization separation element 10, in particular, a method for manufacturing the polarization separation layer 13 will be described.

[0046] The manufacturing method of the polarization separation element 10 of this embodiment includes the steps of forming a polarization separation film 131 on the surface (bonding surface 11a) of the first glass substrate 11, forming an inorganic bonding layer 132 made of a silicon compound on the polarization separation film 131, and bonding the second glass substrate 12 to the inorganic bonding layer 132 by plasma bonding.

[0047] (Method 1) 6 is a schematic process diagram showing an example of a method for manufacturing the polarization separation element 10. In this example, a polarization separation film 131 and an inorganic bonding layer 132 are formed on a first glass substrate 11 (FIG. 6A), and the surface of the inorganic bonding layer 132 and the bonding surface 12a of the second glass substrate 12 are polished and planarized (FIG. 6B), and then the inorganic bonding layer 132 and the second glass substrate 12 are directly bonded to each other (FIG. 6C). That is, in this example, after the inorganic bonding layer 132 is formed, the inorganic bonding layer 132 and the bonding surface 12a of the second glass substrate 12 are polished before bonding the second glass substrate 12.

[0048] The method for forming the polarization separation film 131 and the inorganic bonding layer 132 is not particularly limited, and sputtering, ion beam sputtering, vacuum deposition, ion-assisted deposition, etc. can be used. For example, SiO2 can be used as the low-refractive index material layer and Ta2O5 can be used as the high-refractive index material layer in the dielectric multilayer film that constitutes the polarization separation film 131. The thickness and number of each material layer can be appropriately set depending on the required polarization separation characteristics. For example, as shown in FIG. 7, the polarization separation film 131 is made up of 12 dielectric multilayer films, and a silicon dioxide film that constitutes the inorganic bonding layer 132 is formed on the upper layer (13th layer) of these.

[0049] The bonding surface 12a of the inorganic bonding layer 132 and the second glass substrate 12 is polished to a surface roughness (Ra) of 1 nm or less, preferably 0.5 nm or less. The polishing method is not particularly limited, and typically, a high-precision polishing method capable of adjusting the surface roughness on the order of nm is adopted. This allows the desired bonding strength to be obtained by plasma bonding, which will be described later.

[0050] By polishing the surface of the inorganic bonding layer 132, the surface roughness required for bonding to the second glass substrate 12 can be obtained, so the surface roughness of the bonding surface 11a of the first glass substrate 11 and the polarization splitting film 131 formed thereon may be 1 nm or more. This makes it easy to control the processing costs of the bonding surface 11a and the film thickness of the polarization splitting film 131. Furthermore, since the thickness of the inorganic bonding layer 132 can be reduced by polishing, it is formed to a thickness of, for example, 5000 nm and then polished to a thickness of, for example, 2000 nm or less.

[0051] Plasma bonding is used to bond the inorganic bonding layer 132 and the second glass substrate 12. In plasma bonding, first, a plasma activation treatment is performed on the surface of the inorganic bonding layer 132 on the first glass substrate 11 and the bonding surface 12a of the second glass substrate 12. As a result, OH groups are generated on the surface of the inorganic bonding layer 132 and the bonding surface 12a, making them hydrophilic.

[0052] Gases used in the plasma activation process include oxygen (O), nitrogen (N), helium (He), argon (Ar), hydrogen (H), etc. In particular, by using a gas (oxygen in this example) of the same kind as the constituent elements of inorganic bonding layer 132 and bonding surface 12a, it is possible to suppress deterioration of inorganic bonding layer 132 and bonding surface 12a.

[0053] Next, the inorganic bonding layer 132 and the second glass substrate 12 are bonded together, and a temporary bond is formed by hydrogen bonding between the OH groups of each. In this state, heat treatment (annealing) is performed at a temperature of, for example, 200°C or higher to cause a dehydration condensation reaction of the Si-OH at the interface, forming a silicon-oxygen covalent bond or a silicon-silicon covalent bond, thereby completing the plasma bonding.

[0054] (Method 2) 8 is a schematic process diagram showing another example of a method for manufacturing the polarization separation element 10. In this example, the bonding surface 11a of the first glass substrate 11 and the bonding surface 12a of the second glass substrate 12 are flattened by polishing (FIG. 8A). Then, a polarization separation film 131 and an inorganic bonding layer 132 are formed in this order on the bonding surface 11a of the first glass substrate (FIG. 8B). Then, the inorganic bonding layer 132 is directly bonded to the second glass substrate 12 (FIG. 8C). That is, in this example, the bonding surface 11a of the first glass substrate is polished before the polarization separation layer 13 is formed, and the bonding surface 12a of the second glass substrate 12 is polished before the second glass substrate 12 is bonded to the inorganic bonding layer 132.

[0055] In this example, a film formation method that provides a high degree of surface flatness is used to form the polarization separation film 131 and the inorganic bonding layer 132. Examples of such a film formation method include ion beam sputtering, bias sputtering, and other methods that provide a low surface roughness on the film formation surface, thereby forming a vapor-deposited film with a high degree of flatness, such as a surface roughness (Ra) of 0.5 nm or less. Forming the polarization separation layer 131 using such a film formation method allows the surface of the inorganic bonding layer 132 to be formed with a desired degree of flatness without the need for a polishing process, and therefore the thickness of the inorganic bonding layer 132 can be reduced to, for example, approximately 200 nm.

[0056] In the step of bonding the inorganic bonding layer 132 and the second glass substrate 12, a plasma bonding process similar to that of the above-described Method 1 is performed. In this example, the thickness of the inorganic bonding layer 132 can be reduced, which has the advantage of reducing the amount of gas released from the inorganic bonding layer 132 during annealing.

[0057] In the polarization conversion element 100 of this embodiment configured as described above, the joint between the polarization separation layer 13 and the joint surface 12a of the second glass substrate 12 is formed by the inorganic joint layer 132 made of a silicon compound, thereby achieving improved heat resistance and light resistance. Furthermore, since the inorganic joint layer 132 is directly joined to the joint surface 12a, there is a refractive index difference at the joint interface, and the thickness of the joint interface is 1 nm or less, which is sufficiently small compared to the wavelength, so that reflection due to the refractive index difference can be eliminated and transmittance can be improved.

[0058] For example, Fig. 9 shows the optical characteristics of a polarization splitter element 10 fabricated by the above-mentioned method 1. Fig. 9 confirms that a high polarization extinction ratio can be obtained in the visible light range. Although not shown, it has been confirmed that optical characteristics similar to those in Fig. 9 can also be obtained by a polarization splitter element fabricated by the above-mentioned method 2.

[0059] Generally, when forming a polarization separation film using general-purpose glass (such as white plate glass, blue plate glass, or BK7) with a refractive index (nd) of around 1.5 as the glass substrate, it is difficult to obtain the desired optical characteristics (transmittance) without using MgF2 (magnesium fluoride, nd: 1.38), a low-refractive index material. However, MgF2 has high film stress, making it difficult to form a dielectric multilayer film, and the multilayer film is destroyed when the temperature during bonding is raised to 200°C. For this reason, it is not possible to bond the polarization separation film to the glass substrate by direct bonding such as plasma bonding, and organic adhesives such as ultraviolet-curing adhesives have been required. However, since an organic adhesive is used at the joint between the glass substrate and the polarization splitting film, the heat resistance is low and deterioration due to light is unavoidable.

[0060] In contrast, the polarization separation element 10 of this embodiment does not have an organic adhesive at the joint between the glass substrate and the polarization separation film, improving heat resistance and light resistance and enabling it to adequately accommodate higher light source output or higher optical energy density. Furthermore, since there is no adhesive on the optical path of the light, there is a refractive index difference at the joint interface, but the thickness of the joint interface is 1 nm or less, which is sufficiently small compared to the wavelength, and therefore reflection due to the refractive index difference can be eliminated, thereby improving transmittance.

[0061] Moreover, in this embodiment, since glass materials with a refractive index of 1.6 or more and 1.8 or less are used for the first and second glass substrates 11 and 12, the desired optical characteristics can be ensured by using silicon dioxide as the low refractive index material of the polarization separation film 131 and common materials such as TiO2 and Ta2O5 as the high refractive index material.

[0062] Furthermore, according to the polarization conversion element 100 of this embodiment, the inorganic wave plate 20 is supported in common by the support 30 that also supports the polarization separation element 10, so that the inorganic wave plate 20 can be disposed in a non-contact manner with respect to the light exit surface 102 of the polarization separation element 10, without the need for an organic adhesive on the optical path from the polarization separation element 10 to the inorganic wave plate 20. This makes it possible to improve the heat resistance, light resistance, and light transmittance of the polarization conversion element 100.

[0063] This technology can also be applied when using MgF2, which has a high film stress, as a low-refractive-index material for quartz, which generally has a refractive index (nd) of 1.45, or general-purpose glass (white plate glass, blue plate glass, BK7, Bolofloat, etc.) with a refractive index of around 1.5. In this case, microcracks may occur in the multilayer film when the temperature is raised during bonding, and the optical properties may be deteriorated, but it is still possible to fabricate elements.

[0064] Similarly, silicon dioxide, which has low film stress, can be used as a low-refractive-index material for quartz, which has a refractive index (nd) of 1.45, or general-purpose glass (white plate glass, blue plate glass, BK7, Bolofloat, etc.), which has a refractive index of around 1.5. In this case, the optical properties will be inferior, but it is still possible to fabricate elements.

[0065] <Second embodiment> Next, a description will be given of an image display device equipped with an illumination optical system having the polarization conversion element 100 configured as above. Fig. 10 is a schematic configuration diagram showing an image display device 200 according to an embodiment of the present technology.

[0066] The image display device 200 of this embodiment includes an illumination optical system 240 that emits polarized light, a spectroscopic optical system 250 that spectroscopically separates the light emitted from the illumination optical system 240, and liquid crystal panels 63, 68, and 73 that modulate the light separated by the spectroscopic optical system 250. The image display device 200 also includes a light combining unit 80 that combines the light modulated by the liquid crystal panels 63, 68, and 73, and a projection lens 90 that projects the light combined by the light combining unit 80.

[0067] In the illumination optical system 240, white light emitted from a light source 41, such as an ultra-high pressure mercury lamp, is reflected by a reflector 42 and passes through explosion-proof glass 43 before being emitted. A UV-cut filter 44 removes ultraviolet light from the light that has passed through the explosion-proof glass 43. The light that has passed through the UV-cut filter 44 has its brightness unevenness reduced by a first fly-eye lens 45 and a second fly-eye lens 46, and then enters the polarization conversion element 100. The polarization conversion element 100 converts the incident light into, for example, P-polarized light. This P-polarized light is then emitted from the illumination optical system 240.

[0068] The light emitted from the illumination optical system 240 is collimated by a condenser lens 48 and enters the spectroscopic optical system 250. The spectroscopic optical system 250 includes a dichroic mirror 49 that transmits blue light and reflects red and green light out of the white light from the illumination optical system 240. The spectroscopic optical system 250 also includes a dichroic mirror 53 that is disposed on the optical path of the light reflected by the dichroic mirror 49 and reflects green light and transmits red light.

[0069] The blue light transmitted through dichroic mirror 49 passes through UV absorption filter 51, where ultraviolet rays are filtered out. The blue light transmitted through UV absorption filter 51 is reflected by mirror 52 and enters condenser lens 61. The polarization direction of the blue light condensed by condenser lens 61 is aligned to linear polarization by incident-side polarizing plate 62, and the light enters liquid crystal panel 63. An exit-side polarizing plate 64 is arranged downstream of liquid crystal panel 63 as an analyzer, and transmits only light that has a predetermined polarization direction out of the light that has passed through liquid crystal panel 63.

[0070] The liquid crystal panel 63 may be, for example, a twisted nematic type. In this case, a signal voltage for blue light corresponding to image information is applied to each pixel of the liquid crystal panel 63, and the polarization direction of the blue light passing through each pixel is rotated in response to this voltage. By passing blue light having a different polarization direction for each pixel through the exit-side polarizing plate 64, blue image light having an intensity distribution corresponding to the image information is obtained. The blue light passing through the exit-side polarizing plate 64 passes through a half-wave film 65 provided on the incident surface of the light combining unit 80, where its polarization direction is rotated by 90°, and then enters the light combining unit 80, such as a combining prism.

[0071] The green light reflected by dichroic mirror 53 enters condenser lens 66. The green light collected by condenser lens 66 is converted into linearly polarized light by incident-side polarizer 67 and enters liquid crystal panel 68. Liquid crystal panel 68 rotates the polarization direction of the green light passing through each pixel in accordance with image information. The green light that has passed through liquid crystal panel 68 passes through exit-side polarizer 69, thereby obtaining green image light having an intensity distribution corresponding to the image information. The green light that has passed through exit-side polarizer 69 enters light combining unit 80.

[0072] On the other hand, the red light transmitted through dichroic mirror 53 is incident on wavelength-selective filter 56 via condenser lens 54 and mirror 55. Wavelength-selective filter 56 is composed of a band-pass filter or the like, and transmits only effective red light to the subsequent stage. The red light transmitted through wavelength-selective filter 56 is incident on condenser lens 71 via condenser lens 57 and mirror 58.

[0073] The red light condensed by condenser lens 71 is converted into linearly polarized light by incident-side polarizer 72 and enters liquid crystal panel 73. Liquid crystal panel 73 rotates the polarization direction of the red light passing through each pixel in accordance with image information. The red light that has passed through liquid crystal panel 73 passes through exit-side polarizer 74, thereby obtaining red image light having an intensity distribution corresponding to the image information. The red light that has passed through exit-side polarizer 74 passes through half-wave film 75 provided on the entrance surface of light combining unit 80, whereby the polarization direction of the red light is rotated by 90°, before entering light combining unit 80.

[0074] The light combining unit 80 combines the red, green, and blue lights onto the same optical path. The combined light emitted from the combining prism is enlarged and projected by the projection lens 90 onto a screen (not shown).

[0075] Here, a transmissive liquid crystal panel is shown as a modulator that modulates light according to image information, but modulation may also be performed using other methods such as a reflective liquid crystal panel or a GLV (Grating Light Valve).

[0076] According to the image display device 200 of this embodiment, since the polarization conversion element 100 described in the first embodiment is provided in the illumination optical system 240, it is possible to construct an illumination optical system that is excellent in heat resistance, light resistance, and light transmittance. Furthermore, since it is possible to accommodate higher output of the light source or higher density of light energy, it is possible to form a high-brightness image.

[0077] Although the embodiments of the present technology have been described above, it goes without saying that the present technology is not limited to the above-described embodiments and various modifications can be made.

[0078] For example, in the above embodiment, the polarization separation film 131 of the polarization separation element 10 is configured with an optical function film that reflects S-polarized light and transmits P-polarized light, but is not limited to this and may be configured with an optical function film that reflects P-polarized light and transmits S-polarized light. Alternatively, the inorganic wave plate 20 is not limited to a wave plate that converts S-polarized light to P-polarized light, and a wave plate that converts P-polarized light to S-polarized light may be used.

[0079] The number of layers in the polarization splitting film 131 is not limited to 12, and may be, for example, 9 to 13. The thickness of each layer can also be set arbitrarily. The total thickness of the polarization splitting film 131 is also not particularly limited, and can be set appropriately, for example, to 1500 to 2000 nm.

[0080] Furthermore, in the above embodiments, a polarization separation element having a polarization separation film has been used as an example of an optical element, but this is not limited to this, and the present technology can also be applied to optical elements having optically functional films such as anti-reflection films and wavelength selection films.

[0081] The present technology can also be configured as follows. (1) a first glass substrate having a first bonding surface; a second glass substrate having a second bonding surface; an optically functional film covering the first bonding surface; an inorganic bonding layer made of a silicon compound provided between the optical function film and the second bonding surface and bonded to the second bonding surface by direct bonding; An optical element comprising: (2) The optical element according to (1), The silicon compound is silicon oxide. Optical elements. (3) The optical element according to (1) or (2), The direct bonding is plasma bonding. Optical elements. (4) The optical element according to any one of (1) to (3) above, The surface roughness (Ra) of the inorganic bonding layer and the second bonding surface is 2 nm or less. Optical elements. (5) The optical element according to any one of (1) to (4) above, The thickness of the inorganic bonding layer is 200 nm or more and 1000 nm or less. Optical elements. (6) The optical element according to any one of (1) to (5) above, The optical functional film is an optical multilayer film in which a first dielectric having a first refractive index and a second dielectric having a second refractive index different from the first refractive index are alternately laminated. Optical elements. (7) The optical element according to (6), The optical multilayer film is a polarization separation film. Optical elements. (8) The optical element according to (7), The refractive index (n d ) is between 1.6 and 1.8 Optical elements. (9) A polarization separation element including a first glass substrate having a first bonding surface, a second glass substrate having a second bonding surface, an optical function film provided on the first bonding surface, and an inorganic bonding layer made of a silicon compound provided between the optical function film and the second bonding surface and directly bonded to the second bonding surface; an inorganic wave plate that converts the first polarized light transmitted through the inorganic bonding layer into a second polarized light that is orthogonal to the first polarized light; a support that commonly supports the polarization separation element and the inorganic wave plate so that the inorganic wave plate faces the polarization separation element with a gap therebetween; A polarization conversion element comprising: (10) A polarization separation element including a first glass substrate having a first bonding surface, a second glass substrate having a second bonding surface, an optical function film provided on the first bonding surface, and an inorganic bonding layer made of a silicon compound provided between the optical function film and the second bonding surface and directly bonded to the second bonding surface; an inorganic wave plate that converts the first polarized light transmitted through the inorganic bonding layer into a second polarized light that is orthogonal to the first polarized light; a support that commonly supports the polarization separation element and the inorganic wave plate so that the inorganic wave plate faces the polarization separation element with a gap therebetween; A polarization conversion element having An image display device comprising: (11) forming an optically functional film on the surface of a first glass substrate; forming an inorganic bonding layer made of a silicon compound on the optical functional film; A second glass substrate is bonded to the inorganic bonding layer by plasma bonding. A method for manufacturing an optical element. (12) The method for producing an optical element according to (11) above, further comprising: After forming the inorganic bonding layer, and before bonding the second glass substrate, the bonding surfaces of the inorganic bonding layer and the second glass substrate are polished. A method for manufacturing an optical element. (13) The method for producing an optical element according to (11) above, further comprising: Before forming the optically functional film, the surface of the first glass substrate is polished; Before bonding the second glass substrate to the inorganic bonding layer, the bonding surface of the second glass substrate is polished. A method for manufacturing an optical element. (14) A method for producing an optical element according to any one of (11) to (13) above, The inorganic bonding layer is formed by ion beam sputtering or bias sputtering. A method for manufacturing an optical element. [Explanation of symbols]

[0082] 10...Polarization separation element 11...First glass substrate 12...Second glass substrate 13...Polarization separation layer 14...Reflection layer 20...Inorganic wave plate 30...Support 100...wavelength conversion element 131...Polarized light separation film 132...Inorganic bonding layer 200...Image display device

Claims

1. a polarization separation element having a light incident surface and a light exit surface, the polarization separation element including: a first glass substrate having a first bonding surface; a second glass substrate having a second bonding surface; an optically functional film provided on the first bonding surface; and a bonding layer including a silicon compound, which is an inorganic material, provided between the optically functional film and the second bonding surface and bonded to the second bonding surface; a wave plate that converts the first polarized light transmitted through the bonding layer into a second polarized light that is orthogonal to the first polarized light; a support body including a first support frame disposed on the light incident surface side and having a plurality of apertures, a second support frame disposed on the light exit surface side and supporting the wave plate, and an adhesive member for bonding the second support frame and the wave plate, wherein the first support frame and the second support frame are joined together to form a support body that commonly supports the polarization separation element and the wave plate such that the wave plate faces the polarization separation element via a gap; A polarization conversion element comprising:

2. The polarization conversion element according to claim 1, The adhesive member is disposed in an area that is not irradiated with incident light. Polarization conversion element.

3. 3. The polarization conversion element according to claim 1, The silicon compound is silicon oxide. Polarization conversion element.

4. The polarization conversion element according to any one of claims 1 to 3, The polarization separation element is configured by arranging a plurality of parallelepiped prisms in a single axis direction parallel to the light incident surface. Polarization conversion element.

5. 5. The polarization conversion element according to claim 1, The optical functional film is composed of 9 or more layers. Polarization conversion element.

6. 6. The polarization conversion element according to claim 1, The bonding layer is formed to a thickness of about 5000 nm. Polarization conversion element.

7. 7. The polarization conversion element according to claim 1, The bonding layer is formed to a thickness greater than that of the optically functional film. Polarization conversion element.

8. The polarization conversion element according to any one of claims 1 to 7, The second bonding surface and the bonding layer are bonded by plasma bonding. Polarization conversion element.

9. 9. The polarization conversion element according to claim 1, The surface roughness (Ra) of the bonding layer and the second bonding surface is 2 nm or less. Polarization conversion element.

10. 10. The polarization conversion element according to claim 1, The thickness of the bonding layer is 200 nm or more and 1000 nm or less. Polarization conversion element.

11. The polarization conversion element according to any one of claims 1 to 10, The optical functional film is an optical multilayer film in which a first dielectric having a first refractive index and a second dielectric having a second refractive index different from the first refractive index are alternately laminated. Polarization conversion element.

12. The polarization conversion element according to claim 11, The optical multilayer film is a polarization separation film. Polarization conversion element.

13. The polarization conversion element according to any one of claims 1 to 12, The refractive index (nd) of each of the first glass substrate and the second glass substrate is 1.6 or more and 1.8 or less. Polarization conversion element.

14. 14. An illumination optical system comprising: a polarization conversion element according to claim 1; and a light source that generates light that is incident on the polarization conversion element. An image display device comprising:

15. The image display device according to claim 14, the illumination optical system further includes a first fly-eye lens and a second fly-eye lens; The first fly-eye lens and the second fly-eye lens reduce unevenness in brightness of light incident on the polarization conversion element. Image display device.

16. 16. The image display device according to claim 14 or 15, The light source emits white light. Image display device.

17. 17. The image display device according to claim 14, The illumination optical system further includes a lens for collimating the light emitted from the illumination optical system. Image display device.

Images