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 permeability, a polarization conversion element and an image display device including the same, and a method for manufacturing the optical element.SOLUTION: An optical element according to one form of the present technique is provided with a first glass base material, a second glass base material, an optical functional film, and an inorganic joint layer. The first glass base material has a first joint surface. The second glass base material has a second joint surface. The optical functional film covers the first joint surface. The inorganic joint layer is provided between the optical functional layer and the second joint surface, and is formed of a silicon compound joined to the second joint surface by direct joining.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 a polarization conversion element of this kind having 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] JP 2010-113056 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, in order to realize high brightness images in projection type image display devices, the output of light sources or the density of light energy has been increased. For this reason, further improvements in heat resistance, light resistance, and light transmittance are required for polarization separation elements. However, conventional polarization separation elements use an organic adhesive at the joint between the glass substrate and the polarization separation film, which results in low heat resistance and unavoidable deterioration 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 having excellent heat resistance, light resistance, and light transmittance, a polarization conversion element, an image display device including the same, and 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 optically functional film covers the first bonding surface. The inorganic bonding layer is provided between the optically functional 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 optically functional film and the second bonding surface is made of an inorganic bonding layer made of a silicon compound. Furthermore, the bonding layer is directly bonded to the second bonding surface, so that the refractive index difference at the interface is small, and therefore the transmittance can be improved.

[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 polarized light 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 waveplate 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 wave 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 waveplate 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 a 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 base material before bonding the second glass base material after forming the inorganic bonding layer.

[0019] Alternatively, the method for manufacturing an optical element may include polishing a surface of the first glass substrate before forming the optical functional film, and polishing a 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 an ion beam sputtering method or a bias sputtering method. Effect 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. Note that the effects described herein are not necessarily limited to those described herein, and may be any of the effects described in this disclosure. [Brief description 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; [Diagram 2] 2 is a schematic cross-sectional view showing a configuration of a main part of the polarization conversion element. FIG. [Diagram 3] 3 is a schematic cross-sectional view of a main part showing a 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. [Diagram 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 producing 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 illustrating another example of the method for producing the polarization separation element. [Figure 9] 5A to 5C 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 PREFERRED EMBODIMENTS

[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 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 (polarizing beam splitter) that transmits or reflects the 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, a polarization separation layer 13 that reflects S-polarized light and transmits P-polarized light, and a reflection layer 14 that reflects 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 composed 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 composed 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 a first dielectric material having a first refractive index and a second dielectric material having a second refractive index different from the first refractive index are alternately laminated.

[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 according to 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 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 base material 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 base material 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 base material 12. That is, the inorganic bonding layer 132 functions as a buffer layer for forming the bonding interface. The buffer layer constitutes a part of the polarization separation layer 13 and is laminated on the polarization separation film 131 to perform a predetermined polarization separation function.

[0031] Examples of silicon compounds constituting the inorganic bonding layer 132 include silicon oxide (SiO2, SiO), silicon nitride (SiN), silicon oxynitride (SiON), silicon oxide carbide (SiOC), etc. Since the inorganic bonding layer 132 is directly bonded to the bonding surface 12a of the second glass substrate 12, the inorganic bonding layer 132 can be integrally bonded to the bonding surface 12a without the need for an adhesive at the interface.

[0032] An example of the direct bonding is plasma bonding. In the 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, so that the inorganic bonding layer 132 is firmly fixed to the bonding surface 12a. In addition to plasma bonding, a solid-state bonding method such as diffusion bonding may be used for the direct bonding.

[0033] In this embodiment, the inorganic bonding layer 132 is made of silicon oxide, particularly silicon dioxide. This provides a refractive index close to that of a glass material mainly composed of SiO2, and therefore, although there is a refractive index difference at the bonding interface between the inorganic bonding layer 132 and the second glass base material 12, the thickness of the bonding interface is 1 nm or less, which is sufficiently small compared to the wavelength, and therefore reflection caused by 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. This allows stable direct bonding treatment by plasma bonding of the inorganic bonding layer 132 to the second glass substrate 12. 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, and may have a thickness of, for example, 200 nm or more and 1000 nm or less. This allows the bonding thickness between the first and second glass substrates 11 and 12 to be reduced, thereby enabling the polarization separation element 10 and the polarization conversion element 100 to be miniaturized, and the amount of gas generated by heating during bonding with the second glass substrate 12 to be suppressed. By setting the thickness of the inorganic bonding layer 132 to 200 nm or more, the inorganic bonding layer 132 can function as a part (low refractive index material layer) of the polarization separation layer 13. 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 the dielectric multilayer film is a multilayer film in which silicon oxide and titanium oxide are alternately laminated. The reflective layer 14 may be made of a dielectric multilayer film.

[0037] After the dielectric multilayer film is formed on the surface (the surface opposite to the bonding surface 11a) of the first glass substrate 11, the reflective layer 14 is bonded to the surface (the surface opposite to the bonding surface 12a) of the second glass substrate 12. 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 reflection layer 14 are formed, along a cutting line C. As shown in FIGS. 5A to 5C, both ends of each individual polarization separation element 10p in the longitudinal direction are lapped and polished, and antireflection films 101m and 102m are formed on a light incident surface 101 and a light exit surface 102, and then both 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 interval on the light exit surface 102 of the polarization separation element 10.

[0040] An antireflection film 21 is formed on each of the light incident side and light exit side surfaces of the inorganic wave plate 20. The antireflection film 21 is a dielectric multilayer film, and is composed of, for example, a dielectric multilayer film of magnesium fluoride (MgF2), silicon dioxide (SiO2), TiO2, Ta2O5, 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 commonly supported by a second support frame 120.

[0042] [Support] The support 30 is composed of a joint 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 joined 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 waveplate 20 such that the inorganic waveplate 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 waveplate 20 without bonding the polarization separation element 10 and the inorganic waveplate 20 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 waveplate 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 the surface to support the inorganic wave plate 20. The first and second support frames 110, 120 are reinforced at the periphery to ensure the bonding strength between them. The constituent material of the first and second support frames 110, 120 is not particularly limited, and is typically made of a metal material. The adhesive layer 130 is made of an organic material such as an ultraviolet curing resin, bonds between the second support frame 120 and the inorganic wave plate 20 and the polarization separation element 10, and is arranged in an area where the incident light L is not irradiated. This makes it possible to avoid deterioration of the adhesive layer 130 due to irradiation with light.

[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 manufacturing method of 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 flattened by polishing (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 of 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 applied. 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 for the dielectric multilayer film constituting the polarization separation film 131. The thickness and number of layers of each material layer can be appropriately set according to the required polarization separation characteristics. As an example, as shown in FIG. 7, the polarization separation film 131 is composed of 12 dielectric multilayer films, and a silicon dioxide film constituting the inorganic bonding layer 132 is formed on the upper layer (13th layer).

[0049] The inorganic bonding layer 132 and the bonding surface 12a of the second glass substrate 12 are polished to a surface roughness (Ra) of 1 nm or less, more 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 nm order 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 separation film 131 formed thereon may be 1 nm or more. This makes it easy to control the processing cost of the bonding surface 11a and the film thickness of the polarization separation film 131. In addition, since the thickness of the inorganic bonding layer 132 is 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 for bonding the inorganic bonding layer 132 and the second glass substrate 12. In the 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 may include oxygen (O2), nitrogen (N2), helium (He), argon (Ar), hydrogen (H2), etc. In particular, by using a gas (oxygen in this example) of the same kind as the constituent elements of the inorganic bonding layer 132 and the bonding surface 12a, deterioration of the inorganic bonding layer 132 and the bonding surface 12a can be suppressed.

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

[0054] (Method 2) 8 is a schematic process diagram showing another example of a manufacturing method of 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), the polarization separation film 131 and the inorganic bonding layer 132 are formed in order on the bonding surface 11a of the first glass substrate (FIG. 8B), and then the inorganic bonding layer 132 and the second glass substrate 12 are directly bonded (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 embodiment, a film formation method that provides high surface flatness is used for the polarization separation film 131 and the inorganic bonding layer 132. As such a film formation method, for example, a film formation method that provides low surface roughness of the film formation surface, such as ion beam sputtering or bias sputtering, can be applied, and thus a vapor deposition film with high flatness, such as a surface roughness (Ra) of 0.5 nm or less, can be formed. By forming the polarization separation layer 13 by such a film formation method, the surface of the inorganic bonding layer 132 can be formed with a desired flatness without the need for polishing, and the thickness of the inorganic bonding layer 132 can be reduced to, for example, about 200 nm.

[0056] In the step of bonding the inorganic bonding layer 132 and the second glass substrate 12, a plasma bonding process is performed similar to that in the above-described method 1. 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 the present 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 configured with the inorganic joint layer 132 made of a silicon compound, so that it is possible to realize 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, but the thickness of the joint interface is 1 nm or less, which is sufficiently small compared to the wavelength, so that it is possible to eliminate reflection caused by the refractive index difference and improve the transmittance.

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

[0059] Generally, when forming a polarization separation film using general-purpose glass (white plate glass, blue plate glass, BK7, etc.) with a refractive index (nd) of about 1.5 as the glass substrate, it is difficult to obtain the desired optical characteristics (transmittance) unless MgF2 (magnesium fluoride, nd: 1.38), which is a low refractive index material, is used. However, since MgF2 has a large film stress, it is difficult to form a dielectric multilayer film, and the multilayer film is destroyed when the temperature is raised to 200°C during bonding. 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 it is necessary to use an organic adhesive such as an ultraviolet-curing adhesive. However, since an organic adhesive is used at the joint between the glass substrate and the polarization separation film, the heat resistance is low and deterioration due to light is unavoidable.

[0060] In contrast, according to the polarization separation element 10 of this embodiment, since no organic adhesive is interposed in the joint between the glass substrate and the polarization separation film, heat resistance and light resistance are improved, and it becomes possible to fully cope with higher output of the light source or higher density of the light energy. In addition, since there is no adhesive on the optical path of the light, although there is a refractive index difference at the joint interface, the thickness of the joint interface is 1 nm or less, which is sufficiently small compared to the wavelength, so that it is possible to eliminate reflection caused by the refractive index difference and improve the 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, 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, Ta2O5 as the high refractive index material.

[0062] Furthermore, according to the polarization conversion element 100 of this embodiment, since the inorganic waveplate 20 is supported in common by the support 30 that supports the polarization separation element 10, the inorganic waveplate 20 can be disposed in a non-contact manner with the light exit surface 102 of the polarization separation element 10 without interposing an organic adhesive on the optical path from the polarization separation element 10 to the inorganic waveplate 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 large 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 about 1.5. In this case, microcracks may occur in the multilayer film when the temperature is raised during bonding, and the optical properties may deteriorate, but it is possible to fabricate the element.

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

[0065] <Second embodiment> Next, a description will be given of an image display device including 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 disperses the light emitted from the illumination optical system 240, and liquid crystal panels 63, 68, and 73 that modulate the light dispersed 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 extra-high pressure mercury lamp is reflected by a reflector 42 and passes through an explosion-proof glass 43 before being emitted. A UV cut filter 44 removes ultraviolet rays 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 luminance unevenness reduced by a first fly-eye lens 45 and a second fly-eye lens 46, and is then incident on 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 light 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 blue light condensed by condenser lens 61 has its polarization direction aligned to linear polarization by entrance side polarizing plate 62, and enters liquid crystal panel 63. An exit side polarizing plate 64 is disposed after liquid crystal panel 63 as an analyzer, which transmits only light having a predetermined polarization direction out of the light transmitted 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 according to this voltage. By passing blue light having a different polarization direction for each pixel through the exit polarizing plate 64, blue image light having an intensity distribution corresponding to the image information is obtained. The blue light passing through the exit polarizing plate 64 has its polarization direction rotated by 90° by passing through a 1 / 2 wavelength film 65 provided on the entrance surface of the light combining unit 80, 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 linearly polarized by entrance 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 polarizer 69, thereby obtaining green image light having an intensity distribution corresponding to the image information. The green light that has passed through exit polarizer 69 enters light combining section 80.

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

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

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

[0075] Although a transmissive liquid crystal panel is shown here as a modulator that modulates light in accordance with image information, modulation may also be performed by 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 excellent in heat resistance, light resistance and light transmittance. In addition, since it is possible to cope with an increase in the output of the light source or an increase in the density of the light energy, it is possible to form an image with high brightness.

[0077] Although the embodiments of the present technology have been described above, the present technology is not limited to the above-described embodiments, and various modifications can be made, as a matter of course.

[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 waveplate 20 is not limited to a waveplate that converts S-polarized light to P-polarized light, and a waveplate that converts P-polarized light to S-polarized light may be used.

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

[0080] Furthermore, in the above embodiments, a polarization separation element having a polarization separation film has been described 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 a 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 greater than or equal to 1.6 and less than or equal to 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 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; an inorganic wave plate that converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light perpendicular to the first polarized light; a support that 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; 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 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; an inorganic wave plate that converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light perpendicular to the first polarized light; a support that 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; A polarization conversion element having An image display device comprising: (11) forming an optically functional film on a 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 base material, the bonding surfaces of the inorganic bonding layer and the second glass base material 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, comprising the steps of: 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 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 perpendicular 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 adhering the second support frame and the wave plate, the first support frame and the second support frame being joined together to commonly support the polarization separation element and the wave plate such that the wave plate faces the polarization separation element with a gap therebetween; A polarization conversion element comprising:

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

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

4. A polarization conversion element according to any one of claims 1 to 3, The bonding layer includes silicon, carbon, and oxygen. Polarization conversion element.

5. A polarization conversion element according to any one of claims 1 to 4, The polarization separation element is configured by arranging a plurality of parallelepiped prisms in one axial direction. Polarization conversion element.

6. A polarization conversion element according to any one of claims 1 to 5, A layer containing silicon and oxygen is provided on the first bonding surface as a first layer of the optical function film. Polarization conversion element.

7. A polarization conversion element according to any one of claims 1 to 6, The optical functional film is composed of 9 or more layers. Polarization conversion element.

8. A polarization conversion element according to any one of claims 1 to 7, The bonding layer is formed to a thickness of about 5000 nm. Polarization conversion element.

9. A polarization conversion element according to any one of claims 1 to 8, The bonding layer is formed to a thickness greater than that of the optically functional film. Polarization conversion element.

10. The polarization conversion element according to any one of claims 1 to 9, The second bonding surface and the bonding layer are bonded by plasma bonding. Polarization conversion element.

11. The polarization conversion element according to any one of claims 1 to 10, The surface roughness (Ra) of the bonding layer and the second bonding surface is 2 nm or less. Polarization conversion element.

12. The polarization conversion element according to any one of claims 1 to 11, The thickness of the bonding layer is 200 nm or more and 1000 nm or less. Polarization conversion element.

13. The polarization conversion element according to any one of claims 1 to 12, 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.

14. The polarization conversion element according to claim 13, The optical multilayer film is a polarization separation film. Polarization conversion element.

15. The polarization conversion element according to any one of claims 1 to 14, 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.

16. An illumination optical system having a polarization conversion element according to any one of claims 1 to 15 and a light source that generates light incident on the polarization conversion element. An image display device comprising:

17. The image display device according to claim 16, 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 luminance of light incident on the polarization conversion element. Image display device.

18. An image display device according to claim 16 or claim 17, The light source emits white light. Image display device.

19. An image display device according to any one of claims 16 to 18, The illumination optical system further includes a lens for collimating the light emitted from the illumination optical system. Image display device.

Images