JP7597165B2 - Polarization conversion element and image display device - Google Patents

Description

This technology relates to an optical element having an optically functional film, a polarization conversion element and an image display device including the same, and a method for manufacturing the optical element.

Projection-type image display devices (projectors) use polarization conversion elements to increase 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.

JP 2010-113056 A

In recent years, in the field of projection-type image display devices, efforts have been made to increase the output of light sources or the density of light energy in order to achieve higher image brightness. 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 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.

In view of the above circumstances, the objective of this technology is to provide an optical element, a polarization conversion element, and an image display device including the same, that are excellent in heat resistance, light resistance, and light transmittance, as well as a method for manufacturing the optical element.

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.

The optical element has excellent heat resistance and light resistance because the joint between the optically functional film and the second joint surface is made of an inorganic joint layer made of a silicon compound. Furthermore, because the joint layer is directly bonded to the second joint surface, the refractive index difference at the interface is small, and therefore the transmittance can be improved.

The silicon compound may be silicon oxide.

The direct bonding may be plasma bonding.

In this case, the surface roughness (Ra) of the inorganic bonding layer and the second bonding surface can be 2 nm or less.

The thickness of the inorganic bonding layer can be 200 nm or more and 1000 nm or less.

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 laminated.

The optical multilayer film can be a polarization separation film.

The refractive index (n _d ) of each of the first glass substrate and the second glass substrate may be 1.6 or more and 1.8 or less.

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.

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.

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.

The method for manufacturing the optical element may further include polishing the 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.

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

The optically functional film may be formed by ion beam sputtering or bias sputtering.

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.

1 is an exploded perspective view showing a configuration of a polarization conversion element according to an embodiment of the present technology; 2 is a schematic cross-sectional view showing a configuration of a main part of the polarization conversion element. FIG. 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. 3A to 3C are diagrams illustrating a method for producing the polarization separation element. 3A to 3C are diagrams illustrating a method for producing the polarization separation element. 3A to 3C are schematic process diagrams illustrating an example of a method for producing the polarization separation element. 3 is a schematic diagram showing an example of a layer structure of a polarization separation film in the polarization separation element. FIG. 5A to 5C are schematic process diagrams illustrating another example of the method for producing the polarization separation element. 5A to 5C are diagrams illustrating an example of optical characteristics of the polarization separation element. 1 is a schematic configuration diagram illustrating an image display device according to an embodiment of the present technology.

Embodiments of this technology are described below with reference to the drawings.

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).

[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.

The polarization separation element 10 is formed, for example, by bonding multiple parallelepiped-shaped prisms together in the Z-axis direction. In this embodiment, the multiple prisms have 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 arranged alternately.

Figure 3 is a schematic cross-sectional view of the main part of 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.

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 having a first refractive index and a second dielectric having a second refractive index different from the first refractive index are alternately laminated.

The first dielectric is made of a material having a smaller refractive index (nd) than the second dielectric. The refractive indexes of the first dielectric and the second dielectric 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 SiO ₂ (nd: 1.46) and the second dielectric is Ta ₂ O ₅ (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).

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 a part of the polarization separation layer 13 and performs a predetermined polarization separation function by being laminated on the polarization separation film 131.

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. The inorganic bonding layer 132 is directly bonded to the bonding surface 12a of the second glass substrate 12, and therefore the inorganic bonding layer 132 can be integrally bonded to the bonding surface 12a without the need for an adhesive at the interface.

An example of direct bonding is plasma bonding. In plasma bonding, silicon-oxygen covalent bonds or silicon-silicon covalent bonds are 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 also be used for direct bonding.

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 SiO ₂ , and therefore, although there is a refractive index difference at the bonding interface between the inorganic bonding layer 132 and the 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 caused by the refractive index difference can be eliminated.

The surface roughness (Ra) of the inorganic bonding layer 132 and the bonding surface 12a is 2 nm or less. This allows for stable direct bonding processing 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.

The thickness of the inorganic bonding layer 132 may be sufficient to form the bonding interface, and may be, 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 making it possible to miniaturize the polarization separation element 10 and the polarization conversion element 100, and suppressing the amount of gas generated by heating during bonding with the second glass substrate 12. By making the thickness of the inorganic bonding layer 132 200 nm or more, the inorganic bonding layer 132 can function as a 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.

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 composed 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 be composed of a dielectric multilayer film.

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). There are no particular limitations on the bonding method, and the bonding 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.

The polarization separation element 10 is formed, for example, as shown in FIG. 4, 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, each individual polarization separation element 10p is lapped and polished at both ends in the longitudinal direction, anti-reflection films 101m and 102m are formed on the light entrance surface 101 and the light exit surface 102, and then both ends are bonded together in the longitudinal direction.

[Inorganic Waveplate]
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.

An anti-reflection film 21 is formed on each of the light incident and light exiting surfaces of the inorganic wave plate 20. The anti-reflection 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.

The inorganic wave plates 20 have a rectangular shape extending in the X-axis direction, and are arranged at intervals on the optical path of the reflected light (S-polarized light Ls) from the reflective layer 14 as shown in FIG. 1. Each inorganic wave plate 20 is commonly supported by the second support frame 120.

[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 therebetween.

The support 30 supports both the polarization separation element 10 and the inorganic wavelength plate 20 so that the inorganic wavelength plate 20 faces a predetermined position of 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 wavelength plate 20 without bonding them to each other with an adhesive or the like. This makes it possible to avoid a decrease in heat resistance, light resistance, and light transmittance due to the presence of an adhesive between the polarization separation element 10 and the inorganic wavelength plate 20.

The first support frame 110 has a frame shape and contacts the light incidence 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 their mutual bonding strength. 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 the second support frame 120 to 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.

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

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.

(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 forming the inorganic bonding layer 132, 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.

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).

The inorganic bonding layer 132 and the bonding surface 12a of the second glass substrate 12 are polished so that the surface roughness (Ra) is 1 nm or less, more preferably 0.5 nm or less. There are no particular limitations on the polishing method, and typically, a high-precision polishing method capable of adjusting the surface roughness on the nm order is used. This allows the desired bonding strength to be obtained by plasma bonding, which will be described later.

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 easier 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.

Plasma bonding is used to bond the inorganic bonding layer 132 to the second glass substrate 12. In plasma bonding, first, a plasma activation process 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.

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 type 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.

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, 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.

(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), and 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.

In this example, the polarization separation film 131 and the inorganic bonding layer 132 are formed by a film formation method that provides a high degree of surface flatness. For example, a film formation method that provides a low surface roughness of the film formation surface, such as ion beam sputtering or bias sputtering, can be used as such a film formation method, and this makes it possible to form a vapor deposition film with a high degree of flatness, such as a surface roughness (Ra) of 0.5 nm or less. 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 degree of flatness without the need for a polishing process, and the thickness of the inorganic bonding layer 132 can be reduced to, for example, about 200 nm.

In the bonding process between the inorganic bonding layer 132 and the second glass substrate 12, a plasma bonding process similar to that of the above-mentioned 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 outgassing from the inorganic bonding layer 132 during annealing.

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 composed of an 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 reflections caused by the refractive index difference and improve the transmittance.

For example, FIG. 9 shows the optical characteristics of the polarization separation element 10 produced 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 the same optical characteristics as those in FIG. 9 can be obtained by the polarization separation element produced by the above-mentioned method 2.

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 a 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.

In contrast, according to the polarization separation element 10 of this embodiment, since no organic adhesive is present at the joint between the glass substrate and the polarization separation film, heat resistance and light resistance are improved, and it is possible to fully respond to higher output from light sources or higher density light energy. Furthermore, 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 reflections caused by the refractive index difference can be eliminated and transmittance can be improved.

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.

Furthermore, according to the polarization conversion element 100 of this embodiment, the inorganic wavelength plate 20 is commonly supported by the support 30 that supports the polarization separation element 10, so that the inorganic wavelength plate 20 can be placed in a non-contact manner with 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 wavelength plate 20. This makes it possible to improve the heat resistance, light resistance, and light transmittance of the polarization conversion element 100.

In addition, this technology can also be applied when _MgF2, which has a large film stress, is used 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 be deteriorated, but it is possible to fabricate an element.

Similarly, silicon dioxide, which has low film stress, may 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 about 1.5. In this case, the optical properties will be inferior, but it is possible to fabricate the element.

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.

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.

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. The 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 brightness 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.

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 from the white light from the illumination optical system 240 and reflects red light and green light. 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, reflects green light, and transmits red light.

The blue light that passes through the dichroic mirror 49 passes through a UV absorbing filter 51 to block ultraviolet rays. The blue light that passes through the UV absorbing filter 51 is reflected by a mirror 52 and enters a condenser lens 61. The blue light that is condensed by the condenser lens 61 has its polarization direction aligned to linear polarization by an entrance polarizing plate 62 and enters a liquid crystal panel 63. An exit polarizing plate 64 is arranged behind the liquid crystal panel 63 as an analyzer, and transmits only light that has a specified polarization direction out of the light that has passed through the liquid crystal panel 63.

For example, a twisted nematic type can be used for the liquid crystal panel 63. 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 with 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.

The green light reflected by the dichroic mirror 53 enters the condenser lens 66. The green light collected by the condenser lens 66 is linearly polarized by the entrance polarizer 67 and enters the liquid crystal panel 68. The liquid crystal panel 68 rotates the polarization direction of the green light passing through each pixel according to the image information. The green light that has passed through the liquid crystal panel 68 passes through the exit polarizer 69, thereby obtaining green image light having an intensity distribution corresponding to the image information. The green light that has passed through the exit polarizer 69 enters the light combining unit 80.

Meanwhile, the red light that passes through the dichroic mirror 53 passes through the condenser lens 54 and the mirror 55 and enters the wavelength selection filter 56. 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 that passes through the wavelength selection filter 56 passes through the condenser lens 57 and the mirror 58 and enters the condenser lens 71.

The red light collected by the condenser lens 71 is linearly polarized by the entrance polarizer 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 according to the image information. The red light that has passed through the liquid crystal panel 73 passes through the exit polarizer 74, thereby obtaining red image light having an intensity distribution corresponding to the image information. The red light that has passed through the exit polarizer 74 passes through a 1/2 wavelength film 75 provided on the entrance surface of the light combining unit 80, whereby the polarization direction is rotated by 90°, and then the red light enters the light combining unit 80.

The light combining unit 80 combines the red, green, and blue lights on 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).

Note that, 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 using other methods such as a reflective liquid crystal panel or a GLV (Grating Light Valve).

According to the image display device 200 of this embodiment, since the illumination optical system 240 is provided with the polarization conversion element 100 described in the first embodiment, it is possible to construct an illumination optical system with excellent heat resistance, light resistance, and light transmittance. In addition, since it can also accommodate high-output light sources or high-density light energy, it is possible to form images with high brightness.

The above describes the embodiments of the present technology, but the present technology is not limited to the above-mentioned embodiments, and various modifications can be made.

For example, in the above embodiment, the polarization separation film 131 of the polarization separation element 10 is configured with an optically functional film that reflects S-polarized light and transmits P-polarized light, but this is not limited to this, and it may be configured with an optically functional 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.

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

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

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 optically functional film and the second bonding surface and bonded to the second bonding surface by direct bonding.
(2) The optical element according to (1),
The silicon compound is a silicon oxide.
(3) The optical element according to (1) or (2),
The direct bonding is plasma bonding.
(4) The optical element according to any one of (1) to (3),
The optical element, wherein the inorganic bonding layer and the second bonding surface have a surface roughness (Ra) of 2 nm or less.
(5) The optical element according to any one of (1) to (4),
The optical element, wherein the inorganic bonding layer has a thickness of 200 nm or more and 1000 nm or less.
(6) The optical element according to any one of (1) to (5) above,
The optical element, wherein 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.
(7) The optical element according to (6) above,
The optical element, wherein the optical multilayer film is a polarization separation film.
(8) The optical element according to (7) above,
The optical element, wherein the refractive index (n _d ) of each of the first glass substrate and the second glass substrate is 1.6 or more and 1.8 or less.
(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;
a polarization conversion element comprising: an inorganic wavelength plate that converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light perpendicular to the first polarized light; and a support that commonly supports the polarization separation element and the inorganic wavelength plate such that the inorganic wavelength plate faces the polarization separation element with a gap therebetween.
(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 image display device comprising: a polarization conversion element having: an inorganic wavelength plate that converts a first polarized light transmitted through the inorganic bonding layer into a second polarized light perpendicular to the first polarized light; and a support that commonly supports the polarization separation element and the inorganic wavelength plate so that the inorganic wavelength plate faces the polarization separation element with a gap therebetween.
(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.
(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, polishing bonding surfaces of the inorganic bonding layer and the second glass base material.
(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;
a bonding surface of the second glass substrate is polished before bonding the second glass substrate to the inorganic bonding layer.
(14) A method for producing an optical element according to any one of (11) to (13) above, comprising the steps of:
The method for manufacturing an optical element, wherein the inorganic bonding layer is formed by an ion beam sputtering method or a bias sputtering method.

REFERENCE SIGNS LIST 10 Polarization separation element 11 First glass substrate 12 Second glass substrate 13 Polarization separation layer 14 Reflection layer 20 Inorganic wavelength plate 30 Support 100 Wavelength conversion element 131 Polarization separation film 132 Inorganic bonding layer 200 Image display device

Claims (19)

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 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 polarization conversion element comprising: a first support frame arranged on the light incident surface side and having a plurality of apertures; a second support frame arranged on the light exit surface side and supporting the inorganic wavelength plate; and an adhesive member for adhering the second support frame and the inorganic wavelength plate , the first support frame and the second support frame being joined together to commonly support the polarization separation element and the inorganic wavelength plate so that the inorganic wavelength plate faces the polarization separation element with a gap therebetween. The polarization conversion element according to claim 1 ,
The adhesive member is disposed in an area of the polarization conversion element that is not irradiated with incident light. 3. The polarization conversion element according to claim 1,
The silicon compound is a silicon oxide. The polarization conversion element according to any one of claims 1 to 3,
The direct bonding is plasma bonding. The polarization conversion element according to any one of claims 1 to 4,
The inorganic bonding layer and the second bonding surface each have a surface roughness (Ra) of 2 nm or less. The polarization conversion element according to any one of claims 1 to 5,
A polarization conversion element, wherein the inorganic bonding layer has a thickness of 200 nm or more and 1000 nm or less. The polarization conversion element according to any one of claims 1 to 6,
A polarization conversion element, wherein 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 stacked. The polarization conversion element according to claim 7,
The optical multilayer film is a polarization separation film. The polarization conversion element according to claim 8 ,
A polarization conversion element, wherein 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. 1. An image display device comprising an illumination optical system having a polarization conversion element and a light source that generates light incident on the polarization conversion element,
The polarization conversion element is a polarization separation element having a light incident surface and a light exit surface,
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;
An image display device comprising: a first support frame arranged on the light incident surface side and having a plurality of apertures; a second support frame arranged on the light exit surface side and supporting the inorganic wavelength plate; and an adhesive member for adhering the second support frame and the inorganic wavelength plate , the first support frame and the second support frame being joined together to commonly support the polarization separation element and the inorganic wavelength plate so that the inorganic wavelength plate faces the polarization separation element with a gap therebetween. The image display device according to claim 10,
The image display device, wherein the adhesive member is disposed in an area where incident light is not irradiated. The image display device according to claim 10 or 11,
a spectroscopic optical system having at least one dichroic mirror that separates the light polarized by the polarization conversion element into light corresponding to a predetermined color;
at least one liquid crystal panel that modulates the light separated by the spectroscopic optical system;
a light combining unit that combines the light modulated by the liquid crystal panel;
and a projection lens that projects the light combined by the light combining unit. The image display device according to any one of claims 10 to 12,
The image display device, wherein the silicon compound is a silicon oxide. The image display device according to any one of claims 10 to 13,
The image display device, wherein the direct bonding is plasma bonding. The image display device according to any one of claims 10 to 14,
The image display device, wherein the inorganic bonding layer and the second bonding surface have a surface roughness (Ra) of 2 nm or less. The image display device according to any one of claims 10 to 15,
The image display device, wherein the inorganic bonding layer has a thickness of 200 nm or more and 1000 nm or less. The image display device according to any one of claims 10 to 16,
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 stacked. The image display device according to claim 17,
The image display device, wherein the optical multilayer film is a polarization separation film. The image display device according to claim 18,
The image display device, wherein 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.

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