Optical element, method for manufacturing the same, and projection-type image display device

Abstract

Provided is an optical element or the like that is excellent in durability when a laser light source is used. The optical element includes a substrate that is transparent to light of a wavelength band of use; an antireflection layer; a matching layer; and a birefringent layer composed of an oblique angle deposition film, and has an optical loss of 1.0% or less with respect to light of the wavelength band of use.

Description

Technical Field

[0001] This invention relates to optical elements and their manufacturing methods, as well as projection-type image display devices. Background Technology

[0002] Laser light sources, which can produce high-brightness and high-output light, are attracting much attention as a light source for projectors.

[0003] Optical elements made of angled vapor-deposited films have been used for a long time (for example, see Patent Document 1).

[0004] However, this type of optical element has the problem of aging relative to the laser light source.

[0005] [Existing Technical Documents]

[0006] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2012-256024. Summary of the Invention

[0008] [The problem the invention aims to solve]

[0009] The present invention aims to solve the aforementioned problems and achieve the following objective: to provide an optical element with excellent durability even when using a laser light source, a method for manufacturing the same, and a projection-type image display device incorporating the optical element.

[0010] [Solutions for solving the problem]

[0011] As a solution to the aforementioned problem, the following is provided. That is,

[0012] <1> An optical element, characterized in that it comprises:

[0013] A substrate that is transparent to light using the specified wavelength band;

[0014] Anti-reflective layer;

[0015] Matching layer; and

[0016] A birefringent layer composed of angled vapor-deposited films.

[0017] The optical loss relative to the wavelength band used is less than 1.0%.

[0018] <2> According to the optical element described in <1>, the antireflective layer is a multilayer film consisting of two or more inorganic oxide films with different refractive indices.

[0019] <3> An optical element according to any one of <1> to <2>, wherein the matching layer is a multilayer film consisting of two or more inorganic oxide films with different refractive indices.

[0020] <4> A method for manufacturing an optical element according to any one of <1> to <3>, characterized in that it comprises:

[0021] At least one of the antireflective layer and the matching layer is formed by reactive sputtering with an oxygen flow ratio within a predetermined range, such that the optical loss of the optical element relative to the light used in the wavelength band is less than 1.0%.

[0022] <5> According to the manufacturing method of the optical element described in <4>, wherein,

[0023] At least one of the antireflective layer and the matching layer has an oxide film containing Nb (containing Nb oxide film).

[0024] The method for manufacturing the optical element includes: forming the Nb-containing oxide film using a mixture of inert gas and oxygen via reactive sputtering with Nb as the target.

[0025] When forming the Nb oxide film, the oxygen flow rate ratio in the mixed gas [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] is 18% or more.

[0026] <6> A method for manufacturing an optical element according to any one of <4> to <5>, wherein,

[0027] At least one of the antireflective layer and the matching layer has a Si-containing oxide film (containing Si oxide film).

[0028] The method for manufacturing the optical element includes: forming the Si oxide film by reactive sputtering with Si as a target using a mixture of inert gas and oxygen.

[0029] The oxygen flow rate ratio [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] in the mixed gas during the formation of the Si oxide film is 8% or more.

[0030] <7> A projection-type image display device, characterized in that it comprises: an optical element, a light modulation device, a light source for emitted light, and a projection optical system for projecting modulated light, as described in any one of <1> to <3>.

[0031] The light modulation device and the optical element are arranged in the optical path between the light source and the projection optical system.

[0032] [Invention Effects]

[0033] According to the present invention, an optical element and a method for manufacturing the same thereof, which can solve the aforementioned problems and have excellent durability when using a laser light source, as well as a projection-type image display device having the optical element, can be provided. Attached Figure Description

[0034] Figure 1 This is a cross-sectional view showing an example of the structure of an optical element.

[0035] Figure 2 This is a schematic diagram of the cross-section of the anti-reflective layer.

[0036] Figure 3 This is a slanted view of an angled vapor-deposited film.

[0037] Figure 4 This is a schematic diagram illustrating an example of an angled vapor deposition method for forming an angled vapor deposition film.

[0038] Figure 5 This is a schematic diagram showing an example of the orientation of the vapor deposition direction projected from the vapor deposition source onto the surface to be vaporized.

[0039] Figure 6 This is a flowchart illustrating a method for manufacturing optical elements.

[0040] Figure 7 This is a schematic diagram illustrating an example of the structure of a projection-type image display device.

[0041] Figure 8 This diagram supplements the explanation of the measurement methods for transmittance and reflectance.

[0042] Figure 9A This is a graph showing the transmittance of one sample from Example 1.

[0043] Figure 9B This is a graph showing the reflectance of one sample from Example 1.

[0044] Figure 9C This is a graph showing the optical loss of one sample of Example 1.

[0045] Figure 10A This is a graph showing the transmittance of one sample from Comparative Example 1.

[0046] Figure 10B This is a graph showing the reflectance of one sample from Comparative Example 1.

[0047] Figure 10C This is a graph showing the optical loss of one sample of Comparative Example 1. Detailed Implementation

[0048] Hereinafter, embodiments of the present technology will be described in detail with reference to the accompanying drawings and in the following order.

[0049] 1. Optical components

[0050] 2. Manufacturing methods for optical components

[0051] 3. Projection-type image display device

[0052] 4. Example

[0053] (Optical components)

[0054] The optical element according to this embodiment includes: a substrate that is transparent to light using the wavelength band; an anti-reflective layer; a matching layer; and a birefringent layer composed of a beveled vapor-deposited film. The optical element may also include other components as needed.

[0055] The optical loss of the optical element relative to the light used in the wavelength band is less than 1.0%.

[0056] Optical loss refers to the value of subtracting the transmittance and reflectance of light for the wavelength band used from 100%, which can be expressed by the following formula (1).

[0057] Optical loss (%) = 100% - Transmittance (%) - Reflectance (%) Equation (1)

[0058] There are no particular restrictions on the lower limit of optical loss, and it can be appropriately selected according to the purpose. However, there are situations where productivity may decrease if optical loss is further reduced. Therefore, optical loss can be above 0.1%, above 0.3%, or above 0.5%.

[0059] The wavelength band used can be light, for example, light with a wavelength band of 400nm to 700nm, or light with a wavelength of 455nm.

[0060] Regarding optical loss, it is preferable to use optical loss of less than 1.0% across the entire wavelength band.

[0061] Preferably, the optical loss is below 1.0% across the entire wavelength range of 450nm to 700nm. Furthermore, the longer the wavelength, the lower the optical loss.

[0062] The transmittance and reflectance of optical elements relative to the wavelength band in which they are used can be measured, for example, using a spectrophotometer V-570 manufactured by Nippon Spectrophotometer Co., Ltd.

[0063] Examples of optical elements with such a structure include phase difference elements that impart a phase difference to incident light and phase difference compensation elements.

[0064] Figure 1This is a cross-sectional view showing an example of the structure of an optical element. For example... Figure 1 As shown, the optical element 10 includes: a transparent substrate 11; a matching layer 12 on which high-refractive-index films and low-refractive-index films are alternately stacked, with each layer having a thickness below the operating wavelength; a birefringent layer 13 formed on the matching layer 12, consisting of angled vapor-deposited films; and a protective layer 14 formed on the birefringent layer 13, consisting of a dielectric film. Additionally, a first anti-reflective layer 15A is provided on the transparent substrate 11 side, and a second anti-reflective layer 15B is provided on the protective layer 14 side.

[0065] <Transparent substrate>

[0066] The transparent substrate 11 is transparent to light within the wavelength band in which it is used. The transparent substrate 11 has high transmittance to light within the wavelength band in which it is used. Examples of materials for the transparent substrate 11 include glass, quartz, crystal, and sapphire. The transparent substrate 11 is generally square, but a shape appropriate to the purpose can be selected. The thickness of the transparent substrate 11 is preferably, for example, 0.1 mm or more and 3.0 mm or less.

[0067] <Anti-reflective layer>

[0068] The first anti-reflective layer 15A is provided, for example, in contact with the surface of the transparent substrate 11 opposite to the side of the birefringent layer 13.

[0069] The second antireflective layer 15B is provided as needed, for example, in contact with the side of the protective layer 14 and the birefringent layer 13.

[0070] The first anti-reflective layer 15A and the second anti-reflective layer 15B have anti-reflective functions in the desired operating wavelength band.

[0071] Figure 2 This is a schematic diagram of the cross-section of the first anti-reflective layer. (See diagram below.) Figure 2 The first antireflective layer 15A shown is a multilayer film consisting of two or more inorganic oxide films with different refractive indices. For example, it is formed by alternately stacking a first oxide film 151 and a second oxide film 152 with different refractive indices. The number of antireflective layers can be appropriately determined according to needs, and from a productivity perspective, 5 to 40 layers are preferred. Furthermore, the second antireflective layer 15B is also constructed in the same way as the first antireflective layer 15A.

[0072] The larger the refractive index difference between the first oxide film 151 and the second oxide film 152, the better. However, considering the ease of obtaining the material and the film-forming properties, a difference of 0.5 or more and 1.0 or less is preferred. Furthermore, the refractive index is, for example, the refractive index at a wavelength of 550 nm.

[0073] The oxide film of the first antireflective layer 15A and the oxide film of the second antireflective layer 15B are each composed of an oxide film containing, for example, at least one of Ti, Si, Ta, Al, Ce, Zr, Nb and Hf.

[0074] For example, the antireflective layer can be configured as a multilayer film consisting of an alternating layer of a first oxide film 151 made of niobium oxide with a relatively high refractive index (refractive index 2.3 at wavelength 550 nm) and a second oxide film 152 made of silicon oxide with a relatively low refractive index (refractive index 1.5 at wavelength 550 nm).

[0075] Furthermore, the oxides constituting the antireflective layer can also be non-stoichiometric substances. That is, the atomic ratios of the constituent elements of the oxide may not be simple integer ratios. This is because if an oxide film is formed using methods such as sputtering, the oxide is more likely to be non-stoichiometric. In addition, it is difficult to reliably measure the elemental ratios in the oxide after film formation, making it difficult to determine the elemental ratios in the oxide.

[0076] Given that oxides are non-stoichiometric, for example, oxides containing Nb can be represented by the following formula.

[0077]

[0078] For example, oxides containing Si can be represented by the following formula.

[0079]

[0080] When forming the antireflective layer, reducing the oxygen defects in the formed oxide can reduce the light absorption of the antireflective layer and reduce the optical loss of the optical components.

[0081] The thickness of the antireflective layer is not particularly limited and can be appropriately selected according to the purpose; for example, it can be 250 nm or more and 2,300 nm or less. Furthermore, in this specification, the layer thickness (film thickness) refers to the average film thickness.

[0082] <Matching Layer>

[0083] The matching layer 12 is, for example, a multilayer film consisting of two or more inorganic oxide films with different refractive indices. The matching layer 12 is disposed between the transparent substrate 11 and the birefringent layer 13. The matching layer 12 is designed to eliminate interface reflection light through interference, preventing reflection at the interface between the transparent substrate 11 and the birefringent layer 13. That is, the matching layer 12 is designed to eliminate interface reflection light between the transparent substrate 11 and the matching layer 12, and between the matching layer 12 and the birefringent layer 13.

[0084] The matching layer 12 is composed of an oxide film containing, for example, at least one of Ti, Si, Ta, Al, Ce, Zr, Nb and Hf.

[0085] Furthermore, the oxides constituting the matching layer 12 can also be non-stoichiometric substances. That is, the atomic ratio of the constituent elements of the oxides may not be a simple integer ratio. This is because if an oxide film is formed by methods such as sputtering, the oxides are more likely to be non-stoichiometric.

[0086] When forming the matching layer 12, reducing the oxygen defects of the formed oxide can reduce the light absorption of the matching layer 12 and reduce the optical loss of the optical element.

[0087] The thickness of the matching layer 12 is not particularly limited and can be appropriately selected according to the purpose. For example, it can be above 140nm or below 240nm.

[0088] <Birefringent layer>

[0089] The birefringent layer 13 is composed of a beveled vapor-deposited film.

[0090] In the optical element of the present invention, the birefringent layer 13 is a layer that provides a phase difference.

[0091] exist Figure 1 In the optical element 10 shown, the birefringent layer 13 is disposed between the matching layer 12 and the protective layer 14.

[0092] The birefringent layer 13 may include, for example, a birefringent film made of an inorganic material. As an inorganic material, a dielectric material is preferred, and examples include oxides containing at least one of Si, Nb, Zr, Ti, La, Ta, Al, Hf, and Ce.

[0093] As an inorganic material, tantalum oxide (e.g., Ta2O5) is preferred.

[0094] Examples of the thickness of the birefringent layer 13 include, for example, 200 nm or more and 4, 200 nm or less.

[0095] Figure 3 This is a slanted view of an angled vapor-deposited film. (Example) Figure 3 As shown, the angled vapor-deposited film 23 constituting the birefringent layer 13 is formed by depositing vapor-deposited material along a direction inclined relative to the surface of the transparent substrate 11, or by depositing vapor-deposited material along a direction inclined relative to the normal S orthogonal to the surface to be vapor-deposited 21. The inclination angle relative to the normal S of the surface to be vapor-deposited 21 is preferably 60° or more and 80° or less.

[0096] Birefringent layers are typically formed by depositing multiple layers of such birefringent films.

[0097] Each birefringent film is deposited along a direction inclined relative to the normal S to form a film, and the angle between the film-forming direction of the inorganic material constituting the birefringent film and the surface of the transparent substrate is not 90°.

[0098] Regarding each birefringent film, a method where the angle between the film-forming direction of the inorganic material and the surface of the transparent substrate is not 90° is preferred. For example, a method of forming a birefringent film by oblique evaporation using an oblique evaporation from the evaporation source is preferred. In the case of forming a birefringent layer by multiple oblique evaporations, the evaporation angle is changed and the oblique evaporation is repeated to obtain the final birefringent layer.

[0099] Figure 4 This is a schematic diagram illustrating an example of an angled vapor deposition method for forming an angled vapor deposition film. Figure 5 This is a schematic diagram illustrating an example of projecting the direction of the incoming vapor deposition material from the vapor deposition source onto the orientation (vapor deposition direction) of the surface to be vaporized.

[0100] like Figure 4 As shown, in the case of depositing a film at an angle along the direction of the vapor deposition material from the vapor deposition source R toward the transparent substrate 11, d represents the orientation of the line segment that projects the film deposition direction of the birefringent film onto the surface of the transparent substrate.

[0101] like Figure 4 and Figure 5 As shown, a film is formed by alternatingly depositing films using vapor deposition from the first vapor deposition direction 31 and vapor deposition from the second vapor deposition direction 32. Specifically, after depositing a film using vapor deposition from the first vapor deposition direction 31, the object surface to be deposited is rotated 180° around a centerline perpendicular to the object surface and passing through its center, thereby depositing a film using vapor deposition from the second vapor deposition direction 32. This film deposition process is repeated to obtain a film in which a first obliquely deposited film having a first oblique direction relative to the normal of the object surface to be deposited and a second obliquely deposited film having a second oblique direction are alternately deposited.

[0102] <Protective Layer>

[0103] The protective layer 14 is made of a dielectric film and is grounded to the angled vapor-deposited film of the birefringent layer 13. This prevents the optical element 10 from warping and improves the moisture resistance of the angled vapor-deposited film.

[0104] The dielectric material used for the protective layer 14 is not particularly limited as long as it can adjust the stress applied to the optical element 10 and is effective in improving moisture resistance; it can be appropriately selected according to the purpose. Examples of such dielectric materials include oxides containing at least one of Si, Ta, Ti, Al, Nb, and La, MgF2, etc.

[0105] The thickness of the protective layer 14 is not particularly limited and can be appropriately selected according to the purpose, for example, it can be above 10nm or below 100nm.

[0106] (Manufacturing method of optical components)

[0107] Next, the manufacturing method of the optical element involved in this embodiment will be described.

[0108] In the manufacturing method of the optical element according to this embodiment, the optical element according to this embodiment is manufactured.

[0109] In the method for manufacturing an optical element according to this embodiment, at least one of the anti-reflection layer and the matching layer is formed by reactive sputtering with an oxygen flow ratio within a predetermined range so that the optical loss of the optical element relative to the light used in the wavelength band is 1.0% or less.

[0110] In the manufacturing method of the optical element involved in this embodiment, it is preferable to include at least one of the steps of forming a Nb oxide film and forming a Si oxide film.

[0111] <Process for forming Nb oxide films>

[0112] In the manufacturing method of the optical element according to this embodiment, for example, at least one of the anti-reflective layer and the matching layer has an oxide containing Nb.

[0113] In the antireflective layer or matching layer, a Nb oxide film is used, for example, as a high refractive index layer.

[0114] The method for manufacturing the optical element according to this embodiment includes, for example, the steps of forming an Nb oxide film by reactive sputtering with Nb as the target using a mixture of inert gas and oxygen.

[0115] Furthermore, the oxygen flow rate ratio [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] in the mixed gas when forming the Nb oxide film is preferably 18% or higher. If the oxygen flow rate ratio is 18% or higher, oxygen defects in the oxides of the antireflective layer or matching layer can be reduced, and the light absorption of the antireflective layer or matching layer can be decreased. As a result, the optical loss of the optical element is easily reduced.

[0116] Furthermore, there is no particular limit to the upper limit of the oxygen flow rate ratio, which can be appropriately selected according to the purpose, for example, it can be 30% or 25%. If the oxygen flow rate ratio is high, the film formation time of the film containing Nb oxide tends to be longer, so the oxygen flow rate ratio is preferably 25% or less.

[0117] Here, the units for inert gas flow rate and oxygen flow rate are gas volume / time (e.g., mL / min).

[0118] <Process for forming a film containing Si oxide>

[0119] In the manufacturing method of the optical element according to this embodiment, for example, at least one of the anti-reflection layer and the matching layer has an oxide containing Si.

[0120] In the antireflective layer or matching layer, a Si oxide film is included, for example, as a low refractive index layer.

[0121] The method for manufacturing the optical element according to this embodiment includes, for example, the steps of forming a Si oxide film by reactive sputtering with Si as the target using a mixture of inert gas and oxygen.

[0122] Furthermore, the oxygen flow rate ratio (oxygen flow rate / (inert gas flow rate + oxygen flow rate)) in the mixed gas during Si film formation is preferably 8% or higher. If the oxygen flow rate ratio is 8% or higher, oxygen defects in the oxides of the antireflective layer or matching layer can be reduced, and the light absorption of the antireflective layer or matching layer can be decreased. As a result, the optical loss of the optical element is easily reduced.

[0123] Furthermore, there is no particular limit to the upper limit of the oxygen flow rate ratio, which can be appropriately selected according to the purpose, for example, it can be 20% or 15%. If the oxygen flow rate ratio is high, there is a tendency for the film formation time of the Si film to become longer, so the oxygen flow rate ratio is preferably 15% or less.

[0124] The following are specific examples of methods for manufacturing optical elements. Figure 1 The manufacturing method of the optical element of the structural example shown will be described. Figure 6 This is a flowchart illustrating a method for manufacturing optical elements.

[0125] <<S1>>

[0126] First, in step S1, a transparent substrate 11 is prepared.

[0127] <<S2>>

[0128] Next, in step S2, in order to prevent reflection at the interface between the birefringent layer 13 and the transparent substrate 11, a matching layer 12 formed by stacked oxide films is formed on the transparent substrate 11.

[0129] In forming the matching layer 12, the aforementioned steps of forming a Nb oxide film and forming a Si oxide film are performed alternately to form the matching layer 12. This process yields a matching layer 12 with low light absorption.

[0130] <<S3>>

[0131] Next, in step S3, a first anti-reflection layer 15A (back AR (Anti-reflection) layer) is formed on the opposite side of the transparent substrate 11 where the matching layer 12 is not formed.

[0132] In forming the first antireflective layer 15A, the aforementioned steps of forming a film containing Nb oxide film and forming a film containing Si oxide film are performed alternately to form the first antireflective layer 15A. This process results in a first antireflective layer 15A with low light absorption.

[0133] <<S4>>

[0134] Next, in step S4, a birefringent layer 13 is formed on the matching layer 12 using an angled vapor deposition method. For example, as... Figure 4 and Figure 5 As shown, after film formation using vapor deposition from the first vapor deposition direction 31, the vapor deposition target surface is rotated 180° around a centerline perpendicular to the vapor deposition target surface and passing through the center of the vapor deposition target surface, thereby forming a film using vapor deposition from the second vapor deposition direction 32. Furthermore, this film formation is repeated to obtain a film in which a first oblique angle vapor deposition film having a first oblique direction relative to the normal of the vapor deposition target surface and a second oblique angle vapor deposition film having a second oblique direction are alternately formed.

[0135] <<S5>>

[0136] Next, in step S5, the birefringent layer 13 is annealed at a temperature of 200°C to 600°C. More preferably, the birefringent layer 13 is annealed at a temperature of 300°C to 500°C, and even more preferably, at a temperature of 400°C to 500°C. This stabilizes the properties of the birefringent layer 13.

[0137] <<S6>>

[0138] Next, in step S6, a protective layer 14 is formed on the birefringent layer 13. For example, if SiO2 is formed as the protective layer 14, TEOS (tetraethoxysilane) gas and O2 are preferably used as the SiO2 material, and a plasma CVD apparatus is used.

[0139] SiO2 CVD films formed by plasma CVD devices differ from physical vapor phase growth methods such as sputtering. They are characterized by the use of vaporized material gas, which allows TEOS gas to more easily penetrate the voids in the columnar structure, thereby further improving the adhesion with the birefringent layer 13.

[0140] <<S7>>

[0141] Next, in step S7, a second anti-reflective layer 15B (surface AR layer) is formed on the protective layer 14.

[0142] In forming the second antireflective layer 15B, the aforementioned steps of forming a film containing Nb oxide film and forming a film containing Si oxide film are performed alternately to form the second antireflective layer 15B. This process yields a second antireflective layer 15B with low light absorption.

[0143] <<S8>>

[0144] Finally, in step S8, the cutting is performed according to the specified dimensions.

[0145] The above manufacturing methods can produce optical components that have excellent resistance to high-brightness and high-output light from laser light sources and the like.

[0146] (Projection-type image display device)

[0147] The aforementioned optical elements have excellent tolerance to high brightness and high output light. Therefore, projection-type image display devices equipped with the aforementioned optical elements are suitable for projector applications such as liquid crystal projectors, DLP (Digital Light Processing) projectors, LCOS (Liquid Crystal On Silicon) projectors, and GLV (Grating Light Valve) projectors.

[0148] That is, the projection-type image display device according to this embodiment includes: the aforementioned optical element, light modulation device, light source for emitting light, and projection optical system for projecting modulated light, wherein the light modulation device and the optical element are arranged in the optical path between the light source and the projection optical system.

[0149] <Optical Modulation Device>

[0150] Examples of light modulation devices include liquid crystal display devices with transmissive liquid crystal panels, micromirror display devices with DMD (Digital Micro-mirror Device), reflective liquid crystal display devices with reflective liquid crystal panels, and one-dimensional diffractive display devices with one-dimensional diffractive light modulation elements (GLV).

[0151] For example, in a projection-type image display device using a liquid crystal display device, the liquid crystal display device has at least a liquid crystal panel, a first polarizing plate, and a second polarizing plate, and may also have other components as needed.

[0152] <<LCD Panel>>

[0153] The liquid crystal panel has no particular limitations; for example, it may have a substrate and a VA-mode liquid crystal layer. This VA-mode liquid crystal layer contains liquid crystal molecules with a pretilt angle in an orthogonal direction relative to the main surface of the substrate, which modulates the incident light beam. VA mode (vertical alignment mode) refers to the method of using a vertical electric field in the vertical direction to move liquid crystal molecules that are vertically (or with a pretilt angle) aligned with the substrate.

[0154] <<First Polarizing Plate and Second Polarizing Plate>>

[0155] The first polarizer is disposed on the incident side of the liquid crystal panel, and the second polarizer is disposed on the emitting side of the liquid crystal panel. From a durability perspective, the first and second polarizers are preferably inorganic polarizers.

[0156] <Optical Components>

[0157] The optical element is the optical element of this invention.

[0158] Optical elements, for example, are Figure 1 The optical elements of the structural example shown are arranged at the desired positions in the optical path that constitutes the projection-type image display device.

[0159] In addition, in projection-type image display devices that use micromirror display devices, optical elements are also combined with diffusers or polarizing beam splitters and arranged on the same optical path.

[0160] <Light Source>

[0161] As a light source, there are no particular limitations as long as the component emits light, and it can be appropriately selected according to the purpose. In this embodiment, the liquid crystal display device has optical elements with excellent durability, so a laser light source that emits high brightness and high output light can be used.

[0162] Wavelengths used as laser light sources include, for example, 455nm.

[0163] Projection Optical System

[0164] As a projection optical system, there are no particular restrictions as long as it is a component that projects modulated light, and it can be appropriately selected according to the purpose. For example, a projection lens that projects modulated light onto a screen can be cited.

[0165] Based on this configuration, the projection-type image display device can display high-brightness and high-output images using high-brightness and high-output light from sources such as laser light sources.

[0166] Figure 7This is a schematic diagram illustrating an example of the structure of the projection-type image display device according to this embodiment. The projection-type image display device 115A is a so-called three-panel liquid crystal projector device that uses three liquid crystal panels for displaying color images, each with red, green, and blue colors. Figure 7 As shown, the projection-type image display device 115A includes: liquid crystal display devices 101R, 101G, and 101B, a light source 102, dichroic mirrors 103 and 104, a total reflection mirror 105, polarizing beam splitters 106R, 106G, and 106B, a combining prism 108, and a projection lens 109.

[0167] The light source 102 emits light (white light) L, which includes blue light LB, green light LG, and red light LR, required for color image display. For example, it may be equipped with a halogen lamp, a metal halide lamp, a xenon lamp, or a laser light source.

[0168] Dichroic mirror 103 has the function of separating the light source L into blue light LB and other colored light LRG. Dichroic mirror 104 has the function of separating the light LRG passing through dichroic mirror 103 into red light LR and green light LG. Total internal reflection mirror 105 reflects the blue light LB separated by dichroic mirror 103 toward polarizing beam splitter 106B.

[0169] Polarizing beam splitters 106R, 106G, and 106B are prism-type polarization separating elements arranged along the optical paths of red light (LR), green light (LG), and blue light (LB), respectively. These polarizing beam splitters 106R, 106G, and 106B each have polarization separating surfaces 107R, 107G, and 107B, which function to separate incident light of each color into two mutually orthogonal polarization components. The polarization separating surfaces 107R, 107G, and 107B reflect one polarization component (e.g., the S-polarization component) and transmit the other polarization component (e.g., the P-polarization component).

[0170] Colored light with a predetermined polarization component (e.g., the S-polarization component), separated by the polarization separation surfaces 107R, 107G, and 107B of polarization beamsplitters 106R, 106G, and 106B, is incident on liquid crystal display devices 101R, 101G, and 101B. Liquid crystal display devices 101R, 101G, and 101B are driven in response to a driving voltage provided by an image signal, and have the function of modulating the incident light and reflecting the modulated light toward the polarization beamsplitters 106R, 106G, and 106B.

[0171] Between the polarization beamsplitters 106R, 106G, and 106B and the liquid crystal panels 111 of the liquid crystal display devices 101R, 101G, and 101B, quarter-wavelength plates 113R, 113G, and 113B and optical elements 10 are respectively disposed. The quarter-wavelength plates 113R, 113G, and 113B perform two transmissions—one when incident on the liquid crystal panel and one when exiting from the liquid crystal panel—thus functioning as half-wavelength plates. (For example, they convert S-polarization components to P-polarization components.) Furthermore, the quarter-wavelength plates 113R, 113G, and 113B have the function of correcting the contrast decrease caused by the angle dependence of the incident light due to the polarization beamsplitters 106R, 106G, and 106B. The optical elements 10 have the function of compensating for the residual phase difference of the liquid crystal panels constituting the liquid crystal display devices 101R, 101G, and 101B. In one embodiment, the quarter-wave plate is the optical element involved in this embodiment. In another embodiment, optical element 10 is the optical element involved in this embodiment.

[0172] The combining prism 108 has the function of combining colored light emitted from the liquid crystal display devices 101R, 101G, and 101B and after passing through the polarization beam splitters 106R, 106G, and 106B with a predetermined polarization component (e.g., the P-polarization component). The projection lens 109 has the function of projecting the combined light emitted from the combining prism 108 toward the screen 110.

[0173] Next, the operation of the projection-type image display device 115A configured as described above will be explained.

[0174] First, the white light L emitted from the light source 102 is separated into blue light LB and other colored light (red light and green light) LRG by the function of the dichroic mirror 103. Among them, the blue light LB is reflected towards the polarizing beam splitter 106B by the function of the total reflection mirror 105.

[0175] On the other hand, other colored light (red and green light) LRG is further separated into red light LR and green light LG by the function of dichroic mirror 104. The separated red light LR and green light LG are incident on polarizing beam splitters 106R and 106G, respectively.

[0176] Polarizing beam splitters 106R, 106G, and 106B separate incident light of various colors into two mutually orthogonal polarization components on polarization separation surfaces 107R, 107G, and 107B. At this time, polarization separation surfaces 107R, 107G, and 107B cause one polarization component (e.g., the S-polarization component) to be reflected towards the liquid crystal display device 101R, 101G, and 101B. The liquid crystal display device 101R, 101G, and 101B are driven in response to a driving voltage provided by an image signal and modulate the incident light of a predetermined polarization component on a pixel-by-pixel basis.

[0177] Liquid crystal display devices 101R, 101G, and 101B cause modulated light of various colors to be reflected toward polarizing beamsplitters 106R, 106G, and 106B. Polarizing beamsplitters 106R, 106G, and 106B only transmit a predetermined polarization component (e.g., the P-polarization component) of the reflected light (modulated light) from liquid crystal display devices 101R, 101G, and 101B, and emit it toward the combining prism 108.

[0178] The combining prism 108 combines the colored light with predetermined polarization components obtained by the polarization beam splitters 106R, 106G, and 106B, and emits it toward the projection lens 109. The projection lens 109 projects the combined light emitted from the combining prism 108 toward the screen 110. As a result, the screen 110 displays the image corresponding to the light modulated by the liquid crystal display device 101R, 101G, and 101B, thus achieving the desired image display.

[0179] [Example]

[0180] The following describes specific embodiments of the present invention. However, the present invention is not limited to these embodiments. Furthermore, for convenience, the terms SiO2 film and Nb2O5 film are used, but these films are more likely to be non-stoichiometric.

[0181] (Example 1)

[0182] <Fabrication of Optical Components>

[0183] A matching layer is formed by alternately stacking five SiO2 and Nb2O5 films on one side of a glass substrate (average thickness 0.7 mm) using a sputtering method.

[0184] The SiO2 film was formed by reactive sputtering using a Si target and introducing Ar and O2 gases. The O2 gas flow rate ratio was 12%.

[0185] In addition, the O2 gas flow rate ratio can be calculated as follows.

[0186] O2 gas flow rate ratio = O2 gas flow rate / (Ar gas flow rate + O2 gas flow rate)

[0187] The Nb₂O₅ film was formed by reactive sputtering using a Nb target and introducing Ar and O₂ gases. The O₂ gas flow rate ratio was 22%.

[0188] Next, using Nb2O5 film and SiO2 film, seven layers are alternately stacked on another side of the glass substrate by sputtering to form an anti-reflective layer.

[0189] The SiO2 film was formed by reactive sputtering using a Si target and introducing Ar and O2 gases. The O2 gas flow rate ratio was 12%.

[0190] The Nb₂O₅ film was formed by reactive sputtering using a Nb target and introducing Ar and O₂ gases. The O₂ gas flow rate ratio was 22%.

[0191] Next, Ta2O5 vapor deposition material was used on the matching layer, and the vapor deposition source was arranged at a position 70° tilted relative to the normal direction of the glass substrate. The first vapor deposition direction was 0° and the second vapor deposition direction was 180°. The oblique angle vapor deposition was performed alternately to obtain a birefringent layer composed of oblique angle vapor deposition film.

[0192] After vapor deposition, annealing was performed at 400℃ to stabilize the properties. After annealing, a SiO2 film was formed by plasma CVD using TEOS (tetraethoxysilane) gas and O2.

[0193] Next, an anti-reflective layer was formed by alternately stacking seven layers of Nb2O5 and SiO2 films using a sputtering method.

[0194] The SiO2 film was formed by reactive sputtering using a Si target and introducing Ar and O2 gases. The O2 gas flow rate ratio was 12%.

[0195] The Nb₂O₅ film was formed by reactive sputtering using a Nb target and introducing Ar and O₂ gases. The O₂ gas flow rate ratio was 22%.

[0196] The optical element was obtained through the above process.

[0197] (Comparative Example 1)

[0198] The O2 gas flow rate during the SiO2 film formation for the matching layer and antireflective layer was set to 8%. Additionally, the O2 gas flow rate during the Nb2O5 film formation was set to 18%. Apart from these, the optical element was fabricated using the same process as in Example 1.

[0199] (Measurement of transmittance and reflectance)

[0200] like Figure 8 As shown, S-polarized light with wavelengths from 400 nm to 700 nm is incident at an angle of 5°. The intensity of the transmitted light and the intensity of the reflected light are measured, and the transmittance and reflectance are calculated.

[0201] Transmittance = Transmitted light intensity / Incident light intensity (%)

[0202] Reflectivity = Reflected light intensity / Incident light intensity (%)

[0203] Optical loss (%) = 100% - Transmittance (%) - Reflectance (%)

[0204] Based on the measurements of 30 samples, the optical loss of the sample in Example 1 was 0.5-0.9%, while the optical loss of the sample in Comparative Example 1 was 1.2-1.6%.

[0205] Additionally, the transmittance, reflectance, and optical loss of one sample from Example 1 are shown in the figure.

[0206] Figure 9A This is a graph showing the transmittance of one sample from Example 1.

[0207] Figure 9B This is a graph showing the reflectance of one sample from Example 1.

[0208] Figure 9C This is a graph showing the optical loss of one sample of Example 1.

[0209] Additionally, the transmittance, reflectance, and optical loss of one sample from Comparative Example 1 are shown in the figure.

[0210] Figure 10A This is a graph showing the transmittance of one sample from Comparative Example 1.

[0211] Figure 10B This is a graph showing the reflectance of one sample from Comparative Example 1.

[0212] Figure 10C This is a graph showing the optical loss of one sample of Comparative Example 1.

[0213] <Laser Irradiation Experiment>

[0214] Laser irradiation conditions:

[0215] • Wavelength: 455nm - CW

[0216] Laser power: 50W

[0217] • Power density: 8.3W / mm 2

[0218] • Irradiation time: 3 minutes

[0219] Under the laser irradiation conditions described above, 30 samples from both Example 1 and Comparative Example 1 were irradiated with laser light, and the presence or absence of damage was visually confirmed. The results are shown below.

[0220] • Example 1 Number of damaged items: 0 / Number of experiments: 30

[0221] • Comparative Example 1: Number of damaged items: 10 / Number of experiments: 30

[0222] It can be seen that if the optical loss is less than 1.0%, there will be no damage in the laser irradiation experiment, and the laser resistance is good.

[0223] [Industry Applicability]

[0224] The optical element of the present invention also exhibits excellent durability when using a laser light source, and is therefore suitable for use in projection-type image display devices that use a laser light source.

[0225] [Label Explanation]

[0226] 10 Optical element; 11 Transparent substrate; 12 Matching layer; 13 Birefringent layer; 14 Protective layer; 15A, 15B Anti-reflective layer; 21 Evaporation target surface; 23 Angled evaporation film; 31 First evaporation direction; 32 Second evaporation direction; 102 Light source; 101R, 101G, 101B Liquid crystal display device; 109 Projection lens; 111 Liquid crystal panel; 115A Projection type image display device; 151 First oxide film; 152 Second oxide film.

Claims

1. An optical element, characterized by, comprises: a substrate which is transparent to light of a wavelength band used; an antireflection layer; a matching layer; and a birefringent layer composed of a slant angle evaporation film, the optical element is an optical element which provides a phase difference only by the birefringent layer, at least either of the antireflection layer and the matching layer has a Nb-containing oxide film and a Si-containing oxide film, the Nb-containing oxide film is a Nb-containing oxide film formed by a reactive sputtering method using a mixed gas of an inert gas and oxygen, with an oxygen flow ratio [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] of 18% or more and 25% or less, and the Si-containing oxide film is a Si-containing oxide film formed by a reactive sputtering method using a mixed gas of an inert gas and oxygen, with an oxygen flow ratio (oxygen flow rate / (inert gas flow rate + oxygen flow rate)) of 12% or more and 20% or less, so that an optical loss with respect to light of the wavelength band used is 1.0% or less. the antireflection layer is a multilayer film in which two or more inorganic oxide films having different refractive indexes are stacked.

2. The optical element according to claim 1, wherein the matching layer is a multilayer film in which two or more inorganic oxide films having different refractive indexes are stacked.

3. The optical element according to any one of claims 1 to 2, wherein, a method for manufacturing the optical element includes:

4. A method for manufacturing an optical element of any one of claims 1 to 3, characterized by, forming at least either of the antireflection layer and the matching layer by a reactive sputtering method in which an oxygen flow ratio is a predetermined range, in a manner such that an optical loss of the optical element with respect to light of a wavelength band used is 1.0% or less.

5. The method for manufacturing the optical element according to claim 4, wherein at least either of the antireflection layer and the matching layer has a Nb-containing oxide film, the method for manufacturing the optical element includes forming the Nb-containing oxide film by a reactive sputtering method using a mixed gas of an inert gas and oxygen with a target of Nb, an oxygen flow ratio [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] of the mixed gas when forming the Nb-containing oxide film is 18% or more.

6. The method for manufacturing the optical element according to any one of claims 4 to 5, wherein at least either of the antireflection layer and the matching layer has a Si-containing oxide film, the method for manufacturing the optical element includes forming the Si-containing oxide film by a reactive sputtering method using a mixed gas of an inert gas and oxygen with a target of Si, an oxygen flow ratio [oxygen flow rate / (inert gas flow rate + oxygen flow rate)] of the mixed gas when forming the Si-containing oxide film is 8% or more.

7. A projection-type image display device characterized by comprising the optical element according to any one of claims 1 to 3, a light modulating device, a light source of an outgoing light, and a projection optical system which projects the modulated light, the light modulating device and the optical element are disposed on an optical path between the light source and the projection optical system. ​ ​

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