Optical device, virtual image display apparatus, and head mounted display

Abstract

The main purpose of the present invention is to provide an optical device which, when used in a see-through display or the like, suppresses the deterioration of the light amount balance between RGB of an output display image with respect to input image information, thereby making the color tone difficult to change. An optical device according to the present technology includes: a first light guide plate having a first light guide path formed of a first material; and a second light guide plate having a second light guide path formed of a second material different from the first material, where the second material has a higher transmittance than the first material.

Description

Technical Field

[0001] The present technology relates to an optical device including two or more types of light guide plates each having a light guide path formed of a different material, a virtual image display device including the optical device, and a head-mounted display including the virtual image display device. Background Art

[0002] Conventionally, a virtual image display device is known which transmits image information formed by an image forming unit through a light guide path of an optical device and provides the image information as an enlarged virtual image, and is used for a head-mounted display such as glasses or a perspective display for a window display or the like.

[0003] For example, Patent Document 1 below discloses an optical device in which a plurality of internal coupling optical elements selectively deflect light of a specific wavelength so that the light propagates through waveguides different for each specific wavelength.

[0004] Citation List

[0005] Patent Document

[0006] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-519445 Summary of the Invention

[0007] Technical Problem

[0008] However, some materials forming the light guide path significantly absorb light in a shorter wavelength range. As a result, the hue may change due to deterioration of the light quantity balance among RGB. For example, the output display image may appear yellower than the input image information. In the case where the hue of the output display image has changed, it is necessary to perform control in consideration of the light absorption of the material so as to increase the input of light in the shorter wavelength range, for example. This leads to an increase in the cost of the device.

[0009] In view of such circumstances, the present technology has been proposed. The main object of the present technology is to provide an optical device that suppresses deterioration of the light quantity balance among RGB of a display image output with respect to input image information when used for a perspective display or the like, so that the hue is less likely to change.

[0010] Solution to the Problem

[0011] The optical device according to the present technology includes: a first light guide plate having a first light guide path formed of a first material; and a second light guide plate having a second light guide path formed of a second material different from the first material, wherein the second material has a higher transmittance than the first material.

[0012] Here, "having a higher transmittance" particularly means having a relatively high transmittance for light with a shorter wavelength. For example, having a relatively high transmittance for wavelengths below 493 nm corresponding to the upper limit wavelength of blue light.

[0013] In addition, a virtual image display device including an optical device according to the present technology includes: an image forming unit that outputs image light; and an optical lens that converts the image light output from the image forming unit into parallel light and can be configured to cause the parallel light to enter a light guide plate of the optical device according to the present technology.

[0014] Furthermore, a virtual image display device including an optical device according to the present technology can be widely used in general applications of see-through displays, such as head-mounted displays and display windows. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 are a side cross-sectional view and a plan view showing a configuration example of an optical device according to the present technology.

[0016] Figure 2 is a schematic diagram showing a configuration example of a virtual image display device according to the present technology.

[0017] Figure 3 is a schematic diagram showing an example of the shape of a diffraction grating that can be used in an optical device according to the present technology.

[0018] Figure 4 is a diagram showing an example of the arrangement of optical components of an optical device according to the present technology.

[0019] Figure 5 is a diagram showing an example of the arrangement of a protective substrate in an optical device according to the present technology.

[0020] Figure 6 is a schematic diagram showing a modified example of a virtual image display device according to the present technology.

[0021] Figure 7 is a schematic diagram showing a modified example of a virtual image display device according to the present technology.

[0022] Figure 8 is a schematic diagram showing a modified example of a virtual image display device according to the present technology.

[0023] Figure 9 is a schematic diagram showing a modified example of a virtual image display device according to the present technology.

[0024] Figure 10 is a conceptual diagram showing an example of the installation of a head-mounted display according to the present technology.

[0025] Figure 11It is a graph showing the relationship between the refractive index and wavelength dispersion of two materials that can be used in an optical device.

[0026] Figure 12 It is a graph showing the relationship between the transmittance and wavelength dispersion of two materials that can be used in an optical device.

[0027] Figure 13 It is a diagram showing a schematic view of a method for manufacturing a virtual image display device according to the present technology.

[0028] Figure 14 It is a graph showing the transmittance and refractive index of an optical device according to the present technology. Detailed Description of the Invention

[0029] Hereinafter, preferred embodiments of the present technology will be described. It should be noted that the embodiments shown below are examples of representative embodiments of the present technology, and the present technology is not limited to the following preferred embodiments and can be freely modified within the scope of the present technology.

[0030] The optical device according to the present technology includes at least two or more types of light guide plates, such as a first light guide plate and a second light guide plate. The first light guide plate has a first light guide path formed of a first material. The second light guide plate has a second light guide path formed of a second material different from the first material.

[0031] There is no particular limitation as long as the light guide plate of the optical device according to the present technology includes a light guide path capable of propagating incident light. The light guide plate may include one or more optical components on the light guide path. The one or more optical components can change the traveling direction of light. The one or more optical components are, for example, a diffraction grating, a reflector, or an optical lens.

[0032] Glass, resin, etc. including optical glass (e.g., quartz glass and BK7) can be appropriately used. In recent years, resin has attracted attention as a material for forming a light guide path due to its crack resistance and cost advantage.

[0033] The resin that can form a light guide path is a material that has plasticity among organic high molecular compounds and can propagate incident light. Examples of the resin may include highly transparent resins such as polycarbonate resin (PC), cycloolefin resin (COP), acrylic resin (PMMA), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS).

[0034] The first material and the second material of the light guiding path of the optical device that can be used in accordance with the present technology are different materials. The transmittance of the second material is higher than that of the first material. For a highly transparent resin, the transmittance of the material generally tends to decrease as the wavelength of light becomes shorter. Thus, for wavelengths below 493 nm corresponding to the upper limit wavelength of blue light, which is the shortest wavelength among RGB, the second material preferably has a relatively high transmittance compared to the first material. The optical device according to the present technology uses two or more types of light guide plates having light guiding paths formed of materials with different transmittances, so that light with a shorter wavelength that is easily absorbed by the light guiding path of one light guide plate can be propagated through the light guiding path of another light guide plate. Thus, it is possible to output light while maintaining the light quantity balance among RGB of the input image information. It should be noted that the optical device according to the present technology can be configured to include a plurality of light guide plates of one type selected from the above two or more types of light guide plates.

[0035] In particular, by setting the transmittance of the second material for light with a wavelength of 435 nm corresponding to the lower limit wavelength of blue light to 85% or more, preferably 90% or more, more preferably 95% or more, the light entering the light guiding path can be effectively propagated.

[0036] In the present disclosure, red light, green light, and blue light represented as RGB refer to those lights including one or more wavelengths within each of the following ranges.

[0037] Red light: 620 - 780 nm

[0038] Green light: 492 - 577 nm

[0039] Blue light: 435 - 493 nm

[0040] In addition, the display viewing angle of the perspective display depends on the refractive index of the material forming the light guiding path. Thus, the material forming the light guiding path of the optical device according to the present technology is preferably a material with a high refractive index. When the material forming the light guiding path is a material with a high refractive index, a larger total reflection angle at the interface inside the light guiding path can be obtained when image information enters the light guiding path. Therefore, the image area that can be captured can be expanded.

[0041] In the present disclosure, the display viewing angle has substantially the same meaning as the field of view angle. It represents the angle of the range within which the content of the displayed image is correctly visible. It refers to the angle at which the contrast and color are similar to those when viewed from the front. Specifically, it can be calculated based on the size of the captured image obtained by capturing the output display image using a camera.

[0042] For a highly transparent resin, the refractive index of the material generally tends to decrease as the wavelength of light becomes longer. Thus, by using two or more types of light guide plates having light guide paths formed of different materials as a constituent example of the optical device according to the present technology, a decrease in the refractive index for light with a longer wavelength can be suppressed. It is also expected that as an entire optical device, the difference in refractive index between RGB can be reduced, and the viewing angle can be increased when it is used for a see-through display. Specifically, regarding the refractive index of light with a wavelength of 492 nm corresponding to the lower limit wavelength of green light, which is the shortest wavelength among RGB, the first material is preferably higher than the second material.

[0043] That is, the optical device according to the present technology more preferably uses two or more types of light guide plates: a light guide plate having a light guide path formed of a material with excellent transmittance for light with a shorter wavelength and a light guide plate having a light guide path formed of a material with excellent refractive index for light with a longer wavelength. Thus, in order to improve the propagation of light with a shorter wavelength and improve the refractive index of light with a longer wavelength, it is possible to simultaneously achieve suppression of deterioration in the light quantity balance between RGB of the output display image with respect to the input image information and an expansion of the viewing angle.

[0044] As a material with excellent refractive index for a longer wavelength, when the refractive index of the first material for light with a wavelength of 492 nm corresponding to the lower limit of green light is set to 1.60 or more, preferably 1.65 or more, and more preferably 1.68 or more, an increase in the viewing angle for light with a longer wavelength can also be expected.

[0045] When the refractive index of the second material for light with a wavelength of 493 nm corresponding to the upper limit of blue light is set to 1.58 or more, preferably 1.60 or more, an increase in the viewing angle for light with a shorter wavelength can also be expected.

[0046] Considering the relationship between the wavelength dispersion of the material and the transmittance or refractive index, the optical device according to the present technology can be configured to further include a third light guide plate having a third light guide path formed of a third material different from the first material and the second material. Additionally, it can be configured to include multiple types of light guide plates having light guide paths formed of materials different from these materials. By providing an optimal light guide path corresponding to the light with the wavelength to be propagated, deterioration in the light quantity balance between RGB can be more appropriately suppressed, or an expansion of the viewing angle can be achieved.

[0047] Hereinafter, preferred embodiments of the present technology will be described in more detail with reference to the accompanying drawings.

[0048] (1) Stacked configuration of the light guide plate

[0049] Figure 1It is a side sectional view and a plan view showing a configuration example of the optical device 10 according to the present technology. As shown in the side sectional view, the first light guide plate 11 and the second light guide plate 13 constituting the optical device 10 according to the present technology are superimposed and fixed to each other. In addition, in the case where three or more types of light guide plates constitute the optical device according to the present technology, the light guide plates are also superimposed and fixed to each other.

[0050] In the optical device according to the present technology, the fixed light guide plates can be stacked in direct contact. However, when they are stacked via a medium 16 having a refractive index lower than that of the material forming the light guide path as the bonding surface of the light guide plate, the refractive index difference between the material forming the light guide path and the medium with a lower refractive index can be increased. Then, the critical angle of the light propagating through the light guide path at the light guide path interface decreases, and the angular band of the light that can be guided increases. Therefore, the light entering the light guide path can be effectively propagated.

[0051] Examples of the medium with a lower refractive index may include air, but are not limited thereto. The thickness of the medium with a lower refractive index can be about 100 μm, for example, a thickness of 50 μm to 200 μm, but is not limited to this range.

[0052] The method of fixing the light guide plates to each other is not particularly limited as long as it can fix the target light guide plates to each other. For example, the light guide plates can be appropriately fixed with an adhesive.

[0053] In the case of fixing them with an adhesive, the adhesive to be used is not particularly limited as long as it can appropriately adhere the materials (for example, the first material and the second material) of the light guide path as the bonding surface of the light guide plate to each other.

[0054] In the case of fixing them with an adhesive, the bonding surfaces are not particularly limited as long as they are areas where the target light guide plates can be fixed to each other. For example, a configuration can be provided in which, as Figure 1 shown, by fixing the ends of the light guide plates with the adhesive 15A, due to the thickness of the adhesive 15A, the light guide plates are stacked via the air layer 16, and the air layer 16 is a medium having a refractive index lower than that of the material forming the light guide path as the bonding surface of the light guide plate.

[0055] (2) Optical component

[0056] As Figure 1As shown in A of, the optical device 10 according to the present technology includes an incident-side diffraction grating 17A serving as a first optical component and an output-side diffraction grating 18A serving as a second optical component. The incident-side diffraction grating 17A is arranged on the incident side of the light associated with the image information on the first light guide path, and the output-side diffraction grating 18A is arranged on the output side of the image information. And it includes an incident-side diffraction grating 17B serving as a third optical component and an output-side diffraction grating 18B serving as a fourth optical component. The incident-side diffraction grating 17B is arranged on the incident side of the light associated with the image information on the second light guide path, and the output-side diffraction grating 18B is arranged on the output side of the image information. In addition, in the case where the optical device according to the present technology is constituted by three or more types of light guide plates, the optical components may also be arranged on the incident side and the output side of the light guide path of each light guide plate.

[0057] Figure 1 Example constituted by three types of light guide plates is shown in B of. In Figure 1 In B of, the third light guide plate 19 includes an incident-side diffraction grating 17C serving as a fifth optical component and an output-side diffraction grating 18C serving as a sixth optical component. The incident-side diffraction grating 17C is arranged on the incident side of the light associated with the image information, and the output-side diffraction grating 18C is arranged on the output side of the image information.

[0058] As Figure 1 shown in the plan view in, the optical components on the output side of the image information are arranged wider than the optical components on the incident side of the light associated with the image information. In this way, the input image information can be enlarged and output.

[0059] Figure 2 It is a schematic diagram showing a configuration example of the virtual image display device 20 according to the present technology. Figure 2 It shows a state where the light output from the image forming unit 21 enters the first light guide path 12 and the second light guide path 14 of the optical device 10 and the information of the light reaches the pupil 26 of the observer.

[0060] In the case where the optical device according to the present technology includes two types of light guide plates, by using the incident-side diffraction grating 17A serving as the first optical component and the output-side diffraction grating 18A serving as the second optical component arranged on the first light guide path 12 to reflect the light with a longer wavelength, and the incident-side diffraction grating 17B serving as the third optical component and the output-side diffraction grating 18B serving as the fourth optical component arranged on the second light guide path 14 to reflect the light with a shorter wavelength, the light with a longer wavelength can be propagated through the first light guide path, and the light with a shorter wavelength can be propagated through the second light guide path. In addition, in the case where three or more types of light guide plates constitute the optical device according to the present technology, by arranging the optical components that reflect the light with the optimal wavelength depending on the characteristics of the material forming the light guide path, the light with the optimal wavelength can also be propagated through each light guide path.

[0061] Examples of the light with a longer wavelength may include the light with a wavelength of more than 492 nm corresponding to the lower limit of green light. Examples of the light with a shorter wavelength may include the light with a wavelength of less than 493 nm corresponding to the upper limit of blue light.

[0062] The corresponding optical components described above are not limited to diffraction gratings as long as they can change the traveling direction of light. For example, reflectors, optical lenses, prisms, etc. can be appropriately used. These optical components can be adopted and processed into any shape such as reflective or transmissive according to the design of the optical device for propagating light.

[0063] In the case of using a diffraction grating as the optical component on the light guide path of the light guide plate, they can be integrally formed with the light guide plate by injection molding. Thus, due to its manufacturing cost, the diffraction grating is preferred. In addition, as the optical component on the light guide path of the light guide plate, a prism can also be integrally formed with the light guide plate by injection molding. In particular, in the case of using a prism as the optical component on the incident surface side, in some cases, they can reduce the loss of light when image information is input into the light guide plate.

[0064] In the case where the optical device according to the present technology uses a diffraction grating as the optical component, the material of the diffraction grating can also be the same material as the material forming the light guide path. The use of the same material facilitates the manufacture of the light guide plate by injection molding. Thus, this is preferred.

[0065] On the other hand, in the case where the diffraction grating serving as the optical component is formed of a material different from the material forming the light guide path, for the material, one of the materials exemplified above as the material capable of guiding light can be appropriately selected. In addition, the diffraction grating formed of a material different from the material forming the light guide path can be appropriately attached to the light guide plate by injection molding or imprinting technology.

[0066] In the case where a diffraction grating is used as an optical component in an optical device according to the present technology, the shape of the diffraction grating may also be a uniaxial diffraction grating having a periodic structure only in the X-axis direction, or may be a biaxial diffraction grating having a periodic structure in both the X-axis direction and the Y-axis direction.

[0067] Examples of the shape of the diffraction grating may include Figure 3 the shapes shown in A to D of Figure 1 etc., but are not limited thereto. The diffraction grating can be designed into any shape by well-known methods. In addition, although the diffraction grating can also be arranged along the light guide path as shown in

[0068] etc., the diffraction grating can also be arranged obliquely with respect to the light guide path. Adjusting the shape and arrangement of the diffraction grating can optimize the diffraction angle, diffraction efficiency, etc., and can selectively reflect or transmit light of a specific wavelength.

[0069] In addition, in an optical device according to the present technology, a color filter can also be arranged between the light guide plates. Therefore, it is expected that the wavelength selectivity of optical components such as the diffraction grating will be improved.

[0070] Figure 4 is a schematic diagram showing an example of the arrangement of optical components in an optical device according to the present technology. Figure 4 shows an example in which a diffraction grating is used as an optical component, and shows examples of the use of reflective and transmissive optical components. Figure 4 The constitution of the optical device shown in Figure 2 except for the diffraction grating serving as an optical component is similar to the constitution of the virtual image display device shown in

[0071] As shown below, on the light guide path of the light guide plate of an optical device according to the present technology, the reflective or transmissive optical component can take Figure 4 the 4 arrangements shown in A to D of

[0072] Regarding Figure 4 the first light guide plate 11 in the optical device 10 shown in A of

[0073] Regarding Figure 4In the first light guide plate 11 of the optical device 10 shown in B, a transmissive incident-side diffraction grating 17A and a reflective exit-side diffraction grating 18A are arranged on the first light guide path 12.

[0074] Regarding Figure 4 In the first light guide plate 11 of the optical device 10 shown in C, a reflective incident-side diffraction grating 17A and a transmissive exit-side diffraction grating 18A are arranged on the first light guide path 12.

[0075] Regarding Figure 4 In the first light guide plate 11 of the optical device 10 shown in D, a transmissive incident-side diffraction grating 17A and a transmissive exit-side diffraction grating 18A are arranged on the first light guide path 12.

[0076] As Figure 4 As shown in A to D, it is preferable to arrange a transmissive diffraction grating on the image information incident surface side of the light guide path, and arrange a reflective diffraction grating on the surface of the light guide path on the opposite side of the image information incident surface. In addition, depositing a metal film on the surface of the light guide plate on the opposite side of the reflective diffraction grating can also improve the reflectivity and reduce the loss of light input.

[0077] It should be noted that although Figure 4 By using the first light guide plate as an example, examples of four types of arrangements of optical components arranged on the first light guide path are shown, but for Figure 4 each of the four types of first light guide plates shown as examples of arrangements in A to D, the second light guide plate can also adopt four types of arrangements for the optical components in the same way as the example of the first light guide plate. That is, in the case where the optical device according to the present technology includes two types of light guide plates, a configuration in which four types of first light guide plates and four types of second light guide plates are combined as appropriate can be adopted. In addition, in the case where an optical device according to the present technology is composed of three or more types of light guide plates, a configuration in which four types of light guide plates are combined as appropriate can also be adopted.

[0078] (3) Protective substrate

[0079] Although the optical device according to the present technology can be disposable, for example, when the optical components are soiled or damaged, a protective substrate for protecting the optical components can be provided. The provided protective substrate can protect the optical components such as diffraction gratings arranged exposed from, for example, contamination or damage, and is expected to extend the product life of the optical device.

[0080] That is, in the case where a reflective optical component is arranged on the outermost light guiding path on the incident surface side of the optical device according to the present technology (the incident side diffraction grating 17A and the output side diffraction grating 18A are arranged on the outer surface side of the light guiding path of the optical device), as shown in Figure 5 A of Figure 5 , in order to protect the optical component, it is preferable to provide a protective substrate 25 on the output surface side of the optical device, and this output surface is the surface on the opposite side of the surface in contact with the light guiding path.

[0081] In the case where a transmissive optical component is arranged on the light guiding path arranged at the outermost position on the output surface side of the optical device according to the present technology (the incident side diffraction grating 17B and the output side diffraction grating 18B are arranged on the outer surface side of the light guiding path of the optical device), as shown in Figure 5 B of Figure 5 , in order to protect the optical component, it is preferable to provide a protective substrate 25 on the incident surface side of the optical device, and this incident surface is the surface on the opposite side of the surface in contact with the light guiding path.

[0082] In the case where a transmissive optical component is arranged on the light guiding path arranged at the outermost position on the incident surface side of the optical device according to the present technology, and a reflective optical component is further arranged on the light guiding path arranged at the outermost position on the output surface side, as shown in Figure 5 C of Figure 5 , by providing the protective substrate 25 on both the incident surface side and the output surface side of the optical device, the optical component can be appropriately protected, and the incident surface and the output surface are the surfaces on the opposite side of the surface in contact with the light guiding path.

[0083] Although the protective substrate can be stacked in direct contact with the optical component, by stacking via a medium having a refractive index lower than that of the material forming the light guiding path on which the optical component is arranged, the refractive index difference between the material forming the light guiding path and the medium with a lower refractive index can be increased. Then, the critical angle of the light propagating through the light guiding path at the light guiding path interface decreases, and the angular band of the light that can be guided increases. Therefore, the light entering the light guiding path can be effectively propagated.

[0084] Examples of the medium with a lower refractive index may include air, but are not limited thereto. The thickness of the medium with a lower refractive index can be about 100 μm, for example, a thickness of 50 μm to 200 μm, but is not limited to this range.

[0085] The method of fixing the protective substrate and the light guide plate to each other is not particularly limited as long as it can fix the target protective substrate and the target light guide plate to each other. For example, the protective substrate and the light guide plate can be appropriately fixed with an adhesive or the like.

[0086] In the case of fixing them with an adhesive, the adhesive to be used is not particularly limited as long as it can appropriately adhere the material of the protective substrate, which is the bonding surface of the light guide plate, and the material of the light guiding path to each other.

[0087] There is no particular limitation on the bonding surface in the case of fixing them with an adhesive, as long as it is an area where the target protective substrate and the target light guide plate can be fixed to each other. For example, as Figure 5 shown in, by fixing the end portion of the light guide plate with the adhesive 15B, a configuration can be adopted in which the protective substrate and the light guide plate are stacked via the air layer 16 due to the thickness of the adhesive 15B, and the air layer 16 is a medium having a refractive index lower than that of the material forming the light guide path.

[0088] There is no particular limitation on the material forming the protective substrate, as long as the transmittance of the material to light having a wavelength of 435 nm is 90% or more. For example, glass or a highly transparent resin can be appropriately used. Examples of the highly transparent resin can include polycarbonate resin (PC), cycloolefin resin (COP), acrylic resin (PMMA), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polystyrene (PS).

[0089] (4) Virtual image display device

[0090] A virtual image display device including an optical device according to the present technology includes an image forming unit that outputs image light and an optical lens that converts the image light output from the image forming unit into parallel light, and can be configured to cause the parallel light to enter the light guide plate of the optical device according to the present technology.

[0091] The Figure 2 and Figure 6 that use schematic diagrams showing a configuration example and a modified example of the virtual image display device according to the present technology will be used to describe the virtual image display device in detail.

[0092] The image forming unit 21 is a device that divides image light associated with image information into a plurality of color beams and outputs them. The light source of the image forming unit 21 can be a silicon-based liquid crystal (LCOS) type having an illumination system with even self-luminescence, or a high-temperature polysilicon (HTPS) type. Alternatively, the light source of the image forming unit 21 can be a digital light processing (DLP) type. When the light source of the image forming unit is self-luminous, it can be a light emitting diode (LED) light source integrated with and dispersed on the panel, a laser diode (LD) light source, or an organic electroluminescence (EL) light source. In addition, a configuration in which the image forming unit is provided with a color filter can be adopted.

[0093] The position where the image forming unit 21 is arranged is not limited, as long as it can cause the image light to enter the first light guide plate 11 and the second light guide plate 13. For example, as Figure 2 shown in, the image forming unit 21 can be arranged to face the light guide plate. Alternatively, as Figure 6 shown in, the image forming unit 21 can be arranged to be inclined with respect to the light guide plate.

[0094] As Figure 2 shown, when the image forming unit is arranged to face the light guide plate, the virtual image display device can be easily designed to be a compact type with a small width, and due to its structure, the virtual image display device can also be easily assembled.

[0095] On the other hand, as Figure 6 shown, when the image forming unit is arranged to be inclined with respect to the light guide plate, light can enter at an angle at which it is easy to complete total reflection of the light propagating through the light guide path at the light guide path interface, while avoiding reflection of the image light output from the image forming unit on the surface of the light guide plate when entering the light guide plate. Thus, for example, optical components such as a diffraction grating on the incident side can be expected to be easily designed.

[0096] The optical lens 22 is arranged between the image forming unit 21 and the optical device 10 including the first light guide plate 11 and the second light guide plate 13. The optical lens 22 converts the image light output from the image forming unit 21 into parallel light. The optical lens 22 is not particularly limited as long as it has the above function.

[0097] As Figure 2 or Figure 6 shown, the optical lens 22 can be arranged to face the image forming unit 21. Alternatively, the optical lens 22 can be arranged to be inclined with respect to the image forming unit 21.

[0098] The image light converted into parallel light by the optical lens 22 enters the optical device 10. Among the incident image light, the image light with a longer wavelength propagates through the first light guide path 12 associated with the first light guide plate 11. The image light with a shorter wavelength propagates through the second light guide path 14 associated with the second light guide plate 13 and is output to the outside.

[0099] The virtual image display device according to the present technology uses two or more types of light guide plates having light guide paths formed of two different materials, so that light with a shorter wavelength that is easily absorbed by the light guide path of one light guide plate can be propagated through the light guide path of another light guide plate. Thus, it is possible to expect to output light while maintaining the light quantity balance among RGB of the input image information.

[0100] In addition, the virtual image display device according to the present technology uses two or more types of light guide plates having light guide paths formed of two different materials, so that light with a longer wavelength whose refractive index is easily reduced can be propagated through the light guide path formed of a material with a higher refractive index. Thus, it is also possible to expect to reduce the difference in refractive index among the wavelengths of RGB and increase the display viewing angle when it is used for a see-through display.

[0101] That is, the virtual image display device according to the present technology preferably uses two or more types of light guide plates: a light guide plate having a light guide path formed of a material with excellent transmittance for light with a shorter wavelength, and a light guide plate having a light guide path formed of a material with excellent refractive index for a longer wavelength. Thus, in order to improve the propagation of light with a shorter wavelength and improve the refractive index of light with a longer wavelength, it is possible to simultaneously achieve suppression of deterioration in the light quantity balance among RGB of the output display image with respect to the input image information and expansion of the display viewing angle.

[0102] The arrangement of the first light guide plate 11 and the second light guide plate 13 relative to the image forming unit 21 is not limited. However, it is preferable to arrange the first light guide plate 11 on the side opposite to the image forming unit 21 with respect to the second light guide plate 13. With this arrangement, the image light output from the image forming unit 21 first enters the second light guide path 14 formed of the second material having a high transmittance for light with a shorter wavelength, and then enters the first light guide path 12 formed of the first material. Thus, it is possible to expect suppression of absorption of light with a shorter wavelength by the optical device 10.

[0103] In addition, in the case where the virtual image display device according to the present technology includes an optical device composed of three or more types of light guide plates, the light guide plate having a light guide path formed of a material with the highest transmittance for light with a shorter wavelength is also arranged closer to the image forming unit. Thereafter, the light guide plates are arranged in the order of the transmittance of the materials forming the light guide paths for light with a shorter wavelength. This arrangement can minimize the absorption of light with a shorter wavelength by the optical device.

[0104] In the optical device 10 of the virtual image display device 20 according to the present technology, a color filter can also be arranged between the light guide plates. Thus, it is possible to expect an improvement in the wavelength selectivity of optical components such as diffraction gratings. As shown in the modified example of the virtual image display device in Figure 7 , by arranging the color filter 23 between the incident side diffraction grating 17A of the first light guide plate 11 and the incident side diffraction grating 17B of the second light guide plate 13, green light and red light, which are light with a target wavelength, can enter the first light guide plate 11. The output side diffraction grating 18A provided on the first light guide path 12 is designed to have an output angle of light consistent with the wavelengths of green light and red light. Thus, it is possible to expect prevention of blue light from mixing into the light output from the first light guide path 12 and prevention of shaking of the display image output from the optical device 10.

[0105] In the case where the virtual image display device according to the present technology includes an optical device composed of three or more types of light guide plates, a color filter is further arranged between the light guide plates. In this way, light with a target wavelength can enter each light guide plate of the virtual image display device.

[0106] In addition, in the optical device 10 of the virtual image display device 20 according to the present technology, the area of the optical component on the incident side of the light guide plate arranged on the image forming unit side can be designed as a narrower area with respect to the entire incident area of the parallel light output from the image forming unit and converted by the optical lens. Thus, excessive light having a wavelength other than the target wavelength can be prevented from entering the light guide plate arranged on the image forming unit side. As shown in the modified example of the virtual image display device in Figure 8 , the incident side diffraction grating 17B of the second light guide plate 13 arranged on the image forming unit 21 side is narrower with respect to the area of the incident light. Then, green light and red light, which are light having the target wavelength, can enter the first light guide plate 11. Then, it is possible to expect a reduction in the attenuation of the entire image light composed of blue light, green light, and red light entering the light guide plate.

[0107] In the case where the virtual image display device according to the present technology includes an optical device composed of three or more types of light guide plates, the contact area of the optical components on the incident side of each light guide plate is also adjusted. In this way, light having the target wavelength can enter each light guide plate of the virtual image display device.

[0108] In addition, the optical device 10 of the virtual image display device 20 according to the present technology may include holes in the light guide plate arranged on the image forming unit side. The holes are for allowing the parallel light output from the image forming unit and converted by the optical lens to directly enter the light guide plate arranged on the side away from the image forming unit. Thus, light having the target wavelength can directly enter the light guide plate arranged on the side away from the image forming unit. Then, light loss when the light passes through the light guide plate can be avoided. As shown in the modified example of the virtual image display device in Figure 9 , holes 24 are provided at the positions where the light from the image forming unit 21 of the second light guide plate 13 arranged on the image forming unit 21 side enters. Then, green light and red light, which are light having the target wavelength, can directly enter the first light guide plate 11 without passing through the second light guide plate 13.

[0109] In the case where the virtual image display device according to the present technology includes an optical device composed of three or more types of light guide plates, the positions and sizes of the holes in each light guide plate are also adjusted. In this way, light having the target wavelength can effectively enter each light guide plate of the virtual image display device.

[0110] The virtual image display device including the optical device according to the present technology can be widely used in general applications of see-through displays (also referred to as transmissive displays, transparent displays). A see-through display refers to a display through which the back of the screen to which image information is output can be seen. Examples of see-through displays can include head-mounted displays and display windows.

[0111] (5) Head-mounted display

[0112] An example of the use of the head-mounted display 30 shown in Figure 10 will be described using a conceptual diagram as an example of the installation of the head-mounted display 30, as an application example of the virtual image display device according to the present technology as a perspective display. It should be noted that the application of the virtual image display device according to the present technology is not limited to the head-mounted display shown here.

[0113] As Figure 10 shown in the conceptual diagram of, the image light output from the image forming unit 21 is converted into parallel light by the optical lens 22. Then, the image light enters the first light guide path 12 of the first light guide plate 11 and the second light guide path 14 of the second light guide plate 13. The image light propagates through each light guide path. The image light is output from the virtual image display device 20 as image information. In this way, the image light is recognized as a virtual image by the pupil 32 of the observer 31.

[0114] As described above, the first light guide path 12 and the second light guide path 14 are formed of a highly transparent resin. Thus, the observer 31 wearing the head-mounted display 30 according to the present technology can visually recognize the back surface of the image information output from the light guide path of the light guide plate. Therefore, for example, it is also possible to expect the realization of augmented reality (AR) with the head-mounted display according to the present technology.

[0115] It should be noted that although Figure 10 the head-mounted display including two virtual image display devices for the right eye and the left eye is shown, a head-mounted display including one virtual image display device for one eye may also be used. In addition, in the case where the head-mounted display includes two virtual image display devices, the virtual image display devices for the right eye and the left eye may display the same image, or may display different images (for example, images of a three-dimensional image).

[0116] [Example]

[0117] Hereinafter, the present technology will be described more specifically using examples. It should be noted that the present technology is not limited to the content of the examples shown below.

[0118] <Raw materials of the light guide plate>

[0119] Resin A: Thermoplastic polycarbonate EP9000 (manufactured by Mitsubishi Gas Chemical Company, Inc.)

[0120] Resin B: Thermoplastic polycarbonate H4000 (manufactured by Mitsubishi Gas Chemical Company)

[0121] Figure 11 is a graph showing the relationship between the refractive index and wavelength dispersion of EP9000 and H4000. Figure 12It is a graph showing the relationship between the transmittance and wavelength dispersion of EP9000 and H4000.

[0122] As Figure 11 shown in the graph of, although H4000 exhibits a refractive index of 1.60 or more for light having a wavelength of 493 nm or less corresponding to the upper limit wavelength of blue light, it can be confirmed that EP9000 exhibits a relatively high refractive index with respect to H4000.

[0123] As Figure 12 shown in the graph of, H4000 exhibits a relatively high transmittance with respect to EP9000. In particular, for light having a wavelength of 493 nm or less corresponding to the upper limit wavelength of blue light, it can be confirmed that it exhibits a relatively high transmittance.

[0124] <Manufacture of a virtual image display device>

[0125] The method of manufacturing a virtual image display device will be described using Figure 13 which shows a schematic diagram of the method of manufacturing a virtual image display device.

[0126] Using resin H4000 and EP9000 respectively, as Figure 13 shown in A of, a plate-shaped light guide plate is prepared by injection molding, and the light guide plate includes a region of two diffraction gratings (an incident-side diffraction grating 47 and an output-side diffraction grating 48) on one surface of the plate.

[0127] Design is carried out such that the light guide plate 40 has a plate thickness of 1 mm, and the incident-side diffraction grating 47 and the output-side diffraction grating 48 are binary diffraction gratings as Figure 3 shown in A of, with a period of 400 nm, the width of the convex portion of the concave-convex portion being 200 nm, and the depth being 100 nm.

[0128] Using the first light guide plate 41 formed of EP9000 and the second light guide plate 43 formed of H4000 in the light guide plate molded in substantially the same shape as the above design, three types of optical devices 50 according to Example 1, Comparative Example 1, and Comparative Example 2 were manufactured as a combination shown below.

[0129] Example 1 (First light guide plate, second light guide plate)

[0130] Comparative Example 1 (First light guide plate, first light guide plate)

[0131] Comparative Example 2 (Second light guide plate, second light guide plate)

[0132] The light guide plates according to each of the above combinations are as Figure 13They are superposed on each other as shown in B, and their peripheral parts are fixed with a UV curable adhesive 45 (PET base tape / Nitto Denko Corporation).

[0133] In each of the three types of optical devices 50 combined as described above, due to the thickness of the UV curable adhesive 45, the light guide plate is stacked via an air layer 46. The thickness of the air layer 46 is approximately 100 μm.

[0134] As Figure 13 shown in C, a module associated with the three types of virtual image display devices 60 is completed by fixing a projector having an LCOS display 51 corresponding to the image forming section and an optical lens 52 with respect to each of the three types of optical devices 50.

[0135] <Evaluation of Virtual Image Display Device>

[0136] Table 1 shows the evaluation results of the three types of virtual image display devices.

[0137] [Table 1]

[0138] Transmittance (%) Refractive index Display viewing angle (degrees) Example 1 >85％ 1.61-1.67 14-18 Comparative Example 1 80％ 1.65-1.71 17-19 Comparative Example 2 >85％ 1.57-1.61 12-15

[0139] In Table 1, regarding the transmittance, by using the Figure 14 graph showing the relationship between the transmittance and the wavelength dispersion shown in, the transmittance of the light with the lowest transmittance among the RGB lights is set as the transmittance of the optical device of the virtual image display device. In the virtual image display device according to the above example, as Figure 14 shown in A, it is the transmittance of green light. In the virtual image display device according to Comparative Example 1, as Figure 14 shown in B, it is the transmittance of blue light. In the virtual image display device according to Comparative Example 2, as Figure 14 shown in C, it is the transmittance of blue light.

[0140] In Table 1, the refractive index is calculated by the critical angle method. In this evaluation, the wavelength of the blue light used is 450 nm, the wavelength of the green light is 532 nm, and the wavelength of the red light is 650 nm.

[0141] Figure 14 Based on the refractive index data described above, a graph showing the relationship between the refractive index and the wavelength dispersion is drawn according to the Cauchy dispersion formula.

[0142] In Table 1, the display angle of view is calculated based on the size of the captured image obtained by capturing the display image output from each virtual image display device with a camera.

[0143] It has been confirmed that the virtual image display device according to Example 1 can effectively propagate blue light, which is light with a shorter wavelength, in the light guide path in the same manner as other light. Thus, the light quantity balance between RGB can be easily maintained. In addition, a decrease in the refractive index of red light, which is light with a longer wavelength, is suppressed. Thus, the display viewing angle can also be increased when it is used for a see-through display.

[0144] The transmittance of the virtual image display device according to Comparative Example 1 for blue light is 80%, the light quantity balance with respect to other light deteriorates, and the output display image appears yellower.

[0145] The virtual image display device according to Comparative Example 2 can also effectively propagate blue light, which is light with a shorter wavelength, in the light guide path in the same manner as other light. However, the refractive index is low. Thus, the display viewing angle is narrow.

[0146] It should be noted that the present technology can adopt the following configurations.

[0147] (1) An optical device, comprising

[0148] a first light guide plate having a first light guide path formed of a first material; and

[0149] a second light guide plate having a second light guide path formed of a second material different from the first material, wherein

[0150] the second material has a higher transmittance for light with a wavelength of 493 nm or less than the first material.

[0151] (2) An optical device, comprising:

[0152] a first light guide plate having a first light guide path formed of a first material; and

[0153] a second light guide plate having a second light guide path formed of a second material different from the first material, wherein

[0154] the first material has a higher refractive index for light with a wavelength of 492 nm than the second material.

[0155] (3) The optical device according to (1) or (2), wherein

[0156] the transmittance of the second material for light with a wavelength of 435 nm is 85% or more.

[0157] (4) The optical device according to any one of (1) to (3), wherein

[0158] The refractive index of the first material for light with a wavelength of 492 nm is 1.6 or more.

[0159] (5) The optical device according to any one of (1) to (4), wherein

[0160] The refractive index of the second material for light with a wavelength of 493 nm is 1.6 or more.

[0161] (6) The optical device according to any one of (1) to (5), wherein

[0162] The first light guide plate and the second light guide plate are stacked via a medium having a refractive index lower than that of the first material and the second material.

[0163] (7) The optical device according to any one of (1) to (6), further comprising

[0164] A third light guide plate having a third light guide path formed of a third material different from the first material and the second material.

[0165] (8) The optical device according to any one of (1) to (7), wherein

[0166] The first material and the second material are resins.

[0167] (9) The optical device according to any one of (1) to (8), wherein

[0168] The first light guide plate includes a first optical component and a second optical component on the first light guide path, and

[0169] The second light guide plate includes a third optical component and a fourth optical component on the second light guide path.

[0170] (10) The optical device according to any one of (1) to (9), wherein

[0171] The first optical component and the second optical component reflect light with a wavelength of 492 nm or more, and

[0172] The third optical component and the fourth optical component reflect light with a wavelength of 493 nm or less.

[0173] (11) The optical device according to (9) or (10), wherein

[0174] The optical component is a diffraction grating.

[0175] (12) The optical device according to any one of (9) to (11), wherein

[0176] Any one of the optical components is arranged on the outer surface side of any one of the light guiding paths, and includes a protective substrate on the surface of the optical component, the surface being on the side opposite to the surface in contact with the light guiding path, and the transmittance of the protective substrate for light with a wavelength of 435 nm is 90% or more.

[0177] (13) The optical device according to (12), wherein

[0178] The first light guide plate and the protective substrate are stacked via a medium having a refractive index lower than that of the first material and the second material.

[0179] (14) A virtual image display device, comprising:

[0180] An image forming unit that outputs image light;

[0181] An optical lens that converts the image light output from the image forming unit into parallel light; and

[0182] The optical device according to any one of (1) to (13), the optical device causing the parallel light to be incident on the first light guide plate and the second light guide plate.

[0183] (15) The virtual image display device according to (14), wherein

[0184] The first light guide plate is arranged on the side opposite to the image forming unit with respect to the second light guide plate.

[0185] (16) A head-mounted display, comprising

[0186] The virtual image display device according to (14) or (15).

[0187] List of reference numerals

[0188] 10 Optical device

[0189] 11 First light guide plate

[0190] 12 First light guiding path

[0191] 13 Second light guide plate

[0192] 14 Second light guiding path

[0193] 15A, 15B Adhesive

[0194] 16 Low refractive index medium (air layer)

[0195] 17A First optical component (incident side diffraction grating)

[0196] 18A Second optical component (output-side diffraction grating)

[0197] 17B Third optical component (input-side diffraction grating)

[0198] 18B Fourth optical component (output-side diffraction grating)

[0199] 17C Fifth optical component (input-side diffraction grating)

[0200] 18C Sixth optical component (output-side diffraction grating)

[0201] 19 Third light guide plate

[0202] 20 Virtual image display device

[0203] 21 Image forming unit

[0204] 22 Optical lens

[0205] 23 Color filter

[0206] 24 Hole

[0207] 25 Protection substrate

[0208] 26 Observer's pupil

[0209] 30 Head-mounted display

[0210] 31 Observer

[0211] 32 Observer's pupil

[0212] 40 Light guide plate

[0213] 41 First light guide plate

[0214] 43 Second light guide plate

[0215] 45 UV curable adhesive

[0216] 46 Air layer

[0217] 47, 47A, 47B Input-side diffraction grating

[0218] 48, 48A, 48B Output-side diffraction grating

[0219] 50 Optical device

[0220] 51 LCOS display

[0221] 52 Optical lens

[0222] 60 Virtual image display device

Claims

1. An optical device, comprising: A first light guide plate having a first light guiding path formed of a first material; And A second light guide plate having a second light guiding path formed of a second material different from the first material, wherein The second material has a higher transmittance for light with a wavelength of 493 nm or less than the first material.

2. The optical device according to claim 1, wherein The transmittance of the second material for light with a wavelength of 435 nm is 85% or more.

3. The optical device according to claim 1, wherein The refractive index of the first material for light with a wavelength of 492 nm is 1.6 or more.

4. The optical device according to claim 1, wherein The refractive index of the second material for light with a wavelength of 493 nm is 1.6 or more.

5. The optical device according to claim 1, wherein The first light guide plate and the second light guide plate are stacked via a medium having a refractive index lower than that of the first material and the second material.

6. The optical device according to claim 1, further comprising: A third light guide plate having a third light guiding path formed of a third material different from the first material and the second material.

7. The optical device according to claim 1, wherein The first material and the second material are resins.

8. The optical device according to claim 1, wherein The first light guide plate includes a first optical component and a second optical component on the first light guiding path, and The second light guide plate includes a third optical component and a fourth optical component on the second light guiding path.

9. The optical device according to claim 8, wherein The first optical component and the second optical component reflect light with a wavelength of 492 nm or more, and The third optical component and the fourth optical component reflect light with a wavelength of 493 nm or less.

10. The optical device according to claim 8, wherein The optical component is a diffraction grating.

11. The optical device according to claim 8, wherein Any one of the optical components is arranged on the outer surface side of any one of the light guiding paths, and a protective substrate is included on the surface of the optical component, the surface being on the side opposite to the surface in contact with the light guiding path, and the transmittance of the protective substrate for light with a wavelength of 435 nm is 90% or more.

12. The optical device according to claim 11, wherein The first light guide plate and the protective substrate are stacked via a medium having a refractive index lower than that of the first material and the second material.

13. A virtual image display device, comprising: An image forming unit that outputs image light; An optical lens that converts the image light output from the image forming unit into parallel light; And The optical device according to claim 1, which makes the parallel light incident on the first light guide plate and the second light guide plate.

14. The virtual image display device according to claim 13, wherein The first light guide plate is arranged on the side opposite to the image forming unit with respect to the second light guide plate.

15. A head-mounted display, comprising The virtual image display device according to claim 13.

Images