Light guide and image display device

Abstract

The light guide comprises: a substrate having a first reflecting surface and a second reflecting surface, such that incident image light is propagated by total reflection from the first reflecting surface and the second reflecting surface; and a plurality of semi-reflective mirrors having a first surface and a second surface on the back side of the first surface, and comprising a dielectric multilayer film. The plurality of semi-reflective mirrors are arranged in the substrate at an angle relative to the first reflecting surface and the second reflecting surface and spaced apart from each other. The substrate and the plurality of semi-reflective mirrors are configured such that image light incident on the substrate is incident on the first surface and the second surface of at least one of the plurality of semi-reflective mirrors more than once. When the refractive index of the substrate is set to n, the refractive index of the two outermost layers on the first surface side and the second surface side of the dielectric multilayer film is 0.90n to 1.15n.

Description

Technical Field

[0001] This invention relates to a light guide and an image display device. Background Technology

[0002] In recent years, the development of "wearable displays," such as head-mounted displays, which are worn on the body and represent the next generation of image display devices, has been very active.

[0003] A head-mounted display has an optical system that includes a light guide that guides an image output from an image light generating unit to the wearer's eyes. Light guides are broadly classified into reflective types using partially reflective surfaces, volumetric holographic types, and diffractive element types. For example, reflective light guides are disclosed in International Publication No. 2019 / 087576 and Japanese Patent Application Publication No. 2020-118840. The light guides described in these publications propagate image light through total internal reflection, and have a structure that reflects a portion of the image light to the outside, and arranges multiple partially reflective surfaces, some of which are transmitted, approximately parallel to each other along the propagation direction of the image light inside the light guide. Summary of the Invention

[0004] The technical problem to be solved by the invention

[0005] The technical objective of this invention is to provide a light guide and an image display device capable of displaying images with high contrast.

[0006] means for solving technical problems

[0007] The light guide of the present invention comprises: a substrate having a first reflective surface and a second reflective surface, such that incident image light is propagated simultaneously by total internal reflection from the first reflective surface and the second reflective surface; and

[0008] It is composed of multiple semi-reflective mirrors, each having a first surface and a second surface behind the first surface, and comprising a dielectric multilayer film.

[0009] Multiple semi-reflective mirrors are arranged at an angle relative to the first and second reflecting surfaces and spaced apart from each other within the substrate.

[0010] The substrate and multiple semi-reflective mirrors are configured such that image light incident on the substrate is incident on the first and second surfaces of at least one of the multiple semi-reflective mirrors more than once.

[0011] With the refractive index of the substrate set to n, the refractive indices of the two outermost layers on the first and second sides of the dielectric multilayer film are 0.90n to 1.15n.

[0012] In the light guide of the present invention, the refractive index of the outermost layer of the dielectric multilayer film is preferably 0.95n to 1.10n, more preferably 1.00n to 1.05n.

[0013] In the light guide of the present invention, the thickness of the outermost layer of the dielectric multilayer film is set as d [nm], the refractive index is set as n1, and when Δn = {(n-n1) / n} × 100 [%) is set, Δn·d [%·nm] is preferably in the range of -300 to +300.

[0014] In the light guide of the present invention, the tilt angle of the semi-reflective mirror relative to the first and second reflective surfaces is preferably such that when the image light incident into the substrate is incident on the first surface at an incident angle of 5° to 35°, the transmitted light of the incident image light passing through the semi-reflective mirror is reflected by the first or second reflective surface and can then be re-incident from the second surface.

[0015] In the light guide of the present invention, the tilt angle of the semi-reflective mirror is preferably an angle in the range of 55° to 85° when the transmitted light is re-intruded from the second surface.

[0016] In the light guide of the present invention, the dielectric multilayer film preferably consists of alternating layers of a low refractive index layer having a relatively low refractive index and a high refractive index layer having a relatively high refractive index.

[0017] In the light guide of the present invention, at least one of the two outermost layers of the dielectric multilayer film is preferably bonded to the substrate through optical contact.

[0018] In the light guide of the present invention, preferably the two outermost layers of the dielectric multilayer film are in direct contact with the substrate.

[0019] In the light guide of the present invention, it is preferable that there is no adhesive between the semi-reflective mirror and the substrate.

[0020] In the light guide of the present invention, each layer of the dielectric multilayer film may contain silicon, oxygen and nitrogen.

[0021] In the light guide of the present invention, each layer of the dielectric multilayer film can be configured as a metal oxide layer comprising at least one of silicon, niobium, tantalum, aluminum, titanium, tungsten and chromium.

[0022] In the light guide of the present invention, the refractive index of the substrate is preferably 1.5 or higher.

[0023] In the light guide of the present invention, the substrate is preferably a parallel plate with the first reflecting surface and the second reflecting surface parallel.

[0024] In the light guide of the present invention, a plurality of semi-reflective mirrors are preferably arranged parallel to each other in the direction of image light propagation.

[0025] In the light guide of the present invention, the semi-reflective mirror preferably has an average reflectivity of 2% to 4% for light with wavelengths of 400nm to 700nm incident at an incident angle of 5° to 35°, and an average reflectivity of 10% or less for light with wavelengths of 400nm to 700nm incident at an incident angle of 55° to 85°.

[0026] Another aspect of the light guide of the present invention comprises: a substrate having a first reflective surface and a second reflective surface, such that incident image light is propagated simultaneously by total internal reflection from the first reflective surface and the second reflective surface; and

[0027] It is composed of multiple semi-reflective mirrors, each having a first surface and a second surface behind the first surface, and comprising a dielectric multilayer film.

[0028] Multiple semi-reflective mirrors are arranged at an angle relative to the first and second reflecting surfaces and spaced apart from each other within the substrate.

[0029] The substrate and multiple semi-reflective mirrors are configured such that image light incident on the substrate is incident on the first and second surfaces of at least one of the multiple semi-reflective mirrors more than once.

[0030] The average reflectivity of a semi-reflective mirror for light with wavelengths of 400nm to 700nm incident at an angle of incidence of 5° to 35° is 2% to 4%, and the average reflectivity for light with wavelengths of 400nm to 700nm incident at an angle of incidence of 55° to 85° is less than 10%.

[0031] The image display device of the present invention includes: an image light generating unit that generates image light; a light guide body of the present invention that propagates the incident image light; and an optical coupling member that causes the image light generated by the image light generating unit to enter the light guide body.

[0032] Invention Effects

[0033] The light guide and image display device according to the present invention can obtain images with high contrast. Attached Figure Description

[0034] Figure 1 This is an appearance diagram showing the usage state of an HMD, which is an image display device having a light guide 12 according to an embodiment of the present invention.

[0035] Figure 2 This is a picture of user 5 with HMD10 installed, viewed from above.

[0036] Figure 3 This is a magnified view of the light guide 12.

[0037] Figure 4 This is a schematic diagram showing the structure of a half-mirror 30 in the substrate 20.

[0038] Figure 5 This is a schematic diagram illustrating the optical path of the image light in the light guide 12.

[0039] Figure 6 This is a graph showing the relationship between the optical coupling angle θ0 and the incident angle θ1.

[0040] Figure 7 This is a diagram showing the relationship between the incident angles θ1 and θ2.

[0041] Figure 8 This is a graph showing the dependence of the nitrogen / oxygen flux ratio on the refractive index of the oxynitride film relative to light with a wavelength of 540 nm.

[0042] Figure 9 This is a schematic diagram illustrating the formation process of a dielectric multilayer film.

[0043] Figure 10 This is a schematic diagram illustrating the bonding process of the substrate.

[0044] Figure 11 This is a schematic diagram illustrating the bonding process of the substrate.

[0045] Figure 12 of Figure 12 A represents the process of cutting out the light guide from a composite body formed by bonding multiple substrates. Figure 12 B is a diagram showing the light guide cut out from the joint as seen from arrow 12B.

[0046] Figure 13 of Figure 13 A is a graph showing the dependence of the incident angle on the reflectivity of the semi-reflective mirror of Design Example 1 for light with a wavelength of 540 nm. Figure 13 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 1 relative to an incident angle of 25°. Figure 13 C is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 1 relative to an incident angle of 75°.

[0047] Figure 14 of Figure 14 A is a graph showing the dependence of the incident angle on the reflectivity of the semi-reflective mirror for light with a wavelength of 540 nm for Design Example 2. Figure 14 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 2 relative to an incident angle of 25°. Figure 14 C is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 2 relative to an incident angle of 75°.

[0048] Figure 15 of Figure 15 A is a graph showing the dependence of the incident angle on the reflectivity of the semi-reflective mirror of Design Example 3 for light with a wavelength of 540 nm. Figure 15 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 3 relative to an incident angle of 25°. Figure 15 C is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror in Design Example 3 relative to an incident angle of 75°.

[0049] Figure 16 of Figure 16 A represents the Δn dependence of the reflectivity of the semi-reflective mirror in Design Example 1 relative to an incident angle of 75°. Figure 16 B represents the Δn·d dependence of the reflectivity of the semi-reflective mirror in Design Example 1 on light incident at an angle of 75°.

[0050] Figure 17 of Figure 17 A represents the Δn dependence of the reflectivity of the semi-reflective mirror in Design Example 2 relative to an incident angle of 75°. Figure 17 B represents the Δn·d dependence of the reflectivity of the semi-reflective mirror in Design Example 2 on light incident at an angle of 75°.

[0051] Figure 18 of Figure 18 A represents the Δn dependence of the reflectivity of the semi-reflective mirror in Design Example 3 relative to an incident angle of 75°. Figure 18 B represents the Δn·d dependence of the reflectivity of the semi-reflective mirror in Design Example 3 on light incident at an angle of 75°.

[0052] Figure 19 of Figure 19 A is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 1 relative to an incident angle of 25°. Figure 19 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 1 relative to an incident angle of 75°.

[0053] Figure 20 of Figure 20 A is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 2 relative to an incident angle of 25°. Figure 20 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 2 relative to an incident angle of 75°.

[0054] Figure 21 of Figure 21 A is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 3 relative to an incident angle of 25°. Figure 21 B is a graph showing the wavelength dependence of the reflectivity of the semi-reflective mirror of Reference Example 3 relative to an incident angle of 75°.

[0055] Figure 22 This is a diagram used to illustrate the sample pieces used in strength testing.

[0056] Figure 23 This is a schematic diagram used to illustrate the general outline of the strength test. Detailed Implementation

[0057] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0058] The numerical range indicated by “~” in this specification refers to the range included by taking the values ​​before and after “~” as the lower and upper limits.

[0059] "Image display device"

[0060] Figure 1 This shows the appearance of a head-mounted display (HMD) 10, which is an embodiment of the image display device of the present invention. The HMD 10 has one embodiment of the light guide of the present invention. The HMD 10 is used, for example, mounted on the head of a user 5. Figure 2 This is a picture of user 5 with HMD10 installed, viewed from above. Figure 3 This is a magnified view of the light guide 12.

[0061] The HMD10 includes an image light generating unit 11, a light guide 12, and an optical coupling component 13.

[0062] The image light generating unit 11 generates image light and emits it into the optical coupling member 13. The image light generating unit 11 includes, for example, a light source unit; an image light generating element for generating image light; and a projection optics unit for projecting image light.

[0063] The light source unit includes, for example, a light source comprising red, green and blue LEDs (light emitting diodes) or LDs (laser diodes); and a lens for illuminating the image light generating element with light from the light source.

[0064] The image light generating element includes a display element that displays an image based on an image signal, and generates image light by modulating light incident from a light source unit through the display element. Examples of display elements include liquid crystal panels or digital mirror devices (DMDs).

[0065] The projection optics section includes a projection lens consisting of one or more lenses, which projects the image light generated by the image light generating element into the optical coupling component 13.

[0066] The light guide 12 is positioned in front of the user 5's eyes 6 during installation. It receives the image light generated by the image light generating unit 11 and propagates the incident image light. By projecting the image light towards the user 5, the user 5 visually recognizes the image. The image recognized by the user 5 can be a still image or a moving image. For example... Figure 3As shown, the light guide 12 includes a substrate 20 and a plurality of semi-reflective mirrors 30a, 30b, 30c, and 30d disposed within the substrate 20. The substrate 20 has a first reflecting surface 21 and a second reflecting surface 22, and the image light L0 propagates within the substrate 20 by repeated total internal reflection through the first reflecting surface 21 and the second reflecting surface 22. The semi-reflective mirrors 30a, 30b, 30c, and 30d reflect a portion of the incident light and transmit the rest. As an example, the reflectivity of the semi-reflective mirrors 30a, 30b, 30c, and 30d is approximately 2 to 10%. A portion of the image light L0 is reflected from each of the plurality of semi-reflective mirrors 30 disposed within the substrate 20 and emitted from the substrate 20 as an outgoing light L1, enabling the user 5 to visually recognize the image.

[0067] In addition, in this specification, reflectivity is represented by the average of the reflectivity for p-polarized light and the reflectivity for s-polarized light.

[0068] The optical coupling member 13 directs the image light L0 generated by the image light generation unit 11 into the light guide 12. In this example, the optical coupling member 13 is an optical coupling prism. In this embodiment, the optical coupling member 13 is disposed with one side in contact with the first reflecting surface 21 of the light guide 12. The optical coupling member 13 guides the image light L0 into the light guide 12 so that the image light L0 propagates within the light guide 12 at an angle of total internal reflection, incident on the first reflecting surface 21 and the second reflecting surface 22. Furthermore, the optical coupling member 13 guides the image light L0 into the light guide 12 so that it is incident on the first surface 31a of the semi-reflecting mirror 30a at a desired incident angle θ1. The optical coupling member 13 guides the image light L0 into the light guide 12 so that the incident angle θ1 of the image light L0 on the first surface 31a of the semi-reflecting mirror 30a in the light guide 12 is, for example, 5° to 35°. Here, the incident angle refers to the angle between the normal to the surface into which the light is incident and the ray.

[0069] "Light guide"

[0070] The following is a detailed description of the light guide 12.

[0071] The light guide 12 is one embodiment of the light guide of the present invention. As described above, the light guide 12 includes a substrate 20 and a plurality of semi-reflective mirrors 30a, 30b, 30c, and 30d. The substrate 20 has a first reflecting surface 21 and a second reflecting surface 22, so that the incident image light L0 is propagated while being totally reflected by the first reflecting surface 21 and the second reflecting surface 22. In this embodiment, the substrate 20 is a parallel plate with the first reflecting surface 21 and the second reflecting surface 22 parallel to each other. Here, a parallel plate refers to a plate-shaped member in which the first reflecting surface 21 and the second reflecting surface 22 are arranged parallel to each other so that the image light L0 is reflected and propagated. Of course, a plate with unevenness or a portion where the first reflecting surface 21 and the second reflecting surface 22 are not parallel in a part of the outer peripheral surface of the parallel plate that does not affect the propagation of light is also included in the "parallel plate" involved in the technology of the present invention. By using a parallel plate, it is easy to design the optical path. Furthermore, in the substrate 20, as long as the image light L0 is repeatedly reflected by total internal reflection between the first reflecting surface 21 and the second reflecting surface 22 and propagates therethrough, and the image can be visually recognized by the outgoing light L1 reflected by the semi-reflecting mirror 30, the first reflecting surface 21 and the second reflecting surface 22 do not necessarily have to be parallel.

[0072] There are no particular restrictions on the substrate 20 as long as it is a transparent component. The refractive index n of the substrate 20 is preferably 1.5 or higher, more preferably 1.7 or higher, and especially preferably 1.8 or higher. The higher the refractive index, the more light leakage from the light guide to the outside can be reduced, and the better the image can be obtained.

[0073] In this embodiment, a plurality of semi-reflective mirrors 30a, 30b, 30c, and 30d are arranged parallel to each other in the direction of image light propagation. The semi-reflective mirrors 30a, 30b, 30c, and 30d each have a second surface 32a, 32b, 32c, and 32d on the back side of the first surfaces 31a, 31b, 31c, and 31d, respectively. Furthermore, without distinguishing each of the plurality of semi-reflective mirrors, the suffixes a, b, c, and d attached to the symbols are omitted, and they are simply referred to as semi-reflective mirror 30, first surface 31, and second surface 32.

[0074] Multiple semi-reflective mirrors 30 are arranged within the substrate 20 at an angle relative to the first reflecting surface 21 and the second reflecting surface 22 and spaced apart from each other. The angle α of the semi-reflective mirror 30 relative to the first reflecting surface 21 and the second reflecting surface 22 is called the tilt angle α of the semi-reflective mirror 30.

[0075] like Figure 3As shown, the image light L0 incident on the substrate 20 is repeatedly subjected to total internal reflection by the first reflecting surface 21 and the second reflecting surface 22 of the substrate 20, and propagates in a direction A parallel to the first reflecting surface 21 and the second reflecting surface 22. During this time, the image light L0 propagates while passing through the multiple semi-reflecting mirrors 30 provided in the substrate 20 one or more times. When incident on the first surface 31 of the semi-reflecting mirror 30, a portion of the image light L0 is reflected by the semi-reflecting mirror 30 and emitted as the outgoing light L1.

[0076] The substrate 20 and the plurality of semi-reflecting mirrors 30 are configured such that the image light L0 incident on the substrate 20 is incident on the first surface 31 and the second surface 32 of at least one of the semi-reflecting mirrors 30 more than once. For example, as Figure 3 As shown, image light L0, incident on the first reflecting surface 21 of the substrate 20 via the optical coupling member 13 at an optical coupling angle θ0, is incident on the first surface 31a of the semi-reflective mirror 30a. At this time, a portion of the image light L0 is reflected by the semi-reflective mirror 30a and emitted from the substrate 20 as outgoing light L1. The image light L0 that is not reflected and is transmitted through the semi-reflective mirror 30a is incident on point 22a of the second reflecting surface 22. The image light L0 incident on the second reflecting surface 22 is totally internally reflected and is incident on the second surface 32a of the semi-reflective mirror 30a at an incident angle θ2. The image light L0 that is incident on the semi-reflective mirror 30a from the second surface 32a and is transmitted through the semi-reflective mirror 30a is incident on point 21a of the first reflecting surface 21 and undergoes total internal reflection. The image light L0 reflected by the first reflecting surface 21 is again incident on the first surface 31 of the semi-reflective mirror 30a, a portion of which is emitted from the substrate 20 as outgoing light L1. Thus, in Figure 3 In the example shown, the image light L0 incident on the substrate 20 is incident twice on the first surface 31 of the semi-reflective mirror 30a and once on the second surface 32.

[0077] Figure 4 This is a schematic diagram illustrating the structure of a single half-mirror 30 within the substrate 20. (See diagram for example.) Figure 4 As shown, the semi-reflective mirror 30 comprises a dielectric multilayer film 40 formed by stacking multiple dielectric layers 41 to 47. In this embodiment, the semi-reflective mirror 30 is composed of a dielectric multilayer film 40. Figure 4 In the middle, the dielectric multilayer film 40 has 7 dielectric layers 41 to 47, but when it functions as a semi-reflective mirror 30, the number of dielectric layers is not limited.

[0078] The dielectric multilayer film 40 is constructed by stacking multiple dielectric layers with different refractive indices. When the refractive index of the substrate 20 is set to n, the refractive indices of the two outermost layers 41 and 47 constituting the dielectric multilayer film 40 are 0.90n to 1.15n. The refractive indices of the outermost layers 41 and 47 are preferably 0.95n to 1.10n, more preferably 1.00n to 1.05n. Furthermore, the outermost layer in the dielectric multilayer film 40 refers to the outermost layer among the layers that sense incident image light. Here, the layer that senses image light conceptually refers to a layer that has a refractive effect on image light; specifically, it refers to a layer whose optical path length n·d, expressed as the product of the refractive index n and the physical thickness d of the dielectric film, exceeds 10 nm. Therefore, even if a layer with n·d less than 10 nm is disposed between the dielectric multilayer film 40 and the substrate 20, this layer is not considered the outermost layer of the dielectric multilayer film 40.

[0079] As described above, in the light guide 12 of this embodiment, the substrate 20 and the plurality of semi-reflective mirrors 30 are configured such that the image light L0 incident on the substrate 20 is incident on the first surface 31 and the second surface 32 of at least one of the plurality of semi-reflective mirrors 30 more than once. Therefore, as Figure 5 As shown, the image light L0 incident and transmitted from the first surface 31a of the semi-reflecting mirror 30a is reflected by the second reflecting surface 22 and incident on the semi-reflecting mirror 30a again from the second surface 32a. At this time, the light incident from the second surface 32a and reflected by the semi-reflecting mirror 30a becomes stray light LM, a portion of which is emitted to the outside as uncontrollable useless light LM1.

[0080] If the amount of stray light LM incident and reflected from the second surface 32a of the semi-reflecting mirror 30a is large, the amount of image light L0 propagating to the subsequent semi-reflecting mirror 30b and the amount of light emitted as outgoing light L1 reflected by the first surface 31b of the semi-reflecting mirror 30b are greatly reduced. Repeating this process, the reduction in the amount of outgoing light L1 in the subsequent semi-reflecting mirrors becomes significant. If the amount of outgoing light L1 decreases, the visually perceived image becomes darker. Furthermore, a portion of the stray light LM is emitted from the substrate 20 without angle control, sometimes resulting in a blurred image or a ghosting effect. Thus, if the amount of reflected light L0 from the second surface 32a of the semi-reflecting mirror 30 is large, problems such as reduced image contrast occur. This is a unique problem in the light guide 12, which is configured such that the image light L0 is incident on one semi-reflecting mirror 30 multiple times, that is, at least once on the first surface 31b and the second surface 32b respectively.

[0081] The semi-reflective mirror 30 in the light guide 12 is designed to achieve the desired reflectivity when the image light L0 is incident at an angle θ1 onto the first surface 31, where the reflected light is emitted outward as the outgoing light L1. Previously, the structure typically involved the image light L0 only incident on the semi-reflective mirror 30 once, and therefore the reflectivity at the angle θ2 of the image light L0 incident onto the second surface 32 was not considered.

[0082] In contrast, the inventors have discovered that when the refractive index of the substrate 20 is set to n, by setting the refractive index of the two outermost layers 41 and 47 of the plurality of dielectric layers constituting the semi-reflective mirror 30 to 0.90n to 1.15n, the reflectivity of image light L0 incident on the second surface 32 of the semi-reflective mirror 30 can be effectively suppressed (see the design example described later).

[0083] In the light guide 12 of this embodiment, since the refractive index of the outermost layer 41 on the first surface 31 side and the outermost layer 47 on the second surface 32 side of the dielectric multilayer film 40 constituting the semi-reflective mirror 30 is 0.90n to 1.15n, the reflectivity on the second surface 32 of the semi-reflective mirror 30 can be suppressed. Because the reflectivity relative to the incident light onto the second surface 32 of the semi-reflective mirror 30 can be suppressed, the reduction in the amount of image light L0 and the generation of stray light can be suppressed, and a high-contrast image can be obtained.

[0084] Furthermore, the incident angle θ1 of the first surface 31 of the semi-reflector 30 is preferably set to 5° to 35°. And the incident angle θ2 of the second surface 32 of the semi-reflector 30 is preferably set to 55° to 85° (see the verification example described later).

[0085] The incident angle θ1 of the image light L0 onto the first surface 31 of the semi-reflecting mirror 30 varies according to the incident angle θ0 of the guide beam of the image light L0, i.e., the optical coupling angle θ0. For example, when the tilt angle α of the semi-reflecting mirror 30 is 25°, the relationship between the optical coupling angle θ0 and the incident angle θ1 is as follows: Figure 6 As shown. Furthermore, the relationship between the incident angle θ2 and the incident angle θ1 of the image light L0, which is incident on the first surface 31 at an incident angle θ1 and then totally reflected by the second reflecting surface 22 to enter the second surface 32, is as follows: Figure 7 As shown.

[0086] That is, in Figure 6 and Figure 7 In the example shown, when the optical coupling angle θ0 is 50°, the incident angle θ1 becomes 25° and the incident angle θ2 becomes 75°. Furthermore, when the optical coupling angle θ0 is 40°, the incident angle θ1 becomes 15° and the incident angle θ2 becomes 65°. Additionally, the relationship between the optical coupling angle θ0 and the incident angles θ1 and θ2 varies depending on the tilt angle α of the semi-reflective mirror 30.

[0087] In practical systems, the tilt angle α and optical coupling angle θ0 of the semi-reflective mirror are selected to ensure that the incident angles θ1 and θ2 are the desired values. The tilt angle α is, for example, 5° to 35°. Figure 7 In the example shown, generally speaking, the incident angle θ1 of the image light L0 onto the first surface 31 of the semi-reflective mirror 30 differs significantly from the incident angle θ2 onto the second surface 32. Furthermore, generally speaking, the reflectivity of the semi-reflective mirror 30, which is composed of a dielectric multilayer film 40, is incident angle-dependent. As mentioned above, previously only the reflectivity at the incident angle θ1 was considered; therefore, the reflectivity at the incident angle θ2 increases, resulting in a decrease in the contrast of the visually recognized image. Hereinafter, a more specific structure of the semi-reflective mirror 30 for setting the reflectivity at the incident angle θ1 to a desired value and sufficiently suppressing the reflectivity at the incident angle θ2 will be described.

[0088] The dielectric multilayer film 40 forming the semi-reflective mirror 30 is preferably composed of alternating layers of low refractive index with relatively low refractive index and high refractive index with relatively high refractive index. The refractive indices of each layer can be different, but alternating layers of low refractive index and high refractive index with the same refractive index are also possible. Furthermore, for example, the dielectric multilayer film 40 can have the following structure: an intermediate region 48 consisting of alternating layers of low refractive index layers 42, 44, 46 with a refractive index lower than that of the substrate 20 and high refractive index layers 43, 45 with a refractive index higher than that of the substrate 20; and outermost layers 41, 47 with a refractive index n of 0.90n to 1.15n relative to that of the substrate 20. By alternating layers of low and high refractive index, it is easy to design and fabricate a semi-reflective mirror with a desired incident angle-dependent reflectivity.

[0089] Each layer 41 to 47 of the dielectric multilayer film 40 may contain silicon (Si), oxygen (O), and nitrogen (N). Regarding each layer 41 to 47, when it is a silicon oxynitride film, the desired refractive index can be set by changing the Si:O:N content ratio.

[0090] Furthermore, each layer 41 to 47 of the dielectric multilayer film 40 can also be a metal oxide layer containing at least one of silicon, niobium (Nb), tantalum (Ta), aluminum (Al), titanium (Ti), tungsten (W), and chromium (Cr). Depending on the desired refractive index, metal oxides containing one or more metals can be appropriately used.

[0091] When the thickness of the outermost layers 41 and 47 of the dielectric multilayer film 40 is set as d, the refractive index is set as n1, and the percentage difference between the refractive index n and the refractive index n1 of the substrate 20 is set as Δn = {(n-n1) / n} × 100 [%), Δn·d [%·nm] is preferably in the range of -300 to +300. Δn·d is more preferably in the range of -200 to +200. Δn·d is even more preferably in the range of -150 to 150, and particularly preferably in the range of -100 to +100. If Δn·d is in the range of -300 to +300, the reflectivity of image light L0 incident on the second surface 32 of the semi-reflective mirror 30 can be effectively suppressed.

[0092] like Figure 4 As shown, the two outermost layers 41 and 47 of the dielectric multilayer film 40 are preferably arranged in direct contact with the substrate 20. That is, preferably, there is no adhesive between the dielectric multilayer film 40 and the substrate 20. At least one of the two outermost layers 41 and 47 of the dielectric multilayer film 40 is preferably bonded to the substrate 20 by optical contact. Here, bonding by optical contact means bonding without using adhesive. By bonding at least one of the two outermost layers 41 and 47 of the dielectric multilayer film 40 to the substrate 20 by optical contact, there is no adhesive between the two outermost layers 41 and 47 of the dielectric multilayer film 40 and the substrate 20, and the two outermost layers 41 and 47 can directly contact the substrate 20.

[0093] The manufacturing method of the light guide will be described in detail later, but optical adhesives are generally used for bonding optical components. However, if the refractive index of a common optical adhesive is 1.5, and the refractive index n of the substrate 20 is 1.7 or higher, the difference in refractive index between the two is too large, and sometimes the design of the dielectric multilayer film cannot be realized. Furthermore, if adhesives are used for bonding, the probability of the parallelism of the surfaces exceeding the target value increases, and productivity decreases. If optical contact-based bonding is performed, the problems arising from bonding with such adhesives can be solved.

[0094] In the semi-reflective mirror 30, the reflectivity for image light L0 incident on the first surface 31 at an incident angle θ1 is preferably 1% to 4%, more preferably 2% to 4%. Furthermore, in the semi-reflective mirror 30, the reflectivity for image light L0 incident on the second surface 32 at an incident angle θ2 is preferably 10% or less, more preferably 4% or less, even more preferably 3% or less, and particularly preferably 1% or less. Since at least a portion of the image light L0 incident on the first surface 31 needs to be reflected and emitted outwards, a certain degree of reflection is necessary. From the viewpoint of suppressing the reduction in the amount of image light L0 and suppressing stray light LM, a lower reflectivity is more preferable for incident on the second surface 32.

[0095] By setting the reflectivity of the image light L0 at the incident angle θ2 facing the second surface 32 to below 10%, the generation of stray light LM is effectively suppressed, and a high-contrast image can be stably obtained.

[0096] Furthermore, to achieve the above structure, the semi-reflective mirror 30 in the light guide 12 preferably has an average reflectivity of 2% to 4% for light with wavelengths of 400nm to 700nm incident at an angle of incidence of 5° to 35°, and an average reflectivity of 10% or less for light with wavelengths of 400nm to 700nm incident at an angle of incidence of 55° to 85°. The image light is visible light and includes light with wavelengths of 400nm to 700nm. In this specification, the reflectivity of the image light refers to the average reflectivity for light with wavelengths of 400nm to 700nm.

[0097] As described above, the semi-reflective mirror 30 is positioned within the light guide 12 at an angle α such that image light, repeatedly reflected by the first reflecting surface 21 and the second reflecting surface 22, is incident on the first surface 31 of the semi-reflective mirror 30 and then incident again on the second surface 32. Here, the image light incident on the light guide 12 is preferably set to be incident on the first surface 31 at an incident angle θ1 = 5° to 35°, and then on the second surface 32 at an incident angle θ2 = 55° to 85°. Furthermore, if the semi-reflective mirror 30 in the light guide 12 has an average reflectivity of 2% to 4% for light with wavelengths of 400nm to 700nm incident at an incident angle of 5° to 35°, and an average reflectivity of 10% or less for light with wavelengths of 400nm to 700nm incident at an incident angle of 55° to 85°, reflected light on the second surface 32 can be effectively suppressed, thus stray light can be suppressed, and a higher contrast image can be obtained. Even at the same incident angle, the reflectivity of a semi-reflective mirror composed of multilayer films varies with wavelength. Furthermore, even at the same wavelength, the reflectivity changes with the incident angle. The "average reflectivity" in this specification refers to the average reflectivity for light with wavelengths from 400 nm to 700 nm at a specific incident angle. Additionally, if the average reflectivity of the reflected light from the second surface is less than 4%, an image with even higher contrast can be obtained.

[0098] "Methods for manufacturing light guides"

[0099] The following describes an example of the manufacturing method of the light guide 12.

[0100] The light guide 12 undergoes a process of forming dielectric multilayer films on multiple substrates (see reference). Figure 9 ), the bonding process of substrates with dielectric multilayer films (refer to) Figure 10 , 11 ) and the cutting process from the joint formed by joining multiple substrates (see reference) Figure 12 And made.

[0101] The details of each process are as follows.

[0102] -Formation process of dielectric multilayer film-

[0103] Prepare multiple plate-shaped transparent substrates 120, such as Figure 9 As shown, dielectric layers 41 to 47 are sequentially deposited on one side 121 of each substrate 120 to form a dielectric multilayer film 40. The method for forming dielectric layers 41 to 47 is not particularly limited, but methods such as sputtering and plasma CVD (chemical vapor deposition) are preferred, which involve depositing the film in plasma.

[0104] When each layer 41 to 47 of the dielectric multilayer film 40 is composed of silicon oxynitride containing silicon, oxygen, and nitrogen, the film can be formed by sputtering, for example, using a target, by introducing argon (Ar) gas, oxygen gas, and nitrogen gas into the chamber. By changing the oxygen to nitrogen flow rate ratio, the Si:O:N ratio in the film changes. Furthermore, by changing the Si:O:N ratio, the refractive index of the film can be changed. Therefore, the oxygen to nitrogen flow rate ratio can be changed to achieve the desired refractive index for each layer of the dielectric multilayer film.

[0105] Figure 8 This represents the nitrogen / oxygen flow rate ratio dependence of the refractive index of the oxynitride film for light at a wavelength of 540 nm. In this specification, the nitrogen / oxygen flow rate ratio is expressed as the proportion of oxygen in nitrogen (N2) gas + oxygen (O2) gas. From... Figure 8 It can be seen that by changing the nitrogen / oxygen flow ratio, the refractive index of the membrane can be varied within the range of n = 2.027 when nitrogen:oxygen = 1:0 to n = 1.459 when nitrogen:oxygen = 0:1. Regarding Figure 8 The sputtering conditions were: Ar gas flow rate = 60 sccm, O2 + N2 gas flow rate = 60 sccm, sputtering power = 750 W, target diameter = 6 inches, substrate temperature (set) = 300℃, and sputtering pressure = 0.2 Pa. Furthermore, the refractive index of the film was measured using an ELLIP SOMETER VASE (registered trademark) manufactured by JAWoollam CO.,INC.

[0106] Thus, by changing the nitrogen:oxygen flow ratio during sputtering, silicon oxynitride films with the desired refractive index can be obtained.

[0107] In the formation of dielectric multilayer films, stoichiometric metal oxides are generally used. Therefore, the refractive index of the stoichiometric metal oxide is required to design the dielectric multilayer film. However, as mentioned above, the refractive index can be changed by altering the Si:O:N ratio. Therefore, if silicon oxynitride is used, films with arbitrary refractive indices can be obtained, and the design of dielectric multilayer films offers a high degree of freedom.

[0108] Furthermore, sputtering can also be used when each layer 41 to 47 of the dielectric multilayer film 40 is a metal oxide layer containing at least one of Si, Nb, Ta, Al, Ti, W, and Cr. In co-sputtering using two or more metal targets, the refractive index can be controlled by adjusting the target voltage. Moreover, the refractive index of each layer 41 to 47 can be controlled by a method of alternately depositing films containing any metal with a thickness of less than 1 / 100 of the wavelength λ of the image light (for example, see Patent No. 5549342).

[0109] -Jointing Process-

[0110] In the bonding of multiple substrates 120 on which dielectric multilayer films 40 are respectively formed, optical contact is preferred.

[0111] like Figure 10 As shown, the outermost surface 40A of the dielectric multilayer film 40, which is disposed on one side of a plurality of substrates 120 respectively having a dielectric multilayer film 40, and the other side of the substrate 120 where no dielectric multilayer film 40 is formed (hereinafter collectively referred to as bonding surfaces 40A and 122) are irradiated in a vacuum with an ion beam 51. The irradiation of the ion beam 51 is performed using an ion beam irradiation apparatus 50. Specifically, argon ions are irradiated onto the bonding surfaces as the ion beam 51 within a vacuum chamber. Through irradiation with this ion beam 51, contaminants such as organic matter attached to the bonding surfaces 40A and 122 are removed, and the bonding surfaces 40A and 122 are activated.

[0112] After that, as Figure 11 As shown in S1, the dielectric multilayer film 40 disposed on one substrate 120 is sequentially positioned opposite and overlapped with the surfaces 122 of other substrates 120 where no dielectric multilayer film 40 is formed. Thus, as... Figure 11 As shown in S2, the activated bonding surfaces are brought into contact with each other. In addition, by stacking a substrate 120 without dielectric multilayer films 40 on top, a laminate 125 in which each dielectric multilayer film 40 is sandwiched between the substrate 120 is formed.

[0113] After that, as Figure 11 As shown in S3, when a certain load P, for example 500 g / cm, is applied to the laminate 125... 2 By maintaining this state for a certain period of time, such as 1 hour, a joint 126 (reference) is obtained. Figure 12 ).

[0114] After that, as Figure 12 As shown in Figure A, the joint 126 is cut with a cutting surface inclined at a predetermined angle α relative to the substrate surface, thereby cutting out a light guide 127 having a plurality of semi-reflective mirrors 30 in the substrate 20. Figure 12 In line A, the dashed lines form one side of the cutting surface. Figure 12 B is from Figure 12 The diagram shows the light guide 127 cut out from the joint 126, viewed in the direction of arrow 12B. The light guide 127 corresponds to a plurality of light guides 12 arranged parallel to each other at an angle α relative to the first reflecting surface 21 and the second reflecting surface 22 of the semi-reflecting mirror 30. The cut surface is set according to the desired angle α of the semi-reflecting mirror 30. An angle α is preferably set to approximately 10° to 35°, for example.

[0115] The following presents specific design examples and verification results of the dielectric multilayer film constituting the semi-reflective mirror used in the light guide according to the present invention. In the design and verification examples, commercially available thin-film calculation software was used to simulate and determine the film thickness and wavelength dependence. Furthermore, the following refractive index is the refractive index at a wavelength of 540 nm.

[0116] Design Example 1

[0117] Table 1 shows a design example 1 of a dielectric multilayer film using SF11 (manufactured by Schott Co., Ltd.) with a refractive index n = 1.7934 as the substrate. In the simulation, the reflectivity was designed to be 3 ± 0.5% at an incident angle of 25° and the reflectivity was minimized at an incident angle of 75°, thereby optimizing the thickness of each layer.

[0118] [Table 1]

[0119]

[0120] In Design Example 1, the refractive index n1 of the outermost layers 1 and 11 is 1.7950, n1 = 1.0009n.

[0121] Regarding the dielectric multilayer film in Design Example 1, Figure 13 Figure A shows the incident angle dependence of reflectivity for light with a wavelength of 540 nm. For example... Figure 13 As shown in Figure A, a reflectivity of less than 10% is achieved within the incident angle range of 85° or less, a reflectivity of 2 to 4% is achieved within the incident angle range of 0° to 38°, and a reflectivity of less than 4% is achieved within the incident angle range of 63° to 82°.

[0122] Regarding the dielectric multilayer film in Design Example 1, in Figure 13B shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 13 C shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0123] like Figure 13 B and Figure 13 As shown in Figure C, the average reflectivity for light with wavelengths from 400 nm to 700 nm is 2.74% at an incident angle of 25° and 0.69% at an incident angle of 75°. Assuming the incident angle θ1 of the semi-reflective mirror 30 in the substrate 20 relative to the first surface 31 is 25° and the incident angle θ2 relative to the second surface 32 is 75°, the reflectivity when image light is incident on the second surface 32 is very small, less than 1%, enabling the acquisition of images with high contrast.

[0124] Design Example 2

[0125] Table 2 shows a design example 2 of a dielectric multilayer film using S-BSM25 (manufactured by OHARA INC.) with a refractive index n = 1.6621 as the substrate. In the simulation, the reflectivity was designed to be 3 ± 0.5% at an incident angle of 25° and the reflectivity was minimized at an incident angle of 75°, thereby optimizing the thickness of each layer.

[0126] [Table 2]

[0127]

[0128] In design example 2, the refractive index n1 of the outermost layers 1 and 11 is 1.6647, n1 = 1.0015n.

[0129] Regarding the dielectric multilayer film in Design Example 2, in Figure 14 Figure A shows the incident angle dependence of reflectivity for light with a wavelength of 540 nm. For example... Figure 14 As shown in Figure A, a reflectivity of less than 10% is achieved within an incident angle of less than 85°, a reflectivity of 2 to 4% is achieved within an incident angle of 0° to 36°, and a reflectivity of less than 4% is achieved within an incident angle of 60° to 83°.

[0130] Regarding the dielectric multilayer film in Design Example 2, in Figure 14 B shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 14 C shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0131] like Figure 14 B and Figure 14As shown in Figure C, the average reflectivity for light with wavelengths from 400 nm to 700 nm is 2.90% at an incident angle of 25° and 0.91% at an incident angle of 75°. Assuming the incident angle θ1 of the semi-reflective mirror 30 in the substrate 20 relative to the first surface 31 is 25° and the incident angle θ2 relative to the second surface 32 is 75°, the reflectivity when image light is incident on the second surface 32 is very small, less than 1%, enabling the acquisition of images with high contrast.

[0132] Design Example 3

[0133] Table 3 shows a design example 3 of a dielectric multilayer film using BK7 (manufactured by Schott Co., Ltd.) with a refractive index n = 1.5191 as the substrate. In the simulation, the reflectivity was designed to be 3 ± 0.5% at an incident angle of 25° and the reflectivity was minimized at an incident angle of 75°, thereby optimizing the thickness of each layer.

[0134] [Table 3]

[0135]

[0136] In design example 3, the refractive index n1 of the outermost layers 1 and 11 is 1.5197, n1 = 1.0004n.

[0137] Regarding the dielectric multilayer film in Design Example 3, in Figure 15 Figure A shows the incident angle dependence of reflectivity for light with a wavelength of 540 nm. For example... Figure 15 As shown in Figure A, a reflectivity of less than 10% is achieved within the incident angle range of 85° or less, a reflectivity of 2 to 4% is achieved within the incident angle range of 0° to 38°, and a reflectivity of less than 4% is achieved within the incident angle range of 58° to 83°.

[0138] Regarding the dielectric multilayer film in Design Example 3, in Figure 15 B shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 15 C shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0139] like Figure 15 As shown in B and 15C, the average reflectance for light with wavelengths from 400 nm to 700 nm is 2.90% at an incident angle of 25° and 0.93% at an incident angle of 75°.

[0140] Furthermore, the results of investigating the permissible range of the refractive index n1 of the outermost layer for each of the above-mentioned design examples 1 to 3 are presented. For design examples 1 to 3, Tables 4 to 6 show the results of calculating the average reflectance at an incident angle of 25° and an incident angle of 75° for light with wavelengths from 400 nm to 700 nm when the refractive index of the outermost layer relative to the refractive index n of the matrix is ​​changed to 0.85n to 1.20n. In the simulation, for each of design examples 1 to 3, only the refractive index of the outermost layer was changed, while the refractive indices of layers 2 to 10 remained unchanged. The target value for the reflectance at an incident angle of 25° was 3 ± 0.5%, and optimization was performed to minimize the reflectance at 75°.

[0141] Table 4 shows the results when the matrix (SF11) with refractive index n = 1.7934 of Design Example 1 was used.

[0142] [Table 4]

[0143]

[0144] In this example, within the range of n1 = 0.90n to 1.20n, the average reflectivity at an incident angle of 25° is in the range of 3 ± 0.5%, and the average reflectivity at an incident angle of 75° is less than 3%. Furthermore, at n1 = 1.00n, the average reflectivity at an incident angle of 75° can be set to less than 1%.

[0145] Table 5 shows the results when using the matrix (S-BSM25) with a refractive index n = 1.6621 as in Design Example 2.

[0146] [Table 5]

[0147]

[0148] In this example, within the range of n1 = 0.90n to 1.15n, the average reflectivity at an incident angle of 25° is in the range of 3 ± 0.5%, and the average reflectivity at an incident angle of 75° is less than 3%. Furthermore, within the range of n1 = 0.95n to 1.05n, the average reflectivity at an incident angle of 75° can be set to less than 1%.

[0149] Table 6 shows the results when using the matrix (BK7) with a refractive index n = 1.5191 as in Design Example 3.

[0150] [Table 6]

[0151]

[0152] In this example, within the range of n1 = 0.90n to 1.15n, the average reflectivity at an incident angle of 25° is in the range of 3 ± 0.5%, and the average reflectivity at an incident angle of 75° is less than 3%. Furthermore, within the range of n1 = 1.00n to 1.10n, the average reflectivity at an incident angle of 75° can be set to less than 2%.

[0153] In addition, in design examples 2 and 3, when the refractive index of the outermost layer is set to 0.85n, no solution is obtained, so no calculation is performed.

[0154] The results above show that, regardless of whether a low-refractive-index or high-refractive-index matrix is ​​used, as long as the refractive index of the outermost layer is in the range of 0.9n to 1.15n, the average reflectance at a 75° incident angle can be suppressed to below 3%. The refractive index of the outermost layer is preferably 0.95n to 1.10n, more preferably 1.00n to 1.05n. Furthermore, the particularly preferred range of the refractive index of the outermost layer varies slightly depending on the refractive index of the matrix.

[0155] "Verification Example"

[0156] Next, in Design Examples 1 to 3, with the thickness d of the outermost layer of the dielectric multilayer film set to 30 nm, 50 nm, or 100 nm respectively, the dependence of the average reflectivity (hereinafter referred to as average reflectivity (75°)) on the refractive index n1 of the outermost layer and the refractive index n of the substrate was investigated when light with wavelengths from 400 nm to 700 nm was incident at an angle of 75°. Here, Δn[%] = {(n-n1) / n}·100. In the simulation, in the film structures of Design Examples 1 to 3, the thickness of the outermost layer (layer 1 and layer 11) was fixed, and the thicknesses of the other layers 2 to 10 were optimized to achieve a reflectivity of 3 ± 0.5% at an incident angle of 25° and the lowest reflectivity at an incident angle of 75°. Figures 16-18 The results are shown in the figure.

[0157] Figure 16 A and Figure 16 B represents the result when the matrix (SF11) with refractive index n = 1.7950 from Design Example 1 was used. Figure 16 A represents the Δn dependence of the average reflectance (75°). Figure 16 B represents the dependence of the average reflectivity Δn·d on light incident at an angle of incidence of 75°. For example... Figure 16 As shown in Figure A, Δn[%] has a minimum value in the range of -1 to 0 for any of the 30nm, 50nm, and 100nm values. Figure 16As shown in B, when the horizontal axis is set to Δn·d, regardless of the thickness of the outermost layer, if Δn·d[%·nm] is -300 to +300, the average reflectivity (75°) can be set to approximately 10% or less; if Δn·d[%·nm] is -150 to +150, the average reflectivity (75°) can be set to approximately 4% or less; and if Δn·d[%·nm] is -100 to +100, the average reflectivity (75°) can be set to approximately 2% or less.

[0158] Figure 17 A and Figure 17 B indicates the result when the matrix (S-BSM25) with refractive index n = 1.6621 from Design Example 2 was used. Figure 17 A represents the Δn dependence of the average reflectance (75°). Figure 17 B represents the dependence of the average reflectivity Δn·d on light incident at an angle of incidence of 75°. For example... Figure 17 As shown in Figure A, for any of the 30nm, 50nm, and 100nm values, Δn[%] has a minimum value within the range of -2 to 0.5. For example... Figure 17 As shown in Figure B, when the horizontal axis is set to Δn·d, regardless of the thickness of the outermost layer, if Δn·d [%·nm] is -300 to +300, the average reflectivity (75°) can be set to approximately 10% or less; if Δn·d [%·nm] is -200 to +150, the average reflectivity (75°) can be set to approximately 4% or less; and if Δn·d [%·nm] is -150 to +100, the average reflectivity (75°) can be set to approximately 3% or less. Furthermore, if Δn·d [%·nm] is -125 to +25, the average reflectivity (75°) can be set to approximately 1% or less.

[0159] Figure 18 A and Figure 18 B indicates the result when the matrix (BK7) with refractive index n = 1.5191 from Design Example 3 was used. Figure 18 A represents the Δn dependence of the average reflectance (75°). Figure 18 B represents the dependence of the average reflectivity Δn·d on light incident at an angle of incidence of 75°. For example... Figure 18 As shown in Figure A, Δn[%] has a minimum value in the range of -1 to +1 for any of the 30nm, 50nm, and 100nm values. Figure 18As shown in B, when the horizontal axis is set to Δn·d, regardless of the thickness of the outermost layer, if Δn·d[%·nm] is -300 to +300, the average reflectivity (75°) can be set to approximately 10% or less; if Δn·d[%·nm] is -200 to +200, the average reflectivity (75°) can be set to approximately 4% or less; and if Δn·d[%·nm] is -100 to +100, the average reflectivity (75°) can be set to approximately 2% or less.

[0160] Based on the above results, if Δn·d[%·nm] is roughly set to -300 to +300, the average reflectivity (75°) can be set to below 10%. If it is set to -200 to +200, the average reflectivity (75°) can be set to below 4%. If it is set to -150 to +150, the average reflectivity (75°) can be set to below 4% without selecting the refractive index of the substrate.

[0161] Design Example 4

[0162] Table 7 shows a design example 4 of a dielectric multilayer film using S-LAH79 (manufactured by OHARA INC.) with a refractive index n = 2.01339 as the substrate.

[0163] [Table 7]

[0164]

[0165] In Design Example 4, the refractive index n1 of the outermost layers 1 and 11 is 2.03153, n1 = 1.00901n. When the semi-reflective mirror with the dielectric multilayer film of Design Example 4 is placed in the substrate at an angle of 25°, due to the high refractive index of the substrate, the image light propagates through repeated total internal reflection within the substrate even when it is incident on the dielectric multilayer film at an incident angle θ1 = 5°.

[0166] Furthermore, regarding the dielectric multilayer films of Design Examples 1 to 4, the case where the refractive indices of the outermost 1st and 11th layers are the same as the refractive index n of the substrate is set as Design Examples 1A to 4A. Based on the incident angle dependence of the average reflectivity of light with wavelengths of 400nm to 700nm in each example, the preferred incident angle range of the image light to the first and second surfaces of the semi-reflective mirror was verified.

[0167] For the semi-reflective mirrors of Design Examples 1A to 4A, the average reflectivity of light with wavelengths from 400 nm to 700 nm at various incident angles θ1 and θ2 within the range of incident angles θ1 = 5° to 35° and incident angle θ2 = 55° to 85° was evaluated using the following criteria. The results are shown in Table 8.

[0168] -Evaluation of the incident angle θ1-

[0169] A: Average reflectance exceeding 3% and below 4%

[0170] B: Average reflectance exceeding 2% but below 3%

[0171] C: Average reflectance exceeding 1% and below 2%

[0172] D: Average reflectivity exceeds 4%

[0173] -Evaluation of the incident angle θ2-

[0174] A: Average reflectance is less than 1%

[0175] B: Average reflectance exceeding 1% and below 3%

[0176] C: Average reflectance exceeding 3% and below 4%

[0177] D: Average reflectance exceeding 4% and below 10%

[0178] E: Average reflectivity exceeds 10%

[0179] [Table 8]

[0180]

[0181] As the incident angle θ1, a good average reflectivity of more than 2% and less than 4% is obtained in the range of 5° to 35°. On the other hand, as the incident angle θ2, an average reflectivity of less than 10% can be set in the range of 55° to 85°, and in design examples 1A to 3A, an average reflectivity of less than 4% can be set in the range of 70° to 80°. It is preferable to set the tilt angle α and the light coupling angle θ0 of the semi-reflective mirror so that the incident angle θ1 is 5° to 35° and the incident angle θ2 is 55° to 85°. Since the average reflectivity can be set to less than 4%, it is more preferable to set the incident angle θ2 to 70° to 80°. In addition, in practical systems, due to structural constraints, the incident angle θ1 is preferably 10° or more.

[0182] Here, a sensory evaluation was performed on the brightness and darkness pattern of the image when the reflectivity of light incident on the second surface of the semi-reflective mirror in the light guide was changed. In this specification, the brightness and darkness pattern of the image refers to the brightness and darkness pattern based on the light intensity distribution appearing in the image visually perceived through the light guide. This brightness and darkness pattern is considered to be generated by the interference of image light and stray light. This means that the absence of a brightness and darkness pattern represents an ideal high-contrast image, and the higher the visual discernibility of the brightness and darkness pattern, the lower the image contrast.

[0183] Sensory evaluation test

[0184] A light guide having six semi-reflective mirrors made of dielectric multilayer films as shown in Design Example 1 was fabricated (the fabrication method will be described later). The semi-reflective mirror of Design Example 1 can change the average reflectivity from 10% to less than 1% by changing the incident angle of the second surface within the range of 55° to 85°. Furthermore, as an example where the average reflectivity of the second surface exceeds 10%, a light guide having six or fewer semi-reflective mirrors made of dielectric multilayer films as in Comparative Example 1 was fabricated. For the light guide having the semi-reflective mirror of Design Example 1, the incident angle towards the first surface was changed so that the incident angle towards the second surface of the semi-reflective mirror was 55° to 85°, and the degree of brightness and darkness patterns generated by the interference of image light and stray light when the average reflectivity of the second surface was set to less than 1% to 10% was evaluated by sensory evaluation. Furthermore, for the light guide with the semi-reflective mirror of Comparative Example 1, the incident angle toward the first surface was set so that the incident angle toward the second surface of the semi-reflective mirror was 75°, and the same sensory evaluation was performed regarding the case where the average reflectivity of the second surface exceeded 10%.

[0185] [Comparative Example 1]

[0186] Table 9 shows the layer structure of Comparative Example 1, which uses SF11 (manufactured by Schott Co., Ltd.) with a refractive index n = 1.7934 as the substrate. The refractive index n1 of the two outermost layers, the first and eleventh layers, was set to a value outside the range of 0.9n to 1.15n, i.e., 0.83n. In the simulation, the reflectivity at an incident angle of 25° was designed to be 3 ± 0.5%, and the reflectivity at an incident angle of 75° was designed to be the lowest, thereby optimizing the thickness of each layer.

[0187] [Table 9]

[0188]

[0189] Regarding the semi-reflective mirror of Comparative Example 1, Table 10 shows the average reflectivity of light with wavelengths from 400 nm to 700 nm at various incident angles θ1 and θ2, ranging from 5° to 35° and from 55° to 85°.

[0190] [Table 10]

[0191]

[0192] In Comparative Example 1, the average reflectivity of light with wavelengths of 400 nm to 700 nm incident at an incident angle of θ2 = 75° to 85° exceeds 10%.

[0193] As shown in Table 10, in Comparative Example 1, a good reflectivity of more than 2% and less than 4% was obtained in the range of 5° to 35° as the incident angle θ1. On the other hand, when the incident angle θ2 is 75° or more, the average reflectivity for light with wavelengths of 400 nm to 700 nm exceeds 10%.

[0194] Table 11 shows the results of sensory evaluation when the average reflectivity of the second surface of the semi-reflective mirror (the second surface reflectivity in Table 11) is set from less than 1% to more than 10%.

[0195] [Table 11]

[0196] Second surface reflectivity Light and shadow patterns in an image More than 10% The light and dark patterns in the image can be clearly visually identified. Less than 10% and more than 8% The light and dark patterns in the image can be visually discerned with slightly more clarity. Below 8% and above 4% The light and dark patterns in the image were faintly discernible to the eye. Less than 4% and more than 3% The light and shadow patterns in the image were faintly discernible to the naked eye. Less than 3% and more than 1% The light and dark patterns in the image are almost impossible to discern visually. Below 1% Unrecognizable light and dark patterns in the image

[0197] As shown in Table 11, the following results were obtained: if the average reflectivity on the second surface of the semi-reflective mirror exceeds 10%, the light and dark patterns can be clearly visually identified; however, if it is below 10%, the appearance of the light and dark patterns is slightly suppressed. Based on the sensory evaluation results, it can be said that the average reflectivity on the second surface of the semi-reflective mirror is preferably below 10%, more preferably below 4%, further preferably below 3%, and especially preferably below 1%.

[0198] Hereinafter, by way of reference Examples 1 to 3, examples of multilayer films constituting a semi-reflective mirror with an average reflectivity of 2% to 4% for light with wavelengths of 400 nm to 700 nm incident at an angle of incidence of 5° to 35° and an average reflectivity of 10% or less for light incident at an angle of incidence of 55° to 85° are shown.

[0199] [Reference Example 1]

[0200] Table 12 shows the layer structure of a dielectric multilayer film of Reference Example 1, using SF11 (manufactured by Schott Co., Ltd.) with a refractive index n = 1.7934 as the substrate. The refractive index n1 of the first of the two outermost layers of the dielectric multilayer film was set to a value within the range of 0.9n to 1.15n of the refractive index n of the substrate, while the refractive index n1 of the eleventh layer was set to a value outside the range of 0.9n to 1.15n. In the simulation, the target reflectivity at an incident angle of 25° was set to 3 ± 0.5%, and the reflectivity at an incident angle of 75° was minimized, thereby optimizing the thickness of each layer.

[0201] [Table 12]

[0202]

[0203] Regarding the dielectric multilayer film of Reference Example 1, in Figure 19 Figure A shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 19 B shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0204] like Figure 19 A and Figure 19 As shown in B, the average reflectivity for light with wavelengths from 400 nm to 700 nm is 2.79% at an incident angle of 25° and 4.93% at an incident angle of 75°. Assuming an incident angle θ1 of the semi-reflective mirror 30 in the substrate 20 relative to the first surface 31 is 25° and an incident angle θ2 of the semi-reflective mirror 30 relative to the second surface 32 is 75°, the average reflectivity when image light is incident on the second surface 32 exceeds 4%, an increase compared to Design Examples 1-3. However, the average reflectivity when image light is incident on the second surface is less than 10%, thus achieving a suppression effect on bright and dark patterns caused by interference between stray light and image light, i.e., an improvement in image contrast.

[0205] [Reference Example 2]

[0206] Table 13 shows the layer structure of a dielectric multilayer film of Reference Example 2, using S-BSM25 (manufactured by OHARA INC.) with a refractive index n = 1.6621 as the substrate. The refractive index n1 of the first of the two outermost layers of the dielectric multilayer film was set to a value within the range of 0.9n to 1.15n of the refractive index n of the substrate, and the refractive index n1 of the eleventh layer was set to a value outside the range of 0.9n to 1.15n. In the simulation, the target reflectivity at an incident angle of 25° was set to 3 ± 0.5%, and the reflectivity at an incident angle of 75° was minimized, thereby optimizing the thickness of each layer.

[0207] [Table 13]

[0208]

[0209] Regarding the dielectric multilayer film of Reference Example 2, in Figure 20 Figure A shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 20 B shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0210] like Figure 20 A and Figure 20As shown in Figure B, the average reflectivity for light with wavelengths from 400 nm to 700 nm is 2.45% at an incident angle of 25° and 4.32% at an incident angle of 75°. Assuming an incident angle θ1 of the semi-reflective mirror 30 in the substrate 20 relative to the first surface 31 is 25° and an incident angle θ2 of the semi-reflective mirror 30 relative to the second surface 32 is 75°, the average reflectivity when image light is incident on the second surface 32 exceeds 4%, an increase compared to the design example. However, the average reflectivity when image light is incident on the second surface is less than 10%, thus achieving a suppression effect on bright and dark patterns caused by interference between stray light and image light, i.e., an improvement in image contrast.

[0211] [Reference Example 3]

[0212] Table 14 shows a reference example 3 of a dielectric multilayer film using BK7 (manufactured by Schott Co., Ltd.) with a refractive index n = 1.5191 as the substrate. The refractive index n1 of the first of the two outermost layers of the dielectric multilayer film was set to a value within the range of 0.9n to 1.15n of the substrate's refractive index n, while the refractive index n1 of the eleventh layer was set to a value outside the range of 0.95n to 1.15n. In the simulation, the target reflectivity at an incident angle of 25° was set to 3 ± 0.5%, and the reflectivity at an incident angle of 75° was minimized, thereby optimizing the thickness of each layer.

[0213] [Table 14]

[0214]

[0215] Regarding the dielectric multilayer film of Reference Example 3, Figure 21 Figure A shows the wavelength dependence of reflectivity with respect to an incident angle of 25°. Figure 21 B shows the wavelength dependence of reflectivity relative to an incident angle of 75°.

[0216] like Figure 21 A and Figure 21 As shown in Figure B, the average reflectivity for light with wavelengths from 400 nm to 700 nm is 2.73% at an incident angle of 25° and 5.59% at an incident angle of 75°. Assuming an incident angle θ1 of the semi-reflective mirror 30 in the substrate 20 relative to the first surface 31 is 25° and an incident angle θ2 of the semi-reflective mirror 30 relative to the second surface 32 is 75°, the average reflectivity when image light is incident on the second surface 32 exceeds 4%, an increase compared to the design example. However, the average reflectivity when image light is incident on the second surface is less than 10%, thus achieving a suppression effect on bright and dark patterns caused by interference between stray light and image light, i.e., an improvement in image contrast.

[0217] As described above, when comparing Reference Examples 1-3 with Design Examples 1-3, the reflectivity of the second surface is greater. That is, as in Design Examples 1-3, when the refractive index of the substrate is set to n, the refractive index of the two outermost layers of the dielectric multilayer film is 0.90n to 1.15n, thereby more effectively suppressing the reflectivity of the second surface. Furthermore, by setting it to 0.95n to 1.15n, the reflectivity of the second surface can be suppressed even more effectively. On the other hand, as in Design Examples 1-3, even when the condition that the refractive index of the two outermost layers of the dielectric multilayer film is 0.90n to 1.15n or 0.95n to 1.15n when the refractive index of the substrate is set to n is not met, the average reflectivity of image light to the second surface is still less than 10%. Therefore, compared to the case where the average reflectivity of image light to the second surface exceeds 10%, an improvement in image contrast can be achieved.

[0218] "Methods for manufacturing light guides"

[0219] The method for manufacturing the light guide used in the sensory evaluation test is explained.

[0220] Seven SF11 substrates, each 100mm × 100mm × 0.5mm thick, were prepared. A semi-reflective mirror, composed of a dielectric multilayer film, was formed on one side of six of these substrates. Specifically, the dielectric multilayer film shown in Design Example 1 was formed. Each layer in Design Example 1 was set as a silicon oxynitride film.

[0221] At this time, according to Figure 8 The refractive index is shown as a dependence of the nitrogen / oxygen flow rate ratio, with the nitrogen / oxygen flow rates set as described in Table 15 below. Additionally, the film thickness is shown in Table 1. Sputtering conditions were set as follows: Ar gas flow rate = 60 sccm, O2+N2 gas flow rate = 60 sccm, sputtering power = 750 W, target diameter = 6 inches, substrate temperature (set) = 300 °C, and sputtering pressure = 0.2 Pa.

[0222] [Table 15]

[0223]

[0224] After film formation, it is cut into 30mm×30mm size using a slicer.

[0225] Next, the bonding surfaces of the substrate with the dielectric multilayer film and the substrate without the dielectric multilayer film were irradiated with an ion beam, and then cleaned and activated. The apparatus shown in Table 16 was used as the ion beam irradiation device.

[0226] [Table 16]

[0227] Ion gun RF Φ12cm ion beam auxiliary source Grid 3 plates Process Gases Ar

[0228] The conditions for ion beam irradiation are shown in Table 17.

[0229] [Table 17]

[0230] Ar sputtering conditions numerical values Beam voltage [V] 400 Beam current [mA] 75 Accelerator voltage [V] 600 Vacuum level [Pa] 0.05 Irradiation time [min] 5

[0231] After irradiation with the aforementioned ion beam, six substrates with dielectric multilayer films and one substrate without dielectric multilayer films were overlapped in the atmosphere, and then a 500 g / cm² ion beam was applied. 2 The joint was obtained by applying a load and holding it for 1 hour.

[0232] After that, as Figure 12 As shown, by cutting the joint, a functional test light guide was obtained in which six semi-reflective mirrors are tilted at 25° relative to the first and second reflecting surfaces and are arranged at equal intervals in the substrate.

[0233] "Durability Evaluation"

[0234] Next, the results of verifying the mechanical strength and environmental durability of the light guide formed by optical contact bonding as described above will be presented. Furthermore, for durability testing, a light guide 127 with parallelogram-shaped sides was cut from the bonded body manufactured in the same manner as described above, as shown... Figure 22 As shown, 24 rectangular sample pieces S were fabricated by cutting both ends of the light guide 127. The area of ​​the cut end face was set to 9 mm². 2 .

[0235] [Strength Test 1]

[0236] Mechanical strength tests were conducted according to JIS K 6852. A strength testing machine (model DS2-500N) manufactured by IMADA CO.,LTD. was used. Figure 23 As shown, after placing the sample piece S between the probe 101 of the testing machine and the stainless steel stage 102, a load P was gradually applied until failure occurred. Strength tests were performed on 12 sample pieces S used in strength test 1. The results regarding the failure load of each sample piece are shown in Table 18.

[0237] [Table 18]

[0238]

[0239] The fracture results for each sample were confirmed, with zero samples failing at the bonding surface. Generally, in bonded components formed by joining optical parts, failure occurs at the bonding surface; however, for any sample, failure occurred at locations other than the bonding surface. Based on these results, the average bond strength (mean fracture load / sample area) for multiple samples ranged from a fracture strength of 14.86 kgf to a sample area of ​​0.09 cm².2 And 1 kgf = 9.8 N, calculated as 1618 N / cm. 2 Therefore, the adhesive strength of the bonding surface based on optical contact can be estimated as 1500 N / cm. 2 above.

[0240] Furthermore, as a reliability test, assuming the product was placed in a harsh environment, a high temperature and high humidity test and a thermal shock test were conducted, followed by a strength test using the same method as described above.

[0241] [Strength Test 2]

[0242] As part of the high temperature and high humidity test, the six sample pieces S used in strength test 2 were stored at 85°C and 85% RH for 168 hours. Afterwards, the strength test was conducted in the same manner as described above. The results regarding the failure load of each sample piece are shown in Table 19.

[0243] [Table 19]

[0244] Sample ID <![CDATA[Destruction load [kgf / cm 2 > 1 14.46 2 15.56 3 17.31 4 15.94 5 16.28 6 16.22 Average value of failure load 15.96 Standard deviation 0.94

[0245] [Strength Test 3]

[0246] For the thermal shock test, the six sample pieces S used in strength test 3 were subjected to a cycle of 30 minutes in a temperature bath at 80°C and 30 minutes in a temperature bath at -20°C, with the temperature bath movement time set to less than 5 minutes, and this was repeated for 168 cycles. Afterwards, the strength test was conducted in the same manner as described above. The results regarding the failure load for each sample piece are shown in Table 20.

[0247] [Table 20]

[0248] Sample ID <![CDATA[Destruction load [kgf / cm 2 > 1 13.83 2 13.95 3 14.25 4 13.10 5 13.85 6 14.77 Average value of failure load 13.96 Standard deviation 0.55

[0249] In strength tests 2 and 3, fracture of the samples was confirmed. Similar to strength test 1, zero samples failed at the bonding surface. Based on this result, the adhesive strength of the optically bonded surfaces shows almost no deterioration even when exposed to high temperature, high humidity, and thermal shock environments. Furthermore, the bond strength was estimated at 1500 N / cm² in these strength tests. 2 .

[0250] As mentioned above, high mechanical strength and environmental reliability can be achieved by using optical contacts in the manufacture of light guides.

[0251] The entire contents of the invention described in Japanese Patent Application No. 2020-219155, filed on December 28, 2020, are incorporated herein by reference.

[0252] All documents, patent applications and technical standards described in this specification are incorporated herein by reference to the same extent as the individual documents, patent applications and technical standards specifically and separately described and incorporated by reference.

Claims

1. A light guide, comprising: A substrate having a first reflecting surface and a second reflecting surface, such that incident image light is propagated simultaneously by total internal reflection from the first reflecting surface and the second reflecting surface; and Multiple semi-reflective mirrors, each having a first surface and a second surface behind the first surface, are constructed comprising a dielectric multilayer film. The plurality of semi-reflective mirrors are arranged at an angle relative to the first and second reflecting surfaces and spaced apart from each other within the substrate. The substrate and the plurality of semi-reflective mirrors are configured such that the image light incident on the substrate is incident on the first surface and the second surface of at least one of the plurality of semi-reflective mirrors at least once. Assuming the refractive index of the substrate is n, the refractive indices of the two outermost layers on the first and second surfaces of the dielectric multilayer film are 0.90n to 1.15n. The average reflectivity of the semi-reflective mirror for light with wavelengths of 400nm to 700nm incident at an angle of incidence of 5° to 35° is 2% to 4%, and the average reflectivity for the light incident at an angle of incidence of 55° to 85° is less than 10%. In each of the plurality of semi-reflective mirrors disposed in the substrate, a portion of the image light is reflected and emitted from the substrate as outgoing light, enabling the user to visually recognize the image.

2. The light guide according to claim 1, wherein, The refractive index of the outermost layer of the dielectric multilayer film is 0.95n to 1.10n.

3. The light guide according to claim 1, wherein, The refractive index of the outermost layer of the dielectric multilayer film is 1.00n to 1.05n.

4. The light guide according to any one of claims 1 to 3, in, Let the thickness of the outermost layer of the dielectric multilayer film be d [nm], the refractive index be n1, and Δn = {(n-n1) / n} × 100 [%], then Δn·d [%·nm] is in the range of -300 to +300.

5. The light guide according to any one of claims 1 to 3, wherein, The tilt angle of the semi-reflective mirror relative to the first and second reflecting surfaces is as follows: when the image light incident on the substrate is incident on the first surface at an incident angle of 5° to 35°, the transmitted light in the incident image light that has passed through the semi-reflective mirror is reflected by the first or second reflecting surface and can then be re-incident from the second surface.

6. The light guide according to claim 5, wherein, The tilt angle of the semi-reflective mirror is an angle in the range of 55° to 85° when the transmitted light is re-intruded from the second surface.

7. The light guide according to any one of claims 1 to 3, wherein, The dielectric multilayer film alternately stacks low-refractive-index layers and high-refractive-index layers, wherein the low-refractive-index layers have a relatively low refractive index and the high-refractive-index layers have a relatively high refractive index.

8. The light guide according to any one of claims 1 to 3, wherein, At least one of the two outermost layers of the dielectric multilayer film is bonded to the substrate via optical contact.

9. The light guide according to any one of claims 1 to 3, wherein, The two outermost layers of the dielectric multilayer film are in direct contact with the substrate.

10. The light guide according to any one of claims 1 to 3, wherein, There is no adhesive between the semi-reflective mirror and the substrate.

11. The light guide according to any one of claims 1 to 3, wherein, Each layer of the dielectric multilayer film contains silicon, oxygen, and nitrogen.

12. The light guide according to any one of claims 1 to 3, wherein, Each layer of the dielectric multilayer film is a metal oxide layer containing at least one of silicon, niobium, tantalum, aluminum, titanium, tungsten and chromium.

13. The light guide according to any one of claims 1 to 3, wherein, The refractive index of the matrix is ​​1.5 or higher.

14. The light guide according to any one of claims 1 to 3, wherein, The substrate is a parallel plate that is parallel to the first reflective surface and the second reflective surface.

15. The light guide according to any one of claims 1 to 3, wherein, The plurality of semi-reflective mirrors are arranged parallel to each other in the direction of the propagation of the image light.

16. An image display device comprising: The image light generation unit generates image light; The light guide according to any one of claims 1 to 15, which propagates the incident image light; and An optical coupling component that allows the image light generated by the image light generating unit to be incident into the light guide body.

Images