WO2017033975A1

WO2017033975A1 - Hologram recording structure, optical device, and manufacturing method

Info

Publication number: WO2017033975A1
Application number: PCT/JP2016/074681
Authority: WO
Inventors: 拓也小倉; 善行小川
Original assignee: コニカミノルタ株式会社
Priority date: 2015-08-27
Filing date: 2016-08-24
Publication date: 2017-03-02

Abstract

A hologram recording structure has a hologram recording medium on a transparent substrate. The hologram recording medium has, in sequence from the transparent substrate side, a stress-absorbing layer, a base film, a hologram photosensitive material, and a cover film, each contacting the adjacent layers. The stress-absorbing layer has a lower Young's modulus than the transparent substrate and the base film.

Description

Hologram recording structure, optical device and manufacturing method

The present invention relates to a hologram recording structure, an optical device, and a manufacturing method. More specifically, the present invention relates to a hologram recording structure having a hologram recording medium on a transparent substrate and a hologram optical element (HOE: holographic optical element) between cemented prisms. ), An image display device that projects and displays an image of the display element on the observer's eye using the hologram optical element, and an optical see-through display (for example, an HMD ( head mounted display), HUD (head-up display), etc.).

The hologram optical element is very useful as a combiner mounted on, for example, a head mounted display (HMD) or a head up display (HUD). For example, by sandwiching the hologram optical element between two prisms, an optical device that is not easily affected by the external environment such as humidity and oxygen can be obtained. Furthermore, the optical device can constitute an optical system in which the image light provided from the image display element is totally reflected inside the prism and guided to the hologram optical element. Then, by optimizing the prism shape, hologram shape, etc., it is also possible to ensure the see-through property of the external image while maintaining the optical performance of the hologram optical element.

The optical device as described above, after pasting a hologram photosensitive material (for example, photopolymer) on one prism, performing hologram exposure in an interference fringe formation process, and then passing through a hologram stabilization process (fixing / baking process) It can be manufactured by adhering to the other prism with an adhesive. However, the cover film provided on the hologram photosensitive material in order to enhance durability may shrink due to heat in the stabilization process, or the hologram photosensitive material may shrink due to heat or light in the interference fringe forming process. May end up. In either case, since the shrinkage of the hologram photosensitive material adversely affects the interference fringes, the optical characteristics of the hologram optical element are deteriorated. Further, the shrinkage of the hologram photosensitive material causes deformation of the prism, which causes a decrease in the optical performance of the optical device. Methods for solving such problems are proposed in Patent Document 1 and Patent Document 2.

JP-A-8-137373 JP 2012-88643 A

In the multilayer hologram recording body described in Patent Document 1, an attempt is made to suppress deterioration of the optical characteristics of the hologram optical element due to shrinkage of the cover layer (cover film) by providing an absorption layer against expansion and contraction stress. Nothing is considered about its own contraction. In the hologram optical element described in Patent Document 2, an internal stress due to shrinkage of the hologram photosensitive material is attempted to be reduced by providing a photosensitive recording layer (hologram photosensitive material) and a buffer layer between the first and second substrates. However, when the hologram photosensitive material is in direct contact with the buffer layer, the hologram photosensitive material easily contracts and wrinkles and the like are generated. As a result, a desired interference fringe cannot be formed, leading to a reduction in video quality.

The present invention has been made in view of such a situation, and an object thereof is to suppress the hologram recording structure capable of preventing the shrinkage of the hologram photosensitive material and the occurrence of the shrinkage unevenness, and the deformation of the hologram optical element and the prism. It is an object to provide an optical device capable of stably obtaining good optical performance and a manufacturing method thereof, an image display device capable of see-through display with a high-quality image superimposed on an external image, and an optical see-through display. .

In order to achieve the above object, the hologram recording structure of the first invention is a hologram recording structure having a hologram recording medium on a transparent substrate,
The hologram recording medium has the stress buffer layer, the base film, the hologram photosensitive material, and the cover film in the state of being in contact with each other in order from the transparent substrate side,
The stress buffer layer has a Young's modulus smaller than that of the transparent substrate and the base film.

The hologram recording structure of the second invention is characterized in that, in the first invention, the hologram photosensitive material is made of a photopolymer.

An optical device of a third invention is an optical device having a structure in which a first prism and a second prism are joined so as to sandwich a hologram optical element,
The hologram optical element has, in order from the first prism side, a stress buffer layer, a base film, a hologram layer, and a cover film in contact with each other.
The stress buffer layer has a Young's modulus smaller than that of the first prism and the base film, and has substantially the same refractive index as that of the first and second prisms.

The optical device according to a fourth invention is characterized in that, in the third invention, the hologram layer is a volume phase reflection hologram.

An optical device according to a fifth invention is the optical device according to the third or fourth invention, wherein the first and second prisms are transparent, and the hologram optical element is attached to the first prism, The bonding of the first prism and the second prism is performed by an adhesive provided between the first prism and the hologram optical element and the second transparent prism. .

The optical device according to a sixth aspect of the present invention is the optical device according to any one of the third to fifth aspects, wherein an acute angle forming surface that forms an acute angle with respect to a bonding surface between the first prism and the second prism; The first and second prisms each have an obtuse angle forming surface for forming an obtuse angle, and the hologram optical element is provided on the first prism in a state inclined with respect to the acute angle forming surface and the obtuse angle forming surface. It is characterized by being.

A method for manufacturing an optical device according to a seventh aspect is a method for manufacturing an optical device having a structure in which a first prism and a second prism are joined so as to sandwich a hologram optical element.
Applying a hologram photosensitive material on a base film and drying to form a film;
A step of attaching a cover film to the surface opposite to the base film in the film-shaped hologram photosensitive material;
A step of attaching a stress buffer layer to a surface of the base film opposite to the surface on which the hologram photosensitive material is applied;
By sticking the stress buffer layer to the first prism, the stress buffer layer, the base film, the hologram photosensitive material, and the cover film are adjacent to each other in order from the first prism side. Forming a holographic recording medium in contact with the first prism;
Forming the hologram layer by hologram exposure of interference fringes to the hologram photosensitive material, thereby making the hologram recording medium the hologram optical element;
Bonding the first prism attached to the hologram recording medium and the second prism with an adhesive so as to sandwich the hologram optical element between the first and second prisms,
The stress buffer layer has a Young's modulus smaller than that of the first prism and the base film, and has substantially the same refractive index as that of the first and second prisms.

According to an eighth aspect of the present invention, there is provided an image display apparatus comprising: the optical device according to any one of the third to sixth aspects of the present invention; and a display element that displays an image. It is characterized by diffracting light of a specific wavelength in the image light.

According to a ninth aspect of the present invention, there is provided the video display device according to the eighth aspect, wherein the first prism totally reflects the image light from the display element and guides it to the hologram optical element.

According to a tenth aspect of the present invention, in the eighth or ninth aspect, the optical device constitutes an eyepiece optical system in which the optical device enlarges the image displayed on the display element and guides it to the observer's eye as a virtual image. It is characterized by that.

According to an eleventh aspect of the present invention, in the tenth aspect of the invention, the hologram optical element is a combiner that simultaneously guides an image displayed on the display element and an external image to an observer's eye. .

An optical see-through display according to a twelfth aspect of the invention is equipped with the image display device according to the tenth or eleventh aspect of the invention, thereby having a function of projecting and displaying the image on the observer's eye with the hologram optical element. It is characterized by that.

An optical see-through display according to a thirteenth aspect of the present invention is the head mounted display according to the twelfth aspect of the present invention, further comprising a support member that supports the video display device so that the hologram optical element is positioned in front of the observer's eye. It is characterized by.

According to the present invention, a hologram recording structure that can prevent the occurrence of shrinkage and shrinkage unevenness of the hologram photosensitive material, an optical device that can stably obtain good optical performance by suppressing deformation of the hologram optical element and the prism, and the optical device A manufacturing method, an image display device capable of see-through display in which a high-quality image is superimposed on an external image, and an optical see-through display can be realized.

The schematic sectional drawing which shows typically the manufacturing method of the optical device using one Embodiment of a hologram recording structure. The schematic sectional drawing which shows typically one Embodiment of the video display apparatus which has an optical device obtained with the manufacturing method of FIG. The optical block diagram which shows the optical path from the light source in the video display apparatus of FIG. 2 to the optical pupil. The perspective view which shows the spectacles type head mounted display provided with the video display apparatus of FIG. The schematic diagram for demonstrating comparing the hologram recording structure of FIG. 1 with another type.

Hereinafter, a hologram recording structure, an optical device, a manufacturing method thereof, an image display device, an optical see-through display, and the like according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is mutually attached | subjected to the part which is the same in each embodiment etc., and the corresponding part, and duplication description is abbreviate | omitted suitably.

5A to 5E show five types of hologram recording structures in cross-sectional structure. The hologram recording structure of FIG. 5 (E) shows the hologram recording structure according to one embodiment of the present invention, and the hologram recording structures of FIGS. 5 (A) to (D) are forms for comparison with the hologram recording structure. Is shown. Each of the hologram recording structures has a configuration in which a hologram recording medium is provided on a prism 11 that is a transparent substrate, and the hologram recording medium has a hologram photosensitive material (for example, photopolymer) Lp. By hologram exposure of the interference fringes to the hologram photosensitive material Lp, the hologram photosensitive material Lp becomes a hologram layer Lh (for example, a volume phase type reflection hologram), and the hologram recording medium becomes a hologram optical element (HOE).

In the hologram recording structure of FIG. 5A, a hologram photosensitive material Lp is directly provided on the prism 11, and a cover film Lc for improving durability is provided thereon. The hologram photosensitive material Lp such as photopolymer shrinks itself by heat and light in the interference fringe forming process, and the amount of shrinkage becomes large. Since the shrinkage of the hologram photosensitive material Lp adversely affects the interference fringes, the optical characteristics of the hologram optical element are deteriorated. Further, the shrinkage of the hologram photosensitive material Lp causes deformation of the prism 11, which causes a decrease in the optical performance of an optical device on which the hologram optical element is mounted, such as instability in image plane.

The hologram recording structure in FIG. 5B has a configuration in which a stress buffer layer (buffer layer) La is provided between the prism 11 and the hologram photosensitive material Lp in the hologram recording structure in FIG. When the stress buffer layer La is provided in this manner, the deformation of the prism 11 due to the contraction of the hologram photosensitive material Lp is eliminated, but the contraction amount of the hologram photosensitive material Lp on the surface in contact with the stress buffer layer La increases, and interference fringes are generated. Instability of the interval and local shrinkage unevenness occur, leading to deterioration of the optical characteristics of the hologram optical element.

The hologram recording structure in FIG. 5C has a configuration in which a stress buffer layer (buffer layer) Laa is provided between the cover film Lc and the hologram photosensitive material Lp in the hologram recording structure in FIG. 5B. Yes. However, similarly to the hologram recording structure of FIG. 5B, the shrinkage of the hologram photosensitive material Lp itself causes the stability of the interference fringe spacing and local shrinkage unevenness, leading to deterioration of the optical characteristics of the hologram optical element.

In the hologram recording structure of FIG. 5D, a hologram photosensitive material Lp and a stress buffer layer La are provided between the

prisms

11 and 12. When the hologram photosensitive material Lp and the stress buffer layer La are provided in this way, the internal stress due to the shrinkage of the hologram photosensitive material Lp with respect to the prism 12 can be relieved. However, when the hologram photosensitive material Lp is in direct contact with the stress buffer layer La, the hologram photosensitive material Lp easily contracts and wrinkles or the like are generated. As a result, a desired interference fringe cannot be formed, leading to a reduction in video quality. Similarly to the hologram recording structure shown in FIG. 5A, the shrinkage of the hologram photosensitive material Lp causes the prism 11 to be deformed. This causes the optical performance of the optical device to deteriorate, for example, the image surface property is not stable.

In the hologram recording structure shown in FIG. 5E, the hologram recording medium provided on the prism 11 includes, in order from the prism 11, the stress buffer layer La, the base film Lb, the hologram photosensitive material Lp, and the cover film Lc. The stress buffer layer La has a Young's modulus smaller than that of the prism 11 and the base film Lb. Here, the hologram photosensitive material Lp is sandwiched between the base film Lb and the cover film Lc and is in a contact state, and the Young's modulus of the stress buffer layer La is set to be small (that is, the stress absorption performance is high). Thus, it is possible to solve the problem caused by the shrinkage of the hologram photosensitive material Lp. These feature points will be described in detail below.

As described above, it is known that the photopolymer constituting the hologram photosensitive material Lp is greatly contracted by heat or light (that is, has heat shrinkability and light shrinkability). In particular, in the interference fringe forming process, it contracts due to optical load and thermal load. At that time, when the hologram photosensitive material Lp and the stress buffer layer La are in contact with each other (FIG. 5B, etc.), the hologram The effect of limiting the shrinkage of the photosensitive material Lp is small. Therefore, the larger the shrinkage amount, the more difficult it is to control the lattice spacing of the interference fringes formed in the hologram photosensitive material Lp, and further local shrinkage unevenness occurs, leading to deterioration of the hologram optical characteristics. In the hologram recording structure of FIG. 5E, the shrinkage of the hologram photosensitive material Lp is limited by the base film Lb in contact with one surface of the hologram photosensitive material Lp and the cover film Lc in contact with the other surface. The Therefore, since the robustness with respect to the heat shrinkability and light shrinkability of the hologram photosensitive material Lp is improved, the lattice spacing of the interference fringes formed in the hologram photosensitive material Lp can be easily controlled, and the local shrinkage unevenness is further reduced. Occurrence is also suppressed.

As described above, the shrinkage of the hologram photosensitive material Lp causes the prism 11 to be deformed, which causes the optical performance of the optical device to deteriorate, for example, the image surface property is not stable. In the hologram recording structure of FIG. 5E, the stress buffer layer La is easily deformed because the Young's modulus of the stress buffer layer La is set small. That is, the base film Lb, the hologram photosensitive material Lp, and the cover film Lc are integrally mounted on the stress buffer layer La that is easily deformed. Therefore, the stress due to the shrinkage of the hologram photosensitive material Lp is absorbed and relaxed by the deformation of the stress buffer layer La, and is difficult to be transmitted to the prism 11, so that the deformation of the prism 11 is prevented.

FIG. 1 schematically shows a manufacturing method of the optical device 10 (FIG. 2) using the hologram recording structure 15, and FIG. 2 shows an image including the optical device 10 and the display element 20 obtained by the manufacturing method. 1 shows a schematic longitudinal sectional structure of a display device 1. The hologram recording structure 15 in FIG. 1 corresponds to the hologram recording structure in FIG. 5E, and the hologram recording medium 13P includes a stress buffer layer La, a base film Lb, and a hologram photosensitive material in order from the prism 11 side. The material Lp and the cover film Lc are in contact with each other, and the stress buffer layer La has a Young's modulus smaller than that of the prism 11 and the base film Lb. 2 has a structure in which the first prism 11 and the second prism 12 are joined so as to sandwich the hologram optical element 13, and the hologram optical element 13 is arranged from the prism 11 side. In order, the stress buffer layer La, the base film Lb, the hologram layer Lh, and the cover film Lc are adjacent to each other, and the stress buffer layer La is smaller in Young's modulus than the prism 11 and the base film Lb. And has substantially the same refractive index as the

prisms

11 and 12.

The stress buffer layer La is made of a member having an adhesive force on both sides, such as a double-sided tape, and an example of the constituent material thereof is an adhesive. More specifically, an acrylic pressure-sensitive adhesive, MHM-FWD25 manufactured by Nichiei Kako, can be mentioned. The thickness of the stress buffer layer La depends on the width of the joint ridge line between the first prism 11 and the second prism 12 and is preferably as thin as possible. However, if the thickness is too thin, the stress buffering action is reduced. Therefore, the thickness of the stress buffer layer is preferably 5 μm to 50 μm, more preferably 5 μm to 25 μm.

In the hologram recording medium 13P, the film in contact with the surface of the hologram photosensitive material Lp on the prism 11 side is the base film Lb, and the film in contact with the opposite surface is the cover film Lc. There is no difference in properties and performance from the film Lc. Examples of the constituent material of the base film Lb and the cover film Lc include a PET (polyethylene terephthalate) film and a TAC (triacetylcellulose) film. Since the thickness of the base film Lb and the cover film Lc depends on the width of the joining ridge line between the first prism 11 and the second prism 12, the thinner the film, the better. Therefore, the thickness of the base film Lb and the cover film Lc is preferably 75 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less. The base film Lb and the cover film Lc are preferably set to have the same thickness in order to avoid a difference in film shrinkage between the upper and lower sides of the hologram photosensitive material Lp due to baking or the like.

The refractive index difference at the constituent material interface of the hologram recording structure 15 is preferably 0.1 or less. 0.05 or less is still more preferable, and 0.02 or less is still more preferable. When the refractive indexes of the stress buffer layer La, the base film Lb, the hologram photosensitive material Lp, the cover film Lc, and the prism 11 are made close to each other, light refraction and scattering at the respective interfaces are reduced, and the hologram optics of the obtained optical device 10 is obtained. Through the element 13, the observer can visually recognize the external image without any problem.

1 shows hologram exposure on the hologram recording medium 13P when the optical device 10 is manufactured, and FIG. 2 shows hologram reproduction with the hologram optical element 13 when the optical device 10 is used. As shown in FIG. 1, hologram exposure is performed by irradiating the hologram recording medium 13P with laser light from two directions. One of the laser beams from two directions is the object beam 31 and the other is the reference beam 32, and hologram recording of interference fringes is performed by two-beam exposure of the object beam 31 and the reference beam 32.

When the first prism 11 and the second prism 12 are joined with the adhesive 14 so that the hologram optical element 13 (FIG. 2) obtained by the hologram exposure (FIG. 1) is sandwiched between the two

prisms

11 and 12, The optical device 10 in a state where hologram reproduction (FIG. 2) is possible is obtained. In the hologram reproduction, as shown in FIG. 2, when the image light (reproduction illumination light) 41 enters the hologram optical element 13, the reproduction image light 42 is diffracted and reflected. The reproduced image light 42 enters the observer's eye EY together with the external image light 43 transmitted through the hologram optical element 13. Therefore, the observer can observe the external image together with the display image.

The manufacturing method of the optical device 10 includes the following steps:
(# 1) A step of, for example, applying a liquid hologram photosensitive material (for example, photopolymer) Lp on the base film Lb and drying to form a film,
(# 2) A step of attaching a cover film Lc to the surface opposite to the base film Lb in the film-like hologram photosensitive material Lp,
(# 3) A step of applying a stress buffer layer La to the surface of the base film Lb opposite to the surface on which the hologram photosensitive material Lp is applied,
(# 4) By attaching the stress buffer layer La to the first prism 11, the stress buffer layer La, the base film Lb, the hologram photosensitive material Lp, and the cover film Lc are sequentially formed from the first prism 11 side. Forming a hologram recording medium 13P adjacent to each other on the first prism 11;
(# 5) Hologram recording medium 13P is formed into a hologram by forming hologram layer Lh by hologram exposure of interference fringes on hologram photosensitive material Lp (for example, two-beam exposure of object beam 31 and reference beam 32 shown in FIG. 1). And (# 6) the first prism 11 and the second prism to which the hologram recording medium 13P is attached so that the hologram optical element 13 is sandwiched between the first and

second prisms

11 and 12. 12 with an adhesive 14,
The manufacturing method which has this. If necessary, a fixing process by ultraviolet irradiation, a baking process, and the like may be included after the hologram exposure in the process (# 5).

The hologram photosensitive material Lp is most easily contracted in the step (# 5) of performing the hologram exposure of the interference fringes, but the hologram recording medium 13P is brought into contact with the hologram photosensitive material Lp sandwiched between the base film Lb and the cover film Lc. In addition, since the Young's modulus of the stress buffer layer La is set small, as described above (FIG. 5E), local shrinkage unevenness due to shrinkage of the hologram photosensitive material Lp and deformation of the prism 11 are prevented. Can be prevented. Examples of the deformation of the prism 11 that can be prevented include bending of an acute angle portion at the tip of the prism 11. When the acute angle portion at the tip of the prism 11 is bent, the second reflection of light (FIG. 2) is greatly affected. For example, the bending of the acute angle portion at the tip of the prism 11 acts so that the portion of the hologram optical element 13 closer to the tip of the prism 11 is closer to the image position of the image.

The optical device 10 (FIG. 2) is composed of transparent first and

second prisms

11 and 12; a hologram optical element 13 and the like, and a hologram optical element is provided between the first prism 11 and the second prism 12. The structure has the element 13. The hologram optical element 13 is affixed to the first prism 11, and the first prism 11 and the second prism 12 are bonded by an adhesive 14 provided between the first and

second prisms

11 and 12. The hologram optical element 13 is bonded so as to sandwich it. That is, the first prism 11 and the second prism 12 are joined by the adhesive 14 provided between the first prism 11 and the hologram optical element 13 and the second prism 12. Yes. Since the hologram optical element 13 is provided on the joint surface of the

transparent prisms

11 and 12, the see-through property of the external image through the joint surface is ensured. In addition, since light rays related to diffraction reflection do not pass through the cover film Lc and the second prism 11, the relationship between the adhesive 14, the cover film Lc, and the prism 12 affects the function of the eyepiece optical system of the optical device 10. There is no.

In the hologram optical element 13, the hologram layer Lh is sandwiched between the base film Lb and the cover film Lc, and the Young's modulus of the stress buffer layer La is set smaller than the Young's modulus of the prism 11 and the base film Lb. ing. For this reason, by suppressing the deformation of the hologram optical element 13 and the

prisms

11 and 12, it is possible to achieve the optical device 10 that can stably obtain good optical performance such as image plane property.

The stress buffer layer La is optically transparent and has substantially the same refractive index as that of the

prisms

11 and 12. Therefore, light refraction / scattering at the interface between the stress buffer layer La and the

prisms

11 and 12 is reduced, and the observer can view the external image without any problem through the joint portion of the

prisms

11 and 12 via the hologram optical element 13. Visual recognition is possible. As a configuration in which the stress buffer layer La has substantially the same refractive index as the

prisms

11 and 12, the difference in refractive index is preferably 0.1 or less, more preferably 0.05 or less, and even more preferably 0.02 or less. preferable.

As shown in FIG. 2, the video display device 1 includes a display element 20 for displaying video in addition to the optical device 10. Examples of the display element 20 include a reflective or transmissive liquid crystal display element (LCD), a digital micromirror device, and an organic EL (organic electro-luminescence) display. . Furthermore, you may arrange | position the illuminating device for illuminating the display element 20. FIG. Examples of the illuminating device include a light source such as an LED (light emitting diode) or the like, and an illuminating device including a condensing optical element (lens, mirror, etc.).

FIG. 3 shows a more specific optical configuration of the video display device 1 (FIG. 2). FIG. 3 shows an optical path from the light source 21 to the optical pupil EP in the video display device 1 having an illumination device or the like. In addition to the illumination device, the video display device 1 includes a polarizing plate 24, a polarizing beam splitter 25, a display element 20, and an optical device 10 that functions as an eyepiece optical system.

The illumination device illuminates the display element 20 and includes a light source 21, an illumination mirror 22, and a diffusion plate 23. The light source 21 is composed of an RGB integrated LED that emits light in three wavelength bands whose center wavelengths are, for example, 465 nm, 520 nm, and 635 nm. The illumination mirror 22 reflects light (illumination light) emitted from the light source 21 toward the diffusion plate 23, and also optical elements (for example, for bending the illumination light so that the optical pupil EP and the light source 21 are substantially conjugate with each other) Free-form surface mirror). The diffusing plate 23 diffuses illumination light from the light source 21, and the degree of diffusion varies depending on the direction (for example, a unidirectional diffusing plate having a diffusing action only in the lateral direction).

The polarizing plate 24 has a diffusion plate 23 bonded and held on the surface thereof, and transmits light having a predetermined polarization direction out of light incident through the diffusion plate 23 and guides it to the polarizing beam splitter 25. The directions of the polarizing beam splitter 25 are aligned so that the polarized light transmitted through the polarizing plate 24 is reflected by the polarizing beam splitter 25. The polarization beam splitter 25 reflects the light transmitted through the polarizing plate 24 in the direction of the reflective display element 20, while the light corresponding to the image signal ON (reflecting the polarizing plate 24) among the light reflected by the display element 20. The transmitted light is a flat plate-shaped polarization separating element that transmits light having a polarization direction orthogonal to the light, and is attached to the prism surface 11 c of the prism 11.

The display element 20 is a display element that displays the image IM by modulating light from the illumination device (that is, light reflected by the polarization beam splitter 25). In the image display device 1, a reflective liquid crystal display element is used. Assumed. The display element 20 may have a configuration including a color filter, or may be configured to be driven in a time division manner for each RGB.

The display element 20 is arranged so that light incident from the polarizing beam splitter 25 substantially perpendicularly is reflected almost vertically and travels toward the polarizing beam splitter 25. This facilitates optical design that increases the resolution compared to a configuration in which light is incident on the reflective display element at a large incident angle. The display element 20 is disposed on the same side as the light source 21 with respect to the optical path from the illumination mirror 22 toward the polarization beam splitter 25. Thereby, the whole optical system from an illuminating device to the display element 20 can be comprised compactly. The display element 20 may be supported on the same substrate as the light source 21 or may be supported on a separate substrate.

The optical device 10 includes a prism 11, a prism 12, and a hologram optical element 13, and the

prisms

11 and 12 are made of plastic (for example, acrylic resin, polycarbonate, cycloolefin resin, or the like). The optical device 10 has non-axisymmetric (non-rotationally symmetric) positive optical power, and thereby functions as an eyepiece optical system for guiding the image light from the display element 20 to the optical pupil EP. The prism 11 guides the image light incident from the display element 20 via the polarization beam splitter 25 inside, and transmits the light of the external image (external light). The shape is thicker toward the upper end and thinner at the lower end toward the lower end.

The prism surface 11c to which the polarization beam splitter 25 is attached in the prism 11 is an optical surface on which the image light from the display element 20 first enters. Also, the two

prism surfaces

11a and 11b that are positioned substantially parallel to the optical pupil EP and face each other are total reflection surfaces that guide the image light by total reflection. Among them, the prism surface 11 a on the optical pupil EP side also serves as an exit surface for image light diffracted and reflected by the hologram optical element 13.

The prism 11 is joined to the prism 12 with an adhesive 14 so as to sandwich the hologram optical element 13 disposed at the lower end thereof, thereby forming a substantially parallel plate. By bonding the prism 12 to the prism 11, refraction when external light passes through the wedge-shaped lower end of the prism 11 can be canceled by the prism 12, and distortion of the observed external field image is prevented. be able to. The hologram optical element 13 is provided in contact with the prism surface 11 d of the prism 11 and is a volume phase type reflection type hologram optical element that diffracts and reflects the image light guided inside the prism 11. The RGB diffraction wavelength of the hologram optical element 13 substantially corresponds to the wavelength of RGB image light (the emission wavelength of the light source 21).

In the above configuration, the light emitted from the light source 21 of the illumination device is reflected by the illumination mirror 22 and diffused only in one direction by the diffusion plate 23, and then only the light in a predetermined polarization direction passes through the polarizing plate 24. To Penetrate. The light transmitted through the polarizing plate 24 is reflected by the polarization beam splitter 25 and enters the display element 20. In the display element 20, incident light is modulated according to the image signal. At this time, the image light corresponding to the image signal ON is converted by the display element 20 into light having a polarization direction orthogonal to that of the incident light, and is emitted, so that the image light is transmitted through the polarization beam splitter 25 and is transmitted from the prism surface 11c to the prism. 11 is incident on the inside. On the other hand, since the image light corresponding to the image signal OFF is emitted without being converted in the polarization direction by the display element 20, it is blocked by the polarization beam splitter 25 and does not enter the prism 11.

In the prism 11, the incident video light is totally reflected once by the two

prism surfaces

11 a and 11 b facing the prism 11 and then enters the hologram optical element 13. In the hologram optical element 13, only light of specific wavelengths (three wavelengths corresponding to RGB) is diffracted and reflected and emitted from the prism surface 11a to reach the optical pupil EP. Accordingly, the observer can observe the image IM displayed on the display element 20 at the position of the optical pupil EP as a virtual image. On the other hand, since the prism 11, the prism 12, and the hologram optical element 13 transmit almost all of the external light, the observer can observe the outside world image with see-through. Therefore, the virtual image of the video IM displayed on the display element 20 is observed while overlapping a part of the external image.

As described above, the optical device 10 displays the display image as a virtual image so that the image of the display element 20 overlaps the external image via the hologram optical element 13 between the joined first and

second prisms

11 and 12. It functions as an eyepiece optical system for projecting and displaying on the observer eye EY (FIG. 2). Therefore, the hologram optical element 13 is desirably a volume phase type reflection hologram. Since the volume phase type reflection hologram has a high light transmittance of the external image, if the volume phase type reflection hologram is used as the hologram optical element 13, the observer can clearly observe the display image and the external image. It becomes possible.

As shown in FIGS. 2 and 3, the hologram optical element 13 is used in a state of being embedded in the prisms 11 and 12 (that is, in a state of being sandwiched between the two prisms 11 and 12). It is not affected by the external environment such as (preventing degradation due to the environment). Further, the optical device 10 is employed as an eyepiece optical system that guides the image light provided from the display element 20 to the hologram optical element 13 by totally reflecting the image light provided from the display element 20 by the configuration embedded in the

prisms

11 and 12. Is possible. Then, by optimizing the shape of the

prisms

11 and 12 and the shape of the hologram optical element 13, the see-through property (combiner function) of the external image can be ensured while maintaining the optical performance of the hologram optical element 13.

As described above, the video display apparatus 1 (FIGS. 2 and 3) includes the optical device 10 and the display element 20 that displays video, and the hologram optical element 13 is included in the video light from the display element 20. It is desirable to diffract light of a specific wavelength. If comprised in this way, the see-through display by which the high quality image | video was superimposed on the external field image will be attained. Therefore, it is possible to observe a high-quality image provided from the display element 10 through the optical device 10 and at the same time, it is possible to observe an external image through the optical device 10 in a see-through manner.

As shown in FIGS. 2 and 3, the first prism 11 constituting the optical device 10 desirably has a configuration in which the image light from the display element 20 is totally reflected and guided to the hologram optical element 13. With such a configuration, it is possible to provide a bright image to the observer by using the image light provided from the display element 20 without waste. In addition, the display element 20 can be arranged at a position away from the optical device 10, and a wide field of view of the observer with respect to the outside world can be secured.

As described above, it is desirable that the optical device 10 constitutes an eyepiece optical system that enlarges an image displayed on the display element 20 and guides it to the observer eye EY (FIG. 2) as a virtual image. According to this structure, the observer can fully visually recognize the image displayed on the display element 10 as a virtual image. Since the eyepiece optical system provides the viewer with the display image of the display element 20 as an enlarged virtual image, the optical device 10 constituting the eyepiece optical system can be reduced in size and weight, and the video display device 1 can be reduced in size and weight. Is possible. The eyepiece optical system configured by the optical device 10 desirably has non-axisymmetric (positive) optical power. With such a configuration, it is possible to provide an observer with an image that is favorably corrected for aberrations even if the eyepiece optical system is downsized.

It is desirable that the hologram optical element 13 is inclined with respect to the surface of the first prism 11 facing the observer eye EY. Further, an acute angle forming surface (prism surfaces 11a and 12b) that forms an acute angle with respect to the joint surface between the first prism 11 and the second prism 12, and an obtuse angle forming surface (prism surfaces 11b and 12a) that forms an obtuse angle. And the first and

second prisms

11 and 12, respectively, and the hologram optical element 13 is provided on the first prism 11 in a state inclined with respect to the acute angle forming surface and the obtuse angle forming surface. desirable. When the hologram optical element 13 is tilted as described above, the degree of optical freedom is increased, and the reflection at the hologram optical element 13 can be set to an angle close to regular reflection. As a result, the observer can observe an image with high efficiency and optically good aberration correction.

It is desirable that the hologram optical element 13 is a combiner that simultaneously guides an image displayed on the display element 20 and an external image to the observer eye EY. In this case, the observer can observe the image provided from the display element 10 and the external image simultaneously through the hologram optical element 13. Therefore, by mounting the above-described video display device 1 (FIGS. 2 and 3), an optical see-through display having a function of projecting and displaying the video IM on the observer eye EY with the optical device 10 can be configured. it can.

As described above, it is desirable that the image display device 1 is mounted on the optical see-through display so that the hologram optical element 13 has a function of projecting and displaying the image on the observer's eye EY. The optical see-through display also includes a head-mounted display that includes a support member that supports the image display device 1 so that the hologram optical element 13 is positioned in front of the observer's eye EY (that is, supports in front of the observer's eyes). It is desirable that Examples of the optical see-through display include a head-mounted display (HMD) and a head-up display (HUD). Here, a spectacle-type head-mounted display provided with the video display device 1 will be described as an example.

FIG. 4 shows a schematic configuration of a glasses-type head mounted display 2 provided with the video display device 1. The head mounted display 2 includes the video display device 1 and the support member 3 described above. The display element 20 and the lighting device of the video display device 1 are accommodated in the housing 7, and the upper end portion of the optical device 10 that is an eyepiece optical system is also located in the housing 7. As described above, the optical device 10 is configured by bonding the two

prisms

11 and 12 which are prisms, and has a shape like one lens of a pair of glasses (lens for right eye in FIG. 4) as a whole. ing.

Further, the display element 20, the light source 21 and the like in the housing 7 are connected to a circuit board (not shown) through a cable 8 provided through the housing 7, and the display element 20, Driving power and video signals are supplied to the light source 21 and the like. The video display device 1 further includes an imaging device that captures still images and moving images, a microphone, a speaker, an earphone, and the like, and information on the captured image and the display image via an external server or terminal and a communication line such as the Internet. Or a configuration for exchanging (transmitting / receiving) audio information.

The support member 3 is a support mechanism corresponding to a frame of glasses, and supports the image display device 1 in front of the observer's eyes (in front of the right eye in FIG. 4). The support member 3 includes

temples

4R and 4L that are in contact with the left and right temporal regions of the observer, and

nose pads

5R and 5L that are in contact with the nose of the observer. The support member 3 also supports the lens 6 in front of the left eye of the observer, but this lens 6 is a dummy lens.

When the head-mounted display 2 is mounted on the observer's head and an image is displayed on the display element 20, the image light is guided to the optical pupil EP (FIG. 3) via the optical device 10. Accordingly, by aligning the observer's pupil (observer's eye EY) with the position of the optical pupil EP, the observer can observe an enlarged virtual image of the display image on the image display device 1. At the same time, the observer can observe an external image through the optical device 10 with see-through.

As described above, when the video display device 1 is supported by the support member 3, the observer can observe the display video and the external image provided from the video display device 1 at the same time in a hands-free and stable manner. The desired work can be performed with open hands. In addition, since the observation direction of the observer is determined in one direction, there is an advantage that the observer can easily find the display image even in a dark environment. In addition, you may enable it to observe an image | video with both eyes using two image display apparatuses 1. FIG.

1 Video display device 2 Head mounted display (optical see-through display)
3

Support member

4R,

4L Temple

5R, 5L Nose pad 6 Lens 7 Housing 8 Cable 10 Optical device (eyepiece optical system)
11 Prism (first prism, transparent substrate)
11a, 11b, 11c, 11d Prism surface 12 Prism (second prism)
13 Hologram optical element 13P Hologram recording medium La Stress buffer layer Lb Base film Lc Cover film Lh Hologram layer Lp Hologram photosensitive material (photopolymer)
DESCRIPTION OF SYMBOLS 14 Adhesive 15 Hologram recording structure 20 Display element 21 Light source 22 Illumination mirror 23 Diffusion plate 24 Polarizing plate 25 Polarizing beam splitter 31 Object light 32 Reference light 41 Image light 42 Reproduction image light 43 External image light IM Image EY Observer eye EP Optical pupil

Claims

A hologram recording structure having a hologram recording medium on a transparent substrate,
The hologram recording medium has the stress buffer layer, the base film, the hologram photosensitive material, and the cover film in the state of being in contact with each other in order from the transparent substrate side,
The hologram recording structure, wherein the stress buffer layer has a Young's modulus smaller than that of the transparent substrate and the base film.
The hologram recording structure according to claim 1, wherein the hologram photosensitive material is made of a photopolymer.
An optical device having a structure in which a first prism and a second prism are joined so as to sandwich a hologram optical element,
The hologram optical element has, in order from the first prism side, a stress buffer layer, a base film, a hologram layer, and a cover film in contact with each other.
The optical device, wherein the stress buffer layer has a Young's modulus smaller than that of the first prism and the base film, and has substantially the same refractive index as the first and second prisms.
4. The optical device according to claim 3, wherein the hologram layer is a volume phase type reflection hologram.
The first and second prisms are transparent, the hologram optical element is attached to the first prism, and the first prism and the second prism are joined together by the first prism. 5. The optical device according to claim 3, wherein the optical device is made of an adhesive provided between a prism and a hologram optical element and the second transparent prism.
The first and second prisms each have an acute angle forming surface that forms an acute angle and an obtuse angle forming surface that forms an obtuse angle with respect to the joint surface between the first prism and the second prism, The optical device according to any one of claims 3 to 5, wherein the hologram optical element is provided on the first prism in a state inclined with respect to the acute angle forming surface and the obtuse angle forming surface. .
A method of manufacturing an optical device having a structure in which a first prism and a second prism are joined so as to sandwich a hologram optical element,
Applying a hologram photosensitive material on a base film and drying to form a film;
A step of attaching a cover film to the surface opposite to the base film in the film-shaped hologram photosensitive material;
A step of attaching a stress buffer layer to a surface of the base film opposite to the surface on which the hologram photosensitive material is applied;
By sticking the stress buffer layer to the first prism, the stress buffer layer, the base film, the hologram photosensitive material, and the cover film are adjacent to each other in order from the first prism side. Forming a holographic recording medium in contact with the first prism;
Forming the hologram layer by hologram exposure of interference fringes to the hologram photosensitive material, thereby making the hologram recording medium the hologram optical element;
Bonding the first prism attached to the hologram recording medium and the second prism with an adhesive so as to sandwich the hologram optical element between the first and second prisms,
The manufacturing method, wherein the stress buffer layer has a Young's modulus smaller than that of the first prism and the base film, and has substantially the same refractive index as that of the first and second prisms.
An optical device according to any one of claims 3 to 6 and a display element for displaying an image, wherein the hologram optical element diffracts light having a specific wavelength out of image light from the display element. A video display device characterized by being caused to perform.
The image display device according to claim 8, wherein the first prism guides the image light from the display element to the hologram optical element by totally reflecting the image light internally.
10. The image display device according to claim 8, wherein the optical device constitutes an eyepiece optical system that enlarges an image displayed on the display element and guides the image to a viewer's eye as a virtual image.
11. The image display device according to claim 10, wherein the hologram optical element is a combiner that simultaneously guides an image displayed on the display element and an external image to an observer's eye.
12. An optical see-through display comprising the image display device according to claim 10 or 11, wherein the hologram optical element has a function of projecting and displaying the image on a viewer's eye through the hologram optical element.
The optical see-through display according to claim 12, wherein the optical see-through display is a head-mounted display including a support member that supports the video display device so that the hologram optical element is positioned in front of an observer's eye.