阅读说明：本技术 光学元件、光学元件的制造方法以及显示装置 (Optical element, method for manufacturing optical element, and display device ) 是由 斋藤淳 于 2020-08-26 设计创作，主要内容包括：提供光学元件、光学元件的制造方法以及显示装置,能够抑制伴随着基板的变形的性能降低。本发明的光学元件的特征在于,该光学元件具有：全息层；树脂基板,其粘贴有全息层；以及保持部,其支承树脂基板,并且热膨胀系数比树脂基板的热膨胀系数小,保持部和树脂基板中的一方具有沿着在树脂基板的板厚方向上延伸的轴的抵接面,保持部和树脂基板中的另一方具有按压抵接面的按压面。(Provided are an optical element, a method for manufacturing the optical element, and a display device, wherein the performance reduction caused by the deformation of a substrate can be suppressed. An optical element of the present invention is characterized by comprising: a holographic layer; a resin substrate to which a hologram layer is attached; and a holding portion that supports the resin substrate and has a thermal expansion coefficient smaller than that of the resin substrate, one of the holding portion and the resin substrate having an abutment surface along an axis extending in a plate thickness direction of the resin substrate, and the other of the holding portion and the resin substrate having a pressing surface that presses the abutment surface.)

1. An optical element, comprising:

a holographic layer;

a resin substrate to which the hologram layer is attached; and

a holding portion that supports the resin substrate and has a thermal expansion coefficient smaller than that of the resin substrate,

one of the holding portion and the resin substrate has an abutment surface along an axis extending in a plate thickness direction of the resin substrate,

the other of the holding portion and the resin substrate has a pressing surface that presses the contact surface.

2. The optical element according to claim 1,

the holding portion has an elastic modulus higher than that of the resin substrate.

3. Optical element according to claim 1 or 2,

one of the resin substrate and the holding portion has a recess,

the other of the resin substrate and the holding portion has a convex portion inserted into the concave portion,

one of the concave portion and the convex portion constitutes the contact surface,

the other of the concave portion and the convex portion constitutes the pressing surface.

4. Optical element according to claim 3,

the planar shapes of the concave part and the convex part are frame-shaped.

5. The optical element according to claim 1,

the resin substrate has a curved shape.

6. A method for manufacturing an optical element according to any one of claims 1 to 5,

the method for manufacturing the optical element includes a step 1 of bringing the pressing surface into contact with the contact surface at a temperature higher than any one of an upper limit value of a usage environment temperature in which the optical element is used and an exposure environment temperature in interference exposure in which interference fringes are formed in the hologram layer in the step 1.

7. A method for manufacturing an optical element according to any one of claims 1 to 5,

the method for manufacturing the optical element includes a step 1 of bringing the pressing surface into contact with the contact surface at a temperature lower than either a lower limit of a use environment temperature in which the optical element is used or an exposure environment temperature in interference exposure in which interference fringes are formed in the hologram layer in the step 1.

8. The method for manufacturing an optical element according to claim 6 or 7,

in the step 1, a hologram material for forming the hologram layer is attached to the resin substrate,

after the step 1, the hologram layer is formed by performing interference exposure on the hologram material attached to the resin substrate.

9. A display device, characterized by comprising:

an image light generation device that generates image light; and

an optical system including a diffraction element that diffracts the image light emitted from the image light generation device,

the diffraction element is constituted by the optical element according to any one of claims 1 to 4.

10. The display device according to claim 9,

the display device has a frame for wearing the optical element on the head of an observer in such a manner that the holographic layer is disposed in front of the eyes of the observer,

the holding portion is a part of the frame.

Technical Field

The invention relates to an optical element, a method for manufacturing the optical element, and a display device.

Background

As a display device using a diffraction element such as a hologram (holographic) element, a display device has been proposed in which image light emitted from an image light generation device is deflected by the diffraction element toward the eyes of an observer (see patent document 1). The diffraction element is formed by attaching a hologram layer to a resin substrate.

Patent document 1: japanese laid-open patent publication (JP 2015-191026)

The diffraction element forms interference fringes of the hologram layer by subjecting the hologram material attached to the resin substrate to interference exposure by laser light. Since the hologram material expands or contracts in the interference exposure, the resin substrate may expand or contract together with the hologram material to be deformed. In this way, if the resin plate is deformed in the interference exposure, the hologram material is exposed in a deformed state, thereby forming interference fringes of different diffraction angles in the hologram layer, and desired performance cannot be obtained.

In the diffraction element, the resin substrate expands or contracts depending on the ambient temperature at the time of actual use, and the hologram layer attached to the resin substrate is deformed. When the hologram layer is deformed like this, interference fringes in the hologram layer change. When the interference fringes thus change, the diffraction angle of the hologram layer greatly changes, and desired performance cannot be obtained.

Disclosure of Invention

In order to solve the above problem, an optical element according to an aspect of the present invention includes: a holographic layer; a resin substrate to which the hologram layer is attached; and a holding portion that supports the resin substrate and has a thermal expansion coefficient smaller than that of the resin substrate, one of the holding portion and the resin substrate having an abutment surface along an axis extending in a plate thickness direction of the resin substrate, and the other of the holding portion and the resin substrate having a pressing surface that presses the abutment surface.

The holding portion may have a higher elastic modulus than that of the resin substrate.

One of the resin substrate and the holding portion may have a concave portion, the other of the resin substrate and the holding portion may have a convex portion inserted into the concave portion, one of the concave portion and the convex portion may constitute the contact surface, and the other of the concave portion and the convex portion may constitute the pressing surface.

The projection and the recess may have a frame-like planar shape.

The resin substrate may have a curved shape.

The method of manufacturing the optical element may include a step 1 of bringing the pressing surface into contact with the contact surface at a temperature higher than either a use environment temperature in which the optical element is used or an exposure environment temperature in interference exposure in which interference fringes are formed in the hologram layer in the step 1.

The method of manufacturing the optical element may include a step 1 of bringing the pressing surface into contact with the contact surface in the step 1 at a temperature lower than either one of a use environment temperature in which the optical element is used and an exposure environment temperature in which interference exposure is performed to form interference fringes in the hologram layer.

The following manufacturing method is possible: in the step 1, a hologram material for forming the hologram layer is attached to the resin substrate, and after the step 1, the hologram layer is formed by performing interference exposure on the hologram material attached to the resin substrate.

The display device of the present invention is characterized by comprising: an image light generation device that generates image light; and an optical system including a diffraction element for diffracting the image light emitted from the image light generation device, wherein the diffraction element is composed of the optical element.

The display device may be configured to have a frame that is configured to mount the optical element on the head of an observer such that the hologram layer is disposed in front of the eyes of the observer, and the holding portion may be a part of the frame.

Drawings

Fig. 1 is an external view showing one embodiment of the external appearance of the display device according to embodiment 1.

Fig. 2 is an external view showing another mode of the external appearance of the display device.

Fig. 3 is an explanatory diagram showing one embodiment of an optical system of the display device.

Fig. 4 is a sectional view showing the structure of the main part of the 2 nd diffraction element.

Fig. 5A is a view showing a manufacturing process of the 2 nd diffraction element.

Fig. 5B is a diagram illustrating a manufacturing process of the 2 nd diffraction element.

Fig. 5C is a diagram illustrating a manufacturing process of the 2 nd diffraction element 70.

Fig. 6 is a diagram showing a dimensional change between projections due to an ambient temperature.

Fig. 7A is a diagram showing an example of arrangement of the convex portions and the concave portions.

Fig. 7B is a diagram showing an example of arrangement of the convex portions and the concave portions.

Fig. 7C is a diagram showing an example of arrangement of the convex portions and the concave portions.

Fig. 7D is a diagram showing an example of arrangement of the convex portions and the concave portions.

Fig. 8 is an explanatory diagram showing diffraction characteristics of the 1 st diffraction element and the 2 nd diffraction element.

Fig. 9A is an explanatory diagram in the case where the 1 st diffraction element and the 2 nd diffraction element have a conjugate relationship.

Fig. 9B is an explanatory diagram in the case where the 1 st diffraction element and the 2 nd diffraction element do not have a conjugate relationship.

Fig. 9C is an explanatory diagram in the case where the 1 st diffraction element and the 2 nd diffraction element do not have a conjugate relationship.

Fig. 10A is an explanatory diagram showing a tolerance for a deviation from the conjugate relationship between the 1 st diffraction element and the 2 nd diffraction element.

Fig. 10B is an explanatory diagram illustrating another mode of tolerance to deviation from the conjugate relationship.

Fig. 11 is a light ray diagram of an optical system.

Fig. 12 is a sectional view showing the structure of a main part of the 2 nd diffraction element of embodiment 2.

Fig. 13A is a diagram illustrating a manufacturing process of the 2 nd diffraction element in embodiment 2.

Fig. 13B is a diagram illustrating a manufacturing process of the 2 nd diffraction element in embodiment 2.

Fig. 14 is a diagram showing a fixing structure of a modification.

Description of the reference symbols

10: an optical system; 31: an image light generating device; 70: a 2 nd diffraction element (optical element); 71: a resin substrate; 72: a holographic layer; 72M: a holographic material; 80. 180: a holding section; 74: interference fringes; 75: a convex portion; 81. 82: a recess; 91: a frame; 100: a display device; e: an eye; l0, L0a, L0 b: image light; l1, L2, L3: a light; o: a shaft.

Detailed Description

(embodiment 1)

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the dimensions and angles of the layers and the members are different from those in actual cases so that the layers and the members have a size that can be recognized.

Fig. 1 is an external view showing one embodiment of the external appearance of a display device 100 according to the present embodiment. Fig. 2 is an external view showing another mode of another external appearance of the display device 100. Fig. 3 is an explanatory diagram illustrating one embodiment of the optical system 10 of the display device 100 illustrated in fig. 1. In fig. 1 to 3, the front-rear direction of the observer wearing the display device is defined as the direction along the Z axis, one side in the front-rear direction, the front of the observer wearing the display device is defined as the front side Z1, the other side in the front-rear direction, and the rear of the observer wearing the display device is defined as the rear side Z2. The left-right direction of the observer wearing the display device is defined as a direction along the X axis, one side of the left-right direction is defined as a right side X1, the other side of the left-right direction is defined as a left side X2, and the left side of the observer wearing the display device is defined as a left side X1. The vertical direction with respect to the observer wearing the display device is defined as the direction along the Y axis direction, one side in the vertical direction, the upper side of the observer wearing the display device is defined as the upper side Y1, the other side in the vertical direction, and the lower side of the observer wearing the display device is defined as the lower side Y2.

The display device 100 shown in fig. 1 is a head-mounted display device, and includes a right-eye optical system 10a for causing image light L0a to enter a right eye Ea, and a left-eye optical system 10b for causing image light L0b to enter a left eye Eb. The display device 100 is formed in a shape like glasses, for example. Specifically, the display device 100 further includes a housing 90 that holds the right-eye optical system 10a and the left-eye optical system 10 b. The display device 100 is worn on the head of the observer through the housing 90.

The display device 100 includes a frame 91, a temple 92a provided on the right side of the frame 91 and engaged with the right ear of the observer, and a temple 92b provided on the left side of the frame 91 and engaged with the left ear of the observer as a frame 90. The frame 91 has storage spaces 91s at both side portions, and each member such as an image light projection device constituting the optical system 10 described later is stored in the storage space 91 s. The temples 92a, 92b are foldably joined to the frame 91 by hinges 95.

The right-eye optical system 10a and the left-eye optical system 10b have the same basic configuration. Therefore, in the following description, the optical system 10 will be described as the right-eye optical system 10a and the left-eye optical system 10b without distinction.

In the display device 100 shown in fig. 1, the image light L0 is made to travel in the left-right direction along the X axis, but as shown in fig. 2, the image light L0 may be configured to travel from the upper side Y1 to the lower side Y2 and be emitted to the eyes E of the observer, or the optical system 10 may be configured to be disposed in a range from the top of the head to the front of the eyes E.

The basic structure of the optical system 10 of the display device 100 is explained with reference to fig. 3. Fig. 3 is an explanatory diagram illustrating one embodiment of the optical system 10 of the display device 100 illustrated in fig. 1. In fig. 3, light L2 on the long wavelength side (one-dot chain line) and light L3 on the short wavelength side (broken line) with respect to the specific wavelength are shown in addition to light L1 (solid line) on the specific wavelength of image light L0.

As shown in fig. 3, in the optical system 10, along the traveling direction of the image light L0 emitted from the image light generation device 31, a1 st optical portion L10 having positive power, a 2 nd optical portion L20 having positive power, a 3 rd optical portion L30 having positive power, and a 4 th optical portion L40 having positive power are arranged.

In the present embodiment, the 1 st optical portion L10 having positive refractive power is constituted by the projection optical system 32. The 2 nd optical portion L20 having positive refractive power is constituted by the reflective 1 st diffraction element 50. The 3 rd optical portion L30 having positive refractive power is constituted by the light guide system 60. The 4 th optical portion L40 having positive refractive power is constituted by the reflective 2 nd diffraction element 70. In the present embodiment, the 1 st diffraction element 50 and the 2 nd diffraction element 70 are reflective diffraction elements.

In the optical system 10, focusing on the traveling direction of the image light L0, the image light generation device 31 emits the image light L0 toward the projection optical system 32, the projection optical system 32 emits the incident image light L0 toward the 1 st diffraction element 50, and the 1 st diffraction element 50 emits the incident image light L0 toward the light guide system 60. The light guide system 60 emits the incident image light L0 to the 2 nd diffraction element 70, and the 2 nd diffraction element 70 emits the incident image light L0 to the eye E of the observer.

In the present embodiment, the image light generation device 31 generates image light L0.

The image light generation device 31 may be provided with a display panel 31a such as an organic electroluminescence display element. According to this embodiment, the display device 100 can be provided which is small and can display an image with high image quality. The image light generation device 31 may be configured to include an illumination light source (not shown) and a display panel 31a such as a liquid crystal display element that modulates illumination light emitted from the illumination light source. According to this aspect, since the illumination light source can be selected, there is an advantage that the degree of freedom of the wavelength characteristic of the image light L0 is increased. Here, the image light generation device 31 may be configured to include 1 display panel 31a capable of color display. The image light generation device 31 may be configured to include a plurality of display panels 31a corresponding to the respective colors and a synthesis optical system for synthesizing the image light of the respective colors emitted from the plurality of display panels 31 a. Further, the image light generation device 31 may be configured to modulate laser light by a micromirror device.

The projection optical system 32 is an optical system that projects the image light L0 generated by the image light generation device 31, and is configured by a plurality of lenses 32 a. In fig. 3, the case where the number of lenses 32a in the projection optical system 32 is 3 is exemplified, but the number of lenses 32a is not limited thereto, and the projection optical system 32 may have 4 or more lenses 32 a. The lenses 32a may be bonded to form the projection optical system 32. The lens 32a may be a lens having a free-form surface.

The light guide system 60 includes a lens system 61 on which the image light L0 emitted from the 1 st diffraction element 50 enters, and a mirror 62 that emits the image light L0 emitted from the lens system 61 in an oblique direction. The lens system 61 is configured by arranging a plurality of lenses 611 in the front-rear direction along the Z axis. The reflecting mirror 62 has a reflecting surface 620 inclined in the front-rear direction. In the present embodiment, the reflecting mirror 62 is a total reflection mirror. However, the mirror 62 may be a half-transmissive mirror, and in this case, the range in which external light can be viewed can be widened.

Next, the structures of the 1 st diffraction element 50 and the 2 nd diffraction element 70 will be described.

In the present embodiment, the 1 st diffraction element 50 and the 2 nd diffraction element 70 have the same basic structure. The following description will be given taking the structure of the 2 nd diffraction element 70 as an example.

The 2 nd diffraction element (optical element) 70 is a reflection type volume hologram element. The 2 nd diffraction element 70 constitutes a partially transmissive and reflective combiner. Therefore, since the external light is incident on the eye E via the 2 nd diffraction element 70, the observer can recognize an image in which the image light L0 formed by the image light generation device 31 and the external light (background) overlap.

As shown in fig. 3, the 2 nd diffraction element 70 faces the eye E of the observer, and an incident surface 70a of the 2 nd diffraction element 70 on which the image light L0 is incident is concave in a direction away from the eye E. In other words, the incident surface 70a has a shape in which the central portion is recessed and curved with respect to the peripheral portion in the incident direction of the image light L0. Therefore, the 2 nd diffraction element 70 can efficiently condense the image light L0 to the eye E of the observer.

Fig. 4 is a sectional view showing the structure of the main part of the 2 nd diffraction element 70. Fig. 4 shows a state of the 2 nd diffraction element 70 when the display device 100 is used at an ambient temperature of, for example, -20 to 40 ℃.

As shown in fig. 4, the 2 nd diffraction element 70 includes a resin substrate 71, a holding portion 80 for supporting the resin substrate 71, and a hologram layer 72 attached to the resin substrate 71. The resin substrate 71 has a curved surface shape curved so that the outer surface 71b is convex with respect to the inner surface 71 a.

As a material for forming the resin substrate 71, for example, plastic such as polymethyl methacrylate resin (PMMA), polycarbonate resin (PC), polyethylene terephthalate resin (PET), polyamide resin (PA), or the like can be used. The thickness of the resin substrate 71 is, for example, 500 μm to 5 mm.

In the present embodiment, the holding portion 80 and the resin substrate 71 have different thermal expansion coefficients. The holding portion 80 and the resin substrate 71 also have different elastic moduli. The thermal expansion coefficient of the resin substrate 71 is, for example, 60 ppm/DEG C to 80 ppm/DEG C, whereas the thermal expansion coefficient of the holding portion 80 is 30 ppm/DEG C or less. That is, the thermal expansion coefficient of the holding portion 80 is smaller than that of the resin substrate 71. Specifically, as a material of the holding portion 80 of the present embodiment, super invar (thermal expansion coefficient: 1 ppm/DEG C) is used. In the present embodiment, the holding portion 80 is formed by a part of the frame 91 of the display device 100 shown in fig. 1. The frame 91 allows the 2 nd diffraction element 70 to be worn on the head of the observer so that the hologram layer 72 is disposed in front of the eyes of the observer. In this way, by using a part of the frame 91 as the holding portion 80, the number of parts can be reduced, and cost reduction can be achieved.

Further, the elastic modulus of the resin substrate 71 was 350kg/mm²Hereinafter, the elastic modulus of the holding portion 80 is 1000kg/mm²As described above, the elastic modulus of the holding portion 80 is larger than that of the resin substrate 71.

The hologram layer 72 is formed by attaching a hologram material in which a photosensitive monomer such as an acrylic polymer is dispersed in a binder resin such as a urethane resin, an epoxy resin, or a cellulose resin to the resin substrate 71 and then performing interference exposure. In the hologram layer 72, a change in refractive index, a change in transmittance, a change in shape such as a concave-convex pattern, and the like are recorded as interference fringes 74 inside by interference exposure. Therefore, as shown in fig. 3, the 2 nd diffraction element 70 diffracts and deflects the image light L0 in a predetermined direction. The specific wavelength and the specific incident angle correspond to the wavelength and the incident angle of the image light L0.

In the present embodiment, the holographic layer 72 has a thickness of 5 to 25 μm and an elastic modulus of 350kg/mm²The following. In addition, the elastic modulus of the hologram layer 72 is lower than that of the resin substrate 71. Therefore, when the resin substrate 71 is deformed, the hologram layer 72 can be deformed following the deformation of the resin substrate 71.

The resin substrate 71 has a convex portion 75 formed on the inner surface 71a so as to extend in the plate thickness direction of the resin substrate 71. The convex portion 75 is integrally formed on the inner surface 71a of the resin substrate 71. The side surface 75a of the convex portion 75 is a surface along the axis O extending in the plate thickness direction of the resin substrate 71. In the present embodiment, the side surface 75a of the convex portion 75 intersects (is perpendicular to) the inner surface 71a of the resin substrate 71. The side surface 75a of the convex portion 75 is not limited to the case of being perpendicular to the inner surface 71a of the resin substrate 71 along the axis extending in the plate thickness direction of the resin substrate 71, and may be slightly inclined. The generation of stray light can be suppressed by applying light-shielding ink to the surface of the projection 75 to absorb external light incident on the projection 75.

The holding portion 80 includes a support plate portion 80a that supports the resin substrate 71, and a side plate portion 80b that is provided at an outer edge end portion of the support plate portion 80a and extends upward from the support plate portion 80 a. The holding portion 80 has a concave portion 81 into which the convex portion 75 of the resin substrate 71 is inserted. The concave portion 81 is formed in the support plate portion 80 a. The support plate portion 80a is formed with a through hole 80a 1. The through hole 80a1 exposes the inner surface 71a of the resin substrate 71. The through hole 80a1 is formed so that the hologram layer 72 is positioned inside. The light diffracted by the hologram layer 72 and the external light transmitted through the hologram layer 72 are favorably guided to the eyes of the observer via the through holes 80a 1. The recess 81 has an inner surface 81a located on the center side of the inner surface 71a of the resin substrate 71 and an outer surface 81b located on the outer edge side of the inner surface 71a of the resin substrate 71. The inner surface 81a and the outer surface 81b of the recess 81 are surfaces along an axis O extending in the plate thickness direction of the resin substrate 71.

As shown in fig. 4, at the use environment temperature (-20 ℃ to 40 ℃), the resin substrate 71 is attached to the holding portion 80 in a state where the convex portion 75 is in contact with the inner surface 81a of the concave portion 81 and the contraction force of the resin substrate 71 is inhibited. Thus, the resin substrate 71 of the present embodiment is fixed to the holding portion 80 in a state where tensile stress acts thereon.

The convex portion 75 and the concave portion 81 are pressed against each other. That is, in the present embodiment, one of the side surface 75a of the convex portion 75 and the inner surface 81a of the concave portion 82 constitutes a contact surface that makes the holding portion 80 contact the resin substrate 71, and the other of the side surface 75a of the convex portion 75 and the inner surface 81a of the concave portion 82 constitutes a pressing surface that presses the contact surface.

Next, a method for manufacturing the 2 nd diffraction element 70 will be described with reference to the drawings. Hereinafter, the ambient temperature is the temperature of the ambient environment when the 2 nd diffraction element 70 is manufactured.

Fig. 5A to 5C are diagrams illustrating a manufacturing process of the 2 nd diffraction element 70.

First, as shown in fig. 5A, the resin substrate 71 having the hologram material 72M bonded to the outer surface 71b is attached to the holding portion 80 in a state where the ambient temperature is set to 80 ℃.

Specifically, the resin substrate 71 is disposed in the holding portion 80 such that the convex portion 75 of the resin substrate 71 is fitted into the concave portion 81 of the holding portion 80. Here, the concave portion 81 of the holding portion 80 is formed in a shape larger than the shape of the convex portion 75 of the resin substrate 71. The convex portion 75 and the concave portion 81 are designed to coincide with each other in the center thereof under an environment of 80 ℃.

Subsequently, the ambient temperature was returned to 20 ℃ at which interference exposure described later was performed. At this time, the resin substrate 71 having a large thermal expansion coefficient is more greatly contracted than the holding portion 80 having a small thermal expansion coefficient as the ambient temperature is lowered. For example, when the ambient temperature is lowered to about 50 ℃, as shown in fig. 5B, the convex portion 75 of the resin substrate 71 comes into contact with the inner surface 81a of the concave portion 81 of the holding portion 80. When the ambient temperature is lower than 50 ℃, the resin substrate 71 is intended to be further shrunk, but the resin substrate 71 cannot be shrunk by the convex portions 75 coming into contact with the concave portions 81 of the holding portion 80. That is, when the ambient temperature is 50 ℃ or lower, the tensile stress S1 acts on the resin substrate 71.

As described above, the manufacturing method of the present embodiment includes the following step 1: the convex portions 75 are brought into contact with the inner side surfaces 81a of the concave portions 81 in an environment of 50 ℃ which is higher than either the upper limit of the temperature of the environment in which the display device 100 is used (40 ℃) or the exposure environment temperature (20 ℃) when interference exposure is performed to form the interference fringes 74 on the hologram layer 72, which will be described later.

Next, the holographic material 72M was subjected to interference exposure at an ambient temperature of 20 ℃.

As shown in fig. 5C, in the interference exposure, the reference light Lr and the object light Ls are interfered with the hologram material 72M to perform exposure, thereby obtaining the hologram layer 72 having interference fringes 74. The reference light Lr and the object light Ls may use any one of a plane wave and a spherical wave.

In the present embodiment, the image light L0 of red light, green light, and blue light is incident on the 2 nd diffraction element 70, and the incident image light L0 is diffracted and emitted in a predetermined direction. The interference fringes 74 of the hologram layer 72 shown in fig. 5C include, for example, interference fringes formed at a pitch corresponding to red image light of, for example, a wavelength of 615nm in a wavelength range of 580nm to 700nm, interference fringes formed at a pitch corresponding to green image light of, for example, a wavelength of 535nm in a wavelength range of 500nm to 580nm, and interference fringes formed at a pitch corresponding to blue image light of, for example, a wavelength of 460nm in a wavelength range of 400nm to 500 nm.

The hologram material 72M of the present embodiment is configured by laminating hologram photosensitive layers having sensitivity corresponding to each wavelength. Therefore, in the interference exposure, the interference fringes 74 are formed by performing the interference exposure on each hologram photosensitive layer using the reference light and the object light of each wavelength.

Thereby, the 2 nd diffraction element 70 of the present embodiment is manufactured.

Further, a photosensitive material having sensitivity corresponding to each wavelength may be dispersed in the hologram photosensitive layer in advance, and the hologram photosensitive layer may be subjected to interference exposure using reference light and object light of each wavelength, thereby forming interference fringes 74 in which interference fringes corresponding to red light, green light, and blue light are superimposed in one layer.

In addition, the hologram material 72M expands or contracts during a reaction process in which interference fringes 74 are formed in the hologram layer 72 by interference exposure. Whether it expands or contracts depends on the composition of the material, the reaction process. The resin substrate 71 is intended to be deformed together with the hologram material 72M by expansion or contraction of the hologram material 72M at the time of interference exposure. At this time, as described above, the convex portion 75 and the concave portion 81 are fitted to each other so as to press each other, thereby generating the tensile stress S1 on the resin substrate 71. That is, as long as the state in which the convex portion 75 is in contact with the inner side surface 81a of the concave portion 81 is maintained, the resin substrate 71 is restrained by the holding portion 80 without dimensional change.

According to the manufacturing method of the present embodiment, even when the resin substrate 71 is intended to expand or contract when the interference exposure is performed on the hologram layer 72, the deformation of the resin substrate 71 can be suppressed by the holding portion 80. Therefore, since the interference fringes 74 are formed in the hologram layer 72 in a state where the deformation of the resin substrate 71 is suppressed, the performance degradation of the hologram layer 72 accompanying the deformation of the resin substrate 71 can be suppressed.

As described above, the 2 nd diffraction element 70 of the present embodiment is manufactured by bringing the convex portions 75 into contact with the inner side surfaces 81a of the concave portions 81 at a temperature (50 ℃) higher than the upper limit value (40 ℃) of the use environment temperature of the display device 100 and the exposure environment temperature (20 ℃) when interference exposure is performed, thereby fixing the resin substrate 71 to the holding portion 80.

The size between the convex portions 75 in the 2 nd diffraction element 70 varies depending on the ambient temperature. Hereinafter, a change in the size between the convex portions 75 according to the ambient temperature will be described. Further, the effect of the 2 nd diffraction element 70 obtained by the dimensional change between the convex portions 75 will be described.

Fig. 6 is a diagram illustrating a dimensional change between the convex portions 75 of the resin substrate 71 due to the ambient temperature. In fig. 6, the horizontal axis represents the ambient temperature, and the vertical axis represents the dimension between the convex portions 75.

In fig. 6, the dimension between the convex portions 75 of the resin substrate 71 at an ambient temperature of 80 ℃ is W0. That is, W0 corresponds to the dimension between the convex portions 75 in the state shown in fig. 5A.

As shown in fig. 6, when the ambient temperature is reduced to 50 ℃, the size between the convex portions 75 is changed to W1 because the resin substrate 71 shrinks.

Here, for the sake of simplifying the explanation, it is assumed that the thermal expansion coefficient of the holding portion 80 is 0ppm/° c. In this case, as shown in fig. 6, even if the ambient temperature is lower than 50 ℃, the dimension between the convex portions 75 of the resin substrate 71 is kept W1. At this time, the convex portion 75 interferes with the shrinkage of the resin substrate 71 in a state of being in contact with the inner side surface 81a of the concave portion 81 as described above, and therefore tensile stress acts on the resin substrate 71.

In addition, a case of-20 ℃ as the lower limit of the use environment temperature is considered. At this time, although the resin substrate 71 is further shrunk, the dimension change is restricted by the contact of the convex portions 75 with the inner side surfaces 81a of the concave portions 81, and therefore the dimension W1 is maintained between the convex portions 75. Therefore, according to the 2 nd diffraction element 70 of the present embodiment, the state in which the convex portions 75 are in contact with the inner side surfaces 81a of the concave portions 81 is maintained at the lower limit value (-20 ℃) of the usage environment temperature.

In addition, a case of 40 ℃ as an upper limit of the use environment temperature is considered. At this time, since the resin substrate 71 expands, the convex portion 75 is deformed in a direction away from the inner surface 81a of the concave portion 81. However, since the convex portion 75 and the concave portion 81 are designed to be in contact with each other at a temperature of 50 ℃ or lower as described above, the convex portion 75 does not separate from the inner surface 81a of the concave portion 81 unless the usage environment temperature is higher than 50 ℃. Therefore, when the usage environment temperature is 40 ℃, the resin substrate 71 is intended to expand, but the dimensional change is not more than the amount of deformation due to the thermal expansion coefficient of the holding portion 80 because the state in which the convex portion 75 is in contact with the inner side surface 81a of the concave portion 81 is maintained. Therefore, the dimension between the convex portions 75 remains W1 unchanged. Therefore, according to the 2 nd diffraction element 70 of the present embodiment, the state in which the convex portions 75 are in contact with the inner side surfaces 81a of the concave portions 81 is maintained at the upper limit value (40 ℃) of the usage environment temperature.

Further, the change in the size between the convex portions 75 in the interference exposure will be described in detail with reference to fig. 6. In fig. 6, it is assumed that the dimension between the convex portions 75 of the resin substrate 71 when interference exposure is performed without being fixed to the holding portion 80 is W2. At this time, the interference exposure expands together with the hologram material 72M, and thereby the dimension extension α between the convex portions 75 of the resin substrate 71 changes to the dimension W3. In this case, if the expanded dimension W3(W2+ α) is smaller than W1 and satisfies the relationship W3 < W1, the convex portion 75 does not separate from the inner surface 81a of the concave portion 81. Therefore, the dimension between the convex portions 75 remains W1 unchanged. Therefore, according to the 2 nd diffraction element 70 of the present embodiment, when interference exposure of the hologram layer 72 is performed, the state in which the convex portions 75 are in contact with the inner side surfaces 81a of the concave portions 81 is maintained.

The resin substrate 71 and the holding portion 80 are preferably fixed to each other by the convex portion 75 and the concave portion 81 at least 4 points or more.

Fig. 7A to 7D are diagrams illustrating arrangement examples of the convex portions 75 and the concave portions 81. Fig. 7A to 7D are views of the 2 nd diffraction element 70 when viewed from the holding portion 80 side, and for simplification, the resin substrate 71 having a curved shape and the holding portion 80 are shown in a state of being spread out in a plate shape.

As shown in fig. 7A, the convex portion 75 is formed in a frame shape along the four sides of the rectangular resin substrate 71. The recess 81 is formed in a frame shape surrounding the rectangular through hole 80a 1. According to this structure, deformation of the resin substrate 71 can be suppressed in the entire direction. Therefore, the performance degradation of the hologram layer 72 accompanying the deformation of the resin substrate 71 can be suppressed to the maximum.

As shown in fig. 7B, the convex portion 75 may be formed along a pair of short sides among the four sides of the rectangular resin substrate 71. In this case, the concave portion 81 is formed so as to extend along both sides of the rectangular through hole 80a 1. With this configuration, deformation of the resin substrate 71 on the long side, which is easily affected by dimensional changes, can be suppressed by the convex portions 75 and the concave portions 81. Further, since the convex portions 75 and the concave portions 81 are not disposed above and below the resin substrate 71 and the holding portion 80, the dimension of the 2 nd diffraction element 70 in the vertical direction can be suppressed.

As shown in fig. 7C, the convex portions 75 may be formed at four corners of the rectangular resin substrate 71. In this case, the recessed portions 81 are formed in the vicinity of four corners of the rectangular through hole 80a 1. With this configuration, deformation of the resin substrate 71 toward the long side and the short side can be suppressed.

In the case where the convex portions 75 are formed at the four corners of the resin substrate 71, as shown in fig. 7D, the pair of convex portions 75 may be arranged so as to face each other in the diagonal direction. According to this structure, deformation of the resin substrate 71 having a large size amount in the diagonal direction can be suppressed.

According to the 2 nd diffraction element 70 of the present embodiment, since the resin substrate 71 is fixed to the holding portion 80 by bringing the convex portions 75 into contact with the inner side surfaces 81a of the concave portions 81 at a temperature (50 ℃) higher than the upper limit value (40 ℃) of the use environment temperature and the exposure environment temperature (20 ℃) when interference exposure is performed, it is possible to generate tensile stress in the resin substrate 71 even at the time of interference exposure of the hologram material 72M or at the use environment temperature (-20 ℃ to 40 ℃). Therefore, even at the time of interference exposure of the hologram material 72M or at the use environment temperature (-20 ℃ to 40 ℃), the dimensional change of the resin substrate 71 can be suppressed to be equal to or more than the amount of deformation due to the thermal expansion coefficient of the holding portion 80.

Therefore, the 2 nd diffraction element 70 of the present embodiment can suppress the performance degradation of the hologram layer 72 accompanying the deformation of the resin substrate 71, and thus can obtain a desired diffraction performance. In addition, since the 2 nd diffraction element 70 of the present embodiment suppresses the performance degradation of the hologram layer 72 caused by the deformation of the resin substrate 71 at the use environment temperature (-20 ℃ to 40 ℃), a desired diffraction performance can be obtained. Therefore, as shown in fig. 3, the 2 nd diffraction element 70 of the present embodiment can efficiently condense the image light L0 to the eye E of the observer.

The 1 st diffraction element 50 having the same basic structure as the 2 nd diffraction element 70 is also constituted by a reflection type volume hologram element. Since the 1 st diffraction element 50 is manufactured by the same manufacturing method as the 2 nd diffraction element 70, the same effects as the 2 nd diffraction element 70 can be obtained. That is, the 1 st diffraction element 50 suppresses a performance decrease of the hologram layer 72 accompanying the deformation of the resin substrate 71, and thus can provide a diffraction element that obtains a desired diffraction performance.

In addition, since the 2 nd diffraction element 70 of the present embodiment uses the resin substrate 71 as a support substrate for supporting the hologram layer 72, it is a light-weight diffraction element which is less likely to be broken and has excellent durability, compared to a case where a glass substrate is used as a support substrate.

The 1 st diffraction element 50 has a concave curved surface shape in which an incident surface 50a on which the image light L0 is incident is recessed. In other words, the incident surface 50a has a shape in which the central portion is recessed and curved with respect to the peripheral portion in the incident direction of the image light L0. Therefore, as shown in fig. 3, the 1 st diffraction element 50 can efficiently deflect the image light L0 to the light guide system 60.

Fig. 8 is an explanatory diagram showing diffraction characteristics of the 1 st diffraction element 50 and the 2 nd diffraction element 70 shown in fig. 3. Fig. 8 shows a difference in diffraction angle between a specific wavelength and a peripheral wavelength when a light ray is incident on a point on the volume hologram element. In fig. 8, when the specific wavelength is 531nm, the solid line L526 indicates the deviation of the diffraction angle of light having a peripheral wavelength of 526nm, and the broken line L536 indicates the deviation of the diffraction angle of light having a peripheral wavelength of 536 nm. As shown in fig. 8, even in the case where light is incident on the same interference fringes recorded in the hologram element, light having a longer wavelength is diffracted more largely, and light having a shorter wavelength is hardly diffracted. Therefore, when 2 diffraction elements, that is, the 1 st diffraction element 50 and the 2 nd diffraction element 70 are used as in the present embodiment, if the light beams are incident without considering the angles of the light beams with respect to the long wavelength light and the short wavelength light of the specific wavelength, the wavelength compensation cannot be performed appropriately. That is, the chromatic aberration generated in the 2 nd diffraction element 70 cannot be eliminated. In addition, since the diffraction angle differs depending on the number of interference fringes, the interference fringes need to be considered.

In the optical system 10 shown in fig. 3, as described in japanese patent application laid-open No. 2017-167181, since the incident direction or the like to the 2 nd diffraction element 70 is optimized depending on whether the sum of the number of formation times of the intermediate image between the 1 st diffraction element 50 and the 2 nd diffraction element 70 and the number of reflection times of the mirror 62 is an odd number or an even number, wavelength compensation, that is, chromatic aberration can be eliminated.

Specifically, as shown in fig. 3, the image light L0 incident on the 1 st diffraction element 50 is deflected by being diffracted by the 1 st diffraction element 50. At this time, the diffraction angle θ of the light L2 with the specific wavelength being the long wavelength side₂Diffraction angle theta of light L1 with specific wavelength₁Is large. The diffraction angle θ of the light L3 having a specific wavelength on the short wavelength side₃Diffraction angle theta of light L1 with specific wavelength₁Is small. Therefore, the image light L0 emitted from the 1 st diffraction element 50 is deflected and dispersed for each wavelength.

The image light L0 emitted from the 1 st diffraction element 50 enters the 2 nd diffraction element 70 via the light guide system 60, and is diffracted and deflected by the 2 nd diffraction element 70. At this time, in the optical path from the 1 st diffraction element 50 to the 2 nd diffraction element 70, formation of the primary intermediate image is performed, and reflection by the mirror 62 is performed. Therefore, when the angle between the image light L0 and the normal to the incident surface of the 2 nd diffraction element 70 is set as the incident angle, the incident angle θ of the light L2 having a longer wavelength side than the specific wavelength is larger than the incident angle θ of the light L1 having the specific wavelength₁₁Large angle of incidence theta₁₂An incident angle theta of the light L3 with the short wavelength side relative to the light L1 with the specific wavelength is larger than that of the light L3578 with the specific wavelength₁₁Small angle of incidence theta₁₃. Further, as described above, the diffraction angle θ with respect to the light L2 having the specific wavelength on the long wavelength side₂Diffraction angle theta of light L1 with specific wavelength₁Large, diffraction angle theta with respect to light L3 with a short wavelength side of a specific wavelength₃Diffraction angle theta of light L1 with specific wavelength₁Is small.

Therefore, the light L2 having a longer wavelength than the specific wavelength enters the 1 st diffraction element 50 at a larger incident angle than the light L1 having the specific wavelength, but the diffraction angle of the light L2 having a longer wavelength than the specific wavelength is larger than the diffraction angle of the light L1 having the specific wavelength, and as a result, the light L2 having a longer wavelength than the specific wavelength and the light L1 having the specific wavelength become substantially parallel light when the light L2 and the light L1 having the specific wavelength are emitted from the 2 nd diffraction element 70. On the other hand, the light L3 on the short wavelength side of the specific wavelength enters the 1 st diffraction element 50 at an incident angle smaller than the light L1 on the specific wavelength side, but the diffraction angle with respect to the light L3 on the short wavelength side of the specific wavelength is smaller than the diffraction angle with respect to the light L1 on the specific wavelength side, and as a result, the light L3 on the short wavelength side of the specific wavelength and the light L1 on the specific wavelength become substantially parallel light when emitted from the 2 nd diffraction element 70. Thus, as shown in fig. 3, the image light L0 emitted from the 2 nd diffraction element 70 is incident on the eye E of the observer as substantially parallel light, and therefore deviation of the imaging position on the retina E0 is suppressed for each wavelength. Therefore, chromatic aberration generated in the 2 nd diffraction element 70 can be eliminated.

The 1 st diffraction element 50 and the 2 nd diffraction element 70 of the present embodiment are manufactured by the above-described manufacturing method, and therefore have interference fringes that obtain desired diffraction performance because the influence of warpage generated at the time of interference exposure can be reduced. Therefore, according to the 1 st and 2 nd diffraction elements 50 and 70 of the present embodiment, chromatic aberration can be eliminated with high accuracy as described above.

Next, the conjugate relationship between the 1 st diffraction element 50 and the 2 nd diffraction element 70 will be described.

Fig. 9A is an explanatory diagram in the case where the 1 st diffraction element 50 and the 2 nd diffraction element 70 have a conjugate relationship. Fig. 9B and 9C are explanatory diagrams in the case where the 1 st diffraction element 50 and the 2 nd diffraction element 70 do not have a conjugate relationship. Fig. 10A and 10B are explanatory diagrams showing tolerance for deviation from the conjugate relationship of the 1 st diffraction element 50 and the 2 nd diffraction element 70 shown in fig. 9B and 9C. In fig. 10A and 10B, light having a specific wavelength is indicated by a solid line Le, light having a wavelength of-10 nm is indicated by a one-dot chain line Lf, and light having a wavelength of +10nm is indicated by a two-dot chain line Lg. In fig. 9A to 9C, 10A, and 10B, in order to facilitate understanding of the light traveling, the 1 st diffraction element 50, the 2 nd diffraction element 70, and the light guide system 60 are illustrated as transmissive type, and the 1 st diffraction element 50, the 2 nd diffraction element 70, and the light guide system 60 are illustrated by arrows.

As shown in fig. 9A, when the 1 st diffraction element 50 and the 2 nd diffraction element 70 are in a conjugate relationship, divergent light emitted from the point a (1 st position) of the 1 st diffraction element 50 is condensed by the light guide system 60 having positive refractive power, and enters the point B (the 2 nd position corresponding to the 1 st position) of the 2 nd diffraction element 70. Therefore, chromatic aberration caused by diffraction generated at the point B can be compensated for at the point a.

On the other hand, as shown in fig. 9B and 9C, when the 1 st diffraction element 50 and the 2 nd diffraction element 70 do not have a conjugate relationship, the divergent light emitted from the point a of the 1 st diffraction element 50 is condensed by the light guide system 60 having positive refractive power at the center, but enters at a position farther than the point B or a position closer to the point B on the 2 nd diffraction element 70 so as to intersect with each other. Therefore, the point a and the point B are not in a 1-to-1 relationship. Here, since the compensation effect is improved when the interference fringes in the region are uniform, the compensation effect is weakened when the 1 st diffraction element 50 and the 2 nd diffraction element 70 do not have a conjugate relationship. On the other hand, it is difficult to compensate the entire projection area of the 2 nd diffraction element 70 by the 1 st diffraction element 50. Therefore, in the case of the systems shown in fig. 9B and 9C, since sufficient wavelength compensation cannot be performed, the resolution deteriorates.

In addition, although there is an error of about ± 0.4mm with respect to the point B reached by the light having the specific wavelength, with respect to the light having the wavelength of ± 10nm with respect to the specific wavelength, the resolution is not significantly reduced. As a result of examining this allowable range, as shown in fig. 10A, when the light beam having a specific wavelength intersects at a position in front of the point B on the ideal 2 nd diffraction element 70 and enters a range of ± 0.8mm, the resolution is not significantly reduced. As shown in fig. 10B, when the light having a specific wavelength intersects at a position rearward of the point B on the ideal 2 nd diffraction element 70 and enters the range of ± 0.8mm, the resolution is not significantly reduced. Therefore, in the case where the 1 st diffraction element 50 and the 2 nd diffraction element 70 are in a substantially conjugate relationship, if not in a complete conjugate relationship, and reach a range of ± 0.8mm from the ideal B point, a decrease in resolution can be tolerated. That is, in the present embodiment, the fact that the 1 st diffraction element 50 and the 2 nd diffraction element 70 have the conjugate relationship means that the incident position of the light of the specific wavelength is within an error range of ± 0.8mm with respect to the ideal incident point.

Fig. 11 is a light ray diagram in the optical system 10 of the present embodiment. In fig. 11, the optical portions arranged along the optical axis are indicated by thick arrows. The light rays emitted from 1 pixel of the image light generation device 31 are indicated by solid lines La, the principal light rays emitted from the end of the image light generation device 31 are indicated by dashed lines Lb, and the positions having a conjugate relationship with the 1 st diffraction element 50 are indicated by long dashed lines Lc. Here, the "intermediate image" refers to a portion where light rays (solid line La) emitted from 1 pixel converge, and the "pupil" refers to a portion where principal light rays (one-dot chain line Lb) of each angle of view converge. Fig. 11 shows the progress of light emitted from the image light generation device 31. In fig. 11, all optical portions are illustrated as transmissive for the sake of simplicity.

As shown in fig. 11, in the optical system 10 of the present embodiment, along the optical path of the image light emitted from the image light generation device 31, a1 st optical portion L10 having positive power, a 2 nd optical portion L20 having a1 st diffractive element 50 and having positive power, a 3 rd optical portion L30 having positive power, and a 4 th optical portion L40 having a 2 nd diffractive element 70 and having positive power are provided.

The focal length of the 1 st optical part L10 is L/2, and the focal lengths of the 2 nd optical part L20, the 3 rd optical part L30 and the 4 th optical part L40 are all L. Therefore, the optical distance from the 2 nd optical portion L20 to the 3 rd optical portion L30 is equal to the optical distance from the 3 rd optical portion L30 to the 4 th optical portion L40.

In the optical system 10, a1 st intermediate image P1 of the image light is formed between the 1 st optical portion L10 and the 3 rd optical portion L30, a pupil R1 is formed between the 2 nd optical portion L20 and the 4 th optical portion L40, a 2 nd intermediate image P2 of the image light is formed between the 3 rd optical portion L30 and the 4 th optical portion L40, and the 4 th optical portion L40 makes the image light parallel to actinic rays to form an exit pupil R2. At this time, the 3 rd optical portion L30 freely controls the image light emitted from the 2 nd optical portion L20 to be divergent light, convergent light, or parallel light, and enters the 4 th optical portion L40. The 2 nd optical portion L20 causes the image light emitted from the 1 st optical portion L10 to enter the 3 rd optical portion L30 as convergent light. In the optical system 10 of the present embodiment, the pupil R1 is formed in the vicinity of the 3 rd optical portion L30 between the 2 nd optical portion L20 and the 4 th optical portion L40. The vicinity of the 3 rd optical portion L30 is a position between the 2 nd optical portion L20 and the 3 rd optical portion L30 closer to the 3 rd optical portion L30 than the 2 nd optical portion L20, or a position between the 3 rd optical portion L30 and the 4 th optical portion L40 closer to the 3 rd optical portion L30 than the 4 th optical portion L40.

In addition, for the 1-point image light from the image light generation device 31, the 3 rd optical portion L30 causes the light of the peripheral wavelength deflected by the 1 st diffraction element 50 and shifted from the specific wavelength to enter the predetermined range of the 2 nd diffraction element 70. That is, the 1 st diffraction element 50 and the 2 nd diffraction element 70 have a conjugate or substantially conjugate relationship. Here, the absolute value of the magnification of the projection formed by the 1 st diffraction element 50 on the 2 nd diffraction element 70 via the 3 rd optical portion L30 is 0.5 times to 10 times, and the absolute value of the magnification is preferably 1 time to 5 times.

Therefore, according to the optical system 10 of the present embodiment, the 1 st intermediate image P1 of the image light is formed between the projection optical system 32 and the light guide system 60, the pupil R1 is formed in the vicinity of the light guide system 60, the 2 nd intermediate image P2 of the image light is formed between the light guide system 60 and the 2 nd diffractive element 70, and the 2 nd diffractive element 70 makes the image light parallel-actinic to form the exit pupil R2.

In the optical system 10 of the present embodiment, the 1 st intermediate image P1 is formed between the 1 st optical portion L10 (projection optical system 32) and the 2 nd optical portion L20 (1 st diffractive element 50).

According to the optical system 10 of the present embodiment, 4 conditions (conditions 1, 2, 3, and 4) shown below are satisfied.

Condition 1: the light emitted from a point of the image light generating means 31 is imaged as a point on the retina E0.

Condition 2: the entrance pupil of the optical system is conjugate to the pupil of the eyeball.

Condition 3: the 1 st diffraction element 50 and the 2 nd diffraction element 70 are appropriately configured to compensate for the peripheral wavelength.

Condition 4: the 1 st diffraction element 50 and the 2 nd diffraction element 70 have a conjugate or substantially conjugate relationship.

More specifically, as is clear from the solid line La shown in fig. 11, the light ray emitted from 1 point of the image light generation device 31 satisfies the condition 1 that the light ray is imaged as 1 point on the retina E0, and therefore the observer can see 1 pixel. As is clear from the solid line La shown in fig. 11, since the condition 2 that the entrance pupil of the optical system 10 and the pupil E1 of the eye E have a conjugate (conjugate of pupil) is satisfied, the entire region of the image generated by the image light generation device 31 can be seen. Further, since the condition 3 that the 1 st diffraction element 50 and the 2 nd diffraction element 70 are appropriately arranged to compensate for the peripheral wavelengths is satisfied, chromatic aberration generated in the 2 nd diffraction element 70 can be eliminated by performing the wavelength compensation. As is clear from the long broken line Lc shown in fig. 11, since the condition 4 that the 1 st diffraction element 50 and the 2 nd diffraction element 70 have a conjugate or substantially conjugate relationship is satisfied, the 1 st diffraction element 50 and the 2 nd diffraction element 70 can cause light to enter the same portion of the interference fringes, and wavelength compensation can be appropriately performed. Therefore, deterioration in resolution of the image light can be suppressed.

Therefore, according to the optical system 10 of the present embodiment, it is possible to make the observer view a good image with the resolution degradation suppressed by appropriately performing the wavelength compensation. The optical system 10 of the present embodiment includes the 1 st diffraction element 50 and the 2 nd diffraction element 70 which are lightweight and have excellent impact resistance by using a plastic substrate as a support. Therefore, the optical system 10 of the present embodiment is lightweight and excellent in impact resistance, and is therefore suitable for use as an optical system of the display device 100 to be worn on the head of an observer.

(embodiment 2)

Next, the optical system of embodiment 2 will be explained. The present embodiment differs from embodiment 1 in the ambient temperature in the step of bringing the resin substrate into contact with the holding portion. The same components as those in embodiment 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

In this embodiment, the description will be given by taking the structure of the 2 nd diffraction element as an example, but the same can be said for the 1 st diffraction element.

Fig. 12 is a sectional view showing a main part structure of the 2 nd diffraction element of the present embodiment. FIG. 12 shows the state of the 2 nd diffraction element at the use environment temperature (-20 ℃ C. to 40 ℃ C.).

As shown in fig. 12, in the 2 nd diffraction element 170 of the present embodiment, the resin substrate 71 is attached to the holding portion 80 in a state where the convex portion 75 abuts against the outer side surface 81b of the concave portion 81 at the use environment temperature (-20 ℃ to 40 ℃) and the expansion force that tends to expand the resin substrate 71 itself is inhibited. In the present embodiment, the resin substrate 71 is fixed to the holding portion 80 in a state where a compressive stress acts thereon. The convex portion 75 and the concave portion 81 are pressed against each other.

Next, a method for manufacturing the 2 nd diffraction element 170 will be described with reference to the drawings.

Fig. 13A and 13B are diagrams illustrating a manufacturing process of the 2 nd diffraction element 170.

First, as shown in fig. 13A, the resin substrate 71 having the hologram material 72M adhered to the outer surface 71b is attached to the holding portion 80 in a state where the ambient temperature is set to-50 ℃.

Subsequently, the ambient temperature was returned to 20 ℃ at which the interference exposure was performed. At this time, the resin substrate 71 having a large thermal expansion coefficient expands more greatly than the holding portion 80 having a small thermal expansion coefficient as the ambient temperature increases. For example, when the ambient temperature rises to about-30 ℃, as shown in fig. 13B, the convex portion 75 of the resin substrate 71 comes into contact with the outer side surface 81B of the concave portion 81 in the holding portion 80. When the ambient temperature is higher than-30 ℃, the resin substrate 71 is intended to expand further, but the resin substrate 71 cannot expand due to the contact of the convex portions 75 with the concave portions 81 of the holding portion 80. That is, when the ambient temperature is-30 ℃ or higher, the compressive stress S2 acts on the resin substrate 71.

As described above, the manufacturing method of the present embodiment includes the following step 1: the convex portion 75 is brought into contact with the inner surface 81a of the concave portion 81 in an environment of-30 ℃ which is lower than either of the lower limit (-20 ℃) and the exposure environment temperature (20 ℃) of the use environment temperature of the display device 100.

Next, the holographic material 72M was subjected to interference exposure at an ambient temperature of 20 ℃. In the manufacturing method of the present embodiment, the convex portion 75 and the concave portion 81 are fitted so as to press each other, and a compressive stress S2 is generated in the resin substrate 71 in which the resin substrate 71 is intended to be deformed due to expansion or contraction of the hologram material 72M at the time of interference exposure. Therefore, as long as the state in which the convex portion 75 abuts against the outer side surface 81b of the concave portion 81 is maintained, the resin substrate 71 is restrained by the holding portion 80 without dimensional change. Therefore, since the interference fringes 74 are formed in the hologram layer 72 in a state where the deformation of the resin substrate 71 is suppressed, the performance degradation of the hologram layer 72 accompanying the deformation of the resin substrate 71 can be suppressed.

As described above, the 2 nd diffraction element 170 of the present embodiment is manufactured by bringing the convex portions 75 into contact with the outer side surfaces 81b of the concave portions 81 and fixing the resin substrate 71 to the holding portion 80 at a temperature (-30 ℃) lower than the lower limit value (-20 ℃) of the use environment temperature of the display device 100 and the exposure environment temperature (20 ℃) when interference exposure is performed.

In the 2 nd diffraction element 170 of the present embodiment, for example, at 40 ℃.

In the diffraction element 170 of the 2 nd embodiment, the resin substrate 71 contracts at-20 ℃, which is the lower limit of the usage environment temperature, and the convex portions 75 are intended to be deformed in a direction away from the outer side surfaces 81b of the concave portions 81. However, since the convex portion 75 and the concave portion 81 are designed to abut at-30 ℃ as described above, the convex portion 75 does not separate from the outer surface 81b of the concave portion 81 unless the usage environment temperature is lower than-30 ℃. Therefore, when the use environment temperature is-20 ℃, the resin substrate 71 is intended to contract, but the dimensional change is not more than the deformation amount due to the thermal expansion coefficient of the holding portion 80 because the state in which the convex portion 75 is in contact with the outer side surface 81b of the concave portion 81 is maintained.

Therefore, according to the 2 nd diffraction element 170 of the present embodiment, since the convex portions 75 are brought into contact with the outer side surfaces 81b of the concave portions 81 and the resin substrate 71 is fixed to the holding portions 80 at a temperature (-30 ℃) lower than the lower limit value (-20 ℃) of the use environment temperature and the exposure environment temperature (20 ℃) when the interference exposure is performed, the resin substrate 71 can be subjected to a compressive stress even at the time of the interference exposure of the hologram material 72M or at the use environment temperature (-20 ℃ to 40 ℃). Therefore, even at the time of interference exposure of the hologram material 72M or at the use environment temperature (-20 ℃ C. to 40 ℃ C.), the dimensional change of the resin substrate 71 is suppressed to be not less than the amount of deformation due to the thermal expansion coefficient of the holding portion 80.

Therefore, the 2 nd diffraction element 170 of the present embodiment suppresses the performance degradation of the hologram layer 72 accompanying the deformation of the resin substrate 71, and thus can obtain a desired diffraction performance. Therefore, according to the 2 nd diffraction element 170 of the present embodiment, as shown in fig. 3, the image light L0 can be efficiently condensed toward the eye E of the observer.

The above embodiment is a preferred embodiment of the present invention, and the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the case where the convex portion 75 formed on the resin substrate 71 and the concave portion 81 formed on the holding portion 80 are fitted is described as an example, but the convex portion formed on the holding portion 80 may be fitted into the concave portion formed on the resin substrate 71.

The method of fixing the resin substrate 71 and the holding portion 80 is not limited to the configuration using the convex portion 75 and the concave portion 81. Fig. 14 is a sectional view showing a fixing structure of a modification.

As shown in fig. 14, for example, the resin substrate 71 and the holding portion 180 may be fixed by bringing the outer peripheral surface 180a of the circular frame-shaped holding portion 180 into contact with the inner side surface 75a of the circular cylindrical projection 75. In this case, one of the side surface 75a of the convex portion 75 and the outer peripheral surface 180a of the holding portion 180 constitutes a contact surface, and the other of the side surface 75a and the outer peripheral surface 180a constitutes a pressing surface. The planar shapes of the holding portion 180 and the projection 75 are not particularly limited, and may be formed into a quadrangular frame shape, for example.

In the above-described embodiments, the reflection type volume hologram element was described as an example, but the present invention can also be applied to a transmission type volume hologram element.

In the above embodiment, the holding portion 80 supports the viewer side (inner surface 71a) of the resin substrate 71, but the holding portion 80 may support the hologram layer 72 side of the resin substrate 71. If the holding portion 80 is provided so as to support the hologram layer 72 side in this manner, deformation of the hologram layer 72 during exposure interference is further suppressed.

In the above embodiment, the holding portion 80 is made of super-invar steel as an example, but a metal having a small thermal expansion coefficient and a large elastic modulus, such as titanium, stainless steel, or aluminum, may be used as the material of the holding portion 80 as compared with the resin substrate 71. In addition, a plastic filled with a filler such as silica may be used.