Patent Publication Number: US-2023133805-A1

Title: Optical device, method for manufacturing optical device, and image display device

Description:
TECHNICAL FIELD 
     The present technology relates to an optical device, a method for manufacturing the optical device, and an image display device. 
     BACKGROUND ART 
     In recent years, attention has been focused on a technology related to a display (for example, a head-mounted display (HMD)) that displays an image from an image forming apparatus on an optical device disposed in front of an observer&#39;s eyes. 
     For example, Patent Document 1 proposes a technology related to a display including a flat optical waveguide portion, an input diffraction grating, an intermediate diffraction grating, and an output diffraction grating. In this technology, the input diffraction grating is positioned to be entirely positioned in a geographical area of the intermediate diffraction grating, and a grating vector of the input diffraction grating and a grating vector of the intermediate diffraction grating are oriented in different directions. 
     CITATION LIST 
     Patent Document 
     Patent Document 1: Japanese Published Patent Publication No. 2017-504063 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, in the technology proposed in Patent Document 1, it is sometimes difficult to make the sum of the grating vectors of diffraction gratings (optical elements) formed in the optical waveguide portion (light guide plate) zero, and there is a possibility that further improvement of optical characteristics cannot be achieved. 
     In this regard, the present technology has been made in view of such a situation, and a main object of the present technology is to provide an optical device capable of easily making a sum of grating vectors of optical elements disposed on a light guide plate zero and realizing further improvement of optical characteristics, a method for manufacturing the optical device, and an image display device including the optical device. 
     Solutions to Problems 
     As a result of intensive studies to solve the above-described object, the present inventors have surprisingly succeeded in realizing further improvement of optical characteristics and have completed the present technology. 
     That is, in a first aspect according to the present technology, 
     there is provided an optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; and 
     an output optical element that is disposed on the light guide plate and emits light propagated by total reflection in the light guide plate, to an outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the input optical element, and 
     the first optical element and the input optical element are disposed to face each other with the second optical element interposed therebetween. 
     The optical device according to the first aspect of the present technology further may include: 
     a plurality of the first optical elements; a plurality of the input optical elements; a plurality of the second optical elements; and a plurality of the output optical elements. 
     Each of the plurality of first optical elements, the plurality of input optical elements, the plurality of second optical elements, and the plurality of output optical elements may have a laminated structure. 
     In the optical device according to the first aspect of the present technology, 
     the light guide plate may have a first surface and a second surface facing the first surface, 
     the first optical element, the input optical element, and the output optical element may be disposed on the first surface of the light guide plate, and 
     the second optical element may be disposed on the second surface of the light guide plate. 
     The optical device according to the first aspect of the present technology further may include: 
     a plurality of the first optical elements; a plurality of the input optical elements; a plurality of the second optical elements; and a plurality of the output optical elements. 
     The input optical element, the second optical element, and the first optical element may be disposed in this order on the light guide plate, 
     one set including the input optical element, the second optical element, and the first optical element may be repeatedly disposed, and 
     the plurality of output optical elements may have a laminated structure. 
     The optical device according to the first aspect of the present technology further may include: 
     a plurality of the first optical elements; and a plurality of the input optical elements. 
     The plurality of first optical elements and the plurality of input optical elements may be disposed to face each other with the second optical element interposed therebetween. 
     In the optical device according to the first aspect of the present technology, 
     the light guide plate may have a first surface and a second surface facing the first surface, 
     the input optical element may be disposed on the first surface of the light guide plate, 
     the first optical element may be disposed on the second surface of the light guide plate, 
     the second optical element may be disposed in the light guide plate, and 
     the first optical element and the input optical element may be disposed to face each other with the second optical element interposed therebetween. 
     Furthermore, in a second aspect according to the present technology, 
     there is provided an optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; and 
     an output optical element that is disposed on the light guide plate and emits light propagated by total reflection in the light guide plate, to an outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the output optical element, and 
     the first optical element and the output optical element are disposed to face each other with the second optical element interposed therebetween. 
     In the optical device according to the first aspect and the optical device according to the second aspect of the present technology, 
     the input optical element may include a light reflecting member. 
     In the optical device according to the first aspect and the optical device according to the second aspect of the present technology, 
     the second optical element may be a reflection type or transmission type volume hologram. 
     Further, in a third aspect according to the present technology, 
     provided an optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; 
     a third optical element that is disposed on the light guide plate; and 
     an output optical element that is disposed on the light guide plate and emits light propagated, by total reflection, in the light guide plate to the outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the second optical element, 
     the third optical element has substantially the same grating vector as a grating vector of the input optical element, and 
     the first optical element and the third optical element, and the second optical element and the input optical element are disposed to face each other with the output optical element interposed therebetween. 
     In the optical device according to the third aspect of the present technology, the input optical element may include a light reflecting member. 
     In the optical device according to the third aspect of the present technology, the output optical element may be a reflection type or transmission type volume hologram. 
     In a fourth aspect according to the present technology, there is provided an image display device including: 
     an image forming apparatus; and 
     an optical device where light emitted from the image forming apparatus is incident, guided, and emitted, in which 
     the optical device includes the optical device of the first aspect according to the present technology, the optical device of the second aspect according to the present technology, or the optical device of the third aspect according to the present technology. 
     Furthermore, in a fifth aspect according to the present technology, 
     there is provided a method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the input optical element; 
     forming an output optical element on the light guide plate; and 
     forming a second optical element by using an interference between first diffracted light obtained when reference light having a substantially opposite vector to a vector included in reproduction reference light is incident on the first optical element and second diffracted light obtained when object light having a substantially opposite vector to a vector included in reproduction light is incident on the output optical element. 
     In a sixth aspect according to the present technology, 
     there is provided a method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming an output optical element on the light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the output optical element; and 
     forming a second optical element by using an interference between third diffracted light obtained when object light having substantially the same vector as a vector of reproduction light is incident on the first optical element and fourth diffracted light obtained when reference light having substantially the same vector as a vector of reproduction reference light is incident on the input optical element. 
     In a seventh aspect according to the present technology, 
     there is provided a method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming a second optical element on the light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the second optical element; 
     forming a third optical element on the light guide plate, the third optical element having substantially the same grating vector as a grating vector of the input optical element; and 
     forming an output optical element by using an interference between fifth diffracted light, which is obtained when reference light having a substantially opposite vector to a vector of reproduction reference light is incident on the third optical element, and light emitted from the third optical element is incident on the first optical element, and object light having a substantially opposite vector to the vector of the reproduction light. 
     According to the present technology, the sum of the grating vectors of the optical elements disposed on the light guide plate can be easily made zero, and the optical characteristics can be further improved. Note that the effects described herein are not necessarily limited, and may be any of the effects described in the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a diagram illustrating a configuration example of an optical device of a first embodiment to which the present technology is applied. 
         FIG.  2    is a diagram illustrating a configuration example of an image display device (reproduction optical system) of an eighth embodiment including the optical device of the first embodiment to which the present technology is applied. 
         FIG.  3    is a diagram for explaining that light (light beam) emitted from an image forming apparatus (light source) is incident on a light source device of the first embodiment to which the present technology is applied, is guided in the light source device, and is emitted to the outside of the light source device. 
         FIG.  4    is a diagram illustrating a grating vector formed in the image display device (reproduction optical system) of the eighth embodiment illustrated in  FIGS.  2  and  3   . 
         FIG.  5    is a diagram illustrating an example of an optical path of an input optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  6 ( a )  is a diagram illustrating an example of the optical path of the input optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  6 ( b )  is a vector diagram of the optical path of the input optical element illustrated in  FIG.  6 ( a ) . 
         FIG.  7 ( a )  is a diagram illustrating an example of the optical path of the input optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  7 ( b )  is a vector diagram of the optical path of the input optical element illustrated in  FIG.  7 ( a ) . 
         FIG.  8 ( a )  is a diagram illustrating an example of the optical path of the input optical element included in the optical device of the first embodiment to which the present technology is applied,  FIG.  8 ( b )  is a vector diagram of the optical path of the input optical element illustrated in  FIG.  8 ( a ) , and  FIG.  8 ( c )  is a vector diagram of the optical path of the input optical element illustrated in  FIG.  8 ( a ) . 
         FIG.  9    is a diagram illustrating an example of an optical path of a second optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  10 ( a )  is a diagram illustrating an example of the optical path of the second optical element included in the optical device of the first embodiment to which the present technology is applied,  FIG.  10 ( b )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  10 ( a ) , and  FIG.  10 ( c )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  10 ( a ) . 
         FIG.  11 ( a )  is a diagram illustrating an example of the optical path of the second optical element included in the optical device of the first embodiment to which the present technology is applied,  FIG.  11 ( b )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  11 ( a ) , and  FIG.  11 ( c )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  11 ( a ) . 
         FIG.  12    is a diagram illustrating an example of the optical path of the second optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  13 ( a )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  12   ,  FIG.  13 ( b )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  12   , and  FIG.  13 ( c )  is a vector diagram of the optical path of the second optical element illustrated in  FIG.  12   . 
         FIG.  14    is a diagram illustrating an example of an optical path of an output optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  15 ( a )  is a diagram illustrating an example of the optical path of the output optical element included in the optical device of the first embodiment to which the present technology is applied,  FIG.  15 ( b )  is a vector diagram of the optical path of the output optical element illustrated in  FIG.  15 ( a ) , and  FIG.  15 ( c )  is a vector diagram of the optical path of the output optical element illustrated in  FIG.  15 ( a ) . 
         FIG.  16    is a diagram illustrating an example of a production optical path from the output optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  17 ( a )  is a diagram illustrating an example of the production optical path from the output optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  17 ( b )  is a vector diagram of the production optical path from the output optical element illustrated in  FIG.  17 ( a ) . 
         FIG.  18 ( a )  is a diagram illustrating an example of the production optical path from the output optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  18 ( b )  is a vector diagram of the production optical path from the output optical element illustrated in  FIG.  18 ( a ) . 
         FIG.  19    is a diagram illustrating an example of the production optical path from the output optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  20 ( a )  is a vector diagram of the production optical path from the output optical element illustrated in  FIG.  19   ,  FIG.  20 ( b )  is a vector diagram of the production optical path from the output optical element illustrated in  FIG.  19   , and  FIG.  20 ( c )  is a vector diagram of the production optical path from the output optical element illustrated in  FIG.  19   . 
         FIG.  21    is a diagram illustrating an example of a production optical path from a first optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  22 ( a )  is a diagram illustrating an example of the production optical path from the first optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  22 ( b )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  22 ( a ) . 
         FIG.  23 ( a )  is a diagram illustrating an example of the production optical path from the first optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  23 ( b )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  23 ( a ) . 
         FIG.  24    is a diagram illustrating an example of the production optical path from the first optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  24 ( b )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  24 ( a ) . 
         FIG.  25    is a diagram illustrating an example of the production optical path from the first optical element included in the optical device of the first embodiment to which the present technology is applied, and  FIG.  25 ( b )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  25 ( a ) . 
         FIG.  26    is a diagram illustrating an example of the production optical path from the first optical element included in the optical device of the first embodiment to which the present technology is applied. 
         FIG.  27 ( a )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  26   ,  FIG.  27 ( b )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  26   , and  FIG.  27 ( c )  is a vector diagram of the production optical path from the first optical element illustrated in  FIG.  26   . 
         FIG.  28    is a vector diagram at the time of producing the second optical element. 
         FIG.  29    is a diagram illustrating a configuration example of an optical device of a second embodiment to which the present technology is applied. 
         FIG.  30    is a diagram illustrating a configuration example of an optical device of a third embodiment to which the present technology is applied. 
         FIG.  31    is a diagram illustrating a configuration example of an optical device of a fourth embodiment to which the present technology is applied. 
         FIG.  32    is a diagram illustrating a configuration example of an optical device of a fifth embodiment to which the present technology is applied. 
         FIG.  33 ( a )  is a diagram illustrating a configuration example of an optical device of a sixth embodiment to which the present technology is applied, and  FIG.  33 ( b )  is a diagram illustrating a configuration example of an optical device of a seventh embodiment to which the present technology is applied. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, preferred modes for carrying out the present technology will be described. An embodiment described below illustrates an example of a representative embodiment of the present technology, and the scope of the present technology is not narrowly interpreted by the embodiment. Note that in the description using the drawings, the same or equivalent elements or members are denoted by the same reference sign, and redundant description is omitted. Furthermore, the size of the circle illustrated in each vector diagram merely represents a reference for comparing the sizes of a plurality of vectors in the one diagram, and does not represent a reference for comparing the sizes of a plurality of vectors between the diagrams. 
     Note that the description will be given in the following order. 
     1. Outline of Present Technology 
     2. First embodiment (Example 1 of Optical Device and Example 1 of Method for Manufacturing Optical Device) 
     3. Second Embodiment (Example 2 of Optical Device) 
     4. Third Embodiment (Example 3 of Optical Device) 
     5. Fourth Embodiment (Example 4 of Optical Device) 
     6. Fifth Embodiment (Example 5 of Optical Device) 
     7. Sixth Embodiment (Example 6 of Optical Device and Example 2 of Method for Manufacturing Optical Device) 
     8. Seventh Embodiment (Example 7 of Optical Device and Example 3 of Method for Manufacturing Optical Device) 
     9. Eighth Embodiment (Example of Image Display Device) 
     1. Outline of Present Technology 
     First, an outline of the present technology will be described. The present technology relates to an optical device, a method for manufacturing the optical device, and an image display device. 
     First, an example of a technology different from the present technology will be described. 
     As Example 1 of the different technology, there is a technology for reducing deterioration of optical characteristics such as a monochrome eccentric aberration and a diffraction chromatic aberration in a light guide plate. 
     In Example 1, reflection type volume holographic gratings which capture and emit light in the light guide plate are arranged symmetrically with a predetermined symmetry plane interposed therebetween, thereby compensating for aberration due to diffraction and reducing the deterioration of optical characteristics. When the symmetric relationship is broken, the compensation effect is lost, and the optical characteristics are deteriorated. It is not clear how to realize the symmetrical arrangement. 
     As Example 2 of the different technology, there is a technology of obtaining a wide viewing angle in a single plate full color in the light guide plate. 
     Example 2 includes a design for achieving a large FoV (for example, 45×30°) in a single waveguide for a plurality of different wavelengths. The sum of grating vectors of diffractive optical elements (DOEs) formed on the light guide plate (waveguide) becomes zero. However, it is not clear how to close the grating vector. 
     As Example 3 of the different technology, there is a technology of adjusting the grating vector while aligning the grating vector at the time of producing a sample in the light guide plate. 
     Example 3 is a technology of a method of adjusting each grating vector in a so-called biaxial light guide system. Furthermore, there is also a technology of trying to reduce the misalignment of the grating vector by pressing one overall grating structure having a common orientation. However, in the above-described method, it is necessary to change the direction of the vector with a mirror, and it is necessary to prepare a highly accurate reflection surface at a waveguide end. In this regard, in Example 3, a diffractive optical element (DOE) structure necessary for input is produced from the back surface of the light guide plate (mirror is unnecessary), a plurality of light beams is guided at the time of production, and an alignment is performed while observing the state of the emitted light, thereby reducing the misalignment and suppressing the deterioration of optical characteristics. 
     As described above, there is a technology of suppressing aberration in the light guide plate by arranging reflection type volume holograms symmetrically with respect to the predetermined symmetry plane. Furthermore, there is a technology that can realize a single plate, a full color, and a high viewing angle by making the sum of grating vectors of the DOEs arranged on the light guide plate zero. In addition, in order to reduce luminance unevenness and color unevenness, there is a technology of continuously changing the inclination of an interference fringe to satisfy the Bragg condition. 
     In these technologies, a desired effect can be obtained by making an arrangement such that the sum of the grating vectors of the optical elements formed on the light guide plate becomes zero. However, a specific method for realizing the sum of the grating vectors to be zero is not clear in each technology. In order to realize the sum of the grating vectors to be zero, a technology of producing the grating vector with high accuracy and a technology of aligning a relative positional relationship with each grating vector are required, and there are many cases where it is difficult to form the volume hologram and the DOE. 
     As described above, as a technology for reducing the misalignment of the grating vectors, there is a technology for forming the DOE while observing reproduction light. By using a UV (ultraviolet) curable resin and an imprinting process, an alignment is made in an uncured state, and curing is performed to form the grating vector. However, a high alignment accuracy is still required. In addition, in the imprinting process, it is necessary to peel off an original plate after the alignment, and it is conceivable that the original plate is displaced from an alignment position in the process. Therefore, there are many cases where it is difficult to apply the technology to a complex shape such as an oblique interference fringe that is difficult to demold. 
     The present technology has been made in view of the above circumstances. 
     In the present technology, an input optical element, a second optical element (referred to as an intermediate grating in some cases) (the same applies hereinafter), an output optical element, and a first optical element are disposed on the light guide plate. Then, at least one optical element among the input optical element, the second optical element, the output optical element, and the first optical element may be formed as a separate element on the light guide plate or may be formed as an element (for example, an element including an uneven portion formed on the light guide plate) integrated with the light guide plate. 
     In the present technology, the first optical element may have substantially the same grating vector as the grating vector of the input optical element and be disposed to face the input optical element with the second optical element interposed therebetween. At this time, it is not necessary to make a symmetrical arrangement, and it is sufficient if the arrangement is made such that the vectors of the light introduced into the light guide plate overlap each other on the second optical element by the input optical element and the first optical element. Furthermore, in the present technology, the first optical element may have substantially the same grating vector as the grating vector of the output optical element and be disposed to face the output optical element with the second optical element interposed therebetween, or the first optical element may have substantially the same grating vector as the grating vector of the second optical element and be disposed to face the second optical element with the output optical element interposed therebetween. 
     Further, in the present technology, for example, the second optical element may include a volume hologram, and in this case, and each optical element except the second optical element is not limited as long as it is possible to totally reflect light in the light guide plate and emit the light to the outside of the light guide plate. The input optical element and the first optical element (referred to as a production optical element in some cases) are desirably elements having high coupling efficiency of light to the light guide plate, and are desirably diffraction elements in which a metal film is deposited on the DOE. Then, the sum of the grating vectors by the second optical element, the input optical element, and the output optical element is zero (the grating vectors are closed). Furthermore, in the present technology, for example, the output optical element may include a volume hologram, and in that case, a reflection type volume hologram is desirable in order to prevent stray light due to external light. 
     As a material (a photopolymer material configuring a photosensitive material precursor layer before irradiation with object light and reference light) configuring the volume hologram, any photopolymer material can be used as long as the material includes at least a photopolymerizable compound, a binder resin, and a photopolymerization initiator. 
     As the photopolymerizable compound, for example, known photopolymerizable compounds such as an acrylic monomer, a methacrylic monomer, a styrene monomer, a butadiene monomer, a vinyl monomer, and an epoxy monomer can be used. The compounds may be copolymers or may be monofunctional or polyfunctional. Furthermore, these monomers may be used alone or in combination. Also for the binder resin, any known binder resin can be used, and specific examples thereof include a cellulose acetate resin, an acrylic resin, an acrylic acid ester resin, a methacrylic acid resin, an epoxy resin, a urethane resin, a polypropylene resin, a polyvinyl ether resin, a polycarbonate resin, a polyamide resin, polyvinyl acetate, a vinyl chloride resin, a urea resin, a styrene resin, a butadiene resin, a natural rubber resin, polyvinyl carbazole, polyethylene glycol, a phenol resin, or a copolymer or gelatin thereof. 
     The binder resins may be used alone or in combination. Also for the photopolymerization initiator, any known photopolymerization initiator can be used. 
     The photopolymerization initiator may be used alone, in combination of a plurality of photopolymerization initiators, or in combination with a plurality of or a single photosensitizing dye. 
     A plasticizer, a chain transfer agent, and other additives may be appropriately added to the photosensitive material precursor layer. As a material configuring the protective layer for protecting a volume hologram diffraction grating, any material can be used as long as the material is transparent, and the material may be formed by coating, or a previously formed film may be laminated on the photosensitive material precursor layer. Examples of a material configuring the protective layer include a polyvinyl alcohol (PVA) resin, an acrylic resin, a polyurethane resin, a polyethylene terephthalate (PET) resin, a triacetyl cellulose (TAC) resin, a polymethyl methacrylate (PMMA) resin, a polypropylene resin, a polycarbonate resin, and a polyvinyl chloride resin. 
     According to the present technology, a structure in which the sum of the grating vectors of the optical elements becomes zero with respect to the reproduction reference light used at the time of reproduction can be produced in a self-forming manner. As a result, the present technology can realize excellent optical characteristics capable of reducing luminance unevenness, color unevenness, and the like without image quality degradation due to grating vector misalignment. Furthermore, according to the present technology, there is no process of aligning the grating vectors, and thus a manufacturing takt time can be shortened as compared with the prior art, and both high quality and low cost can be realized. 
     Note that the present technology may be applied not only to the biaxial light guide system but also to a uniaxial light guide system. In a case where the present technology is applied to the uniaxial light guide system, the first optical element, the input optical element, and the output optical element can be used in the optical device according to the present technology. 
     Next, specific embodiments for carrying out the present technology will be described in detail with reference to the drawings. First to eighth embodiments described below are examples of a representative embodiment of the present technology, and the scope of the present technology is not narrowly interpreted by these embodiments. 
     2. First Embodiment (Example 1 of Optical Device and Example of Method for Manufacturing Optical Device) 
     An optical device and a method for manufacturing the optical device according to a first embodiment (Example 1 of the optical device and an example of the method for manufacturing the optical device) according to the present technology will be described with reference to  FIGS.  1  to  28   . 
     First, a configuration of the optical device according to the first embodiment of the present technology will be described with reference to  FIG.  1   .  FIG.  1    is a plan view (a planar layout view, a view (x-y plan view) of an x-axis direction and a y-axis direction) of an optical device  100  according to the first embodiment of the present technology. 
     The optical device  100  includes a light guide plate  1  which totally reflects and guides incident light, a first optical element  5  which is disposed on the light guide plate  1 , an input optical element  2  which is disposed on the light guide plate  1  and introduces the incident light into the light guide plate  1 , a second optical element  3  which is disposed on the light guide plate  1  and bends light propagated, by total reflection, in the light guide plate  1  in a direction different from a direction of the light, and an output optical element  4  which is disposed on the light guide plate  1  and emits light propagated, by total reflection, in the light guide plate  1  to the outside of the light guide plate  1 . In the optical device  100 , the first optical element  5  has substantially the same grating vector as the grating vector of the input optical element  2 . Then, the first optical element  5  and the input optical element  2  are disposed to face each other with the second optical element  3  interposed therebetween. 
     The image display device (reproduction optical system) will be described with reference to  FIGS.  2  to  4   . Note that details of the configuration of the image display device (reproduction optical system) will be described in the section of the eighth embodiment (an example of the image display device) according to the present technology described later.  FIG.  2    is a diagram illustrating an image display device (reproduction optical system)  1000  including the optical device  100  according to the first embodiment of the present technology.  FIG.  3    is a diagram for explaining that light (light beam) emitted from an image forming apparatus (light source) is incident on a light source device  100 , is guided in the light source device  100 , and is emitted to the outside of the light source device  100 . 
     As illustrated in  FIG.  2   , the image display device  1000  includes an image forming apparatus  200  and the optical device  100 . The image forming apparatus  200  includes at least a light source  6  and a projection optical system  7 . 
     The description will be given with reference to  FIG.  3   . The light beam emitted from the light source  6  is shaped by the projection optical system  7  and then is incident, as reproduction reference light L 1 , on the input optical element  2 . In the input optical element  2 , diffracted light L 2  is generated toward the inside of the light guide plate  1 . The diffracted light L 2  is incident on the second optical element  3  while being totally reflected in the light guide plate  1 . In the second optical element  3 , diffraction occurs toward the output optical element  4 , and enlarged light L 3  is emitted. The enlarged light L 3  is guided while being totally reflected in the light guide plate  1 , and is incident on the output optical element  4 . The light is diffracted out of the medium by the output optical element  4 , and reproduction light L 4  is obtained. The reproduction light L 4  reaches a pupil (eyeball)  500  of an observer. 
       FIG.  4    is a diagram illustrating a grating vector formed in the image display device (reproduction optical system)  1000 .  FIG.  4    is a kxky coordinate system represented by two coordinate axes of a kx axis (the horizontal direction in  FIG.  4   ) and a ky axis (the vertical direction in  FIG.  4   ). A grating vector (k vector input ) V 12  is in a +y direction with the origin (the intersection of the kx axis and the ky axis) as a start point, a grating vector (k vector intermediate) V 13  is in a +x-y direction with the end point of the grating vector (k vector input ) V 12  as a start point, and a grating vector (k vector output ) V 14  is in the a −x direction with the end point of the grating vector (k vector intermediate) V 13  as a start point and the origin as an end point. That is, a triangle is formed by the grating vector (k vector input ) V 12 , the grating vector (k vector intermediate ) V 13 , and the grating vector (k vector output ) V 14 , and starts from the origin and returns to the origin, and the grating vectors are closed. Therefore, the reproduction light L 4  having a substantially opposite vector to the reproduction reference light L 1  incident on the light guide plate  1  is obtained. 
     Then, the following equation is established among the grating vector (k vector input ) V 12 , the grating vector (k vector intermediate ) V 13 , and the grating vector (k vector output ) V 14 . 
       grating vector( k  vector input ) V 12+grating vector( k  vector intermediate ) V 13+grating vector( k  vector output ) V 14=0  (1)
 
     The function of the input optical element  2  included in the optical device  100  will be described in detail with reference to  FIGS.  5  to  8   . 
       FIG.  5    is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) illustrating an optical path of the input optical element  2  included in the optical device  100 . 
       FIG.  6 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and a z-axis direction) illustrating an optical path- 1  of the input optical element  2  included in the optical device  100 .  FIG.  6 ( b )  is a vector diagram of the optical path- 1  of the input optical element  2  illustrated in  FIG.  6 ( a ) .  FIG.  6 ( b )  is a kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  6 ( b )  and a kz axis (the vertical direction in  FIG.  6 ( b ) ). 
       FIG.  7 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating an optical path- 2  of the input optical element  2  included in the optical device  100 .  FIG.  7 ( b )  is a vector diagram of the optical path- 2  of the input optical element  2  illustrated in  FIG.  7 ( a ) .  FIG.  7 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  7 ( b ) ) and the kz axis (the vertical direction in  FIG.  7 ( b ) ). 
       FIG.  8 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating an optical path- 12  obtained by combining the optical path- 1  and the optical path- 2  of the input optical element  2  included in the optical device  100 .  FIG.  8 ( b )  is a vector diagram of the optical path- 12  of the input optical element  2  illustrated in  FIG.  8 ( a ) .  FIG.  8 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  8 ( b ) ) and the kz axis (the vertical direction in  FIG.  8 ( b ) ).  FIG.  8 ( c )  is a vector diagram (grating vector diagram) of the optical path- 12  of the input optical element  2  illustrated in  FIG.  8 ( a ) .  FIG.  8 ( c )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  8 ( c ) ) and the kz axis (the vertical direction in  FIG.  8 ( c ) ). 
     As illustrated in  FIGS.  6 ( a ),  7 ( a ) , and  8 , in order from the left side in  FIGS.  6 ( a ),  7 ( a ) , and  8 , the first optical element  5  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  6 ( a ),  7 ( a ) , and  8 ), the second optical element  3  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  6 ( a ),  7 ( a ) , and  8 ), and the input optical element  2  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  6 ( a ),  7 ( a ) , and  8 ). 
     When the reproduction reference light L 1  is incident on the input optical element  5 , the diffracted light L 2  is generated. A grating vector V 15  (here, a k vector′ input ) can be expressed by a relationship between a vector VL 1  of the reproduction reference light L 1  and a vector VL 2  of the diffracted light L 2 , and is illustrated in  FIG.  6 ( b ) . 
     The diffracted light L 2  is totally reflected in the light guide plate  1 , and reflected light L 5  which is the reflected light is incident on the second optical element  3 . As illustrated in  FIG.  7 ( b ) , wavevector components in the x and y directions do not change in the total reflection. As illustrated in  FIG.  8 ( b ) , a grating vector V 17  (represented by a k vector″ input ) can be expressed by a relationship between the vector VL 1  of the reproduction reference light L 1  and the vector VL 5  of the reflected light L 5 . As illustrated in  FIG.  8 ( c ) , the grating vector (k vector input ) V 12  and the grating vector V 17  (represented by the k vector″ input ) are different in magnitude in a kz-axis direction, but in the kx axis-ky axis (in a kx-ky plane), the grating vector (k vector input ) V 12  and the grating vector V 17  (represented by the k vector″ input ) coincide with each other. 
     The function of the second optical element  3  included in the optical device  100  will be described in detail with reference to  FIGS.  9  to  13   . 
       FIG.  9    is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) illustrating an optical path of the second optical element  3  included in the optical device  100 . 
       FIG.  10 ( a )  is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating an optical path- 3  of the second optical element  3  included in the optical device  100 .  FIG.  10 ( b )  is a vector diagram of the optical path- 3  of the second optical element  3  illustrated in  FIG.  10 ( a ) .  FIG.  10 ( b )  is the kxky coordinate system represented by two coordinate axes of the x axis (the horizontal direction in  FIG.  10 ( b ) ) and the ky axis (the vertical direction in  FIG.  10 ( b ) ).  FIG.  10 ( c )  is a vector diagram of the optical path- 3  of the second optical element  3  illustrated in  FIG.  10 ( a ) .  FIG.  10 ( c )  is a kxkz coordinate system represented by two coordinate axes of the x axis (the horizontal direction in  FIG.  10 ( c ) ) and the kz axis (the vertical direction in  FIG.  10 ( c ) ). 
       FIG.  11 ( a )  is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating an optical path- 4  of the second optical element  3  included in the optical device  100 .  FIG.  10 ( b )  is a vector diagram of the optical path- 4  of the second optical element  3  illustrated in  FIG.  10 ( a ) .  FIG.  11 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  11 ( b ) ) and the kz axis (the vertical direction in  FIG.  11 ( b ) ).  FIG.  11 ( c )  is a vector diagram of the optical path- 4  of the second optical element  3  illustrated in  FIG.  11 ( a ) .  FIG.  11 ( c )  is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  11 ( c ) ) and the ky axis (the vertical direction in  FIG.  10 ( c ) ). 
       FIG.  12    is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating an optical path- 34  obtained by combining the optical path- 3  and the optical path- 4  of the second optical element  3  included in the optical device  100 . 
       FIG.  13 ( a )  is a vector diagram of the optical path- 34  of the second optical element  3  illustrated in  FIG.  12   .  FIG.  13 ( a )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  13 ( a ) ) and the kz axis (the vertical direction in  FIG.  13 ( a ) ).  FIG.  13 ( b )  is a vector diagram (grating vector diagram) of the optical path- 34  of the second optical element  2  illustrated in  FIG.  12   .  FIG.  13 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  13 ( b ) ) and the kz axis (the vertical direction in  FIG.  13 ( b ) ).  FIG.  13 ( c )  is a vector diagram of the optical path- 34  of the second optical element  2  illustrated in  FIG.  12   .  FIG.  13 ( c )  is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  13 ( c ) ) and the ky axis (the vertical direction in  FIG.  13 ( c ) ). 
     As illustrated in  FIGS.  10 ( a ),  11 ( a ) , and  12 , in order from the left side in  FIGS.  10 ( a ),  11 ( a ) , and  12 , the output optical element  4  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  10 ( a ),  11 ( a ) , and  12 ), and the second optical element  3  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  10 ( a ),  11 ( a ) , and  12 ). 
     When the reflected light L 5  is incident (incident from the back side of the paper in  FIG.  10 ( a ) ) on the second optical element  3 , the enlarged light L 3  is generated as illustrated in  FIG.  10 ( a ) . As illustrated in  FIG.  10 ( b ) , the grating vector V 13  (k vector intermediate ) can be expressed by a relationship between the vector VL 5  of the reflected light L 5  and the enlarged light VL 3 . 
     As illustrated in  FIG.  11 ( a ) , similarly to the case of the input optical element  2  described above, propagation is performed with total reflection, but the magnitudes of the kx and ky components of the vector VL 3  of the enlarged light L 3  and the vector VL 6  of the reflected light L 6  do not change ( FIGS.  11  ( b ) and  11 ( c ) ). 
     The vectors from the reflected light L 5  incident on the second optical element  3  to the incidence on the output optical element  4  are combined as illustrated in  FIGS.  12  and  13   . As illustrated in  FIG.  13 ( a ) , a grating vector V 32  (referred to as k vector′ intermediate ) can be expressed by the vector VL 5  of the reflected light L 5  and the vector VL 6  of the reflected light L 6 . As illustrated in  FIGS.  4 ,  13   ( b ), and  13 ( c ), the grating vector V 13  (k vector intermediate ) and the grating vector V 32  (referred to as k vector intermediate ) coincide with each other in the kx and ky components. 
     The function of the output optical element  4  included in the optical device  100  will be described in detail with reference to  FIGS.  14  and  15   . 
       FIG.  14    is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) illustrating an optical path of the output optical element  4  included in the optical device  100 . 
       FIG.  15 ( a )  is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating an optical path- 5  of the output optical element  4  included in the optical device  100  when observed in the direction of an arrow P 14  by the observer&#39;s eyes  501  illustrated in  FIG.  14   .  FIG.  15 ( b )  is a vector diagram of the optical path- 5  of the output optical element  4  illustrated in  FIG.  15 ( a ) .  FIG.  15 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  15 ( b ) ) and the kz axis (the vertical direction in  FIG.  15 ( b ) ).  FIG.  15 ( c )  is a vector diagram (grating vector diagram) of the optical path- 5  of the output optical element  4  illustrated in  FIG.  15 ( a ) .  FIG.  15 ( c )  is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  15 ( c ) ) and the ky axis (the vertical direction in  FIG.  15 ( c ) ). 
     As illustrated in  FIG.  15 ( a ) , in order from the left side in  FIG.  15 ( a ) , the output optical element  4  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  15 ( a ) ), and the second optical element  3  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  15 ( a ) ). 
     When the reflected light L 6  is incident on the output optical element  4 , the reproduction light L 4  is generated as illustrated in  FIGS.  14  and  15   ( a ). As illustrated in  FIG.  15  ( b ) , the grating vector (k vector output ) V 14  can be expressed by a relationship between the vector VL 6  of the reflected light L 6  and the vector VL 4  of the reproduction light L 4 . Then, as illustrated in  FIG.  15 ( c ) , the grating vector (k vector output ) V 14  is in the −x direction with the origin (the intersection of the kx axis and the ky axis) as a start point, and coincides with the grating vector illustrated in  FIG.  4   . 
     As described above, the grating vectors of the optical elements (the input optical element  2 , the second optical element (intermediate grating)  3 , and the output optical element  4 ) disposed on the light guide plate  1  are closed (the sum is zero) as illustrated in  FIG.  4    and has a function of emitting a light beam having a substantially opposite vector to the light beam incident on the light guide plate  1 . 
     Next, a method for manufacturing the optical device according to the first embodiment of the present technology will be described with reference to  FIGS.  16  to  28   . One of the features of the method for manufacturing the optical device according to the first embodiment of the present technology is to form the grating vector illustrated in  FIG.  4    by using the first optical element  5 . 
     First, a production optical path from the output optical element  4  will be described with reference to  FIGS.  16  to  20   . 
       FIG.  16    is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) illustrating the production optical path from the output optical element  4  included in the optical device  100 . 
       FIG.  17 ( a )  is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating a production optical path- 11  from the output optical element  4  included in the optical device  100  when observed in the direction of an arrow P 16  by the observer&#39;s eyes  501  illustrated in  FIG.  16   .  FIG.  17 ( b )  is a vector diagram of the optical path- 11  of the output optical element  4  illustrated in  FIG.  17 ( a ) .  FIG.  17 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  17 ( b ) ) and the kz axis (the vertical direction in  FIG.  17 ( b ) ). 
       FIG.  18 ( a )  is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating a production optical path- 12  from the output optical element  4  included in the optical device  100  when observed in the direction of the arrow P 16  by the observer&#39;s eyes  501  illustrated in  FIG.  16   .  FIG.  18 ( b )  is a vector diagram of the production optical path- 12  from the output optical element  4  illustrated in  FIG.  18 ( a ) .  FIG.  18 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  18 ( b ) ) and the kz axis (the vertical direction in  FIG.  18 ( b ) ). 
       FIG.  19    is a cross-sectional view (a view (x-z plan view) of the x-axis direction and the z-axis direction) illustrating a production optical path- 1112  obtained by combining the production optical path- 11  and the production optical path- 12  from the output optical element  4  included in the optical device  100 . 
       FIG.  20 ( a )  is a vector diagram of the production optical path- 1112  from the output optical element  4  illustrated in  FIG.  19   .  FIG.  20 ( a )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  20 ( a ) ) and the kz axis (the vertical direction in  FIG.  20 ( a ) ).  FIG.  20 ( b )  is a vector diagram of the production optical path- 1112  from the output optical element  4  illustrated in  FIG.  19   .  FIG.  20 ( b )  is the kxkz coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in FIG.  20 ( b )) and the kz axis (the vertical direction in  FIG.  20 ( b ) ).  FIG.  20 ( c )  is a vector diagram of the production optical path- 1112  from the output optical element  4  illustrated in  FIG.  19   .  FIG.  20 ( c )  is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  20 ( c ) ) and the ky axis (the vertical direction in  FIG.  20 ( c ) ). 
     As illustrated in  FIGS.  17 ( a ),  18 ( a ) , and  19 , in order from the left side in  FIGS.  17 ( a ),  18 ( a ) , and  19 , the output optical element  4  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  17 ( a ),  18 ( a ) , and  19 ), and the second optical element  3  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  17 ( a ),  18 ( a ) , and  19 ). 
     When object light M 1  having a substantially opposite vector to the reproduction light L 4  is incident on the output optical element  4 , diffracted light M 2  is generated as illustrated in  FIGS.  16  and  17   ( a ). 
     As illustrated in  FIG.  17 ( b ) , a grating vector (here, k vector′ output ) V 19  can be expressed by a vector VM 1  of the object light M 1  and a vector VM 2  of the diffracted light M 2 . 
     As illustrated in  FIG.  18 ( a ) , similarly to the case of the input optical element  2  described above, propagation is performed with total reflection, but the magnitudes of the kx and ky components of the vector VM 2  of the diffracted light M 2  and a vector VM 3  of reflected light M 3  do not change (FIG.  11 ( b )). 
     The vectors from the object light M 1  incident on the output optical element  4  to the incidence on the second optical element  3  are combined as illustrated in  FIG.  19   . As illustrated in  FIG.  20 ( a ) , a grating vector (here, k vector″ output ) V 29  can be expressed by the vector VM 1  of the object light M 1  and the vector VM 3  of the reflected light M 3 . Then, in the grating vector (k vector′ output ) V 19  and the grating vector (k vector″ output ) V 29 , the kx components have substantially the same magnitude and substantially the same direction, and in the grating vector (k vector′ output ) V 19  and the grating vector (k vector″ output ) V 29 , and the grating vector (k vector output ) V 14 , the kx components have substantially the same magnitude but substantially opposite directions. 
     When a positive oblique shadow of the vector VM 3  of the reflected light M 3  incident on the second optical element  3  on the kx axis is set as a vector VM 3 - 1 , the vector VM 3 - 1  can be expressed in a kx/ky space (x-y coordinate system) as illustrated in  FIG.  20 ( c ) . 
     A production optical path from the first optical element  5  will be described with reference to  FIGS.  21  to  27   . 
       FIG.  21    is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) illustrating the production optical path from the first optical element  5  included in the optical device  100 . 
       FIG.  22 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating a production optical path- 13  from the first optical element  5  included in the optical device  100  when observed in the direction of an arrow P 21  by the observer&#39;s eyes  501  illustrated in  FIG.  21   .  FIG.  22 ( b )  is a vector diagram of the production optical path- 13  from the first optical element  5  illustrated in  FIG.  22 ( a ) .  FIG.  22 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  22 ( b ) ) and the kz axis (the vertical direction in  FIG.  22 ( b ) ). 
       FIG.  23 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating a production optical path- 14  from the first optical element  5  included in the optical device  100  when observed in the direction of the arrow P 21  by the observer&#39;s eyes  501  illustrated in  FIG.  21   .  FIG.  23 ( b )  is a vector diagram of the production optical path- 14  from the first optical element  5  illustrated in  FIG.  23 ( a ) .  FIG.  23 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  23 ( b ) ) and the kz axis (the vertical direction in  FIG.  23 ( b ) ). 
       FIG.  24 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating a production optical path- 15  from the first optical element  5  included in the optical device  100  when observed in the direction of the arrow P 21  by the observer&#39;s eyes  501  illustrated in  FIG.  21   .  FIG.  24 ( b )  is a vector diagram of the production optical path- 15  from the first optical element  5  illustrated in  FIG.  24 ( a ) .  FIG.  24 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  24 ( b ) ) and the kz axis (the vertical direction in  FIG.  24 ( b ) ). 
       FIG.  25 ( a )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating a production optical path- 16  from the first optical element  5  included in the optical device  100  when observed in the direction of the arrow P 21  by the observer&#39;s eyes  501  illustrated in  FIG.  21   .  FIG.  25 ( b )  is a vector diagram of the production optical path- 16  from the first optical element  5  illustrated in  FIG.  25 ( a ) .  FIG.  25 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  25 ( b ) ) and the kz axis (the vertical direction in  FIG.  25 ( b ) ). 
       FIG.  26    is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) illustrating a production optical path- 1316  obtained by combining the production optical path- 13  to the production optical path- 16  from the first optical element  5  included in the optical device  100 . 
       FIG.  27 ( a )  is a vector diagram of the production optical path- 1316  from the first optical element  5  illustrated in  FIG.  26   .  FIG.  27 ( a )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  27 ( a ) ) and the kz axis (the vertical direction in  FIG.  27 ( a ) ). 
       FIG.  27 ( b )  is a vector diagram of the production optical path- 1316  from the first optical element  5  illustrated in  FIG.  26   .  FIG.  27 ( b )  is the kykz coordinate system represented by two coordinate axes of the ky axis (the horizontal direction in  FIG.  27 ( b ) ) and the kz axis (the vertical direction in  FIG.  27 ( b ) ).  FIG.  27 ( c )  is a vector diagram of the production optical path- 1316  from the first optical element  5  illustrated in  FIG.  26   .  FIG.  27 ( c )  is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  27 ( c ) ) and the ky axis (the vertical direction in  FIG.  27 ( c ) ). 
     As illustrated in  FIGS.  22 ( a ),  23 ( a ),  24 ( a ),  25 ( a ) , and  26 , in order from the left side of  FIGS.  22 ( a ),  23 ( a ),  24 ( a ),  25 ( a ) , and  26 , the first optical element  5  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  22 ( a ),  23 ( a ),  24 ( a ),  25 ( a ) , and  26 ), the second optical element  3  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  22 ( a ),  23 ( a ),  24 ( a ),  25 ( a ) , and  26 ), and the input optical element  2  is disposed on the light guide plate  1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIGS.  22 ( a ),  23 ( a ),  24 ( a ),  25 ( a ) , and  26 ). 
     When reference light N 1  having a substantially opposite vector to the reproduction reference light L 1  is incident on the first optical element  5 , diffracted light N 2  is generated as illustrated in  FIG.  22 ( a ) . 
     As illustrated in  FIG.  22 ( b ) , a grating vector V 51  (here, k vector production ) can be expressed by a relationship between a vector VN 1  of the reference light N 1  and a vector VN 2  of the diffracted light N 2 . 
     As illustrated in  FIG.  23 ( a ) , similarly to the case of the input optical element  2  described above, propagation is performed with total reflection, but the magnitudes of the kx and ky components of the vector VN 2  of the diffracted light N 2  and the vector VN 3  of the reflected light N 3  do not change ( FIG.  23 ( b ) ). 
     Furthermore, as illustrated in  FIG.  24 ( a ) , similarly to the case of the input optical element  2  described above, propagation is performed with total reflection, but the magnitudes of the kx and ky components of the vector VN 3  of the reflected light N 3  and the vector VN 4  of the reflected light N 4  do not change ( FIG.  24 ( b ) ). 
     Further, as illustrated in  FIG.  25 ( a ) , similarly to the case of the input optical element  2  described above, propagation is performed with total reflection, but the magnitudes of the kx and ky components of the vector VN 4  of the reflected light N 4  and the vector VN 5  of the reflected light N 5  do not change ( FIG.  25 ( b ) ). 
     The reference light N 1  incident on the first optical element  5  to the reflection by the second optical element  3  are combined as illustrated in  FIG.  26   . As illustrated in  FIG.  27 ( a ) , a grating vector (here, k vector′ production ) V 27  can be expressed by the vector VN 1  of the reference light N 1  and the vector VN 5  of the reflected light N 5 . In the grating vector V 17  (represented by the k vector″ input ) and the grating vector (k vector production ) V 27 , the ky components have substantially the same magnitude but substantially opposite directions. 
     Furthermore, when a positive oblique shadow of the vector VN 5  of the reflected light N 5  emitted from the second optical element  3  on the ky axis is set as a vector VN 5 - 1 , the vector VN 5 - 1  can be expressed in the kx axis/ky axis space as illustrated in  FIG.  27 ( c ) . 
     Finally, formation of the second optical element will be described with reference to a vector diagram illustrated in  FIG.  28   . 
       FIG.  28    is the vector diagram at the time of producing the second optical element  3  and is the kxky coordinate system represented by two coordinate axes of the kx axis (the horizontal direction in  FIG.  28   ) and the ky axis (the vertical direction in  FIG.  28   ). 
     When the object light M 1  and the reference light N 1  having vectors substantially opposite to each other at the time of reproduction are incident on each of the output optical element  4  and the first optical element  5 , light having the vector VM 3 - 1  illustrated in  FIG.  20 ( c )  and light having the vector VN 5 - 1  illustrated in  FIG.  27 ( c )  are incident on the second optical element  3 . 
     By using the second optical element  3  as the volume hologram, an interference between the above-described two beams of light (the light having the vector VM 3 - 1  and the light having the vector VN 5 - 1 ) forms an interference fringe having a grating vector V 30  (k vector′ intermediate ) illustrated in  FIG.  28    (grating vector V 30  (k vector′ intermediate )=vector VN 5 - 1 −vector VM 3 - 1 ). The grating vector V 30  (k vector′ intermediate ) and the grating vector (k vector intermediate) V 13  illustrated in  FIG.  4    are substantially opposite vectors, and it can be understood that interference fringes having the same function are formed on the basis of the conjugation property of the interference fringe. 
     As a first modification of the optical device of the first embodiment (Example 1 of the optical device and Example 1 of the method for manufacturing the optical device) according to the present technology, in at least a part (at least a part of the angle of view of the image display device) of each optical element of the optical device of the first embodiment according to the present technology, the grating vector at the time of reproduction may not be closed (the sum of the grating vectors may not be zero). 
     A second modification of the optical device of the first embodiment (Example 1 of the optical device and Example 1 of the method for manufacturing the optical device) according to the present technology is an optical device in which the light guide plate  1  has a first surface and a second surface facing the first surface, the input optical element  2  is disposed on the first surface of the light guide plate  1 , the first optical element  5  is disposed on the second surface of the light guide plate  1 , the second optical element  3  is disposed in the light guide plate  1 , and the first optical element  5  and the input optical element  2  are disposed to face each other with the second optical element  3  interposed therebetween. In the second modification of the optical device of the first embodiment according to the present technology, total reflection in the light guide plate  1  may not be used, and diffracted light of light (light beam) incident on each optical element may be directly incident on the next optical element. 
     In a third modification of the optical device of the first embodiment (Example 1 of the optical device and Example 1 of the method for manufacturing the optical device) according to the present technology, the input optical element  2  includes a light reflecting member (for example, a mirror). In the third modification of the optical device of the first embodiment according to the present technology, reflected light by the light reflecting member included in the input optical element  2  is used. Note that in any one embodiment of the optical devices of second to eighth embodiments according to the present technology, the input optical element  2  may include the light reflecting member. 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the first embodiment (Example 1 of the optical device and Example 1 of the method for manufacturing the optical device) according to the present technology and the method for manufacturing the optical device can be applied to the optical devices of the second to fifth embodiments, the sixth and seventh optical devices, and the methods for manufacturing the optical devices described later according to the present technology. 
     3. Second Embodiment (Example 2 of Optical Device) 
     An optical device of a second embodiment (Example 2 of the optical device) according to the present technology will be described with reference to  FIG.  29   . 
       FIG.  29    is a diagram illustrating a configuration example of the optical device (optical device  200 ) of the second embodiment (Example 2 of the optical device) according to the present technology.  FIG.  29 ( a )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of the optical device  200  according to the second embodiment of the present technology, and  FIG.  29 ( b )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) of the optical device  200  according to the second embodiment of the present technology when observed in the direction of an arrow P 29  by the observer&#39;s eyes  501  illustrated in  FIG.  29 ( a ) . 
     As illustrated in  FIG.  29 ( a ) , the optical device  200  includes a light guide plate  12  which totally reflects and guides incident light, a laminate  52  of the first optical elements which is disposed on the light guide plate  12 , a laminate  22  of the input optical elements which is disposed on the light guide plate  12  and introduces the incident light into the light guide plate  12 , a laminate  32  of the second optical elements which is disposed on the light guide plate  12  and bends light propagated, by total reflection, in the light guide plate  12  in a direction different from a direction of the light, and a laminate  42  of the output optical elements which is disposed on the light guide plate  12  and emits light propagated, by total reflection, in the light guide plate  12  to the outside of the light guide plate  12 . In the optical device  200 , the laminate  52  of the first optical elements has substantially the same grating vector as the grating vector of the laminate  22  of the input optical elements. Then, the laminate  52  of the first optical elements and the laminate  22  of the input optical elements are disposed to face each other with the laminate  32  of the second optical elements interposed therebetween. 
     As illustrated in  FIG.  29 ( b ) , the laminate  52  of the first optical elements includes a first optical element  52 - 1  and a first optical element  52 - 2 , the laminate  32  of the second optical elements includes a second optical element  32 - 1  and a second optical element  32 - 2 , and the laminate  22  of the input optical elements includes an input optical element  22 - 1  and an input optical element  22 - 2 . 
     The first optical element  52 - 1  and the first optical element  52 - 2  are laminated in this order (z-axis direction) on the light guide plate  12  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  29 ( b ) ), the second optical element  32 - 1  and the second optical element  32 - 2  are laminated in this order (z-axis direction) on the light guide plate  12  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  29 ( b ) ), and the input optical element  22 - 1  and the input optical element  22 - 2  are laminated in this order (z-axis direction) on the light guide plate  12  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  29 ( b ) ). Note that, although not illustrated in  FIG.  29 ( b ) , the laminate  42  of the output optical elements is also configured by laminating a plurality of output optical elements on the light guide plate  12  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  29 ( b ) ) in the z-axis direction. 
     According to the optical device  200 , the first optical elements are configured as the laminate  52 , the second optical elements are configured as the laminate  32 , the input optical elements are configured as the laminate  22 , and the output optical elements are configured as the laminate  42 . Thus, space saving can be achieved by sharing the coordinates on the light guide plate  12 . 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the second embodiment (Example 2 of the optical device) according to the present technology can be applied to the optical device of the first embodiment and the method for manufacturing the optical device described above according to the present technology, and further to the optical devices of the third to fifth embodiments, the sixth and seventh optical devices, and the methods for manufacturing the optical devices described later according to the present technology. 
     4. Third Embodiment (Example 3 of Optical Device) 
     An optical device of a third embodiment (Example 3 of the optical device) according to the present technology will be described with reference to  FIG.  30   . 
       FIG.  30    is a diagram illustrating a configuration example of the optical device (optical device  300 ) of the third embodiment (Example 3 of the optical device) according to the present technology.  FIG.  30 ( a )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of the optical device  300  according to the third embodiment of the present technology, and  FIG.  30 ( b )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) of the optical device  300  according to the third embodiment of the present technology when observed in the direction of an arrow P 30  by the observer&#39;s eyes  501  illustrated in  FIG.  30 ( a ) . 
     As illustrated in  FIG.  30 ( a ) , the optical device  300  includes a light guide plate  13  which totally reflects and guides incident light, a first optical element  53  which is disposed on the light guide plate  13 , an input optical element  23  which is disposed on the light guide plate  13  and introduces the incident light into the light guide plate  13 , a second optical element  33  which is disposed on the light guide plate  13  and bends light propagated, by total reflection, in the light guide plate  13  in a direction different from a direction of the light, and an output optical element  43  which is disposed on the light guide plate  13  and emits light propagated, by total reflection, in the light guide plate  13  to the outside of the light guide plate  13 . In the optical device  300 , the first optical element  53  has substantially the same grating vector as the grating vector of the input optical element  22 . Then, the first optical element  53  and the input optical element  23  are disposed to face each other with the second optical element  33  interposed therebetween. 
     The first optical element  53  is disposed on an upper surface S 3 - 1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  30 ( b ) ) of the light guide plate  13 , and the input optical element  23  is disposed on the upper surface S 3 - 1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  30 ( b ) ) of the light guide plate  13 . On the other hand, the second optical element  33  is disposed on a lower surface S 3 - 2  (which is a surface in the x-axis direction and the y-axis direction and is the lower surface in  FIG.  30 ( b ) ) of the light guide plate  13 . Note that, although not illustrated in  FIG.  30 ( b ) , the output optical element  43  is disposed on the upper surface S 3 - 1  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  30 ( b ) ) of the light guide plate  13 . 
     According to the optical device  300 , the first optical element  53  and the input optical element  23  are disposed on the upper surface S 3 - 1  of the light guide plate  13 , and the second optical element  33  is disposed on the lower surface S 3 - 2  of the light guide plate  13 . Thus, space saving can be achieved by sharing the coordinates on the light guide plate  13 . 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the third embodiment (Example 3 of the optical device) according to the present technology can be applied to the optical device of the first embodiment and the method for manufacturing the optical device described above according to the present technology and the optical device of the second embodiment according to the present technology, and further to the optical devices of the fourth and fifth embodiments described later according to the present technology, the sixth and seventh optical devices, and the methods for manufacturing the optical devices. 
     5. Fourth Embodiment (Example 4 of Optical Device) 
     An optical device of a fourth embodiment (Example 4 of the optical device) according to the present technology will be described with reference to  FIG.  31   . 
       FIG.  31    is a diagram illustrating a configuration example of the optical device (optical device  400 ) of the fourth embodiment (Example 4 of the optical device) according to the present technology.  FIG.  31 ( a )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of the optical device  400  according to the fourth embodiment of the present technology, and  FIG.  31 ( b )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) of the optical device  400  according to the fourth embodiment of the present technology when observed in the direction of an arrow P 31  by the observer&#39;s eyes  501  illustrated in  FIG.  31 ( a ) . 
     As illustrated in  FIG.  31 ( a ) , the optical device  400  includes a light guide plate  14  which totally reflects and guides incident light, two first optical elements  54 - 1  and  54 - 2  which are disposed on the light guide plate  14 , two input optical elements  24 - 1  and  24 - 2  which are disposed on the light guide plate  14  and introduce the incident light into the light guide plate  14 , two second optical elements  34 - 1  and  34 - 2  which are disposed on the light guide plate  14  and bend light propagated, by total reflection, in the light guide plate  14  in a direction different from a direction of the light, and a laminate  44  of the output optical elements which is disposed on the light guide plate  14  and emits light propagated, by total reflection, in the light guide plate  14  to the outside of the light guide plate  14 . In the optical device  400 , the first optical elements  54 - 1  and  54 - 2  have substantially the same grating vectors as the grating vectors of the input optical elements  24 - 1  and  24 - 2 . Then, the first optical element  54 - 1  and the input optical element  24 - 1  are disposed to face each other with the second optical element  34 - 1  interposed therebetween, and the first optical element  54 - 2  and the input optical element  24 - 2  are disposed to face each other with the second optical element  34 - 2  interposed therebetween. 
     The input optical element  24 - 1 , the second optical element  34 - 1 , and the first optical element  54 - 1  are disposed in this order from the upper side of  FIG.  31 ( a ) , and one set is configured by the input optical element  24 - 1 , the second optical element  34 - 1 , and the first optical element  54 - 1 . Then, the input optical element  24 - 2 , the second optical element  34 - 2 , and the first optical element  54 - 2  are disposed in this order from the upper side of  FIG.  31 ( a ) , and another set is configured by the input optical element  24 - 2 , the second optical element  34 - 2 , and the first optical element  54 - 2 . These two sets are disposed in the vertical direction in  FIG.  31 ( a ) . Note that although  FIG.  31 ( a )  illustrates two sets as described above, the optical device  400  may include three or more sets. 
     The first optical element  54 - 2  is disposed on the light guide plate  14  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  31 ( b ) ). The laminate  44  of the output optical elements includes the output optical elements  44 - 1  and  44 - 2 , and the output optical element  44 - 1  and the output optical element  44 - 2  are laminated in this order (lamination in the z-axis direction) on the light guide plate  14  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  31 ( b ) ). Note that, although not illustrated in  FIG.  31 ( b ) , each of the second optical element  34 - 2 , the input optical element  24 - 2 , the first optical element  54 - 1 , the second optical element  34 - 1 , and the input optical element  24 - 1  is disposed on the light guide plate  14  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  31 ( b ) ). 
     In the optical device  400 , the input optical element  24 - 1 , the second optical element  34 - 1 , the first optical element  54 - 1 , the input optical element  24 - 2 , the second optical element  34 - 2 , the first optical element  54 - 2 , and, further, the laminate  44  of the output optical elements are disposed on the light guide plate  14  such that the sum of a plurality of grating vectors becomes zero (the grating vectors are closed). 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the fourth embodiment (Example 4 of the optical device) according to the present technology can be applied to the optical device of the first embodiment and the method for manufacturing the optical device described above according to the present technology and the optical devices of the second and third embodiments according to the present technology, and further to the optical device of the fifth embodiment, the sixth and seventh optical devices, and the methods for manufacturing the optical devices according to the present technology described later. 
     6. Fifth Embodiment (Example 5 of Optical Device) 
     An optical device of a fifth embodiment (Example 5 of the optical device) according to the present technology will be described with reference to  FIG.  32   . 
       FIG.  32    is a diagram illustrating a configuration example of the optical device (optical device  500 ) of the fifth embodiment (Example 5 of the optical device) according to the present technology.  FIG.  32 ( a )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of the optical device  500  according to the fifth embodiment of the present technology, and  FIG.  32 ( b )  is a cross-sectional view (a view (y-z plan view) of the y-axis direction and the z-axis direction) of the optical device  500  according to the fifth embodiment of the present technology when observed in the direction of an arrow P 32  by the observer&#39;s eyes  501  illustrated in  FIG.  32 ( a ) . 
     As illustrated in  FIG.  32 ( a ) , the optical device  500  includes a light guide plate  15  which totally reflects and guides incident light, two first optical elements  55 - 1  and  55 - 2  which are disposed on the light guide plate  15 , two input optical elements  25 - 1  and  25 - 2  which are disposed on the light guide plate  15  and introduce the incident light into the light guide plate  15 , a second optical element  35  which is disposed on the light guide plate  14  and bends light propagated, by total reflection, in the light guide plate  15  in a direction different from a direction of the light, and an output optical element  45  which is disposed on the light guide plate  15  and emits light propagated, by total reflection, in the light guide plate  15  to the outside of the light guide plate  14 . In the optical device  500 , the first optical elements  55 - 1  and  55 - 2  have substantially the same grating vectors as the grating vectors of the input optical elements  25 - 1  and  25 - 2 . Then, the two first optical elements  55 - 1  and  55 - 2  and the two input optical elements  25 - 1  and  25 - 2  are disposed to face each other with the second optical element  35  interposed therebetween. 
     The first optical element  55 - 2  is disposed on the light guide plate  15  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  32 ( b ) ), the second optical element  35  is disposed on the light guide plate  15  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  32 ( b ) ), and the input optical element  25 - 2  is disposed on the light guide plate  15  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  32 ( b ) ). Note that, although not illustrated in  FIG.  32 ( b ) , each of the first optical element  55 - 1 , the input optical element  25 - 1 , and the output optical element  45  is disposed on the light guide plate  15  (which is a surface in the x-axis direction and the y-axis direction and is the upper surface in  FIG.  32 ( b ) ). 
     In the optical device  500 , at least two types of interference fringes can be formed in the second optical element  35  by using the light emitted from each of the two first optical elements  55 - 1  and  55 - 2  (so-called multiple exposure). Note that, for example, at least two types of interference fringes may be formed in the output optical element by multiple exposure using at least two first optical elements. Furthermore, as illustrated in  FIG.  29    described above, for example, by multiple exposure using the laminate  52  of the first optical elements, interference fringes different from each other can be formed respectively in the first optical element  32 - 1  and the second optical element  32 - 2  configuring the laminate  32  of the first optical elements. 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the fifth embodiment (Example 5 of the optical device) according to the present technology can be applied to the optical device of the first embodiment and the method for manufacturing the optical device described above according to the present technology and the optical devices of the second to fourth embodiments according to the present technology, and further to the sixth and seventh optical devices and the methods for manufacturing the optical devices described later. 
     7. Sixth Embodiment (Example 6 of Optical Device and Example 2 of Method for Manufacturing Optical Device) 
     An optical device and a method for manufacturing the optical device according to a sixth embodiment (Example 6 of the optical device and Example 2 of the method for manufacturing the optical device) of the present technology will be described with reference to  FIG.  33 ( a ) . 
       FIG.  33 ( a )  is a diagram illustrating a configuration example of the optical device (optical device  700 - 1 ) of the sixth embodiment (Example 6 of the optical device) according to the present technology.  FIG.  33 ( a )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of the optical device  700 - 1  according to the sixth embodiment of the present technology. 
     The optical device  700 - 1  includes a light guide plate  17 - 1  which totally reflects and guides incident light, a first optical element  57 - 1 - 1  which is disposed on the light guide plate  17 - 1 , an input optical element  27 - 1  which is disposed on the light guide plate  17 - 1  and introduces the incident light into the light guide plate  17 - 1 , a second optical element  37 - 1  which is disposed on the light guide plate  17 - 1  and bends light propagated, by total reflection, in the light guide plate  17 - 1  in a direction different from a direction of the light, a third optical element  57 - 1 - 2  which is disposed on the light guide plate  17 - 1 , and an output optical element  47 - 1  which is disposed on the light guide plate  17 - 1  and emits light propagated, by total reflection, in the light guide plate  17 - 1  to the outside of the light guide plate  17 - 1 . The first optical element  57 - 1 - 1  has substantially the same grating vector as the grating vector of the second optical element  37 - 1 , and the third optical element  57 - 1 - 2  has substantially the same grating vector as the grating vector of the input optical element  27 - 1 . Then, the first optical element  57 - 1 - 1  and the third optical element  57 - 1 - 2 , and the second optical element  37 - 1  and the input optical element  27 - 1  are disposed to face each other with the output optical element  47 - 1  interposed therebetween. 
     First, the method for manufacturing the optical device  700 - 1  includes a step of forming the input optical element  27 - 1  on the light guide plate  17 - 1 , a step of forming the second optical element  37 - 1  on the light guide plate  17 - 1 , a step of forming the third optical element  57 - 1 - 2  having substantially the same grating vector as the grating vector of the input optical element  27 - 1  on the light guide plate  17 - 1 , and a step of forming the first optical element  57 - 1 - 1  having substantially the same grating vector as the grating vector of the second optical element  37 - 1  on the light guide plate  17 - 1 . 
     Then, in the method for manufacturing the optical device  700 - 1 , the output optical element  47 - 1  can be formed by using an interference between the diffracted light (fifth diffracted light), which is obtained when the reference light having the substantially opposite vector to the vector of the reproduction reference light is incident on the third optical element  57 - 1 - 2 , and the light emitted from the third optical element  57 - 1 - 2  is incident on the first optical element  57 - 1 - 1 , and the object light having the substantially opposite vector to the vector of the reproduction light. The output optical element  47 - 1  may be a volume hologram. 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the sixth embodiment (Example 6 of the optical device) according to the present technology can be applied to the optical device of the first embodiment and the method for manufacturing the optical device described above according to the present technology and the optical devices of the second to fifth embodiments according to the present technology, and further to the seventh optical device and the method for manufacturing the optical device described later. 
     8. Seventh Embodiment (Example 7 of Optical Device) 
     An optical device and a method for manufacturing the optical device according to a seventh embodiment (Example 7 of the optical device and Example 3 of the method for manufacturing the optical device) of the present technology will be described with reference to  FIG.  33 ( b ) . 
       FIG.  33 ( b )  is a diagram illustrating a configuration example of the optical device (optical device  700 - 2 ) of the seventh embodiment (Example 7 of the optical device) according to the present technology.  FIG.  33 ( b )  is a plan view (a planar layout view, a view (x-y plan view) of the x-axis direction and the y-axis direction) of an optical device  700 - 2  according to the seventh embodiment of the present technology. 
     The optical device  700 - 2  includes a light guide plate  17 - 2  which totally reflects and guides incident light, a first optical element  57 - 2  which is disposed on the light guide plate  17 - 2 , an input optical element  27 - 2  which is disposed on the light guide plate  17 - 2  and introduces the incident light into the light guide plate  17 - 2 , a second optical element  37 - 2  which is disposed on the light guide plate  17 - 2  and bends light propagated, by total reflection, in the light guide plate  17 - 2  in a direction different from a direction of the light, and an output optical element  47 - 2  which is disposed on the light guide plate  17 - 2  and emits light propagated, by total reflection, in the light guide plate  17 - 2  to the outside of the light guide plate  17 - 2 . The first optical element  57 - 2  has substantially the same grating vector as the grating vector of the output optical element  47 - 2 . Then, the first optical element  57 - 2  and the output optical element  47 - 2  are disposed to face each other with the second optical element  37 - 2  interposed therebetween. 
     First, the method for manufacturing the optical device  700 - 2  includes a step of forming the input optical element  27 - 2  on the light guide plate  17 - 2 , a step of forming the output optical element  47 - 2  on the light guide plate  17 - 2 , and a step of forming the first optical element  57 - 2  having substantially the same grating vector as the grating vector of the output optical element  47 - 2  on the light guide plate  17 - 2 . 
     Then, in the method for manufacturing the optical device  700 - 2 , the second optical element  37 - 2  can be formed by using an interference between the diffracted light (third diffracted light), which is obtained when the object light having substantially the same vector as the vector of the reproduction light is incident on the first optical element  57 - 2 , and the diffracted light (fourth diffracted light), which is obtained when the reference light having substantially the same vector as the vector of the reproduction reference light is incident on the input optical element  27 - 2 . The second optical element  37 - 2  may be a volume hologram. 
     As described above, unless there is a particular technical contradiction, the contents described for the optical device of the seventh embodiment (Example 7 of the optical device) according to the present technology can be applied to the optical devices of the first and sixth embodiments and the methods of manufacturing the optical devices described above according to the present technology, and further to the optical devices of the second to fifth embodiments according to the present technology. 
     9. Eighth Embodiment (Example of Image Display Device) 
     An image display device according to an eighth embodiment (an example of the image display device) of the present technology will be described with reference to  FIG.  2   . 
       FIG.  2    is a diagram illustrating the image display device  1000  according to the eighth embodiment (an example of the image display device) of the present technology. As described above, the image display device (reproduction optical system)  1000  includes the image forming apparatus  200  and the optical device  100 . The image forming apparatus  200  includes at least the light source  6  and the projection optical system  7 , and may further include a spatial light modulation device such as a liquid crystal display device. The image display device  1000  can be applied to, for example, an eyewear display, a head mounted display, or the like. 
     The light source  6  may be configured by a light emitting element, and specific examples of the light emitting element may include a red light emitting element, a green light emitting element, a blue light emitting element, and a white light emitting element, and white light may be obtained by mixing red light, green light, and blue light emitted from the red light emitting element, the green light emitting element, and the blue light emitting element by using a light pipe and uniformizing luminance. Examples of the light emitting element include a semiconductor laser element, a solid-state laser, and an LED. For example, a collimating optical system which collimates the light emitted from the light source  6  may be used as the projection optical system  7 . 
     Note that, in addition to the optical device  100 , the optical device  200 , the optical device  300 , the optical device  400 , the optical device  500 , the optical device  700 - 1 , or the optical device  700 - 2  also may be applied to the image display device  1000 . 
     Note that, the embodiments according to the present technology are not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present technology. 
     The effects described in the present specification are merely examples and are not limited, and other effects may be provided. 
     The present technology can also have the following configurations. 
     [1] 
     An optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; and 
     an output optical element that is disposed on the light guide plate and emits light propagated by total reflection in the light guide plate, to an outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the input optical element, and 
     the first optical element and the input optical element are disposed to face each other with the second optical element interposed therebetween. 
     [2] 
     The optical device according to [ 1 ], further including: 
     a plurality of the first optical elements; a plurality of the input optical elements; a plurality of the second optical elements; and a plurality of the output optical elements, in which 
     each of the plurality of first optical elements, the plurality of input optical elements, the plurality of second optical elements, and the plurality of output optical elements has a laminated structure. 
     [3] 
     The optical device according to [1], in which 
     the light guide plate has a first surface and a second surface facing the first surface, 
     the first optical element, the input optical element, and the output optical element are disposed on the first surface of the light guide plate, and 
     the second optical element is disposed on the second surface of the light guide plate. 
     [4] 
     The optical device according to [1], further including: 
     a plurality of the first optical elements; a plurality of the input optical elements; a plurality of the second optical elements; and a plurality of the output optical elements, in which 
     the input optical element, the second optical element, and the first optical element are disposed in this order on the light guide plate, 
     one set including the input optical element, the second optical element, and the first optical element is repeatedly disposed, and 
     the plurality of output optical elements has a laminated structure. 
     [5] 
     The optical device according to [1], further including: 
     a plurality of the first optical elements; and a plurality of the input optical elements, in which 
     the plurality of first optical elements and the plurality of input optical elements are disposed to face each other with the second optical element interposed therebetween. 
     [6] 
     The optical device according to [1], in which 
     the light guide plate has a first surface and a second surface facing the first surface, 
     the input optical element is disposed on the first surface of the light guide plate, 
     the first optical element is disposed on the second surface of the light guide plate, 
     the second optical element is disposed in the light guide plate, and 
     the first optical element and the input optical element are disposed to face each other with the second optical element interposed therebetween. 
     [7] 
     An optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; and 
     an output optical element that is disposed on the light guide plate and emits light propagated by total reflection in the light guide plate, to an outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the output optical element, and 
     the first optical element and the output optical element are disposed to face each other with the second optical element interposed therebetween. 
     [8] 
     The optical device according to any one of [1] to [7], in which the input optical element includes a light reflecting member. 
     [9] 
     The optical device according to any one of [1] to [8], in which the second optical element is a reflection type or transmission type volume hologram. 
     [10] 
     An optical device including: 
     a light guide plate that totally reflects and guides incident light; 
     a first optical element that is disposed on the light guide plate; 
     an input optical element that is disposed on the light guide plate and introduces the incident light into the light guide plate; 
     a second optical element that is disposed on the light guide plate and bends light propagated by total reflection in the light guide plate, in a direction different from a direction of the light; 
     a third optical element that is disposed on the light guide plate; and 
     an output optical element that is disposed on the light guide plate and emits light propagated, by total reflection, in the light guide plate to the outside of the light guide plate, in which 
     the first optical element has substantially the same grating vector as a grating vector of the second optical element, 
     the third optical element has substantially the same grating vector as a grating vector of the input optical element, and 
     the first optical element and the third optical element, and the second optical element and the input optical element are disposed to face each other with the output optical element interposed therebetween. 
     [11] 
     The optical device according to [10], in which the input optical element includes a light reflecting member. 
     The optical device according to [10] or [11], in which the output optical element is a reflection type or transmission type volume hologram. 
     An image display device including: 
     an image forming apparatus; and 
     an optical device where light emitted from the image forming apparatus is incident, guided, and emitted, in which 
     the optical device includes the optical device according to any one of [1] to [12]. 
     [14] 
     A method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the input optical element; 
     forming an output optical element on the light guide plate; and 
     forming a second optical element by using an interference between first diffracted light obtained when reference light having a substantially opposite vector to a vector included in reproduction reference light is incident on the first optical element and second diffracted light obtained when object light having a substantially opposite vector to a vector included in reproduction light is incident on the output optical element. 
     [15] 
     A method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming an output optical element on the light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the output optical element; and 
     forming a second optical element by using an interference between third diffracted light obtained when object light having substantially the same vector as a vector of reproduction light is incident on the first optical element and fourth diffracted light obtained when reference light having substantially the same vector as a vector of reproduction reference light is incident on the input optical element. 
     [16] 
     A method of manufacturing an optical device including: 
     forming an input optical element on a light guide plate; 
     forming a second optical element on the light guide plate; 
     forming a first optical element on the light guide plate, the first optical element having substantially the same grating vector as a grating vector of the second optical element; 
     forming a third optical element on the light guide plate, the third optical element having substantially the same grating vector as a grating vector of the input optical element; and 
     forming an output optical element by using an interference between fifth diffracted light, which is obtained when reference light having a substantially opposite vector to a vector of reproduction reference light is incident on the third optical element, and light emitted from the third optical element is incident on the first optical element, and object light having a substantially opposite vector to the vector of the reproduction light. 
     REFERENCE SIGNS LIST 
     
         
           1 ,  12 ,  13 ,  14 ,  15 ,  17 - 1 ,  17 - 2  Light guide plate 
           2 ,  22 - 1 ,  22 - 2 ,  23 ,  24 - 1 ,  24 - 2 ,  25 - 1 ,  25 - 2 ,  27 - 1 ,  27 - 2  Input optical element 
           3 ,  32 - 1 ,  32 - 2 ,  33 ,  34 - 1 ,  34 - 2 ,  35 ,  37 - 1 ,  37 - 2  Second optical element 
           4 ,  42 ,  43 ,  44 - 1 ,  44 - 2 ,  45 ,  47 - 1 ,  47 - 2  Output optical element 
           5 ,  52 - 1 ,  52 - 2 ,  53 ,  54 - 1 ,  54 - 2 ,  55 - 1 ,  55 - 2 ,  57 - 1 - 1 ,  57 - 2  First optical element 
           6  Light source 
           7  Projection optical system 
           22  Laminate of input optical elements 
           32  Laminate of second optical elements 
           42 ,  44  Laminate of output optical elements 
           52  Laminate of first optical elements 
           57 - 1 - 2  Third optical element 
           100 ,  200 ,  300 ,  400 ,  500 ,  700 - 1 ,  700 - 2  Optical device 
           200  Image forming apparatus 
           500  Pupil (eyeball) 
           501  Observer&#39;s eyes 
           1000  Image display device 
         L 1  Reproduction reference light 
         L 2  Diffracted light 
         L 3  Enlarged light 
         L 4  Reproduction light 
         S 3 - 1  First surface of light guide plate 
         S 3 - 1  Second surface of light guide plate