Patent Publication Number: US-2013242555-A1

Title: Image display device and image generating device

Description:
BACKGROUND 
     The present disclosure relates to an image display device and an image generating device, and more particularly to an image display device suitable for use in a head mounted display (HMD), and an image generating device suitable for use in the image display device. 
     A virtual display device (image display device) for allowing an observer to observe a two-dimensional (2D) image formed by an image generating device as a virtual image enlarged by a virtual image optical system is well known, for example, from Japanese Patent Application Publication No. 2006-162767. 
     As illustrated in a conceptual diagram of  FIG. 26 , an image display device  1100  includes an image generating device  111  having a plurality of pixels arranged in a 2D matrix, a collimating optical system  112 , which collimates light output from a pixel of the image generating device  111  into parallel light, and a light guide unit  120  on which the parallel light from the collimating optical system  112  is incident, through which the light is guided, and from which the light is output. The light guide unit  120  includes a light guide plate  121 , which outputs the incident light after the incident light propagates through the inside according to total reflection, a first deflecting unit  130  (for example, including a light reflecting film of one layer), which reflects the light incident on the light guide plate  121  so that the light incident on the light guide plate  121  is totally reflected inside the light guide plate  121 , and a second deflecting unit  140  (for example, including a light reflecting multi-film having a multi-layer laminated structure), which outputs from the light guide plate  121  the light propagating through the inside of the light guide plate  121  according to the total reflection. A weight and size of a device can be reduced, for example, when the HMD is formed according to such an image display device  1100 . 
     Alternatively, in order to allow an observer to observe a 2D image formed by the image generating device as a virtual image enlarged by the virtual image optical system, a virtual image display device (image display device) using hologram diffraction gratings is well known, for example, from Japanese Patent Application Publication No. 2007-094175. 
     As illustrated in a conceptual diagram of  FIG. 27 , an image display device  1300  basically includes an image generating device  111 , which displays an image, a collimating optical system  112 , and a light guide unit  320  on which light displayed on the image generating device  111  is incident and through which the incident light is guided to a pupil  21  of the observer. Here, the light guide unit  320  includes a light guide plate  321  and a first diffraction grating member  330  and a second diffraction grating member  340  formed by reflective volume hologram diffraction gratings provided on the light guide plate  321 . Light output from each pixel of the image generating device  111  is incident on the collimating optical system  112 , and parallel light is generated by the collimating optical system  112  and incident on the light guide plate  321 . The parallel light is incident on and output from a first surface  322  of the light guide plate  321 . On the other hand, the first diffraction grating member  330  and the second diffraction grating member  340  are mounted on a second surface  323  of the light guide plate  321  parallel to the first surface  322  of the light guide plate  321 . 
     SUMMARY 
     The light output from the image generating device  111  becomes a group of parallel fluxes having different view angles (that is, output angles of light beams output from pixels of the image generating device  111 ) in the collimating optical system  112  on an XY plane illustrated in  FIG. 27 . The parallel flux group becomes a group of light fluxes having different view angles in an XZ plane orthogonal thereto, and is incident on the light guide plate  321 . In  FIG. 27 , representative parallel light fluxes in the XY plane are indicated as parallel light flux r 1  (indicated by a solid line), r 2  (indicated by a dashed-dotted line) and r 3  (indicated by a dotted line). In  FIG. 28 , representative parallel light fluxes in the XZ plane are indicated as parallel light flux R 1  (indicated by a solid line), R 2  (indicated by a dashed-dotted line) and R 3  (indicated by a dotted line). In the illustrated image display device  1300 , a left-right (horizontal) direction is set as a Y direction and an up-down (vertical) direction is set as a Z direction. That is, light for displaying a video, various types of information, and the like is guided from a lateral direction with respect to the pupil  21  of the observer, and incident on the pupil  21 . 
     Incidentally, in this configuration, there are problems as will be described later due to a difference in behavior of parallel light flux in the XY plane of light guided through the inside of the light guide plate  321  and parallel light flux in the XZ plane.  FIG. 29A  is a diagram illustrating a problem in the image display device of the related art, and  FIG. 29B  is a diagram schematically illustrating a propagation state of light output from a center portion and an upper portion of the collimating optical system and guided through the light guide plate.  FIG. 29A  is a diagram schematically illustrating a propagation state of light, which is output from the image generating device and guided through the light guide unit, and reaches the pupil, within a plane corresponding to an inside of the XZ plane and the XY plane. 
     That is, in the above-described configuration, light incident from the first surface  322  of the light guide plate  321  is incident on the first diffraction grating member  330  disposed on the second surface  323 . A distance from the center of the collimating optical system  112  to the center of the first diffraction grating member  330  is set as L 1 , a distance from the center of the first diffraction grating member  330  to the center of the second diffraction grating member  340  is set as L 2 , and a distance from the second diffraction grating member  340  to the pupil  21  is set as L 3 . 
     In terms of an X direction component of the XY plane, the light fluxes r 1 , r 2 , and r 3  are diffracted and reflected by the first diffraction grating member  330 , are guided inside the light guide plate  321  while being iteratively totally reflected between the first surface  322  and the second surface  323  in a state of parallel light fluxes, and move in a Y direction toward the second diffraction grating member  340  provided on the other end of the light guide plate  321 . Parallel light of each view angle incident on the second diffraction grating member  340  is output from the light guide plate  321  under a total reflection condition according to diffraction reflection and incident on the pupil  21  of the observer. Here, in a travelling direction of the parallel light fluxes, the number of reflections within the light guide plate  321  differs according to a view angle. That is, an optical path length is different. However, because all light fluxes to propagate are parallel light fluxes, a light flux group moves to be folded. Accordingly, in terms of light of an X direction component of the XY plane, a substantial distance from the center of the collimating optical system  112  to the pupil  21  becomes (L 1 +L 3 ) because the distance L 2  from the center of the first diffraction grating member  330  to the center of the second diffraction grating member  340  can be neglected. In addition, this system can be generally regarded as a telecentric optical system, and a position of the first diffraction grating member  330  becomes an exit pupil position in terms of light of the X direction component of the XY plane. 
     On the other hand, although the X direction component is iteratively reflected within the light guide plate  321  in terms of incident light beams R 1 , R 2 , and R 3  in the XZ plane, a Z direction component reaches the second diffraction grating member  340  without being reflected. That is, light output from the collimating optical system  112  converges in the XZ plane to be incident from the first surface  322  and moves in the Y direction inside the light guide plate  321 . These light fluxes move while being reflected by the first surface  322  and the second surface  323  of the light guide plate  321  so that the light fluxes are narrow in the Z direction, and reach the second diffraction grating member  340 . The light fluxes are reflected, diffracted, and output by the second diffraction grating member  340  and incident on the pupil  21  of the observer. That is, in terms of light of the Z direction component of the XZ plane, a substantial distance from the center of the collimating optical system  112  to the pupil  21  generally becomes (L 1 +L 2 /sin(Φ)+L 3 ) when it is necessary to consider the distance L 2  from the center of the first diffraction grating member  330  to the center of the second diffraction grating member  340  and a total reflection angle is Φ as illustrated in  FIG. 1 . In addition, in terms of light of the Z direction component of the XZ plane in a non-telecentric optical system, a position of the pupil  21  or a position in the vicinity of the pupil  21  becomes an exit pupil position. 
     Therefore, although light of a spatial region having diagonal lines from the top right to the bottom left reaches the pupil  21 , for example, in terms of incident light R 3 ′, as illustrated in  FIG. 29A , light of a spatial region having diagonal lines from the top left to the bottom right does not reach the pupil  21 . That is, part of light flux does not reach the pupil  21 , and a type of vignetting occurs. In other words, there are problems that the utilization efficiency of light output from the image generating device  111  is low and that the low utilization efficiency of light leads to an increase in power consumption in the image generating device  111 . 
     For example, as is well known from Japanese Patent Application Publication No. 10-170859, an image display device displays an image on a display surface formed by a plurality of pixels of an image generating unit, guides light flux output from the image transmitted and illuminated by an illuminating unit to the pupil of the observer via an optical system, and allows the observer to view a virtual image of the image formed by the light flux. In this image display device, light flux output from each pixel is incident on the optical system as light flux of a divergence angle different between a first direction and a second direction by setting the first direction and the second direction substantially orthogonal to the first direction within a plane on which the virtual image is formed and controlling divergence angles of the first direction and the second direction using a divergence angle conversion unit provided in the vicinity of each pixel for every pixel. However, it is difficult to solve a problem that the utilization efficiency of light is low even when light flux of a divergence angle different between the first direction and the second direction is incident on the optical system as described above. 
     It is desirable to provide an image display device having a configuration and structure that can improve the utilization efficiency of light output from the image generating device and further reduce power consumption in an image generating device and an image generating device suitable for use in the image display device. 
     In accordance with an embodiment of the present disclosure, there is provided an image display device including: 
     (A) an image generating device; and 
     (B) a light guide unit on which light from the image generating device is incident, through which the light is guided, and from which the light is output toward a pupil of an observer. 
     The image generating device of the present disclosure has the light guide unit, which includes 
     a light guide plate from which the incident light is output after the incident light propagates through an inside according to total reflection, 
     a first deflecting unit configured to deflect the light incident on the light guide plate so that the light incident on the light guide plate is totally reflected inside the light guide plate, and 
     a second deflecting unit configured to deflect the light propagating through the inside of the light guide plate according to the total reflection a plurality of times so that the light propagating through the inside of the light guide plate according to the total reflection is output from the light guide plate. The term “total reflection” unit internal total reflection or total reflection inside the light guide plate. Hereinafter, the same is also true. 
     In the image display device of the present disclosure or the image generating device of the present disclosure, when a point at which light output from a center of the image generating device is incident on the light guide unit is set as a point O, a normal line passing through the point O in a portion of the light guide unit is set as an X axis, an axis of the light guide unit passing through the point O in a portion of the light guide unit is set as a Y axis, an optical axis of light incident at the point O of the light guide unit among light beams output from a center of the image generating device is set as ζ axis, and a virtual plane including the axis and the Y axis is set as a ζY plane, light output from the image generating device and incident at a point (0, Y 1 , Z 1 ) of the light guide unit forms an angle θ Z  with the ζY plane and forms an angle θ Y  with an XZ plane. When Z 1 ≠0, θ Z ≠θ Y  is satisfied. 
     In the image display device or the image generating device of the present disclosure, when Z 1 ≠0, θ Z ≠θ Y  is satisfied. Accordingly, part of light flux output from the light guide unit does not reach the pupil, the occurrence of a phenomenon that a type of vignetting occurs can be suppressed, and the utilization efficiency of light output from the image generating device can be improved. Consequently, power consumption in the image generating device can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual diagram of an image display device of Embodiment 1; 
         FIGS. 2A and 2B  are diagrams schematically illustrating a propagation state of light when viewed from an XZ plane and a propagation state of light when viewed from an XY plane among light beams output from a light emitting unit positioned in an upper portion of an image generating device of Embodiment 1; 
         FIGS. 3A and 3B  are diagrams schematically illustrating a propagation state of light when viewed from the XZ plane and a propagation state of light when viewed from the XY plane among light beams output from a light emitting unit positioned in a center portion of the image generating device of Embodiment 1; 
         FIG. 4A  is a diagram schematically illustrating a propagation state of light, which is output from the image generating device of Embodiment 1 and guided through a light guide unit, and reaches a pupil, within a plane corresponding to an inside of the XZ plane and the XY plane; 
         FIG. 4B  is a diagram schematically illustrating light output from each light emitting unit of the image generating device; 
         FIGS. 4C and 4D  are diagrams illustrating a relationship between the light guide unit and a central incident light beam when the light guide unit is viewed from the side; 
         FIG. 5  is a schematic diagram of the image display device of Embodiment 1 viewed from above; 
         FIG. 6  is a schematic diagram of the image display device of Embodiment 1 viewed from the side; 
         FIG. 7  is a schematic diagram of the image display device of Embodiment 1 viewed from the front; 
         FIG. 8  is a diagram illustrating a state in which the image display device of Embodiment 1 is mounted on a head of an observer viewed from above (only the image display device is illustrated and the illustration of the frame is omitted); 
         FIG. 9  is a conceptual diagram of an image display device of Embodiment 2; 
         FIGS. 10A and 10B  are conceptual diagrams of an image display device of Embodiment 3; 
         FIG. 11  is a conceptual diagram of an image display device of Embodiment 4; 
         FIG. 12  is a schematic diagram of an image display device of Embodiment 5 viewed from the side; 
         FIG. 13  is a schematic diagram of an image display device of Embodiment 6 viewed from the front; 
         FIG. 14  is a schematic diagram of an image display device of Embodiment 6 viewed from above; 
         FIG. 15  is a schematic diagram of an HMD of Embodiment 7 viewed from the front; 
         FIG. 16  is a schematic diagram of an HMD of Embodiment 7 (in a state in which a frame is assumed to be removed) viewed from the front; 
         FIG. 17  is a schematic diagram of the HMD of Embodiment 7 viewed from above; 
         FIG. 18  is a schematic diagram of an HMD of Embodiment 8 viewed from the front; 
         FIG. 19  is a schematic diagram of the HMD of Embodiment 8 (in a state in which a frame is assumed to be removed) viewed from the front; 
         FIG. 20  is a schematic diagram of the HMD of Embodiment 8 viewed from above; 
         FIG. 21  is a conceptual diagram of a modified example of an image generating device suitable for use in Embodiment 1 or 3; 
         FIG. 22  is a conceptual diagram illustrating another modified example of the image generating device suitable for use in Embodiment 1 or 3; 
         FIG. 23  is a conceptual diagram illustrating still another modified example of the image generating device suitable for use in Embodiment 1 or 3; 
         FIG. 24  is a conceptual diagram illustrating still another modified example of the image generating device suitable for use in Embodiment 1 or 3; 
         FIG. 25  is a conceptual diagram illustrating still another modified example of the image generating device suitable for use in Embodiment 1 or 3; 
         FIG. 26  is a conceptual diagram of an image display device of the related art; 
         FIG. 27  is a conceptual diagram of the image display device of the related art having another form different from that illustrated in  FIG. 26 ; 
         FIG. 28  is a conceptual diagram of the image display device of the related art of the form illustrated in  FIG. 27  viewed from another direction; 
         FIG. 29A  is a diagram illustrating a problem in the image display device of the related art; 
         FIG. 29B  is a diagram schematically illustrating a propagation state of light that is output from a center portion and an upper portion of a collimating optical system and guided through a light guide plate; and 
         FIG. 30  is a schematic diagram of a form of image display device of the related art viewed from the side. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENT(S) 
     Hereinafter, although the present disclosure will be described based on embodiments with reference to the drawings, the present disclosure is not limited to the embodiments, and various numerical values and materials mentioned in the embodiments are exemplary. Description will be given in the following order. 
     1. Overall Description of Image Display Device and Image Generating Device of Present Disclosure 
     2. Embodiment 1 (Image Display Device and Image Generating Device: First Form of Image Generating Device/First Form of Light Guide Unit) 
     3. Embodiment 2 (Modification of Embodiment 1: Second Form of Image Generating Device/First Form of Light Guide Unit) 
     4. Embodiment 3 (Modification of Embodiment 1: First Form of Image Generating Device/Second Form of Light Guide Unit) 
     5. Embodiment 4 (Modification of Embodiment 1: Second Form of Image Generating Device/Second Form of Light Guide Unit) 
     6. Embodiment 5 (Modification of Embodiments 1 to 4) 
     7. Embodiment 6 (Other Modification of Embodiments 1 to 4) 
     8. Embodiment 7 (Modification of Embodiments 1 to 6) 
     9. Embodiment 8 (Modification of Embodiment 7) and Others 
     [Overall Description of Image Display Device and Image Generating Device of Present Disclosure] 
     In the image display device or image generating device of the present disclosure (hereinafter, these may be collectively referred to as the “image display device and the like of the present disclosure”), 
     a value of θ Y  is constant regardless of a value of Y 1 , and 
     an absolute value of θ Z  can be increased when an absolute value of Z 1  is increased. In the image display device or the like of the present disclosure of a preferred form as described above, the absolute value of θ Z  can be formed to be increased monotonically or stepwise when the absolute value of Z 1  is increased. Although θ Y  is not specifically limited when the value of θ Y  is constant regardless of the value of Y 1 , it is only necessary that, for example, θ Y =0. 
     Further, the image display device and the like of the present disclosure of these forms can have a configuration in which: 
     the image generating device has a light emitting unit (light output unit) disposed in a 2D matrix, 
     a microlens array in which a plurality of microlenses are arranged in a 2D matrix is disposed in the image generating device, 
     light output from each light emitting unit is output from the image generating device through a microlens facing the light emitting unit, and 
     shift amounts of an optical axis of the light emitting unit and an optical axis of the microlens facing the light emitting unit are defined based on a value of (0, Y 1 , Z 1 ). In this case, although the microlens is not limited, the microlens can be formed by a cylindrical lens or an anamorphic lens. In addition, in these cases, a radiation angle (divergence angle) ω 1  of light output from the microlens can be configured to be less than a radiation angle (divergence angle) ω 0  of light output from the light emitting unit. 
     Alternatively, the image display device and the like of the present disclosure of a preferred form as described above can have a configuration in which: 
     an image generating device is provided with a light output angle control member, and 
     light is output from the image generating device to a light guide unit through the light output angle control member. In this case, there is provided a configuration in which: 
     the image generating device has light emitting units (light output units) arranged in a 2D matrix, 
     the light output angle control member is formed by a microlens array in which a plurality of microlenses are arranged in a 2D matrix, and 
     light output from each light emitting unit is output from the image generating device through a microlens facing the light emitting unit. Further, in this case, shift amounts of an optical axis of the light emitting unit and an optical axis of the microlens facing the light emitting unit can be configured to be defined based on a value of (0, Y 1 , Z 1 ). In these configurations, although the microlens is not limited, the microlens can be formed by a cylindrical lens or an anamorphic lens. A radiation angle (divergence angle) ω 1  of light output from the microlens can be configured to be less than a radiation angle (divergence angle) ω 0  of light output from the light emitting unit. 
     The microlens or microlens array can be manufactured through a well-known method. In addition, the optical axis of the microlens can be configured to be inclined based on a value of (0, Y 1 , Z 1 ) instead of shifting the optical axis of the light emitting unit and the optical axis of the microlens facing the light emitting unit based on the value of (0, Y 1 , Z 1 ). In this case, it is only necessary to appropriately design a curvature factor of a light output plane of the microlens. 
     Further, in the image display device of the present disclosure including a preferred form and configuration as described above, the light guide unit can include: 
     (B-1) a light guide plate from which the incident light is output after the incident light propagates through an inside according to total reflection, 
     (B-2) a first deflecting unit configured to deflect the light incident on the light guide plate so that the light incident on the light guide plate is totally reflected inside the light guide plate, and 
     (B-3) a second deflecting unit configured to deflect the light propagating through the inside of the light guide plate according to the total reflection a plurality of times so that the light propagating through the inside of the light guide plate according to the total reflection is output from the light guide plate. 
     Further, in the image display device and the like of the present disclosure including a preferred form and configuration as described above, for example, a liquid crystal display (LCD) device, an organic electro luminescence (EL) display device, an inorganic EL display device, or a light emitting element array in which a plurality of light emitting elements are arranged in a 2D matrix can be included as the image generating device. In this image display device, the image generating device can further include a parallel light outputting optical system formed by a collimating optical system that collimates light output from each light emitting unit (a pixel or a virtual pixel) and passing through the microlens array or the light output angle control member into parallel light, and light from the parallel light outputting optical system (collimating optical system) can be configured to be incident on the light guide unit. For convenience, this image generating device is referred to as the “first form of image generating device.” 
     Alternatively, the image generating device includes 
     a light source, 
     a collimating optical system, which collimates light output from the light source into parallel light, 
     a scanning unit, which scans the parallel light output from the collimating optical system, and 
     a parallel light outputting optical system formed by a relay optical system, 
     which relays the parallel light scanned by the scanning unit, wherein light output from the scanning unit and passing through a microlens array or a light output angle control member can be configured to be incident on the parallel light outputting optical system (relay optical system) and light from the parallel light outputting optical system (relay optical system) can be configured to be incident on the light guide unit. For convenience, this image generating device is referred to as the “second form of image generating device.” Light output from the scanning unit (optical points) is arranged in a 2D matrix in a space, and each optical point corresponds to a light emitting unit (a virtual pixel). 
     In addition, for example, an image generating device including a reflective spatial light modulating device and a light source; an imaging generating device including a transmissive spatial light modulating device and a light source; and an image generating device formed by a light emitting element array including light emitting elements such as an organic EL, an inorganic EL, and light emitting diodes (LEDs) can be included as the image generating device in the first form of image generating device. A light valve, for example, a transmissive or reflective LCD device such as liquid crystal on silicon (LCOS) or a digital micromirror device (DMD), can be included as the spatial light modulating device, and a light emitting element can be included as the light source. Further, the reflective spatial light modulating device can be formed by an LCD device and a polarization beam splitter that reflects part of light from the light source to guide the reflected part of the light to the LCD device and passes part of light reflected by the LCD device to guide the part of the light to the parallel light emitting optical system. As the light emitting element constituting the light source, a red light emitting element, a green light emitting element, a blue light emitting element, and a white light emitting element can be included. Alternatively, white light may be obtained by mixing red, green, and blue light beams output from the red light emitting element, the green light emitting element, and the blue light emitting element using the light pipe and performing luminance equalization. As the light emitting element constituting the light emitting element array, for example, there are examples of a semiconductor laser element, a solid-state laser, and an LED. The number of light emitting units (pixels or virtual pixels) may be determined based on specifications necessary for the image display device. As a specific value of the number of light emitting units, there are examples of 320×240, 432×240, 640×480, 854×480, 1024×768, and 1920×1080. As the parallel light outputting optical system (collimating optical system), there is an example of an optical system having positive optical power as a whole using a convex lens, a concave lens, a free-form surface prism, and a hologram lens independently or in combination. A light shielding member having an opening portion to prevent undesired light from being output from the parallel light outputting optical system may be disposed between the parallel light outputting optical system (the collimating optical system or relay optical system) and the light guide unit. 
     On the other hand, a light emitting element can be included as a light source in the second form of image generating device, and specifically include a red light emitting element, a green light emitting element, a blue light emitting element, and a white light emitting element. Alternatively, white light may be obtained by mixing red, green, and blue light beams output from the red light emitting element, the green light emitting element, and the blue light emitting element using the light pipe and performing luminance equalization. As the light emitting element, for example, there are examples of a semiconductor laser element, a solid-state laser, and an LED. In the second form of imaging generating device, the number of light emitting units (virtual pixels) may be determined based on specifications necessary for the image display device. As a specific value of the number of light emitting units (virtual pixels), there are examples of 320×240, 432×240, 640×480, 854×480, 1024×768, and 1920×1080. In addition, when the light source includes the red light emitting element, the green light emitting element, and the blue light emitting element, it is preferable to perform color synthesis, for example, using a cross prism. As the scanning unit, for example, a micro electro mechanical system (MEMS), which has a micro minor rotatable in a 2D direction to horizontally and vertically scan light output from the light source, or a galvano minor can be included. It is only necessary to form the relay optical system constituting the parallel light outputting optical system by a well-known relay optical system. 
     There are examples of the following configurations in addition to a combination of a backlight that emits white light as a whole, for example, as an image generating device or a light source including a light emitting element and a light valve, and an LCD device having a red light emitting pixel, a green light emitting pixel, and a blue light emitting pixel. 
     [Image Generating Device A] 
     The image generating device A includes: 
     (α) a first image generating device formed by a first light emitting panel in which first light emitting elements for emitting blue light are arranged in a 2D matrix, 
     (β) a second image generating device formed by a second light emitting panel in which second light emitting elements for emitting green light are arranged in a 2D matrix, 
     (γ) a third image generating device formed by a third light emitting panel in which third light emitting elements for emitting red light are arranged in a 2D matrix, and 
     (δ) a unit (for example, a dichroic prism, which is also substantially the same as in the following description) for integrating light output from the first, second, and third image generating devices into one optical path, 
     wherein a light emitting/non-light-emitting state of each of the first, second, and third light emitting elements is controlled. 
     [Image Generating Device B] 
     The image generating device B includes: 
     (α) a first image generating device formed by a first light emitting element for emitting blue light and a first light passage control device (which is a type of light valve, and, for example, formed by an LCD device, a DMD, or an LCOS, which is substantially the same as in the following description) for controlling passage/non-passage of the light output from the first light emitting element for emitting the blue light, 
     (β) a second image generating device formed by a second light emitting element for emitting green light and a second light passage control device (light valve) for controlling passage/non-passage of the light output from the second light emitting element for emitting the green light, 
     (γ) a third image generating device formed by a third light emitting element for emitting red light and a third light passage control device (light valve) for controlling passage/non-passage of the light output from the third light emitting element for emitting the red light, and 
     (δ) a unit for integrating light passing through the first, second, and third light passage control devices into one optical path, 
     wherein an image is displayed by controlling passage/non-passage of the light output from the light emitting elements using the light passage control devices. As a unit (light guide member) for guiding the light output from the first, second, and third light emitting elements to the light passage control device, there are examples of a light guide member, a microlens array, a mirror, a reflecting plate, and a condensing lens. 
     [Image Generating Device C] 
     The image generating device C includes: 
     (α) a first image generating device formed by a first light emitting panel in which first light emitting elements for emitting blue light are arranged in a 2D matrix and a blue light passage control device (light valve) for controlling passage/non-passage of the output light output from the first light emitting element for emitting the blue light, 
     (β) a second image generating device formed by a second light emitting panel in which second light emitting elements for emitting green light are arranged in a 2D matrix and a green light passage control device (light valve) for controlling passage/non-passage of the output light output from the second light emitting panel, 
     (γ) a third image generating device formed by a third light emitting panel in which third light emitting elements for emitting red light are arranged in a 2D matrix and a red light passage control device (light valve) for controlling passage/non-passage of the output light output from the third light emitting panel, and 
     (δ) a unit for integrating light passing through the blue, green, and red light passage control devices into one optical path, 
     wherein an image is displayed by controlling passage/non-passage of the output light output from the first, second, and third light emitting panels using the light passage control devices (light valves). 
     [Image Generating Device D] 
     The image generating device D is a field sequential color-display image generating device, and includes: 
     (α) a first image generating device having a first light emitting element for emitting blue light, 
     (β) a second image generating device having a third light emitting element for emitting green light, 
     (γ) a third image generating device having a second light emitting element for emitting red light, 
     (δ) a unit for integrating light output from the first, second, and third image generating devices into one optical path, and 
     (∈) a light passage control device (light valve) for controlling passage/non-passage of light output from the unit for integration into the one optical path, 
     wherein an image is displayed by controlling passage/non-passage of the light output from the light emitting elements using the light passage control devices. 
     [Image Generating Device E] 
     The image generating device E is also a field sequential color-display image generating device, and includes: 
     (α) a first image generating device formed by a first light emitting panel in which first light emitting elements for emitting blue light are arranged in a 2D matrix, 
     (β) a second image generating device formed by a second light emitting panel in which second light emitting elements for emitting green light are arranged in a 2D matrix, 
     (γ) a third image generating device formed by a third light emitting panel in which third light emitting elements for emitting red light are arranged in a 2D matrix, 
     (δ) a unit for integrating light output from the first, second, and third image generating devices into one optical path, and 
     (∈) a light passage control device (light valve) for controlling passage/non-passage of light output from the unit for integration into the one optical path, 
     wherein an image is displayed by controlling passage/non-passage of the light output from the light emitting panels using the light passage control device. 
     [Image Generating Device F] 
     The image generating device F is a passive or active matrix type of color-display image generating device, which displays an image by controlling a light-emitting/non-light-emitting state of each of first, second, and third light emitting elements. 
     [Image Generating Device G] 
     The image generating device G is a field sequential color-display image generating device, which includes a light passage control device (light valve) for controlling passage/non-passage of light output from light emitting element units arranged in a 2D matrix, and displays an image by controlling a light-emitting/non-light-emitting state of each of first, second, and third light emitting elements in the light emitting element units in time division, and further controlling passage/non-passage of light output from the first, second, and third light emitting elements using the light passage control device. 
     Light, which is output from a center of the image generating device, passes through a nodal point of the image generating device of the parallel light emitting optical system, and is incident on the light guide unit, is referred to as a “central incident light beam.” The central incident light beam is incident at a point O of the light guide unit. The point O may be referred to as the center point of the light guide unit. As described above, an axial line that passes through the center point of the light guide unit and is parallel to an axial direction of the light guide unit is set as a Y axis and an axial line that passes through the center point of the light guide unit and is consistent with a normal line of the light guide unit is set as an X axis. 
     A first deflecting unit can be configured to reflect light incident on the light guide plate, and a second deflecting unit can be configured to transmit and reflect light propagating through the inside of the light guide plate according to the total reflection a plurality of times. In this case, the first deflecting unit can be configured to function as a reflecting mirror, and the second deflecting unit can be configured to function as a semi-transmissive mirror. For convenience, this light guide unit is referred to as the “first form of light guide unit.” 
     In this configuration, the first deflecting unit can include a light reflecting film (a type of minor), which is formed of a metal including an alloy and reflects light incident on the light guide plate or a diffraction grating (for example, a hologram diffraction grating film) that diffracts the light incident on the light guide plate. In addition, the second deflecting unit can include a multi-layer laminated structure in which a plurality of dielectric laminated films are laminated, a semi-transmissive minor, a polarization beam splitter, or a hologram diffraction grating film. Although the first or second deflecting unit is disposed inside the light guide plate (embedded inside the light guide plate), parallel light incident on the light guide plate is reflected or diffracted so that the parallel light incident on the light guide plate is totally reflected inside the light guide plate in the first deflecting unit. On the other hand, in the second deflecting unit, the parallel light propagating through the inside of the light guide plate according to the total reflection is reflected or diffracted a plurality of times, and output from the light guide plate in a state of parallel light. 
     Alternatively, the first deflecting unit can be configured to diffract light incident on the light guide plate, and the second deflecting unit can be configured to diffract light propagating through the inside of the light guide plate according to the total reflection a plurality of times. For convenience, this light guide unit is referred to as the “second form of light guide unit.” In this case, the first deflecting unit and the second deflecting unit can be formed by diffraction grating elements. Further, the diffraction grating element can be formed by a reflective diffraction grating element or a transmissive diffraction grating element. Alternatively, one diffraction grating element can be formed by the reflective diffraction grating element and the other diffraction grating element can be formed by the transmissive diffraction grating element. A reflective volume hologram diffraction grating can be included as the reflective diffraction grating element. For convenience, the first deflecting unit formed by the reflective volume hologram diffraction grating may be referred to as a “first diffraction grating member,” and the second deflecting unit formed by the reflective volume hologram diffraction grating may be referred to as a “second diffraction grating member.” That is, the diffraction direction is the Y direction and interference fringes extend in the Z direction. 
     The image display device in accordance with the present disclosure can perform a single-color (for example, green) image display. When color image display is performed, P diffraction grating layers, each of which is formed by a reflective volume hologram diffraction grating, can be laminated to cause the first diffraction grating member or the second diffraction grating member to cope with diffraction/reflection of P types of light having P types (for example, P=3, that is, three types of red, green, and blue) of different wavelength bands (or wavelengths). Each diffraction grating layer is provided with interference fringes corresponding to one type of wavelength band (or wavelength). Alternatively, to cope with diffraction and reflection of P types of light having P types of different wavelength bands (or wavelengths), P types of interference fringes can be configured to be formed in the first diffraction grating member or the second diffraction grating member formed by one diffraction grating layer. Alternatively, for example, the angle of view can be divided into three equal parts, and the first diffraction grating member or the second diffraction grating member can be configured by laminating diffraction grating layers corresponding to angles of view. By adopting these configurations, it is possible to increase the diffraction efficiency and acceptable diffraction angle and optimize the diffraction angle when light beams having the wavelength bands (or wavelengths) are diffracted and reflected by the first diffraction grating member or the second diffraction grating member. 
     The first diffraction grating member and the second diffraction grating member can be formed of a photopolymer material. It is only necessary that the material and basic structure of the first diffraction grating member and the second diffraction grating member formed by the reflective volume hologram diffraction gratings be the same as those of the reflective volume hologram diffraction gratings of the related art. The reflective volume hologram diffraction grating refers to a hologram diffraction grating that diffracts and reflects only +1-order diffracted light. Although the diffraction grating member is provided with interference fringes extending from the inner side to the outer side of the diffraction grating member, a method of forming the interference fringes may be the same as adopted in the related art. Specifically, for example, it is only necessary that a material (e.g., a photopolymer material) constituting the diffraction grating member be irradiated with object light in a first predetermined direction on one side, a material constituting the diffraction grating member be simultaneously irradiated with reference light in a second predetermined direction on the other side, and interference fringes formed by the object light and the reference light be recorded in the material constituting the diffraction grating member. By appropriately selecting the first predetermined direction, the second predetermined direction, and wavelengths of the object light and the reference light, a desired pitch of the interference fringes and a desired slant angle of the interference fringes on the surfaces of the diffraction grating member can be obtained. The slant angle of the interference fringes refers to the angle formed between the surfaces of the diffraction grating member (or the diffraction grating layer) and the interference fringes. When the first diffraction grating member and the second diffraction grating member are formed by a laminated structure in which P diffraction grating layers, each of which is formed by a reflective volume hologram diffraction grating, are laminated, it is only necessary to separately manufacture P diffraction grating layers and then laminate (adhere) the P diffraction grating layers, for example, using an ultraviolet curing resin adhesive. In addition, the P diffraction grating layers may be formed by manufacturing one diffraction grating layer using an adhesive photopolymer material, and then adhering layers of the adhesive photopolymer material thereon in order to manufacture diffraction grating layers. 
     Alternatively, in the image display device in accordance with the present disclosure, the light guide unit can be formed by a semi-transmissive mirror on which light output from the image generating device is incident and from which the incident light is reflected and output toward the pupil of the observer. A structure in which the light output from the image generating device propagates through the air and is incident on the semi-transmissive minor may be provided. For example, a structure in which the light output from the image generating device propagates inside a transparent member such as a glass plate or a plastic plate (specifically, a member formed of the same material as the material constituting the light guide plate to be described later) and incident on a semi-transmissive mirror may be provided. The semi-transmissive minor may be mounted on the image generating device via the transparent member, and the semi-transmissive mirror may be mounted on the image generating device via a member separate from the transparent member. 
     In the first or second form of image display device, a plurality of parallel light beams formed by the parallel light outputting optical system including the collimating optical system or the relay optical system are incident on the light guide plate. The requirement for parallel light beams is based on the fact that it is necessary to store light wave-front information obtained when the light beams are incident on the light guide plate even after the light beams are output from the light guide plate via the first deflecting unit and the second deflecting unit. To generate a plurality of parallel light beams, specifically, for example, it is only necessary that the light output unit of the image generating device be positioned in a place (position) of the focal length of the parallel light emitting optical system. The parallel light outputting optical system has a function of converting position information of pixels or virtual pixels into angle information in the light guide unit. 
     In the image display device, the light guide plate has two parallel surfaces (first and second surfaces) extending in parallel to a light propagation direction (Y direction) according to internal total reflection of the light guide plate. When a surface of the light guide plate on which light is incident is an incidence surface of the light guide plate and a surface of the light guide plate from which light is output is an output surface of the light guide plate, both the incidence surface and the output surface of the light guide plate may be defined by the first surface, or the incidence surface of the light guide plate may be defined by the first surface and the output surface of the light guide plate may be defined by the second surface. 
     For example, the light guide plate can be formed of a glass material including optical glass such as quartz glass or BK7, or a plastic material (e.g., poly methyl methacrylate (PMMA), a polycarbonate resin, an acrylic resin, amorphous polypropylene resin, or a styrene resin including acrylonitrile styrene (AS) resin). The shape of the light guide plate is not limited to a flat plate, but may be curved. 
     According to the image display device of the present disclosure, for example, an HMD can be configured, a weight and size of the device can be reduced, the discomfort when the device is mounted can be significantly reduced, and manufacturing cost can be reduced. 
     The HMD includes: 
     (a) an eyeglass type frame to be mounted on an observer&#39;s head, and 
     (b) the image display device of the present disclosure. According to the HMD, the number of image display devices of the present disclosure may be one (monocular type) or two (binocular type). The light guide unit can be a semi-transmissive type (see-through type). Specifically, at least a portion of the light guide unit facing pupils (both eyes) of an observer is configured to be semi-transmissive (see-through), so that the outside scene can be viewed through the portion of the light guide unit. 
     A frame is formed by a front portion arranged on the front side of the observer, two temple portions pivotably mounted on both ends of the front portion via hinges, and an ear bend portion mounted on the tip end portion of each temple portion, and further includes nose pads. When the entire HMD is seen, an assembly of the frame and the nose pads has a structure that is substantially the same as that of ordinary glasses, except that there is no rim. The material constituting the frame may be a metal, alloy, or plastic, or a combination thereof and may be the same material as the material constituting ordinary glasses. The nose pads may also have a well-known configuration and structure. 
     From the viewpoint of design of the HMD or ease of wearing the HMD, it is preferable that wirings (signal lines, power lines, or the like) from one or two image generating devices be formed to extend from the tip end portion of the ear bend portion to the outside via the temple portion and the inside of the ear bend portion and to be connected to the control device (a control unit or a control circuit). Further, it is preferable to configure a form in which each image generating device includes a headphone unit, and a wiring for the headphone unit from each image generating device extends from the tip end portion of the ear bend portion to the headphone unit via the temple portion and the inside of the ear bend portion. Examples of the headphone unit are an inner-ear type of headphone unit and a canal type of headphone unit. More specifically, it is preferable to configure a form in which the wiring for the headphone unit from the tip end portion of the ear bend portion wraps around the rear side of the auricle (auditory capsule) and extends to the headphone unit. 
     In addition, in the HMD, an imaging device can be formed to be mounted on a center portion of the front portion. Specifically, the imaging device is formed by a solid-state imaging device, for example, formed by a CCD or a CMOS sensor and a lens. It is only necessary that a wiring extending from the imaging device be connected to one image display device, for example, through the back of the front portion and further included in a wiring extending from the image display device. 
     There is no limitation in the image display device in accordance with the present disclosure, and a central incident light beam can be configured to intersect the XY plane at an angle (θ Z0 ≠0 degrees) other than zero degrees, that is, an incidence angle θ Z0  for the XY plane (an XY plane incidence angle) can be configured to be θ Z0 ≠0 degrees. Accordingly, the limitation on the mounting angle of the image display device at the time of mounting of the image display device on a mounting portion of the eyeglass type frame can be reduced, and a high degree of freedom for design can be obtained. When the XY plane is assumed to be consistent with the horizontal plane, the angle θ Z0  at which the central incident light beam intersects the XY plane can be configured to be an elevation angle. That is, the central incident light beam may be configured to collide with the XY plane from the lower side of the XY plane toward the XY plane. In such a case, it is preferable that the XY plane intersect the vertical surface at an angle other than zero degrees, and it is more preferable that the XY plane intersect the vertical surface at an angle θ Z0 ′. Although the maximum value of the angle θ Z0 ′ is not limited, the maximum value can include 5 degrees. Here, the horizontal plane includes a line of sight (horizontal line of sight of an observer) when the observer views a target (for example, a target located at an infinite distance or the horizon) located in the horizontal direction and is a plane in which the two horizontally positioned pupils of the observer are included. In addition, the vertical plane is a plane perpendicular to the horizontal plane. Alternatively, the central incident light beams output from the light guide unit and incident on the pupils of the observer can be formed to form a depression angle when the observer views a target (for example, a target located at an infinite distance or the horizon) located in the horizontal direction. The depression angle for the horizontal plane, for example, can be in the range of 5 degrees to 45 degrees. 
     Where the HMD is the binocular type, it is preferable that the light guide unit further include: 
     a connecting member, which is disposed on the side of the center of the observer&#39;s face as a whole rather than the image generating device and interconnects the two image display devices, 
     wherein the connecting member is mounted on a side facing the observer in a center portion of a frame located between the two pupils of the observer, and 
     wherein a projected image of the connecting member is included in a projected image of the frame. 
     As described above, according to a structure in which the connecting member is mounted on the center portion of the frame located between the observer&#39;s two pupils, that is, when a structure in which the image display devices are directly mounted on the frame is not provided, a displacement (positional change) of the image generating device or the light guide unit is not caused by deformation of the frame even when the temple portions are expanded to the outside when the frame is mounted on the observer&#39;s head and hence the frame is deformed, or such displacement, if any, is very small. Therefore, it is possible to reliably prevent angles of convergence of left and right images from being changed. Moreover, because it is unnecessary to enhance the rigidity of the front portion of the frame, it is possible to avoid causing an increase in the weight of the frame, a decrease in design quality, or an increase in cost. In addition, because the image display devices are not directly mounted on the eyeglass type frame, the design, color and the like of the frame can be freely selected according to the observer&#39;s preference, there are few restrictions imposed on the design of the frame, so that the degree of freedom on a design basis is high. In addition, the connecting member is disposed between the observer and the frame, and moreover, the projected image of the connecting member is included in the projected image of the frame. In other words, the connecting member is hidden behind the frame when the HMD is viewed from the front side of the observer. Accordingly, high design quality can be given to the HMD. 
     It is preferable to mount the connecting member on a side facing the observer in a center portion of the front portion (corresponding to a portion of a bridge in an ordinary pair of eyeglasses) located between the two pupils of the observer. 
     Although the two image display devices are connected by the connecting member, the image generating devices can be specifically formed to be mounted on both end portions of the connecting member, respectively, so that the mounting state is adjustable. In this case, it is preferable that each of the image generating devices be located outside the observer&#39;s pupil. In such a configuration, further, it is desirable that the condition of 0.01×L≦α≦0.30×L, preferably, 0.05×L≦α≦0.25×L, the condition of 0.35×L≦β≦0.65×L, preferably, 0.45×L≦β≦0.55×L, and the condition of 0.70×L≦γ≦0.99×L, preferably 0.75×L≦γ≦0.95×L, be satisfied, where α is the distance between the mounting-portion center of the image generating device on one side and one end portion (one wraparound end piece) of the frame, β is the distance from the center of the connecting member to the one end portion (one end piece) of the frame, γ is the distance between the mounting-portion center of the image generating device on the other side and the one end portion (one end piece) of the frame, and L is the length of the frame. For the mounting of the image generating devices on both end portions of the connecting member, specifically, for example, the connecting member is provided with through-holes at three positions in each of the end portions thereof, the image generating devices are each provided with screw-engagement portions corresponding to the through-holes, and screws are passed through the through-holes and engaged with the screw-engagement portions provided in the image generating devices. A spring is inserted between each screw and the screw-engagement portion. The mounting state of the image generating device (the inclination of the image generating device relative to the connecting member) can be adjusted according to the fastening state of each of the screws. 
     Here, the mounting-portion center of the image generating device is a bisection point along an axial direction of the frame in an overlapping area in which the projected image of the image generating device obtained upon projection of the image generating device and the frame onto a virtual plane overlaps the projected image of the frame in a state in which the image generating device is mounted on the connecting member. In addition, the center of the connecting member is a bisection point along the axial direction of the frame in a portion in which the connecting member is in contact with the frame in a state in which the connecting member is mounted on the frame. The length of the frame is the length of the projected image of the frame when the frame is curved. The direction of projection is set as a direction perpendicular to the observer&#39;s face. 
     Alternatively, although the two image display devices are connected by the connecting member, the two light guide units can also be specifically formed to be connected by the connecting member. The two light guide units are manufactured in an integrated manner, and in such a case, the connecting member is mounted on the light guide unit manufactured in the integrated manner, but this form is also included in the form in which the connecting member connects the two light guide units. Where the distance between the center of the image generating device on one side and one end portion of the frame is α′ and the distance between the center of the image generating device on the other side and the one end portion of the frame is γ′, it is desirable that the values of α′ and γ′ also be substantially the same as the above-described values of α and γ. The center of the image generating device is a bisection point along the axial direction of the frame in a portion in which the projected image of the image generating device obtained upon projection of the image generating device and the frame onto a virtual plane overlaps the projected image of the frame in a state in which the image generating device is mounted on the light guide unit. 
     The shape of the connecting member is basically freely settable insofar as the projected image of the connecting member is included in the projected image of the frame, and, for example, can include a rod shape and an elongated plate shape. Also, examples of the material for forming the connecting member include metals, alloys, plastics, and combinations thereof. 
     Embodiment 1 
     Embodiment 1 relates to an image display device and an image generating device of the present disclosure. Specifically, the image display device of Embodiment 1 includes the first form of image generating device/first form of light guide unit. Although a conceptual diagram of the image display device of Embodiment 1 is illustrated in  FIG. 1 , the image display device of Embodiment 1 is embedded in the HMD. In addition, a propagation state of light when viewed from an XZ plane and a propagation state of light when viewed from an XY plane among light beams output from a light emitting unit positioned in an upper portion of an image generating device of Embodiment 1 are schematically illustrated in  FIGS. 2A and 2B . A propagation state of light when viewed from the XZ plane and a propagation state of light when viewed from the XY plane among light beams output from a light emitting unit positioned in a center portion of the image generating device of Embodiment 1 are schematically illustrated in  FIGS. 3A and 3B . A propagation state of light, which is output from the image generating device of Embodiment 1 and guided through a light guide unit, and reaches a pupil, within a plane corresponding to an inside of the XZ plane is schematically illustrated in  FIG. 4A . Light output from each light emitting unit of the image generating device is schematically illustrated in  FIG. 4B . Diagrams illustrating a relationship between the light guide unit and a central incident light beam when the light guide unit is viewed from the side are illustrated in  FIGS. 4C and 4D . Further, a schematic diagram of the image display device viewed from above is illustrated in  FIG. 5 . A schematic diagram of the image display device viewed from the side is illustrated in  FIG. 6 . A schematic diagram of the image display device of Embodiment 1 viewed from the front is illustrated in  FIG. 7 . A diagram illustrating a state in which the image display device of Embodiment 1 is mounted on a head of an observer viewed from above (only the image display device is illustrated and the illustration of the frame is omitted) is illustrated in  FIG. 8 . 
     An image display device  100 ,  200 ,  300 ,  400 , or  500  of Embodiment 1 or any one of Embodiments 2 to 8 to be described later includes: 
     (A) an image generating device  111  or  211 , and 
     (B) a light guide unit  120 ,  320 , or  520  on which light from the image generating device  111  or  211  is incident, through which the light is guided, and from which the light is output toward a pupil  21  of an observer  20 . 
     In addition, the image generating device  111  or  211  of Embodiment 1 is an image generating device that outputs light to the light guide unit  120 ,  320 , or  520 . 
     Here, an HMD includes: 
     (a) an eyeglass type frame  10  mounted on a head of the observer  20 , and 
     (b) the image display device  100 ,  200 ,  300 ,  400 , or  500 . The number of image display devices may be one (monocular type) or two (binocular type). In the embodiment, there is a binocular type in which two image display devices are provided. The image display device  100 ,  200 ,  300 ,  400 , or  500  may be fixedly attachable to or detachable from the frame. The image generating device  111  or  211  displays a single-color (for example, green) image. In addition, the light guide units  120 ,  320 , and  520  are a semi-transmissive type (see-through type). Specifically, at least a portion (more specifically, a light guide plate  121  or  321  and a second deflecting unit  140  or  340  to be described later) of the light guide unit facing both pupils (eyes)  21  of the observer  20  is semi-transmissive (see-through). 
     Here, in Embodiment 1 or any one of Embodiments 2 to 8 to be described later, a point at which light (central incident light beam CL) output from the center of the image generating device  111  or  211 , passing through the nodal point of the image generating device of the parallel light outputting optical system  112  or  254 , and incident on the light guide unit  120 ,  320 , or  520  is incident on the light guide unit  120 ,  320 , or  520  is set as a point O (light-guide-unit center point O). A normal line that passes through the light-guide-unit center point O in a portion of the light guide unit  120 ,  320 , or  520  is set as an X axis, and an axial line of the light guide unit  120 ,  320 , or  520  that passes through the light-guide-unit center point O in a portion of the light guide unit  120 ,  320 , or  520  is set as a Y axis. The center point of the first deflecting unit  130  or  330  to be described later is the light-guide-unit center point O. In addition, an optical axis of light incident at the point O (light-guide-unit center point O) of the light guide unit  120  or  320  among light beams output from the center of the image generating device  111  or  211  is set as a axis. Here, a relationship between an (X, Y, Z) orthogonal coordinate system and a (ζ, η, ξ) orthogonal coordinate system when the (ζ, η, ξ) orthogonal coordinate system is assumed becomes a relationship in which the η axis is consistent with the y axis, and the ξ axis is consistent with the z axis when an (x, y, z) orthogonal coordinate system is assumed in a state in which the X axis is caused to be consistent with the ζ axis according to rotational movement. In Embodiments 1 to 4 and Embodiments 6 to 8, the ζ axis is consistent with the X axis, the η axis is consistent with the Y axis, and the ξ axis is consistent with the Z axis. 
     In Embodiment 1 or any one of Embodiments 2 to 5 and Embodiments 7 and 8 to be described later, the light guide unit  120  or  320  includes: 
     (B-1) a light guide plate  121  or  321  from which incident light is output after the incident light propagates through an inside according to total reflection, 
     (B-2) a first deflecting unit  130  or  330 , which deflects light incident on the light guide plate  121  or  321  so that the light incident on the light guide plate  121  or  321  is totally reflected inside the light guide plate  121  or  321 , and 
     (B-3) a second deflecting unit  140  or  340 , which deflects light propagating through the inside of the light guide plate  121  or  321  according to the total reflection a plurality of times so that the light propagating through the inside of the light guide plate  121  or  321  according to the total reflection is output from the light guide plate  121  or  321 . 
     In Embodiment 1, the first deflecting unit  130  and the second deflecting unit  140  are disposed inside the light guide plate  121 . The first deflecting unit  130  reflects light incident on the light guide plate  121 , and the second deflecting unit  140  transmits and reflects light propagating through the inside of the light guide plate  121  according to total reflection a plurality of times. That is, the first deflecting unit  130  functions as a reflecting mirror, and the second deflecting unit  140  functions as a semi-transmissive minor. More specifically, the first deflecting unit  130  provided inside the light guide plate  121  includes a light reflecting film (a type of mirror) formed of aluminum (Al), which reflects light incident on the light guide plate  121 . On the other hand, the second deflecting unit  140  provided inside the light guide plate  121  is formed by a multilayer laminated structure in which a plurality of dielectric laminated films are laminated. The dielectric laminated film is formed by, for example, a TiO 2  film as a high-dielectric-constant material and a SiO 2  film as a low-dielectric-constant material. A multi-layer laminated structure in which a plurality of dielectric laminated films are laminated is disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) 2005-521099. Although a six-layer dielectric laminated film is illustrated in the drawing, the present disclosure is not limited thereto. A thin section formed of the same material as the material constituting the light guide plate  121  is sandwiched between dielectric laminated films. In the first deflecting unit  130 , the parallel light incident on the light guide plate  121  is reflected (or diffracted) so that the parallel light incident on the light guide plate  121  is totally reflected inside the light guide plate  121 . On the other hand, in the second deflecting unit  140 , the parallel light propagating through the inside of the light guide plate  121  according to total reflection is reflected (or diffracted) a plurality of times, and output toward the pupil  21  of the observer  20  in a state of parallel light from the light guide plate  121 . 
     For the first deflecting unit  130 , it is only necessary that a slant surface on which the first deflecting unit  130  is to be formed on the light guide plate  121  be provided by cutting out a portion  124  on which the first deflecting unit  130  of the light guide plate  121  is provided, and the cut-out portion  124  of the light guide plate  121  be adhered to the first deflecting unit  130  after a light reflecting film is vacuum evaporated on the slant surface. In addition, for the second deflecting unit  140 , it is only necessary that a multilayer laminated structure in which a plurality of membranes of the same material (e.g., glass) as the material constituting the light guide plate  121  and a plurality of dielectric laminated films (for example, formable by vacuum evaporation) are laminated be manufactured, a slant surface be formed by cutting out a portion  125  on which the second deflecting unit  140  of the light guide plate  121  is provided, the multilayer laminated structure be adhered to the slant surface, and the external form be arranged by polishing or the like. Thereby, the light guide unit  120  having the first deflecting unit  130  and the second deflecting unit  140  provided inside the light guide plate  121  can be obtained. 
     Here, in Embodiment 1 or any one of Embodiments 2 to 5 and Embodiments 7 and 8 to be described later, the light guide plate  121  or  321  formed of an optical glass material or a plastic material has two parallel surfaces (a first surface  122  or  322  and a second surface  123  or  323 ) extending in parallel to the light propagating direction (Y direction) according to internal total reflection of the light guide plate  121  or  321 . The first surface  122  or  322  and the second surface  123  or  323  face each other. Parallel light is incident from the first surface  122  or  322  corresponding to a light incidence surface, and the incident parallel light propagates through the inside according to total reflection and then is output from the first surface  122  or  322  corresponding to a light output surface. However, the present disclosure is not limited thereto, and the light incidence surface may be formed by the second surface  123  or  323 , and the light output surface may be formed by the first surface  122  or  322 . 
     In Embodiment 1 or 3 to be described later, the image generating device  111  is the first form of image generating device, which has a plurality of light emitting units (light output units, pixels, or virtual pixels) arranged in a 2D matrix. Specifically, the image generating device  111  includes a reflective spatial light modulating device  150  and a light source  154  formed by LEDs that emits white light. Each entire image generating device  111  is fitted inside a housing  113  (denoted by a dashed-dotted line in  FIG. 1 ), and an opening portion (not illustrated) is provided in the housing  113 , and light is output from the parallel light outputting optical system (collimating optical system  112 ) through the opening portion. The reflective spatial light modulating device  150  is formed by an LCD device (LCD)  151  formed by an LCOS as a light valve and a polarization beam splitter  152  that reflects part of the light output from the light source  154  to guide the reflected light to the LCD device  151  and passes part of light reflected by the LCD device  151  to guide the passed light to the collimating optical system  112 . The liquid crystal display device  151  includes a plurality (for example, 640×480) of pixels (liquid crystal cells) arranged in a 2D matrix. The polarization beam splitter  152  has a well-known configuration and structure. Unpolarized light output from the light source  154  collides with the polarization beam splitter  152 . The polarization beam splitter  152  passes and outputs a P-polarized component outside the system. On the other hand, an S-polarized component is reflected by the polarization beam splitter  152 , incident on the LCD device  151 , reflected inside the LCD device  151 , and output from the LCD device  151 . Here, a large number of P-polarized components are included in light output from pixels used for displaying “white” in the light output from the LCD device  151 , and a large number of S-polarized components are included in light output from pixels used for displaying “black.” Accordingly, the P-polarized component within the light that is output from the LCD device  151  and collides with the polarization beam splitter  152  passes through the polarization beam splitter  152  and is guided to the collimating optical system  112 . On the other hand, the S-polarized component is reflected by the polarization beam splitter  152  and returned to the light source  154 . The collimating optical system  112 , for example, includes a convex lens. To generate parallel light, the light output unit of the image generating device  111  (more specifically, the LCD device  151 ) is disposed at a place (position) of a focal distance of the collimating optical system  112 . In the case of a color display, one pixel includes a red light emitting sub-pixel for outputting red light, a green light emitting sub-pixel for outputting green light, and a blue light emitting sub-pixel for outputting blue light. 
     The frame  10  is formed by a front portion  11  arranged on the front side of the observer  20 , two temple portions  13  pivotably mounted on both ends of the front portion  11  via hinges  12 , and ear bend portions (also referred to as tip cells or ear pads)  14  mounted on tip end portions of the temple portions  13 . In addition, nose pads  10 ′ are mounted thereon. That is, the assembly of the frame  10  and the nose pads  10 ′ has basically substantially the same structure as ordinary glasses. Further, each housing  113  is mounted on the temple portion  13  using a mounting member  19 . The frame  10  is manufactured using metal or plastic. Each housing  113  may be attachable to or detachable from the temple portion  13  using the mounting member  19 . Further, when the observer owns and wears glasses, each housing  113  may be attachable to or detachable from the temple portion of the frame of the glasses owned by the observer using the mounting member  19 . 
     Further, wirings (signal lines, power lines, and the like)  15  extending from the image generating devices  111 A and  111 B extend from the tip end portion of the ear bend end portion  14  toward the outside via the temple portion  13  and the inside of the ear bend portion  14 , and are connected to the control device (the control circuit or the control unit)  18 . For example, an external image signal is wirelessly transmitted to the control device  18  or an image signal (image data) is stored in the control device  18 . The control device  18  performs an image display process for an image signal. The control device  18  can include a well-known circuit. In addition, each of the image generating devices  111 A and  111 B has a headphone unit  16 , and a headphone wiring  16 ′ extending from each of the image generating devices  111 A and  111 B extends from the tip end portion of the ear bend portion  14  to the headphone unit  16  via the temple portion  13  and the inside of the ear bend portion  14 . More specifically, the headphone wiring  16 ′ extends from the tip end portion of the ear bend portion  14  so as to wrap around the rear side of the auricle (auditory capsule) and extends to the headphone unit  16 . According to such a configuration, the image display device can be neatly formed without giving an impression that the headphone unit  16  and the headphone wiring  16 ′ are cluttered. 
     In addition, an imaging device  17  having a solid-state imaging device formed by a CCD or CMOS sensor and a lens (these are not illustrated) are mounted on a center portion  11 ′ of the front portion  11  using an appropriate mounting member (not illustrated), if necessary. A signal output from the imaging device  17  is transmitted to the image generating device  111 A via a wiring (not illustrated) extending from the imaging device  17 . 
     Incidentally, an optical axis of light (central incident light beams CL) incident at the point O (light-guide-unit center point O) of the light guide unit  120  or  320  among light beams output from the center of the image generating device  111  or  211  is set as the ζ axis, and a virtual plane including the ζ axis and the Y axis is set as the ζY plane. Because the ζ axis is consistent with the X axis, the η axis is consistent with the Y axis, and the ξ axis is consistent with the Z axis as described above with reference to Embodiments 1 to 4 and Embodiments 6 to 8, the XY plane, the XZ plane, and YZ plane are consistent with the ζη plane, the ζξ plane, and the ηξ plane, respectively, and the ζY plane is consistent with the XY plane. Then, light output from the image generating device  111  or  211  and incident at a point (0, Y 1 , Z 1 ) of the light guide unit  120 ,  320 , or  520  forms an angle θ Z  with the ζY plane (the XY plane in Embodiments 1 to 4 and Embodiments 6 to 8) and forms an angle θ Y  with the XZ plane. When Z 1 ≠0, θ Z ≠θ Y  is satisfied. When an incidence angle (XY plane incidence angle) for the XY plane of the light guide unit  120 ,  320 , or  520  is θ Z0 , the light (central incident light beams CL) output from the image generating device  111  or  211  and incident at a point (0, 0, 0) of the light guide unit  120 ,  320 , or  520  has θ Z0 =0 degrees (see  FIG. 4C ). In addition, θ Y =0 is set. 
     In Embodiment 1, a value of θ Y  is constant regardless of a value of Y 1 , and an absolute value of θ Z  is increased when an absolute value of Z 1  is increased. The absolute value of θ Z  may be increased monotonically or stepwise when the absolute value of Z 1  is increased. It is only necessary to optimize the value of θ Z  or a shift amount to be described later by performing various tests or simulations based on specifications and designations of the image display device, the image generating device, and the light guide unit. 
     Specifically, in Embodiment 1, a microlens array  60  in which a plurality of microlenses  61  are arranged in a 2D matrix is disposed in the image generating device  111 . Light output from each light emitting unit (light output unit) is output from the image generating device  111  through a microlens  61  facing the light emitting unit. Alternatively, the image generating device  111  is provided with a light output angle control member, and light is output from the image generating device  111  to the light guide unit  120 ,  320 , or  520  through the light output angle control member. The image generating device  111  has light emitting units arranged in a 2D matrix, the light output angle control member is specifically formed by the microlens array  60  in which the plurality of microlenses  61  are arranged in a 2D matrix, and light output from each light emitting unit is output from the image generating device  111  through the microlens  61  facing the light emitting unit. 
     The microlens  61 , for example, is formed by a cylindrical lens or an anamorphic lens. Here, the axial line (cylindrical axis) of the microlens  61  extends in parallel to a direction of the image generating device  111  or  211  corresponding to the Y direction of the light guide unit  120  or  320 , a cross-sectional shape when the microlens  61  is cut in the virtual plane of the image generating device corresponding to the XZ plane of the light guide unit partially has a curve such as a semicircle, arc, or ellipse, and a cross-sectional shape when the microlens  61  is cut in the virtual plane of the image generating device corresponding to the YZ plane of the light guide unit is mainly a rectangle. 
     Here, light output from the polarization beam splitter  152  corresponds to light output from each light emitting unit (light output unit), a light output point of the polarization beam splitter  152  corresponds to a virtual pixel  153 , and each virtual pixel  153  corresponds to a light emitting unit. Hereinafter, the light emitting unit is denoted by reference numeral  153 . A propagation state of light when viewed from the XZ plane among light beams output from a light emitting unit  153   E  positioned in an upper portion of the image generating device  111  (specifically, an upper portion of the polarization beam splitter  152 ) of Embodiment 1 and passing through an opposite microlens  61   E  is schematically illustrated in  FIG. 2A . A propagation state of light when viewed from the XY plane is schematically illustrated in  FIG. 2B . Further, a propagation state of light when viewed from the XZ plane among light beams output from a light emitting unit  153   C  positioned in a center portion of the image generating device  111  (specifically, a center portion of the polarization beam splitter  152 ) of Embodiment 1 and passing through an opposite microlens  61   C  is schematically illustrated in  FIG. 3A . A propagation state of light when viewed from the XY plane is schematically illustrated in  FIG. 3B . In  FIGS. 2A and 2B  and  FIGS. 3A and 3B , the light emitting units  153   C  and  153   E  are surrounded by the solid lines. 
     Here, shift amounts of an optical axis (a normal line passing through the center of the light emitting unit  153 ) AX 1  of the light emitting unit  153  and an optical axis (a normal line passing through the center of the microlens  61 ) AX 2  of the microlens  61  facing the light emitting unit  153  are defined based on a value of (0, Y 1 , Z 1 ). In the example illustrated in  FIG. 3A , because of light output from the light emitting unit  153   C  positioned in the center portion of the image generating device  111  of Embodiment 1, the value is (0, Y 1 , 0) and the shift amounts of the optical axis AX 1  of the light emitting unit  153  and the optical axis AX 2  of the microlens  61  facing the light emitting unit  153  are “0.” On the other hand, in the example illustrated in  FIG. 2A , because of light output from the light emitting unit  153   E  positioned in the upper portion of the image generating device  111  of Embodiment 1, the shift amounts of the optical axis AX 1  of the light emitting unit  153  and the optical axis AX 2  of the microlens  61  facing the light emitting unit  153  are maximum. Light output from each light emitting unit  153  of the image generating device  111  is schematically illustrated in  FIG. 4B . In  FIG. 4B , a circle represents the light emitting unit  153 , and an arrow or black dot drawn in the light emitting unit  153  schematically indicates a direction in which light output from the light emitting unit  153  and passing through the light output angle control member (microlens array)  60  is directed. 
     In addition, a radiation angle (divergence angle) ω 1  of light output from the microlens  61  can be configured to be less than a radiation angle (divergence angle) ω 0  of light output from the light emitting unit  153  (see  FIGS. 2A and 3A ). Thereby, the utilization efficiency of light output from the image generating device  111  can be further improved. The radiation angle (divergence angle) is a radiation angle (divergence angle) when light flux is projected on the XZ plane. 
     A propagation state of light, which is output from the image generating device  111  of Embodiment 1 and guided through the light guide unit  120 , and reaches the pupil  21 , within a plane corresponding to an inside of the XZ plane and the XY plane is schematically illustrated in  FIG. 4A . Incidentally, as described above, because an absolute value of θ Z  is increased when an absolute value of Z 1  is increased in Embodiment 1, all light fluxes (indicated by fine dotted lines R 3  in  FIG. 4A ) output from the image generating device  111  and guided through the light guide unit  120  via the light output angle control member (microlens array)  60  and the parallel light outputting optical system (collimating optical system  112 ) can be caused to reach the pupil  21 . Therefore, the utilization efficiency of light output from the image generating device  111  can be improved and power consumption in the image generating device  111  can be reduced. When the light output angle control member (microlens array)  60  is not provided in  FIG. 4A , light flux output from the light emitting unit  153  and reaching the pupil  21  is indicated by a coarse dotted line R 3 ′. problem that part of the light flux does not reach the pupil  21 , a type of vignetting occurs, and the utilization efficiency of light output from the image generating device  111  is low leads to an increase in power consumption in the image generating device  111 . 
     Embodiment 2 
     Embodiment 2 is a modification of Embodiment 1. The image display device of Embodiment 2 includes the second form of image generating device/first form of light guide unit. In an image display device  200  or  400  of Embodiment 2 or Embodiment 4 to be described later as illustrated in conceptual diagrams of  FIGS. 9 and 11 , an image generating device  211  includes a light source  251  and a scanning unit  253 , which scans parallel light output from the light source  251 . More specifically, the image generating device  211  includes: 
     the light source  251 , 
     a collimating optical system  252 , which collimates light output from the light source  251  into parallel light, 
     the scanning unit  253 , which scans the parallel light output from the collimating optical system  252 , and 
     a parallel light outputting optical system (relay optical system)  254 , which relays and outputs the parallel light scanned by the scanning unit  253 . The entire image generating device  211  is fitted inside a housing  213  (indicated by a dashed-dotted line in  FIGS. 9 and 11 ), an opening portion (not illustrated) is arranged in the housing  213 , and light is output from the relay optical system  254  via the opening portion. Each housing  213  is mounted on a temple portion  13  in an attachable/detachable state or a fixed state using a mounting member  19 . 
     The light source  251  includes a light emitting device that emits white light. The light output from the light source  251  is incident on the collimating optical system  252  having positive optical power as a whole and output as parallel light. Alternatively, the light source includes a red light emitting element, which emits red light, a green light emitting element, which emits green light, and a blue light emitting element, which emits blue light, and each light emitting element is formed by a semiconductor laser element. Because light of three primary colors output from the light source passes through a cross prism, color synthesis is performed, an optical path is integrated, and the light is incident on the collimating optical system  252  having positive optical power as a whole and output as parallel light. The parallel light is reflected by a total-reflection minor  256 , a micromirror is configured to be rotatable in a 2D direction, horizontal scanning and vertical scanning are performed by the scanning unit  253  formed by the MEMS capable of two-dimensionally scanning the incident parallel light, one type of 2D image is formed, and a light emitting unit (light output unit) including virtual pixels (the number of the pixels, for example, can be the same as in Embodiment 1) is generated. Then, light output from the light emitting unit (virtual pixels) passes through the parallel light outputting optical system including a well-known relay optical system  254 , and the light flux formed as the parallel light is incident on the light guide unit  120 . 
     The light output angle control member (microlens array)  60  described in Embodiment 1 is disposed between the scanning unit  253  and the parallel light outputting optical system (relay optical system)  254 . 
     Because the light guide unit  120  on which the light flux formed as the parallel light by the relay optical system  254  is incident, through which the incident light flux is guided, and from which the guided light flux is output has the same configuration and structure as described in Embodiment 1, detailed description thereof is omitted. In addition, because the image display device and the HMD of Embodiment 2 have the same configurations and structures as the image display device and the HMD of Embodiment 1 except for the differences described above, detailed description thereof is omitted. 
     Embodiment 3 
     Embodiment 3 is also a modification of the image display device of Embodiment 1. The image display device of Embodiment 3 includes the first form of image generating device/second form of light guide unit. The conceptual diagram of an image display device  300  of Embodiment 3 is illustrated in  FIG. 10A . In addition, a schematic cross-sectional view in which part of a reflective-type volume hologram diffraction grating is enlarged is illustrated in  FIG. 10B . In Embodiment 3, as in Embodiment 1, an image generating device  111  includes the first form of image generating device. The basic configuration and structure of a light guide unit  320  are the same as those of the light guide unit  120  of Embodiment 1, except for differences in the configurations and the structures of first and second deflecting units. 
     In Embodiment 3, the first deflecting unit and the second deflecting unit are disposed on a surface of a light guide plate  321  (specifically, a second surface  323  of the light guide plate  321 ). The first deflecting unit diffracts light incident on the light guide plate  321 , and the second deflecting unit diffracts light propagating through the inside of the light guide plate  321  according to total reflection a plurality of times. Here, the first deflecting unit and the second deflecting unit are formed by diffraction grating elements, specifically, reflective diffraction grating elements, and more specifically, reflective volume hologram diffraction gratings. In the following description, the first deflecting unit formed by the reflective volume hologram diffraction grating is referred to as a “first diffraction grating member  330 ” for convenience, and the second deflecting unit formed by the reflective volume hologram diffraction grating is referred to as a “second diffraction grating member  340 ” for convenience. 
     In Embodiment 3 or Embodiment 4 to be described later, the first diffraction grating member  330  and the second diffraction grating member  340  include one diffraction grating layer. In each diffraction grating layer formed by a photopolymer material, interference fringes corresponding to one type of wavelength band (or wavelength) are formed, and manufactured using a method of the related art. The pitch of the interference fringes formed in the diffraction grating layer (diffractive optical element) is constant, and the interference fringes have a linear shape and extend in parallel to the Z axis. The axial lines of the first diffraction grating member  330  and the second diffraction grating member  340  are parallel to the Y axis, and the normal lines thereof are parallel to the X axis. 
     To cope with the diffraction and the reflection of P types (for example, P=3, and three types of red, green and blue) of light having P different types of wavelength bands (or wavelengths), the first diffraction grating member  330  and the second diffraction grating member  340  can be formed by laminating the P diffraction grating layers formed by the reflective volume hologram diffraction gratings. Interference fringes corresponding to one type of wavelength band (or the wavelength) are formed on each diffraction grating layer formed by the photopolymer material, and manufactured using a method of the related art. More specifically, the first diffraction grating member  330  and the second diffraction grating member  340  have a structure in which a diffraction grating layer that diffracts and reflects red light, a diffraction grating layer that diffracts and reflects green light, and a diffraction grating layer that diffracts and reflects blue light are laminated. The pitch of the interference fringes formed in the diffraction grating layer (diffraction grating element) is constant, and the interference fringes have a linear shape and extend in parallel to the Z direction. In  FIGS. 10A and 11 , the first diffraction grating member  330  and the second diffraction grating member  340  are illustrated in one layer. By adopting such a configuration, an increase in the diffraction efficiency, an increase in the diffraction acceptance angle, and the optimization of the diffraction angle when light having each wavelength band (or the wavelength) is diffracted and reflected in the first diffraction grating member  330  and the second diffraction grating member  340  can be achieved. 
     A schematic partial cross-sectional view in which the reflective volume hologram diffraction grating is enlarged is illustrated in  FIG. 10B . In the reflective volume hologram diffraction grating, interference fringes having a slant angle θ are formed. Here, the slant angle φ represents an angle formed by the surface of the reflective volume hologram diffraction grating and the interference fringes. The interference fringes are formed from the inside of the reflective volume hologram diffraction grating to the surface thereof. The interference fringes satisfy a Bragg condition. Here, the Bragg condition is a condition that satisfies the following Expression (A). In Expression (A), m represents a positive integer, λ represents a wavelength, d represents the pitch of the grating surface (a gap of virtual planes including the interference fringes in the direction of the normal line), and Θ represents a complementary angle of an angle at which light is incident on the interference fringes. In addition, when light penetrates into the diffraction grating member at an incidence angle ψ, the relationship among the complementary angle Θ, the slant angle φ, and the incidence angle ψ is shown in Expression (B). 
         m·λ= 2 ·d ·sin(Θ)  (A)
 
       Θ=90°−(φ+ψ)  (B)
 
     As described above, the first diffraction grating member  330  is arranged on (adhered to) the second surface  323  of the light guide plate  321  and diffracts and reflects parallel light incident on the light guide plate  321  so that the parallel light incident from the first surface  322  to the light guide plate  321  is totally reflected inside the light guide plate  321 . Further, as described above, the second diffraction grating member  340  is arranged on (adhered to) the second surface  323  of the light guide plate  321  and diffracts and reflects the parallel light propagating through the inside of the light guide plate  321  according to total reflection a plurality of times, and the parallel light is directly output from the first surface  322  of the light guide plate  321 . However, the present disclosure is not limited thereto. The light-guide-plate incidence surface may be configured by the second surface  323 , and the light-guide-plate output surface may be configured by the first surface  322 . 
     Then, the parallel light propagates through the inside of the light guide plate  321  according to total reflection and then is output therefrom. Alternatively, parallel light of three colors of red, green, and blue propagates through the inside according to total reflection and then is output therefrom. At this time, because the light guide plate  321  is thin, and a path of light that propagates through the inside of the light guide plate  321  is long, the number of total reflections until the parallel light reaches the second diffraction grating member  340  differs according to a view angle (horizontal view angle). In further detail, the number of reflections of parallel light incident at an angle (horizontal view angle) in a direction close to the second diffraction grating member  340  among parallel light beams incident on the light guide plate  321  is less than that of parallel light incident on the light guide plate  321  at an angle in a direction away from the second diffraction grating member  340 . This is because parallel light incident on the light guide plate  321  at an angle close to the second diffraction grating member  340  among parallel light beams diffracted and reflected in the first diffraction grating member  330  has a larger angle formed with the normal line of the light guide plate  321  when light propagating through the inside of the light guide plate  321  collides with the inner surface of the light guide plate  321  than parallel light incident on the light guide plate  321  at an angle in a direction reverse thereto. In addition, the shape of the interference fringes formed inside the second diffraction grating member  340  and the shape of the interference fringes formed inside the first diffraction grating member  330  are symmetrical with respect to the XZ plane of the light guide plate  321 . 
     A light guide plate  321  in accordance with Embodiment 4 to be described later also basically has the same configuration and structure as the light guide plate  321  described above. The image display device and the HMD of Embodiment 3 has the same configuration and structure as the image display devices and the HMDs of Embodiments 1 and 2 except for the differences described above, and thus detailed description thereof is omitted. 
     Embodiment 4 
     Embodiment 4 is a modification of the image display device in accordance with Embodiment 3. Specifically, the image display device of Embodiment 4 includes the second form of image generating apparatus/second form of light guide unit. A conceptual diagram of the image display device of Embodiment 4 is illustrated in  FIG. 11 . A light source  251 , a collimating optical system  252 , a scanning unit  253 , a parallel light outputting optical system (relay optical system  254 ), and the like in the image display device  400  of Embodiment 4 have the same configurations and structures (the second form of image generating device) as those of Embodiment 2. In addition, a light guide unit  320  in accordance with Embodiment 4 has the same configuration and structure as those of the light guide unit  320  in accordance with Embodiment 3. Because the image display device and the HMD of Embodiment 4 substantially have the same configuration and structure as the image display devices and the HMDs of Embodiments 1 and 2 except for the differences described above, detailed description thereof is omitted. 
     Embodiment 5 
     Embodiment 5 is a modification of the image display devices in accordance with Embodiments 1 to 4. In addition, a schematic diagram of the image display device of Embodiment 5 viewed from the side is illustrated in  FIG. 12 . 
     In Embodiments 1 to 4, in the image display device  100  or  300 , the central incident light beam CL output from the center of the image generating device  111  or  211  and passing through the nodal point of the parallel light outputting optical system  112  or  254  is designed to be incident at an incidence angle (XY plane incidence angle) θ Z0  of 0 degrees for the XY plane of the light guide plate  121  or  321 . That is, θ Z0 =0 degrees. 
     That is, in such an image display device represented by the image display device  100 , as illustrated in  FIG. 29B , the central incident light beam CL output from the center of the image generating device  111  on the optical axis of the collimating optical system  112  is converted into approximately parallel light by the collimating optical system  112  and then incident on the first surface (incidence surface)  122  of the light guide plate  121 . The parallel light propagates in a propagation direction A while being totally reflected between the first surface  122  and the second surface  123  by the first diffraction unit  130 . Subsequently, the central incident light beam CL is reflected and diffracted by the second deflecting unit  140  and output from the first surface  122  of the light guide plate  121  within the XY plane, and reaches the pupil  21  of the observer  20 . 
     In a see-through type image display device, it is preferable to shift the light guide unit  120 ,  320 , or  520  to be arranged below the line of sight of the observer in the horizontal direction (the horizontal-direction line of sight of the observer) so that the light guide unit  120 ,  320 , or  520  does not interfere with viewing when the observer  20  views an observation target located in the horizontal direction. In such a case, the entire image display device  100  or  300  is arranged below the horizontal-direction line of sight of the observer. In such a configuration, as illustrated in  FIG. 30 , which illustrates a form of image display device of the related art, it is necessary to incline the entire image display device  100  by an angle θ Z0 “, and the angle θ Z0 ” by which the image display device  100  can be inclined may be limited, or the degree of freedom in design may decrease from the relationship with the mounting portion (temple portion) of the eyeglass type frame to be mounted on the head of the observer. Therefore, it is more preferable to form the arrangement of a high degree of freedom and an image display device having a high degree of freedom in design without interfering with the horizontal-direction line of sight of the observer. 
     In Embodiment 5, the central incident light beam CL is formed to intersect the XY plane at an angle (0 Z0 ≠0) other than zero degrees (see  FIG. 4D  and  FIG. 12 ). The central incident light beam CL is included within the XZ plane. In addition, in Embodiment 5, the angle θ Z0  at which the central incident light beam CL intersects the XY plane is an elevation angle. That is, the central incident light beam CL is directed from the lower side of the XY plane to the XY plane, and collides with the XY plane. The XY plane intersects the vertical surface at an angle other than zero degrees, specifically, at an angle θ Z0 . 
     In Embodiment 5, the angle θ Z0 0=5 degrees. That is, the light guide unit  120 ,  320 , or  520  is inclined by the angle θ Z0  with respect to the vertical surface. In other words, the light guide unit  120 ,  320 , or  520  is inclined by an angle of (90−θ Z0 ) degrees with respect to the horizontal surface. In addition, the central incident light beam CL output from the light guide unit  120 ,  320 , or  520  is inclined by an angle  2 θ Z0  with respect to the horizontal surface. That is, when the observer  20  views a target located at an infinite distance in the horizontal direction, the central incident light beam CL output from the light guide unit  120 ,  320 , or  520  and incident on the pupil  21  of the observer  20  forms a depression angle θ Z0 ′ (=2θ Z0 ). The angle formed by the central incident light beam CL and the normal line of the light guide unit  120 ,  320 , or  520  is θ Z0 . 
     In the image display device of Embodiment 5, the central incident light beam CL intersects the XY plane at an angle (θ Z0 ) other than zero degrees. Here, the central incident light beam CL output from the light guide unit  120  or  320  and incident on the pupil  21  of the observer  20  forms a depression angle θ Z0 &#39;, but there is a relationship of θ Z0 ′=2θ Z0 . On the other hand, in the example illustrated in  FIG. 30 , in order to obtain the same depression angle, it is necessary to incline the entire image display device by an angle θ Z0 ″. Here, the relationship between θ Z0 ″ and θ Z0  is θ Z0 ″=2θ Z0 , and hence the light guide unit should be inclined by 2θ Z0  with respect to the vertical surface in the example illustrated in  FIG. 30 . On the other hand, in Embodiment 5, it is only necessary to incline the light guide unit by θ Z0  with respect to the vertical surface, and to horizontally hold the image generating device. Accordingly, a mounting angle of the image display device at the time of mounting the image display device on a mounting portion of the eyeglass type frame is less limited and a high degree of freedom in the design can be obtained. In addition, because the inclination of the light guide unit with respect to the vertical surface is less than that of the example illustrated in  FIG. 30 , a phenomenon that external light is reflected by the light guide unit and incident on the pupil  21  of the observer  20  does not easily occur. Therefore, an image having higher quality can be displayed. 
     Because the image display device of Embodiment 5 has the same configuration and structure as the image display devices of Embodiments 1 to 4 except for the differences described above, detailed description thereof is omitted. 
     Embodiment 6 
     Embodiment 6 is also a modification of the image display devices in Embodiments 1 to 4. A schematic diagram of an image display device of Embodiment 6 viewed from the front is illustrated in  FIG. 13 , and a schematic diagram thereof viewed from above is illustrated in  FIG. 14 . 
     In Embodiment 6, a light guide unit  520  includes a semi-transmissive mirror on which light output from the image generating devices  111 A and  111 B is incident and from which the light is output toward the pupil  21  of the observer  20 . In addition, although a structure in which the light output from the image generating devices  111 A and  111 B propagates through the inside of a transparent member  521  such as a glass plate or a plastic plate and is incident on the light guide unit  520  (semi-transmissive minor) is provided in Embodiment 6, a structure in which the light propagates through the air and is incident on the light guide unit  520  may be provided. In addition, the image generating device may be configured as the image generating device  211  described in Embodiment 2. 
     Each of the image generating devices  111 A and  111 B is mounted on a front portion  11 , for example, using a screw. In addition, the member  521  is mounted on each of the image generating devices  111 A and  111 B, and the light guide unit  520  (semi-transmissive mirror) is mounted on the member  521 . Because the image display device of Embodiment 6 has substantially the same configuration and structure as the image display devices of Embodiments 1 to 4 except for the differences described above, detailed description thereof is omitted. 
     Embodiment 7 
     Embodiment 7 relates to an HMD in which the image display device of the present disclosure, specifically, any one of the image display devices  100 ,  200 ,  300 ,  400 , and  500  described in Embodiments 1 to 6, is embedded. A schematic diagram of the HMD of Embodiment 7 viewed from the front is illustrated in  FIG. 15 . A schematic diagram of the HMD of Embodiment 7 (in a state in which a frame is assumed to be removed) viewed from the front is illustrated in  FIG. 16 . In addition, a schematic diagram of the HMD of Embodiment 7 viewed from above is illustrated in  FIG. 17 . In addition, although the image display device represented by the image display device  100  will be described, needless to say, the image display devices  200 ,  300 ,  400 , and  500  can be applied. 
     The HMD of Embodiment 7 includes: 
     (A) an eyeglass type frame  10  mounted on a head of an observer  20 , and 
     (B) two image display devices  100 . The HMD in accordance with Embodiment 7 or 8 to be described later is also a binocular type in which two image display devices  100  are provided. 
     In addition, the HMD of Embodiment 7 further includes a connecting member  70 , which connects the two image display devices  100 . The connecting member  70  is mounted on a side facing the observer (that is, between the observer  20  and the frame  10 ) in a center portion  11 ′ of a front portion  11  of the frame  10  (corresponding to a portion of a bridge in an ordinary pair of eyeglasses) located between two pupils  21  of the observer  20  using screws (not illustrated). In addition, nose pads  10 ′ are mounted on a side facing the observer  20  in the connecting member  70 . In  FIGS. 17 and 20 , the illustration of the nose pads  10 ′ is omitted. The frame  10  and the connecting member  70  are formed of a metal or plastic, and the shape of the connecting member  70  is a curved rod shape. 
     Further, the projected image of the connecting member  70  is included within the projected image of the frame  10 . That is, when the HMD is viewed from the front side of the observer  20 , the connecting member  70  is hidden behind the frame  10 , so that the connecting member  70  is not visible. In addition, although the two image display devices  100  are connected by the connecting member  70 , the image generating devices  111 A and  111 B can be specifically accommodated in the housing  113  and mounted on both end portions of the connecting member  70 , respectively, so that the mounting state is adjustable. Each of the image generating devices  111 A and  111 B is located outside the pupil  21  of the observer  20 . Specifically, α=0.1×L, β=0.5×L, and γ=0.9×L, where α is the distance between a mounting-portion center  111 A C  of the image generating device  111 A on one side and one end portion (one end piece)  10 A of the frame  10 , β is the distance from a center  70   C  of the connecting member  70  to the one end portion (one end piece)  10 A of the frame, γ is the distance between a mounting-portion center  111 B C  of the image generating device  111 B on the other side and the one end portion (one end piece)  10 A of the frame, and L is the length of the frame. 
     For the mounting of the image generating devices (specifically, the image generating devices  111 A and  111 B) on the end portions of the connecting member  70 , specifically, the connecting member  70  is provided with through-holes (not illustrated) at three positions in each end portion thereof, and the image generating devices  111 A and  111 B are provided with tapped holes (screw-engagement portions (not illustrated)) corresponding to the through-holes. Screws (not illustrated) pass through the through-holes, and are screw engaged with the holes formed in the image generating devices  111 A and  111 B. A spring is inserted between the screw and the hole. Thus, the mounting state of each image generating device (the inclination of each image generating device relative to the connecting member) can be adjusted according to the fastening states of the screws. After the mounting, the screws are hidden by a cover (not illustrated). In  FIGS. 16 and 19 , connecting members  70  and  80  are hatched with diagonal lines so that the connecting members  70  and  80  are clearly shown. 
     As described above, in the HMD of Embodiment 7, the connecting member  70  connects the two image display devices  100 . The connecting member  70  is mounted on the center portion  11 ′ of the frame  10  located between the two pupils  21  of the observer  20 . That is, a structure in which the image display devices  100  are directly mounted on the frame  10  is not adopted here. Accordingly, a displacement (positional change) of the image generating device  111 A or  111 B is not caused by deformation of the frame  10  even when the temple portions  13  are expanded to the outside when the frame  10  is mounted on the head of the observer  20  and hence the frame  10  is deformed, or such displacement, if any, is very small. Therefore, it is possible to reliably prevent angles of convergence of left and right images from being changed. Moreover, because it is unnecessary to enhance the rigidity of the front portion  11  of the frame  10 , it is possible to avoid causing an increase in the weight of the frame  10 , a decrease in design quality, or an increase in cost. In addition, because the image display devices  100  are not directly mounted on the eyeglass type frame  10 , the design, color and the like of the frame  10  can be freely selected according to the observer&#39;s preference. Thus, there are few restrictions imposed on the design of the frame  10 , so that the degree of freedom in design is high. In addition, the connecting member  70  is hidden behind the frame  10  when the HMD is viewed from the front side of the observer. Accordingly, high design quality can be given to the HMD. 
     Embodiment 8 
     Embodiment 8 is a modification of Embodiment 7. A schematic diagram of an HMD of Embodiment 8 viewed from the front is illustrated in  FIG. 18 . A schematic diagram of the HMD of Embodiment 8 (in a state in which a frame is assumed to be removed) viewed from the front is illustrated in  FIG. 19 . In addition, a schematic diagram of the HMD of Embodiment 8 viewed from above is illustrated in  FIG. 20 . 
     In the HMD of Embodiment 8, a rod-shaped connecting member  80  is different from Embodiment 7, and connects two light guide units  120  instead of connecting the two image generating devices  111 A and  111 B. The two light guide units  120  are manufactured in an integrated manner, and the connecting member  80  can be formed to be mounted on the light guide unit  120  manufactured in the integrated manner. 
     Here, even in the HMD of Embodiment 8, the connecting member  80  is mounted on the center portion  11 ′ of the frame  10  located between the two pupils  21  of the observer  20 , for example, using screws, and each image generating device  111  is located outside the pupil  21  of the observer  20 . Each image generating device  111  is mounted on the end portion of the light guide unit  120 . When a distance from a center  80   C  of the connecting member  80  to one end portion of the frame  10  is set as β and a length of the frame  10  is set as L, β=0.5×L is satisfied. Even in Embodiment 8, values of α′ and γ′ are the same as values of α and γ of Embodiment 7. 
     The frame  10  and each image display device of Embodiment 8 have the same configurations and structures as the frame  10  and the image display device of Embodiment 7, and therefore detailed description thereof is omitted. In addition, because the HMD of Embodiment 8 also has substantially the same configuration and structure as the HMD of Embodiment 7 except for the differences described above, detailed description thereof is omitted. 
     Although the present disclosure has been described based on the preferred embodiments, the present disclosure is not limited to these embodiments. The configurations and structures of the image display device and the image generating device described in the embodiments are merely exemplary, and can be changed appropriately. Although a Y direction is set as a direction generally horizontal to the observer in Embodiment 1, the Y direction may be set as a direction generally perpendicular to the observer depending upon arrangement states of the image display device, the image generating device, and the light guide unit. In addition, an angle θ Y  may be an angle other than zero degrees. In this case, light incident at a point (0, Y 1 , Z 1 ) of the light guide unit penetrates the light guide unit in a direction reverse to a light guide direction of light in the light guide unit. That is, the light incident at a point (0, Y 1 , Z 1 ) of the light guide unit forms an acute angle as a whole with the light guide direction of light in the light guide unit. Further, in other words, it is preferable that an angle formed by a projected image for the XY plane of the light incident at the point (0, Y 1 ,Z 1 ) of the light guide unit and the Y axis be an acute angle. 
     In addition, for example, a surface relief-type hologram (see U.S. Patent No. 20040062505 A1) may be arranged on the light guiding plate. In addition, in the light guide unit of Embodiment 3 or 4, the first deflecting unit formed by a transmissive hologram can be configured to be disposed on the first surface  332  of the light guide plate  321 , and the second deflecting unit formed by a reflective hologram can be configured to be disposed on the second surface  323 . In such a configuration, light incident on the first deflecting unit is diffracted, satisfies a total reflection condition within the light guide plate, and propagates to the second deflecting unit. In the second deflecting unit, light is diffracted, reflected, and output from the light guide plate. In the light guide unit of Embodiment 3 or 4, the diffraction grating element can be formed by a transmissive diffraction grating element. Alternatively, any one of the first and second deflecting unit can be formed by a reflective diffraction grating element and the other can be formed by the transmissive diffraction grating element. Alternatively, the diffraction grating element can be a reflective blazed grating element or a surface relief hologram. Although a binocular type in which two image display devices are provided has been described in the embodiment, a monocular type in which one image display device is provided may be provided. 
     As a modification of an image generating device suitably for use in Embodiments 1 and 3, for example, as illustrated in a conceptual view of  FIG. 21 , an active matrix type of image generating device can include a light emitting panel in which light emitting elements  501  formed by semiconductor light emitting elements are arranged in a 2D matrix, and display an image by controlling a light emitting/non-light-emitting state of each light emitting element  501  so that the light emitting state of the light emitting element  501  is directly visible. Light output from the image generating device is incident on a light guide plate  121  or  321  via a light output angle control member (microlens array)  60  and a collimating optical system  112 . 
     Alternatively, as illustrated in a conceptual diagram of  FIG. 22 , a color-display image generating device can include: 
     (α) a red light emitting panel  511 R in which red light emitting elements  501 R for emitting red light are arranged in a 2D matrix; 
     (β) a green light emitting panel  511 G in which green light emitting elements  501 G for emitting green light are arranged in a 2D matrix; 
     (γ) a blue light emitting panel  511 B in which blue light emitting elements  501 B for emitting blue light are arranged in a 2D matrix; and 
     (δ) a unit (e.g., a dichroic prism  503 ) for integrating light output from the red, green, and blue light emitting panels  511 R,  511 G, and  511 B into one optical path. Light emitting/non-light-emitting states of the red, green, and blue light emitting elements  501 R,  501 G, and  501 B are controlled independently. Light output from this image generating device is also incident on the light guide plate  121  or  321  via the light output angle control member (microlens array)  60  and the collimating optical system  112 . Reference numeral  512  denotes microlenses for condensing light output from the light emitting elements. 
     Alternatively, a conceptual view of an image generating device including light emitting panels  511 R,  511 G, and  511 B in which light emitting elements  501 R,  501 G, and  501 B are arranged in a 2D matrix is illustrated in  FIG. 23 . Light output from the light emitting panels  511 R,  511 G, and  511 B is incident on a dichroic prism  503  after passage/non-passage thereof is controlled by light passage control devices  504 R,  504 G, and  504 B. The optical paths of the light beams are integrated into one optical path, and the light beams are incident on the light guide plate  121  or  321  via the light output angle control member (microlens array)  60  and the collimating optical system  112 . 
     Alternatively, a conceptual view of an image generating device including light emitting panels  511 R,  511 G, and  511 B and the like in which light emitting elements  501 R,  501 G, and  501 B are arranged in a 2D matrix is illustrated in  FIG. 24 . Light output from the light emitting panels  511 R,  511 G, and  511 B is incident on a dichroic prism  503  and optical paths thereof are integrated into one optical path. Passage/non-passage of the light output from the dichroic prism  503  is controlled by a light passage control device  504 , and the light is incident on the light guide plate  121  or  321  via the light output angle control member (microlens array)  60  and the collimating optical system  112 . 
     Alternatively, as illustrated in  FIG. 25 , an image generating device can include a light emitting element  501 R for emitting red light, a light passage control device (e.g., an LCD device  504 R), which is a type of light valve for controlling passage/non-passage of the red light output from the light emitting element  501 R, a light emitting element  501 G for emitting green light, a light passage control device (e.g., an LCD device  504 G), which is a type of light valve for controlling passage/non-passage of the green light output from the light emitting element  501 G, a light emitting element  501 B for emitting blue light, a light passage control device (e.g., an LCD device  504 B), which is a type of light valve for controlling passage/non-passage of the blue light output from the light emitting element  501 B, light guide members  502  for guiding the light output from the light emitting elements  501 R,  501 G, and  501 B formed by GaN semiconductors, and a unit (e.g., a dichroic prism  503 ) for integrating the optical paths of the light into one optical path. The light output from the dichroic prism  503  is incident on the light guide plate  121  or  321  via the light output angle control member (microlens array)  60  and the collimating optical system  112 . 
     Additionally, the present technology may also be configured as below. 
     (1) An image display device including: 
     (A) an image generating device; and 
     (B) a light guide unit on which light from the image generating device is incident, through which the light is guided, and from which the light is output toward a pupil of an observer, 
     wherein when a point at which light output from a center of the image generating device is incident on the light guide unit is set as a point O, a normal line passing through the point O in a portion of the light guide unit is set as an X axis, an axis of the light guide unit passing through the point O in a portion of the light guide unit is set as a Y axis, an optical axis of light incident at the point O of the light guide unit among light beams output from a center of the image generating device is set as a ζ axis, and a virtual plane including the ζ axis and the Y axis is set as a ζY plane, light output from the image generating device and incident at a point (0, Y 1 , Z 1 ) forms an angle θ Z  with the ζY plane and forms an angle θ Y  with an XZ plane, and 
     wherein when Z 1 ≠0, θ Z #θ Y  is satisfied. 
     (2) The image display device according to (1), 
     wherein a value of θ Y  is constant regardless of a value of Y 1 , and 
     wherein an absolute value of θ Z  is increased when an absolute value of Z 1  is increased. 
     (3) The image display device according to (2), 
     wherein the absolute value of θ Z  can be increased monotonically or stepwise when the absolute value of Z 1  is increased. 
     (4) The image display device according to (2) or (3), 
     wherein the image generating device has a light emitting unit arranged in a two-dimensional (2D) matrix, 
     wherein a microlens array in which a plurality of microlenses are arranged in a 2D matrix is disposed in the image generating device, 
     wherein light output from each light emitting unit is output from the image generating device through a microlens facing the light emitting unit, and 
     wherein shift amounts of an optical axis of the light emitting unit and an optical axis of the microlens facing the light emitting unit are defined based on a value of (0, Y 1 , Z 1 ). 
     (5) The image display device according to (4), 
     wherein the microlens is formed by a cylindrical lens or an anamorphic lens. 
     (6) The image display device according to (4) or (5), 
     wherein a radiation angle of light output from the microlens is less than a radiation angle of light output from the light emitting unit. 
     (7) The image display device according to any one of (1) to (3), 
     wherein an image generating device has a light output angle control member, and 
     wherein light is output from the image generating device to a light guide unit through the light output angle control member. 
     (8) The image display device according to (7), 
     wherein the image generating device has light emitting units arranged in a 2D matrix, 
     wherein the light output angle control member is formed by a microlens array in which a plurality of microlenses are arranged in a 2D matrix, and 
     wherein light output from each light emitting unit is output from the image generating device through a microlens facing the light emitting unit. 
     (9) The image display device according to (8), 
     wherein shift amounts of an optical axis of the light emitting unit and an optical axis of the microlens facing the light emitting unit are defined based on a value of (0, Y 1 , Z 1 ). 
     (10) The image display device according to (8) or (9), 
     wherein the microlens is formed by a cylindrical lens or an anamorphic lens. 
     (11) The image display device according to any one of (8) to (10), 
     wherein a radiation angle of light output from the microlens is less than a radiation angle of light output from the light emitting unit. 
     (12) The image display device according to any one of (1) to (11), 
     wherein the light guide unit includes 
     (B-1) a light guide plate from which the incident light is output after the incident light propagates through an inside according to total reflection, 
     (B-2) a first deflecting unit configured to deflect the light incident on the light guide plate so that the light incident on the light guide plate is totally reflected inside the light guide plate, and 
     (B-3) a second deflecting unit configured to deflect the light propagating through the inside of the light guide plate according to the total reflection a plurality of times so that the light propagating through the inside of the light guide plate according to the total reflection is output from the light guide plate. 
     (13) The image display device according to any one of (1) to (12), 
     wherein the image generating device is formed by a liquid crystal display device, an organic electro luminescence display device, or a light emitting element array. 
     (14) An image generating device for outputting light to a light guide unit including a light guide plate from which incident light is output after the incident light propagates through an inside according to total reflection, a first deflecting unit configured to deflect light incident on the light guide plate so that the light incident on the light guide plate is totally reflected inside the light guide plate, and a second deflecting unit configured to deflect light propagating through the inside of the light guide plate according to the total reflection a plurality of times so that the light propagating through the inside of the light guide plate according to the total reflection is output from the light guide plate, 
     wherein, when a point at which light output from a center of the image generating device is incident on the light guide unit is set as a point O, a normal line passing through the point O in a portion of the light guide unit is set as an X axis, an axis of the light guide unit passing through the point O in a portion of the light guide unit is set as a Y axis, an optical axis of light incident at the point O of the light guide unit among light beams output from a center of the image generating device is set as a ζ axis, and a virtual plane including the ζ axis and the Y axis is set as a ζY plane, light output from the image generating device and incident at a point (0, Y 1 , Z 1 ) forms an angle θ Z  with the Y plane and forms an angle θ Y  with an XZ plane, and 
     wherein when Z 1 ≠0, θ Z #θ Y  is satisfied. 
     It should be appreciated from the foregoing that some embodiments of the invention provide an image display device, comprising: a plurality of light emitting units, arranged in an array comprising a plurality of rows extending in a first direction, each of the plurality of light emitting units having an optical axis; and a plurality of microlenses, arranged in an array so that light emitted from each of the plurality of light emitting units passes through a corresponding one of the plurality of microlenses, each of the plurality of microlenses having an optical axis; wherein the optical axis of light emitting units in at least one of the plurality of rows is offset from the optical axis of the corresponding microlenses in the at least one of the plurality of rows. 
     The plurality of rows of light emitting units may comprise at least one first row, and an offset between the optical axis of a light emitting unit in a particular row and the optical axis of a corresponding microlens may vary as function of a distance between the particular row and the at least one first row. For example, an offset between the optical axis of a light emitting unit in the particular row and the optical axis of a corresponding microlens increases as the distance between the particular row and the at least one first row increases. The at least one first row may, for example, reside substantially in a center of the plurality of rows. 
     The plurality of rows of light emitting units may comprise rows below the at least one first row in the array, and the optical axes of light emitting units in the rows below the at least one first row may reside at an offset above the optical axis of corresponding microlenses. The plurality of rows of light emitting units may comprise rows above the at least one first row in the array, and the optical axes of light emitting units in the rows above the at least one first row may reside at an offset below the optical axis of corresponding microlenses. 
     The plurality of rows of light emitting units may comprise a first row, a second row adjacent the first row in the array, and a third row adjacent the second row in the array, and a first distance between an optical axis of light emitting units in the first row and an optical axis of light emitting units in the second row is greater than a second distance between an optical axis of light emitting units in the second row and an optical axis of light emitting units in the third row. The first row may, for example, reside substantially in a center of the plurality of rows. In some embodiments, the second row may reside above the first row in the array, and the third row may reside above the second row in the array. In other embodiments, the second row may reside below the first row in the array, and the third row may reside below the second row in the array. 
     The plurality of rows may comprise at least one edge row farthest away from the at least one first row in the array, and the at least one of the plurality of rows in which the optical axis of light emitting units is different than the optical axis of the corresponding microlenses may comprise the at least one edge row. In some embodiments, the at least one edge row may comprise a row below the at least one first row in the array, and the optical axis of light emitting units in the at least one edge row may reside above the optical axis of the corresponding microlenses. In other embodiments, the at least one edge row may comprise a row above the at least one first row in the array, and the optical axis of light emitting units in the at least one edge row may reside below the optical axis of the corresponding microlenses. 
     In some embodiments, the array in which the plurality of light emitting units are arranged may comprise a plurality of columns. 
     Some embodiments of the invention provide a head-mounted display, comprising: an eyeglass type frame configured for mounting on a head; and an image display device, affixed to the eyeglass type frame. The head-mounted display may comprise an optical waveguide configured to propagate light from the light emitting unit along the first direction. In some embodiments, the image display device may be affixed to the eyeglass type frame so that, when the eyeglass type frame is mounted on a head, the first direction in which the plurality of rows extends is substantially horizontal. In other embodiments, the image display device may be affixed to the eyeglass type frame so that, when the eyeglass type frame is mounted on a head, the first direction in which the plurality of rows extends is substantially vertical. 
     Some embodiments of the invention provide a head-mounted display, comprising: an optical system; an optical waveguide; a first diffraction grating and a second diffraction grating, each residing on a portion of the optical waveguide; a frame, configured for mounting on a head; and an image display device, affixed to the frame. 
     Some embodiments of the invention provide an image display device, comprising: a plurality of light emitting units, arranged in an array comprising a plurality of rows, the plurality of rows comprising at least one first row; and a plurality of microlenses, arranged in an array so that light emitted from each of the plurality of light emitting units passes through a corresponding one of the plurality of microlenses, each of the plurality of microlenses having an optical axis; wherein light from a light emitting unit in a particular row passes through a corresponding microlens at an angle to the optical axis, and the angle varies as a function of a distance between the particular row and the at least one first row. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 
     The present disclosure contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2012-057452 filed in the Japan Patent Office on Mar. 14, 2012, the entire content of which is hereby incorporated by reference.