Patent Publication Number: US-10330934-B2

Title: Image relay optical system and virtual image display device including the same

Description:
This is a Divisional Application of application Ser. No. 13/419,099 filed Mar. 13, 2012 which claims priority to JP 2011-062542 filed Mar. 22, 2011. The disclosure of the prior application is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image relay optical system used for a head mounted display mounted on the head and used and a virtual image display device including the image relay optical system. 
     2. Related Art 
     In recent years, as a virtual image display device for enabling formation and observation of a virtual image such as a head mounted display, various virtual image display devices of a type for guiding image light from a display device to the pupils of an observer with a light guide plate are proposed. As the light guide plate for such virtual image display device, there is a light guide plate including a light guide pipe that can cause plural optical modes having different light guide angles to proceed (see JP-T-2008-535001). 
     In an optical system disclosed in JP-T-2008-535001, a liquid crystal panel is illuminated with collimated light set to a different incident angle for each of the optical modes on condition that images in the plural optical modes are positionally shifted from one another. Display contents are changed in the optical modes and displays in the optical modes are sequentially executed to join images in the optical modes and obtain an overall image. In this case, an image in the center and images on the left and right included in the overall image have to be displayed while being changed with a time lag by one liquid crystal panel. As a result, a virtual image display device is complicated and an observation image is darkened. 
     There is also a virtual image display device for enabling observation of a virtual image with a light guide member in which a concave reflecting surface is provided accompanying a light incident surface and a convex reflecting surface is provided accompanying a light emitting surface. In the virtual image display device, it is unnecessary to join images with a time lag (see U.S. Pat. No. 7,477,453). An afocal system is formed by the two inclining reflecting surfaces. Aberration such as distortion is not reduced. Therefore, a projection optical system for collimate is complicated and image processing is necessary. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide an image relay optical system that can simply display a large bright virtual image with relatively small aberration and a virtual image display device incorporating the image relay optical system. 
     An aspect of the invention is directed to an image relay optical system including (a) an optical coupling member that is formed of a light transmissive material and on which image light is made incident and (b) a light guide member that is formed of a light transmissive material and guides the image light from the optical coupling member and emits the image light to the outside. (c) The optical coupling member includes at least a first light incident surface, a coupling member reflecting surface, and a first light emitting surface in order of incidence of the image light. (d) At least one of the first light incident surface, the coupling member reflecting surface, and the first light emitting surface is a curved surface. (e) The light guide member includes at least a second light incident surface, first and second total reflecting surfaces opposed to and extending in parallel to each other, a light guide member reflecting surface, and a second light emitting surface. (f) The light guide member reflecting surface is a curved surface. (g) The second light emitting surface is a flat surface. In the image relay optical system, the optical coupling member is provided before the incidence of the image light on the light guide member. At least one of the first light incident surface, the coupling member reflecting surface, and the first light emitting surface provided in the optical coupling member is the curved surface. Therefore, it is possible to display a large bright virtual image with reduced aberration. 
     A specific aspect of the invention is directed to the image relay optical system, wherein the coupling member reflecting surface is a total reflection mirror that reflects most of the image light and the light guide member reflecting surface is a concave convergent surface that converts the image light, which is focused as an intermediate image in the light guide member, into parallel beams. The total reflection includes reflecting nearly 100% of light by, for example, providing a reflection film. In this case, a loss of light on the coupling member reflecting surface is reduced. A substantially infinite virtual image can be formed by the conversion into the parallel beams on the light guide member reflecting surface. 
     Another aspect of the invention is directed to the image relay optical system, wherein in the optical coupling member, the first light incident surface is a surface functioning as a total reflecting surface, the coupling member reflecting surface is a concave convergent surface, and the first light emitting surface is a convex convergent surface. In the light guide member, the second light incident surface is a convex convergent surface. In this case, the convergent surfaces provided in the optical coupling member and the light guide member enable correction of distortion and the like. A bright virtual image with reduced aberration can be formed. A loss of light is reduced by the total reflection on the first light incident surface. 
     Still another aspect of the invention is directed to the image relay optical system, wherein in the optical coupling member, the first light incident surface is a convex convergent surface, the coupling member reflecting surface is a concave convergent surface, and the first light emitting surface is a convex convergent surface. In the light guide member, the second light incident surface is a convex convergent surface. In this case, the convergent surfaces provided in the optical coupling member and the light guide member enable correction of distortion and the like. A bright virtual image with reduced aberration can be formed. 
     Yet another aspect of the invention is directed to the image relay optical system, wherein in the optical coupling member, the first light incident surface is a convex convergent surface, the coupling member reflecting surface is a concave convergent surface, and the first light emitting surface is a convex convergent surface. In the light guide member, the second light incident surface is a surface functioning as a first total reflecting surface. The light guide member includes a total reflection opposed reflecting surface that includes a concave convergent surface opposed to the second light incident surface and reflects the image light from the second light incident surface to the first total reflecting surface. The image relay optical system includes a convergent lens arranged between the first light emitting surface of the optical coupling member and the second light incident surface of the light guide member. In this case, the convergent surfaces provided in the optical coupling member and the light guide member enable correction of distortion and the like. The convergent lens arranged between the first light emitting surface and the second light incident surface enables adjustment of beams of the image light. Consequently, a bright virtual image with reduced aberration can be formed. 
     Still yet another aspect of the invention is directed to the image relay optical system, wherein in the optical coupling member, the first light incident surface is a surface functioning as a total reflecting surface, the coupling member reflecting surface is a total reflection concave convergent surface, and the first light emitting surface is a convex convergent surface. In the light guide member, the second light incident surface is a convex convergent surface. The image relay optical system includes a convergent lens arranged to be opposed to the first light incident surface of the optical coupling member. In this case, the convergent surfaces provided in the optical coupling member and the light guide member enable correction of distortion and the like. A loss of light is reduced on the optical coupling member and the coupling member reflecting surface. Further, the convergent lens arranged to be opposed to the first light incident surface of the optical coupling member enables adjustment of beams of the image light. Consequently, a bright virtual image with reduced aberration can be formed. 
     Further another aspect of the invention is directed to the image relay optical system, wherein the light guide member reflecting surface of the light guide member is a semi-transmissive mirror. The image relay optical system includes a light transmitting member that includes a curved surface joined to the semi-transmissive mirror and makes it possible to see an external image through the second light emitting surface and the light guide member reflecting surface. In this case, the light transmitting member joined to the back of the semi-transmissive mirror enables satisfactory see-through observation. 
     Still further another aspect of the invention is directed to the image relay optical system, wherein at least one of a refractive index and dispersion of the optical coupling member is different from a refractive index and dispersion of the light guide member. In this case, various kinds of aberration including chromatic aberration of the image light can be corrected by adjusting the reflective index and the dispersion between the optical coupling member and the light guide member. Yet further aspect of the invention is directed to a virtual image display device including the image relay optical system explained above and an image forming device that forms image light guided by the image relay optical system. In this case, the virtual image display device can simply display a large bright virtual image with relatively small aberration by using the image relay optical system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a plan view showing a one eye side of an image relay optical system and a virtual image display device incorporating the image relay optical system according to a first embodiment. 
         FIG. 2  is a plan view showing the entire virtual image display device. 
         FIG. 3  is a perspective view showing a light transmitting member. 
         FIG. 4  is a plan view showing a virtual image display device according to a second embodiment. 
         FIG. 5  is a plan view showing a virtual image display device according to a third embodiment. 
         FIG. 6  is a plan view showing a virtual image display device according to a fourth embodiment. 
         FIG. 7  is a plan view showing an image relay optical system according to a modification. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     First Embodiment 
     An image relay optical system for a virtual image display device and a virtual image display device incorporating the image relay optical system according to a first embodiment of the invention are explained below with reference to the accompanying drawings. 
     A. Structure of the Image Relay Optical System and the Virtual Image Display Device 
     A virtual image display device  100  according to this embodiment shown in  FIG. 1  is applied to a headmounted display and includes an image forming device  10  and an image relay optical system  20  as a set. 
     The virtual image display device  100  causes an observer to recognize image lights generated by a virtual image and causes the observer to observe an external image in a see-through manner.  FIG. 1  shows only the virtual image display device  100  for the left eye. However, as the entire virtual image display device  100 , the set of the image forming device  10  and the image relay optical system  20  is provided to correspond to each of the right eye and the left eye of the observer. Since the virtual image display device  100  for the right eye and the virtual image display device  100  for the left eye are symmetrical, only the virtual image display device  100  for the left eye is explained. Detailed explanation of the virtual image display device  100  for the right eye is omitted. As shown in  FIG. 1 , the image forming device  10  includes an illumination device  31  that emits two-dimensional illumination light, a liquid crystal display device  32 , which is a transmissive spatial light modulating device, and an emission angle adjusting member  33  arranged between the illumination device  31  and the liquid crystal display device  32 . The liquid crystal display device  32  spatially modulates the illumination light emitted from the illumination device  31  and forms image lights that should be a display target such as a moving image. The emission angle adjusting member  33  changes an emission angle distribution of the illumination light according to a position in a screen and adjusts the image lights emitted from an emitting surface  32   a  of the liquid crystal display device  32  such that the image lights are efficiently made incident on an eye EY of the observer. The image relay optical system  20  includes an optical coupling member  21 , a light guide member  22 , and a light transmitting member  23 . The optical coupling member  21  is a member that is formed of a light transmissive material and propagates image lights from the image forming device  10  while converging the image lights as appropriate and emits the image lights to the light guide member  22 . The light guide member  22  is a member that is formed of a light transmissive material and guides the image lights from the optical coupling member  21  and finally emits the image lights to the outside as image lights converted into parallel beams. The light transmitting member  23  is formed of a light transmissive material having a refractive index same as the refractive index of the light guide member  22 . The light transmitting member  23  is joined to the interior side of the light guide member  22  and enables the observer to see an external image through the light transmitting member  23 . As shown in  FIG. 2 , the light transmitting member  23  is arranged between a pair of light guide members  22 ,  22  provided to correspond to the left and right eyes EY, EY of the observer and is joined to the pair of light guide members  22 ,  22 . Consequently, the pair of light guide members  22 ,  22  and the light transmitting member  23  are connected and integrated as one member. In other words, the light transmitting member  23  is a suspended member suspended from one light guide member  22  to the other light guide member  22 . 
     As shown in  FIG. 1 , the optical coupling member  21  is a columnar light guide member extending in a Y direction and includes a first light incident surface  21   a , a coupling member reflecting surface  21   b , and a first light emitting surface  21   c . When a route of the image lights is considered, the surfaces  21   a ,  21   b , and  21   c  are arrayed in order of incidence of the image lights. A connecting surface CF 1 , which is a surface for connecting the first light incident surface  21   a  and the coupling member reflecting surface  21   b  and is not optically used, is present between the first light incident surface  21   a  and the coupling member reflecting surface  21   b . A connecting surface CF 2  is present between the coupling member reflecting surface  21   b  and the first light emitting surface  21   c . The first light incident surface  21   a  and the first light emitting surface  21   c  are adjacent to and directly connected to each other. Among these optically used surfaces, the first light incident surface  21   a  is a flat surface extending while being opposed to the emitting surface  32   a  of the liquid crystal display device  32  and is a surface for capturing the image lights emitted from the image forming device  10  into the optical coupling member  21 . The first light incident surface  21   a  includes an extended surface ES, which is a surface on an extended region outside a region on which the image lights are made incident from the image forming device  10 . The coupling member reflecting surface  21   b  is a concave convergent surface (specifically, a concave spherical surface or aspherical surface). The coupling member reflecting surface  21   b  includes a reflection film ML, which is formed by aluminum evaporation or the like, to function as a total reflection mirror that reflects most of the image lights captured from the first light incident surface  21   a . In other words, nearly 100% of the image lights are reflected by the reflection film ML. The first light emitting surface  21   c  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). The first light emitting surface  21   c  emits the image lights to the light guide member  22  located on a downstream side in an optical path. 
     The light guide member  22  is a tabular light guide member extending in a YZ direction and includes a second light incident surface  22   a , first and second total reflecting surfaces  22   b  and  22   c , a light guide member reflecting surface  22   d , and a second light emitting surface  22   e . When the route of the image lights is considered, the surfaces  22   a ,  22   b ,  22   c ,  22   d , and  22   e  are arrayed in order of incidence of the image lights. A connecting surface CF  3  is present between the second light incident surface  22   a  and the second total reflecting surface  22   c . Adjacent surfaces of the other surfaces are directly connected to each other. Among these optically used surfaces, the second light incident surface  22   a  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). The second light incident surface  22   a  is arranged to be opposed to the first light emitting surface  21   c  of the optical coupling member  21 . The image lights emitted from the optical coupling member  21  are made incident on the second light incident surface  22   a . The first and second total reflecting surfaces  22   b  and  22   c  are surfaces extending in a Z direction in an opposed and parallel state. The first and second total reflecting surfaces  22   b  and  22   c  guide the image lights made incident from the second light incident surface  22   a  from an entrance side to an interior side in the light guide member  22  by totally reflecting the image lights. The light guide member reflecting surface  22   d  is a concave convergent surface (specifically, a concave spherical surface or aspherical surface). The light guide member reflecting surface  22   d  bends the image lights while converting the image lights into parallel beams. The light guide member reflecting surface  22   d  is formed as a semi-transmissive mirror accompanied by a half mirror layer  24 , which is a reflection film having transmissivity (i.e., a semi-transmissive reflection film). The second light emitting surface  22   e  is a surface present on the extension of the second total reflecting surface  22   c  and extending along a flat surface, i.e., a YZ plane. The second light emitting surface  22   e  emits the image lights, which have passed through the light guide member reflecting surface  22   d , to the eyes of the observer. In other words, the image lights are emitted from the second light emitting surface  22   e  to the outside of the light guide member  22  and reach the eye EY of the observer. 
     As explained above, both of the optical coupling member  21  and the light guide member  22  include the concave and convex curved surfaces (specifically, the first light emitting surface  21   c , the second light incident surface  22   a , etc.) to make it possible to change states of convergence and divergence of the image lights. The shapes of the curved surfaces defined by a curvature, a curvature center, an aspherical coefficient, and the like are adjusted as appropriate to apply reflection and refraction action matching the arrangement of the curved surfaces to the image lights. This makes it possible to reduce occurrence of aberration represented by distortion. In the optical coupling member  21  and the light guide member  22 , at least one of characteristics of a refractive index and dispersion are set different from each other to vary the reflection and refraction action applied to the image lights. This makes it possible to cope with occurrence of chromatic aberration. 
     As shown in  FIGS. 1 to 3 , the light transmitting member  23  has a refractive index same as the refractive index of the main body of the light guide member  22  and includes a first surface  23   a , a second surface  23   b , and a third surface  23   c . The first and second surfaces  23   a  and  23   b  extend onto extended planes of the first and second total reflecting surfaces  22   b  and  22   c  along the YZ plane. The third surface  23   c  is formed as a curved surface arranged along the light guide member reflecting surface  22   d  of the light guide member  22 . In other words, the light transmitting member  23  is formed as a member including a wedge-like member WP held between the second surface  23   b  and the third surface  23   c . The third surface  23   c  is formed as a joined surface joined to the half mirror layer  24  of the light guide member  22 . Like the light guide member  22 , the light transmitting member  23  indicates high light transmissivity in a visible range. Therefore, it is possible to see an external image through the second light emitting surface  22   e  and the light guide member reflecting surface  22   d  of the light guide member  22 . For example, the observer can observe image light GL reduced to 20% and external light GL′ reduced to 80% superimposed one on top of the other by the adjustment of the reflectance of the half mirror layer  24 . 
     B. Optical Paths of Image Lights 
     Optical paths of image lights are explained below. Among components of image lights emitted from the image forming device  10  shown in  FIG. 1 , optical paths of image lights GL 1 , GL 2 , and GL 3  emitted from the center and both the end sides of the liquid crystal display device  32  are traced and explained. Optical paths of components of the other image lights are intermediate optical paths of the optical paths of the image lights GL 1 , GL 2 , and GL 3  and are the same as the optical paths of the image lights GL 1 , GL 2 , and GL 3 . Therefore, explanation of the optical paths is omitted. 
     First, the image light GL 1  emitted from the center on the emitting surface  32   a  of the liquid crystal display device  32  is emitted to the optical coupling member  21  in a state in which the image light GL 1  diverges from one point on the emitting surface  32   a . The image light GL 1  is made incident on the first light incident surface  21   a , which is a flat surface. The image light GL 1  passing through the first light incident surface  21   a  and propagating in the optical coupling member  21  is reflected on the coupling member reflecting surface  21   b . When the image light GL 1  is reflected, since the coupling member reflecting surface  21   b  is a concave convergent surface, the image light GL 2  changes to a state in which the image light GL 2  is converted into substantially parallel beams. A traveling direction of the image light GL 2  is bent. The image light GL 2  travels to the first light incident surface  21   a  again. An angle with respect to the first light incident surface  21   a  and an incident position of the image light GL 1  change from those during first incidence according to the reflection action on the coupling member reflecting surface  21   b . In this case, the image light GL 1  is adapted to be made incident at an angle at which the image light GL 1  is totally reflected without requiring a reflection film or the like, i.e., an angle equal to or larger than a critical angle on the first light incident surface  21   a  including the extended surface ES. In other words, the first light incident surface  21   a  in this case functions as a total reflecting surface that totally reflects the image light GL 1 . According to the total reflection, the image light GL 1  travels to the first light emitting surface  21   c  while hardly losing a light amount. The image light GL 1  is subjected to converging action on the first light emitting surface  21   c  and emitted from the first light emitting surface  21   c  to the light guide member  22 . Consequently, the image light GL 1  emitted from the optical coupling member  21  is made incident on the second light incident surface  22   a  of the light guide member  22 . 
     Subsequently, the image light GL 1  captured into the light guide member  22  from the second light incident surface  22   a  is subjected to the converging action on the second light incident surface  22   a . Specifically, both of the first light emitting surface  21   c  and the second light incident surface  22   a  are convex convergent surfaces and, according to the refraction action on the surfaces, the image light GL 1  changes from a state in which the image light GL 1  is converted into substantially parallel beams to a state in which the image light GL 1  converges. The image light GL 1  passed through the second light incident surface  22   a  is first totally reflected on the first total reflecting surface  22   b  located on a +X side of the first and second total reflecting surfaces  22   b  and  22   c  opposed to and extending in parallel to each other in the Z direction, i.e., parallel to the YZ plane. Thereafter, the image light GL 1  is totally reflected on the second total reflecting surface  22   c  located on a −X side. While being totally reflected on the total reflecting surfaces  22   b  and  22   c  in this way, the image light GL 1  in the converged state is once focused and then changes to the diverged state again and travels to the light guide member reflecting surface  22   d . The light guide member reflecting surface  22   d  is a concave convergent surface. Therefore, the optical path of the image light GL 1  is bent according to the reflection action on the light guide member reflecting surface  22   d . The image light GL 1  changes from the diverged state to the converted state into parallel beams and travels to the second light emitting surface  22   e . The image light GL 1  is emitted as parallel beams, which form a virtual image, to the eye EY of the observer perpendicularly to a +Z direction from the center side of the second light emitting surface  22   e , i.e., in a −X direction. 
     The image light GL 2  emitted from the end on a +Z side on the emitting surface  32   a  of the liquid crystal display device  32  and the image light GL 3  emitted from the end on a −Z side on the emitting surface  32   a  of the liquid crystal display device  32  follow optical paths similar to the optical path of the image light GL 1 . Specifically, the image lights GL 2  and GL 3  are emitted to the optical coupling member  21  in a state in which the image lights GL 2  and GL 3  diverge from one point on the emitting surface  32   a , pass through the surfaces of the optical coupling member  21  and the light guide member  22 , and, after once being focused in the light guide member  22 , are emitted to the eye EY of the observer as virtual image lights. The image light GL 2  is emitted at an acute angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 2  passes through the second light emitting surface  22   e . The image light GL 3  is emitted at an obtuse angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 3  passes through the second light emitting surface  22   e . All components of the image lights GL 2  and GL 3  and the other image lights other than the image light GL 1  are subjected to the refraction and reflection action at different degrees on the first light incident surface  21   a , the first light emitting surface  21   c , the second light incident surface  22   a , and the like having the concave and convex curved surface shapes. 
     In general, when image light is emitted from an oblique direction or a reflection optical system is used, aberration such as distortion particularly tends to occur. Therefore, in the optical system in this embodiment, it is highly likely that aberration occurs. On the other hand, in the image relay optical system  20 , all the components of the image lights are subjected to the refraction and reflection action at different degrees on the first light emitting surface  21   c , the second light incident surface  22   a , and the like. Therefore, the image relay optical system  20  enables correction of distortion that occurs in the image relay optical system  20 . In correcting the distortion, the image relay optical system  20  also enables correction of chromatic aberration. 
     All the beams of the image lights change to the diverged state and then travel to the light guide member reflecting surface  22   d  after once being focused in the light guide member  22 . Therefore, when the image lights are emitted from the image relay optical system  20 , the image lights are converted into parallel beams by the light guide member reflecting surface  22   d , which is the concave convergent surface. In other words, the light guide member reflecting surface  22   d  is a surface for converting image lights focused as an intermediate image into parallel beams in the light guide member  22 . The image lights converted into the parallel beams on the light guide member reflecting surface  22   d  are combined in the position of the eye EY of the observer and recognized as a virtual image. As explained above, the image lights are made incident on the light guide member reflecting surface  22   d  in a state in which the image lights are already subjected to correction of distortion or the like further on an upstream side in the optical path than the light guide member reflecting surface  22   d . Therefore, the image lights passed through the light guide member reflecting surface  22   d  are in a satisfactory state in which the image lights are corrected. When aberration occurs because of the reflection on the light guide member reflecting surface  22   d , the image lights can be corrected in the optical system further on the upstream side on the optical path than the light guide member reflecting surface  22   d  taking into account even this aberration in advance. As explained above, chromatic aberration of the image lights can also be corrected by adjusting the refractive indexes and the dispersion of the optical coupling member  21  and the light guide member  22 . In this case, since the image relay optical system  20  includes the curved surfaces, an angle of view ϕ of the image lights indicated by the image light GL 2  to the image light GL 3  can be set relatively large on the eye EY side. Further, the width of the parallel beams converted from the image lights can be increased. As a result, an eye ring diameter PP, which is an effective pupil diameter, can be increased. 
     In the total reflection on all of the first light incident surface  21   a  and the first and second total reflecting surfaces  22   b  and  22   c , the image light GL 2  among the components of the image lights has the largest total reflection angle. On the other hand, the image light GL 3  has the smallest total reflection angle. Therefore, if the image light GL 3  having strictest condition is adapted to propagate at an angle that satisfies the total reflection condition, all the image lights can be totally reflected without requiring a reflection film or the like. 
     As explained above, the light guide member reflecting surface  22   d  is the semi-transmissive half mirror surface and the light transmitting member  23  is formed of the light transmissive material. Therefore, the observer can recognize the external light GL′ together with the image lights via the light transmitting member  23  and the light guide member reflecting surface  22   d.    
     As explained above, in the image relay optical system  20  according to this embodiment, the optical coupling member  21  is provided before the incidence of the image lights on the light guide member  22 . The curved surface is present among the first light incident surface  21   a , the coupling member reflecting surface  21   b , and the first light emitting surface  21   c  provided in the optical coupling member  21 . Therefore, a large bright virtual image with reduced aberration can be displayed. In this case, since the image relay optical system  20  includes the two sections: the optical coupling member  21  and the light guide member  22 , it is possible to hold an air layer between the optical coupling member  21  and the light guide member  22  to provide a refractive index difference and increase action by refraction. 
     Second Embodiment 
     A second embodiment obtained by modifying the first embodiment is explained below with reference to  FIG. 4 . An image relay optical system and a virtual image display device according to this embodiment have structure same as the structure shown in  FIG. 1  except the optical coupling member  21  and the light guide member  22 . Therefore, explanation is omitted concerning components serving as functional components of the image forming device  10  and the like. The light transmitting member is not shown in the figure. 
     As shown in  FIG. 4 , in this embodiment, in the optical coupling member  21  of the image relay optical system  20 , the first light incident surface  21   a  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface), the coupling member reflecting surface  21   b  is a concave convergent surface (specifically, a concave spherical surface or aspherical surface), and the first light emitting surface  21   c  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). In the light guide member  22 , the second light incident surface  22   a  is a convex convergent surface (specifically, a convex spherical or aspherical surface). Image lights are subjected to the reflection and refraction action as appropriate by these surfaces. 
     In this case, the image lights GL 1 , GL 2 , and GL 3  emitted from the image forming device  10  are made incident on the optical coupling member  21  from the first light incident surface  21   a  and totally reflected on the coupling member reflecting surface  21   b  to be converted into substantially parallel beams. The image lights GL 1 , GL 2 , and GL 3  directly travel to the first light emitting surface  21   c  without returning to the first light incident surface  21   a  side. The image lights GL 1 , GL 2 , and GL 3  are subjected to the converging action on the first light emitting surface  21   c  and emitted from the first light emitting surface  21   c.    
     Subsequently, the image lights GL 1 , GL 2 , and GL 3  are made incident on the second light incident surface  22   a  of the light guide member  22 , subjected to the converging action, and totally reflected on the first and second total reflecting surfaces  22   b  and  22   c  opposed to and extending in parallel to each other in the Z direction. While being totally reflected, the image lights GL 1 , GL 2 , and GL 3  are once focused from the converged state, change to the diverged state again, and travel to the light guide member reflecting surface  22   d . The optical paths of the image lights GL 1 , GL 2 , and GL 3  are bent by the reflection action on the light guide member reflecting surface  22   d , which is a concave convergent surface (specifically, a concave spherical surface or aspherical surface). The image lights GL 1 , GL 2 , and GL 3  change from the diverged state to the converted state into the parallel beams and travel to the second light emitting surface  22   e.    
     Consequently, when the image light GL 1  passes through the second light emitting surface  22   e , the image light GL 1  is emitted to the eye EY of the observer perpendicularly to the +Z direction from the center side of the second light emitting surface  22   e , i.e., in the −X direction. The image light GL 2  is emitted at an acute angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 2  passes through the second light emitting surface  22   e . The image light GL 3  is emitted at an obtuse angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 3  passes through the second light emitting surface  22   e.    
     As explained above, in this embodiment, as in the first embodiment, a large bright virtual image with reduced aberration can be displayed by the curved surfaces of the optical coupling member  21  and the light guide member  22 . 
     Third Embodiment 
     A third embodiment obtained by modifying the first embodiment is explained below with reference to  FIG. 5 . An image relay optical system and a virtual image display device according to this embodiment have structure same as the structure shown in  FIG. 1  except the section from the optical coupling member  21  to the light guide member  22 . Therefore, explanation is omitted concerning components serving as functional components of the image forming device  10  and the like. The light transmitting member is not shown in the figure. 
     As shown in  FIG. 5 , in this embodiment, in the optical coupling member  21  of the image relay optical system  20 , the first light incident surface  21   a  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface), the coupling member reflecting surface  21   b  is a concave convergent surface (specifically, a concave spherical surface or aspherical surface), and the first light emitting surface  21   c  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). In the light guide member  22 , the second light incident surface  22   a  is a plane functioning as a first total reflecting surface. In other words, in the light guide member  22 , the second light incident surface  22   a  and the first total reflecting surface  22   b  are formed as an integral surface continuing to the same plane. The light guide member  22  includes, as a surface opposed to the second light incident surface  22   a , an opposed reflecting surface  22   f  between the second light incident surface  22   a  and the second total reflecting surface  22   c . The opposed reflecting surface  22   f  is a concave convergent surface (specifically, a concave spherical or aspherical surface) and is a total reflecting surface that includes the reflection film ML and reflects image lights from the second light incident surface  22   a  to the first total reflecting surface. Further, in the image relay optical system  20 , a convergent lens  25  (specifically a convex spherical or aspherical lens) is arranged between the first light emitting surface  21   c  of the optical coupling member  21  and the second light incident surface  22   a  of the light guide member  22 . The image lights are subjected to the reflection and refraction action as appropriate by these surfaces and the lens. 
     In this case, the image lights GL 1 , GL 2 , and GL 3  emitted from the image forming device  10  are made incident on the optical coupling member  21  from the first light incident surface  21   a  and totally reflected on the coupling member reflecting surface  21   b . The image lights GL 1 , GL 2 , and GL 3  travel to the first light emitting surface  21   c  and are emitted from the first light emitting surface  21   c.    
     Subsequently, the image lights GL 1 , GL 2 , and GL 3  are made incident on the lens  25  and subjected to the refraction action to be converted into substantially parallel beams and made incident on the light guide member  22 . 
     Subsequently, the image lights GL 1 , GL 2 , and GL 3  are made incident on the second light incident surface  22   a  of the light guide member  22  and returned to the second light incident surface  22   a  side by the reflection on the opposed reflecting surface  22   f  while being subjected to the converging action. When the image lights GL 1 , GL 2 , and GL 3  are returned, since an angle of the image lights GL 1 , GL 2 , and GL 3  with respect to the second light incident surface  22   a , i.e., the first total reflecting surface  22   b  changes, the image lights GL 1 , GL 2 , and GL 3  are totally reflected on the first total reflecting surface  22   b . The image lights GL 1 , GL 2 , and GL 3  are repeatedly totally reflected on the first and second total reflecting surfaces  22   b  and  22   c  opposed to and extending in parallel to each other in the Z direction. While being totally reflected, the image lights GL 1 , GL 2 , and GL 3  are once focused from the converged state, change to the diverged state again, and travel to the light guide member reflecting surface  22   d . The optical paths of the image lights GL 1 , GL 2 , and GL 3  are bent by the reflection action on the light guide member reflecting surface  22   d , which is a concave convergent surface (specifically, a concave spherical surface or aspherical surface). The image lights GL 1 , GL 2 , and GL 3  change from the diverged state to the converted state into the parallel beams and travel to the second light emitting surface  22   e.    
     Consequently, when the image light GL 1  passes through the second light emitting surface  22   e , the image light GL 1  is emitted to the eye EY of the observer perpendicularly to the +Z direction from the center side of the second light emitting surface  22   e , i.e., in the −X direction. The image light GL 2  is emitted at an acute angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 2  passes through the second light emitting surface  22   e . The image light GL 3  is emitted at an obtuse angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 3  passes through the second light emitting surface  22   e.    
     As explained above, in this embodiment, as in the first and second embodiments, a large bright virtual image with reduced aberration can be displayed by the curved surfaces of the optical coupling member  21  and the light guide member  22 . 
     Fourth Embodiment 
     A fourth embodiment obtained by modifying the first embodiment is explained below with reference to  FIG. 6 . An image relay optical system and a virtual image display device according to this embodiment have structure same as the structure shown in  FIG. 1  except the optical coupling member  21 , the light guide member  22 , and the like. Therefore, explanation is omitted concerning components serving as functional components of the image forming device  10  and the like. The light transmitting member is not shown in the figure. 
     As shown in  FIG. 6 , in this embodiment, in the optical coupling member  21  of the image relay optical system  20 , the first light incident surface  21   a  is a plane functioning as a total reflecting surface, the coupling member reflecting surface  21   b  is a total reflection concave convergent surface (specifically, a concave spherical surface or aspherical surface), and the first light emitting surface  21   c  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). Specifically, in the optical coupling member  21 , the first light incident surface  21   a  includes an extended surface ES 1 , which is a surface on an extended region outside a region on which image lights are made incident from the outside. The first light incident surface  21   a  including the extended surface ES 1  functions as a total reflecting surface for the image lights as well. The coupling member reflecting surface  21   b  is a total reflecting surface and can reflect the image lights reflected on the extended surface ES 1 . In the light guide member  22 , the second light incident surface  22   a  is a convex convergent surface (specifically, a convex spherical surface or aspherical surface). Further, in the image relay optical system  20 , a convergent lens  12  (specifically a convex spherical or aspherical lens) is arranged to be opposed to the first light incident surface  21   a  of the optical coupling member  21  between the image forming device  10  and the optical coupling member  21 . The image lights are subjected to the reflection and refraction action as appropriate by these surfaces and the lens. 
     In this case, the image lights GL 1 , GL 2 , and GL 3  emitted from the image forming device  10  are converted into substantially parallel beams by the convergent lens  12 , made incident on the optical coupling member  21  from the first light incident surface  21   a , and totally reflected on the coupling member reflecting surface  21   b . The image lights GL 1 , GL 2 , and GL 3  travel to the first light incident surface  21   a  including the extended surface ES while being subjected to the converging action. When the image lights GL 1 , GL 2 , and GL 3  travel to the first light incident surface  21   a , since an angle of the image lights GL 1 , GL 2 , and GL 3  with respect to the first light incident surface  21   a  changes, the image lights GL 1 , GL 2 , and GL 3  are totally reflected on the first light incident surface  21   a . The image lights GL 1 , GL 2 , and GL 3  totally reflected on the first light incident surface  21   a  are totally reflected on the coupling member reflecting surface  21   b  again and travel to the first light emitting surface  21   c  while hardly losing a light amount. The image lights GL 1 , GL 2 , and GL 3  are subjected to the converging action on the first light emitting surface  21   c  and emitted from the first light emitting surface  21   c.    
     Subsequently, the image lights GL 1 , GL 2 , and GL 3  are made incident on the second light incident surface  22   a  of the light guide member  22 , subjected to the conversing action, and totally reflected on the first and second total reflecting surfaces  22   b  and  22   c  opposed to and extending in parallel to each other in the Z direction. While being totally reflected, the image lights GL 1 , GL 2 , and GL 3  are once focused from the converged state, change to the diverged state again, and travel to the light guide member reflecting surface  22   d . The optical paths of the image lights GL 1 , GL 2 , and GL 3  are bent by the reflection action on the light guide member reflecting surface  22   d , which is a concave convergent surface (specifically, a concave spherical surface or aspherical surface). The image lights GL 1 , GL 2 , and GL 3  change from the diverged state to the converted state into the parallel beams and travel to the second light emitting surface  22   e.    
     Consequently, when the image light GL 1  passes through the second light emitting surface  22   e , the image light GL 1  is emitted to the eye EY of the observer perpendicularly to the +Z direction from the center side of the second light emitting surface  22   e , i.e., in the −X direction. The image light GL 2  is emitted at an acute angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 2  passes through the second light emitting surface  22   e . The image light GL 3  is emitted at an obtuse angle with respect to the +Z direction along the second light emitting surface  22   e  when the image light GL 3  passes through the second light emitting surface  22   e.    
     As explained above, in this embodiment, as in the first to third embodiments, a large bright virtual image with reduced aberration can be displayed by the curved surfaces of the optical coupling member  21  and the light guide member  22 . 
     Modification 
     Besides the embodiments explained above, for example, as shown in  FIG. 7 , it is possible to reduce the thickness of the light guide member  22  effectively utilizing components that follow an optical path such as image light GG. Specifically, first, the image light GG passes through the light guide member reflecting surface  22   d  of the light guide member  22  and are totally reflected on the first surface  23   a  of the light transmitting member  23 . The image light GG totally reflected on the first surface  23   a  passes through the light guide member reflecting surface  22   d  again and is totally reflected on the second light emitting surface  22   e  present on the extension of the second total reflecting surface  22   c . The image light GG totally reflected on the second light emitting surface  22   e  travels to the light guide member reflecting surface  22   d  for the third time. This time, the image light GG is reflected on the light guide member reflecting surface  22   d  and reaches the eye EY of the observer. It is possible to realize a reduction in thickness of the light guide member  22  by increasing efficiency of use of image lights also making use of the image light GG that follows the optical path explained above. 
     Others 
     The invention is explained according to the embodiments. However, the invention is not limited to the embodiments and can be carried out in various forms without departing from the spirit of the invention. For example, modifications explained below are also possible. 
     In the above explanation, the transmissive liquid crystal display device is used. However, the liquid crystal display device according to the embodiments is not limited to the transmissive liquid crystal display device. Various liquid crystal display devices can be used. For example, a configuration including a reflective liquid crystal panel is also possible. A digital micro-mirror device or the like can also be used instead of the liquid crystal display device  32 . A configuration including a self-emitting device represented by an LED array or an OLED (organic EL) is also possible. Further, a configuration including a laser scanner in which a laser beam source, a polygon mirror, and other scanners are combined is also possible. 
     In the above explanation, the virtual image display device  100  includes the set of the image forming device  10  and the image relay optical system  20  to correspond to each of the right and left eyes. However, a configuration in which the image forming device  10  and the image relay optical system  20  are provided for one of the right and left eyes to view an image with one eye may be adopted. 
     In the above explanation, the see-through virtual image display device is explained. However, when it is unnecessary to cause the observer to observe an external image, it is possible to set the light reflectance of the light guide member reflecting surface  22   d  to about 100%. 
     In the above explanation, the virtual image display device  100  according to the embodiments is specifically explained assuming that the virtual image display device  100  is the head mounted display. However, the virtual image display device  100  according to the embodiments can be modified to a head-up display. 
     In the above explanation, on the first and second total reflecting surfaces  22   b  and  22   c , the image lights can be totally reflected and guided by an interface with the air without applying a mirror, a half mirror, or the like to the surfaces. However, the total reflection in the invention includes reflection performed by forming a mirror coat or a half mirror film on all or a part of the first and second total reflecting surfaces  22   b  and  22   c . For example, on condition that an incident angle of image lights satisfies a total reflection condition, a mirror coat or the like is applied to all or a part of the total reflecting surfaces  22   b  and  22   c  and substantially all the image lights are reflected. The total reflection includes the reflection in this case. If image lights having sufficient brightness are obtained, all or a part of the total reflecting surfaces  22   b  and  22   c  may be coated with a mirror slightly having transmissivity. 
     The entire disclosure of Japanese Patent Application No. 2011-062542, filed Mar. 22, 2011 is expressly incorporated by reference herein.