Patent Publication Number: US-2022221778-A1

Title: Image display apparatus and image display unit

Description:
TECHNICAL FIELD 
     The present technology relates to an image display apparatus and an image display unit. 
     BACKGROUND ART 
     In the past, an image display apparatus such as a projector has been widely used. In a projection apparatus described in Patent Literature 1, a polarization conversion unit capable of uniformly and omnidirectionally depolarizing projected lights of all RGB is disposed between an emitting side of combined light of a color combination prism and an incident side of a projection lens. This makes it possible to completely eliminate color unevenness of a 3D image with 3D glasses not tilted and to eliminate the color unevenness and a luminance drop of the 3D image with the 3D glasses tilted. As a result, it is possible to significantly improve 3D image quality (see Patent Literature 1, specification paragraphs [0154] and [0155],  FIG. 20 , etc.). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Japanese Patent Application Laid-open No. 2013-113984 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Thus, there is a need for a technology capable of displaying a high-quality image. 
     In view of the above circumstances, an object of the present technology is to provide an image display apparatus and an image display unit that are capable of displaying a high-quality image. 
     Solution to Problem 
     In order to achieve the above-mentioned object, an image display apparatus according to an embodiment of the present technology includes: a light emission unit; and a polarization conversion element. 
     The light emission unit emits image light. 
     The polarization conversion element has an incident surface, converts a polarization state of the image light that enters the incident surface, emits the converted light as image light in an unpolarized state, and is configured such that conversion properties of the polarization state are non-uniform in the incident surface. 
     In this image display apparatus, a polarization conversion element that converts a conversion state of image light and emits the converted light as image light in an unpolarized state is provided. The polarization conversion element is configured such that conversion properties of the polarization state are non-uniform in the incident surface. As a result, it is possible to sufficiently depolarize the image light and display a high-quality image. 
     The polarization conversion element may add a phase difference to the image light that enters the incident surface and may be configured such that the phase difference added to the image light is non-uniform in the incident surface. 
     The polarization conversion element may be configured such that a birefringence with respect to the image light is non-uniform in the incident surface. 
     The polarization conversion element may have an emission surface that emits the image light in the unpolarized state and may be configured such that a thickness from the incident surface to the emission surface in an optical axis direction of the image light is non-uniform in the incident surface. 
     The polarization conversion element may be configured such that conversion properties of the polarization state change in a continuous manner along a predetermined direction in the incident surface. 
     The emission surface may be tilted along a predetermined direction with respect to the incident surface. 
     The predetermined direction may be a direction corresponding to an up-and-down direction or a right-and-left direction of an image formed by the image light. 
     The polarization conversion element may be configured such that a difference between a minimum phase difference and a maximum phase difference added to the image light is equal to or larger than ¼ of a reference wavelength of the image light. 
     The reference wavelength may be a wavelength included in a blue wavelength band. 
     The image display apparatus may further include a suppression member that has a suppression incident surface and a suppression emission surface, the image light in the unpolarized state emitted from the polarization conversion element entering the suppression incident surface, the suppression emission surface emitting the image light in the unpolarized state that enters the suppression incident surface. In this case, the suppression member may be configured to be capable of emitting the image light from the suppression emission surface while suppressing a variation in an optical distance of the image light from the incident surface to the emission surface of the polarization conversion element. 
     The polarization conversion element may have an emission surface that emits the image light in the unpolarized state. In this case, the suppression member is disposed such that the suppression incident surface comes into contact with the emission surface. Alternatively, the suppression member may be disposed such that the suppression incident surface is close to the emission surface in parallel. 
     The suppression member may be disposed such that the suppression emission surface is parallel to the incident surface. 
     The suppression member may be configured such that a distance from the incident surface to the suppression emission surface is uniform in the optical axis direction of the image light. 
     The suppression member may have a shape equal to that of the polarization conversion element. 
     The suppression member may be formed of a material having no optical anisotropy. 
     A refractive index of the suppression member may be specified on the basis of a refractive index of the polarization conversion element. 
     The polarization conversion element may be formed of a uniaxial crystal material or a uniaxial organic material. 
     the image display apparatus may further include a projection unit that projects the image light in the unpolarized state emitted from the polarization conversion element. In this case, the light emission unit may include a light modulation element that modulates incident light and emits the image light. 
     An image display unit according to an embodiment of the present technology includes a polarization conversion element. 
     The polarization conversion element has an incident surface, converts a polarization state of the image light that enters the incident surface, emits the converted light as image light in an unpolarized state, and is configured such that conversion properties of the polarization state are non-uniform in the incident surface. 
     The image display unit may further include: a suppression member that has a suppression incident surface and a suppression emission surface, the image light in the unpolarized state emitted from the polarization conversion element entering the suppression incident surface, the suppression emission surface emitting the image light in the unpolarized state that enters the suppression incident surface. In this case, the suppression member may be configured to be capable of emitting the image light from the suppression emission surface while suppressing a variation in an optical distance of the image light from the incident surface to the emission surface of the polarization conversion element. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram showing a configuration example of an image display apparatus according to a first embodiment. 
         FIG. 2  is a diagram for describing an example of converting a polarization state for generating light in an unpolarized state. 
         FIG. 3  is a schematic diagram showing a configuration example of a polarization scrambler. 
         FIG. 4  is a schematic diagram showing a configuration example of the polarization scrambler. 
         FIG. 5  is a diagram schematically showing image light that travels from a reflective light modulation element to a screen  1 . 
         FIG. 6  is a graph for describing a polarization property of the polarization scrambler. 
         FIG. 7  is a graph for describing a polarization property of the polarization scrambler. 
         FIG. 8  is a graph for describing a polarization property of the polarization scrambler. 
         FIG. 9  is a schematic diagram showing another configuration example of the polarization scrambler. 
         FIG. 10  is a schematic diagram showing a configuration example of an image display apparatus according to a second embodiment. 
         FIG. 11  is a schematic diagram showing a configuration example of a suppression member. 
         FIG. 12  is a graph showing results of simulating evaluation of occurrence of astigmatism (with a polarization scrambler having a uniform thickness, without suppression member). 
         FIG. 13  is a graph showing results of simulating evaluation of occurrence of astigmatism (with a polarization scrambler having a non-uniform thickness, without no suppression member). 
         FIG. 14  is a graph showing results of simulating evaluation of occurrence of astigmatism (with a polarization scrambler having a non-uniform thickness and a suppression member). 
         FIG. 15  is a schematic diagram showing another configuration example of the suppression member. 
         FIG. 16  is a schematic diagram showing another configuration example of the image generation unit. 
         FIG. 17  is a schematic diagram showing another configuration example of the image generation unit. 
         FIG. 18  is a schematic diagram showing another configuration example of the image generation unit. 
     
    
    
     MODE(S) FOR CARRYING OUT THE INVENTION 
     Embodiments according to the present technology will now be described below with reference to the drawings. 
     First Embodiment 
     [Image Display Apparatus] 
       FIG. 1  is a schematic diagram showing a configuration example of an image display apparatus according to a first embodiment of the present technology. An image display apparatus  100  is used as a projector for, for example, a presentation or a digital cinema. The present technology described below is also applicable to an image display apparatus used for other applications. 
     The image display apparatus  100  includes a light source unit  101 , a lighting optical system  110 , an image generation unit  130 , and a projection optical system  140 . 
     The light source unit  101  generates white light W and emits the generated white light W to the lighting optical system  110 . In the light source unit  101 , for example, a solid-state light source such as an LED (Light Emitting Diode) and an LD (Laser Diode), a mercury lamp, a xenon lamp, or the like is disposed. 
     For example, a solid-state light source for RGB capable of emitting light of each color of RGB may be used, and the emitted light may be combined to generate the white light W. Alternatively, a solid-state light source that emits light in a blue wavelength band, and a phosphor that is excited by the blue light and emits yellow fluorescence may be disposed. In this case, blue light and yellow light are combined to emit the white light W. 
     The lighting optical system  110  includes an integrator element  111 , a polarization conversion element  112 , polarization elements  113  and  114 , a condenser lens  115 , a cross dichroic mirror  116 , reflection mirrors  117  and  118 , a dichroic mirror  119 , and relay lenses  120 ,  121  and  122 . 
     The integrator element  111  includes first and second fly-eye lenses  111   a  and  111   b.  The white light W is transmitted through the first and second fly-eye lenses  111   a  and  111   b,  and luminance unevenness of the white light W is reduced. 
     The polarization conversion element  112  has a function of making the polarization state of the white light W that enters through the integrator element  111  uniform. As the polarization conversion element  112 , an arbitrary optical element such as a PS converter may be used. The white light W that has passes through the polarization conversion element  112  is emitted to the cross dichroic mirror  116  through the condenser lens  115 . 
     The cross dichroic mirror  116  splits the white light W emitted from the condenser lens  115  into red light R at a long wavelength side and green light G and blue light B at a short wavelength side. The red light R split by the cross dichroic mirror  116  is reflected by the reflection mirror  117  and enters the polarization element  113 . The red light R having the polarization state that has been made uniform by the polarization element  113  is emitted to the image generating section  130  through the relay lens  120 . Note that as the polarization element  113 , an arbitrary optical element such as a polarizing plate may be used. 
     The green light G and the blue light B split by the cross dichroic mirror  116  are reflected by the reflection mirror  118  and enter the polarization element  114 . The green light G and the blue light B having polarized states that have been made uniform by the polarization element  114  are split into the green light G at the long wavelength side and the blue light B at the short wavelength side by the dichroic mirror  119 . 
     The green light G split by the dichroic mirror  119  is emitted to the image generating section  130  through the relay lens  121 . The blue light B split by the dichroic mirror  119  is emitted to the image generation unit  130  through the relay lens  122 . 
     The image generation unit  130  includes a reflective polarization element  131  ( 131 R,  131 G,  131 B), a reflective light modulation element  132  ( 132 R,  132 G,  132 B), a wavelength plate  133  ( 133 R,  133 G,  133 B), and a polarizing plate  134  ( 134 R,  134 G,  134 B), which are disposed for each color of RGB. Further, the image generation unit  130  includes a color combination prism  135  and a polarization scrambler  136 . 
     The reflective polarization element  131  is a wire grid polarizer. In this embodiment, each light of RGB is emitted from each of the relay lenses  120  to  122  shown in  FIG. 1  so as to be P-polarized with respect to an optical plane of the reflective polarization element  131 . 
     The reflective polarization element  131 R emits the P-polarized component of the red light R toward the wavelength plate  133 R. The wavelength plate  133 R functions as a compensation plate for compensating for the flotation of black luminance, rotates a polarization direction of the incident red light R, and emits the red light R to the reflective light modulation element  132 R. A rotation angle of the polarization direction is appropriately set such that an image with high accuracy is projected. 
     The reflective light modulation element  132 R modulates and reflects the incident red light R on the basis of an image signal corresponding to the red light R supplied from outside. The modulated red light R is emitted as image light forming a red image (hereinafter, referred to as image light R using the same reference symbol). As the reflective light modulation element  132 R, a reflective liquid crystal panel is typically used, but the present technology is not limited thereto. 
     The image light R emitted from the reflective light modulation element  132 R enters the reflective polarization element  131 R via the wavelength plate  133 R. The S-polarized component of the image light R is reflected by the optical plane and enters the polarizing plate  134 R disposed on the optical path of the image light R. 
     The polarizing plate  134 R makes the polarization state of the image light R uniform and cuts unnecessary light. For example, linearly polarized light having a polarization direction parallel to a transmission axis (polarization axis) of the polarizing plate  134 R is transmitted through the polarizing plate  134 R and is emitted. It goes without saying that the present technology is not limited to such an arrangement configuration. The image light R emitted from the polarizing plate  134 R is emitted to the color combination prism  135 . 
     Similarly, the green light G and the blue light B are modulated by the reflective light modulation elements  132 G and  132 B, and are emitted as image light G forming a green image and image light B forming a blue image. The image lights G and B are reflected by the reflective polarization elements  131 G and  131 B, and enter the polarizing plates  134 G and  134 B disposed on the optical paths of the image lights G and B, respectively. For example, the image lights G and B are emitted to the color combination prism  135  as linearly polarized lights each having a polarization direction parallel to the transmission axis of each of the polarizing plates  134 G and  134 B. 
     In this embodiment, an inorganic polarizing plate is used as the polarizing plate  134  ( 134 R,  134 G,  134 B). It goes without saying that the present technology is not limited thereto, and a polarizing plate having an arbitrary structure may be used. 
     In this embodiment, the reflective light modulation element  132  ( 132 R,  132 G,  132 B) corresponds to a light modulation element that modulates incident light and emits the image light. 
     The color combination prism  135  is, for example, formed by bonding a plurality of glass prisms (four right isosceles prisms having substantially identical shapes). Two interference films having predetermined optical properties are formed on a bonding surface of each glass prism. The first interference film of the interference films reflects the blue light B and causes the red light R and the green light G to be transmitted therethrough. The second interference film reflects the red light R and causes the blue light B and the green light G to be transmitted therethrough. 
     The image lights R and B are reflected by the bonding surface, and the image light G is transmitted through the bonding surface. As a result, images RGB are combined on the same optical path, and image light  10  forming a color image is generated. The image light  10  is emitted to the polarization scrambler  136 . 
     The polarization scrambler  136  converts the polarization state of the incident light and emits the converted light as light in an unpolarized state. In this embodiment, the polarization state of the image light  10  (image lights R, G, B) that has been transmitted through the polarizing plates  134 R,  134 G, and  134 B and combined is converted, and the converted light is emitted as image light  10 ′ in the unpolarized state. In this embodiment, the polarization scrambler  136  functions as a polarization conversion element. 
     The light in the unpolarized state is light that is not polarized, and includes, for example, natural light. Further, light having polarization directions distributed substantially uniformly in all directions is also included in the light in the unpolarized state. Further, light including lights having various polarization states is also included in the light in the unpolarized state. Further, light including a plurality of lights having polarization components of substantially equal intensity and different polarization directions from each other is also included in the light in the unpolarized state. 
     Hereinafter, the degree of the unpolarized state will be referred to as the scramble degree in some cases. For example, in the case where two lights having the same wavelength band are emitted, the light including more lights in different polarization states is light having the relatively high scramble degree. It goes without saying that the present technology is not limited to the lights having the same wavelength band. Also in the case where lights having wavelength bands different from each other are compared to each other, the light including more lights in different polarization states is light having the relatively high scramble degree. 
     The projection optical system  140  enlarges the image light  10 ′ converted into light in the unpolarized state by the polarization scrambler  136  at a predetermined magnification and projects the enlarged light on a projection target such as a screen. Thus, a color image is displayed. The projection optical system  140  includes, for example, a plurality of projection lenses or the like, and a specific configuration thereof may be appropriately designed. In this embodiment, the projection optical system  140  corresponds to a projection unit that projects the image light in the unpolarized state emitted from the polarization conversion element. 
     By converting the image light  10  into the image light  10 ′ in the unpolarized state, it is possible to prevent color unevenness and a luminance drop due to reflection properties of a projection target such as a screen from occurring. For example, depending on an angle of incidence of the light that enters the projection target and the polarization state, a reflectance of the light differs in some cases. In this case, in the case where there is a difference in the polarization state of each of the image lights of RGB, the reflectance of the light of each color will vary, resulting in the color unevenness and the luminance drop. In this embodiment, since the image light  10  is converted into the image light  10 ′ in the unpolarized state, the reflectances of the lights of the respective colors is substantially equivalent to each other and the color unevenness and the luminance drop are suppressed. 
     Further, there is a system in which light in a predetermined polarization state is caused to be transmitted by 3D glasses and viewed as a right-eye image and a left-eye image. Even in such a system, by converting the image light  10  into the image light  10 ′ in the unpolarized state, it is possible to sufficiently prevent the color unevenness and the luminance drop from occurring. In addition, even in the case where an image is displayed by an ultra-short focus projector or the like, by applying the present technology, it is possible to sufficiently prevent the color unevenness and the luminance drop from occurring. 
     In this embodiment, the component that emits the image light  10  toward the polarization scrambler  136  realizes a light emission unit that emits image light. For example, the reflective polarization element  131 , the reflective light modulation element  132 , the wavelength plates  133  and  134 , and the color combination prism  135  realize a light emission unit. The specific configuration of the light emission unit is not limited, and an arbitrary configuration may be employed. Further, only the color combination prism  135  can be regarded as one embodiment of the light emission unit according to the present technology. 
     Further, in this embodiment, the polarization scrambler  136  realizes an image display unit. The image display unit may be configured to be interchangeable from the image display apparatus  100 . 
     [Example of Generating Image Light  10 ′ in Unpolarized State] 
       FIG. 2  is a diagram for describing an example of converting a polarization state for generating light in an unpolarized state. Here, in order to facilitate understanding of the present technology, a case where a polarization scrambler  900  different from the polarization scrambler  136  illustrated in  FIG. 1  is used will be described. 
     The polarization scrambler  900  is an element that has an optical axis and is capable of converting the polarization state by adding a phase difference to two polarization components, which are perpendicular to each other, of incident light. For example, it is possible to realize the polarization scrambler  900  by a material having an optical anisotropy. Note that the optical axis corresponds to a slow axis or a fast axis. 
     The polarization scrambler  900  is configured to have a uniform thickness in the optical axis direction of incident light. By appropriately controlling the thickness of the polarization scrambler  900 , it is possible to achieve the polarization property shown in Part B of  FIG. 2 . This makes it possible to convert the polarization state of incident light such that the polarization state differs for each wavelength of incident light. 
     For example, when light included in a predetermined wavelength band (light including a plurality of wavelength lights) enters the polarization scrambler  900 , light in the unpolarized state including lights in various polarization states can be generated. 
     Note that the polarization scrambler  900  has the polarization property shown in Part B of  FIG. 2  over the entire incident surface  901  that light enters. That is, the polarization scrambler  900  is configured such that the polarization properties are uniform in the incident surface  901 . In this embodiment, the polarization properties correspond to conversion properties of the polarization state. 
     As shown in Part A of  FIG. 2 , two polarizing plates  15  and  16  are disposed such that their transmission axes  15   a  and  16   a  are substantially perpendicular to each other. Then, the polarization scrambler  900  is disposed therebetween, and the Cross-Nicol transmittance for each wavelength has been measured. 
     As shown in Part B of  FIG. 2 , the transmittance periodically changes for each wavelength. The change in the transmittance corresponds to the change in the polarization state. For example, wavelength light having a transmittance whose value is close to 0% corresponds to light whose polarization state is not converted by the polarization scrambler  900 . Such light is linearly polarized light having a polarization direction parallel to the transmission axis  15   a  of the polarizing plate  15 . 
     Wavelength light having a transmittance whose value is close to 100% corresponds to light whose polarization direction is caused to rotate by substantially 90 degrees by the polarization scrambler  900 . Such light is linearly polarized light having a polarization direction parallel to the transmission axis  16   a  of the polarizing plate  16 . 
     As schematically shown in Part B of  FIG. 2 , wavelength light having a transmittance whose value is close to 50% corresponds to light to be converted into circularly polarized light by the polarization scrambler  900 . Wavelength light having a transmittance in the range of 0% to 50% corresponds to light to be converted into vertically-long elliptically polarized light (elliptically polarized light having many polarization components parallel to the transmission axis  15   a ). Wavelength light having a transmittance in the range of 50% to 100% corresponds to light to be converted into horizontally-long elliptically polarized light (elliptically polarized light having many polarization components parallel to the transmission axis  16   a ). 
     As described above, the light that has entered the polarization scrambler  900  is converted into light in a polarization state different for each wavelength. For example, a red wavelength band  17 R, a green wavelength band  17 G, and a blue wavelength band  17 B, each of which is surrounded by a dashed line, include lights in various polarization states. As a result, the image lights R, G, B of the respective colors are converted into lights R 1 , G 1 , B 1  in the unpolarized states by the polarization scrambler  900 . Note that the wavelength band of each color is not limited to the wavelength band shown in Part B of  FIG. 2 . 
     The polarization scrambler  900  is formed of, for example, a uniaxial crystalline material. It is possible to use an inorganic material having an axis on the material itself, such as quartz, sapphire, lithium niobate, and yttrium vanadate. For example, the polarization scrambler  136  is formed such that the optical axis is other than 0°/90° (45°, 135° is valid) with respect to the image light  10  without Zcut. It goes without saying that the present technology is not limited thereto. 
     Further, the polarization scrambler  900  can be formed of, for example, a uniaxial organic material. For example, it is also possible to realize the polarization scrambler by an organic film such as polycarbonate and polyolefin. 
     In addition, in order to realize the polarization scrambler  900 , an arbitrary configuration may be employed. An arbitrary wavelength plate using quartz, a wavelength plate film, an inorganic phase difference film, or the like can be used as the polarization scrambler  900 . Note that when the polarization scrambler  900  is formed to have each configuration of a multilayer film, a multilayer inorganic deposition film, and a multilayer quartz, the polarization scrambler  900  having the configuration of a multilayer quartz has higher moisture absorption and resistance to deterioration or the like. In view of this, the polarization scrambler  900  using an inorganic material such as quartz is thought to be valid with respect to an image display apparatus of a high-luminance model. It goes without saying that the application of the present technology is not limited to this material or configuration. 
     In the present disclosure, the optical operation of adding a phase difference to two polarization components, which are perpendicular to each other, of incident light is represented as adding a phase difference to incident light in some cases. Further, in the present disclosure, an arbitrary optical element capable of adding a phase difference to incident light is included in a phase difference plate. That is, an arbitrary phase difference plate can be used as the polarization scrambler  900 . 
     [Polarization Scrambler  136 ] 
     The polarization scrambler  136  according to this embodiment will be described in detail.  FIG. 3  and FIG. 
       4  are each a schematic diagram showing a configuration example of the polarization scrambler  136 .  FIG. 5  is a diagram schematically showing the image light  10  ( 10 ′) that travels from the reflective light modulation element  132  to the screen  1 . 
     In  FIG. 5 , in order to make the description easier to understand, a configuration in which the reflective light modulation element  132 , the polarization scrambler  136 , the projection optical system  140 , and the screen  1  are linearly disposed is schematically illustrated. That is, illustration of the color combination prism  135  and the like shown in  FIG. 1  is omitted. Although an example in which the image light  10 ′ in the unpolarized state is generated will be described below with reference to  FIG. 5 , the principle thereof is similarly applied to the configuration illustrated in  FIG. 1 . 
     As illustrated in  FIG. 1 ,  FIG. 5 , or the like, the polarization scrambler  136  is disposed so as to be perpendicular to an optical axis direction C of the image light  10 . The optical axis direction of the image light  10  can be specified by, for example, an axis through which a light beam at the center of the image light  10  (referred to also as pixel light) emitted from a pixel P 1  at the center of the reflective light modulation element  132 . 
     The pixel light is diffused and emitted from each pixel of the reflective light modulation element  132 . The pixel light of each pixel is collected on the screen  1  by the projection optical system  140  or the like. As a result, the respective pixels forming an image  2  are displayed on the screen  1 . For example, the pixel light emitted from the pixel P 1  at the center of the reflective light modulation element  132  is displayed on the screen  1  as a pixel P 2  at the center of the image  2 . 
     Hereinafter, the optical axis direction of the image light  10  (pixel light) that enters the polarization scrambler  136  will be referred to as the Z direction. Further, the direction corresponding to the right-and-left direction of the image  2  formed by the image light  10  will be referred to as the X direction, and the direction corresponding to the up-and-down direction of the image  2  will be referred to as the Y direction. Further, for convenience, description will be made with the X direction, the Y direction, and the Z direction as the right-and-left direction, the up-and-down direction, and the thickness direction respectively with respect to the polarization scrambler  136 . 
     In the configuration illustrated in  FIG. 5 , the right-and-left direction and the up-and-down direction of the polarization scrambler  136  and the right-and-left direction and the up-and-down direction of the image  2  are the same directions, respectively. It goes without saying that the present technology is not limited thereto. Depending on the configurations of the lighting optical system  110 , the image generation unit  130 , and the projection optical system  140 , the right-and-left direction and the up-and-down direction of the polarization scrambler  136  and the right-and-left direction and the up-and-down direction of the image  2  are different directions in some cases. 
     Part A of  FIG. 3  is a front view of the polarization scrambler  136  viewed from the incident surface side. 
     Part B of  FIG. 3  is a top view of the polarization scrambler  136  viewed from above. 
     Part A of  FIG. 4  is a perspective view of the polarization scrambler  136  viewed from the incident surface side. 
     Part B of  FIG. 4  is a perspective view of the polarization scrambler  136  viewed from the emission surface side. 
     The polarization scrambler  136  has an incident surface  20  and an emission surface  21 , the image light  10  entering the incident surface  20 , the emission surface  21  emitting the image light  10 ′ in the unpolarized state. Further, the polarization scrambler  136  has an upper surface  22 , a lower surface  23 , a left side surface  24 , and a right side surface  25  that surround the incident surface  20  from the up, down, left, and right directions as viewed from the front of the incident surface  20 . 
     The polarization scrambler  136  converts the polarization state of the image light  10  that enters the incident surface  20  and emits the converted light as the image light  10 ′ in the unpolarized state from the emission surface  21 . Further, the polarization scrambler  136  is configured such that conversion properties of the polarization states are non-uniform in the incident surface  20 . That is, the polarization property differ depending on the position at which the image light  10  enters in the incident surface  20 . 
     In this embodiment, it is possible to add a phase difference to the image light  10  that enters the incident surface  20 , and the polarization scrambler  136  is configured such that the phase difference added to the image light  10  is non-uniform in the incident surface  20 . That is, the polarization scrambler  136  is configured such that the birefringence with respect to the image light  10  is non-uniform in the incident surface  20 . 
     As shown in  FIG. 3  and  FIG. 4 , the polarization scrambler  136  is formed of a predetermined material having an optical anisotropy such that the thickness from the incident surface  20  to the emission surface  21  in the optical axis direction of the image light  10  is non-uniform in the incident surface  20 . Note that the thickness being non-uniform in the incident surface  20  means that the thickness in the optical axis direction C at each position in the incident surface  20  is non-uniform. 
     The phase difference added to the image light  10  is specified by the product of the thickness and the difference between the refractive index in the slow axis and the refractive index in the fast axis. In this regard, the polarization scrambler  136  is formed of a material that the difference between the refractive index in the slow axis and the refractive index in the fast axis is uniform, such that the thickness is non-uniform. As a result, it is possible to easily realize the configuration in which conversion properties of the polarization state are non-uniform in the incident surface  20 . 
     As shown in  FIG. 3  and  FIG. 4 , in this embodiment, the emission surface  21  is tilted with respect to the incident surface  20  along the right-and-left direction (direction corresponding to the right-and-left direction of the image  2 ). For this reason, as shown in the top view of Part B of  FIG. 3 , the thickness of the polarization scrambler  136  is reduced in a continuous manner along the right-and-left direction. As a result, it is possible to change the conversion properties of the polarization state in a continuous manner along the right-and-left direction in the incident surface  20 . In this embodiment, the right-and-left direction corresponds to the predetermined direction. 
     As shown in Part B of  FIG. 3 , the size of the left side surface  24  along the optical axis direction is the minimum thickness d 1  of the polarization scrambler  136 . The size of the left side surface  24  along the optical axis direction is the maximum thickness d 2  of the polarization scrambler  136 . A difference Δd between the thickness d 1  and the thickness d 2  is a parameter relating to the difference in the polarization properties. That is, the difference Δd is a parameter relating to the phase difference added to the image light  10 . 
     For example, assumption is made that the thickness d 1  is 0.450 mm an the thickness d 2  is 0.500 mm. In this case, the difference Δd is 0.050 mm. With such design, the image light  10  can be sufficiently converted into the image light  10 ′ in the unpolarized state. 
     Note that the method of setting the thickness d 1 , the thickness d 2 , and the difference Ad between the thicknesses is not limited, and they may be arbitrarily set. For example, of the image light  10  that is desired to be converted into light in the unpolarized state, a reference wavelength λ is set. For example, a wavelength that is difficult to convert into light in the unpolarized state, or the like is used as a reference wavelength. It goes without saying that the present technology is not limited thereto. 
     The minimum thickness d 1  and the maximum thickness d 2  are set such that the difference between the minimum phase difference and the maximum phase difference added to the image light  10  is equal to or larger than ¼ of the reference wavelength λ. For example, the polarization scrambler  136  is designed such that the product of the difference between the refractive index in the slow axis and the refractive index in the fast axis and the difference Δd between the thicknesses is equal to or larger than ¼ of the reference wavelength λ. As a result, the image light  10  can be sufficiently converted into the image light  10 ′ in the unpolarized state. 
     [Polarization Property of Polarization Scrambler  136 ] 
       FIG. 6  to  FIG. 8  are each a graph for describing the polarization property of the polarization scrambler  136 . The polarization property of the polarization scrambler  136  will be described with reference to  FIG. 6  to  FIG. 8  and  FIG. 5 . 
     Here, as shown in  FIG. 6  or the like, a case where the white light W is generated by a blue laser beam and yellow light is taken as an example, the blue laser beam having the center wavelength (peak wavelength) of 453 nm, the yellow light being generated by being excited by the blue laser beam. 
     Further, as shown in  FIG. 6  or the like, a bandwidth in which light is emitted, of the white light W, i.e., a wavelength band in which the radiant flux (W/nm) is greater than 0.0, will be described separately as a blue wavelength band B (approximately 446 nm to approximately 463 nm), a green wavelength band G (approximately 490 nm to approximately 575 nm), and a red wavelength band R (approximately 475 nm to approximately 678 nm). 
     Assumption is made that wavelength light of 453 nm is emitted from the pixel P 1  at the center of the reflective light modulation element  132 , with reference to  FIG. 5 . In  FIG. 5 , of the pixel light diffused from the central pixel P 1 , light (light that travels in the optical axis direction C) L 0  that passes through the center of the polarization scrambler  136 , light L 1  that passes through the left end of the center of the polarization scrambler  136 , and light L 2  that passes through the right end are illustrated. 
       FIG. 6  is a graph showing a polarization property S 1  corresponding to the minimum thickness d 1 . For example, it can be said to be the polarization property of the polarization scrambler  900  formed to have the uniform thickness d 1 . The polarization property S 1  shown in  FIG. 6  corresponds to the polarization property acting on the light L 1  that passes through the left end (in the vicinity of the left side surface  24 ) shown in  FIG. 5 . 
     As shown in  FIG. 6 , in the blue wavelength band B, light in the polarization state having the cross Nicol transmittance of 0% to approximately 62% is included. Meanwhile, in the green wavelength band G and the red wavelength band R, light in the polarization state having the transmittance of 0% to 100% is included. Therefore, in the blue wavelength band B having narrow spectral distribution, the scramble degree is lower than those in the green wavelength band G and the red wavelength band R having wide spectral distribution. 
       FIG. 7  is a graph showing the polarization property S 1  corresponding to the minimum thickness d 1 , a polarization property S 2  corresponding to the maximum thickness d 2 , and a polarization property S 3  corresponding to the middle thickness thereof. The polarization property S 2  corresponding to the maximum thickness d 2  corresponds to the polarization property acting on the light L 2  that passes through the right end (in the vicinity of the right side surface  25 ) shown in  FIG. 5 . Further, the polarization property S 3  corresponding to the middle thickness corresponds to the polarization property acting on the light L 0  that travels in the optical axis direction C. 
       FIG. 8  is an enlarged graph showing the portion of wavelength light of 453 nm of the graph shown in  FIG. 7 . In  FIG. 8 , the ratio of the vertical axis and the horizontal axis is different from that in  FIG. 7 . 
     The thickness of the polarization scrambler  136  is changed from the thickness d 1  to the thickness d 2  in a continuous manner along the right-and-left direction. As a result, the polarization property of the polarization scrambler  136  is changed from the polarization property S 1  to the polarization property S 2  in a continuous manner along the right-and-left direction. As a result, as shown in  FIG. 7 , in the blue wavelength band B, it is possible to generate light in the polarization state from the transmittance of 0% to 100%. That is, even with narrow spectral distribution, it is possible to generate light having a high scramble degree, similarly to the green wavelength band G and the red wavelength band R. 
     As shown in  FIG. 5  and  FIG. 8 , the light L 1  that passes through the left end of the polarization scrambler  136  is converted into vertically-long elliptically polarized light by the polarization property S 1 . The light L 0  that passes through the center is converted into circularly polarized light by the polarization property S 3 . The light L 2  that passes through the right end is converted into horizontally-long elliptically polarized light by the polarization property S 2 . Even in the case where only wavelength light of 453 nm is seen, lights from vertically-long elliptically polarized light to horizontally-long elliptically polarized light are generated. Therefore, in the whole blue wavelength band B, light having a sufficiently high scramble degree is generated. It goes without saying that the scramble degree is improved regarding also the green wavelength band G and the red wavelength band R. 
     For example, the polarization property of the polarization scrambler  136  may be designed using, as a reference wavelength, the wavelength of 453 nm included in the blue wavelength band having narrow spectral distribution. It goes without saying that another wavelength of the blue wavelength band may be selected as a reference wavelength. Further, a wavelength included in a green wavelength band or a red wavelength band different from the blue wavelength band may be selected as a reference wavelength. 
     Note that in the polarization scrambler  136  shown in  FIG. 5 , the polarization property does not change in the up-and-down direction of the incident surface  20 . Typically, the image light  10  is emitted such that the luminance distribution is constant across the board. Therefore, by changing the polarization property in a continuous manner along the direction corresponding to the right-and-left direction of the image  2 , it is possible to emit the image light  10 ′ having a high scramble degree. Note that the polarization scrambler  136  may be configured such that the polarization property changes in a continuous manner along the up-and-down direction of the image  2 . That is, the polarization scrambler  136  may be configured such that the thickness changes in a continuous manner along the up-and-down direction of the image  2 . 
       FIG. 9  is a schematic diagram showing another configuration example of a polarization scrambler. Parts A to E of  FIG. 9  show variations in the configuration in which polarization properties of polarization scramblers  30  to  34  are non-uniform in incident surfaces  30   a  to  34   a,  respectively. Specifically, the polarization scramblers  30  to  34  are configured such that the thicknesses are non-uniform in the incident surfaces  30   a  to  34   a , respectively. 
     As shown Part A of  FIG. 9 , a configuration in which the emission surface  30   b  is tilted with respect to the incident surface  30   a  relative to the biaxial direction of the X direction and the Y direction may be employed. In the example shown in Part A of  FIG. 9 , the thickness is changed at the same ratio in each of the X direction and the Y direction. Therefore, the thickness is changed along the middle direction (direction intersecting the X direction and the Y direction at the angle of 45° as viewed from the Z direction) of the X direction and the Y direction. 
     As shown in Part B of  FIG. 9 , the emission surface  31  may have a curved surface shape. For example, the emission surface  31   b  is formed such that the shape viewed from the Y direction is a curved shape from the left side surface of the minimum thickness d 1  toward the right side surface of the maximum thickness d 2 . The specific shape of the curved surface is not limited, and may be arbitrarily designed. 
     As shown in Part C of  FIG. 9 , a step  32   c  may be formed in the emission surface  32   b.  By forming the step  32   c,  it is possible to make the thickness in the incident surface  32   a  non-uniform, and make the polarization property non-uniform. The number, position, size (height), and the like of the step  32   c  may be arbitrarily designed. 
     As shown in Part D of  FIG. 9 , a configuration in which the emission surface  33   b  is formed to have a projecting shape to form a projecting lens shape as a whole may be employed. Further, as shown in Part E of  FIG. 9 , a configuration in which the emission surface  33   b  is formed to have a projecting shape to form a recessed lens shape may be employed. Even with such a configuration, it is possible to make the thickness in the incident surface  32   a  non-uniform and make the polarization property non-uniform. The curvature and the like of the projecting shape and the recessed shape are not limited, and may be arbitrarily designed. In addition, an arbitrary configuration may be employed. For example, by appropriately designing the shape of the polarization scrambler in accordance with the region that the image light  10  enters and the wavelength band or the like of the light source to be used, it is possible to generate and emit sufficiently-scrambled light in the unpolarized state. 
     Further, the thickness may be controlled by changing the shape on the side of the incident surfaces  30   a  to  34   a.    
     Further, the configuration in which the polarization property in the incident surface is made non-uniform is not limited to the case where the thickness is made non-uniform. By appropriately controlling the material forming the polarization scrambler, the physical properties, or the like, it is possible to make the polarization property in the incident surface non-uniform while making the thickness uniform. For example, by appropriately controlling the material forming the polarization scrambler or the physical properties, the polarization scrambler can be configured such that the phase difference added to incident light is non-uniform in the incident surface. Further, the polarization scrambler can be configured such that the birefringence is non-uniform in the incident surface. As a result, it is possible to generate and emit image light in the unpolarized state, which has a high scramble degree. It goes without saying that both the controlling of the thickness and the controlling of the material or the physical properties may be performed. 
     As described above, in the image display apparatus  100  according to this embodiment, the polarization scrambler  136  that converts the conversion state of the image light  10  and emits the converted light as the image light  10 ′ in the unpolarized state is provided. The polarization scrambler  136  is configured such that the conversion properties of the polarization state are non-uniform in the incident surface  20 . As a result, it is possible to sufficiently depolarize the image light  10  and display a high-quality image. 
     Since the image light  10  can be scrambled more, it is possible to make the polarization disturbance in the projection lens or the like less noticeable, and sufficiently reduce the uneven polarization in the case where short-focus projection is executed or a special screen (e.g., a silver screen/bead screen/prism screen/white board) is used. 
     Further, it is possible to generate sufficiently-scrambled light in the unpolarized state even with respect to a narrow-spectral light source such as an LD and LED. 
     Further, since lights in various polarization states can be multiplexed, it is possible to reduce speckles and display a high-quality image. 
     Second Embodiment 
     An image display apparatus according to a second embodiment of the present technology will be described. In the following description, descriptions of configurations and effects similar to those in the image display apparatus  100  described in the above-mentioned embodiment will be omitted or simplified. 
       FIG. 10  is a schematic diagram showing a configuration example of an image display apparatus  200  according to this embodiment. Regarding the image display apparatus  200 , the same components as those in the image display apparatus  100  according to the first embodiment are denoted by the same reference symbols. In the image display apparatus  200  according to this embodiment, a suppression member  137  is disposed on the polarization scrambler  136 . 
       FIG. 11  is a schematic diagram showing a configuration example of the suppression member  137 . As shown in  FIG. 11 , the suppression member  137  includes a suppression incident surface  40  and a suppression emission surface  41 . The suppression incident surface  40  is a surface that the image light  10 ′ in the unpolarized state emitted from the polarization scrambler  136  enters. The suppression emission surface  41  is a surface that emits the image light  10 ′ in the unpolarized state that has entered the suppression incident surface  40 . 
     As shown in Part B of  FIG. 11 , the suppression member  137  is configured to be capable of emitting the image light  10 ′ from the suppression emission surface  41  while suppressing a variation in the optical distance of the image light  10 ′ from the incident surface  20  to the emission surface  21  of the polarization scrambler  136 . This can be said that the variation in the optical distance of the image light  10 ′ from the incident surface  20  of the polarization scrambler  136  to the suppression emission surface  41  of the suppression member  137  can be suppressed. Note that the optical distance is a parameter specified by multiplying the distance that light has actually travelled by the refractive index of an object through which the light has passed. 
     For example, the suppression member  137  is formed of a material having no optical anisotropy, such as optical glass. Further, the suppression member  137  is formed to have a shape equivalent to that of the polarization scrambler  136  shown in  FIG. 11 . That is, the suppression member  137  is configured such that the thickness in the optical axis direction of the image light  10 ′ changes along the right-and-left direction (X direction) at the same ratio as that of the polarization scrambler  136 . 
     Then, as shown in  FIG. 11 , the suppression member  137  is disposed such that the tilted surface of the suppression member  137  as the suppression incident surface  40  comes into contact with the emission surface  21  of the polarization scrambler  136 . The suppression member  137  is disposed such that the polarization scrambler  136  and the suppression member  137  form a rectangular parallelepiped shape as a whole. 
     As a result, the suppression emission surface  41  of the suppression member  137  is parallel to the incident surface of the polarization scrambler  136 . Further, the suppression member  137  is disposed such that the distance from the incident surface  20  to the suppression emission surface  41  is uniform in the optical axis direction of the image light  10 ′. As a result, it is possible to easily emit the image light  10 ′ from the suppression emission surface  41  while suppressing a variation in the optical distance of the image light  10 ′ from the incident surface  20  to the emission surface  21  of the polarization scrambler  136 . 
     Note that the emission surface  21  of the polarization scrambler  136  and the suppression incident surface  40  of the suppression member  137  may come into contact with each other via an arbitrary adhesive or the like. In this case, it is possible to regard the adhesive as part of the suppression member. Further, processing such as polishing is executed on the suppression incident surface  40 , the suppression emission surface  41 , and the like of the suppression member  137 . As a result, it is possible to emit the image light  10 ′ without reducing the accuracy of the transmission wave surface. 
     For example, assumption is made that the polarization scrambler  136  is formed of quartz having a refractive index of approximately 1.58. The refractive index of quartz having optical axis anisotropy can be specified by, for example, the refractive index in the slow axis or the fast axis. The suppression member  137  formed of a material having a refractive index of  1 . 47  to 1.80 is disposed on such a polarization scrambler  136 . As a result, as compared with the case where the suppression member  137  is not provided, i.e., the image light  10 ′ is emitted from the emission surface  21  toward the air of a refractive index  1 , it is possible to emit the image light  10 ′ while suppressing a variation in the optical distance of the image light  10 ′ from the incident surface  20  to the emission surface  21 . 
     That is, it is possible to sufficiently suppress the variation in the optical distance by appropriately specifying the refractive index of the suppression member  137  on the basis of the refractive index of the polarization scrambler  136 . For example, high effects are exhibited by making the refractive index of the suppression member  137  equal to the refractive index of the polarization scrambler  136 . 
       FIG. 12  to  FIG. 14  are each a graph showing results of simulating evaluation of occurrence of astigmatism with respect to the polarization scrambler  136  and the suppression member  137 . 
     The “Modulation” of the vertical axis of the graph an axis indicating how faithfully the image  2  can be reproduced with respect to the original image (axis indicating the contrast of the image  2  focused on the screen  1 ). For example, assuming that the original image is an image in which black and white are alternately displayed for each dot, it is possible to evaluate how faithfully the contrast can be reproduced, by the appearance of the image  2  on the screen  1 . 
     In the vertical axis,  1  corresponds to the state where the contrast can be completely reproduced (black·white·black·white . . . ), and 0 corresponds to the state where the contrast is not reproduced at all (grey·grey·grey·grey . . . ). An intermediate value between 0 and 1 corresponds to the state where the contrast is highly reproduced as the value is closer to 1 (e.g., dark grey·whitish grey·dark grey·whitish grey . . . ) 
     The “Defocusing Position (mm)” of the horizontal axis indicates the focused position in the optical axis direction in the case where a light beam in which light emitted from the image  2  projected on the screen  1  is focused on the reflective light modulation element  132  is drawn. 
     In the graph, the results of light emitted from the same predetermine pixel of the projected image  2  are illustrated. 
     The graph of a solid line indicates light focused in the sagittal direction. The graph of a dashed line indicated light focused in the meridional direction. 
     The peak difference between the solid line and the dashed line indicates the difference between the focused positions in the optical axis direction of the light focused in the sagittal direction and the light focused in the meridional direction. The larger the difference between the positions, the more blurred the focused light will be, The smaller the difference, the clearer the focused light will be. As shown in the graph, the peak difference between the solid line and the dashed line corresponds to the size of the astigmatism. 
     The graph of  FIG. 12  shows the simulation results in the case where the polarization scrambler  136  that is formed of a uniaxial crystalline material and is configured such that the thickness in the optical axis direction of the image light  10 ′ is uniform is disposed. Note that the suppression member  137  is not disposed. As shown in  FIG. 12 , it can be seen that the astigmatism is small and high focusing performance is exhibited. 
     The graph of  FIG. 13  shows the simulation results in the case where the polarization scrambler  136  that is formed of a uniaxial crystalline material and is configured such that the thickness in the optical axis direction of the image light  10 ′ changes in a continuous manner in the right-and-left direction is disposed. That is, the graph of  FIG. 13  shows the simulation results in the case where the polarization scrambler  136  illustrated in  FIG. 3 ,  FIG. 4 , or the like is disposed. Note that the suppression member  137  is not disposed. As shown in  FIG. 13 , it can be seen that the astigmatism increases and the focusing performance is reduced. 
     The graph of  FIG. 14  shows the simulation results in the case where the polarization scrambler  136  that is formed of a uniaxial crystalline material such that the thickness in the optical axis direction of the image light  10 ′ changes in a continuous manner in the right-and-left direction, and the suppression member  137  are disposed. That is, the graph of  FIG. 14  shows the simulation results in the case where the configuration illustrated in  FIG. 11  is employed. As shown in  FIG. 14 , it can be seen that the astigmatism is small and high focusing performance is exhibited. 
     That is, even in the case where the polarization scrambler  136  in which the polarization property is non-uniform in the incident surface  20  is used, it is possible to prevent the focusing performance from being reduced, by disposing the suppression member  137 . 
       FIG. 15  is a schematic diagram showing another configuration example of the suppression member. Parts A to E of  FIG. 15  show variations in the configuration in which suppression members  50  to  53  are disposed on the polarization scrambler  136  to form rectangular parallelepiped shapes as a whole, respectively. 
     As shown in Part A of  FIG. 15 , the suppression member  50  may be configured to have a shape different from that of the polarization scrambler  136 . For example, the suppression incident surface  50   a  comes into contact with the tilted surface (tilted interface) of the polarization scrambler  136  as the emission surface  21 . Then, the suppression emission surface  50   b  is formed to be parallel to the incident surface  20  in accordance with the tip portion in the optical axis direction of the polarization scrambler  136 . As a result, a rectangular parallelepiped shape in which the thickness in the optical axis direction is equal to the maximum thickness d 2  of the polarization scrambler  136  is realized. 
     As shown in Part B of  FIG. 15 , the suppression member  51  that is formed of optical glass or the like and has a rectangular parallelepiped shape is disposed perpendicularly to the optical axis direction. Then, an adhesive  54  is applied between the emission surface  21  that is the tilted interface of the polarization scrambler  136  and a suppression incident surface  51   a  of the suppression member  51 . The suppression member  51  is pressed against the polarization scrambler  136  along the optical axis direction while controlling the position of a suppression emission surface  51   b  of the suppression member  51 . As a result, the polarization scrambler  136  and the suppression member  51  are connected to each other via the adhesive  54 . 
     As described above, the gap between the emission surface  21  of the polarization scrambler  136  and the suppression incident surface  51   a  of the suppression member  51  may be filled with the adhesive  54 . Further, by appropriately setting the refractive index of the adhesive  54 , it is possible to enhance the function of suppressing the variation in the optical distance. 
     In the configuration shown in Part B of  FIG. 15 , the adhesive  54  can be regarded as part of the suppression member. In this case, part of the adhesive  54 , which comes into contact with the emission surface  21  of the polarization scrambler  136 , is a suppression incident surface. Further, in the case where the shape of the adhesive  54  can be properly controlled, it is also possible to realize a suppression member only by the adhesive  54 . 
     As shown in Part C of  FIG. 15 , a gap (air gap)  55  having a very small width may be formed between the emission surface  21  of the polarization scrambler  136  and a suppression incident surface  53   a  of the suppression member  53 . For example, the air gap  55  having a width of approximately 1 to 3 μm is capable of making the influence on the function of suppressing the variation in the optical distance small. As in the configuration shown in Part C of  FIG. 15 , the suppression member  53  may be disposed such that the suppression incident surface  53   a  is close to the emission surface  21  in parallel. 
     In addition, the material, the refractive index, and the like of the suppression member are not limited, and an arbitrary configuration capable of suppressing the variation in the optical distance of the image light  10 ′ from the incident surface  20  to the emission surface  21  of the polarization scrambler  136  may be employed. For example, even in the case where the suppression member is realized by a material having an optical anisotropy, it is possible to suppress the variation in the optical distance of the image light  10 ′. 
     Further, the function of suppressing the variation in the optical distance by the suppression member is valid for the polarization scrambler  136  configured such that the polarization property is non-uniform in the incident surface while the thickness is uniform. By appropriately designing the shape of the suppression member in accordance with the polarization property of the polarization scrambler  136 , it is possible to suppress the variation in the optical distance of the image light from the incident surface  20  to the emission surface  21  of the polarization scrambler  136 . 
     In this embodiment, the polarization scrambler  136  and the suppression member  137  realize the image display unit. This image display unit may be configured to be interchangeable from the image display apparatus  200 . 
     As described above, in the image display apparatus  200  according to this embodiment, the suppression member  137  is disposed on the polarization scrambler  136 . As a result, it is possible to emit the image light  10 ′ from the suppression emission surface  41  while suppressing the variation in the optical distance of the image light  10 ′ from the incident surface  20  to the emission surface  21  of the polarization scrambler  136 . That is, the suppression member  137  makes it possible to add an astigmatism reduction function. As a result, it is possible to make the astigmatism sufficiently small and display a high-quality image. 
     Further, since the astigmatism can be made sufficiently small, it is also possible to improve the focusing performance, axial chromatic aberration, magnification chromatic aberration, and the like. 
     Further, since the tilted interface of the polarization scrambler  136  can be covered with the suppression member  137 , it is possible to prevent the reflected light reflected on the tilted interface from being applied to another unintended optical part. That is, it is possible to prevent ghosts or the like due to the tilted interface from occurring. Further, it is possible to prevent the ANSI contrast from being reduced. 
     Other Embodiments 
     The present technology is not limited to the embodiments described above, and can achieve various other embodiments. 
       FIG. 16  to  FIG. 18  are each a schematic diagram showing another configuration example of the image generation unit. As in an image generation unit  330  shown in  FIG. 16 , another polarization element such as a prism-type beam splitter may be used as a reflective polarization element  331  ( 331 R,  331 G,  331 B) instead of a wire grid polarizer. Further, the orientation in which a reflective light modulation element  332  ( 332 R,  332 G,  332 B) is disposed is not limited, and may be appropriately designed. 
     As in an image generation unit  430  shown in  FIG. 17 , a transmission-type light modulation element  432  ( 432 R,  432 G,  432 B) may be used. For example, a polarization plate or a compensation plate is disposed so as to sandwich the transmission-type light modulation element  432 . In addition, an arbitrary configuration may be employed. 
     In an image generation unit  530  shown in  FIG. 18 , green image light G modulated by a reflective light modulation element  532 G is reflected by a reflective polarization element  531 G and enters a color combination prism  535 . Red image light R modulated by a reflective light modulation element  532 R and image light B modulated by a reflective light modulation element  532 B are emitted along the same optical path by a reflective light modulation element  531 RB, and enter the color combination prism  535 . 
     Also in the configuration shown in  FIG. 16  to  FIG. 18 , a polarization scrambler ( 336 ,  436 ,  536 ) is disposed on the optical path of the image light  10  (image light R, G, B). As a result, it is possible to sufficiently depolarize the polarization state of the image light  10 , and emit the obtained light as the image light  10 ′ in the unpolarized state. As a result, it is possible to display a high-quality image. It goes without saying that a suppression member may be disposed on a polarization scrambler. 
     As the light modulation element, in addition to the liquid crystal panel, an arbitrary device such as a digital micromirror device (DMD) may be used. 
     The configurations of the image display apparatus, the light source unit, the lighting optical system, the image generation unit, the projection optical system, the polarization scrambler, the suppression member, and the like described with reference to the drawings are merely one embodiment, and can be arbitrarily modified without departing from the essence of the present technology. That is, other arbitrary configurations for carrying out the present technology may be employed. 
     In the present disclosure, the concepts specifying the shape, size, positional relationship, state, and the like such as “central”, “middle”, “uniform”, “equal”, “same”, “perpendicular”, “parallel”, “vertical”, “symmetric”, “extend” “axial direction”, “rectangular parallelepiped shape”, “curved surface shape”, “curved shape”, “curved shape”, and “lens shape” are concepts including “substantially central”, “substantially middle”, “substantially uniform”, “substantially equal”, “substantially the same”, “substantially perpendicular”, “substantially parallel”, “substantially vertical”, “substantially symmetric”, “substantially extend” “substantially axial direction”, “substantially rectangular parallelepiped shape”, “substantially curved surface shape”, “substantially curved shape”, “substantially curved shape”, and “substantially lens shape”. 
     For example, the error range with the “completely central”, “completely middle”, “completely uniform”, “completely equal”, “completely the same”, “completely perpendicular”, “completely parallel”, “completely vertical”, “completely symmetric”, “completely extend” “completely axial direction”, “completely axial direction”, “completely rectangular parallelepiped shape”, “completely curved surface shape”, “completely curved shape”, “completely curved shape”, and “completely lens shape”. 
     At least two of the features of the present technology described above can also be combined. In other words, various features described in the respective embodiments may be arbitrarily combined without distinguishing the embodiments. Further, the various effects described above are not limitative but are merely illustrative, and other effects may be provided. 
     Note that the present technology may also take the following configurations. 
     (1) An image display apparatus, including: 
     a light emission unit that emits image light; and 
     a polarization conversion element that has an incident surface, converts a polarization state of the image light that enters the incident surface, emits the converted light as image light in an unpolarized state, and is configured such that conversion properties of the polarization state are non-uniform in the incident surface. 
     (2) The image display apparatus according to (1), in which 
     the polarization conversion element adds a phase difference to the image light that enters the incident surface and is configured such that the phase difference added to the image light is non-uniform in the incident surface. 
     (3) The image display apparatus according to (1) or (2), in which 
     the polarization conversion element is configured such that a birefringence with respect to the image light is non-uniform in the incident surface. 
     (4) The image display apparatus according to any one of (1) to (3), in which 
     the polarization conversion element has an emission surface that emits the image light in the unpolarized state and is configured such that a thickness from the incident surface to the emission surface in an optical axis direction of the image light is non-uniform in the incident surface. 
     (5) The image display apparatus according to any one of (1) to (4), in which 
     the polarization conversion element is configured such that conversion properties of the polarization state change in a continuous manner along a predetermined direction in the incident surface. 
     (6) The image display apparatus according to (4), in which 
     the emission surface is tilted along a predetermined direction with respect to the incident surface. 
     (7) The image display apparatus according to (5) or (6), in which 
     the predetermined direction is a direction corresponding to an up-and-down direction or a right-and-left direction of an image formed by the image light. 
     (8) The image display apparatus according to (2), in which 
     the polarization conversion element is configured such that a difference between a minimum phase difference and a maximum phase difference added to the image light is equal to or larger than ¼ of a reference wavelength of the image light. 
     (9) The image display apparatus according to (8), in which 
     the reference wavelength is a wavelength included in a blue wavelength band. 
     (10) The image display apparatus according to any one of (1) to (9), further including: 
     a suppression member that has a suppression incident surface and a suppression emission surface, the image light in the unpolarized state emitted from the polarization conversion element entering the suppression incident surface, the suppression emission surface emitting the image light in the unpolarized state that enters the suppression incident surface, in which 
     the suppression member is configured to be capable of emitting the image light from the suppression emission surface while suppressing a variation in an optical distance of the image light from the incident surface to the emission surface of the polarization conversion element. 
     (11) The image display apparatus according to (10), in which 
     the polarization conversion element has an emission surface that emits the image light in the unpolarized state, and 
     the suppression member is disposed such that the suppression incident surface comes into contact with the emission surface or the suppression member is disposed such that the suppression incident surface is close to the emission surface in parallel. 
     (12) The image display apparatus according to (10) or (11), in which 
     the suppression member is disposed such that the suppression emission surface is parallel to the incident surface. 
     (13) The image display apparatus according to any one of (10) to (12), in which 
     the suppression member is configured such that a distance from the incident surface to the suppression emission surface is uniform in the optical axis direction of the image light. 
     (14) The image display apparatus according to any one of (10) to (13), in which 
     the suppression member has a shape equal to that of the polarization conversion element. 
     (15) The image display apparatus according to any one of (10) to (14), in which 
     the suppression member is formed of a material having no optical anisotropy. 
     (16) The image display apparatus according to any one of (10) to (15), in which 
     a refractive index of the suppression member is specified on a basis of a refractive index of the polarization conversion element. 
     (17) The image display apparatus according to any one of (1) to (16), in which 
     the polarization conversion element is formed of a uniaxial crystal material or a uniaxial organic material. 
     (18) The image display apparatus according to any one of (1) to (17), further including 
     a projection unit that projects the image light in the unpolarized state emitted from the polarization conversion element, in which 
     the light emission unit includes a light modulation element that modulates incident light and emits the image light. 
     (19) An image display unit, including: 
     a polarization conversion element that has an incident surface, converts a polarization state of the image light that enters the incident surface, emits the converted light as image light in an unpolarized state, and is configured such that conversion properties of the polarization state are non-uniform in the incident surface. 
     (20) The image display unit according to (19), further including 
     a suppression member that has a suppression incident surface and a suppression emission surface, the image light in the unpolarized state emitted from the polarization conversion element entering the suppression incident surface, the suppression emission surface emitting the image light in the unpolarized state that enters the suppression incident surface, in which 
     the suppression member is configured to be capable of emitting the image light from the suppression emission surface while suppressing a variation in an optical distance of the image light from the incident surface to the emission surface of the polarization conversion element. 
     REFERENCE SIGNS LIST 
     C optical axis direction 
     S 1  to S 3  polarization property 
       10  image light 
       10 ′ image light in an unpolarized state 
       20 ,  30   a  to  34   a  incident surface 
       21 ,  30   b  to  34   b  emission surface 
       30  to  34  polarization scrambler 
       40 ,  50   a  to  53   a  suppression incident surface 
       41 ,  50   b  to  53   b  suppression emission surface 
       50  to  53  suppression member 
       54  adhesive 
       55  air gap 
       100 ,  200  image display apparatus 
       110  lighting optical system 
       130 ,  330 ,  430 ,  530  image generation unit 
       135  color combination prism 
       136  polarization scrambler 
       137  suppression member 
       140  projection optical system