Patent Publication Number: US-2017357112-A1

Title: Optical device, display unit, and electronic apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to an optical device, a display unit, and an electronic apparatus that perform switching of display. 
     BACKGROUND ART 
     An existing display unit is known that is configured to be able to perform switching between a regular screen state (a screen display mode) and a mirror surface state (an external light reflection mode) by causing two liquid crystal panels to overlap each other (for example, reference may be made to PTL 1 and PTL 2). Specifically, such a display unit includes a display switching section, for example, on viewer side of a liquid crystal display section. The display switching section includes a reflection-type polarization plate, a liquid crystal panel, and an absorption-type polarization plate that are disposed and stacked in order in a direction from the liquid crystal display section toward the viewer. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Unexamined Patent Application Publication No. 2001-318374 
     PTL 2: Japanese Unexamined Patent Application Publication No. 2004-37943 
     SUMMARY OF THE INVENTION 
     However, the display unit described above allows light that has been sequentially passed through the liquid crystal panel and the absorption-type polarization plate in the display switching section to be visually recognized in both the image display mode and the external light reflection mode. Therefore, image light to be visually recognized by the viewer is to be influenced by transmission characteristics of the liquid crystal panel and the absorption-type polarization plate. This may cause occurrence of coloring due to wavelength dispersion of the absorption-type polarization plate and wavelength dispersion of the liquid crystal panel, leading to degradation of display quality. Further, in a case where it is desired to perform switching only in a certain region or it is desired to perform display in a specific shape upon performing switching of image light, for example, it is necessary to provide an electrode of the liquid crystal panel for switching with a shape in accordance with, for example, its use or its purpose. However, in such a case, it is necessary to change masks, for example, for respective uses or purposes to perform photolithography when the electrode of the liquid crystal panel for switching is formed. This greatly increases the manufacturing cost. 
     Therefore, it is desirable to provide a display unit and an electronic apparatus that each have a superior display performance in both the image display mode and the external light reflection mode. Further, it is desirable to provide an optical device that is able to suppress a great increase in manufacturing cost and a display unit provided with the optical device. 
     A display unit according to one embodiment of the present disclosure includes: a display section that outputs a first linearly-polarized light as image light, the first linearly-polarized light having a first polarization axis; and a display switching section that is disposed to face the display section, and performs switching between an image display mode in which the first linearly-polarized light is allowed to pass through and an external light reflection mode in which external light is reflected. The display section includes a first absorption-type polarization member that allows the first linearly-polarized light to pass through and absorbs second linearly-polarized light having a second polarization axis that intersects the first polarization axis. The display switching section includes a reflection-type polarization member, a switchable transmission polarization axis member, and a second absorption-type polarization member that are disposed in order in a direction being away from the display section. The reflection-type polarization member allows the first linearly-polarized light to pass through and reflects the second linearly-polarized light. The switchable transmission polarization axis member performs switching between a first mode in which the first linearly-polarized light is converted into the second linearly-polarized light to pass through and a second mode in which the first linearly-polarized light is allowed to pass through without being converted into the second linearly-polarized light. The second absorption-type polarization member allows the first linearly-polarized light to pass through and absorbs the second linearly-polarized light. The second absorption-type polarization member has a hue b* value that is equal to or smaller than a hue b* value of the first absorption-type polarization member. Further, an electronic apparatus according to one embodiment of the present disclosure includes the display unit according to the foregoing embodiment of the present disclosure, and a controlling section that controls the display unit. 
     In each of the display unit and the electronic apparatus according to the embodiments of the present disclosure, the switching between the image display mode and the external light reflection mode is performed by the display switching section. Further, the hue b* value of the second absorption-type polarization member is equal to or smaller than the hue b* value of the first absorption-type polarization member. Therefore, coloring due to disposing of the second absorption-type polarization member is reduced, compared to a case where the hue b* value of the second absorption-type polarization member is greater than the hue b* value of the first absorption-type polarization member. 
     An optical device of the present disclosure includes: a polarization control layer that controls polarization on the basis of a control from outside; a polarization layer that is disposed on one surface side of the polarization control layer; and a first reflection layer and a second reflection layer that are disposed on the other surface side of the polarization control layer. The first reflection layer is a reflective polarization layer. The second reflection layer has one or a plurality of openings. 
     Another display unit of the present disclosure includes: a display switching section; a display section that has an output surface that outputs linearly-polarized light as image light; and a controlling section that performs a control on the display switching section. The display switching section includes a polarization control layer that controls polarization on the basis of the control performed by the controlling section, a polarization layer that is disposed at a position on opposite side to the display section in a relationship with the polarization control layer, and a first reflection layer and a second reflection layer that are disposed at respective positions on the side of the display section in a relationship with the polarization control layer. The first reflection layer is a reflective polarization layer. The second reflection layer has one or a plurality of openings. 
     In the optical device and the another display unit of the present disclosure, switching between a mirror state and a display state is performed by means of polarization control performed by the polarization control layer. In the mirror state, for example, the polarization control layer is so controlled that a polarization axis of polarized light that has entered the polarization control layer from the polarization layer side is orthogonal to a polarization axis of a first reflection layer. Accordingly, in the mirror state, the light that has entered the polarization layer is reflected by the first reflection layer and is returned thereby. Therefore, a surface of the optical device functions like a mirror with respect to a user of the optical device. In the display state, for example, the polarization control layer is so controlled that a polarization axis of polarized light (such as image light) that has entered the polarization control layer from the first reflection layer side via the one or the plurality of openings is parallel to the polarization axis of the polarization layer. Accordingly, in the display state, the polarized light that has entered the polarization control layer from the first reflection layer side via the one or the plurality of openings passes through the polarization layer and reaches the user of the optical device. Therefore, the surface of the optical device functions as an image display surface with respect to the user of the optical device. 
     Moreover, in the optical device and the another display unit of the present disclosure, for example, the size and the shape of the one or the plurality of openings is formable, for example, by processing a sheet-shaped member or by molding a molten material in a process of forming the second reflection layer. Accordingly, it is not necessary to change the masks, for example, for the respective uses or purposes to perform photolithography upon forming the electrode to be used for the control of the polarization control layer in a case where it is desired to perform switching only of the display state in the certain region or to perform the display in the desired shape, in the optical device and the another display unit according to the present disclosure. 
     According to the display unit and the electronic apparatus of the embodiments of the present disclosure, it is possible to exhibit a superior display performance both in the image display mode and the external light reflection mode. 
     Moreover, according to the optical device and the another display unit of the present disclosure, the polarization control by the polarization control layer allows the optical device to function like a mirror or a display, and also makes it unnecessary to provide a plurality of electrodes for polarization control with respect to the polarization control layer. As a result, it is possible to suppress a great increase in manufacturing cost. 
     It is to be noted that effects of the present technology are not necessarily limited to effects described here and may be any of effects described in the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a cross-sectional view of a display unit according to a first embodiment of the present disclosure. 
         FIG. 1B  is a conceptual diagram illustrating workings of the display unit illustrated in  FIG. 1A . 
         FIG. 2  is a conceptual diagram illustrating a display unit according to a second embodiment of the present disclosure. 
         FIG. 3  is a cross-sectional view of a display unit according to a third embodiment of the present disclosure. 
         FIG. 4  is a cross-sectional view of a display unit according to a fourth embodiment of the present disclosure. 
         FIG. 5  is a cross-sectional view of a display unit according to a fifth embodiment of the present disclosure. 
         FIG. 6  is a cross-sectional view of a display unit according to a sixth embodiment of the present disclosure. 
         FIG. 7  is a cross-sectional view of a display unit according to a seventh embodiment of the present disclosure. 
         FIG. 8  is a cross-sectional view of a display unit according to an eighth embodiment of the present disclosure. 
         FIG. 9A  is a schematic diagram illustrating a pre-tilt direction of liquid crystal molecules in the display unit illustrated in  FIG. 8 . 
         FIG. 9B  is a schematic diagram illustrating a behavior of the liquid crystal molecule in the display unit illustrated in  FIG. 8 . 
         FIG. 9C  is a schematic diagram illustrating another behavior of the liquid crystal molecule in the display unit illustrated in  FIG. 8 . 
         FIG. 10  is a conceptual diagram illustrating a configuration example of an electronic apparatus provided with a display unit of the present disclosure. 
         FIG. 11  is a characteristic diagram illustrating chromaticity in Experimental Examples 1-1 and 1-2. 
         FIG. 12  is a characteristic diagram illustrating a relationship between a thickness of a resin layer and a Wd value of orange peel in Experimental Examples 2-1 to 2-4. 
         FIG. 13  is a characteristic diagram illustrating a relationship between retardation and transmittance of liquid crystal layers in Experimental Examples 3-1 to 3-3. 
         FIG. 14  is a characteristic diagram illustrating a relationship between a retardation difference Δn and transmittance of liquid crystal layers in Experimental Examples 4-1 to 4-4. 
         FIG. 15  is a diagram illustrating an example of a schematic configuration of a display unit according to a ninth embodiment of the present disclosure. 
         FIG. 16  is a diagram illustrating an example of a cross-sectional configuration of a display section and a display switching section in  FIG. 15 . 
         FIG. 17  is a conceptual diagram for describing an example of workings of a display section and a display switching section in  FIG. 16 . 
         FIG. 18  is a conceptual diagram for describing an example of workings of the display section and the display switching section in  FIG. 16 . 
         FIG. 19  is a diagram illustrating an example of a planar configuration of a second reflection layer in  FIG. 16 . 
         FIG. 20  is a diagram illustrating an example of the planar configuration of the second reflection layer in  FIG. 16 . 
         FIG. 21  is a diagram illustrating an example of wavelength dependence of luminance of light that has passed through a reflective polarization layer used as the first reflection layer and the second reflection layer in  FIG. 16 . 
         FIG. 22  is a diagram illustrating a modification example of the cross-sectional configuration of the display section and the display switching section in  FIG. 15 . 
         FIG. 23  is a conceptual diagram for describing an example of workings of a display section and a display switching section in  FIG. 22 . 
         FIG. 24  is a conceptual diagram for describing an example of the workings of the display section and the display switching section in  FIG. 22 . 
         FIG. 25  is a diagram illustrating a modification example of the cross-sectional configuration of the display section and the display switching section in  FIG. 15 . 
         FIG. 26  is a conceptual diagram for describing an example of workings of a display section and a display switching section in  FIG. 25 . 
         FIG. 27  is a conceptual diagram for describing an example of the workings of the display section and the display switching section in  FIG. 25 . 
         FIG. 28A  is a diagram illustrating an example of an arrangement of a mirror layer to be additionally provided in the display switching section in  FIGS. 16, 22, and 25 . 
         FIG. 28B  is a diagram illustrating an example of the arrangement of the mirror layer to be additionally provided in the display switching section in  FIGS. 16, 22, and 25 . 
         FIG. 29  is a diagram illustrating an example of a cross-sectional configuration of the display section and the display switching section in  FIGS. 16 and 25 . 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     Some embodiments of the present disclosure are described below in detail with reference to the drawings. It is to be noted that the description is given in the following order.
     1. First Embodiment (An example in which a transmission axis of an absorption-type polarization plate and a transmission axis of a reflection-type polarization plate are parallel to each other in a display switching section)   2. Second Embodiment (An example in which the transmission axis of the absorption-type polarization plate and the transmission axis of the reflection-type polarization plate are orthogonal to each other in the display switching section)   3. Third Embodiment (An example in which the absorption-type polarization plate is provided inside a liquid crystal panel in a display section)   4. Fourth Embodiment (An example in which a glass substrate is disposed between the display section and the display switching section)   5. Fifth Embodiment (An example in which a retardation plate is disposed in the display switching section)   6. Sixth Embodiment (An example in which a ferroelectric liquid crystal panel is disposed in the display switching section)   7. Seventh Embodiment (An example in which an antiferroelectric liquid crystal panel is disposed in the display switching section)   8. Eighth Embodiment (An example in which a VA liquid crystal panel is disposed in the display switching section)   9. Application Examples (Electronic Apparatuses)   10. Experimental Examples   11. Ninth Embodiment
       An example in which a first reflection layer is disposed closer to a polarization control layer than a second reflection layer ( FIGS. 15 to 21 )   
       12. Modification Examples of Ninth Embodiment
       Modification Example A: An example in which the second reflection layer is disposed closer to the polarization control layer than the first reflection layer ( FIGS. 22 to 24 )   Modification Example B: An example in which a bezel also serves as the second reflection layer ( FIGS. 25 to 27 )   Modification Example C: An example in which a circular mirror layer is further provided ( FIGS. 28A and 28B )   Modification Example D: An example in which the second reflection layer is larger than the first reflection layer   Modification Example E: An example in which the bezel also serves as the circular mirror layer ( FIG. 29 )   Modification Example F: Variations of an ON-OFF control of the polarization control layer   
       

     1. FIRST EMBODIMENT 
       FIG. 1  illustrates a cross-sectional configuration of a display unit  1  as one embodiment of the present disclosure. This display unit  1  includes two liquid crystal panels that are overlapping each other, and is thereby configured to be able to perform switching between a screen state and a mirror surface state. In such a display unit, light that has passed through the liquid crystal panel provided in a display switching section and an absorption-type polarization plate disposed on the viewer side is to be visually recognized in both the screen state and the mirror surface state. Therefore, a visually-recognized state is determined on the basis of transmission characteristics of the absorption-type polarization plate disposed on the viewer side and the liquid crystal panel in the display switching section. Accordingly, in the existing display unit described above, coloring may occur in some cases due to the wavelength dispersion of the absorption-type polarization plate and the wavelength dispersion of the liquid crystal panel in both of the display state and the mirror state, on the basis of optical characteristics of the absorption-type polarization plate and the liquid crystal panel in the display switching section. Further, in the mirror surface state, a reflection-type polarization plate is disposed between the liquid crystal panel in the display switching section and a display section, and is therefore easily influenced by a flatness level of a surface of the display switching section and a flatness level of a surface of the display section, for example. This also raises concerns for a problem that a blur is easily visually recognized upon mirror surface display. In the mirror surface state, it is required to display an object precisely without any blur and to precisely display the color of the object. The display unit  1  satisfies such a requirement. A detailed description is given below. 
     [Configuration of Display Unit  1 ] 
     The display unit  1  has a display section  10  and a display switching section  20  that are so disposed to face each other that their principal surfaces overlap each other. The display section  10  outputs, toward a viewer, image light that forms a predetermined display state. The display switching section is disposed on the viewer side of the display section  10 , and performs switching between an image display mode that allows the image light from the display section  10  to pass through and an external light reflection mode that reflects external light. It is to be noted that it is sufficient that the display section  10  and the display switching section  20  overlap each other at least partially. 
     (Display Section  10 ) 
     As the display section  10 , various display mechanisms such as an electroluminescent device, a plasma display panel, and an electronic paper are applicable, for example. The present embodiment is described, however, referring to a case in which a liquid crystal display device is used. 
     A drive mode of the display section  10  may be either of an active drive mode and a passive drive mode. The active drive mode includes, for example, active matrix drive that uses an active device such as a TFT (Thin Film Transistor) and a TFD (Thin Film Diode). The passive drive mode includes, for example, simple drive or multiplex drive that does not use any active device as that described above. Further, a panel structure of the display section  10  may be any of a transmission-type panel, a reflection-type panel, and a reflection-semi-transmission-type panel. The present embodiment is described referring to a case in which the transmission-type panel is used. 
     For example, as illustrated in  FIG. 1A , the display section  10  has an absorption-type polarization plate  11 , a liquid crystal panel  13 , an absorption-type polarization plate  14 , and a backlight  15  in order from a position closer to the display switching section  20 . A retardation plate may be further disposed between the absorption-type polarization plate  11  and the liquid crystal panel  13 . 
     The liquid crystal panel  13  has a structure in which a liquid crystal layer  13 C is sandwiched between a substrate  13 A and a substrate  13 B. The substrate  13 A and the substrate  13 B are made of a transparent material such as glass (including quartz), for example. The substrate  13 A and the substrate  13 B are so disposed as to face each other with a predetermined spacing (for example, from about 1.5 μm to about 10 μm). The substrate  13 A and the substrate  13 B are attached to each other, for example, with a sealing material (which is not illustrated). Further, an inner surface of each of the substrates  13 A and  13 B is provided with an unillustrated electrode, which achieves a configuration in which an electric field is applicable to the liquid crystal layer  13 C with these electrodes. 
     As a liquid crystal mode of the liquid crystal panel  13 , for example, a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an IPS (In Plane Switching) mode, an FFS (Fringe Field Switching) mode, an STN (Super Twisted Nematic) mode, or an ECB (Electrically Controlled Birefringence) mode may be employed. Liquid crystal display devices having any of these liquid crystal modes have configurations that achieve a display state with a polarization plate. For this reason, the liquid crystal display devices having any of these liquid crystal modes achieve high display quality while having a relatively-low drive voltage, and are therefore preferable. The VA mode is particularly preferable among the foregoing modes. One reason is that the liquid crystal display device of the VA mode is less likely to cause black floating compared to other liquid crystal modes (for example, the IPS mode), in a case where stress is applied to the absorption-type polarization plates  11  and  14  in the display section  10 . Here, the black floating refers to occurrence of partial leakage of light upon black display. In the display unit  1 , the display section  10  and the display switching section  20  are attached to each other, for example, with a third resin layer  33  (which is hereinafter simply referred to as the resin layer  33 ). When the display section  10  and the display switching section  20  are attached to each other, for example, resin in a gel state is cured and contracted to form the resin layer  33 . In accordance with the curing and contraction of the resin, however, stress is applied to the polarization plate in the display section  10  (in particular, the absorption-type polarization plate  11 ). In this case, for example, when the liquid crystal display device of the IPS mode is used as the display section  10 , the black floating sometimes occurs slightly in a corner of a display region. It is, however, possible to suppress the black floating by using the liquid crystal display device of the VA mode as the display section  10 . A hue b* value of the resin layer  33  is preferably equal to or greater than −0.5 and equal to or smaller than 0.5, for example. Further, a haze value of the resin layer  33  is preferably equal to or smaller than 1, for example. Further, because the display section  10  (the absorption-type polarization plate  11 ) and the display switching section  20  (a reflection-type polarization plate  21  which will be described later) are attached to each other with the resin layer  33  in between, it is possible to suppress occurrence of unevenness in the vicinity of an interface of the absorption-type polarization plate  11  and the reflection-type polarization plate  21  resulting from the attachment. By suppressing the occurrence of such unevenness, it is possible to reduce a blur in the mirror state (the external light reflection mode) resulting from the unevenness. As the resin layer  33 , for example, a highly-transparent baseless tape CTL-NC103 from Lintec Corporation or a baseless optical double-sided adhesive tape DAITAC ZB7010W-10 from DIC Corporation may be used. 
     The absorption-type polarization plates  11  and  14  are set in an arrangement (for example, a crossed Nicols arrangement) that is required on the basis of the configuration of the liquid crystal unit  1 . Each of the absorption-type polarization plates  11  and  14  has a polarization transmission axis. Each of the absorption-type polarization plates  11  and  14  allows linearly-polarized light having an oscillation plane that is parallel to the polarization transmission axis to pass through, and absorbs linearly-polarized light having an oscillation plane that is parallel to a direction that intersects (preferably, is orthogonal to) the polarization transmission axis. As the absorption-type polarization plates  11  and  14 , for example, a film may be used that is provided with a polarization function on both surfaces by causing iodine to be absorbed by stretched polyvinyl alcohol and have the both surfaces provided with protective layers of triacetylcellulose. 
     The backlight  15  may be any backlight that is able to illuminate the liquid crystal panel  13  from its back at almost even illuminance. For example, a backlight of an end surface light emission type that includes a light guide plate and a light source disposed at an end of the light guide plate, and a backlight of a rear surface light emission type that includes a light guide plate and a light source disposed on a rear surface of the light guide plate can be mentioned. 
     (Display Switching Section  20 ) 
     The display switching section  20  includes a reflection-type polarization plate  21 , a liquid crystal panel  22 , and an absorption-type polarization plate  23  that are disposed in order from the foregoing display section  10  toward the viewer. It is to be noted that a viewing angle improvement film may be disposed at least one of a region between the absorption-type polarization plate  23  and the liquid crystal panel  22  and a region between the reflection-type polarization plate  21  and the liquid crystal panel  22 . 
     The reflection-type polarization plate  21  has a transmission polarization axis  21 J (which will be described later). The reflection-type polarization plate  21  allows linearly-polarized light having an oscillation plane that is parallel to the transmission polarization axis  21 J to pass through, and reflects linearly-polarized light having an oscillation plate that is parallel to a direction that intersects (preferably, is orthogonal to) the transmission polarization axis. Specifically, as the reflection-type polarization plate  21 , a reflection-type polarization plate is used that has a function of allowing first linearly-polarized light Lp (which will be described later) outputted from the display section  10  to pass through and of specularly reflecting second linearly-polarized light Ls (which will be described later) that has a transmission polarization axis orthogonal thereto. As such a member, for example, a birefringent reflection-type polarization film including a plurality of layers in which different birefringent polymer films are alternately stacked that is disclosed in International Application No. WO95/27919, or a cholesteric liquid crystal layer provided with a quarter-wave retardation plate on each of the front and the back may be used. As the birefringent reflection-type polarization film, a film having a function of allowing a predetermined linearly-polarized light to pass through and specularly reflecting linearly-polarized light that has a polarization axis orthogonal to a polarization axis of the predetermined linearly-polarized light is commercially provided as the trade name of DBEF from 3M (United States). This may be used as the reflection-type polarization plate  21 . 
     In contrast, in a case where the reflection-type polarization plate  21  is configured of the cholesteric liquid layer provided with a quarter-wave retardation plate on each of the front and the back, a liquid crystal cell containing low-molecular cholesteric liquid crystal between two transparent substrates that have been subjected to an alignment process, or a flat, optically-isotropic, and transparent substrate such as glass and transparent resin provided with high-molecular cholesteric liquid crystal layer may be used. The cholesteric liquid crystal layer exhibits specific optical characteristics based on a helical molecular arrangement. The cholesteric liquid crystal layer allows selective reflection of light that enters in a direction parallel to a helical axis on the basis of a rotation direction in a cholesteric spiral so that circularly-polarized light in one rotation direction is reflected and that in the other is allowed to pass through. A wavelength range of the selective reflection depends on a pitch of the molecular arrangement. It is therefore necessary to use a stack of a plurality of cholesteric liquid crystal layers having different pitches in order to cause the selective reflection in the entire visible wavelength range to occur. In this case, in order to achieve the selective reflection in the entire visible wavelength range, a cholesteric liquid crystal layer having a continuously-varied pitch as that described in Asia Display95 Digest, p735, The Institute of Television Engineers of Japan (ITE) &amp; The Society for Information Display (SID) may be used instead of stacking the plurality of cholesteric liquid crystal layers having different pitches. Further, allowing the wavelength range of the selective reflection, a reflectance on the low wavelength side (from 400 nm to 600 nm) to be on the high wavelength side (a visible light range of 600 nm or greater) makes it possible to allow the hue b* value to be in one direction, which is preferable. 
     Further, in a case where the cholesteric liquid crystal layer provided with the quarter-wave retardation plate on each of the front and the back is used as the reflection-type polarization plate  21 , it is preferable that the quarter-wave retardation plate disposed on the back side of the cholesteric liquid crystal layer, i.e., the quarter-wave retardation plate disposed on the display section  10  side of the cholesteric liquid crystal layer has a slow axis that is set in the following direction. Specifically, its slow axis is disposed so that the first linearly-polarized light Lp that is outputted from the display section  10  and enters the reflection-type polarization plate  21  is converted into circularly-polarized light that passes through the cholesteric liquid crystal layer. Meanwhile, similarly, a slow axis of the quarter-wave retardation plate disposed on the front side of the cholesteric liquid crystal layer, i.e., the quarter-wave retardation plate disposed on the liquid crystal panel  22  side of the cholesteric liquid crystal layer is so disposed that the circularly-polarized light that passes through the cholesteric liquid crystal layer is converted into the first linearly-polarized light Lp. 
     In a case where the second linearly-polarized light Ls enters the reflection-type polarization plate  21  that has the foregoing configuration in which the quarter-wave retardation plates are disposed on the front and the back of the cholesteric liquid crystal layer, that second linearly-polarized light Ls is converted into circularly-polarized light that is opposite-handed to the circularly-polarized light that passes through the cholesteric liquid crystal layer, owing to the working of the quarter-wave retardation plate. That second linearly-polarized light Ls is therefore selectively reflected by the cholesteric liquid crystal layer. When the circularly-polarized light reflected by the cholesteric liquid crystal layer passes through the quarter-wave retardation plate again, the circularly-polarized light reflected by the cholesteric liquid crystal layer is converted into the second linearly-polarized light Ls owing to the working of the quarter-wave retardation plate. 
     Note that it is desirable that a member that functions as the quarter-wave retardation plate in the entire visible wavelength range be used as the quarter-wave retardation plate used for the reflection-type polarization plate  21  having the foregoing configuration. As the quarter-wave retardation plate, a stretched polymer film having a high transmittance in the visible wavelength range such as polyvinyl alcohol, polycarbonate, polysulfone, polystyrene, and polyarylate may be used. Other than these materials, mica, crystal, a liquid crystal layer having molecular axes aligned in a single direction may be used. 
     Moreover, it is generally difficult to configure a retardation plate that functions as the quarter-wave retardation plate with respect to the entire visible wavelength range with a single type of retardation plate, due to wavelength dependence (hereinafter, also referred to as wavelength dispersion) of a refractive index of the material configuring the quarter-wave retardation plate. The retardation plate may be, however, configured to function as the quarter-wave retardation plate in a wide wavelength range by so attaching at least two types of retardation plates that are different in wavelength dispersion that their optical axes are orthogonal to each other. 
     It is preferable that the reflection-type polarization plate  21  and the liquid crystal panel  22  be attached to each other, for example, with a first resin layer  31  (hereinafter, simply referred to as the resin layer  31 ) having the thickness of 25 μm or smaller in between. One reason for this is that it is thereby possible to suppress occurrence of unevenness in the vicinity of the interface of the liquid crystal panel  22  and the reflection-type polarization plate  21  due to the attachment. By suppressing such occurrence of unevenness, it is possible to reduce the blur in the mirror state (the external light reflection mode) resulting from the unevenness. The hue b* value of the resin layer  31  is preferably equal to or greater than −0.5 and equal to or smaller than 0.5, for example. Further, the haze value of the resin layer  31  is preferably equal to or smaller than 1, for example. As such a resin layer  31 , for example, a highly-transparent baseless tape CTL-NC103 from Lintec Corporation or a baseless optical double-sided adhesive tape DAITAC ZB7010W-10 from DIC Corporation may be used. 
     The liquid crystal panel  22  performs switching between a first mode and a second mode. The first mode converts the first linearly-polarized light Lp into the second linearly-polarized light Ls having a polarization axis orthogonal to that of the first linearly-polarized light Lp and allows the converted light to pass through. The second mode allows the first linearly-polarized light Lp to pass through as it is without converting the first linearly-polarized light Lp into the second linearly-polarized light Ls. The liquid crystal panel  22  has a structure in which a liquid crystal layer  22 C is sandwiched between a substrate  22 A and a substrate  22 B. The substrate  22 A and the substrate  22 B are made of a transparent material such as glass (including quartz), for example. The substrate  22 A and the substrate  22 B are so disposed as to face each other with a predetermined spacing (for example, from about 1.5 μm to about 10 μm). The substrate  22 A and the substrate  22 B are attached to each other, for example, with a sealing material (which is not illustrated). A material configuring the substrates  22 A and  22 B may be, other than a material using glass, a material using resin such as plastic. The glass may be used for one of the substrate  22 A and the substrate  22 B, and the resin may be used for the other of the substrate  22 A and the substrate  22 B. By using the resin as the material configuring the substrate  22 A and the substrate  22 B, it is possible to reduce thickness and improve resistance to impact. Further, alkali-free glass is preferable as the glass substrate. 
     Further, an inner surface of each of the substrate  22 A and the substrate  22 B is provided with an unillustrated transparent electrode, which achieves a configuration in which a predetermined electric field is applicable to the liquid crystal layer  22 C with these transparent electrodes. In the case of this liquid crystal panel  22 , the single integral transparent electrode described above that is so configured as to cover inside of almost the entire effective display region may be provided on each side of the liquid crystal layer  22 C. A plurality of transparent electrodes described above may be, however, formed on each side of the liquid crystal layer  22 C, and be so configured to supply electric potentials independently of each other. 
     The absorption-type polarization plate  23  has a polarization transmission axis  23 J (which will be described later), allows linearly-polarized light having an oscillation plane that is parallel to the transmission polarization axis  23 J to pass through, and absorbs linearly-polarized light having an oscillation plane that is parallel to a direction that intersects (preferably, is orthogonal to) the transmission polarization axis  23 J. 
     A display mode of the liquid crystal panel  22  is preferably one of the TN mode, the ECB mode, the STN mode, a BTN (Bistable Twisted Nematic) mode, the VA mode, the IPS mode, a ferroelectric liquid crystal mode, and an antiferroelectric liquid crystal mode. 
     It is preferable that the liquid crystal panel  22  and the absorption-type polarization plate  23  be attached to each other, for example, with a second resin layer  32  (hereinafter, simply referred to as the resin layer  32 ) having the thickness equal to or smaller than 25 μm in between. One reason for this is that it is thereby possible to suppress occurrence of unevenness in the vicinity of the interface of the liquid crystal panel  22  and the absorption-type polarization plate  23  resulting from the attachment. By suppressing such occurrence of unevenness, it is possible to reduce the blur in the mirror surface state (the external light reflection mode) resulting from the unevenness. The hue b* value of the resin layer  32  is preferably equal to or greater than −0.5 and equal to or smaller than 0.5, for example. Further, the haze value of the resin layer  32  is preferably equal to or smaller than 1, for example. As such a resin layer  32 , for example, a highly-transparent baseless tape CTL-NC103 from Lintec Corporation or a baseless optical double-sided adhesive tape DAITAC ZB7010W-10 or DAITAC ZB7011W from DIC Corporation may be used. It is to be noted that a hue b* value of DAITAC ZB7011W is 0.11, and a haze value (JIS K7136) of DAITAC ZB7010W-10 is 0.4. 
     In the display switching section  20 , a retardation plate (which is not illustrated) may be disposed each of a region between the liquid crystal panel  22  and the absorption-type polarization plate  23  and a region between the liquid crystal panel  22  and the reflection-type polarization plate  21 . 
     The reflection-type polarization plate  21  and the absorption-type polarization plate  11  are preferably so disposed that the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  11  be substantially parallel to each other or that the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  11  be substantially orthogonal to each other. Further, in the display unit  1 , it is desirable that the transmission polarization axis of the absorption-type polarization plate  11  and the transmission polarization axis of the absorption-type polarization plate  14  be substantially orthogonal to each other. Accordingly, in a case where the transmission polarization axis of the reflection-type polarization plate  21  and the transmission absorption axis of the absorption-type polarization plate  11  are substantially parallel to each other, it is preferable that the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  14  be substantially orthogonal to each other. In contrast, in a case where the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  11  are substantially orthogonal to each other, it is preferable that the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  14  be substantially parallel to each other. 
     A drive mode of the display switching section  20  may be either of the active drive mode and the passive drive mode as with the drive mode of the display section  10 . The active drive mode includes, for example, active matrix drive that uses an active device such as a TFT and a TFD. The passive drive mode includes, for example, simple drive or multiplex drive that does not use any active device as that described above. 
     In this display unit  1 , in a case where the transmission polarization axis of the absorption-type polarization plate  23  and the transmission polarization axis of the absorption-type polarization plate  11  are substantially orthogonal to each other, the hue b* value of the absorption-type polarization plate  23  is preferably at least equal to or smaller than the hue b* value of the absorption-type polarization plate  11 . In contrast, in a case where the transmission polarization axis of the absorption-type polarization plate  23  and the transmission polarization axis of the absorption-type polarization plate  14  are substantially orthogonal to each other, the hue b* value of the absorption-type polarization plate  23  is preferably at least equal to or smaller than the hue b* value of the absorption-type polarization plate  14 . More preferably, the hue b* value of the absorption-type polarization plate  23  is equal to or smaller than the hue b* value of the absorption-type polarization plate  11  and is equal to or smaller than the hue b* value of the absorption-type polarization plate  14 . 
     As the absorption-type polarization plates  11  and  14  in the display section  10 , for example, SRCZ4QJ from Sumitomo Chemical Co., Ltd. or SKN-18243T from Polatechno Co., Ltd. may be used. A hue b* value of SRCZ4QJ mentioned above is 4.0, and a hue b* value of SKN-18243T mentioned above is 3.55. 
     The hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is preferably equal to or smaller than 3.5 and is further preferably equal to or smaller than 1.5, for example. As the absorption-type polarization plate  23  having the hue b* value that is equal to or smaller than 3.5, for example, SEG1425DU from Nitto Denko Corporation may be used. As the absorption-type polarization plate  23  having the hue b* value that is equal to or smaller than 1.5, for example, EGW1225DU from Nitto Denko Corporation or SKW-18245T from Polatechno Co., Ltd. may be used. A hue b* value of SKW-18245T mentioned above is 0.43. 
     Moreover, in the display section  10 , the hue b* value in a case where the absorption-type polarization plate  11  and the absorption-type polarization plate  14  are so overlapped that the polarization transmission axis of the absorption-type polarization plate  11  and the polarization transmission axis of the absorption-type polarization plate  14  are aligned in the same direction is preferably equal to or smaller than 7, is further preferably equal to or smaller than 3, and still further preferably equal to or smaller than 1. For example, SEG1425DU from Nitto Denko Corporation may be mentioned as a member that achieves the hue b* value that is equal to or smaller than 7 in the case where the two absorption-type polarization plates  11  and  14  are so overlapped that the absorption axes of the respective absorption-type polarization plates  11  and  14  are aligned in the same direction. Further, for example, EGW1225DU from Nitto Denko Corporation or SKW-18245T from Polatechno Co., Ltd. may be mentioned as the member that achieves the foregoing hue b* value that is equal to or smaller than 3. 
     Moreover, the liquid crystal layer  22 C preferably has a retardation value (Δn·d) that is equal to or greater than 0.36 μm and is smaller than 0.54 μm. One reason for this is that, by causing Δn·d of the liquid crystal layer  22 C to fall within the foregoing range, it is possible to reduce coloring of the display image formed by the display section  10  and to make the display image brighter. Further, owing to the small retardation value, the blur in the display image is reduced, and a viewing angle that is wide at some extent is allowed to be secured. 
     Moreover, Δn of the liquid crystal layer  22 C at the wavelength of 550 nm is preferably equal to or greater than 0.09 and smaller than 0.14. One reason for this is that transmission characteristics in the mirror state (the external light reflection mode), in particular, the transmission characteristics of light having the wavelength from 400 nm to 500 nm are improved thereby. 
     [Operation of Display Unit  1 ] 
     In this display unit  1 , for example, by controlling intensity of an electric field to be applied to the liquid crystal layer  22 C of the liquid crystal panel  22  in the display switching section  20  or by performing switching between presence and absence of the application of the electric field, it is possible to cause the display switching section  20  to be in a transmission state (the screen state) or to cause the display switching section  20  to be in the mirror surface state. 
     Here, a description is given, referring to  FIG. 1B  together with  FIG. 1A , of behavior in a case where the liquid crystal panel  22  in the display switching section  20  is a TN-type liquid crystal panel, and the transmission polarization axis of the reflection-type polarization plate  21  and the transmission polarization axis of the absorption-type polarization plate  23  are substantially parallel to each other. 
     (Behavior in Case Where No Electric Field is Applied to Liquid Crystal Layer  22 C) 
     In a case where no electric field is applied to the liquid crystal layer  22 C (refer to an upper part of  FIG. 1B ), the nematic liquid crystal included in the liquid crystal layer  22 C is in a 90-degree twisted state, and is basically in the first mode having optical rotation characteristics of 90 degrees. Under such a situation, external light L 1  that has entered the display switching section  20  passes through the absorption-type polarization plate  23 , and thereby becomes the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  23 J of the absorption-type polarization plate  23 . This first linearly-polarized light Lp later passes through the liquid crystal panel  22 , and is thereby converted into the second linearly-polarized light Ls having the oscillation plane that is orthogonal to the transmission polarization axis  23 J of the absorption-type polarization plate  23 . This second linearly-polarized light Ls has the oscillation plane in a direction orthogonal to the transmission polarization axis  21 J of the reflection-type polarization plate  21 , and is therefore reflected by the reflection-type polarization plate  21 . The reflected second linearly-polarized light Ls passes through the liquid crystal panel  22  again, and thereby becomes the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  23 J of the absorption-type polarization plate  23 . This first linearly-polarized light Lp thereafter passes through the absorption-type polarization plate  23  and is visually recognized by a viewer. 
     In contrast, image light L 2  outputted from the display section  10  is the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  11 J of the absorption-type polarization plate  11  as that described above. This first linearly-polarized light Lp passes through the reflection-type polarization plate  21  as it is and enters the liquid crystal panel  22 . That first linearly-polarized light Lp passes through the liquid crystal panel  22 , and is thereby converted into the second linearly-polarized light Ls having the oscillation plane that is orthogonal to the transmission polarization axis  23 J of the absorption-type polarization plate  23 , which is absorbed by the absorption-type polarization plate  23 . The image light outputted from the display section  10  is therefore not visually recognized from outside. 
     As described above, in the case where no electric field is applied to the liquid crystal layer  22 C, the image light from the display section  10  is not visually recognized from the outside. Further, the external light L 1  is reflected toward the viewer. The display screen is therefore brought into the mirror surface state (the external light reflection mode). 
     (Behavior in Case Where Electric Field is Applied to Liquid Crystal Layer  22 C) 
     Next, a description is given of behavior in a case where an electric field of a predetermined threshold or greater is applied to the liquid crystal layer  22 C (refer to a lower part of  FIG. 1B ). In this case, the twisted state of the nematic liquid crystal included in the liquid crystal layer  22 C is released, and the liquid crystal panel  22  loses optical rotation characteristics with respect to light that passes through in a direction of its optical axis to be brought into the second mode. The light outputted from the display section  10  (i.e., light configuring the display image on the display section  10 ) has been caused, by the absorption-type polarization plate  11 , to become the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  11 J thereof. This first linearly-polarized light Lp passes through the reflection-type polarization plate  21 , and enters the liquid crystal panel  22 . The oscillation plane of the first linearly-polarized light Lp that has entered the liquid crystal panel  22  is not varied. Therefore, the first linearly-polarized light Lp that has entered the liquid crystal panel  22  passes through the absorption-type polarization plate  23  as it is and is visually recognized (the screen state). Further, in this case, the external light L 1  that has entered the display switching section  20  passes through the absorption-type polarization plate  23  and thereby becomes the first linearly-polarized light Lp. Thereafter, this first linearly-polarized light Lp sequentially passes through the liquid crystal panel  22 , the reflection-type polarization plate  21 , the absorption-type polarization plate  11 , and the liquid crystal panel  13  as it is, and enters the absorption-type polarization plate  14 . The first linearly-polarized light Lp has the oscillation plane that is orthogonal to the transmission polarization axis  14 J of the absorption-type polarization plate  14 , and is therefore absorbed by the absorption-type polarization plate  14 . 
     In the liquid crystal panel  22 , however, an electric field may be applied that does not cause the twisted state of the liquid crystal included in the liquid crystal layer  22 C to be completely released and to be released only partially, with an electric field that is equal to or greater than the predetermined threshold. In this case, the liquid crystal panel  22  loses part of the optical rotation characteristics with respect to light that passes through in the direction of the optical axis thereof, and is brought into a third mode. Accordingly, the external light L 1  that has entered the display switching section  20 , the linearly-polarized light Lp generated by passing through the absorption-type polarization plate  23  causes its own oscillation plane to be varied at an angle that is greater than 0 degree and smaller than 90 degrees upon passing through the liquid crystal panel  22 . Accordingly, part of this linearly-polarized light Lp is reflected by the reflection-type polarization plate  21 , and the rest passes through the reflection-type polarization plate  21 . The light reflected by the reflection-type polarization plate  21  passes through the liquid crystal panel  22  again and causes the oscillation plane to be varied in a range that is greater than 0 degree and is smaller than 90 degrees. Part of the light reflected by the reflection-type polarization plate  21  therefore passes through the polarization plate  23  to be visually recognized. The intensity of the reflected light is, however, weaker than that in the mirror surface state described above. 
     The light L 2  outputted from the display section  10  (i.e., display image light configuring the display image on the display section  10 ) has been caused, by the absorption-type polarization plate  11 , to become the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  11 J thereof. This first linearly-polarized light Lp passes through the reflection-type polarization plate  21  as it is, and enters the liquid crystal panel  22 . The first linearly-polarized light Lp causes its oscillation plane to be varied in a range that is greater than 0 (zero) degree and is smaller than 90 degrees upon passing through the liquid crystal panel  22 . Part of the first linearly-polarized light Lp is therefore absorbed by the absorption-type polarization plate  23 , and the rest is allowed to pass through. Accordingly, part of the display image light from the display section  10  is visually recognizable from the outside. As described above, in a state where the electric field that releases only part of the twisted state of the liquid crystal in the liquid crystal panel  22  is applied, part of the external light L 1  is reflected while part of the display image light from the display section  10  is allowed to pass through. Accordingly, the display screen is brought into a so-called half mirror state. 
     Here, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is equal to or smaller than the hue b* values of the absorption-type polarization plates  11  and  14  in the display section  10 . As a result, coloring (in particular, coloring in yellow) in the display image and the reflected image to be visually recognized by the viewer is suppressed. 
     [Workings and Effects of Display Unit  1 ] 
     As the display unit  1 , in the case where the two liquid crystal panels (the liquid crystal panel  13  and the liquid crystal panel  23 ) are overlapped to achieve the configuration in which the switching between the screen state and the mirror surface state is possible, and the transmission-type liquid crystal panel  13  is employed in the display section  10 , the light from the backlight  15  passes through each of the absorption-type polarization plate  11  and the absorption-type polarization plate  14  once (twice in total). In other words, each of the absorption-type polarization plate  11  and the absorption-type polarization plate  14  contributes to the coloring with respect to the light from the backlight  15 . In contrast, in the display switching section  20 , the display image light only passes through the absorption-type polarization plate  23  once in the image display state. Therefore, contribution, of the coloring due to the display switching section  20  (the coloring due to the absorption-type polarization plate  23 ), to the final display image and the final reflected image is about half of the contribution of the display section  10  to the coloring. It therefore seems that an influence, on the coloring, of the provision of the display switching section  20  is small. 
     In fact, however, the absorption-type polarization plate  11  and the absorption-type polarization plate  14  are often so disposed that the light absorption axis of the absorption-type polarization plate  11  and the light absorption axis of the absorption-type polarization plate  14  are orthogonal to each other in the display section  10 . In such a case, the hue b* value representing the coloring in a yellow direction due to the absorption-type polarization plates  11  and  14  is much smaller than the hue b* value in the case where the light absorption axis of the absorption-type polarization plate  11  and the light absorption axis of the absorption-type polarization plate  14  are parallel to each other. In other words, in the case where the light absorption axis of the absorption-type polarization plate  11  and the light absorption axis of the absorption-type polarization plate  14  are orthogonal to each other in the display section  10 , additional provision of the existing display switching section causes the increase in hue b* value to be greater than that in a case where that display switching section is not provided. 
     Moreover, in a case where the mirror surface state is provided in this display unit  1 , the external light sequentially passes through, from the viewer side, the absorption-type polarization plate  23  and the liquid crystal panel  22 , and further passes through the liquid crystal panel  22  and the absorption-type polarization plate  23  again after being reflected by the reflection-type polarization plate  21 . For a reason that the light absorption axis of the absorption-type polarization plate  23  and the light absorption axis of the reflection-type polarization plate  21  are parallel to each other, it can be said that it is a disadvantageous configuration in terms of the coloring in the yellow direction (the increase in hue b* value) due to the absorption-type polarization selecting means. 
     To address this, in the display unit  1  according to the present embodiment, the hue b* value of the absorption-type polarization plate  23  is set to be equal to or smaller than the hue b* value of the absorption-type polarization plate  11  (or the absorption-type polarization plate  14 ) having the transmission polarization axis that is substantially orthogonal to the transmission polarization axis of the absorption-type polarization plate  23 . Such a configuration reduces the coloring (in particular, the coloring in yellow) in the display image and the reflected image that is visually recognized by the viewer. The hue b* value of the absorption-type polarization plate  23  may be a negative value. Hence, according to this display unit  1 , it is possible to exhibit superior display performance in any of the screen mode (the image display mode) and the mirror surface state (the external light reflection mode). 
     Moreover, in the display unit  1 , by employing, as the display mode of the liquid crystal panel  22 , any of the TN mode, the ECB mode, the STN mode, the BTN mode, the VA mode, the IPS mode, the ferroelectric liquid crystal mode, and the antiferroelectric liquid crystal mode, a high contrast ratio is achieved with a relatively-low drive voltage. One reason for this is that the liquid crystal panel  22  employing the foregoing display mode performs display by modulating, with the polarization plate, the polarization state of the light that enters the liquid crystal layer  22 C. Further, in a case where the liquid crystal panel  22  varies the polarization axis by an odd multiple of 90 degrees, it is possible to easily perform the switching between the screen state and the mirror surface state. 
     Moreover, in this display unit  1 , for example, the resin layers  31  to  33  each having the thickness that is equal to or smaller than 25 μm are disposed at the respective predetermined positions. This makes it possible to suppress occurrence of a blur in the mirror surface state resulting from the unevenness on the attachment surface, and to exhibit superior display performance. Further, in a case where the hue b* values of the respective resin layers  31  to  33  are set to have smaller absolute value, for example, are set to be equal to or greater than −0.5 and equal to or smaller than 0.5, it is possible to reduce the coloring in yellow in the display image and the reflected image. In a case where the haze values of the respective resin layers  31  to  33  are equal to or smaller than 1, the display image and the reflected image in the screen of the display unit  1  in the screen state and the mirror surface state becomes more vivid. 
     Moreover, in a case where the liquid crystal layer  22 C of the liquid crystal panel  22  has Δn·d that is equal to or greater than 0.36 μm and smaller than 0.54 μm, it is possible to reduce the coloring in the display image formed by the display section  10 , and to make the display image brighter. Further, a blur in the display image is reduced, and a viewing angle that is wide at some extent is allowed to be secured. 
     Moreover, in a case where Δn of the liquid crystal layer  22 C at the wavelength of 550 nm is set to be equal to or greater than 0.09 and smaller than 0.14, it is possible to improve the transmission characteristics in the mirror surface state, in particular, the transmission characteristics of the light having the wavelength from 400 nm to 500 nm. 
     Moreover, in a case where the hue b* value of the reflection-type polarization plate  21  in the display switching section  20  is equal to or greater than −0.5 and equal to or smaller than 0.5, it is possible to further suppress the coloring in yellow. In particular, in a case where the hue b* value thereof is equal to or greater than −0.5 and smaller than 0, it is possible to further improve the coloring in yellow. 
     Moreover, in the display switching section  20 , the reflection-type polarization plate  21  and the absorption-type polarization plate  23  are so disposed that the transmission polarization axis  21 J and the transmission polarization axis  23 J are substantially parallel to each other. It is therefore possible to achieve the mirror surface state without applying any voltage to the liquid crystal panel  22  in the display switching section  20 . It is therefore possible to reduce power consumption in the mirror surface state. 
     2. SECOND EMBODIMENT 
     [Configuration of Display Unit  2 ] 
       FIG. 2  illustrates a schematic configuration of a display unit  2  according to a second embodiment of the present disclosure. The display unit  2  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment except that the transmission polarization axis  21 J of the reflection-type polarization plate  21  and the transmission polarization axis  23 J of the absorption-type polarization plate  23  are orthogonal to each other in the display switching section  20 . 
     [Operation of Display Unit  2 ] 
     Also in this display unit  2 , for example, by controlling intensity of an electric field to be applied to the liquid crystal layer  22 C of the liquid crystal panel  22  in the display switching section  20  or by performing switching between presence and absence of the application of the electric field, it is possible to cause the display switching section  20  to be in a transmission state (the screen state) or to cause the display switching section  20  to be in the mirror surface state. 
     Here, a description is given, referring to  FIG. 2 , of behavior in a case where the liquid crystal panel  22  in the display switching section  20  is the TN-type liquid crystal panel. 
     (Behavior in Case Where No Electric Field is Applied to Liquid Crystal Layer  22 C) 
     In a case where no electric field is applied to the liquid crystal layer  22 C (refer to an upper part of  FIG. 2 ), the nematic liquid crystal included in the liquid crystal layer  22 C is in a 90-degree twisted state, and is basically in the first mode having optical rotation characteristics of 90 degrees. The light outputted from the display section  10  (i.e., the light configuring the display image on the display section  10 ) has been caused, by the absorption-type polarization plate  11 , to become the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  11 J thereof. This first linearly-polarized light Lp passes through the reflection-type polarization plate  21 , and enters the liquid crystal panel  22 . The first linearly-polarized light Lp passes through the liquid crystal panel  22 , and the oscillation plane of the first linearly-polarized light Lp that has entered the liquid crystal panel  22  is thereby rotated by 90 degrees. This first linearly-polarized light Lp thereby becomes the second linearly-polarized light Ls having the oscillation plane that is parallel to the transmission polarization axis  23 J of the absorption-type polarization plate  23 . That second linearly-polarized light Ls passes through the absorption-type polarization plate  23  as it is and is visually recognized by the viewer (the screen state). Further, in this case, the external light L 1  that has entered the display switching section  20  passes through the absorption-type polarization plate  23  and thereby becomes the second linearly-polarized light Ls. Thereafter, this second linearly-polarized light Ls passes through the liquid crystal panel  22 , and is thereby rotated by 90 degrees, which becomes the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  21 J of the reflection-type polarization plate  21 . That first linearly-polarized light Lp sequentially passes through the reflection-type polarization plate  21 , the absorption-type polarization plate  11 , and the liquid crystal panel  13  as it is, and enters the absorption-type polarization plate  14 . That first linearly-polarized light Lp has the oscillation plane that is orthogonal to the transmission polarization axis  14 J of the absorption-type polarization plate  14 , and is therefore absorbed by the absorption-type polarization plate  14 . 
     (Behavior in Case Where Electric Field is Applied to Liquid Crystal Layer  22 C) 
     Next, a description is given of behavior in a case where an electric field of a predetermined threshold or grater is applied to the liquid crystal layer  22 C (refer to a lower part of  FIG. 2 ). In this case, the twisted state of the nematic liquid crystal included in the liquid crystal layer  22 C is released, and the liquid crystal panel  22  loses optical rotation characteristics with respect to light that passes through in a direction of its optical axis to be brought into the second mode. Under such a situation, the external light L 1  that has entered the display switching section  20  passes through the absorption-type polarization plate  23 , and thereby becomes the second linearly-polarized light Ls having the oscillation plane that is parallel to the transmission polarization axis  23 J of the absorption-type polarization plate  23 . This second linearly-polarized light Ls thereafter passes through the liquid crystal panel  22  as it is without being converted into the first linearly-polarized light Lp, and enters the reflection-type polarization plate  21 . This second linearly-polarized light Ls has the oscillation plane in a direction orthogonal to the transmission polarization axis  21 J of the reflection-type polarization plate  21 , and is therefore reflected by the reflection-type polarization plate  21 . The reflected second linearly-polarized light Ls passes through the liquid crystal panel  22  and the absorption-type polarization plate  23  again, and is visually recognized by the viewer. 
     In contrast, the image light L 2  outputted from the display section  10  is the first linearly-polarized light Lp having the oscillation plane that is parallel to the transmission polarization axis  11 J of the absorption-type polarization plate  11 . This image light L 2  therefore passes through the reflection-type polarization plate  21  as it is, and enters the liquid crystal panel  22 . That first linearly-polarized light Lp passes through the liquid crystal panel  22  as it is, and enters the absorption-type polarization plate  23 . The first linearly-polarized light Lp has the oscillation plane that is orthogonal to the transmission polarization axis  23 J, and is therefore absorbed by the absorption-type polarization plate  23 . The image light outputted from the display section  10  is therefore not visually recognized from outside. 
     As described above, in the case where the electric field is applied to the liquid crystal layer  22 C, the image light from the display section  10  is not visually recognized from the outside. Further, the external light L 1  is reflected toward the viewer. The display screen is therefore brought into the mirror surface state (the external light reflection mode). 
     It is to be noted that the so-called half mirror state is also achievable in the display unit  2  as with the display unit  1 . 
     [Workings and Effects of Display Unit  2 ] 
     As described above, also in the display unit  2 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that are visually recognized by the viewer. 
     Moreover, the reflection-type polarization plate  21  and the absorption-type polarization plate  23  are so disposed that the transmission polarization axis  21 J and the transmission polarization axis  23 J are substantially orthogonal to each other in the display switching section  20 . It is therefore expectable to improve the viewing angle characteristics in the mirror surface state. It is to be noted that a viewing angle improvement film may be disposed at least in one of a region between the absorption-type polarization plate  23  and the liquid crystal panel  22  and a region between the reflection-type polarization plate  21  and the liquid crystal panel  22 . 
     3. THIRD EMBODIMENT 
     [Configuration of Display Unit  3 ] 
       FIG. 3  illustrates a cross-sectional configuration of a display unit  3  according to a third embodiment of the present disclosure. The display unit  3  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment except that a position at which the absorption-type polarization plate  11  is disposed is changed in the display section  10 . 
     Specifically, in the display unit  3 , the absorption-type polarization plate  11  is disposed between the substrate  13 A and the liquid crystal layer  13 C instead of being disposed between the reflection-type polarization plate  21  and the substrate  13 A. 
     [Workings and Effects of Display Unit  3 ] 
     Also in the display unit  3 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that are visually recognized by the viewer. 
     In addition, in the display unit  3 , the absorption-type polarization plate  11  is provided inside the liquid crystal panel  13 . This makes it possible to achieve the attachment of the display section  10  and the display switching section  20  to each other by adhering the reflection-type polarization plate  21  and the substrate  13 A to each other, for example, with a resin layer. It is therefore possible to avoid occurrence of unevenness on the reflection-type polarization plate  21  resulting from the unevenness of the surface of the absorption-type polarization plate  11 , and to suppress occurrence of a blur in the mirror surface state. It is to be noted that, for example, a method disclosed in Japanese Unexamined Patent Application Publication No. 2011-48310 can be referred to as one example of a method of forming the absorption-type polarization plate  11  inside the liquid crystal panel  13 . 
     4. FOURTH EMBODIMENT 
     [Configuration of Display Unit  4 ] 
       FIG. 4  illustrates a cross-sectional configuration of a display unit  4  according to a fourth embodiment of the present disclosure. In the display unit  4 , a glass substrate  16  is disposed between the display section  10  and the display switching section  20 , more specifically, between the absorption-type polarization plate  11  and the reflection-type polarization plate  21 . Except for this point, the display unit  4  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment. 
     [Workings and Effects of Display Unit  4 ] 
     Also in the display unit  4 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that are visually recognized by the viewer. 
     In the display unit  4 , the glass substrate  16  is interposed between the absorption-type polarization plate  11  and the reflection-type polarization plate  21 . It is therefore possible to avoid an influence of the absorption-type polarization plate  11  on the reflection-type polarization plate  21 . In other words, it is possible to prevent occurrence of unevenness on the reflection-type polarization plate  21  by attaching the reflection-type polarization plate  21  to the glass substrate  16 . As a result, it is possible to suppress occurrence of a blur in the mirror surface state. Further, it is possible to reduce, for example, loss in optical transmittance, by using the glass substrate  16 , compared to the case of using the resin layer. 
     5. FIFTH EMBODIMENT 
     [Configuration of Display Unit  5 ] 
       FIG. 5  illustrates a cross-sectional configuration of a display unit  5  according to a fifth embodiment of the present disclosure. In the display unit  5 , the STN mode is employed as the liquid crystal mode of the liquid crystal panel  22 , and a retardation plate  24  is disposed between the liquid crystal panel  22  and the absorption-type polarization plate  23 . A twist angle of the liquid crystal in the liquid crystal layer  22 C in the liquid crystal panel  22  is set to 270 degrees. Further, as a pixel arrangement in the display section  10 , a matrix type in which the pixels are disposed at the respective intersections of a plurality of stripe electrodes is employed. Except for these points, a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment is provided. 
     [Workings and Effects of Display Unit  5 ] 
     Also in the display unit  5 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that are visually recognized by the viewer. 
     In the display unit  5 , the liquid crystal display device of the STN mode is used for the liquid crystal panel  22 . In other words, the liquid crystal panel  22  including a bistable liquid crystal display device is used. This eliminates the necessity of constant driving and therefore achieves reduction in power consumption. In this STN mode, threshold characteristics of the drive voltage are steep. The steep threshold characteristics refer to the fact that the transmission polarization axis is varied drastically with respect to an application voltage. When the threshold characteristics are steep, it is easy to increase the number of scanning lines in the passive drive mode including simple drive and multiplex drive that does not use any active device, which is preferable. 
     6. SIXTH EMBODIMENT 
     [Configuration of Display Unit  6 ] 
       FIG. 6  illustrates a cross-sectional configuration of a display unit  6  according to a sixth embodiment of the present disclosure. The display unit  6  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment except that a liquid crystal panel  25  is provided instead of the liquid crystal panel  22 . 
     The liquid crystal panel  25  is a ferroelectric liquid crystal panel, and has a structure in which a liquid crystal layer  25 C is sandwiched between a substrate  25 A and a substrate  25 B. The substrate  25 A and the substrate  25 B are made of a transparent material such as glass (including quartz), for example. The liquid crystal layer  25 C includes a ferroelectric liquid crystal substance (for example, ZLI3489 from Merck &amp; Co., Inc.). Further, as a spacer for thickness adjustment of the liquid crystal layer  25 C, for example, a spherical spacer made of silica having an average particle diameter of about 1.7 μm is used, for example. The liquid crystal panel  25  is manufactured as follows, for example. Specifically, spin coating with polyimide is so performed that a surface of a transparent electrode (for example, ITO) formed on an inner surface of each of the substrate  25 A and the substrate  25 B is covered, which is thereafter subjected to a heating process at about 180 degrees Celsius for about an hour. Next, rubbing is performed on the surface of that polyimide film, for example, with a nylon cloth (with an indentation amount of about 0.5 mm). Further, the substrate  25 A and the substrate  25 B are so attached to each other that their rubbing directions are parallel to each other. The liquid crystal panel  25  is thus completed. It is to be noted that the polarization plane of light that has passed through the liquid crystal panel  25  is rotated by about 90 degrees between a state in which a voltage is applied to the liquid crystal panel  25  and a state in which no voltage is applied to the liquid crystal panel  25 . Further, the liquid crystal layer  25 C in the liquid crystal panel  25  is a bistable liquid crystal display device that only has two states in which inclination is provided by a tilt angle ±θ with respect to an axis perpendicular to a film surface. It is to be noted that a liquid crystal display device of the BTN mode may be used as the bistable liquid crystal display device. 
     [Workings and Effects of Display Unit  6 ] 
     Also in the display unit  6 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that is visually recognized by the viewer. 
     In the display unit  6 , the liquid crystal panel  25  that is the bistable liquid crystal display device is used as a switchable transmission polarization axis member. This eliminates the necessity of constant driving and therefore achieves reduction in power consumption. Further, chiral smectic liquid crystal may be used as the ferroelectric liquid crystal substance in the liquid crystal layer  25 C in the liquid crystal panel  25 . A response speed of the liquid crystal panel  25  is higher than a response speed of a liquid crystal panel using nematic liquid crystal (for example, time of switching between the screen state and the mirror surface state is within 1 msec at 25 degrees Celsius), which is preferable. 
     7. SEVENTH EMBODIMENT 
     [Configuration of Display Unit  7 ] 
       FIG. 7  illustrates a cross-sectional configuration of a display unit  7  according to a seventh embodiment of the present disclosure. The display unit  7  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment except that a liquid crystal panel  26  is provided instead of the liquid crystal panel  22 . 
     The liquid crystal panel  26  is an antiferroelectric liquid crystal panel, and has a structure in which a liquid crystal layer  26 C is sandwiched between a substrate  26 A and a substrate  26 B. The substrate  26 A and the substrate  26 B are made of a transparent material such as glass (including quartz), for example. For example, an antiferroelectric liquid crystal molecule represented by Formula 1 may be used for the liquid crystal layer  26 C. 
     
       
         
         
             
             
         
       
     
     Further, as a spacer for thickness adjustment of the liquid crystal layer  26 C, for example, a spherical spacer made of silica having an average particle diameter of about 5.5 μm is used. The liquid crystal panel  26  is manufactured as follows, for example. Specifically, spin coating with polyimide is so performed that a surface of a transparent electrode (for example, ITO) formed on an inner surface of each of the substrate  26 A and the substrate  26 B is covered, which is thereafter subjected to a heating process at about 180 degrees Celsius for about an hour. Next, rubbing is performed on the surface of that polyimide film, for example, with a nylon cloth (with an indentation amount of about 0.7 mm). Further, the substrate  26 A and the substrate  26 B are so attached to each other that their rubbing directions are parallel to each other. The liquid crystal panel  26  is thus completed. It is to be noted that the polarization plane of light that has passed through the liquid crystal panel  26  is rotated by about 90 degrees between a state in which a voltage is applied to the liquid crystal panel  26  and a state in which no voltage is applied to the liquid crystal panel  26 . Further, a tilt angle θ of the antiferroelectric liquid crystal molecule in the liquid crystal layer  26 C in the liquid crystal panel  26  is about 45 degrees. 
     [Workings and Effects of Display Unit  7 ] 
     Also in the display unit  7 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that is visually recognized by the viewer. 
     The liquid crystal panel  26  in the display unit  7  is a tristable liquid crystal display device that only has two states in which inclination is provided by a tilt angle ±θ with respect to an axis perpendicular to a film surface and a tilt angle of 0 (zero) degree. In the display unit  7 , the liquid crystal panel  26  that is the tristable liquid crystal display device is used as the switchable transmission polarization axis member. This eliminates the necessity of constant driving and therefore achieves reduction in power consumption. It is to be noted that, in the display unit  7 , when the tilt angle is ±θ, the polarization plane of the light that has passed through the liquid crystal panel  26  may be so set as to be rotated by about 90 degrees, compared to that at the tilt angle of 0 (zero) degree. Alternatively, when the tilt angle is ±θ, the polarization plane of the light that has passed through the liquid crystal panel  26  may be so set as to be rotated by about 45 degrees, compared to that at the tilt angle of 0 (zero) degree. When the polarization plane of the light that has passed through the liquid crystal panel  26  for the tilt angle of ±θ is so set as to be rotated by about 45 degrees compared to that at the tilt angle of 0 (zero) degree, a difference between the tilt angle of +θ and the tilt angle of −θ corresponds rotation of about 90 degrees. In other words, it is possible to achieve, without performing constant driving, the three states, i.e., the tilt angle of +θ (the screen state (the image display mode)), the mirror surface state having the tilt angle of −θ (the external light reflection mode), and the tilt angle of 0 (zero) degree (the half mirror mode). Further, in the display unit  7 , the liquid crystal panel  26  is an antiferroelectric liquid crystal panel, and chiral smectic liquid crystal of the antiferroelectric liquid crystal substance may be used for the liquid crystal layer  26 C thereof. A response speed of the antiferroelectric liquid crystal panel is higher than a response speed of a liquid crystal panel using nematic liquid crystal (for example, time for switching between the screen state and the mirror surface state is within 1 msec at 25 degrees Celsius), which is preferable. Further, the antiferroelectric liquid crystal panel has a wide viewing angle. The antiferroelectric liquid crystal panel achieves even alignment more easily, has alignment that is more difficult to be disturbed by an external impact, and achieves high contrast more easily, compared to the ferroelectric liquid crystal panel. Therefore, the antiferroelectric liquid crystal panel is preferable. 
     8. EIGHTH EMBODIMENT 
     [Configuration of Display Unit  8 ] 
       FIG. 8  illustrates a cross-sectional configuration of a display unit  8  according to an eighth embodiment of the present disclosure. The display unit  8  has a configuration similar to the configuration of the display unit  1  according to the foregoing first embodiment except that a liquid crystal panel  27  is provided instead of the liquid crystal panel  22 . 
     The liquid crystal panel  27  is a VA liquid crystal panel, and has a structure in which a liquid crystal layer  27 C is sandwiched between a substrate  27 A and a substrate  27 B. The substrate  27 A and the substrate  27 B are made of a transparent material such as glass (including quartz), for example. Liquid crystal molecules having negative dielectric constant anisotropy may be used for the liquid crystal layer  27 C. 
     Further, as a spacer for thickness adjustment of the liquid crystal layer  27 C, for example, a spherical spacer made of silica having an average particle diameter of about 3.5 μm may be used, for example. The liquid crystal panel  27  is manufactured as follows, for example. Specifically, a solution of an optical alignment film material (a photosensitive material) having vertical alignment is so applied by spin casting that a surface of a transparent electrode (for example, ITO) formed on an inner surface of each of the substrate  27 A and the substrate  27 B is covered, which is thereafter burned at 180 degrees Celsius for 60 minutes. An alignment film is thus formed. Thereafter, a process such as rubbing may be performed on an as-needed basis. The optical alignment film refers to a film that is formed of a material having alignment regulating force that is varied by light application. It is to be noted that, in the present Example, a material having a photosensitive group (the photosensitive material) (a material having a 4-chalcone group (Formula 2)) was used as the alignment film material. 
     
       
         
         
             
             
         
       
     
     In a case where such a material having the photosensitive group is used and the alignment process by means of light application is performed while, for example, a wavelength, a light amount, an application angle, and a polarization direction are controlled, it is possible to obtain an alignment film that has, for example, a stable pre-tilt angle and a stable alignment direction by controlling, for example, a pre-tilt angle and an alignment direction of the liquid crystal molecule with high accuracy, which is preferable. The pre-tilt angle is an angle formed by a surface of the alignment film and a major axis direction of the liquid crystal molecule in the vicinity of the alignment film, in a state where no voltage is applied to the liquid crystal layer (in an OFF state, upon no voltage application). Subsequently, the alignment process by means of the light application is performed by applying polarized ultraviolet rays to the alignment film. All of the pre-tilt angles of the liquid crystal molecules in the vicinity of the alignment film are thereby set to fall between 87 degrees to 89.7 degrees. A molecule configuring the alignment film has an optical functional group (a photosensitive group) in a side chain of a polymer chain. By this alignment process, however, the optical functional groups form a dimer as a result of dimerization, thereby forms a cross-linked structure (a cross-bridging bonding structure). Further, part of the molecules configuring the alignment film is brought into cis-trans isomerization as a result of an isomerization reaction caused by the alignment process. Further, the rest of the molecules configuring the alignment film are re-aligned. Further, in the present embodiment, for example, an alignment film material may be used that is formed of a material that has at least one photosensitive group selected from groups that include a structure of one type out of other types of chalcone, cinnamate, cinnamoyl, coumarin, maleimide, benzophenone, norbornene, oryzanol, and chitosan besides the 4-chalcone group represented by Formula, as the photoreactive cross-linking functional group (which is a photosensitive group having photosensitivity, for example, photodimerized photosensitive group). Further, an optical alignment film that includes, as the photosensitive functional group, an azobenzene-based compound having an azo group, a compound having imine and aldimine in its skeleton, and/or a compound having a styrene skeleton may be used. 
     For example, after forming a seal and providing the spacer after forming the alignment film, the substrate  27 A and the substrate  27 B are attached to each other. The liquid crystal panel  27  is thus able to be fabricated. It is to be noted that the polarization plane of the light that has passed through the liquid crystal panel  27  is rotated by about 90 degrees between a state in which a voltage is applied to the liquid crystal panel  27  and a state in which no voltage is applied to the liquid crystal panel  27 . 
     [Modification Example 1 of Display Unit  8 ] 
     The liquid crystal panel  27  may be manufactured as follows, for example. Specifically, a solution of an alignment film material having vertical alignment characteristics is so applied by spin casting that a surface of a transparent electrode (for example, ITO) formed on an inner surface of each of the substrate  27 A and the substrate  27 B is covered, which is thereafter burned. An alignment film is thus formed. Any alignment film having the vertical alignment characteristics may be used as the alignment film material. An alignment film configured of an organic material such as polyimide, polyamic acid, and polyorganosiloxane may be used. Thereafter, a process such as rubbing may be performed on an as-needed basis. Further, for example, after forming a seal and providing the spacer, the substrate  27 A and the substrate  27 B are attached to each other. Further, as the liquid crystal layer  27 C, a liquid crystal composition exhibiting negative dielectric constant isotropy in which polymerizable components such as monomers and oligomers having polymerization characteristics is sealed between the substrate  27 A and the substrate  27 B. The monomers are polymerized in a state where the liquid crystal molecules are tilted (inclined) by means of voltage application between the substrate  27 A and the substrate  27 B, by which a polymer is formed. A liquid crystal molecule that is tilted at a predetermined pre-tilt angle and in a direction of the alignment is obtainable even after the voltage application is stopped. It is to be noted that all of the pre-tilt angles of the liquid crystal molecules preferably fall between 87 degrees to 89.7 degrees. A material that is polymerizable, for example, by heat or light (ultraviolet rays) is selected as the monomer. For example, a material represented by General formula (I) below may be used as the polymerizable monomer. 
       P1-S1-A1-(Z1-A2)n-S2-P2   (I)
 
     (In the formula, P 1  and P 2  are the same as each other or are different from each other and represent an acrylate group, a methacrylate group, an acrylamide group, a methacrylamide group, a vinyl group, a vinyloxy group, or an epoxy group. A 1  and A 2  each represent a 1,4-phenylene group, a naphthalene-2,6-diyl group, an anthracene-2,6-diyl group, or a phenanthrene-2,6-diyl group. Z 1  represents COO, OCO, O, direct bonding of A 1  and A 2 , or direct bonding of A 2  and A 2 . “n” is 0, 1, or 2. S 1  and S 2  are the same as each other or are different from each other, and represent —(CH 2 )m- (0≦m≦6), —(CH 2 —CH 2 —O)m- (0≦m≦6), direct bonding of P 1  and A 1 , direct bonding of A 1  and P 2 , or direct bonding of A 2  and P 2 . A hydrogen atom included in A 1  and A 2  may be substituted with a halogen group or a methyl group.) 
     Further, a polymerization initiator such as a radical polymerization initiator for initiating the polymerization reaction of the monomers is sometimes mixed. In a case where no radical polymerization initiator is added, the reaction speed of the polymerization reaction does not increase. This leads to a high possibility that unreacted monomers are left in the liquid crystal layer. Consequently, the unreacted monomers are slowly brought into the polymerization reaction under the influence of the light of the backlight in the general use after completion or an aging process for inspection after the assembling process. As a result, the amount of the pre-tilt angle formed through the polymerization process is varied, which may possibly influence display characteristics. For example, the following Formula 3 may be used as the radical polymerization initiator. 
     
       
         
         
             
             
         
       
     
     [Modification Example 2 of Display Unit  8 ] 
     Further, the liquid crystal panel  27  in the display unit  8  may be manufactured as follows, for example. Specifically, a solution of an alignment film material that has vertical alignment characteristics and includes a polymer compound having, for example, a cross-linking functional group or a photosensitive functional group as a side chain is so applied by spin casting that a surface of a transparent electrode (for example, ITO) formed on an inner surface of each of the substrate  27 A and the substrate  27 B is covered, which is thereafter subjected to a heating process. The temperature of the heating process is preferably equal to or higher than 80 degrees Celsius, and is more preferably equal to or higher than 150 degrees Celsius and equal to or lower than 230 degrees Celsius. Thereafter, a process such as rubbing may be performed on an as-needed basis. Further, for example, after forming a seal and providing the spacer, the substrate  27 A and the substrate  27 B are attached to each other. Further, a liquid crystal material is injected between the substrate  27 A and the substrate  27 B and the cell is sealed. Next, a voltage is applied between the substrate  27 A and the substrate  27 B, which causes the liquid crystal molecules to be tilted (inclined) at a predetermined angle. In that state, by applying ultraviolet rays to the alignment film, an alignment film that causes reactive cross-linking of the cross-linking functional groups of the alignment film is formed. Thus, a liquid crystal molecule that is tilted at a predetermined pre-tilt angle and in a direction of the alignment is obtainable even after the voltage application and ultraviolet ray application are stopped. It is to be noted that all of the pre-tilt angles of the liquid crystal molecules preferably fall between 87 degrees to 89.7 degrees. As the ultraviolet rays, ultraviolet rays including a lot of light components having a wavelength about 365 nm are preferable. In a case where ultraviolet rays including a lot of light components in a short wavelength range are used, the liquid crystal material is subjected to photodecomposition. This may lead to degradation. As the photoreactive cross-linking functional group (a photosensitive group having photosensitivity, for example, a photodimerized photosensitive group), for example, a group including a structure of one type of chalcone, cinnamate, cinnamoyl, coumarin, maleimide, benzophenone, norbornene, oryzanol, and chitosan can be mentioned. Further, an optical alignment film that includes an azobenzene-based compound having an azo group as the photosensitive functional group, a compound having imine and aldimine in its skeleton, or a compound having a styrene skeleton may be used. 
     Moreover, as illustrated in  FIG. 9A , a liquid crystal molecule  27 M in the liquid crystal panel  27  is preferably so inclined as to include a portion that is aligned upward from the substrate  27 B toward the substrate  27 A. Further, inclination in a direction perpendicular to the paper plane of  FIG. 9A  may be provided. In a case where the display unit that performs switching between the screen state and the mirror surface state as in the present disclosure is used in the mirror surface state, it is likely that the liquid crystal panel  27  is more often viewed from the lower position than from the upper position. It is therefore preferable that the viewing angle characteristics in a case where the mirror is viewed from the lower position are superior. As illustrated in  FIG. 9B , in a case where the liquid crystal molecule  27 M is pre-tilted in a direction indicated by an arrow  271  and has a portion that is aligned upward from the substrate  27 B toward the substrate  27 A upon application of no electric field, the liquid crystal molecule  27 M is rotated in a direction indicated by an arrow  272 , i.e., upward, upon application of an electric field (the liquid crystal molecule  27 M falls in a direction of causing retardation), which is preferable. 
     In contrast, as illustrated in  FIG. 9C , in a case where the liquid crystal molecule  27 M is pre-tilted in the direction indicated by the arrow  271  and has a portion that is aligned downward from the substrate  27 B toward the substrate  27 A upon application of no electric field, the liquid crystal molecule  27 M is rotated in the direction indicated by the arrow  272 , i.e., downward, upon application of an electric field (the liquid crystal molecule  27 M falls in a direction of canceling retardation). Accordingly, it is not so preferable in terms of the viewing angle characteristics. It is to be noted that not all of the liquid crystal molecules  27 M included in the liquid crystal layer  27 C are aligned upward from the substrate  27 B toward the substrate  27 A, and part of the liquid crystal molecules  27 M may be aligned upward in such a manner. 
     [Workings and Effects of Display Unit  8 ] 
     Also in the display unit  8 , it is possible to perform the switching between the screen state (the image display mode) and the mirror surface state (the external light reflection mode) by the display switching section  20  as in the foregoing first embodiment. Further, the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  is set to be equal to or smaller than the hue b* values of the respective absorption-type polarization plates  11  and  14  in the display section  10 . Accordingly, it is possible to suppress the coloring (in particular, the coloring in yellow) in the display image and the reflected image that is visually recognized by the viewer. 
     In the display unit  8 , the liquid crystal panel  27  of the VA liquid crystal mode is used as the switchable transmission polarization axis member. The VA liquid crystal panel easily achieves a high contrast ratio, which is preferable. Further, in a case where stress is applied to the absorption-type polarization plate  23  in the display section switching section  20 , black floating is less likely to be caused, compared to other liquid crystal modes (for example, the IPS mode), which is preferable. Further, a pre-tilt at predetermined alignment is provided for the liquid crystal molecule in the liquid crystal layer  27 C. When an electric filed is applied to perform switching of the liquid crystal molecule, a direction in which the liquid crystal responds is determined by the pre-tilt. This suppresses, for example, a leakage of light resulting from falling of the liquid crystal in different directions (occurrence of a defect), or a delay in response. As a result, the reaction speed is improved, which is preferable. 
     9. APPLICATION EXAMPLES (ELECTRONIC APPARATUS) 
     Next, referring to  FIG. 10 , an electronic apparatus  100  provided with the display unit  1  is described.  FIG. 8  is a schematic view of an overall configuration of the electronic apparatus  100 . 
     The electronic apparatus  100  includes the display unit  1  according to the foregoing first embodiment.  FIG. 10  is a block diagram schematically illustrating a display control system of the display unit  100  disposed inside the electronic apparatus  100 . The electronic apparatus  100  includes, besides the display unit  1 , a display driving section  13 X, an illumination driving section  15 X, and a switching driving section  22 X. The electronic apparatus  100  further includes a controlling section  100 X that controls the display driving section  13 X, the illumination driving section  15 X, and the switching driving section  22 X. All of the components described above may be disposed inside the display unit  1 , or may be disposed outside the display unit  1 , i.e., in a region other than the display unit  1  inside the electronic apparatus  100 . Alternatively, part of the components may be disposed inside the display unit  1 , and the rest of the components may be disposed inside the electronic apparatus  100  other than the display unit  1 . 
     The display driving section  13 X drives the liquid crystal panel  13  provided in the display section  10  in the display unit  1 . The display driving section  13 X supplies a driving voltage for driving each of a plurality of pixel regions configured in a liquid crystal driving region of the liquid crystal panel  13 . For example, in the multiplex drive scheme or the active drive scheme, respective scanning signals and respective data signals corresponding to these scanning signals are supplied to a common terminal (a scanning line terminal) and a segment terminal (a data line terminal) in the liquid crystal panel  13  in synchronization. Display data such as image data is transmitted from a main circuit in the electronic apparatus  100  to this display driving section  13 X via the controlling section  100 X. 
     The illumination driving section  15 X drives the backlight  15  in the display section  10 . More specifically, the illumination driving section  15 X controls power supply to the backlight  15 . For example, the illumination driving section  15 X so functions as to perform switching between an ON state and an OFF state of the backlight  15 . 
     The switching driving section  22 X drives the liquid crystal panel  22  provided in the display switching section  20 . The switching driving section  22 X controls an application voltage to be supplied to the liquid crystal panel  22 , and determines whether a voltage of a threshold or greater is applied to a pair of transparent electrodes that face the liquid crystal panel  22 . 
     The controlling section  100 X controls each of the display driving section  13 X, the illumination driving section  15 X, and the switching driving section  22 X, and performs control instruction and data transmission with respect to each of the sections, for example. For example, in a case where the display switching section  20  is brought into the image display mode to cause the display unit  1  to be in the screen state, the liquid crystal panel  13  is driven by the display driving section  13 X to perform image display while the liquid crystal panel  22  is controlled by the switching driving section  22 X to cause the display switching section  20  to be in the transmission state. In contrast, in a case where the display switching section  20  is brought into the external light reflection mode to cause the display unit  1  to be in the mirror surface state, the liquid crystal panel  22  is controlled by the switching driving section  22 X to bring the display switching section  20  in the external light reflection mode while the liquid crystal panel  13  is caused to be in a completely-shut-down state (a shutter closed state) by the display driving section  13 X or the backlight  15  is turned off by the illumination driving section  15 X. 
     As described above, according to the electronic apparatus  100  of the present disclosure, the display unit  1  described above is provided. It is therefore possible to reduce the coloring (in particular, the coloring in yellow) in the display image and the reflected image that are visually recognized by the viewer. Hence, according to the electronic apparatus  100 , it is possible to exhibit superior display performance in any of the screen state (the image display mode) and the mirror surface state (the external light reflection mode). 
     As the electronic apparatus  100 , for example, a television apparatus, a digital camera, a laptop personal computer, a mobile phone, a smartphone, a portable terminal device such as a tablet terminal device, or a video camera can be mentioned. In other words, it is possible to apply the foregoing display unit to an electronic apparatus in various fields that displays, as an image or a picture, an image signal inputted from outside or an image signal generated internally. 
     10. EXPERIMENTAL EXAMPLES 
     Experimental Example 1 
     Experimental Example 1-1 
     A sample of the display unit  1  according to the first embodiment described above was fabricated, and chromaticity of the sample in the screen state was measured. It is to be noted that a display color analyzer CA-210 from Konica Minolta Japan, Inc. was used for the measurement of the chromaticity. A result thereof is illustrated in  FIG. 11 . In  FIG. 11 , a horizontal axis represents chromaticity x and a vertical axis represents chromaticity y. It is to be noted that  FIG. 11  also illustrates a result of the measurement of chromaticity for only the display section  10  together. It is to be noted that SKW-18245T having a hue b* value of 0.43 from Polatechno Co., Ltd. was used as the absorption-type polarization plate  23  in the display switching section  20 , and SKN-18243T having a hue b* value of 3.55 from Polatechno Co., Ltd. was used as the absorption-type polarization plates  11  and  14  in the display section  10 . 
     Experimental Example 1-2 
     A sample of the display unit  1  was fabricated in a manner similar to that in Experimental example 1-1 except that SRCZ4QJ having a hue b* value of 4.0 from Sumitomo Chemical Co., Ltd. was used as the absorption-type polarization plate  23  in the display switching section  20 , and SKN-18243T having a hue b* value of 3.55 from Polatechno Co., Ltd. was used as each of the absorption-type polarization plates  11  and  14  in the display section  10 . The sample was also subjected to measurement of chromaticity.  FIG. 9  also illustrates the result together. 
     As illustrated in  FIG. 9 , the chromaticity y was 0.3042 in Experimental example 1-2 while the chromaticity y was 0.2932 in Experimental example 1-1. Further, the chromaticity y only of the display section  10  was 0.288. That is, it was possible to greatly suppress an increase in chromaticity y due to the addition of the display switching section  20 , compared to that in Experimental example 1-2. Accordingly, it was confirmed that the coloring in yellow in particular was suppressed by setting the hue b* value of the absorption-type polarization plate  23  in the display switching section  20  to be equal to or smaller than the hue b* values of the absorption-type polarization plates  11  and  13  in the display section  10 . 
     Experimental Example 2 
     Experimental Example 2-1 
     A sample of the display unit  1  according to the first embodiment described above was fabricated. Here, the polarization reflection film DBEF (from 3M United States) was used as the reflection-type polarization plate  21 . Further, SKW-18245T having a hue b* value of 0.43 from Polatechno Co., Ltd. was used as the absorption-type polarization plate  23 , and SRCZ4QH having a hue b* value of 3.2 from Sumitomo Chemical Co., Ltd. was used as the absorption-type polarization plates  11  and  14 . Further, an optical transparent adhesive sheet LUCIAS CS9864US having a thickness of 100 μm from Nitto Denko Corporation was used as each of the resin layers  31  to  33 . 
     Experimental Example 2-2 
     A sample of the display unit  1  was fabricated in a manner similar to that in Experimental example 2-1 except that a highly-transparent baseless tape CTL-NC105 having a thickness of 25 μm from Lintec Corporation was used as each of the resin layers  31  to  33 . 
     Experimental Example 2-3 
     A sample of the display unit  1  was fabricated in a manner similar to that in Experimental example 2-1 except that the highly-transparent baseless tape CTL-NC103 having a thickness of 15 μm from Lintec Corporation was used as each of the resin layers  31  to  33 . 
     Experimental Example 2-4 
     A sample of the display unit  1  was fabricated in a manner similar to that in Experimental example 2-1 except that a highly-transparent baseless tape CTL-NC100 series having a thickness of 5 μm from Lintec Corporation was used as each of the resin layers  31  to  33 . 
     A Wd value of orange peel (a measurement wavelength from 3 mm to 10 mm) was measured for each of these samples in Experimental examples 2-1 to 2-4. It is to be noted that a portable orange peel meter from BYK-Gardner was used for the measurement of the Wd value of orange peel. The result is illustrated in  FIG. 12 . In  FIG. 12 , a horizontal axis represents the thicknesses (μm) of the resin layers  31  to  33 , and a vertical axis represents the Wd value of orange peel. 
     As illustrated in  FIG. 12 , the Wd value of orange peel was 7.5 in the case where the thickness of each of the resin layers  31  to  33  was 25 μm (Experimental example 2-2), was 7.8 in the case where the thickness of each of the resin layers  31  to  33  was 15 μm (Experimental example 2-3), and was 3 in the case where the thickness of each of the resin layers  31  to  33  was 5 μm (Experimental example 2-4), while the Wd value of orange peel was 21 in the case where the thickness of each of the resin layers  31  to  33  was 100 μm (Experimental example 2-1). Accordingly, it was found that a blur and the Wd value of orange peel were greatly suppressed by setting the thickness of each of the resin layers  31  to  33  to 25 μm or smaller. It was also found that it was more preferable that the thickness of each of the resin layers  31  to  33  is set to 5 μm or smaller. 
     Experimental Example 3 
     Experimental Example 3-1 
     Next, a sample of the liquid crystal panel  22  in the display unit  1  according to the first embodiment described above was fabricated using the liquid crystal of TN mode as the liquid crystal layer  22 C. Here, a retardation value Δn·d was set to 0.36 μm. 
     Experimental Example 3-2 
     A sample of the liquid crystal panel  22  in the display unit  1  was fabricated that has a configuration similar to that in Experimental example 3-1 except that the retardation value Δn·d was set to 0.45 μm. 
     Experimental Example 3-3 
     A sample of the liquid crystal panel  22  was fabricated that has a configuration similar to that in Experimental example 3-1 except that the retardation value Δn·d was set to 0.54 μm. 
     Simulation of wavelength dependence of transmittance (wavelength was from 380 nm to 500 nm) was performed for each of these samples in Experimental examples 3-1 to 3-3. The result is illustrated in  FIG. 13 . In  FIG. 13 , a horizontal axis represents the wavelength (μm), and a vertical axis represents the transmittance. 
     It is likely that the coloring in the yellow direction occurs when the transmittance on the short wavelength side in the visible light range is decreased. As illustrated in  FIG. 11 , the transmittance is not greatly varied in the case where the Δn·d of the liquid crystal layer  22 C is 0.36 μm (Experimental example 3-1) and 0.45 μm (Experimental example 3-2); however, the transmittance in 420 μm to 480 μm is slightly decreased in the case where the Δn·d is 0.54 μm (Experimental example 3-3). Accordingly, it was found that a decrease in transmittance for wavelength light in 380 nm from 500 nm was further suppressed in the case where the Δn·d was set within a range that was equal to or greater than 0.36 μm and smaller than 0.54 μm. In other words, in the case where the retardation value Δn·d of the liquid crystal layer  22 C was equal to or greater than 0.36 μm and smaller than 0.54 μm, it was possible to cause, for example, the display image and the reflected image to be brighter in addition to that it is possible to reduce the coloring, for example, in the screen state and the mirror surface state formed by the display section  10 . 
     Experimental Example 4 
     Experimental Example 4-1 
     Next, a sample of the liquid crystal panel  22  in the display unit  1  according to the first embodiment described above was fabricated using the liquid crystal of TN mode as the liquid crystal layer  22 C. Here, retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm was set to 0.09. 
     Experimental Example 4-2 
     A sample of the liquid crystal panel  22  was fabricated that has a configuration similar to that in Experimental example 4-1 except that the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm was set to 0.10. 
     Experimental Example 4-3 
     A sample of the liquid crystal panel  22  was fabricated that has a configuration similar to that in Experimental example 4-1 except that the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm was set to 0.12. 
     Experimental Example 4-4 
     A sample of the liquid crystal panel  22  was fabricated that has a configuration similar to that in Experimental example 4-1 except that the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm was set to 0.14. 
     Simulation of wavelength dependence of transmittance (wavelength was from 380 nm to 500 nm) was performed for each of these samples in Experimental examples 4-1 to 4-4. The result is illustrated in  FIG. 14 . In  FIG. 14 , a horizontal axis represents the wavelength (μm), and a vertical axis represents the transmittance. 
     It is likely that the coloring in the yellow direction occurs when the transmittance on the short wavelength side in the visible light range is decreased. As illustrated in  FIG. 12 , the transmittance is not greatly varied in the case where the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm is from 0.09 to 0.12 (Experimental examples 4-1 to 4-3); however, the transmittance in 420 μm to 500 μm is slightly decreased in the case where the retardation Δn is 0.14 (Experimental example 4-4). Accordingly, it was found that a decrease in transmittance for wavelength light in 420 nm to 500 nm was further suppressed in the case where the retardation Δn was set within a range that was equal to or greater than 0.09 and smaller than 0.14. In other words, in the case where the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm was equal to or greater than 0.09 and smaller than 0.14, it was possible to cause the reflected image to be brighter in addition to that it was possible to reduce the coloring in the mirror surface state. 
     The present disclosure has been described above referring to some embodiments; however, the present disclosure is not limited to the embodiments described above, and is variously modifiable. For example, the materials, the thicknesses, etc. of the respective layers described in the foregoing embodiments are mere examples and non-limiting. Other materials and other thicknesses may be employed. For example, the Δn·d of the liquid crystal layer  22 C may be set to be equal to or greater than 0.54 μm and equal to or smaller than 1.7 μm. Further, the retardation Δn of the liquid crystal layer  22 C with respect to the wavelength light of 550 nm may be set to fall within a range that is equal to or greater than 0.07 and smaller than 0.09 or within a range that is equal to or greater than 0.14 and equal to or smaller than 0.16. 
     Further, a polarization conversion member may be disposed between the display section  10  and the display switching section  20 . For example, a retardation plate may be used as the polarization conversion member. The retardation plate may be a half-wave retardation plate. In that case, when the polarized light outputted from the display section  10  passes through the polarization conversion member (for example, the half-wave retardation plate), that polarized light is converted into the second linearly-polarized light having the oscillation plane that is orthogonal to the first linearly-polarized light. In a case where the polarization absorption axis of the polarization member (the absorption-type polarization plate  11 ) that is close to the display switching section in the display section  10  and the polarization absorption axis of the reflection-type polarization member (the reflection-type polarization plate  21 ) in the display switching section  20  are different from each other by 90 degrees, it is possible to cause the polarization absorption axis of the absorption-type polarization plate  11  in the display section  10  and the polarization absorption axis of the reflection-type polarization plate  21  in the display switching section  20  to coincide with each other by disposing the polarization conversion member between the display section  10  and the display switching section  20 . 
     Moreover, for example, the description has been given specifically referring to the configurations of the display units  1  to  7  and the electronic apparatus  100  in the foregoing embodiments; however, it is not necessary to provide all of the components, and other components may be also provided. 
     11. NINTH EMBODIMENT 
     [Configuration] 
       FIG. 15  illustrates an example of a schematic configuration of a display unit  101  according to a ninth embodiment of the present disclosure. The display unit  101  is a so-called mirror display, and has a function of performing alternate switching between a mirror state and a display state. The display unit  101  includes a display section  110 , a display switching section  120 , and a driving circuit  130 , for example. The display section  110  corresponds to one specific example of a “display section” in the present disclosure. The display switching section  120  corresponds to one specific example of an “optical device” in the present disclosure. 
       FIG. 16  illustrates an example of a cross-sectional configuration of the display section  110  and the display switching section  120 . (A) of  FIG. 17  and (A) of  FIG. 18  each conceptually illustrate an example of workings of the display section  10  and the display switching section  120  in a case where a voltage is applied to the display switching section  120  (when the voltage in ON). (B) of  FIG. 17  and (B) of  FIG. 18  each conceptually illustrate an example of workings of the display section  110  and the display switching section  120  in a case where no voltage is applied to the display switching section  120  (when the voltage is OFF). 
     (Display Section  110 ) 
     The display section  110  has an output surface  110 A that outputs linearly-polarized light as image light. The display section  110  has a polarization plate on the output surface  110 A, for example. This polarization plate is an absorption-type polarization plate that has a polarization axis AX 3 , and absorbs light having a polarization component that is orthogonal to the polarization axis AX 3 . The display section  110  outputs, from the output surface  110 A, image light L 102  having a polarization axis ax 2  that is parallel to the polarization axis AX 3  on the basis of an image signal Vsig and a timing signal TP that are supplied from the driving circuit  130 , for example. The display section  110  is configured to include a liquid crystal panel in which the foregoing polarization plate is provided on the output surface  110 A, for example. A display state of the liquid crystal panel used for the display section  110  is in the TN (Twisted Nematic) mode, the VA (Vertical Alignment) mode, the IPS (In Plane Switching) mode, the FFS (Fringe Field Switching) mode, the STN (Super Twisted Nematic) mode, or the ECB (Electrically Controlled Birefringence) mode, for example. The liquid crystal panel used for the display section  110  may be a light-emission-type panel that has a backlight or may be a reflection-type panel without a backlight. The display section  110  may also be an organic EL panel in which the foregoing polarization plate is provided on the output surface  110 A. 
     (Display Switching Section  120 ) 
     The display switching section  120  is attached to the display section  110  with the output surface  110 A in between, for example. The display switching section  120  has a polarization control layer  122 , a polarization layer  121  disposed on one surface side of the polarization control layer  122 , as well as a first reflection layer  123  and a second reflection layer  124  that are disposed on the other surface side of the polarization control layer  122 . The first reflection layer  123  and the second reflection layer  124  are disposed on the display section  110  side in a positional relationship with the polarization control layer  122 . The polarization control layer  122  corresponds to one specific example of a “polarization control layer” in the present disclosure. The polarization layer  121  corresponds to one specific example of a “polarization layer” in the present disclosure. The first reflection layer  123  corresponds to one specific example of a “first reflection layer” in the present disclosure. The second reflection layer  124  corresponds to one specific example of a “second reflection layer” in the present disclosure. 
     The polarization control layer  122  electrically switches a polarization state of light that enters the polarization control layer  122 , on the basis of a switching voltage Vsw supplied from the driving circuit  130 , for example. The switching voltage Vsw may be a constant direct current voltage, or may be a voltage that is varied cyclically. The polarization control layer  122  so performs a polarization control that the display switching section  120  is brought into the mirror state in a case where the switching voltage Vsw is applied, for example. The polarization control layer  122  so performs a polarization control that the display switching section  120  is brought into the display state in a case where the switching voltage Vsw is not applied, for example. In other words, the polarization control layer  122  so performs a polarization control that the display switching section  120  is brought into the mirror state or the display state on the basis of the switching voltage Vsw supplied from the driving circuit  130 . Here, the mirror state refers to a state in which entering light (polarized light L 101 ′) from the polarization layer  121  side is reflected by the first reflection layer  123 . Further, the display state refers to a state in which entering light (the image light L 102 ) from the display section  110  side is allowed to pass through by the display switching section  120 . 
     The polarization control layer  122  controls polarization of light entering from the polarization layer  121  side or the first reflection layer  123  side on the basis of the control performed by the driving circuit  130 . The polarization control layer  122  so controls polarization of light that has entered the polarization control layer  122  that the polarization axis of the light that has entered the polarization control layer  122  is varied by an angle of an odd multiple of 90 degrees or is not varied substantially, on the basis of the control performed by the driving circuit  130 . The polarization control layer  122  controls the polarization of the light that has entered from the polarization layer  121  side that a polarization axis (a polarization axis ax 1  of the polarized light L 101 ′) of the light that has entered from the polarization layer  121  side is parallel or orthogonal to a polarization axis AX 2  of the first reflection layer  123 , on the basis of the control performed by the driving circuit  130 . The polarization control layer  122  controls the polarization of the light that has entered from the first reflection layer  123  side that a polarization axis (the polarization axis ax 2  of the image light L 102 ) of the light that has entered from the first reflection layer  123  side is parallel or orthogonal to a polarization axis AX 1  of the polarization layer  121 , on the basis of the control performed by the driving circuit  130 . 
     The polarization control layer  122  is configured to include a liquid crystal layer  122 A and a pair or a plurality of pairs of light transmissive electrodes  122 B and  122 C that sandwich the liquid crystal layer  122 A in between, for example. A display state of the liquid crystal layer  122 A is in the TN (Twisted Nematic) mode, the ECB (Electrically Controlled Birefringence) mode, the STN (Super Twisted Nematic) mode, the BTN (Bistable Twisted Nematic) mode, the ferroelectric liquid crystal mode, or the antiferroelectric liquid crystal mode, for example. 
     As illustrated in (A) of  FIG. 17  and (A) of  FIG. 18 , for example, the liquid crystal layer  122 A allows the light that has entered the liquid crystal layer  122 A to pass through as it is without rotating its polarization axis when a voltage is applied to the pair or the plurality of pairs of the light transmissive electrodes  122 B and  122 C. As illustrated in (B) of  FIG. 17  and (B) of  FIG. 18 , for example, the liquid crystal layer  122 A varies the polarization axis of the light that has entered the liquid crystal layer  122 A by an angle of an odd multiple of 90 degrees when no voltage is applied to the pair or the plurality of pairs of the light transmissive electrodes  122 B and  122 C. 
     The light transmissive electrodes  122 B and  122 C are each a sheet-like electrode for applying an electric field to the entire liquid crystal layer  122 , for example. The light transmissive electrodes  122 B and  122 C are each configured of a material that allows the polarized light L 101 ′ and the image light L 102  to pass through, and is configured of ITO (Indium Tin Oxide), for example. Edges of the light transmissive electrodes  122 B and  122 C are preferably provided outside of a region that faces the first reflection layer  123 . 
     The polarization layer  121  has the polarization axis AX 1  (a transmission axis). The polarization layer  121  allows a polarization component that is parallel to the polarization axis AX 1  to pass through and absorbs a polarization component that is orthogonal to the polarization axis AX 1  in light entering the polarization layer  121 . The polarization axis AX 1  of the polarization layer  121  is orthogonal to the polarization axis AX 2  of the first reflection layer  123  as illustrated in (A) of  FIG. 17  and (B) of  FIG. 17 , for example. It is to be noted that the polarization axis AX 1  of the polarization layer  121  may be parallel to the polarization axis AX 2  of the first reflection layer  123  as illustrated in (A) of  FIG. 18  and (B) of  FIG. 18 , for example. 
     The first reflection layer  123  is disposed between the polarization control layer  122  and the second reflection layer  124 . The first reflection layer  123  is configured of a reflective polarization layer. The reflective polarization layer that is used for the first reflection layer  123  has the polarization axis AX 2  (the transmission axis) that is parallel or orthogonal to the polarization axis AX 1  of the polarization layer  121 . The reflective polarization layer that is used for the first reflection layer  123  allows a polarization component that is parallel to the polarization axis AX 2  to pass through and reflects a polarization component that is orthogonal to the polarization axis AX 2  in light entering the first reflection layer  123 . The polarization axis AX 2  is parallel to the polarization axis ax 2  of the image light L 102 . Accordingly, the first reflection layer  123  allows the image light L 102  or linearly-polarized light having a polarization axis that is parallel to the polarization axis ax 2  of the image light L 102  to pass through, and reflects linearly-polarized light having a polarization axis that is orthogonal to the polarization axis ax 2  of the image light L 102 . 
     The first reflection layer  123  is configured of a multi-layer reflective birefringent polarization film disclosed in the specification of International Publication WO95/27919 or a cholesteric liquid crystal layer sandwiched by a pair of quarter-wave retardation plates, for example. DBEF (registered trademark of 3M Company) can be mentioned as the multi-layer reflective birefringent polarization film described above, for example. 
     The second reflection layer  124  is disposed on the display section  120  side in a positional relationship with the first reflection layer  123 . The second reflection layer  124  has a single or a plurality of openings  124 A. The single or the plurality of openings  124 A have a shape that is not particularly limited. For example, the shape of the single or the plurality of openings  124 A is a rectangular shape, any polygonal shape, a circular shape, an elliptical shape, or a shape of a combination thereof. The single or the plurality of openings  124 A are filled with airspace (atmosphere), for example. It is to be noted that the single or the plurality of openings  124 A may be filled with an adhesive layer  127  or an adhesive layer  140  which is described later. The second reflection layer  124  has a reflection surface  124 B at a position surrounding the single or the plurality of openings  124 A. The reflection surface  124 B is formed at least on a surface on the polarization control layer  122  side out of the surface on the polarization control layer  122  side and the surface on the display section  120  side of the second reflection layer  124 . For example, as illustrated in  FIGS. 16 to 18 , in a case where the second reflection layer  124  has the single opening  124 , the reflection surface  124 B is a circular reflection surface that is provided on the periphery of the single opening  124 A and along an outer edge of the first reflection layer  123 . In this case, the single opening  124 A is smaller than the polarization plate  121 , the polarization control layer  122 , and the first reflection layer  123 . In other words, the reflection surface  124 B is disposed at least at a position that faces the first reflection layer  123 . Further, the single opening  124 A may be as large as the output surface  110 A of the display section  110 , or may be smaller than the output surface  110 A of the display section  110 . 
       FIG. 19  illustrates an example of a planar configuration of the second reflection layer  124 . In a case where the second reflection layer  124  has the plurality of openings  124 A, the shapes of the respective openings  124 A may be different from each other. For example, as illustrated in  FIG. 19 , one of the openings  124 A may have a circular shape, and the other of the openings  124 A may have a rectangular shape. 
     The second reflection layer  124  is configured of a metallic reflection layer, a multi-layered reflection layer, or a reflective polarization layer, for example.  FIG. 20  illustrates an example of the planar configuration of the second reflection layer  124  in a case where the reflective polarization layer is used as the second reflection layer  124 . The reflective polarization layer used for the second reflection layer  124  has the polarization axis AX 3  (the transmission axis) that is orthogonal to the polarization axis AX 2  (the transmission axis) of the first reflection layer  123 . The reflective polarization layer used for the second reflection layer  124  allows a polarization component that is parallel to the polarization axis AX 3  to pass through and reflects a polarization component that is orthogonal to the polarization axis AX 3  in the light that enters the second reflection layer  124 . The polarization axis AX 3  is orthogonal to the polarization axis AX 2  (the transmission axis) of the first reflection layer  123  as described above. Accordingly, the reflective polarization layer used for the second reflection layer  124  reflects light that has passed through the first reflection layer  123  (the linearly-polarized light). 
     The reflective polarization layer used for the second reflection layer  124  is configured of the reflective birefringent polarization film disclosed in the specification of International Publication WO95/27919 or a cholesteric liquid crystal layer sandwiched by a pair of quarter-wave retardation plates, for example. DBEF (registered trademark of 3M Company) can be mentioned as the reflective birefringent polarization film described above, for example. 
       FIG. 21  illustrates an example of wavelength dependence of luminance of the light that has passed through the respective reflective polarization layers when non-polarized light having predetermined light intensity is applied to three reflective polarization layers that are suitable to be used as the first reflection layer  123  and the second reflection layer  124 . The luminance on a vertical axis of  FIG. 21  is represented by a rate (%) in a case where the luminance of the applied light is 100%.  FIG. 21  illustrates a result of measurement that is performed under a condition that the three reflective polarization layers that are formed of the same material are set as targets of the measurement. 
     The reflective polarization layers used as the first reflection layer  123  and the second reflection layer  124  are configured of the same material as each other, for example. In this case, a reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is equal to or less than 10% in the wavelength range (for example, a wavelength range including 450 nm, 550 nm, and 650 nm) of the polarized light  101 ′ and the image light L 102  is preferably used as the first reflection layer  123  and the second reflection layer  124 , for example. It is to be noted that the reflective polarization layers used as the first reflection layer  123  and the second reflection layer  124  may be configured of materials different from each other. In this case, a reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is greater than 10% in the wavelength range (for example, a wavelength range including 450 nm, 550 nm, and 650 nm) of the polarized light  101 ′ and the image light L 102  is preferably used as the first reflection layer  123  and the second reflection layer  124 , for example. 
     The display switching section  120  is configured of a stack in which respective layers are stacked with adhesive layers, as illustrated in  FIG. 16 , for example. The polarization layer  121  and the polarization control layer  122  are attached to each other with an adhesive layer  125 , for example. The polarization control layer  122  and the first reflection layer  123  are attached to each other with an adhesive layer  126 , for example. The first reflection layer  123  and the second reflection layer  124  are attached to each other with an adhesive layer  127 , for example. Further, the display section  110  and the display switching section  120  are attached to each other with an adhesive layer  140 , for example. The adhesive layer  125 , the adhesive layer  126 , the adhesive layer  127 , and the adhesive layer  140  are configured of a light transmissive adhesive agent, and are preferably configured of an adhesive agent that has small haze and small hue. It is to be noted that the display switching section  120  may include the respective layers that are so disposed as to face each other with airspace in between as illustrated in  FIG. 17  and  FIG. 18 , for example. 
     (Driving Circuit  130 ) 
     Next, the driving circuit  130  is described. For example, as illustrated in  FIG. 15 , the driving circuit  130  includes a signal processing circuit  131 , a timing generating circuit  132 , a driver  133 , and a display switching controlling circuit  134 . The display switching controlling circuit  134  corresponds to one specific example of a “controlling section” in the present disclosure. 
     The signal processing circuit  131 , the timing generating circuit  132 , and the driver  133  control the display section  110 . The signal processing circuit  131  generates an image signal DA for the display section  110  on the basis of an image signal Din, and outputs the generated image signal DA to the driver  133 , for example. The timing generating circuit  132  generates a timing pulse TP for controlling horizontal and vertical writing transmission that also serves as a driving timing pulse for the display section  110 , on the basis of a horizontal synchronization signal and a vertical synchronization signal included in a control signal Tin. The timing generating circuit  132  outputs, to the display section  110 , the generated timing pulse TP at predetermined timing, for example. For example, in a case where a switching signal Ss is supplied from the display switching controlling circuit  134 , the timing generating circuit  132  outputs, to the display section  110 , the generated timing pulse TP at timing based on the switching signal Ss, for example. The timing generating circuit  132  further generates a clock CLK for the driver  133 , and outputs the generated clock CLK to the driver  133 . 
     The driver  133  has a sample and hold circuit, a D/A conversion circuit, and a driver circuit, for example. The sample and hold circuit performs a parallelization process on the serial digital image signal DA, and performs expansion into a plurality of parallel image signals. The sample and hold circuit outputs, to the D/A conversion circuit, the image signals that have been subjected to phase expansion at timing based on the clock CLK from the timing generating circuit  32 . The D/A conversion circuit converts the image signals (the image signals that have been subjected to phase expansion) supplied from the sample and hold circuit into analog signals, and outputs the analog signals to the driver circuit. The driver circuit outputs the analog image signal Vsig to the display section  110  at predetermined timing based on the clock CLK outputted from the timing generating circuit  132 . 
     The display switching controlling circuit  134  controls the display switching section  120 . The display switching controlling circuit  134  so controls the polarization control layer  122  that the polarization axis ax 1  of the polarized light L 101 ′ that has entered the polarization control layer  122  from the polarization layer  121  side to be parallel or orthogonal to the polarization axis AX 2  of the first reflection layer  23 . The display switching controlling circuit  134  generates the switching voltage Vsw from a switching signal Sin, and outputs the generated switching voltage Vsw to the display switching section  120  at predetermined timing. The switching voltage Vsw is a driving voltage for switching the display switching section  120  from the mirror state to the display state or for switching the display switching section  120  from the display state to the mirror state. For example, the display switching controlling circuit  134  so outputs the switching signal Ss to the timing generating circuit  132  in synchronization with the output timing of the switching voltage Vsw that the output of the image light L 102  from the display section  110  is started at timing at which the display switching section  120  is switched from the mirror state to the display state. For example, the display switching controlling circuit  134  so outputs the switching signal Ss to the timing generating circuit  132  in synchronization with the output timing of the switching voltage Vsw that the output of the image light L 102  from the display section  110  is stopped at timing at which the display switching section  120  is switched from the display state to the mirror state. 
     [Operation] 
     Next, an example of an operation of the display unit  101  is described. 
     (Display State) 
     The switching signal Sin for performing the switching from the mirror state to the display state is supplied to the display switching controlling circuit  134 . In response thereto, the display switching controlling circuit  134  generates the switching voltage Vsw from the switching signal Sin, and outputs the generated switching voltage Vsw to the display switching section  120  at predetermined timing. The display switching controlling circuit  134  further generates the switching signal Ss from the switching signal Sin, and outputs the generated switching signal Ss to the timing generating circuit  132  in synchronization with the output timing of the switching voltage Vsw. On the basis of the switching signal Ss, the timing generating circuit  132  outputs the timing pulse TP to the display section  110  at the predetermined timing, and outputs the clock CLK to the driver  133  at the predetermined timing. The driver  133  generates the image signal Vsig from the image signal DA supplied from the signal processing circuit  131 , and outputs the generated image signal Vsig to the display section  110 . 
     When the switching voltage Vsw is supplied to the display switching section  120 , the display switching section  120  is switched from the mirror state to the display state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and the light after passing through the polarization layer  121  (the polarized light L 101 ′) passes through the polarization control layer  122  and the first reflection layer  123 , as illustrated in (B) of  FIG. 17  and (A) of  FIG. 18 , for example. Light that has entered the reflection surface  124 B of the second reflection layer  124  out of the light after passing through the first reflection layer  123  (the polarized light L 101 ′) is reflected by the reflection surface  124 B, and is outputted to the outside via the first reflection layer  123 , the polarization control layer  122 , and the polarization layer  121 . Light that has entered the single or the plurality of openings  124 A of the second reflection layer  124  out of the light (the polarized light L 101 ′) that has passed through the first reflection layer  123  enters the output surface  110 A of the display section  110  via the single or the plurality of openings  124 A. In a case where the display section  110  is provided with a light-emission-type panel, the image light L 102  having the polarization axis ax 2  is outputted from the output surface  110 A irrelevant to the light entering the output surface  110 A. In a case where the display section  110  is provided with a reflection-type panel, the light (the polarized light L 101 ′) that has entered the output surface  110 A is reflected and modulated by the reflection-type panel of the display section  110 . As a result, the image light L 102  is outputted from the output surface  110 A. The image light L 102  outputted from the output surface  110 A is outputted to the outside via the single or the plurality of openings  124 A, the first reflection layer  123 , the polarization control layer  122 , and the polarization layer  121 . At this time, the user feels as if an image emerges in a mirror upon viewing the display switching section  120 , for example. 
     (Mirror State) 
     The switching signal Sin for performing switching from the display state to the mirror state is supplied to the display switching controlling circuit  134 . In response thereto, the display switching controlling circuit  134  generates the switching voltage Vsw from the switching signal Sin, and outputs the generated switching voltage Vsw to the display switching section  120  at predetermined timing. The display switching controlling circuit  134  further outputs a signal that stops calculations in the signal processing circuit  131 , the timing generating circuit  132 , and the driver  133  to the signal processing circuit  131 , the timing generating circuit  132 , and the driver  133  in synchronization with the output timing of the switching voltage Vsw. In response thereto, the signal processing circuit  131 , the timing generating circuit  132 , and the driver  133  stop the calculations. 
     As a result of the supply of the switching voltage Vsw, the display switching section  120  is switched from the display state to the mirror state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and light (the polarized light L 101 ′) after passing through the polarization layer  121  passes through the polarization control layer  122 , is thereafter reflected by the first reflection layer  123 , and is outputted to the outside via the polarization control layer  122  and the polarization layer  121 , as illustrated in (A) of  FIG. 17  and (B) of  FIG. 18 , for example. It is to be noted that, even in a case where the image light L 102  is outputted from the output surface  110 A, the image light L 102  is absorbed by the polarization layer  121 . At this time, the user feels as if the user is looking at a mirror upon viewing the display switching section  120 , for example. 
     [Effects] 
     Next, effects of the display unit  101  are described. 
     In a case where it is desired to perform switching only in a certain region or to perform display in a specific shape upon performing the switching of the image light, for example, it is necessary to provide the electrode of the liquid crystal panel for switching with a shape based on, for example, its use or its purpose. In such a case, however, it is necessary to perform photolithography with changing masks for the uses or the purposes upon forming the electrode of the liquid crystal panel for switching. This greatly increases the manufacturing cost. 
     In contrast, in the display unit  101 , the switching between the mirror state and the display state is performed by a polarization control by the polarization control layer  122 . In the mirror state, the polarization control layer  122  is so controlled that the polarization axis ax 1  of the polarized light L 101 ′ that has entered the polarization control layer  122  from the polarization layer  121  side is orthogonal to the polarization axis AX 2  of the first reflection layer  123 . Accordingly, in the mirror state, the light that has entered the polarization layer  121  is reflected by the first reflection layer  123  and returns. Therefore, the surface of the display switching section  120  functions as a mirror for the user. In the display state, the polarization control layer  122  is so controlled that the polarization axis (for example, the polarization axis ax 2  of the image light L 102 ) of the polarized light that has entered the polarization control layer  122  from the first reflection layer  123  side via the single or the plurality of openings  124 A is parallel to the polarization axis AX 1  of the polarization layer  121 , for example. Accordingly, in the display state, the polarized light (for example, the image light L 102 ) that has entered the polarization control layer  122  from the first reflection layer  123  side via the single or the plurality of openings  124 A passes through the polarization layer  121  to reach the user. Therefore, the entire surface or part of the surface of the display switching section  120  functions like a display for the user. 
     Moreover, in the display unit  101 , for example, the size and the shape of the single or the plurality of openings  124 A are formable, for example, by processing a sheet-like member or molding a material in a molten state in a process of manufacturing the second reflection layer  124 . Accordingly, in a case where it is desired to perform switching only of the display state in a certain region or to perform display in a desired shape in the display unit  101 , it is not necessary to perform photolithography with changing masks for the uses or the purposes upon forming the electrodes (the light transmissive electrodes  122 B and  122 C) that are used for the control of the polarization control layer  122 . It is to be noted that, even in a case where the plurality of pairs of light transmissive electrodes  122 B and  122 C are provided for the polarization control layer  122 , it is not necessary to change, for example, the size and the shape of the plurality of pairs of light transmissive electrodes  122 B and  122 C depending on, for example, the use or the purpose of the display unit  101 . One reason for this is that it is sufficient that, for example, the size and the shape of the single or the plurality of openings  124 A of the second reflection layer  24  are changed depending on, for example, the use or the purpose of the display unit  101 . 
     As described above, in the display unit  101 , the polarization control by the polarization control layer  122  allows the display switching section  120  to function like a mirror or a display. Further, the necessity of providing the polarization control layer  122  with a plurality of electrodes for the polarization control is eliminated. Accordingly, it is possible to suppress a great increase in manufacturing cost. 
     Moreover, in the display unit  101 , in a case where the reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is equal to or smaller than 10% in the wavelength range of the polarized light L 101 ′ and the image light L 102  is used as each of the first reflection layer  123  and the second reflection layer  124 , the light reflected by the first reflection layer  123  and the light reflected by the second reflection layer  124  are allowed to be almost the same in, for example, luminance and hue when the switching between the mirror state and the display state is performed. It is thus possible to make it difficult for the user to notice the change in, for example, luminance or hue around the image generated by the image light L 102  when the switching between the mirror state and the display state is performed. As a result, it is possible to provide the user with an experience as if an image emerges from a mirror when the display switching section  120  is switched from the mirror state to the display state. Further, it is possible to provide the user with an experience as if the image emerged in the mirror disappears into the mirror when the display switching section  120  is switched from the display state to the mirror state. 
     Moreover, in the display unit  101 , in a case where the reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is equal to or smaller than 10% in the wavelength range of the polarized light L 101 ′ and the image light L 102  is used as each of the first reflection layer  123  and the second reflection layer  124 , the light reflected by the first reflection layer  123  and the light reflected by the second reflection layer  124  are allowed to be different enough in, for example, luminance and hue for the user to recognize, when switching between the mirror state and the display state is performed. This allows a region around the image generated by the image light L 2  is allowed to be different in, for example, luminance and hue from those in the mirror state, when the display switching section  20  is switched from the mirror state to the display state. As a result, it is possible to perform an act of providing an apparent change, for example, when the switching is performed from the mirror state to the display state or when the switching is performed from the display state to the mirror state. For example, it is possible to perform an act of accentuating the image generated by the image light L 102 , for example, by decreasing the luminance in the region around the image generated by the image light L 102  or by changing the color temperature in the region around the image generated by the image light L 102 . 
     Moreover, in the display unit  101 , in a case where the edges of the light transmissive electrodes  122 B and  122 C are provided outside the region facing the first reflection layer  123 , it is possible to prevent disturbance in the alignment state of the liquid crystal at the edges of the light transmissive electrodes  122 B and  122 C from being visually recognized by the user as a display error. Moreover, in the display unit  101 , the first reflection layer  123  is disposed closer to the polarization control layer  122  than the second reflection layer  124 . Therefore, the reflection surface at a time when the display switching section  120  is in the mirror state is configured only of the surface of the first reflection layer  123 . Accordingly, it is possible to avoid occurrence of a display error resulting from the single or the plurality of openings  124 A. 
     12. MODIFICATION EXAMPLES 
     Modification examples of the display unit  101  according to the embodiment described above are described below. It is to be noted that the numerals same as numerals attached in the foregoing embodiment are attached below to components that are common to the foregoing embodiment. Further, components different from those in the foregoing embodiment are described mainly, and the description of the components common to the foregoing embodiment is omitted where appropriate. 
     Modification Example A 
       FIG. 22  illustrates a modification example of the cross-sectional configuration of the display section  110  and the display switching section  120 . (A) of  FIG. 23  and (A) of  FIG. 24  each conceptually illustrate an example of workings of the display section  110  and the display switching section  120  in a case where a voltage is applied to the display switching section  120 . (B) of  FIG. 23  and (B) of  FIG. 24  each conceptually illustrate an example of workings of the display section  110  and the display switching section  120  in a case where no voltage is applied to the display switching section  120 . 
     In the foregoing embodiment, the first reflection layer  123  is disposed between the polarization control layer  122  and the second reflection layer  124 ; however, the second reflection layer  124  may be disposed between the polarization control layer  122  and the first reflection layer  123 . In the present modification example, the second reflection layer  124  is configured of a reflective polarization layer. The reflective polarization layer used for the second reflection layer  124  has a polarization axis AX 4  (a transmission axis) that is orthogonal to the polarization axis AX 2  (the transmission axis) of the first reflection layer  123 . A portion corresponding to the reflection surface  124 B out of the reflective polarization layer used for the second reflection layer  124  allows a polarization component that is parallel to the polarization axis AX 4  to pass through and reflects a polarization component that is orthogonal to the polarization axis AX 4  in the light entering the second reflection layer  124 . The polarization axis AX 4  is orthogonal to the polarization axis AX 2  (the transmission axis) of the first reflection layer  123  as described above. Accordingly, the portion corresponding to the reflection surface  124 B out of the reflective polarization layer used for the second reflection layer  124  allows the light (the linearly-polarized light) that has been reflected by the first reflection layer  123  to pass through. 
     The reflective polarization layers used as the first reflection layer  123  and the second reflection layer  124  are configured of the same material as each other, for example. In this case, a reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is equal to or less than 10% in the wavelength range (for example, a wavelength range including 450 nm, 550 nm, and 650 nm) of the polarized light L 101 ′ and the image light L 102  is preferably used as each of the first reflection layer  123  and the second reflection layer  124 , for example. It is to be noted that the reflective polarization layers used as the first reflection layer  123  and the second reflection layer  124  may be configured of materials different from each other. In this case, a reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is greater than 10% in the wavelength range (for example, a wavelength range including 450 nm, 550 nm, and 650 nm) of the polarized light L 101 ′ and the image light L 102  is preferably used as each of the first reflection layer  123  and the second reflection layer  124 , for example. 
     (Display State) 
     In the display unit  101  of the present modification example, when the switching voltage Vsw is supplied to the display switching section  120 , the display switching section  120  is switched from the mirror state to the display state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and the light after passing through the polarization layer  121  (the polarized light L 101 ′) passes through the polarization control layer  122 , as illustrated in (B) of  FIG. 23  and (A) of  FIG. 24 , for example. Light that has entered the reflection surface  124 B of the second reflection layer  124  out of the light after passing through the polarization control layer  122  (the polarized light L 101 ′) is reflected by the reflection surface  124 B, and is outputted to the outside via the polarization control layer  122  and the polarization layer  121 . Light that has entered the single or the plurality of openings  124 A of the second reflection layer  124  out of the light (the polarized light L 101 ′) that has passed through the polarization control layer  122  enters the output surface  110 A of the display section  110  via the single or the plurality of openings  124 A after passing through the first reflection layer  123 . In a case where the display section  110  is provided with a light-emission-type panel, the image light L 102  having the polarization axis ax 2  is outputted from the output surface  110 A irrelevant to the light entering the output surface  110 A. In a case where the display section  110  is provided with a reflection-type panel, the light (the polarized light L 101 ′) that has entered the output surface  110 A is reflected and modulated by the reflection-type panel of the display section  110 . As a result, the image light L 102  is outputted from the output surface  110 A. The image light L 102  outputted from the output surface  110 A is outputted to the outside via the first reflection layer  123 , the single or the plurality of openings  124 A, the polarization control layer  122 , and the polarization layer  121 . At this time, the user feels as if an image emerges in a mirror upon viewing the display switching section  120 , for example. 
     (Mirror State) 
     In the display unit  101  of the present modification example, as a result of the supply of the switching voltage Vsw, the display switching section  120  is switched from the display state to the mirror state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and light (the polarized light L 101 ′) after passing through the polarization layer  121  passes through the polarization control layer  122  and the second reflection layer  124 , is thereafter reflected by the first reflection layer  123 , and is outputted to the outside via the second reflection layer  124 , the polarization control layer  122 , and the polarization layer  121 , as illustrated in (A) of  FIG. 23  and (B) of  FIG. 24 , for example. It is to be noted that, even in a case where the image light L 102  is outputted from the output surface  110 A, the image light L 102  is absorbed by the polarization layer  121 . At this time, the user feels as if the user is looking at a mirror upon viewing the display switching section  120 , for example. 
     Next, effects of the display unit  101  of the present modification example are described. In the present modification example, for example, the size and the shape of the single or the plurality of openings  124 A are formable, for example, by processing a sheet-like member or molding a material in a molten state in a process of manufacturing the second reflection layer  124 . Accordingly, in the present modification example, in a case where it is desired to perform switching only of the display state in a certain region or to perform display in a desired shape, it is not necessary to perform photolithography with changing masks for the uses or the purposes upon forming the electrodes (the light transmissive electrodes  122 B and  122 C) that are used for the control of the polarization control layer  122 . It is to be noted that, even in a case where the plurality of pairs of light transmissive electrodes  122 B and  122 C are provided for the polarization control layer  122 , it is not necessary to change, for example, the size and the shape of the plurality of pairs of light transmissive electrodes  122 B and  122 C depending on, for example, the use or the purpose of the display unit  101 . One reason for this is that it is sufficient that, for example, the size and the shape of the single or the plurality of openings  124 A of the second reflection layer  124  are changed depending on, for example, the use or the purpose of the display unit  101 . As described above, in the present modification example, the polarization control by the polarization control layer  122  allows the display switching section  120  to function like a mirror or a display. Further, the necessity of providing the polarization control layer  122  with a plurality of electrodes for the polarization control is eliminated. Accordingly, it is possible to suppress a great increase in manufacturing cost. 
     Moreover, in the present modification example, in a case where the reflective polarization layer having a difference in luminance (%) illustrated in  FIG. 21  that is equal to or smaller than 10% in the wavelength range of the polarized light L 101 ′ and the image light L 102  is used as each of the first reflection layer  123  and the second reflection layer  124 , the light reflected by the first reflection layer  123  after passing through a portion, of the second reflection layer  124 , other than the openings  124 A and the light reflected by the first reflection layer  123  after passing through a portion, of the second reflection layer  124 , corresponding to the openings  124 A are allowed to be almost the same in, for example, luminance and hue upon switching between the mirror state and the display state. It is thereby possible to make it difficult for the user to notice the difference in, for example, luminance or hue between the region in which image is generated by the image light L 102  and the region around the region in which the image is generated by the image light L 102  when the display switching section  120  is switched between the mirror state and the display state. 
     Modification Example B 
       FIG. 25  illustrates a modification example of the cross-sectional configuration of the display section  110  and the display switching section  120 . (A) of  FIG. 26  and (A) of  FIG. 27  each conceptually illustrate an example of workings of the display section  110  and the display switching section  120  in a case where a voltage is applied to the display switching section  120 . (B) of  FIG. 26  and (B) of  FIG. 27  each conceptually illustrate an example of workings of the display section  110  and the display switching section  120  in a case where no voltage is applied to the display switching section  120 . 
     In the foregoing embodiment, two reflection layers (the first reflection layer  123  and the second reflection layer  124 ) are provided in the display switching section  120 ; however, one of the reflection layers (the second reflection layer  124 ) may not be provided, and a circular bezel  111  that surrounds the output surface  110 A of the display section  110  may also have the function of the second reflection layer  124 . In other words, in the present modification example, the second reflection layer  124  is not provided, and further, the display section  110  has the circular bezel  111  that is provided along an outer edge of the display switching section  120 . The bezel  111  corresponds to one specific example of a “bezel” in the present disclosure. 
     The bezel  111  has a single opening  111 A. A shape of the opening  111 A is not particularly limited; however, the shape of the opening  111 A is a rectangular shape, any polygonal shape, a circular shape, an elliptical shape, or a shape of a combination thereof. The bezel  111  has a circular mirror surface  111 B at a position that surrounds the single opening  111 A. The mirror surface  111 B is formed on a surface on the display switching section  120  side of the bezel  111 . The mirror surface  111 B is provided on the periphery of the single opening  111 A and along an outer edge of the display switching section  120 . In this case, the single opening  111 A is smaller than the polarization plate  121 , the polarization control layer  122 , and the first reflection layer  123 . In other words, the mirror surface  111 B is disposed at least at a position that faces the first reflection layer  123 . At least a portion corresponding to the mirror surface  111 B out of the bezel  111  is configured of a metallic reflection layer or a multi-layered reflection layer, for example. 
     Next, an example of the operation of the display unit  101  is described. 
     (Display State) 
     In the display unit  101  of the present modification example, when the switching voltage Vsw is supplied to the display switching section  120 , the display switching section  120  is switched from the mirror state to the display state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and the light after passing through the polarization layer  121  (the polarized light L 101 ′) passes through the polarization control layer  122  and the first reflection layer  123 , as illustrated in (B) of  FIG. 26  and (A) of  FIG. 27 , for example. Light that has entered the mirror surface  111 B of the bezel  111  out of the light after passing through the first reflection layer  123  (the polarized light L 101 ′) is reflected by the mirror surface  111 B, and is outputted to the outside via the first reflection layer  123 , the polarization control layer  122 , and the polarization layer  121 . Light that has entered the opening  111 A of the bezel  111  out of the light (the polarized light L 101 ′) that has passed through the first reflection layer  123  enters the output surface  110 A of the display section  110  via the opening  111 A. In a case where the display section  110  is provided with a light-emission-type panel, the image light L 102  having the polarization axis ax 2  is outputted from the output surface  110 A irrelevant to the light entering the output surface  110 A. In a case where the display section  110  is provided with a reflection-type panel, the light (the polarized light L 101 ′) that has entered the output surface  110 A is reflected and modulated by the reflection-type panel in the display section  110 . As a result, the image light L 102  is outputted from the output surface  110 A. The image light L 102  outputted from the output surface  110 A is outputted to the outside via the opening  111 A, the first reflection layer  123 , the polarization control layer  122 , and the polarization layer  121 . At this time, the user feels as if an image emerges in a mirror upon viewing the display switching section  120 , for example. 
     (Mirror State) 
     In the display unit  101  of the present modification example, as a result of the supply of the switching voltage Vsw, the display switching section  120  is switched from the display state to the mirror state. At this time, when the non-polarized external light L 101  enters the polarization layer  121 , a polarization component that is parallel to the polarization axis AX 1  out of the external light L 101  passes through the polarization layer  121 , and light (the polarized light L 101 ′) after passing through the polarization layer  121  passes through the polarization control layer  122 , is thereafter reflected by the first reflection layer  123 , and is outputted to the outside via the polarization control layer  122  and the polarization layer  121 , as illustrated in (A) of  FIG. 26  and (B) of  FIG. 27 , for example. It is to be noted that, even in a case where the image light L 102  is outputted from the output surface  110 A, the image light L 102  is absorbed by the polarization layer  121 . At this time, the user feels, for example, as if the user is looking at a mirror upon viewing the display switching section  120 . 
     Next, effects of the display unit  101  of the present modification example are described. In the present modification example, the bezel  111  also has the function of the second reflection layer  124 . It is therefore not necessary to provide the second reflection layer for the display switching section  120 . Accordingly, in the present modification example, in a case where it is desired to perform switching only of the display state in a certain region or to perform display in a desired shape, it is not necessary to perform photolithography with changing masks for the uses or the purposes upon forming the electrodes (the light transmissive electrodes  122 B and  122 C) that are used for the control of the polarization control layer  122 . It is to be noted that, even in a case where the plurality of pairs of light transmissive electrodes  122 B and  122 C are provided for the polarization control layer  122 , it is not necessary to change, for example, the size and the shape of the plurality of pairs of light transmissive electrodes  122 B and  122 C depending on, for example, the use or the purpose of the display unit  101 . One reason for this is that it is sufficient that, for example, the size and the shape of the single or the plurality of openings  124 A of the second reflection layer  124  are changed depending on, for example, the use or the purpose of the display unit  101 . As described above, in the present modification example, the polarization control by the polarization control layer  122  allows the display switching section  120  to function like a mirror or a display. Further, the necessity of providing the polarization control layer  122  with a plurality of electrodes for the polarization control is eliminated. Accordingly, it is possible to suppress a great increase in manufacturing cost. 
     Modification Example C 
       FIGS. 28A and 28B  each illustrate an example of an arrangement of a mirror layer  125  that is additionally provided to the display switching section  120  illustrated in  FIGS. 16, 22, and 25 . In the embodiment, the modification example A, and the modification example B described above, the display switching section  120  may further include a mirror layer  128 . The mirror layer  128  is provided at a position on the opposite side to the polarization control layer  122  in a relationship with the polarization layer  121 , and is provided along an outer edge or the periphery of the polarization layer  121 . The mirror layer  128  has a single opening  128 A. A shape of the opening  128 A is not particularly limited; however, the shape of the opening  128 A is a rectangular shape, any polygonal shape, a circular shape, an elliptical shape, or a shape of a combination thereof, for example. 
     The mirror layer  128  has a mirror surface  128 B at a position that surrounds the opening  128 A. The mirror surface  128 B is formed on a surface on the opposite side to the polarization layer  121  (in other words, on a front most surface of the display switching section  120 ). The mirror surface  128 B is a surface that is formed by depositing, for example, metal on a surface of metal or an organic material, for example. The mirror surface  128 B may be a surface of a metal member that is made of, for example, aluminum, iron, or an alloy thereof, for example. The mirror surface  128 B may perform specular reflection. 
     The mirror surface  128 B is a circular mirror surface that is provided on the periphery of the opening  128 A and along an outer edge or the periphery of the polarization layer  121 . In a case where the mirror layer  128  is provided along the outer edge of the polarization layer  121 , the opening  128 A is smaller than the polarization plate  121 . In this case, the mirror surface  128 B is provided at least at a position that faces the outer edge of the polarization layer  121 . In a case where the mirror layer  128  is provided along the periphery of polarization layer  121 , the opening  128 A is as large as the polarization plate  121 . In this case, the mirror surface  128 B is provided at a position that does not face the polarization layer  121 . 
     In the case where the mirror layer  128  is provided along the outer edge of the polarization layer  121 , the mirror layer  128  may be attached to the polarization layer  121  as illustrated in  FIG. 28A , or may not be attached to the polarization layer  121  and be so disposed as to be away from the polarization layer  121  as illustrated in  FIG. 28B , for example. In the case where the mirror layer  128  is provided along the periphery of the polarization layer  121 , the mirror layer  128  may be so disposed as to be away from the polarization layer  121  as illustrated in  FIG. 28B , or may be disposed at a position that allows the polarization layer  121  to be disposed inside the opening  128 A, for example. 
     In a case where only the single opening  124 A is provided in the second reflection layer  124 , the mirror surface  128 B is disposed at a position that does not face the opening  124 A, and further, is disposed at a position, in the reflection surface  124 B, that does not face at least an inner edge of the reflection surface  124 B. In a case where only the single opening  111 A is provided in the bezel  111 , the mirror surface  128 B is disposed at a position that does not face the opening  111 A, and further, is disposed at a position, in the reflection surface  111 B, that does not face at least an inner edge of the reflection surface  111 B. The mirror layer  128  is disposed at a position that does not interfere with an image when the display switching section  120  is in the display state. In other words, the mirror layer  128  has a role, in the display switching section  120 , that is similar to a role of the bezel  111  in the display section  110 . 
     Next, effects of the display unit  101  of the present modification example are described. In the present modification example, the mirror layer  128  is provided at a position, in the display switching section  120 , that does not interfere with an image when the display switching section  120  is in the display state. Accordingly, when the display switching section  120  is in the display state, an image is allowed to be displayed in a state that the image is surrounded by a mirror-like frame. As a result, it is possible to improve design properties at a time when the display switching section  120  is in the display state. Further, when the display switching section  120  is in the mirror state, the entire front most surface of the display switching section  120  is allowed to be in the mirror state. At this time, in the front most surface of the display switching section  120 , a reflectance and a hue in a region corresponding to the mirror layer  128  are slightly different from a reflectance and a hue in a region surrounded by the mirror layer  128 . Therefore, it is possible to cause the outer edge of the front most surface of the display switching section  120  to serve as a mirror-like frame having a different reflectance and a different hue when the display switching section  120  is in the mirror state. Accordingly, it is possible to improve the design properties at a time when the display switching section  120  is in the mirror state. 
     Modification Example D 
     In the embodiment, the modification example A, and the modification example B described above, the reflection surface  124 B may be a reflection surface that is provided on the periphery of the single of the plurality of openings  124 A and along the outer edge and the periphery of the first reflection layer  123 . In other words, the second reflection layer  124  may be larger than the polarization layer  121 , the polarization control layer  122 , and the first reflection layer  123 . 
     Next, effects of the display unit  101  of the present modification example are described. In the present modification example, the outer edge of the reflection surface  124 B is disposed at a position that does not face the polarization layer  121 , the polarization control layer  122 , and the first reflection layer  123 . Accordingly, when the display switching section  120  is in the display state, an image is allowed to be displayed in a state that the image is surrounded by a mirror-like frame. As a result, it is possible to improve design properties at a time when the display switching section  120  is in the display state. Further, when the display switching section  120  is in the mirror state, the entire front most surface of the display switching section  120  is allowed to be in the mirror state. At this time, in the front most surface of the display switching section  120 , a reflectance and a hue in a region corresponding to the outer edge of the reflection surface  124 B are slightly different from a reflectance and a hue in a region surrounded by the outer edge of the reflection surface  124 B. Therefore, it is possible to cause the outer edge of the front most surface of the display switching section  120  to serve as a mirror-like frame having a different reflectance and a different hue when the display switching section  120  is in the mirror state. Accordingly, it is possible to improve the design properties at a time when the display switching section  120  is in the mirror state. 
     Modification Example E 
     In the embodiment, the modification example A, and the modification example B described above, the display section  110  may have the circular bezel  111  that is provided along the periphery of the display switching section  120 . The bezel  111  corresponds to one specific example of the “bezel” in the present disclosure. 
       FIG. 29  illustrates a modification example of the cross-sectional configuration of the display section  110  and the display switching section  120 . The bezel  111  has the single bezel  111 A. A shape of the opening  111 A is not particularly limited; however, the shape of the opening  111 A is a rectangular shape, any polygonal shape, a circular shape, an elliptical shape, or a shape of a combination thereof, for example. The bezel  111  has a circular mirror surface  111 B at a position that surrounds the single opening  111 A. The mirror surface  111 B is formed on a surface on the display switching section  120  side of the bezel  111 . The mirror surface  111 B is provided along the periphery of the display switching section  120  and is so provided as to surround the output surface  110 A. The display switching section  120  is not in contact with the mirror surface  111 B, and the entire display switching section  120  or part of the display switching section  120  is contained inside the opening  111 A. The display switching section  120  and the output surface  110 A are attached to each other with the adhesive layer  140 , for example. 
     Next, effects of the display unit  101  of the present modification example are described. In the present modification example, the mirror surface  111 B is disposed at a position that does not face the display switching section  120 . Accordingly, when the display switching section  120  is in the display state, an image is allowed to be displayed in a state that the image is surrounded by a mirror-like frame. As a result, it is possible to improve design properties at a time when the display switching section  120  is in the display state. Further, when the display switching section  120  is in the mirror state, the entire front most surface of the display switching section  120  is allowed to be in the mirror state. At this time, a reflectance and a hue in a region corresponding to the mirror surface  111 B are slightly different from a reflectance and a hue in a region surrounded by the mirror surface  111 B. Therefore, it is possible to cause the periphery of the front most surface of the display switching section  120  to serve as a mirror-like frame having a different reflectance and a different hue when the display switching section  120  is in the mirror state. Accordingly, it is possible to improve the design properties at a time when the display switching section  120  is in the mirror state. 
     Modification Example F 
     In the embodiment and the modification examples A to E described above, the liquid crystal layer  122 A allows the light that has entered the liquid crystal layer  122 A to pass through as it is without rotating its polarization axis when a voltage is applied (when a voltage is ON), and varies the polarization axis of the light that has entered the liquid crystal layer  122 A by an angle of an odd multiple of 90 degrees when no voltage is applied (when the voltage is OFF). In the embodiment and the modification examples A to E described above, however, the liquid crystal layer  122 A may vary the polarization axis of the light that has entered the liquid crystal layer  122 A by an angle of an odd multiple of 90 degrees when the voltage is applied (when the voltage is ON), and may allow the light that has entered the liquid crystal layer  122 A to pass through as it is without rotating its polarization axis when no voltage is applied (when the voltage is OFF). 
     The present technology has been described above referring to the embodiments and the modification examples thereof; however, the present technology is not limited to the foregoing embodiments, etc., and may be variously modified. It is to be noted that the effects described in the present description are mere examples. The effects of the present technology are not limited to the effects described in the present description. The present technology may have effects other than the effects described in the present description. Further, the technology may have any of the following configurations.
     (1)
       A display unit including:   a display section that outputs a first linearly-polarized light as image light, the first linearly-polarized light having a first polarization axis; and   a display switching section that is disposed to face the display section, and performs switching between an image display mode in which the first linearly-polarized light is allowed to pass through and an external light reflection mode in which external light is reflected, in which   the display section includes a first absorption-type polarization member that allows the first linearly-polarized light to pass through and absorbs second linearly-polarized light having a second polarization axis that intersects the first polarization axis,   the display switching section includes a reflection-type polarization member, a switchable transmission polarization axis member, and a second absorption-type polarization member that are disposed in order in a direction being away from the display section,   the reflection-type polarization member allows the first linearly-polarized light to pass through and reflects the second linearly-polarized light,   the switchable transmission polarization axis member performs switching between a first mode in which the first linearly-polarized light is converted into the second linearly-polarized light to pass through and a second mode in which the first linearly-polarized light is allowed to pass through without being converted into the second linearly-polarized light,   the second absorption-type polarization member allows the first linearly-polarized light to pass through and absorbs the second linearly-polarized light, and   the second absorption-type polarization member has a hue b* value that is equal to or smaller than a hue b* value of the first absorption-type polarization member.   
       (2)
       The display unit according to (1), in which the polarization conversion member is a liquid crystal device that is one of a TN (Twisted Nematic) liquid crystal device, an STN (Super Twisted Nematic) liquid crystal device, a VA (Vertical Alignment) liquid crystal device, an antiferroelectric liquid crystal device, and a ferroelectric liquid crystal device.   
       (3)
       The display unit according to (1) or (2), in which the polarization conversion member is a bistable liquid crystal display device or a tristable liquid crystal display device.   
       (4)
       The display unit according to any one of (1) to (3), in which the second absorption-type polarization member is provided inside the liquid crystal device.   
       (5)
       The display unit according to any one of (1) to (4), further including   a glass substrate disposed between the first absorption-type polarization member and the reflection-type polarization member, in which   the display section further includes a display panel on opposite side of the first absorption-type polarization member to the display switching section.   
       (6)
       The display unit according to any one of (1) to (5), further including   a first resin layer that attaches the reflection-type polarization member and the switchable transmission polarization axis member to each other, in which   the first resin layer has a thickness that is equal to or smaller than 25 μm.   
       (7)
       The display unit according to any one of (1) to (6), further including   a second resin layer that attaches the second absorption-type polarization member and the switchable transmission polarization axis member to each other, in which   the second resin layer has a thickness that is equal to or smaller than 25 μm.   
       (8)
       The display unit according to any one of (1) to (7), further including   a third resin layer that attaches the reflection-type polarization member and the display section to each other, in which   the third resin layer has a thickness that is equal to or smaller than 25 μm.   
       (9)
       The display unit according to any one of (1) to (8), in which the switchable transmission polarization axis member also performs switching to a third mode in which only part of the first linearly-polarized light is converted into the second linearly-polarized light to pass through and rest of the first linearly-polarized light is allowed to pass through without being converted into the second linearly-polarized light.   
       (10)
       An electronic apparatus including:   a display unit; and   a controlling section that controls the display unit, in which   the display unit includes   a display section that outputs a first linearly-polarized light as image light, the first linearly-polarized light having a first polarization axis; and   a display switching section that is disposed to face the display section, and performs switching between an image display mode in which the first linearly-polarized light is allowed to pass through and an external light reflection mode in which external light is reflected,   the display section includes a first absorption-type polarization member that allows the first linearly-polarized light to pass through and absorbs second linearly-polarized light having a second polarization axis that intersects the first polarization axis,   the display switching section includes a reflection-type polarization member, a switchable transmission polarization axis member, and a second absorption-type polarization member that are disposed in order in a direction being away from the display section,   the reflection-type polarization member allows the first linearly-polarized light to pass through and reflects the second linearly-polarized light,   the switchable transmission polarization axis member performs switching between a first mode in which the first linearly-polarized light is converted into the second linearly-polarized light to pass through and a second mode in which the first linearly-polarized light is allowed to pass through without being converted into the second linearly-polarized light,   the second absorption-type polarization member allows the first linearly-polarized light to pass through and absorbs the second linearly-polarized light, and   the second absorption-type polarization member has a hue b* value that is equal to or smaller than a hue b* value of the first absorption-type polarization member.   
       (11)
       An optical device including:   a polarization control layer that controls polarization on the basis of a control from outside;   a polarization layer that is disposed on one surface side of the polarization control layer; and   a first reflection layer and a second reflection layer that are disposed on other surface side of the polarization control layer, in which   the first reflection layer is a reflective polarization layer, and   the second reflection layer has one or a plurality of openings.   
       (12)
       The optical device according to (11), in which the first reflection layer has a polarization axis that is parallel or orthogonal to a polarization axis of the polarization layer.   
       (13)
       The optical device according to (12), in which   the polarization control layer includes a liquid crystal layer and a pair of or a plurality of pairs of light transmissive electrodes that sandwich the liquid crystal layer, and   the pair or the plurality of pairs of light transmissive electrodes are sheet-shaped electrodes with which an electric field is applied to the entire liquid crystal layer.   
       (14)
       The optical device according to (13), in which the second reflection layer has a reflection surface at a position that surrounds the one or the plurality of openings.   
       (15)
       The optical device according to (14), in which   the second reflection layer has the one opening, and   the reflection surface is a circular reflection surface that is provided on a periphery of the one opening and along an outer edge of the first reflection layer.   
       (16)
       The optical device according to (15), in which the one opening is smaller than the first reflection layer.   
       (17)
       The optical device according to (16), in which the first reflection layer is disposed between the polarization control layer and the second reflection layer.   
       (18)
       The optical device according to (17), in which the second reflection layer is a metallic reflection layer, a multi-layered reflection layer, or a reflective polarization layer having a polarization axis that is orthogonal to the polarization axis of the first reflection layer.   
       (19)
       A display unit including:   a display switching section;   a display section that has an output surface that outputs linearly-polarized light as image light; and   a controlling section that performs a control on the display switching section, in which   the display switching section includes
           a polarization control layer that controls polarization on the basis of the control performed by the controlling section,   a polarization layer that is disposed at a position on opposite side to the display section in a relationship with the polarization control layer, and   a first reflection layer and a second reflection layer that are disposed at respective positions on the side of the display section in a relationship with the polarization control layer,   
           the first reflection layer is a reflective polarization layer, and   the second reflection layer has one or a plurality of openings.   
       (20)
       A display unit including:   a display switching section;   a display section that has an output surface that outputs linearly-polarized light as image light; and   a controlling section that performs a control on the display switching section, in which   the display switching section includes
           a polarization control layer that controls polarization on the basis of the control performed by the controlling section,   a polarization layer that is disposed at a position on opposite side to the display section in a relationship with the polarization control layer, and   a reflection layer that is disposed at a position on side of the display section in a relationship with the polarization control layer,   
           the display section has a bezel having an opening at a position that faces the output surface,   the reflection layer is a reflective polarization layer, and   the bezel includes a circular mirror surface on a periphery of the opening.   
       

     This application is based upon and claims the benefit of priority of the Japanese Patent Application No. 2015-37733 filed in the Japan Patent Office on Feb. 27, 2015 and the Japanese Patent Application No. 2015-57106 filed in the Japan Patent Office on Mar. 20, 2015, the entire contents of which are incorporated herein by reference. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations, and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.