Patent Publication Number: US-2022236563-A1

Title: Optical device, image display, and optometric apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to an optical device, an image display, and an optometric apparatus. 
     BACKGROUND ART 
     In recent years, technologies and products relating to virtual reality (VR) and augmented reality (AR) are getting attention. In particular, application of AR technology to industrial fields is expected as a measure to display digital information which is an additional value in a real space. A head mounted display (HMD) available in a behavioral (working) environment is developed. 
     A mainstream HMD is a transmissive (see-through) HMD that causes a user to visually recognize a virtual image and a real image of an object or the like in a real space in parallel. A HMD that displays a virtual image in front of an eye via a partially reflective film or an image guide structure and a retinal rendering HMD that renders an image directly on a retina via a partially reflective film start to appear in the market. 
     A device that projects scanning light on the retina of an eyeball of a user via an optical part to cause the user to visually recognize an image with projected light is disclosed (for example, see PTL 1). 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] 
         JP-6209662-B 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The device in PTL 1, however, may not cause the user to properly visually recognize the image with the projected light and the real space. 
     An object of the disclosed technology is to improve visual recognizability for an image with projected light and a real space. 
     Solution to Problem 
     An optical device according to an embodiment of the disclosed technology includes a projector configured to project scanning light that is light in a predetermined polarized state. The projector includes an optical member configured to selectively reflect the light in the predetermined polarized state. 
     Advantageous Effects of Invention 
     With the disclosed technology, the image with the projected light can be properly visually recognized. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings are intended to depict example embodiments of the present invention and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. 
         FIG. 1  illustrates an example of a configuration of an image display according to a first embodiment. 
         FIG. 2  illustrates an example of a configuration of a scanning mirror according to the embodiment. 
         FIG. 3  is a block diagram illustrating an example of a hardware configuration of a controller according to the embodiment. 
         FIG. 4  is a block diagram illustrating an example of a functional configuration of the controller according to the embodiment. 
         FIGS. 5A, 5B, and 5C  ( FIG. 5 ) each illustrates an example of a configuration of a reflective liquid crystal optical element according to the embodiment. 
         FIG. 5B  illustrates the example of the configuration of the reflective liquid crystal optical element according to the embodiment. 
         FIG. 6  illustrates an example of an effect of the reflective liquid crystal optical element according to the embodiment. 
         FIG. 7  illustrates an example of an operation of the image display according to the first embodiment. 
         FIG. 8  illustrates an example of a configuration of an image display according to a second embodiment. 
         FIG. 9  illustrates an example of an effect of an image display according to a comparative example. 
         FIG. 10  illustrates an example of an effect of the image display according to the second embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     An embodiment is described below referring to the drawings. Like reference signs are applied to identical or corresponding components throughout the drawings and redundant description thereof may be omitted. 
     In the embodiment, scanning light in a predetermined polarized state is selectively reflected by an optical member to project an image with the scanning light. The image with the scanning light is selectively reflected with high efficiency, and hence is projected with low loss. In contrast, light from an object or the like in a real space including light other than the light in the predetermined polarized state is transmitted through the optical member with high efficiency. Thus, both a virtual image with the scanning light and a real image of the object or the like in the real space are brightly visually recognized on a surface on which scanning light is projected. 
     In the embodiment, an example of an image display including an optical device is described. Described here as an example of the image display is a retina projection head mounted display (HMD) that is a wearable terminal and that projects a picture or an image directly on a retina of a user with use of the Maxwellian view. 
     In the embodiment, an example of an image display that displays an image on the left eyeball of a user is described. However, the image display can be also applied to the right eyeball. Moreover, two image displays may be provided and applied to both eyeballs. 
     In the description of the embodiment, a picture is synonymous with a still picture and an image is synonymous with a movie. A laser ray is synonymous with a laser beam. A laser ray is an example of “light”. 
     A configuration of an image display  100  according to a first embodiment is described referring to  FIG. 1 .  FIG. 1  illustrates an example of the configuration of the image display  100 . 
     As illustrated in  FIG. 1 , the image display  100  includes a laser source  1 , a lens  2 , an opening member  301 , a light reducing element  302 , a polarizer  41 , a quarter wave plate  42 , a scanning mirror  5 , a reflecting mirror  6 , and a reflective liquid crystal optical element  7 . The image display  100  includes an eyeglass frame  8  and a controller  20 . 
     The eyeglass frame  8  includes an arm  81  and a rim  82 . The rim  82  holds an eyeglass lens (not illustrated). The lens  2 , the opening member  301 , the light reducing element  302 , the polarizer  41 , the quarter wave plate  42 , the scanning mirror  5 , and the reflecting mirror  6  are provided inside the arm  81 . The reflective liquid crystal optical element  7  is provided on a surface of the eyeglass lens  8   c  held by the rim  82 . When a user puts the eyeglass frame  8  on an ear of the user, the user can wear the image display  100  on the head. 
     The laser source  1  is a semiconductor laser that emits laser rays with a single wavelength or a plurality of wavelengths. The laser source  1  emits laser rays which have been time modulated in response to a drive signal from the controller  20 . To render a monochrome image, a laser source that emits laser rays with a single wavelength is used. To render a color image, a laser source that emits laser rays with a plurality of wavelengths is used. In this case, the laser source  1  is an example of a “light source”. 
     The opening member  301  is a member having an opening that allows light to pass therethrough. The opening member  301  allows a portion of incident laser rays to pass therethrough and blocks the residual portion of the incident laser rays to shape the laser rays into a desirable sectional shape or a desirable diameter. The diameter of the opening of the opening member  301  is equal to or smaller than the diameter of laser rays collimated by the lens  2  at a light intensity of 1/e 2 . Note that “e” is the base of natural logarithm. 
     The diameter of the opening member  301  is determined so that the diameter of the section of laser rays incident on the scanning mirror  5  after the laser rays pass through the opening member  301  is smaller than the effective diameter of the scanning mirror  5 . In the embodiment, the opening is expected to be a circular opening; however, may be an opening partly having a distortion or having an elliptic shape. The opening member  301 , for example, uniformizes the sectional light intensity distribution to bring laser rays into a desirable state, thereby improving the quality of image rays and images. 
     The light reducing element  302  is an optical element that reduces the light intensity of passing laser rays to obtain a proper light intensity concerning the safety of user&#39;s eye. The light reducing element  302  is, for example, a neutral density (ND) filter including a plate-shaped member made of resin, and an optical thin film provided on the plate-shaped member and having a predetermined transmissivity. 
     The proper light intensity concerning the safety of user&#39;s eye is, for example, a light intensity below Class  1  under the International Electro-technical Commission (IEC) 60825-1 that is an international standard relating to the safety of laser light. Since the light reducing element  302  reduces laser rays emitted from the laser source  1  to a desirable intensity, safe laser rays are projected on the retina, thereby ensuring the safety of user&#39;s eye. 
     The polarizer  41  is an optical element that converts the polarized state of incident light to obtain linear polarized light that oscillates in a predetermined direction. The polarizer  41  can employ a polarizing film that is sandwiched between a pair of transparent plates. The polarizing film is obtained by adding iodine into a polarizing film made of, for example, polyvinyl alcohol (PVA) and drawing the resultant to align the direction of high polymers. The pair of transparent plates can employ glass or resin such as cellulose triacetate. 
     The quarter wave plate  42  is an optical element that converts incident linear polarized light into one of rightward circular polarized light and leftward circular polarized light. The quarter wave plate  42  is a wave plate made of an inorganic crystal material having birefringence, such as crystal. The configuration including the polarizer  41  and the quarter wave plate  42  is an example of a “polarizing section”. 
     The scanning mirror  5  is a mirror that rotates around two different axes. The scanning mirror  5  rotates and changes the angle thereof to provide scanning with incident light in two different directions. In the example in  FIG. 1 , the scanning mirror  5  provides scanning with incident laser rays in an X direction (horizontal direction) and a Y direction (vertical direction). Since the scanning with laser rays is provided in the X and Y directions while the laser rays are synchronized, a picture or an image is projected on the retina of user&#39;s eyeball via the reflective liquid crystal optical element  7 . The scanning mirror  5  is an example of a “scanner”. 
     Although illustration is omitted in  FIG. 1 , the image display  100  can include, for example, a known synchronization detection optical system to synchronize scanning with laser rays in the X and Y direction. 
     The X direction indicated by an arrow in  FIG. 1  corresponds to a main-scanning direction in which pixels are rendered continuously in terms of time and a series of pixel groups are formed, and the Y direction corresponds to a sub-scanning direction which is orthogonal to the main-scanning direction and in which a series of pixels are arranged. The scanning speed in the main-scanning direction is higher than the scanning speed in the sub-scanning direction. 
     The scanning mirror  5  can use a two-axis micro electro mechanical system (MEMS) mirror. The details of the configuration of the scanning mirror  5  will be described later referring to  FIG. 2 . 
     The reflecting mirror  6  is a mirror that reflects the laser rays scanned with the scanning mirror  5  toward the reflective liquid crystal optical element  7 . The surface of the reflecting mirror  6  is not limited to a flat surface, and may have a desirable shape of, for example, a concave surface or a convex surface. 
     The reflective liquid crystal optical element  7  is a flat-plate-shaped optical element including a liquid crystal film containing liquid crystal molecules. The reflective liquid crystal optical element  7  uses a liquid crystal molecule alignment structure including a spiral molecule array of liquid crystal molecules, a spiral pitch, and a local change in orientation to reflect (diffract) one of incident rightward circular polarized light and leftward circular polarized light and to focus the light at a position near the center of a pupil  52  of an eyeball  50 . 
     As indicated in regions P 1  to P 3  in  FIG. 1 , the reflective liquid crystal optical element  7  reflects laser rays in different directions toward the eyeball  50  depending on the region in an X-Y plane. As described above, the reflective liquid crystal optical element  7  has a characteristic in which the magnitude of a light focusing effect on reflected light in a region differs from that in another region so that the reflected light converges at a position near the center of the pupil  52 . As the magnitude of the light focusing effect increases, an effect similar to that the focal length decreases when described in terms of the function as a lens is obtained. As the magnitude of the light focusing effect decreases, an effect similar to that the focal length increases when described in terms of the lens function is obtained. In the example in  FIG. 1 , the magnitude of the light focusing effect increases toward the region P 3  from the region P 1 . 
     The above-described effect is derived from the liquid crystal molecule alignment structure included in the reflective liquid crystal optical element  7 , and is provided by adjusting the orientation distribution of liquid crystal molecules in an element surface. The details of the configuration and effect of the reflective liquid crystal optical element  7  are described later in detail referring to  FIGS. 5 to 7 . 
     The first reflective liquid crystal optical element  7  is an example of a “first reflective liquid crystal optical element”. Moreover, the reflective liquid crystal optical element  7  is an example of an “optical member”, and further is an example of a “projector”. The element surface of the reflective liquid crystal optical element  7  is an example of a “reflecting surface”. 
     The controller  20  is a control device that receives an input of image data serving as a source of an image to be rendered, and that controls emission of laser light by the laser source based on the input image data. The controller  20  controls the drive of the scanning mirror  5  to control scanning with light by the scanning mirror  5 . 
     In  FIG. 1 , the example has been described in which the laser source  1  and the light reducing element  302  are provided in the arm  81 ; however, it is not limited thereto. The laser source  1  and the light reducing element  302  may be provided outside the arm  81  to guide laser rays emitted from the laser source  1  and reduced by the light reducing element  302  to the inside of the arm  81 . The controller  20  may be provided in the arm  81 . Alternatively, the controller  20  may be provided outside the arm  81 , and a drive signal may be supplied from the controller  20  to the inside of the arm  81 . 
     In  FIG. 1 , an example has been described in which the light reducing element  302  is disposed between the opening member  301  and the scanning mirror  5 ; however, it is not limited thereto. The light reducing element  302  may be disposed between the opening member  301  and the lens  2 , and may be disposed at a plurality of positions. The light reducing element may be omitted as far as the intensity of light to be projected on the retina of the user is safe. Proper disposition of the light reducing element  302  can downsize the image display  100 . 
     In  FIG. 1 , the example has been described in which the polarizer  41  and the quarter wave plate  42  are disposed between the light reducing element  302  and the scanning mirror  5 ; however, the polarizer  41  and the quarter wave plate  42  may be disposed between the opening member  301  and the light reducing element  302 , or between the opening member  301  and the lens  2 . 
     In  FIG. 1 , the example has been described in which the reflective liquid crystal optical element  7  is provided on the surface of the eyeglass lens  8   c ; however, it is not limited thereto. The reflective liquid crystal optical element  7  may be provided inside or on a surface of the eyeglass lens  8   c  when the eyeglass lens  8   c  is configured as a light guide plate. 
     The laser source  1  is not limited to a semiconductor laser and may use a solid laser or a gas laser. The polarizer  41  may be provided with a protection film on the outermost surface of a transparent plate to improve durability or a non-reflective coating layer to prevent reflection. 
     When a higher optical extinction ratio is required, it is desirable to use, for example, a wire grid polarizer or a metal dispersion polarizing film. 
     The quarter wave plate  42  is not limited to the wave plate made of an inorganic crystal material, and may use a resin film made of an organic material, such as polycarbonate having birefringence by drawing, or a phase plate including a pair of transparent plates and a high-polymer liquid crystal phase sandwiched between the transparent plates. 
     The scanning mirror  5  is not limited to the MEMS mirror, and may use an optical element that can provide scanning with light, such as a polygon mirror or a galvano mirror, or a combination of these mirrors. Note that using the MEMS mirror is desirable because the image display  100  can be reduced in size and weight. The driving system of the MEMS mirror may employ any system, such as an electrostatic system, a piezoelectric system, or an electromagnetic system. 
     Paths of laser rays in the image display  100  are described next. 
     In  FIG. 1 , the laser rays of divergent light emitted from the laser source  1  (illustration of divergent light is omitted) is converted into substantially parallel light by the lens  2 . The effect by a lens is not limited to making light substantially parallel, and may make light which has passed through a lens convergent or divergent. The substantially parallel laser rays pass through the opening member  301  and the light reducing element  302 , and are converted into laser rays of rightward circular polarized light by the polarizer  41  and the quarter wave plate  42 . The rightward circular polarized light is an example of a “polarized state having chirality”. 
     The laser rays converted into the rightward circular polarized light provide scanning in two-axis directions using the scanning mirror  5 , are reflected by the reflecting mirror  6 , and are incident on the reflective liquid crystal optical element  7 . 
     For example, the reflective liquid crystal optical element  7  selectively reflects the incident laser rays of the rightward circular polarized light and causes the laser rays to be incident in the eyeball  50 . The incident light in the eyeball  50  converges once at a position near the center of the pupil  52  by the light focusing function of the reflective liquid crystal optical element  7 , and then forms an image on a retina  53  at a deep position of the eyeball  50 . The retina  53  is an example of a “surface on which light is projected”. 
     The above-described visual recognition state is generally called the Maxwellian view. Light passing through a position near the center of the pupil  52  reaches the retina  53  irrespective of focus adjustment of a crystalline lens. Thus, ideally, a user can sharply visually recognize a projected image in a focused state when the user adjusts the focus of the eyes at any position in the real space. In contrast, in the actual world, laser rays incident on the eyeball  50  have a limited diameter although the diameter is small, and hence have an influence of a lens effect due to the crystalline lens. Thus, in the present embodiment of the present disclosure, design is made so that laser rays have a diameter from 350 μm to 500 μm when being incident on the eyeball  50 , and an angle of divergence of beam having a positive limited value, that is, to be divergent light due to the lens  2  and the light focusing effect of the reflective liquid crystal optical element  7 . 
     Accordingly, an image to be rendered with the laser rays through scanning using the scanning mirror  5  reaches the retina  53  via the reflective liquid crystal optical element  7  irrespective of the focus adjustment of the crystalline lens. Thus, the user can sharply visually recognize a projected image when the user adjusts the focus of the eyes at any position in the real space. In other words, the image rendered with the laser rays through scanning using the scanning mirror  5  is visually recognized in a focus-free state. 
     The image display  100  can change the current or voltage to be applied to the laser source  1 , and can change the light intensity of laser rays to be emitted. Accordingly, the brightness of a picture or an image can be changed in accordance with the brightness of the surrounding environment in which the image display  100  is used. 
     The details of a configuration of the scanning mirror  5  is described next referring to  FIG. 2 . 
       FIG. 2  illustrates an example of the configuration of the scanning mirror  5 . In  FIG. 2 , respective directions with arrows are referred to as a direction, β direction, and γ direction. As illustrated in  FIG. 2 , the scanning mirror  5  includes a support substrate  91 , a movable portion  92 , a meandering beam portion  93 , a meandering beam portion  94 , and an electrode coupling portion  95 . 
     Among these portions, the meandering beam portion  93  is formed in a meandering manner to have a plurality of folding portions, and has one end coupled to the support substrate  91  and the other end coupled to the movable portion  92 . The meandering beam portion  93  includes a beam portion  93   a  including three beams and a beam portion  93   b  including three beams. The beams of the beam portion  93   a  and the beams of the beam portion  93   b  are alternately formed. Each beam included in the beam portion  93   a  and the beam portion  93   b  individually includes a piezoelectric member. 
     Likewise, the meandering beam portion  94  is formed in a meandering manner to have a plurality of folding portions, and has one end coupled to the support substrate  91  and the other end coupled to the movable portion  92 . The meandering beam portion  94  includes a beam portion  94   a  including three beams and a beam portion  94   b  including three beams. The beams of the beam portion  94   a  and the beams of the beam portion  94   b  are alternately formed. Each beam included in the beam portion  94   a  and the beam portion  94   b  individually includes a piezoelectric member. The number of beams in each of the beam portions  93   a  and  93   b  is not limited to three, and may be desirably determined. 
     Although the piezoelectric members included in the beam portions  93   a ,  93   b ,  94   a , and  94   b  are not illustrated in  FIG. 2 , each beam may have a multilayer structure, and the piezoelectric member may be provided as a piezoelectric layer in a portion of a layer of the beam. In the following description, the piezoelectric members included in the beam portions  93   a  and  94   a  may be collectively referred to as a piezoelectric member  95   a , and the piezoelectric members included in the beam portions  93   b  and  94   b  may be collectively referred to as a piezoelectric member  95   b.    
     When voltage signals in opposite phases are applied to the piezoelectric member  95   a  and the piezoelectric member  95   b  to warp the meandering beam portion  94 , adjacent beam portions are curved in different directions. The curve is accumulated, thereby generating a rotational force to rotate a reflecting mirror  92   a  in a reciprocating manner around an A-axis in  FIG. 2 . 
     The movable portion  92  is sandwiched between the meandering beam portion  93  and the meandering beam portion  94  in the β direction. The movable portion  92  includes the reflecting mirror  92   a , a torsion bar  92   b , a piezoelectric member  92   c , and a support  92   d.    
     The reflecting mirror  92   a  includes, for example, a base member and a metal thin film provided by vapor deposition on the base member. The metal thin film contains, for example, aluminum (Al), gold (Au), or silver (Ag). The torsion bar  92   b  has one end coupled to the reflecting mirror  92   a , extends in the positive and negative a directions, and supports the reflecting mirror  92   a  rotatably. 
     The piezoelectric member  92   c  has one end coupled to the torsion bar  92   b  and the other end coupled to the support  92   d . When a voltage is applied to the piezoelectric member  92   c , the piezoelectric member  92   c  is deformed in a bending manner, thereby generating a twist in the torsion bar  92   b . The twist of the torsion bar  92   b  generates a rotational force and hence the reflecting mirror  92   a  rotates around a B-axis. 
     The rotation of the reflecting mirror  92   a  around the A-axis causes laser rays incident on the reflecting mirror  92   a  to provide scanning in the α direction. The rotation of the reflecting mirror  92   a  around the B-axis causes laser rays incident on the reflecting mirror  92   a  to provide scanning in the β direction. 
     The support  92   d  surrounds the reflecting mirror  92   a , the torsion bar  92   b , and the piezoelectric member  92   c . The support  92   d  is coupled to the piezoelectric member  92   c  and supports the piezoelectric member  92   c . The support  92   d  indirectly supports the torsion bar  92   b  coupled to the piezoelectric member  92   c , and the reflecting mirror  92   a.    
     The support substrate  91  surrounds the movable portion  92 , the meandering beam portion  93 , and the meandering beam portion  94 . The support substrate  91  is coupled to the meandering beam portion  93  and the meandering beam portion  94  to support the meandering beam portion  93  and the meandering beam portion  94 . The support substrate  91  also indirectly supports the movable portion  92  coupled to the meandering beam portion  93  and the meandering beam portion  94 . 
     The MEMS mirror constituting the scanning mirror  5  is made of silicon or glass using a micromachining technology. Using the micromachining technology can form a very small movable mirror with high precision on a substrate integrally with a driver such as the meandering beam portion. 
     Specifically, a silicon on insulator (SOI) substrate is shaped, for example, by etching. The reflecting mirror  92   a , the meandering beam portions  93  and  94 , the piezoelectric members  95   a  and  95   b , the electrode coupling portions, and so forth are integrally formed on the shaped substrate to form the MEMS mirror. The reflecting mirror  92   a  and other components may be formed after the SOI substrate is shaped, or may be formed while the SOI substrate is shaped. 
     The SOI substrate is a substrate in which a silicon oxide layer is provided on a silicon support layer made of monocrystal silicon (Si), and a silicon active layer made of monocrystal silicon is further provided on the silicon oxide layer. The silicon active layer has a smaller thickness in the y direction than the dimensions in the α direction and the β direction. With such a configuration, a member made of the silicon active layer has a function as an elastic portion having elasticity. 
     The SOI substrate does not have to be planar, and may have, for example, a curvature. As long as the substrate can be integrally shaped by etching or the like and can be partly elastic, the member used for forming the MEMS mirror is not limited to the SOI substrate. 
     When scanning is performed in the main-scanning direction, voltages with sine waveforms in opposite phases are applied to the piezoelectric members  95   a  and  95   b  included in the scanning mirror  5 , as drive signals from the controller  20 . The frequency of the voltages with sine waveforms is a frequency corresponding to the resonance mode of the movable portion  92  around the A-axis. When the voltages with sine waveforms are applied, the scanning mirror  5  rotates in a reciprocating manner at a very large rotational angle with low voltage. 
     For the drive signals, voltage signals in a sawtooth waveform can be used. The sawtooth waveform can be generated by superposing sine waveforms. The waveform is not limited to the sawtooth waveform, and may use a waveform having rounded vertices of a sawtooth waveform or a waveform having curved linear regions of a sawtooth waveform. 
     A hardware configuration of the controller  20  according to the embodiment is described next referring to  FIG. 3 .  FIG. 3  is a block diagram illustrating an example of a hardware configuration of the controller  20 . 
     As illustrated in  FIG. 3 , the controller  20  includes a central processing unit (CPU)  22 , a read only memory (ROM)  23 , a random access memory (RAM)  24 , a light-source drive circuit  25 , and a scanning-mirror drive circuit  26 . These components are electrically coupled to one another via a system bus  27 . 
     Among these components, the CPU  22  controls over the operation of the controller  20 . The CPU  22  uses the RAM  24  as a work area and executes a program stored in the ROM  23  to control the entire operation of the controller  20  and implement various functions. 
     The light-source drive circuit  25  is an electric circuit that is electrically coupled to the laser source  1  and applies a current or a voltage to the laser source  1  to drive the laser source  1 . The laser source  1  turns ON or OFF emission of laser rays or changes the light intensity of laser rays to be emitted in accordance with a drive signal that is output from the light-source drive circuit  25 . 
     The scanning-mirror drive circuit  26  is an electric circuit that is electrically coupled to the scanning mirror  5  and applies a voltage to the scanning mirror  5  to drive the scanning mirror  5 . The scanning mirror  5  changes the angle of rotation of the reflecting mirror  92   a  included in the movable portion  92  in accordance with a drive signal that is output from the scanning-mirror drive circuit  26 . 
     A functional configuration of the controller  20  according to the embodiment is described next referring to  FIG. 4 .  FIG. 4  is a block diagram illustrating an example of the functional configuration of the controller  20 . As illustrated in  FIG. 4 , the controller  20  includes an emission controller  31 , a light-source driver  32 , a scan controller  33 , and a scanning-mirror driver  34 . 
     Among these components, the respective functions of the emission controller  31  and the scan controller  33  are implemented by, for example, the CPU  22 . The function of the light-source driver  32  is implemented by, for example, the light-source drive circuit  25 , and the function of the scanning-mirror driver  34  is implemented by, for example, the light-source drive circuit  25 . 
     Among these components, the emission controller  31  receives an input of image data which is a base of an image to be rendered, and outputs a control signal for controlling the drive of the laser source  1  to the light-source driver  32  based on the received image data. 
     The scan controller  33  receives an input of image data which is a base of an image to be rendered, and outputs a control signal for controlling the drive of the scanning mirror  5  to the scanning-mirror driver  34  based on the received image data. 
     When an image to be visually recognized at a desirable position has a distortion or the like, the emission controller  31  and the scan controller  33  may perform control to correct a distortion or the like. 
     The light-source driver  32  applies a current or a voltage to the laser source  1  to drive the laser source  1  based on a control signal that is input from the emission controller  31 . The scanning-mirror driver  34  applies a voltage to the scanning mirror  5  to drive the scanning mirror  5  based on a control signal that is input from the scan controller  33 . 
     The details of the configuration of the reflective liquid crystal optical element  7  are described next referring to  FIGS. 5A and 5B .  FIGS. 5A and 5B  illustrate an example of the configuration of the reflective liquid crystal optical element  7 .  FIG. 5A  is a perspective view of the reflective liquid crystal optical element  7 .  FIG. 5B  illustrates a portion of a section spatial distribution of liquid crystal directors  71  included in the reflective liquid crystal optical element  7 .  FIG. 5C  illustrates a portion of an in-plane spatial distribution, in an element surface, of the liquid crystal directors  71  included in the reflective liquid crystal optical element  7 . 
     As illustrated in  FIG. 5 , the element surface of the reflective liquid crystal optical element  7  represents an x-y plane that is a plane parallel to the liquid crystal directors  71  or the substrate surface, and the section represents a plane perpendicular to the element surface, for example, an x-z plane. 
     As illustrated in  FIG. 5A , the reflective liquid crystal optical element  7  is formed of a flat-plate-shaped liquid crystal film. The reflective liquid crystal optical element  7  is fabricated such that a desirable molecular alignment structure is formed using a photopolymerizable liquid crystal material, then the molecule alignment structure is fixed by irradiation with UV rays, and the substrate is eliminated. Polymerization hardens the orientation and position of liquid crystal molecules while the state before polymerization is kept. Thus, the liquid crystal molecule alignment structure may represent the state before or after polymerization. 
     As illustrated in  FIGS. 5B and 5C , the liquid crystal molecule alignment structure in which the liquid crystal directors  71  have three-dimensional periodicity is enclosed in the reflective liquid crystal optical element  7 . The liquid crystal directors  71  have an average molecule alignment direction in which liquid crystal molecules are arranged with long-axis directions thereof aligned. 
     The liquid crystal material according to the embodiment of the present disclosure is cholesteric liquid crystal in which a chiral agent is added to nematic liquid crystal made of achiral molecules, or cholesteric liquid crystal in which liquid molecules have chirality. In cholesteric liquid crystal, a twist is induced in molecule orientation between adjacent molecules, thereby forming a spiral periodic structure having chirality in a direction perpendicular to the liquid crystal directors  71 . That is, the liquid crystal directors  71  formed of liquid crystal molecules enclosed in the reflective liquid crystal optical element  7  according to the embodiment of the present disclosure form a spiral molecule array having chirality in a depth direction perpendicular to the element surface, that is, in a z direction. Cholesteric liquid crystal depends on the chirality of the spiral and hence has characteristics of Bragg reflection to selectively reflect synchronous chiral circular polarized light. 
     In the reflective liquid crystal optical element  7 , the start position of the spiral structure, that is, the alignment direction of the liquid crystal directors  71  in the element surface is adjusted. That is, as illustrated in  FIG. 5C , the in-plane orientation distribution of the liquid crystal directors  71  in the element surface of the reflective liquid crystal optical element  7  has a periodic array in which molecule orientation periodically radially changes in the element surface from a substantially center portion of the element surface. More specifically, the liquid crystal directors  71  have an orientation distribution in which the alignment direction is periodically rotated in a radial direction that can be a desirable direction from the element center portion, and the period gradually decreases from the center portion toward an edge portion, that is, the period nonlinearly changes. 
     Note that  FIG. 5C  schematically illustrates a portion of the in-plane spatial distribution, and it is not limited thereto. The in-plane spatial distribution may have a proper number of periods based on the element size and the required function. 
     With such an in-plane orientation distribution, for example, as illustrated in  FIG. 5B , a phase distribution may be formed in the reflective liquid crystal optical element  7 . In the phase distribution, an equiphase surface  72  is curved in a concave shape in the positive z direction that is the incident direction of light, in the spiral molecule array. That is, the molecular orientation distribution that locally varies provides a concave phase deviation in reflected light. Thus, the reflective liquid crystal optical element  7  has reflecting and focusing effects for light incident in the positive z direction. 
     As illustrated in  FIG. 1 , the reflective liquid crystal optical element  7  reflects laser rays in different directions toward the eyeball depending on the region in the x-y plane. When the reflective liquid crystal optical element  7  is divided along an a-axis that is parallel to the x-y plane, into a first region (x− region with respect to the a-axis) and a second region (x+ region with respect to the a-axis), the in-plane orientation distribution in the first region is asymmetric to that in the second region. More specifically, the period in the second region including the P 3  region illustrated in  FIG. 1  may be entirely smaller than the period in the first region including the P 1  region illustrated in  FIG. 1 . That is, the curvature radius of the concave phase deviation which is provided over region is smaller in the second region. In other words, the magnitude of the light focusing effect is larger in the second region. As described above, the reflective liquid crystal optical element  7  includes at least two regions with different magnitudes of the light focusing effects in the element surface. Thus, the reflective liquid crystal optical element  7  can reflect incident laser rays so that the laser rays converge at a position near the center of the pupil  52 . That is, the reflective liquid crystal optical element  7  functions as an aspherical surface mirror, or further a free-form surface mirror, and can provide the Maxwellian view. 
     When the number (the number of periods) of spiral pitches  73  illustrated in  FIG. 5B  is six or more, for example, it is desirable because reflection with a high efficiency of a peak reflection intensity of 90% or more can be provided. 
     A known technology can be applied to the technology to exhibit an optical function using a phase distribution formed of a liquid crystal molecule alignment structure like one described above (for example, Nature Photonics Vol. 10 (2016), p. 389 etc.), and hence the more detailed description is omitted here. 
     The phase distribution in the reflective liquid crystal optical element  7  can be adjusted by adjusting the initial alignment direction of the liquid crystal directors  71  in the element surface. Such adjustment can use a photo alignment technique. The photo alignment technique spatially divides an alignment film applied on a substrate and exposes each of the divided regions with linear polarized light polarized in a predetermined direction to spatially adjust the initial alignment direction of liquid crystal molecules. 
     The liquid crystal material may use one of a polymerizable liquid crystal material and a non-polymerizable liquid crystal material. The chiral agent may use one of a polymerizable chiral agent and a non-polymerizable chiral agent. One kind of a chiral agent may be used or two or more kinds of chiral agents may be combined and used. When liquid crystal molecules have chirality, the chiral agent may be omitted. 
     For a method of fabricating the reflective liquid crystal optical element  7  according to the embodiment of the present disclosure, a desirable molecule alignment structure is formed by using a photopolymerizable liquid crystal material, then the structure is fixed by irradiation with UV rays, and the substrate is eliminated. However, it is not limited thereto. The embodiment may be desirably changed in response to a request, such as an embodiment stacked on a transparent support substrate, or an embodiment sandwiched between transparent support substrates. In an embodiment in which a liquid crystal film is exposed to the air, a protection film or the like for increasing durability may be provided on the outermost surface. The shape of the reflective liquid crystal optical element  7  is not limited to a flat-plate shape, and may be a desirable proper shape in accordance with the form of the eyeglass lens  8   c , such as a curved-surface form. In this case, the liquid crystal alignment structure of the reflective liquid crystal optical element  7  is adjusted in accordance with the form of the eyeglass lens  8   c , and can reflect incident laser rays so that the laser rays converge at a position near the center of the pupil  52 . 
     An effect of the reflective liquid crystal optical element  7  is described next referring to  FIG. 6 .  FIG. 6  illustrates an example of the effect of the reflective liquid crystal optical element  7 .  FIG. 6  illustrates an example in which rightward circular polarized light  61  and leftward circular polarized light  62  are incident on the reflective liquid crystal optical element  7  having liquid crystal molecules having a rightward twist spiral array. 
     The reflective liquid crystal optical element  7 , due to the spiral array having chirality as described above, reflects by Bragg reflection circular polarized light that is light with a predetermined wavelength band and that has the same chirality as that of the spiral rotation direction of liquid crystal molecules with high diffraction efficiency. In this case, a bandwidth Δλ in a predetermined wavelength band is determined by Δλ=Δnp cos θ, where Δn is a birefringence of a liquid crystal composition, p is a spiral pitch of liquid crystal, and θ is an incident angle of rays. The bandwidth Δλ is adjustable using the birefringence of the liquid crystal composition, and is from about 30 to 100 nm. This is very narrow compared with the bandwidth of visible light of from 380 to 780 nm. 
     As illustrated in  FIG. 6 , when a laser ray incident on the reflective liquid crystal optical element  7  is rightward circular polarized light  61  having the same chirality as that of the spiral rotation direction of liquid crystal molecules, incident laser light is selectively reflected with ideal efficiency. 
     The reflective liquid crystal optical element  7  transmits light with a wavelength band other than the predetermined wavelength band, and light with the predetermined wavelength band that is circular polarized light having chirality in a direction opposite pairing up with the spiral rotation direction of liquid crystal molecules. In  FIG. 6 , leftward circular polarized light  62  is transmitted through the reflective liquid crystal optical element  7 . 
     While the phase deviation provided on reflected light is determined by the orientation distribution of the liquid crystal directors  71  in the element surface, a selective reflection characteristic of cholesteric liquid crystal is not lost by a change in molecule alignment direction. The reflective liquid crystal optical element  7  can reflect light that is light with the predetermined wavelength band and that is circular polarized light having the same chirality as that of the spiral array of liquid crystal molecules. In addition, the reflective liquid crystal optical element  7  can cause the reflected circular polarized light to converge at a position near the center of the pupil  52  because of the light focusing effect due to phase deviation that is determined by the in-plane molecule orientation distribution. 
     The spiral pitch of cholesteric liquid crystal changes with temperature. Thus, it is desirable to form the reflective liquid crystal optical element  7  using a liquid crystal film the structure of which is fixed so that the predetermined wavelength band does not change with temperature. 
       FIG. 6  illustrates the example of the reflective liquid crystal optical element  7  in which liquid crystal molecules form the rightward spiral array; however, in the present embodiment, a reflective liquid crystal optical element  7  in which liquid crystal molecules have a leftward spiral array may be used. In this case, the reflective liquid crystal optical element  7  selectively reflects and converges leftward circular polarized light having the same chirality as that of the orientation of the spiral rotation direction of liquid crystal molecules, and transmits light other than the leftward circular polarized light. 
     An operation of the image display  100  is described next referring to  FIG. 7 .  FIG. 7  illustrates the operation of the image display  100 . 
     Referring to  FIG. 7 , the scanning mirror  5  provides scanning with a laser ray of rightward circular polarized light, and the reflecting mirror  6  folds back the laser ray toward the reflective liquid crystal optical element  7 . Then, the reflective liquid crystal optical element  7  selectively reflects the rightward circular polarized ray with ideal efficiency, converges the ray once at a position near the center of the pupil  52  of the eyeball  50  of the user, and then is projected on the retina  53  of the user. The user can visually recognize an image with the laser ray projected on the retina  53 . 
     In contrast, light that propagates in the negative z direction from an object  70  in a real space is random polarized light with a wide wavelength band. Thus, the reflective liquid crystal optical element  7  transmits, among light from the object  70 , light with a wavelength band other than the predetermined wavelength band, and transmits light of other than light having a rightward circular polarized light component, even when the light is within the predetermined wavelength band. 
     The bandwidth of the predetermined wavelength band at the reflective liquid crystal optical element  7  is very narrow compared with the wavelength band of visible light. Hence the reflective liquid crystal optical element  7  has good transmissivity. Thus, a major portion of light propagating from the object  70  in the real space toward the eyeball  50  is transmitted through the reflective liquid crystal optical element  7 , and reaches the retina  53  of the user. Accordingly, the image of the object  70  in the real space is visually recognized with sufficient brightness. 
     In this way, the user wearing the image display  100  can visually recognize a virtual image and a real image of an object in a real space in parallel, and can visually recognize both the virtual image and the real image in the real space in a bright state. 
     Related art discloses a device that projects scanning light on a retina of an eyeball of a user via an optical part to cause the user to visually recognize an image with projected light. However, in an image display of the related art, such as a transmissive HMD that causes a virtual image and a real image of, for example, an object in a real space to be visually recognized in parallel has a trade-off relationship between brightness of a real image of the object or the like in the real space transmitted through an eyeglass and brightness of a virtual image reflected by the eyeglass. Thus, when the real image of the object or the like in the real space is brightened, the projected virtual image is darkened, and the virtual image may not be properly visually recognized. 
     In the present embodiment, the reflective liquid crystal optical element  7  selectively reflects scanning light of rightward circular polarized light and projects an image with the scanning light. In contrast, the reflective liquid crystal optical element  7  transmits light from a real space with high efficiency. Thus, the user with a virtual image projected on his/her retina can brightly visually recognize both the virtual image and the real image of the object or the like in the real space. In other words, visual recognizability for an image with projected light and a real space can be increased. 
     In the present embodiment, since an image is rendered directly on the retina of the user using the Maxwellian view, the user can be visually recognize the image in parallel and sharply when the user focuses at any position in the real space. Accordingly, for example, when the user is a worker at a manufacturing site, the user can properly visually recognize a digital content such as a work instruction in a clear field of view without an interruption of a work in a real space, and can work without visual stress because of the focus-free state. 
     In the present embodiment, using a flat-plate-shaped and thin reflective liquid crystal optical element  7  can reduce the image display  100  in size, and allows the image display  100  to be easily mounted. 
     In the present embodiment, the reflective liquid crystal optical element  7  includes the liquid crystal molecule alignment structure in which the magnitude of the focusing effect varies depending on the region. Thus, a laser ray can be properly converged at a position near the center of the pupil  52 , thereby providing the Maxwellian view. 
     When the number of the spiral pitches  73  in the liquid crystal molecule spiral array is six or more, it is desirable because the laser ray can be reflected with further high efficiency. 
     In the present embodiment, the HMD is described as an example of the image display. However, the image display such as a HMD is not limited to one that is directly mounted on the head of a user, and may be one that is indirectly mounted on the head of a user via a member such as a securing portion. 
     In the present embodiment, the example of using the reflective liquid crystal optical element  7  in which liquid crystal molecules form the rightward spiral array is described; however, a reflective liquid crystal optical element  7  in which liquid crystal molecules form a leftward spiral array may be used. In this case, a laser ray from the laser source  1  is converted into leftward circular polarized light by the polarizer  41  and the quarter wave plate  42  and is incident on the reflective liquid crystal optical element  7 , thereby obtaining an advantageous effect similar to that described above. 
     In the present embodiment, the example of using the reflective liquid crystal optical element  7  having one layer is described; however, a plurality of reflective liquid crystal optical elements  7  stacked in a multilayer form may be used. For example, a reflective liquid crystal optical element  7  may include three layers including a reflective liquid crystal optical element having a predetermined wavelength band of red (R), a reflective liquid crystal optical element having a predetermined wavelength band of green (G), and a reflective liquid crystal optical element having a predetermined wavelength band of blue (B). Hence, a full-color image can be projected on the retina using RGB laser sources. 
     An image display  100   a  according to a second embodiment is described. 
     The state of a laser ray incident on the eyeball may change in the field of view due to the function of converging reflected light by the reflective liquid crystal optical element. In this case, the state of a laser ray includes the diameter of laser ray and the angle of divergence of beam. When an image is projected at a viewing angle at which vignetting due to an eyeball motion does not occur, the state of the laser ray incident on the eyeball is desirably uniformized within a range where an image is projected on the retina. 
     In the present embodiment, a laser ray is incident on a reflective liquid crystal optical element via a correction reflective liquid crystal optical element to uniformize the state of the laser ray that is reflected by the reflective liquid crystal optical element and is incident on the eyeball. A configuration of the image display  100   a  according to the second embodiment is described. 
       FIG. 8  illustrates an example of the configuration of the image display  100   a . The image display  100   a  includes a correction reflective liquid crystal optical element  9 . The correction reflective liquid crystal optical element  9  is an example of a “second reflective liquid crystal optical element”. 
     Like the reflective liquid crystal optical element  7 , the correction reflective liquid crystal optical element  9  is a flat-plate-shaped optical element that reflects circular polarized light having the same chirality as that of the spiral rotation direction of liquid crystal molecules with a predetermined wavelength band, with high efficiency and focuses the light. A light focusing effect determined by the in-plane orientation distribution of liquid crystal molecules included in the correction reflective liquid crystal optical element  9  is adjusted to uniformize the state of laser rays that are incident on the eyeball  50  within a range where an image is projected on the retina  53 . 
     Before the effect of the correction reflective liquid crystal optical element  9  is described, an image display according to a comparative example is described referring to  FIG. 9 .  FIG. 9  illustrates an example of an effect of an image display according to a comparative example. 
     Referring to  FIG. 9 , a scanning mirror  5  provides scanning with laser rays L 1  to L 3  that are reflected by a reflecting mirror  6  and then are incident on a reflective liquid crystal optical element  7 . In this case, the laser ray L 2  is a laser ray corresponding to the center of an image. The laser ray L 1  is a laser ray corresponding to one end of the image in the X direction, and the laser ray L 3  is a laser ray corresponding to the other end of the image in the X direction. In other words, the laser ray L 1  corresponds to one end of a range of a retina  53  where the image is projected, and the laser ray L 3  corresponds the other one end of the range of the retina  53  where the image is projected. 
     The laser ray L 1  is reflected in a region P 1  of the reflective liquid crystal optical element  7  and is incident on an eyeball  50 . The laser ray L 2  is reflected in a region P 2  of the reflective liquid crystal optical element  7  and is incident on the eyeball  50 . The laser ray L 3  is reflected in a region P 3  of the reflective liquid crystal optical element  7  and is incident on the eyeball  50 . 
     As described above, in the reflective liquid crystal optical element  7 , to reflect the laser rays toward the eyeball  50 , converge the laser rays at a position near the center of the pupil, and then project the rays on the retina  53 , the regions P 1  to P 3  are sequentially arranged so that the magnitude of the light focusing effect increases in the positive X direction. 
     As illustrated in  FIG. 9 , when a reflective liquid crystal optical element is arranged in front of the eyeball  50 , the optical path length increases in the order of the laser rays L 1  to L 3 . The states of laser rays when being incident on the eyeball  50  differ from one another among the laser rays L 1  to L 3 . 
     For example, when it is expected that the laser ray L 2  passing through the center of the field of view is incident on the eyeball  50  in a state substantially parallel to a Z-axis in  FIG. 9 , the laser ray L 1  is incident on the eyeball in a state more divergent compared with the laser ray L 2 . In contrast, the laser L 3  is incident on the eyeball in a state more convergent compared with the laser ray L 2 . In this way, with the image display according to the comparative example, the state of laser rays incident on the eyeball  50  becomes non-uniform within the range where the image is projected, and a resolution characteristic and a focus characteristic may not be uniformized. 
     An image display  100   a  according to the present embodiment is described next referring to  FIG. 10 .  FIG. 10  illustrates an example of an effect of the image display  100   a.    
     Referring to  FIG. 10 , a laser ray reflected in a region C 1  of a correction reflective liquid crystal optical element  9  is incident on a region P 1  of the reflective liquid crystal optical element  7 . A laser ray reflected in a region C 2  of the correction reflective liquid crystal optical element  9  is incident on a region P 2  of the reflective liquid crystal optical element  7 . A laser ray reflected in a region C 3  of the correction reflective liquid crystal optical element  9  is incident on a region P 3  of the reflective liquid crystal optical element  7 . 
     The reflective liquid crystal optical element  7  and the correction reflective liquid crystal optical element  9  are made of the same liquid crystal material, and the liquid crystal molecules form a rightward spiral array having chirality the same as the chirality of polarized light in correspondence with the laser ray of the incident rightward circular polarized light. As described above, the liquid crystal molecule alignment structure is designed so that the correction reflective liquid crystal optical element  9  cancels the reflective liquid crystal optical element  7  in terms of the magnitude of the light focusing effect to uniformize the state of laser rays incident on the eyeball  50  within a range where an image is projected. 
     More specifically, the in-plane orientation distribution of liquid crystal molecules is determined so that the reflective liquid crystal optical element  7  has a light focusing effect having a magnitude that increases in the order of the regions P 1  to P 3  in the positive X direction, and the correction reflective liquid crystal optical element  9  has a light focusing effect having a magnitude that increases in the order of the regions C 3  to C 1  in the negative X direction. 
     With such a configuration, a laser ray L 1  that is reflected in the region C 1  having a large magnitude of the light focusing effect of the correction reflective liquid crystal optical element  9  is incident on a region P 1  having a small magnitude of the light focusing effect of the reflective liquid crystal optical element  7 ; and a laser ray L 3  that is reflected in the region C 3  having a small magnitude of the light focusing effect of the correction reflective liquid crystal optical element  9  is incident on a region P 3  having a large magnitude of the light focusing effect of the reflective liquid crystal optical element  7 . 
     Accordingly, the balance between the magnitudes of the light focusing effects is adjusted in each region, and as illustrated in  FIG. 10 , the state of the laser ray that is reflected by the reflective liquid crystal optical element  7  and is incident on the eyeball  50  as well as the diameter of laser rays and the angle of divergence of beam are uniformized. 
     Also with the image display  100   a  according to the present embodiment, like the above-described image display  100 , the incident light in the eyeball  50  converges once at a position near the center of the pupil  52  by the light focusing function of the reflective liquid crystal optical element  7 , and then projects an image using the Maxwellian view which forms an image on the retina  53  at a deep position of the eyeball  50 . Thus, in the present embodiment, design is made such that laser rays have, as desirable conditions for the Maxwellian view, a diameter from 350 μm to 500 μm when the laser rays are incident on the eyeball  50 , and an angle of divergence of beam of a positive limited value, that is, to be divergent light due to the lens  2 , and the light focusing effects of the correction reflective liquid crystal optical element  9  and the reflective liquid crystal optical element  7 . 
     As described above, in the present embodiment, the laser rays are incident on the reflective liquid crystal optical element  7  via the correction reflective liquid crystal optical element  9 . Accordingly, the state of the laser rays that are reflected by the reflective liquid crystal optical element  7  and are incident on the eyeball  50  can be uniformized to cause the user to visually recognize an image having uniform resolution characteristics and focus characteristics within the rage where the image is projected. 
     In the present embodiment, using the flat-plate-shaped and thin correction reflective liquid crystal optical element  9  can reduce the image display  100   a  in size and weight, and allows the image display  100   a  to be easily mounted. Advantageous effects other than the above are similar to those described in the first embodiment. 
     An optometric apparatus according to a third embodiment is described next. 
     For example, the optical device and the image display according to the embodiments of the present disclosure can be also applied to an optometric apparatus. The optometric apparatus represents an apparatus capable of performing various inspections, such as an eyesight inspection, an ocular refractive-power inspection, an ocular tension inspection, and an ocular axial length inspection. The optometric apparatus is an apparatus that can inspect an eyeball in a non-contact manner. The optometric apparatus includes a support that supports the face of a subject, an ocular inspection window, a display section that projects inspection information on the eyeball of the subject during the ocular inspection, a controller, and a measurement section. The subject secures the face at the support and stares at the inspection information projected on the display section through the ocular inspection window. At this time, the optical device according to the present embodiment can be used for the display section. Moreover, using the image display according to the present embodiment implements an optometric apparatus in a form of glasses. Accordingly, a space for inspection and a large optometric apparatus are no longer required and an inspection is available with a simple configuration in any place. 
     The optical device, image display, and optometric apparatus according to the embodiments have been described above; however, the present disclosure is not limited to the above-described embodiments and can be modified and improved in various ways within the scope of the present disclosure. 
     In the present embodiment, the HMD in the form of glasses is described as an example of the image display. However, the image display such as a HMD is not limited to one that is directly mounted on the head of a “person”, and may be one that is indirectly mounted on the head of a “person” via a member such as a securing portion. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. 
     This patent application is based on and claims priority pursuant to Japanese Patent Application No. 2019-120427, filed on Jun. 27, 2019 and Japanese Patent Application No. 2020-066158, filed on Apr. 1, 2020, in the Japan Patent Office, the entire disclosure of which are hereby incorporated by reference herein. 
     REFERENCE SIGNS LIST 
     
         
           1  laser source 
           2  lens 
           301  opening member 
           302  light reducing element 
           41  polarizer 
           42  quarter wave plate 
           5  scanning mirror (example of scanner) 
           6  reflecting mirror 
           7  reflective liquid crystal optical element (example of optical member, example of projector, example of first reflective liquid crystal optical element) 
           71  liquid crystal director 
           72  equiphase surface 
           8  eyeglass frame 
           81  arm 
           82  rim 
           9  correction reflective liquid crystal optical element (example of second reflective liquid crystal optical element) 
           20  controller 
           22  CPU 
           23  ROM 
           24  RAM 
           25  light-source drive circuit 
           26  scanning-mirror drive circuit 
           27  system bus 
           31  emission controller 
           32  light-source driver 
           33  scan controller 
           34  scanning-mirror driver 
           35  pupil position estimator 
           36  posture controller 
           37  stage driver 
           50  eyeball 
           52  pupil 
           53  retina 
           61  rightward circular polarized light 
           62  leftward circular polarized light 
           100  image display 
         P reflection point