Patent Publication Number: US-2020285048-A1

Title: Optical scanner, display system, and mobile body

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C, § 119(a) to Japanese Patent Application No. 2019-042798, filed on Mar. 8, 2019, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to an optical scanner, a display system, and a mobile body. 
     Description of the Related Art 
     There is known an optical scanner having an optical scanning range including a detection area and an image drawing area used for drawing an image. The image drawing area includes an area adjacent to the detection area in a main-scanning direction, and an area adjacent to the detection area in a sub-scanning direction. 
     It is an object of the present invention to provide the optical scanner, the display system, and the mobile body each being capable of increasing the proportion of the image area in the scanning range. 
     SUMMARY 
     In one aspect of this disclosure, there is provided an improved optical scanner including a light source; a light deflector configured to perform scanning in a first scanning direction and a second scanning direction orthogonal to the first scanning direction with irradiation light emitted from the light source; and a screen on which the light deflector performs the scanning with the irradiation light. The optical scanner is configured to turn on the light source based on image information to form an image on the screen in an image area included in a scanning range on the screen. The light deflector is configured to perform the scanning in the scanning range with the irradiation light. The image area has an outer periphery having at least one intersecting side intersecting with both the first scanning direction and the second scanning direction. 
     With the disclosure, the optical scanner, the display system, and the mobile body each being capable of increasing the proportion of the image area in the scanning range can be provided. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       A more complete appreciation of the disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG. 1  illustrates an example of a system configuration of a display system according to an embodiment; 
         FIG. 2  illustrates an example of a configuration of an on-board device according to the embodiment, 
         FIG. 3  is a top view of the on-board device according to the embodiment; 
         FIG. 4  is a side view of the on-board device according to the embodiment; 
         FIG. 5  is a side cross-sectional view of the on-board device according to the embodiment; 
         FIG. 6  is a top cross-sectional view of the on-board device according to the embodiment; 
         FIG. 7  illustrates an example of a configuration of a display device according to the embodiment; 
         FIG. 8  illustrates attachment and detachment of a screen unit to and from the display device according to the embodiment; 
         FIG. 9  illustrates an example of a hardware configuration of the display device according to the embodiment; 
         FIG. 10  illustrates an example of a functional configuration of the display device according to the embodiment; 
         FIG. 11  illustrates an example of a specific configuration of a light source device according to the embodiment; 
         FIG. 12  illustrates an example of a specific configuration of a light deflecting device according to the embodiment; 
         FIG. 13  illustrates an example of a specific configuration of a screen according to the embodiment; 
         FIGS. 14A and 14B  illustrate a difference in effect of a microlens array due to a difference in the magnitude relationship between the diameter of an incident light beam and the diameter of a lens; 
         FIG. 15  illustrates correspondence between a mirror of the light deflecting device and a scanning range; 
         FIG. 16  illustrates an example of a scanning line trajectory during two-dimensional scanning; 
         FIG. 17  is a plan view of the screen unit in view from an upstream side of an optical path; 
         FIG. 18  illustrates an image area and a detection area in the scanning range according to the embodiment; 
         FIGS. 19A and 19B  illustrate image areas and detection areas according to the embodiment and a comparative example; and 
         FIG. 20  illustrates an example of a virtual image according to the embodiment. 
     
    
    
     The accompanying drawings are intended to depict 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. 
     DETAILED DESCRIPTION 
     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. 
     Hereafter, an embodiment for implementing the disclosure is described with reference to the drawings. Like reference signs are applied to identical or corresponding components throughout the description of the drawings and redundant description thereof is omitted. 
       FIG. 1  illustrates an example of a system configuration of a display system  1  according to an embodiment. 
     The display system  1  causes a transmitting/reflecting member to project projection light projected from an on-board device  100  serving as an example of a projector to enable an observer  3  to visually recognize a display image. The display image is an image that is displayed as a virtual image  45  in a superimposed manner on the sight of the observer  3 . The display system  1  is included in, for example, a mobile body, such as a vehicle, an aircraft, or a ship; or an immobile body, such as a driving simulation system or a home theater system. In the embodiment, a case where the display system  1  is included in an automobile serving as an example of a mobile body  1 A is described. However, the way of using the display system  1  is not limited thereby. Hereafter, coordinate axes are defined such that X denotes a travel direction of the mobile body  1 A, Y denotes right and left directions, and Z denotes upward and downward directions. 
     The display system  1  enables the observer  3  (a driver) to visually recognize, via a windshield  50 , for example, navigation information required for driving a vehicle (information, such as the speed of the vehicle, route information, the distance to a destination, the name of the current location, the presence and position of an object in front of the vehicle, traffic signs of speed limit etc., and traffic jam information). In this case, the windshield  50  functions as a transmitting/reflecting member that transmits a portion of incident light and reflects at least a portion of the residual portion of the incident light. The distance from the viewpoint position of the observer  3  to the windshield  50  is in a range of from several tens of centimeters to about 1 meter. Instead of the windshield  50 , a combiner that is made of a transparent small plastic disk or the like may be used as a transmitting/reflecting member. 
     The on-board device  100  is, for example, a head-up display device (a HUD device). The on-board device  100  may be disposed at any position in accordance with the interior design of the automobile. For example, the on-board device  100  may be disposed below a dashboard  2  of the automobile or may be embedded in the dashboard  2  in the embodiment, a case where the on-board device  100  is mounted in the dashboard  2  is described. 
       FIG. 2  illustrates an example of a configuration of the on-board device  100  according to the embodiment. The on-board device  100  includes a display device  10  serving as an example of an optical scanner, a free-form surface mirror  30 , and the windshield  50 . 
     The display device  10  includes a light source device  11 , a light deflecting device (a light deflector)  13 , and a screen  15 . The light source device  11  emits a laser beam, which is emitted from a light source, to the outside of the light source device  11 . The light source device  11  may emit, for example, a laser beam in which laser beams of three colors including R, G, and B are combined. The laser beam emitted from the light source device  11  is guided to a reflecting surface of the light deflecting device  13 . The light source device  11  includes, as a light source, a semiconductor light emitting element such as a laser diode (LD). The light source is not limited to this. The light source may include a semiconductor light emitting element such as a light emitting diode (LED). 
     The light deflecting device  13  is an example of an image forming device that receives irradiation light emitted from the light source device  11  and emits image light to form an image. The light deflecting device  13  changes the travel direction of the laser beam by using microelectromechanical systems (MEMS) or the like. The light deflecting device  13  includes, for example, a scanner, such as a single very small MEMS mirror that swings about two orthogonal axes or a mirror system including two MEMS mirrors that each swing or rotate about one axis. The laser beam emitted from the light deflecting device  13  scans the screen  15 . The light deflecting device  13  may include a polygon mirror or the like instead of the MEMS mirror. 
     The screen  15  is an example of a screen on which image light emitted from the light deflecting device  13  forms an image. The screen  15  is a diverging member having a function of diverging a laser beam at a predetermined angle of divergence. The screen  15  includes, for example, as a form of an exit pupil expander (EPE), a transmissive optical element having light diffusing effect, such as a microlens array (MLA) or a diffusion plate. The screen  15  may be a reflective optical element having light diffusing effect such as a micromirror array. The laser beam emitted from the light deflecting device  13  scans the screen  15  to form an intermediate image  40 , which is a two-dimensional image, on the screen  15 . 
     Projection methods of the display device  10  include a “panel method” of using an imaging device, such as a liquid crystal panel, a digital micromirror device (DMD) panel, or a vacuum fluorescent display (VFD), to form the intermediate image  40 ; and a “laser scanning method” of using a scanner that performs scanning with the laser beam emitted from the light source device  11  to form the intermediate image  40 . 
     The display device  10  according to the embodiment uses the “laser scanning method”. The “laser scanning method” can assign one of emission and non-emission to each pixel and hence can typically form a high-contrast image. Alternatively, the display device  10  may use the “panel method” as the projection method. 
     The virtual image  45 , which is projected on the free-form surface mirror  30  and the windshield  50  with the laser beam (light beam) emitted from the screen  15 , is magnified from the intermediate image  40  and displayed. The free-form surface mirror  30  is designed and disposed so as to cancel out the inclination, distortion, positional deviation, and so forth, of an image, which occur due to a curved shape of the windshield  50 . The free-form surface mirror  30  may be disposed rotatably around a predetermined rotation shaft. Thus, the free-form surface mirror  30  can adjust the reflection direction of the laser beam (light beam) emitted from the screen  15  to change the display position of the virtual image  45 . 
     The free-form surface mirror  30  is designed by using existing optical design simulation software, to have a certain focal power so that the virtual image  45  can be formed at a desirable position. In the display device  10 , the focal power of the free-form surface mirror  30  is set so that the virtual image  45  is displayed, for example, at a position (depth position) in a range of from 1 m to 30 m (preferably 10 m or less) from the viewpoint position of the observer  3 . The free-form surface mirror  30  may be a concave mirror or another optical element having focal power. The free-form surface mirror  30  is an example of an image forming optical system. 
     The windshield  50  is a transmitting/reflecting member that has a function (partial reflection function) of transmitting a portion of a laser beam (light beam) and reflecting at least a portion of the residual portion of the laser beam. The windshield  50  functions as a semi-transmissive mirror that enables the observer  3  to visually recognize the front view and the virtual image  45 . The virtual image  45  is, for example, image information that enables the observer  3  to visually recognize vehicle information (speed, travel distance, and so forth), navigation information (route guide, traffic information, and so forth), and warning information (collision warning and so forth). The transmitting/reflecting member may be a front windshield or the like that is provided independently from the windshield  50 . The windshield  50  is an example of a reflecting member. 
     The virtual image  45  may be displayed to be superimposed on the view in front of the windshield  50 . The windshield  50  is not flat but curved. Thus, the position at which the virtual image  45  is formed is determined by the curved surfaces of the free-form surface mirror  30  and the windshield  50 . The windshield  50  may use a semi-transmissive mirror (combiner) that is an independent transmitting/reflecting member having a partial reflection function. 
     With such a configuration, a laser beam (light beam) emitted from the screen  15  is projected toward the free-form surface mirror  30 , and is reflected by the windshield  50 . With the light reflected by the windshield  50 , the observer  3  can visually recognize the virtual image  45 , which is a magnified image of the intermediate image  40  formed on the screen  15 . 
       FIG. 3  is a top view of the on-board device  100 . As illustrated in  FIG. 3 , the on-board device  100  includes two attachment portions  41   a  and  41   b  at a right surface portion, and two attachment portions  41   c  and  41   d  at a left surface portion. The attachment portions  41   a  to  41   d  are used to attach the on-board device  100  to the mobile body  1 A. The attachment portions  41   a  to  41   d  have respective screw holes, and the on-board device  100  is attached to the mobile body  1 A via the screw holes. 
       FIG. 4  is a right side view of the on-board device  100  attached to the mobile body  1 A. The mobile body  1 A includes an attachment bracket  42  welded or fastened to the dashboard  2 , and an attachment bracket  44  welded or fastened to a cross car beam  43 . The attachment bracket  42  and the attachment bracket  44  are examples of an installation portion. The attachment portions  41   a  and  41   c  are fastened to the attachment bracket  42  using screws or the like. The attachment portions  41   b  and  41   d  are fastened to the attachment bracket  44  using screws or the like. Thus the on-board device  100  is attached to the mobile body  1 A. 
       FIG. 5  is a side cross-sectional view of the on-board device  100  in view in the right direction (from the right side in the Y direction).  FIG. 6  is a top cross-sectional view of the on-board device  100  in view in the upward direction (the Z direction).  FIGS. 5 and 6  illustrate specific arrangement in the on-board device  100 . 
     The on-board device  100  includes, in addition to the display device  10  and the free-form surface mirror  30  illustrated in  FIG. 2 , a folding mirror  25  that is housed in a housing  102  and that reflects a laser beam projected from the display device  10  toward the freeform surface mirror  30 . The housing  102  includes an emission window  104  serving as an example of a transmitting member. The emission window  104  transmits reflected light reflected by the free-form surface mirror  30  and projects the reflected light onto the windshield  50 . The display device  10  and the screen  15  are disposed so that the laser beam is projected in the right direction (toward the right side in the Y direction). 
       FIG. 7  illustrates an example of a configuration of the display device  10 . The display device  10  includes, in addition to the light source device  11 , the light deflecting device  13 , and the screen  15  illustrated in  FIG. 2 ; a filter  307  that optically modulates the laser beam emitted from the light source device  11 ; a condenser lens  410  that condenses the modulated beam optically modulated by the filter  307  toward the light deflecting device  13 ; a mirror  401  that reflects the deflected beam deflected by the light deflecting device  13 ; and a second mirror  402  that reflects the reflected beam reflected by the mirror  401  toward the screen  15 . 
     The light source device  11  includes light source elements  1118 ,  111 G, and  111 B (hereafter, referred to as light source element  111  unless the elements are distinguished from one another); coupling (collimate) lenses  112 R,  112 G, and  112 B; and combining elements  114 ,  115 , and  116 . 
     The light source elements  111 R,  111 G, and  111 B for three colors (R, G, B) are, for example, laser diodes (LDs) each having a single emission point or multiple emission points. The light source elements  111 R,  111 G, and  111 B emit laser beams (light beams) having different wavelengths λR, λG, and λB (for example, λR=640 nm, λG=530 nm, and λB=445 nm). 
     The emitted laser beams (light beams) are respectively coupled by the coupling lenses  1128 ,  112 G, and  112 B and become substantially parallel light beams. The coupled laser beams (light beams) are combined by the three combining elements  114 ,  115 , and  116 . The combining elements  114 ,  115 , and  116  are plate-shaped or prism-shaped dichroic mirrors, and reflect or transmit laser beams (light beams) in accordance with the wavelength to combine the laser beams into a single light beam. The combined light beam passes through the filter  307  and the condenser lens  410  and is guided to the light deflecting device  13 . 
     The display device  10  is formed by assembling a housing  10 A, a mirror unit (a mirror holding member)  305 , and a screen unit  300 . The housing  10 A holds and houses the light source elements  111 R,  111 G, and  111 B; the coupling lenses  112 R,  112 G, and  112 B; the combining elements  114 ,  115 , and  116 ; the filter  307 ; the condenser lens  410 ; and the light deflecting device  13 . The mirror unit  305  holds the mirror  401  and the second mirror  402 . The screen unit  300  is an example of a holding member that holds the screen  15 . 
     A light source unit  110  is attachable to and detachable from the housing  10 A and holds the light source elements  111 R,  111 G, and  111 B. 
       FIG. 8  illustrates attachment and detachment of the screen unit  300  to and from the display device  10 . The screen unit  300  is attachable to and detachable from the housing  10 A without removing the light source unit  110  and the mirror unit  305  from the housing  10 A. The screen unit  300  is attachable to and detachable from the housing  10 A without removing the light source device  11 , the filter  307 , the condenser lens  410 , and the light deflecting device  13  from the housing  10 A. 
     The housing  10 A is molded by die casting with aluminum, and the mirror unit  305  is molded with resin. The housing  10 A has a higher thermal conductivity than the mirror unit  305 . 
     Image light diverging due to the screen  15  reaches the windshield  50  along an optical path illustrated in  FIGS. 1 and 2 . In actual use, sunlight incident on the windshield  50  may travel reversely along the optical path and may reach the screen  15  and the screen unit  300 . In this case, the screen  15  may be deformed and discolored due to heat of sunlight, and image quality may be decreased. 
     In the embodiment, the screen unit  300  is attached to the housing  10 A. Thus, compared with a case where the screen unit  300  is attached to the mirror unit  305  located on the upstream side in the optical path, heat of the screen  15  and the screen unit  300  is more likely dissipated, thereby reducing a decrease in image quality. 
     The screen unit  300  is attachable to and detachable from the housing  10 A without removing the mirror  401  and the second mirror  402  held by the mirror unit  305 , the light deflecting device  13 , and so forth, from the housing  10 A. Thus, the screen unit  300  alone can be easily replaced and maintained. Even if the screen  15  is deformed and discolored, a decrease in image quality can be reduced through replacement and maintenance of the screen  15 . 
     Moreover, the curvature of the windshield  50  varies depending on the type (model) of the mobile body  1 A, and hence the size, position, and angle of the screen  15  are required to be finely adjusted in accordance with the image forming optical system (the free-form surface mirror  30 ). However, since the screen unit  300  is attachable to and detachable from the housing  10 A, the housing  10 A can be standardized, thereby increasing productivity. 
       FIG. 9  illustrates an example of a hardware configuration of the display device  10  according to the embodiment. A component may be added to or omitted from the hardware configuration illustrated in  FIG. 9  if required. 
     The display device  10  includes a control device  17  that controls the operation of the display device  10 . The control device  17  is a controller that is one of a circuit board, an IC chip, and so forth, mounted in the display device  10 . The control device  17  includes a field-programmable gate array (FPGA)  1001 , a central processing unit (CPU)  1002 , a read only memory (ROM)  1003 , a random access memory (RAM)  1004 , an interface (I/F)  1005 , a bus line  1006 , an LD driver  1008 , a MEMS controller  1010 , and a motor driver  1012 . 
     The FPGA  1001  is an integrated circuit whose setting can be changed by the designer of the display device  10 . The LD driver  1008 , the MEMS controller  1010 , and the motor driver  1012  generate drive signals in accordance with control signals from the FPGA  1001 . The CPU  1002  is an integrated circuit that performs processing for control over the display device  10 . The ROM  1003  is a storage device that stores programs to control the CPU  1002 . The RAM  1004  is a storage device that functions as a work area of the CPU  1002 . The I/F  1005  is an interface for communication with an external device. The I/F  1005  is coupled to, for example, a controller area network (CAN) of an automobile. 
     An LD  1007  is, for example, a semiconductor light emitting element partly constituting the light source device  11 . The LD driver  1008  is a circuit that generates a drive signal for driving the  1007 . A MEMS  1009  is a device that partly constitutes the light deflecting device  13  and that displaces a scanning mirror. The MEMS controller  1010  is a circuit that generates a drive signal for driving the MEMS  1009 . A motor  1011  is an electric motor that rotates the rotation shaft of the free-form surface mirror  30 . The motor driver  1012  is a circuit that generates a drive signal for driving the motor  1011 . 
       FIG. 10  illustrates an example of a functional configuration of the display device  10  according to the embodiment. The functions implemented by the display device  10  include a vehicle information receiving unit  171 , an external information receiving unit  172 , an image generation unit  173 , and an image display section  174 . 
     The vehicle information receiving unit  171  is a function of receiving automobile information (information such as the speed and the travel distance) from the CAN and so forth. The vehicle information receiving unit  171  is implemented by processing performed by the I/F  1005  and the CPU  1002  illustrated in  FIG. 9 , a program stored in the RUM  1003 , and so forth. 
     The external information receiving unit  172  is a function of receiving information on the outside of the automobile (position information from the GPS, one of route information and traffic information from a navigation system, and so forth) from an external network. The external information receiving unit  172  is implemented by processing performed by the I/F  1005  and the CPU  1002  illustrated in  FIG. 9 , a program stored in the ROM  1003 , and so forth. 
     The image generation unit  173  is a function of generating image information for displaying the intermediate image  40  and the virtual image  45  based on the information that is input by the vehicle information receiving unit  171  and the external information receiving unit  172 . The image generation unit  173  is implemented by processing performed by the CPU  1002  illustrated in  FIG. 9 , a program stored in the RUM  1003 , and so forth. 
     The image display section  174  is a function of forming the intermediate image  40  on the screen  15  and projecting a laser beam (light beam) constituting the intermediate image  40  toward the windshield  50  to display the virtual image  45  based on the image information generated by the image generation unit  173 . The image display section  174  is implemented by processing performed by the CPU  1002 , the FPGA  1001 , the LD driver  1008 , the MEMS controller  1010 , and the motor driver  1012  illustrated in  FIG. 9 , a program stored in the ROM  1003 , and so forth. 
     The image display section  174  includes a controller  175 , an intermediate image forming unit  176 , and a projection unit  177 . The controller  175  generates control signals for controlling the operations of the light source device  11  and the light deflecting device  13  to form the intermediate image  40 . Moreover, the controller  175  generates a control signal for controlling the operation of the free-form surface mirror  30  to display the virtual image  45  at a predetermined position. 
     The intermediate image forming unit  176  forms the intermediate image  40  on the screen  15  based on the control signal generated by the controller  175 . The projection unit  177  projects a laser beam constituting the intermediate image  40  onto a transmitting/reflecting member (the windshield  50  or the like) to form the virtual image  45 , which is to be visually recognized by the observer  3 . 
       FIG. 11  illustrates an example of a specific configuration of the light source device  11  according to the embodiment. The light source device  11  includes, in addition to the configuration illustrated in  FIG. 7 , apertures  113 R,  113 G, and  113 B; an optical-path branch element  117 ; a condenser lens  118 , and a light receiving element  119 . The apertures  113 R,  113 G, and  113 B are disposed between the coupling lenses  1128 ,  112 G, and  112 B and the combining elements  114 ,  115 , and  116 . The apertures  1138 ,  113 G, and  113 E respectively shape laser beams (light beams) coupled by the coupling lenses  1128 ,  112 G, and  112 B. The apertures  113 R,  113 G, and  113 B have shapes (for example, circular shapes, elliptical shapes, rectangular shapes, or square shapes) appropriate for predetermined conditions, such as the angles of divergence of the laser beams (light beams). 
     The optical-path branch element  117  transmits a portion of the laser beam (light beam) emitted from the combining element  116 , guides the laser beam to the filter  307  illustrated in  FIG. 7 , reflects another portion of the laser beam, and guides the laser beam to the condenser lens  118 . The light receiving element  119  is an example of a light detector that detects irradiation light emitted from the combining element  116  serving as an example of a light source. The light receiving element  119  detects the intensity of the laser beam condensed by the condenser lens  118 . The controller  175  illustrated in  FIG. 10  controls the intensity of the laser beam emitted from the light source device  11  based on intensity information on the laser beam detected by the light receiving element  119 . 
       FIG. 12  illustrates an example of a specific configuration of the light deflecting device  13  according to the embodiment. The light deflecting device  13  is a MEMS mirror that is manufactured through a semiconductor process, and includes a mirror  130 , a meandering beam portion  132  ( 132   a ,  132   h ), a frame member  134 , and a piezoelectric member  136 . The light deflecting device  13  is an example of a light deflector that performs scanning in a main-scanning direction which is an example of a first scanning direction, and a sub-scanning direction which is an example of a second scanning direction intersecting with (orthogonal to) the first scanning direction. 
     The mirror  130  has a reflecting surface that reflects the laser beam emitted from the light source device  11  toward the screen  15 . The light deflecting device  13  defines a pair of meandering beam portions  132  with the mirror  130  interposed therebetween. The meandering beam portions  132  have a plurality of folding portions. The folding portions include first beam portions  132   a  and second beam portions  132   b  that are alternately arranged. The meandering beam portions  132  are supported by the frame member  134 . The piezoelectric member  136  is disposed to couple the first beam portion  132   a  and the second beam portion  132 . b  that are adjacent to each other. The piezoelectric member  136  applies different voltages to the first beam portion  132   a  and the second beam portion  132   b  to respectively warp the beam portions  132   a  and  132   b.    
     Thus, the first and second adjacent beam portions  132   a  and  132   b  are twisted in different directions. As twists are accumulated, the mirror  130  rotates in the vertical direction around an axis in the right and left directions. With such a configuration, the light deflecting device  13  can perform optical scanning in the vertical direction with a low voltage. Optical scanning in the horizontal direction around an axis in the upward and downward directions is performed by resonance using a torsion bar or the like that is coupled to the mirror  130 . 
       FIG. 13  illustrates an example of a specific configuration of the screen  15  according to the embodiment. A laser beam emitted from the LD  1007  partly constituting the light source device  11  forms an image on the screen  15 . The screen  15  is a diverging member that diverges a laser beam at a predetermined angle of divergence. The screen  15  illustrated in  FIG. 13  has a microlens array structure in which a plurality of microlenses  150  (convex portions each serving as an example of a curved portion), each having a hexagonal shape, are arranged with no gap therebetween. This microlens structure serves as an example in which a plurality of curved portions are arranged so as to diverge light. The microlenses  150  each have a lens diameter (the distance between two opposite sides) of about 200 μm. The plurality of microlenses  150  of the screen  15  each have a hexagonal shape to arrange the microlenses  150  with high density. The details of a microlens array  200  and the microlenses  150  according to the embodiment are described later. 
       FIGS. 14A and 14B  illustrate a difference in effect of the microlens array due to a difference in the magnitude relationship between the diameter of an incident light beam and the diameter of a lens. In  FIG. 14A , the screen  15  includes an optical plate  151  in which the microlenses  150  are arranged in an array. When incident light  152  scans the optical plate  151 , the incident light  152  is diverged by the microlenses  150  and becomes divergent beams  153 . Due to the structure of the microlenses  150 , the screen  15  can diverge the incident light  152  at a desirable angle of divergence  154 . The microlenses  150  are designed to each have a lens diameter  155  that is larger than the diameter  156   a  of the incident light  152 . Thus, the screen  15  does not cause interference between the lenses and reduces occurrence of interference noise. 
       FIG. 14B  illustrates an optical path of divergent beams when the diameter  156   b  of the incident light  152  is twice the lens diameter  155  of each of the microlenses  150 . The incident light  152  is incident on two microlenses  150   a  and  150   b , which respectively generate divergent beams  157  and  158 . At this time, the two divergent beams are present in an area  159 , and hence interference between the divergent beams may occur. When the interference light enters the eyes of the observer, the observer visually recognizes the interference light as interference noise. 
     With consideration of the above, in order to reduce interference noise, the lens diameter  155  of each of the microlenses  150  is designed to be larger than the diameter  156  of incident light. In  FIGS. 14A and 14B , the lenses are convex lenses. However, concave lenses may provide advantageous effects similar to those of the convex lenses. 
       FIG. 15  illustrates correspondence between a mirror  130  of the light deflecting device  13  and the scanning range. The FPGA  1001  controls the emission intensity, the on/off timing, and the light waveform of each of the light source elements of the light source device  11 . Each of the light source elements of the light source device  11  is driven by the LD driver  1008  and emits a laser beam. As illustrated in  FIG. 15 , a laser beam that is formed by combining the optical paths of laser beams emitted from the respective light source elements is two-dimensionally deflected by the mirror  130  of the light deflecting device  13  around the α axis and around the β axis. Then, the laser beam is emitted as scanning light onto the screen  15  via the mirror  130 . That is, the screen  15  is two-dimensionally scanned through main scanning and sub-scanning by the light deflecting device  13 . 
     The scanning range is the entire range that can be scanned by the light deflecting device  13 . The scanning light scans the scanning range of the screen  15  in one way in the sub-scanning direction at a low frequency of about several tens of hertz, while performing vibration scanning (two-way scanning) in the main-scanning direction at a high frequency in a range of from about 20000 Hz to about 40000 Hz, That is, the light deflecting device  13  performs raster scan on the screen  15 . In this case, since the emission of each of the light source elements is controlled in accordance with the scanning position (the position of scanning light), the display device  10  can perform drawing per pixel or displaying of a virtual image. 
     The time required for drawing one screen, that is, the scanning time for one frame (one period of two-dimensional scanning) is several tens of milliseconds, because the sub-scanning period is several tens of hertz as described above. For example, if the main scanning frequency is 20000 Hz and the sub-scanning frequency is 50 Hz, the scanning time for one frame is 20 msec. 
       FIG. 16  illustrates an example of a scanning line trajectory during two-dimensional scanning. As illustrated in  FIG. 16 , the screen  15  includes an image area  61  (effective scanning area) which the intermediate image  40  is formed (irradiated with light modulated in accordance with image data), and a frame area  62  that surrounds the image area  61 . 
     The scanning range is a range of the screen  15  including the image area  61  and a portion of the frame area  62  (a portion near the outer edge of the image area  61 ). In  FIG. 16 , the trajectory of a scanning line in the scanning range is indicated by a zigzag line. In  FIG. 16 , for convenience of illustration, the number of scanning lines is smaller than the actual number. 
     As described above, the screen  15  includes a transmissive optical element that has light diverging effect, such as the microlens array  200 . The image area  61  may not be a rectangular surface or a flat surface, and may be a polygonal surface or a curved surface. Depending on the device layout, the screen  15  may be, for example, a reflective optical element that has light diffusing effect, such as a micromirror array. In the following description, the embodiment is described on the assumption that the screen  15  includes the microlens array  200 . 
     The screen  15  includes a synchronous detection system  60  that is in a peripheral area of the image area  61  (a portion of the frame area  62 ) of the scanning range and that includes a light receiving element. Referring to  FIG. 16 , the synchronous detection system  60  is disposed at a corner of the image area  61  on the −X side and on the +Y side. The synchronous detection system  60  detects an operation of the light deflecting device  13  and outputs a synchronous signal for determining a scanning start timing and a scanning end timing to the FPGA  1001 . 
       FIG. 17  is a plan view of the screen unit  300  in view from the upstream side of the optical path. 
     The screen unit  300  includes a shield  74  located upstream of the screen  15  in the optical path. The shield  74  shields a portion of scanning light with which the light deflecting device  13  performs scanning. The shield  74  has an opening window  75  that transmits the scanning light. The area having the opening window  75  corresponds to the image area  61 . 
     The inner periphery of the opening window  75 , or in other words the inner periphery of the shield  74  has intersecting side portions  75 A and  75 B intersecting with both the main-scanning direction and the sub-scanning direction. 
     The intersecting side portion  75 A is an end portion in the main-scanning direction and an end portion in the sub-scanning direction of the opening window  75 , and is disposed at an upper left position in  FIG. 17 . The intersecting side portion  75 B is an end portion in the main-scanning direction and an end portion in the sub-scanning direction of the opening window  75 , and is disposed at an upper right position in  FIG. 17 . The intersecting side portions  75 A and  75 B both are arranged so that the opening window  75  expands downward. 
     As described above, since the area having the opening window  75  corresponds to the image area  61 , the outer periphery of the image area  61  has intersecting sides  61 A and  61 B intersecting with both the main-scanning direction and the sub-scanning direction to correspond to the intersecting side portions  75 A and  75 B. 
     The intersecting side  61 A is an end portion in the main-scanning direction and an end portion in the sub-scanning direction of the image area  61 , and is disposed at an upper left position in  FIG. 17 . The intersecting side  61 B is an end portion in the main-scanning direction and an end portion in the sub-scanning direction of the outer periphery of the image area  61 , and is disposed at an upper right position in  FIG. 17 . 
     In the embodiment, since the upward and downward directions of the image area  61  agree with the upward and downward directions of the virtual image  45 , the intersecting sides  61 A and  61 B both are arranged in an upper portion of the image area in the virtual image  45  and are arranged so that the image area expands downward. 
     The shield  74  is provided with optical sensors  60 A and  60 B as an example of a synchronous detection system. The optical sensors  60 A and  60 B face the upstream side of the optical path. Synchronous detection areas  600 A and  600 B serving as an example of a detection area indicate areas to be irradiated with scanning light for the optical sensors  60 A and  60 B. 
     In addition to the shield  74  in the optical path, a shield that shields a portion of the scanning light with which the light deflecting device  13  performs scanning may be provided immediately downstream of at least one of the mirror  401  and the light deflecting device  13  of the optical path. 
       FIG. 18  illustrates the image area and the detection area in the scanning range according to the embodiment. 
     A scanning range  63  in which the light deflecting device  13  performs two-dimensional scanning in the main-scanning direction and the sub-scanning direction is provided at the position at which the screen  15  and the shield  74  are disposed in the optical path. The scanning range  63  includes the image area  61  where an image is formed and the synchronous detection area  600 A. The synchronous detection area  600 B illustrated in  FIG. 17  is not illustrated in  FIG. 18 ; however, has a configuration similar to the synchronous detection area  600 A. 
     The image area  61  may be shifted from or rotated about the center of the scanning range  63 . The image area  61  may not be rectangular, and may be trapezoidal, elliptical, or polygonal as far as the image area  61  provides proper display. 
     The synchronous detection area  600 A is disposed to overlap the image area  61  in the main-scanning direction and the sub-scanning direction. Thus the proportion of the image area  61  in the scanning range  63  can be increased. 
     The outer periphery of the synchronous detection area  600 A has a facing and intersecting side  600 R facing the intersecting side  61 A of the outer periphery of the image area  61 , and intersecting with both the main-scanning direction and the sub-scanning direction. The facing and intersecting side  600 R is parallel to the intersecting side  61 A with a distance L interposed in the main-scanning direction. 
       FIGS. 19A and 19B  illustrate image areas and detection areas according to the embodiment and a comparative example. 
       FIG. 19A  illustrates the details of the image area and the detection area according to the comparative example. The outer periphery of the image area  61  has a step-shaped side  61 X. The optical sensor  60 A includes photosensors  60 A 1  and  60 A 2  extending in the sub-scanning direction. A synchronous detection area  600 X is defined to have a margin  60 R on the right side of the photosensor  60 A 1  and a margin  60 L on the left side of the photosensor  60 A 2 , and has sides parallel to the sub-scanning direction to have a constant distance from the side  61 X in the main-scanning direction. 
       FIG. 19B  illustrates the details of the image area and the detection area according to the embodiment. The outer periphery of the image area  61  has the intersecting side  61 A. The optical sensor  60 A includes photosensors  60 A 1  and  60 A 2  extending in the sub-scanning direction. The synchronous detection area  600 A is defined to have a margin  60 R on the right side of the photosensor  60 A 1  and a margin  60 L on the left side of the photosensor  60 A 2 , and has a facing and intersecting side  600 R parallel to the intersecting side  61 A and an intersecting side  600 L parallel to the facing and intersecting side  600 R to have a constant distance from the intersecting side  61 A in the main-scanning direction. 
     Since the image area  61  has the intersecting side  61 A illustrated in  FIG. 19B , the image area  61  can be larger compared with the case where the image area  61  has the side  61 X illustrated in  FIG. 19A . 
     Since the facing and intersecting side  600 R and the intersecting side  600 L illustrated in  FIG. 19B  are provided, the synchronous detection area  600 A illustrated in  FIG. 19B  can be smaller than the synchronous detection area  600 X illustrated in  FIG. 19A . Thus, an influence on an image formed in the image area  61  by, for example, light reflected by the synchronous detection area  600 A can be reduced. 
       FIG. 20  illustrates an example of a virtual image  45  according to the embodiment. The virtual image  45  includes superimposition information  45   a  that is superimposed on a leading vehicle (the mobile body  1 A) and character information  45   b . The image area in the virtual image  45  includes intersecting sides  45 A and  45 B to correspond to the intersecting sides  61 A and  61 B of the image area  61 . The intersecting sides  45 A and  45 B are arranged in an upper portion of the image area in the virtual image  45  and are arranged so that the image area expands downward. 
     As illustrated in  FIG. 20 , a far object is recognized as being small in an upper section and a close object is recognized as being large in a lower section of the sight of the observer  3  via the windshield  50 , like lane lines in  FIG. 20 . Although the image area in the virtual image  45  is limited by the intersecting sides  45 A and  45 B, the limited image area does not give the observer  3  unnatural feeling. 
     The display device, the display system, and the mobile body according to the embodiment of the disclosure have been described above. However, the disclosure is not limited to the embodiment described above, and the embodiment may be modified within a scope conceivable by a person having ordinary skill in the art. 
     The display device according to the embodiment of the disclosure is not limited to a HUD device, and may be, for example, a head mount display device, a prompter device, a projector device, or the like. For example, when the display device according to the embodiment of the disclosure is applied to a projector device, the projector device may be configured in a similar way to the display device  10 . That is, the display device  10  may project image light via the free-form surface mirror  30  onto a projection screen, a wall surface, or the like. The display device  10  may project image light via the screen  15  onto a projection screen, a wall surface, or the like without using the free-form surface mirror  30 . 
     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.