Patent Publication Number: US-2022221712-A1

Title: Optical deflection apparatus and image projection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2021-002102, filed Jan. 8, 2021, the content of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure relates to an optical deflection apparatus and an image projection apparatus. 
     2. Description of the Related Art 
     Conventionally, an image projection apparatus projects an image onto a scan-target surface using an optical deflection apparatus that deflects, at a reflection surface, light emitted from a light emitting unit. 
     Furthermore, for example, Japanese Patent No. 5492765 discloses an image projection apparatus that includes a first deflector that deflects light into a first direction and a scanning optical system that is disposed between the first deflector and the scan-target surface. 
     In the configuration of Japanese Patent No. 5492765, in order to reduce TV distortion and trapezoidal distortion of images to be projected, the central axes of the respective optical members constituting the scanning optical system are located on the same straight line to serve as the optical axis of the scanning optical system, and the center of the scan-target surface is shifted in position in a second direction with respect to an intersection between the optical axis and the plane including the scan-target surface. Also, the first deflector is provided such that the axis of the first deflector is inclined with respect to the second direction by a first angle within a plane including the optical axis and the second direction. 
     SUMMARY 
     The present disclosure provides an optical deflection apparatus that includes a first optical deflection part configured to deflect light incident on a first reflection surface, by swinging the first reflection surface about a first swing axis, and a second optical deflection part configured to deflect the light deflected by the first reflection surface, by swinging a second reflection surface about a second swing axis crossing the first swing axis, wherein the first swing axis crosses a first incidence plane including a central axis of the light incident on the first reflection surface and a central axis of the light deflected by the first reflection surface, and the second swing axis crosses a second incidence plane including a central axis of the light incident on the second reflection surface and a central axis of the light deflected by the second reflection surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a configuration example of the entirety of an image projection apparatus according to an embodiment. 
         FIG. 2A  is a plan view illustrating a configuration example of an optical deflection apparatus according to the embodiment. 
         FIG. 2B  is a left side view illustrating the configuration example of the optical deflection apparatus according to the embodiment. 
         FIG. 2C  is a front view illustrating the configuration example of the optical deflection apparatus according to the embodiment. 
         FIG. 2D  is a cross-sectional view taken along line A-A of  FIG. 2C . 
         FIG. 3  is a perspective view illustrating a configuration example of a first optical deflection part according to the embodiment. 
         FIG. 4A  is a drawing for explaining an example of a horizontal driving signal. 
         FIG. 4B  is a drawing for explaining an example of a vertical driving signal. 
         FIG. 5  is a perspective view illustrating a configuration example of a second optical deflection part according to the embodiment. 
         FIG. 6A  is a drawing illustrating an example of arrangement of the optical deflection apparatus according to the embodiment as seen from a first swing axis direction. 
         FIG. 6B  is a drawing illustrating an example of arrangement of the optical deflection apparatus according to the embodiment as seen from a second swing axis direction. 
         FIG. 7  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus according to the embodiment. 
         FIG. 8  is a drawing illustrating a configuration of an optical deflection apparatus according to a first comparative example. 
         FIG. 9A  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus according to the first comparative example as seen from the first swing axis direction. 
         FIG. 9B  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus according to the first comparative example as seen from the second swing axis direction. 
         FIG. 10  is a perspective view illustrating a configuration of an optical deflection apparatus according to a second comparative example. 
         FIG. 11  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus according to the second comparative example. 
         FIG. 12A  is a drawing illustrating an example of distortion according to the first comparative example. 
         FIG. 12B  is a drawing illustrating an example of distortion according to the second comparative example. 
         FIG. 12C  is a drawing illustrating an example of distortion according to the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, an embodiment will be described with reference to the drawings. In the drawings, the same components are denoted with the same numerals and duplicate descriptions about the same components may be omitted. 
     The embodiment shown below is an example of an optical deflection apparatus and an image projection apparatus for implementing the technical idea of the present disclosure, and the present disclosure is not limited to the embodiment shown below. Unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described below are not intended to limit the scope of the present disclosure to those described, but are intended to show examples. Furthermore, the sizes and the arrangements of the members shown in the drawings may be exaggerated for the sake of clarification of the explanation. 
     The optical deflection apparatus according to the embodiment includes a first optical deflection part configured to deflect light incident on a first reflection surface by swinging the first reflection surface about a first swing axis. In addition, the optical deflection apparatus according to the embodiment includes a second optical deflection part configured to deflect light deflected by the first reflection surface by swinging a second reflection surface about a second swing axis that crosses the first swing axis. 
     For example, such an optical deflection apparatus is used to scan a scan-target surface by deflecting light with an image projection apparatus and the like that projects an image onto the scan-target surface. The image projection apparatus may be, for example, a projector, a welcome projector of a vehicle, a head-up display, a head-mounted display, a headlamp of a vehicle, an object recognition apparatus, a distance measurement apparatus, an ocular fundus camera, or the like. 
     The welcome projector of the vehicle is a projector provided on a door or the like of the vehicle to project a desired image including a logo when the door is opened. The object recognition apparatus is an apparatus that detects and recognizes a presence or absence of an object or detects and recognizes a distance to an object, on the basis of reflected light or scattered light of projected light reflected or scattered by the object. 
     With such an image projection apparatus, distortion may occur in the projected image. The distortion refers to a phenomenon in which a projected image is distorted. Types of distortions include a barrel type in which image magnification decreases with distance from the center; a pincushion type distortion in which image magnification increases with distance from the center; a mustache type distortion that is a mixture of both of the barrel type and the pincushion type distortions, i.e., the barrel type distortion occurs close to the center of the image and the distortion gradually turns into the pincushion type distortion towards the periphery of the image; and the like. The term “distortion” as used in the embodiment is meant to include any of the types of distortions described above, and also meant to include a distortion in which the types of distortions described above occur in a mixed manner in a single image. 
     According to another aspect, the distortion includes: an optical distortion meaning distortion that is corrected by image processing and the like; and TV distortion meaning a distortion that is not corrected by image processing and the like. The term “distortion” as used in the embodiment can be considered to be TV distortion as it is not expected to be corrected by image processing and the like. 
     In the embodiment, the first swing axis crosses a first incidence plane that includes the central axis of the light that is incident on the first reflection surface and the central axis of the light deflected by the first reflection surface. Further, the second swing axis crosses a second incidence plane that includes the central axis of the light that is incident on the second reflection surface and the central axis of the light that is reflected by the second reflection surface. According to this configuration, in the optical deflection apparatus, the mechanism for reducing distortion of a projected image can be simplified. 
     In this case, the central axis of the light refers to an axis that passes through the center of a luminous flux that propagates as light. For example, in a case where light is laser light (laser beam), the central axis of the laser light means an axis that passes the center of a cross section of the laser light taken along a plane perpendicular to the propagation direction of the laser light, the axis being along the traveling direction of the laser light. 
     The term “deflection light” as used in the embodiment means to change the traveling direction of light. In the embodiment, light is deflected by causing the light to be reflected by the reflection surface. 
     Hereinafter, an embodiment is explained with reference to the image projection apparatus including the optical deflection apparatus according to the embodiment as an example. 
     In the following drawings, directions may be indicated by the X axis, the Y axis, and the Z axis. The X direction along the X axis indicates a direction in which the first optical deflection part provided in the optical deflection apparatus according to the embodiment deflects and scans light. The Y direction along the Y axis indicates a direction in which the second optical deflection part provided in the optical deflection apparatus according to the embodiment deflects and scans light. The X axis and the Y axis are substantially perpendicular to each other. The Z direction along the Z axis indicates a direction substantially perpendicular to both of the X axis and the Y axis. 
     A direction indicated by an arrow in the X direction is denoted as +X direction, a direction opposite to +X direction is denoted as −X direction, a direction indicated by an arrow in the Y direction is denoted as +Y direction, a direction opposite to +Y direction is denoted as −Y direction, a direction indicated by an arrow in the Z direction is denoted as +Z direction, and a direction opposite to the +Z direction is denoted as −Z direction. However, the above is not intended to impose limitation on the direction in which the optical deflection apparatus and the image projection apparatus are used, and the optical deflection apparatus and the image projection apparatus may be provided in any desired direction. 
     &lt;Configuration Example of Image Projection Apparatus  100 &gt; 
     First, a configuration example of the entirety of an image projection apparatus  100  according to the embodiment and the configuration of an optical deflection apparatus  20  provided in the image projection apparatus  100  are explained with reference to  FIG. 1  and  FIGS. 2A to 2D . 
       FIG. 1  is a perspective view illustrating the configuration example of the entirety of the image projection apparatus  100  according to an embodiment.  FIG. 2A  is a plan view illustrating a configuration example of the optical deflection apparatus  20  according to the embodiment.  FIG. 2B  is a left side view illustrating the configuration example of the optical deflection apparatus  20  according to the embodiment.  FIG. 2C  is a front view illustrating the configuration example of the optical deflection apparatus  20  according to the embodiment.  FIG. 2D  is a cross-sectional view taken along line A-A of  FIG. 2C . 
     As illustrated in  FIG. 1 , the image projection  2 C apparatus  100  includes a light emitting unit  10 , the optical deflection apparatus  20 , and a control unit  30 , which are provided in the body of the image projection apparatus  100 . 
     The image projection apparatus  100  causes the optical deflection apparatus  20  to scan, in the X direction and the Y direction, the laser light in respective wavelengths, i.e., red, green, blue, and IR (infrared), emitted by the light emitting unit  10 , under the control of the control unit  30  to project an image  201  in full color onto a scan-target surface  200 . 
     In the present embodiment, as an example, the Y direction corresponds to the gravity direction, and the X direction corresponds to a horizontal direction substantially perpendicular to the gravity direction. The optical deflection apparatus  20  deflects laser light of each of the wavelengths of red, green, blue, and IR emitted by the light emitting unit  10  to scan the laser light in two directions, i.e., the X direction and the Y direction, on the scan-target surface  200 . 
     However, the image  201  projected by the image projection apparatus  100  is not limited to images in full color, and may be monochrome images and the like. In a case where a monochrome image is projected, the image projection apparatus  100  scans the monochrome laser light on the scan-target surface  200 . 
     In a case where the image projection apparatus  100  is a projector, the scan-target surface  200  corresponds to a screen and the like. In a case where the image projection apparatus  100  is a head-up display, the scan-target surface  200  corresponds to a front windshield and the like of an automobile. 
     In a case where the image projection apparatus  100  is a head-mounted display or an ocular fundus camera, the scan-target surface  200  corresponds to a hologram optical element, the retina of an eyeball, and the like. In a case where the image projection apparatus  100  is a headlamp, an object recognition apparatus, or a distance measurement apparatus of a vehicle, the scan-target surface  200  corresponds to a virtual plane in a space. 
     The light emitting unit  10  includes an LD (Laser Diode) emitting laser light in red, an LD emitting laser light in green, an LD emitting laser light in blue, and an LD emitting laser light in IR. The light emitting unit  10  causes laser light of respective wavelengths, i.e., red, green, blue, and IR, emitted from the LDs of the respective wavelengths, to be incident on the optical deflection apparatus  20 . The laser light in respective wavelengths is an example of light emitted by a light emitting unit. 
     As illustrated in  FIG. 1  and  FIG. 2 , the optical deflection apparatus  20  includes an input window  1 , a first optical deflection unit  2 , a second optical deflection unit  3 , an output window  4 , and a housing  5 . 
     The input window  1  is a plate-shaped member that functions as a window through which the laser light emitted by the light emitting unit  10  is input to the inside of the housing  5 . The input window  1  is made of materials transparent with respect to the wavelength of laser light in each color emitted by the light emitting unit  10 , such as optical glass, heat-resistant glass, hard glass, optical plastic, and hard plastic. It is preferable to provide antireflection films on both sides of the input window  1  to prevent reflection of the laser light. 
     The first optical deflection unit  2  includes a first optical deflection part  21  and a first package  2   a  for holding the first optical deflection part  21 . The first optical deflection unit  2  deflects the laser light in each color that is input through the input window  1  and causes the deflected laser light to be incident upon the second optical deflection unit  3 . 
     The second optical deflection unit  3  includes a second optical deflection part  31  and a second package  3   a  for holding the second optical deflection part. The second optical deflection unit  3  further deflects the laser light in each color deflected by the first optical deflection unit  2 , and scans the laser light on the scan-target surface  200  in each direction, i.e., the X direction and the Y direction. 
     The first package  2   a  and the second package  3   a  are configured to include: alumina ceramic; a metal material such as aluminum, aluminum alloy, or stainless steel; or a plastic material. Further, the first package  2   a  and the second package  3   a  include a circuit board and the like constituted by fiber reinforced plastics (FRP), flexible printed circuits (FPC), or the like. 
     Each configuration of the first optical deflection unit  2  and the second optical deflection unit  3  is explained later with reference to  FIG. 3  to  FIG. 6  and the like. 
     The output window  4  is a plate-shaped member that functions as a window through which the laser light deflected by the first optical deflection unit  2  and thereafter further deflected by the second optical deflection unit  3  is output from the inside of the housing  5 . The output window  4  is made of materials transparent with respect to the wavelength of laser light in each color emitted by the light emitting unit  10 , such as optical glass, heat-resistant glass, hard glass, optical plastic, and hard plastic. It is preferable to provide antireflection films on both sides of the output window  4  to prevent reflection of the laser light. 
     The housing  5  is a member that fixes and holds each of the input window  1 , the first optical deflection unit  2 , the second optical deflection unit  3 , and the output window  4 . In addition, the housing  5  has a function of preventing dust, debris, or the like from adhering to the first optical deflection unit  2  or the second optical deflection unit  3  by preventing dust, debris, or the like from entering the inside. 
     The material of the housing  5  is not particularly limited, but may be configured to include: alumina ceramic; a metal material such as aluminum, aluminum alloy, or stainless steel; or a plastic material. 
     For example, the housing  5  is preferably configured to include an opaque material that is not transparent with respect to the wavelength of visible light, because external light such as indoor lighting and sunlight is prevented from being incident on the inside of the housing  5 , and furthermore, the laser light emitted by the light emitting unit  10  is prevented from leaking to the outside of the housing  5 . 
     The control unit  30  controls the light emission of the LD of each color achieved by the light emitting unit  10  by applying a driving signal such as a driving voltage to the light emitting unit  10 . The control unit  30  controls the scanning of the laser light achieved by the optical deflection apparatus  20  by applying a driving signal such as a driving voltage to the optical deflection apparatus  20 . 
     Some of the functions of the control unit  30  may be achieved by an electric circuit, and some other of the functions may be achieved by software that is executable by a central processing unit (CPU). 
     &lt;Configuration Example of First Optical Deflection Part  21 &gt; 
     Next, the configuration of the first optical deflection part  21  is explained with reference to  FIG. 3 .  FIG. 3  is a perspective view for explaining an example of the configuration of the first optical deflection part  21 . For the sake of explanation,  FIG. 3  illustrates the first optical deflection part  21  with the first package  2   a  of the first optical deflection unit  2  being detached. 
     The first optical deflection part  21  deflects the laser light incident on the first reflection surface  22  by swinging the first reflection surface  22  about the first swing axis A. The first optical deflection part  21  is, for example, a MEMS (Micro Electro Mechanical Systems) mirror or the like that drives the first reflection surface  22  by a piezoelectric element. 
     As illustrated in  FIG. 3 , the first optical deflection part  21  includes a first reflection surface  22 , a first movable portion  23 , torsional beams  24   a  and  24   b , a first support portion  25 , first driving beams  26   a  and  26   b , and first drive sources  27   a  and  27   b.    
     The first reflection surface  22  is a surface that reflects light. The first reflection surface  22  has a substantially circular outer shape and is supported on the upper surface of the first movable portion  23 . The first reflection surface  22  may be a surface formed on the upper surface of the first movable portion  23 . 
     Both ends of the first movable portion  23  are connected to the ends of torsional beams  24   a  and  24   b . The torsional beams  24   a  and  24   b  constitute the first swing axis A, extending along the direction of the first swing axis A and supporting the first movable portion  23  from both sides in the direction of the first swing axis A. 
     When the torsional beams  24   a  and  24   b  are twisted, the first reflection surface  22  supported by the first movable portion  23  swings about the first swing axis A. When the first reflection surface  22  is twisted, laser light that is incident on and reflected by the first reflection surface  22  can be deflected and scanned about the first swing axis A. The torsional beams  24   a  and  24   b  are connected by and supported on the first support portion  25 . 
     In the first movable portion  23 , slits  28  are formed along the circumference of the first reflection surface  22 . With the slits  28 , while the stress concentration generated by the torsional motion of the torsional beams  24   a  and  24   b  can be dispersed to prevent damage to the first reflection surface  22 , the torsion caused by the torsional beams  24   a  and  24   b  can be transmitted to the first reflection surface  22 . 
     The first driving beams  26   a  and  26   b  constitute a pair and are provided such that the first reflection surface  22  and the first movable portion  23  are interposed between the first driving beams  26   a  and  26   b  in the direction perpendicular to the torsional beams  24   a  and  24   b . The first drive source  27   a  is formed on the upper surface of the first driving beam  26   a , and the first drive source  27   b  is formed on the upper surface of the first driving beam  26   b.    
     The first drive source  27   a  includes: an upper electrode formed in a thin film of a piezoelectric element (hereinafter also referred to as a “piezoelectric thin film”) on the upper surface of the first driving beam  26   a ; and a lower electrode formed in a piezoelectric thin film on the lower surface of the first driving beam  26   a . The first drive source  27   a  expands and contracts depending on the polarity of the driving voltage applied to the upper and lower electrodes. 
     Likewise, the first drive source  27   b  includes: an upper electrode formed in a piezoelectric thin film on the upper surface of the first driving beam  26   b ; and a lower electrode formed in a piezoelectric thin film on the lower surface of the first driving beam  26   b . The first drive source  27   b  contracts, or expands and contracts depending on the polarity of the driving voltage applied to the upper and lower electrodes. 
     When voltages of different phases are applied alternately to the first driving beam  26   a  and the first driving beam  26   b , the first driving beam  26   a  and the first driving beam  26   b  alternately vibrate, on the left side and the right side of the first reflection surface  22 , to the opposite sides in the vertical direction. Accordingly, the first reflection surface  22  can swing about the first swing axis A, which includes the torsional beams  24   a  and  24   b . For example, resonant vibration is used to swing the first driving beams  26   a  and  26   b , so that the first reflection surface  22  can swing at a high speed. 
     In this case,  FIG. 4A  is a drawing for explaining an example of a horizontal driving signal.  FIG. 4B  is a drawing for explaining an example of a vertical driving signal. 
     As illustrated in  FIGS. 4A and 4B , both of the horizontal driving signal AHp and a horizontal driving signal AHn are sine waves with the same cycle and amplitude, and a horizontal driving signal AHn is shifted by half the cycle with respect to the horizontal driving signal AHp. Specifically, the horizontal driving signals AHp and AHn are in such a relationship that the potentials of the horizontal driving signals AHp and AHn are inverted with respect to the intermediate potential. The first reflection surface  22  is driven according to a potential difference between the horizontal driving signal AHp and the horizontal driving signal AHn, and the swing angle of the first reflection surface  22  corresponds to the amplitude of the horizontal driving signal AHp and the horizontal driving signal AHn. 
     The first optical deflection part  21  can be produced by, for example, a semiconductor process using a SOI (Silicon On Insulator) substrate including a support layer, a BOX (Buried Oxide) layer, and an active layer. 
     &lt;Configuration Example of Second Optical Deflection Part  31 &gt; 
     Next, the configuration of the second optical deflection part  31  is explained with reference to  FIG. 5 .  FIG. 5  is a perspective view illustrating a configuration example of the second optical deflection part  31 . For the sake of explanation,  FIG. 5  illustrates the second optical deflection part  31  with the second package of the second optical deflection unit  3  being detached. 
     The second optical deflection part  31  deflects the laser light deflected by the first reflection surface  22  by swinging a second reflection surface  32  about a second swing axis B crossing the first swing axis A. The second optical deflection part  31  is, for example, a MEMS mirror or the like that drives the second reflection surface  32  by a piezoelectric element. 
     As illustrated in  FIG. 5 , the second optical deflection part  31  includes a second reflection surface  32 , a second movable portion  33 , first connection portions  34   a  and  34   b , second driving beams  35   a  and  35   b , second drive sources  36   a  and  36   b , second connection portions  37   a  and  37   b , and a second support portion  38 . 
     The second reflection surface  32  is a surface that reflects light. The second reflection surface  32  has a substantially circular outer shape and is supported on the upper surface of the second movable portion  33 . The second reflection surface  32  may be a surface formed on the second movable portion  33 . 
     The second movable portion  33  is connected via the first connection portion  34   a  to one end of the second driving beam  35   a . The second driving beam  35   a  includes: multiple vertical beams in a rectangular shape extending in a direction perpendicular to the second swing axis B; and a folded portion for connecting the ends of adjacent vertical beams with each other, and has a zigzag shape as a whole. The other end of the second driving beam  35   a  is connected to and supported by the second support portion  38  via the second connection portion  37   a.    
     Also, the second movable portion  33  is connected via the first connection portion  34   b  to one end of the second driving beam  35   b . The second driving beam  35   b  includes: multiple vertical beams in a rectangular shape extending in the direction perpendicular to the second swing axis B; and a folded portion for connecting the ends of adjacent vertical beams with each other, and has a zigzag shape as a whole. The other end of the second driving beam  35   b  is connected to and supported by the second support portion  38  via the second connection portion  37   b.    
     For each of the vertical beams each of which is a rectangular unit not including a curved portion, the second drive source  36   a  is formed on the upper surface of the second driving beam  35   a . The second drive source  36   a  includes: an upper electrode formed in a piezoelectric thin film on the upper surface of the second driving beam  35   a ; and a lower electrode formed in a piezoelectric thin film on the lower surface of the second driving beam  35   a.    
     For each of the vertical beams that are rectangular units not including curved portions, the second drive source  36   b  is formed on the upper surface of the second driving beam  35   b . The second drive source  36   b  includes: upper electrodes formed in a piezoelectric thin film on the upper surface of the second driving beam  35   b ; and lower electrodes formed in a piezoelectric thin film on the lower surface of the second driving beam  35   b.    
     By applying a driving voltage to the vertical beams adjacent to each other of the second drive sources  36   a  and  36   b , the second driving beams  35   a  and  35   b  bend all the vertical beams in an upward direction to transmit the accumulation of bending of each vertical beam to the second movable portion  33 . According to this operation, the second driving beams  35   a  and  35   b  swing the second reflection surface  32  about the second swing axis B. For example, non-resonant vibration can be used to drive the second driving beams  35   a  and  35   b  to swing. In the present embodiment, although, for example, resonant driving is used for the first optical deflection part  21  and non-resonant driving is used for the second optical deflection part  31 , resonant driving may be used for both of the first optical deflection part  21  and the second optical deflection part  31 . Alternatively, non-resonant driving may be used for both of the first optical deflection part  21  and the second optical deflection part  31 . 
     For example, the second drive source  36   a  includes second drive sources  36   a   1  and  36   a   2  arranged in a direction away from the second movable portion  33 . Also, the second drive source  36   b  includes second drive sources  36   b   1  and  36   b   2  arranged in a direction away from the second movable portion  33 . 
     In this case, the same sawtooth-shaped waveforms are applied to the second drive sources  36   a   1  and  36   b   2  and right-and-left inverted sawtooth-shaped waveforms are applied to the second drive sources  36   a   2  and  36   b   1 , so that the second movable portion  33  swings about the second swing axis B. The second optical deflection part  31  as illustrated in  FIG. 5  has a point symmetrical structure, but in a case where the second optical deflection part  31  has a line symmetrical structure, the second drive sources  36   a   1 ,  36   b   1 ,  36   a   2 , and  36   b   2  are driven by applying right-and-left inverted sawtooth-shaped waveforms to the second drive sources  36   a   1 ,  36   b   1 ,  36   a   2 , and  36   b   2 . 
     The second reflection surface  32  is connected to the second driving beams  35   a  and  35   b  via the first connection portions  34   a  and  34   b  arranged at point symmetrical positions, and therefore, the vertical driving signals are applied as shown in the relationship of  FIG. 4B . The vertical beams bend only in the upward direction, not bending in the opposite directions, i.e., upward and downward directions. The driving signals applied to the piezoelectric thin films are similar to  FIG. 4B . 
     Both of vertical driving signals AVp and AVn are sawtooth-shaped waveforms having the same cycle and amplitude, and the vertical driving signals AVp and AVn have potentials that are inverted with respect to the intermediate potential. The second reflection surface  32  is driven according to the potential difference between the vertical driving signals AVp and AVn, and the swing angle of the second reflection surface  32  corresponds to the amplitude of the vertical driving signals AVp and AVn. 
     The driving wires for applying driving voltages to the upper electrodes and the lower electrodes of the second drive sources  36   a  and  36   b  are connected to predetermined terminals included in a terminal group provided in the second support portion  38 . 
     Like the first optical deflection part  21 , the second optical deflection part  31  can be produced by, for example, a semiconductor process using a SOI (Silicon On Insulator) substrate including a support layer, a BOX (Buried Oxide) layer, and an active layer. 
     &lt;Example of Arrangement of Optical Deflection Apparatus  20 &gt; 
     Next, an arrangement of the optical deflection apparatus  20  is explained with reference to  FIGS. 6A and 6B .  FIGS. 6A and 6B  are drawings illustrating an example of arrangement of the optical deflection apparatus  20 . For the sake of explanation,  FIGS. 6A and 6B  illustrate the first optical deflection unit  2  and the second optical deflection unit  3  with the housing  5  and the like of the optical deflection apparatus  20  being detached. 
       FIG. 6A  is a drawing illustrating the first optical deflection unit  2  and the second optical deflection unit  3  as seen from the right side in the first swing axis A. The direction in which  FIG. 6A  is depicted is the same as the direction in which  FIG. 2C  is depicted.  FIG. 6B  is a drawing illustrating the first optical deflection unit  2  and the second optical deflection unit  3  as seen from the right side in the second swing axis B. The direction in which  FIG. 6B  is depicted is the same as the direction in which  FIG. 2B  is depicted. 
     As illustrated in  FIG. 6 , the first optical deflection unit  2  includes the first optical deflection part  21  and the first package  2   a . The second optical deflection unit  3  includes a second optical deflection part  31  and a second package  3   a.    
     The second optical deflection unit  3  is arranged so that the second swing axis B of the second optical deflection part  31  is along the X axis. The first optical deflection unit  2  is arranged so that the first swing axis A of the first optical deflection part  21  is substantially perpendicular to the second swing axis B. 
     The first optical deflection part  21  is arranged so that the laser light that is incident on the first reflection surface  22  can be deflected by swinging the first reflection surface  22  about the first swing axis A, so that the second reflection surface  32  is scanned with the deflected laser light along the second swing axis B. 
     As illustrated in  FIG. 6A , an inclination of the second swing axis B with respect to the first reflection surface  22  that is not swinging is an angle θ 1 . This angle θ 1  is preferably 30 degrees. However, it is tolerated that the angle θ 1  has a margin of 9.0 degrees, which is 1/10 of 90 degrees, i.e., a variation of ±4.5 degrees, in view of a variation in manufacture and the like. Therefore, the angle θ 1  is preferably 25.5 degrees or more and 34.5 degrees or less. 
     A scan angle range η 1  indicated by broken lines of  FIG. 6A  indicates a scan angle range of the center of the intensity of laser light scanned by the first optical deflection part  21 . Scan center laser light  63  passing through the center of the scan angle range η 1  is incident upon the second reflection surface  32  from a direction substantially perpendicular to the second swing axis B. Specifically, an angle θ 3  formed by the scan center laser light  63  and the second swing axis B is approximately 90 degrees. 
     As illustrated in  FIG. 6B , an inclination of the first swing axis A with respect to the second reflection surface  32  that is not swinging is an angle θ 2 . This angle θ 2  is preferably 35 degrees. However, it is tolerated that the angle θ 2  has a variation of ±4.5 degrees in view of a variation in manufacture and the like. The angle θ 2  is preferably 30.5 degrees or more and 39.5 degrees or less. 
     A scan angle range η 2  indicated by broken lines of  FIG. 6B  indicates a scan angle range of the center of the intensity of laser light scanned by the second optical deflection part  31 . 
     &lt;Incidence Example of Laser Light of Optical Deflection Apparatus  20 &gt; 
     Next, incidence of laser light to the optical deflection apparatus  20  is explained with reference to  FIG. 7 .  FIG. 7  is a perspective view for explaining an example of incidence of laser light to the optical deflection apparatus  20 . 
       FIG. 7  illustrates laser light that is incident on and deflected by each of the first optical deflection unit  2  and the second optical deflection unit  3 , with the housing  5  and the like of the optical deflection apparatus  20  being detached. 
     Only one of the laser lights of Red, Green, Blue, and IR is shown as the laser light that is incident on and deflected by each of the first optical deflection unit  2  and the second optical deflection unit  3 . The first optical deflection unit  2  and the second optical deflection unit  3  perform the same operation for the laser light of any wavelength. 
     As illustrated in  FIG. 7 , incident laser light L 1  is laser light that is incident on the first reflection surface  22  of the first optical deflection part  21  of the first optical deflection unit  2 . An incidence central axis L 10  indicated by a broken line arrow is the central axis of the incident laser light L 1 . The incident laser light L 1  propagates in the direction indicated by the arrow of the incidence central axis L 10  and is incident on the first reflection surface  22 . Thereafter, the incident laser light L 1  is reflected by the first reflection surface  22  toward the second reflection surface  32  of the second optical deflection part  31  of the second optical deflection unit  3 . 
     Reflected laser light L 2  is laser light that is reflected by the first reflection surface  22  and is incident on the second reflection surface  32 . A reflection central axis L 20  indicated by a broken line arrow is the central axis of the reflected laser light L 2 . In a case where the first reflection surface  22  and the second reflection surface  32  are not swinging, the reflected laser light L 2  propagates in the direction indicated by the arrow of the reflection central axis L 20  and is incident on the second reflection surface  32 . Thereafter, the reflected laser light L 2  is reflected by the second reflection surface  32 . 
     Output laser light L 3  is laser light that is reflected by the second reflection surface  32  and is output from the inside to the outside of the optical deflection apparatus  20 . An output central axis L 30  indicated by a broken line arrow is the central axis of the output laser light L 3 . In a case where the first reflection surface  22  and the second reflection surface  32  are not swinging, the output laser light L 3  propagates in the direction indicated by the arrow of the output central axis L 30 , and is output from the optical deflection apparatus  20 . 
     The first optical deflection part  21  deflects the incident laser light L 1  by swinging the first reflection surface  22  about the first swing axis A. The reflected laser light L 2  reflected and deflected by the first reflection surface  22  is scanned along the second swing axis B on the second reflection surface  32 . 
     The second optical deflection part  31  deflects the reflected laser light L 2  by swinging the second reflection surface  32  about the second swing axis B. The output laser light L 3  reflected and deflected by the second reflection surface  32  is output from the optical deflection apparatus  20 , and is scanned along each of the X direction and the Y direction on the scan-target surface  200  (see  FIG. 1 ). 
     In this case, a first incidence plane P 1  indicated by a parallelogram of a long dashed short dashed line in  FIG. 7  is a plane including the incidence central axis L 10  of the incident laser light L 1  and the reflection central axis L 20  of the reflected laser light L 2 . In the present embodiment, the first swing axis A is configured to be substantially perpendicular to the first incidence plane P 1 . In other words, an angle ϕ 1  formed between the first swing axis A and the first incidence plane P 1  is configured to be approximately 90 degrees. Being “substantially perpendicular” is an example of “crossing”. 
     Also, a second incidence plane P 2  indicated by a parallelogram of a long dashed short dashed line in  FIG. 7  is a plane including the reflection central axis L 20  of the reflected laser light L 2  and the output central axis L 30  of the output laser light L 3 . In the present embodiment, the second swing axis B is configured to be substantially perpendicular to the second incidence plane P 2 . In other words, an angle ϕ 2  formed between the second swing axis B and the second incidence plane P 2  is configured to be approximately 90 degrees. 
     A direction in which the reflected laser light L 2  is incident on the second reflection surface  32  changes according to the scanning with the first optical deflection part  21 , and accordingly, the direction of the second incidence plane P 2  changes. Therefore, the second swing axis B and the second incidence plane P 2  may be shifted from the perpendicular state. 
     In contrast, in the present embodiment, the scan center laser light  63  passing through the center of the scan angle range η 1  of scanning performed by the first optical deflection part  21  is incident on the second reflection surface  32  from the direction substantially perpendicular to the second swing axis B (see  FIG. 6 ). Therefore, even in a case where the reflected laser light L 2  is scanned by the first optical deflection part  21 , the second incidence plane P 2 , formed by the scanned reflected laser light L 2 , and the second swing axis B are brought closer to such a state that the second incidence plane P 2  and the second swing axis B are perpendicular to each other. 
     &lt;Operations of Optical Deflection Apparatus  20 &gt; 
     Next, operations of the optical deflection apparatus  20  are explained. First, before the explanation about the operations, the configuration and arrangement of each of an optical deflection apparatus  20   a  according to the first comparative example and an optical deflection apparatus  20   b  according to the second comparative example are explained. 
     (Configuration and Arrangement of Optical Deflection Apparatus  20   a  According to First Comparative Example) 
       FIG. 8  is a drawing illustrating a configuration of an optical deflection part  31   a  of the optical deflection apparatus  20   a  according to the first comparative example. The optical deflection apparatus  20   a  scans laser light in two directions using the single optical deflection part  31   a.    
     In  FIG. 8 , the optical deflection part  31   a  swings a reflection surface  32   a  about both of a first swing axis Aa and a second swing axis Ba, so that the laser light reflected by the reflection surface  32   a  is deflected and scanned in two directions, i.e., about the first swing axis Aa and about the second swing axis Ba. The optical deflection part  31   a  is, for example, a MEMS mirror or the like that drives the reflection surface  32   a  by a piezoelectric element. 
     The configuration of the optical deflection part  31   a  is equivalent to a configuration in which the first optical deflection part  21  as illustrated in  FIG. 3  is provided instead of the second movable portion  33  of the second optical deflection part  31  as illustrated in  FIG. 5 , and the second driving beams  35   a  and  35   b  are connected to the first support portion  25 . Therefore, in the following explanation, redundant explanation about the configuration of the optical deflection part  31   a  is omitted. 
       FIG. 9A  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus  20   a  as seen from the direction of the first swing axis A.  FIG. 9B  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus  20   b  as seen from the direction of the second swing axis B. 
     As illustrated in  FIG. 9 , the optical deflection part  31   a  is held on a package  2   aa . Incident laser light L 1   a  is laser light that is incident on the reflection surface  32   a  of the optical deflection part  31   a . An incidence central axis L 10   a  indicated by a broken line arrow is the central axis of the incident laser light L 1   a . The incident laser light L 1   a  propagates in the direction indicated by the arrow of the incidence central axis L 10   a  and is incident on the reflection surface  32   a . Thereafter, the incident laser light L 1   a  is reflected by the reflection surface  32   a.    
     The reflected laser light L 2  is laser light that is reflected by the reflection surface  32   a  and is output from the inside to the outside of the optical deflection apparatus  20   a . A reflection central axis L 20   a  indicated by a broken line arrow is the central axis of reflected laser light L 2   a . The reflected laser light L 2   a  propagates in the direction indicated by the arrow of the reflection central axis L 20   a , and is output from the optical deflection apparatus  20   a.    
     The optical deflection part  31   a  deflects the incident laser light L 1   a  by swinging the reflection surface  32   a  about the first swing axis Aa. Also, the optical deflection part  31   a  deflects the incident laser light L 1   a  by swinging the reflection surface  32   a  about the second swing axis Ba. The reflected laser light L 2   a  reflected and deflected by the reflection surface  32   a  is output from the optical deflection apparatus  20   a , and, for example, the reflected laser light L 2   a  is scanned in each of the X direction and the Y direction on the scan-target surface  200  (see  FIG. 1 ). 
     In this case, an incidence plane P 1   a  indicated by a parallelogram of a long dashed short dashed line in  FIG. 9  is a plane including the incidence central axis L 10   a  of the incident laser light L 1   a  and the reflection central axis L 20   a  of the reflected laser light L 2   a . In the first comparative example, the first swing axis Aa is configured to be substantially parallel to the incidence plane P 1   a.    
     In this manner, the optical deflection apparatus  20   a  is different from the optical deflection apparatus  20  according to the embodiment in that laser light is scanned in two directions by the single optical deflection part  31   a . Also, the optical deflection apparatus  20   a  is different from the optical deflection apparatus  20  in that the first swing axis Aa is configured to be substantially parallel to the incidence plane P 1   a.    
     (Configuration and Arrangement of Optical Deflection Apparatus  20   a  According to Second Comparative Example) 
     Next,  FIG. 10  is a perspective view for explaining the optical deflection apparatus  20   b  according to the second comparative example. The optical deflection apparatus  20   b  scans laser light in two directions by using a first optical deflection unit  2   b  and a second optical deflection unit  3   b.    
     As illustrated in  FIG. 10 , the first optical deflection unit  2   b  includes a first optical deflection part  21   b  and a first package  2   ab  for holding the first optical deflection part  21   b.    
     The first optical deflection part  21   b  swings a first reflection surface  22   b  about a first swing axis Ab, so that the laser light deflected by the first reflection surface  22   b  is deflected about the first swing axis Ab. The first optical deflection part  21   b  is, for example, a MEMS mirror or the like that drives the first reflection surface  22   b  by a piezoelectric element. 
     Also, as illustrated in  FIG. 10 , the second optical deflection unit  3   b  includes a second optical deflection part  31   b  and a second package  3   ab  for holding the second optical deflection part  31   b.    
     The second optical deflection part  31   b  swings a second reflection surface  32   b  about a second swing axis Bb, so that the laser light deflected by the second reflection surface  32   b  is deflected about the second swing axis Bb. The second optical deflection part  31   b  is, for example, a MEMS mirror or the like that drives the second reflection surface  32   b  by a piezoelectric element. 
     The configuration of the first optical deflection unit  2   b  is equivalent to the first optical deflection unit  2 , and the configuration of the second optical deflection unit  3   b  is equivalent to the second optical deflection unit  3 . Therefore, in this case, redundant explanation about the configuration of the first optical deflection unit  2   b  and the second optical deflection unit  3   b  is omitted. 
     Next,  FIG. 11  is a drawing illustrating an example of incidence of laser light to the optical deflection apparatus  20   b.    
     As illustrated in  FIG. 11 , incident laser light L 1   b  is laser light incident on the first reflection surface  22   b  of the first optical deflection part  21   b  of the first optical deflection unit  2   b . An incidence central axis L 10   b  indicated by a broken line arrow is the central axis of the incident laser light L 1   b . The incident laser light L 1   b  propagates in the direction indicated by the arrow of the incidence central axis L 10   b  and is incident on the first reflection surface  22   b . Thereafter, the incident laser light L 1   b  is reflected by the first reflection surface  22   b  toward the second reflection surface  32   b  of the second optical deflection part  31   b  of the second optical deflection unit  3   b.    
     Reflected laser light L 2   b  is laser light that is reflected by the first reflection surface  22   b  and is incident on the second reflection surface  32   b . A reflection central axis L 20   b  indicated by a broken line arrow is the central axis of the reflected laser light L 2   b . The reflected laser light L 2   b  propagates in the direction indicated by the arrow of the reflection central axis L 20   b  and is incident on the second reflection surface  32   b . Thereafter, the reflected laser light L 2   b  is reflected by the second reflection surface  32   b.    
     Output laser light L 3   b  is laser light that is reflected by the second reflection surface  32   b  and is output from the inside to the outside of the optical deflection apparatus  20   b . An output central axis L 30   b  indicated by a broken line arrow is the central axis of the output laser light L 3   b . The output laser light L 3   b  propagates in the direction indicated by the arrow of the output central axis L 30   b , and is output from the optical deflection apparatus  20   b.    
     The first optical deflection part  21   b  deflects the incident laser light L 1   b  by swinging the first reflection surface  22   b  about the first swing axis Ab. The reflected laser light L 2   b  reflected and deflected by the first reflection surface  22   b  is scanned in a direction along the second swing axis Bb on the second reflection surface  32   b.    
     The second optical deflection part  31   b  deflects the reflected laser light L 2   b  by swinging the second reflection surface  32   b  about the second swing axis Bb. The output laser light L 3   b  reflected and deflected by the second reflection surface  32   b  is output from the optical deflection apparatus  20   b , and, for example, the output laser light L 3   b  is scanned in each of the X direction and the Y direction on the scan-target surface  200  (see  FIG. 1 ). 
     In this case, a first incidence plane P 1   b  indicated by a rectangle of a long dashed short dashed line in  FIG. 11  is a plane including the incidence central axis L 10   b  of the incident laser light L 1   b  and the reflection central axis L 20   b  of the reflected laser light L 2   b . In the second comparative example, the first swing axis Ab is configured to be substantially parallel to the first incidence plane P 1   b.    
     A second incidence plane P 2   b  indicated by a rectangle of a long dashed double-short dashed line in  FIG. 11  is a plane including the reflection central axis L 20   b  of the reflected laser light L 2   b  and the output central axis L 30   b  of the output laser light L 3   b . In the second comparative example, the second swing axis Bb is configured to be substantially perpendicular to the second incidence plane P 2   b.    
     In this manner, the optical deflection apparatus  20   b  is different from the optical deflection apparatus  20  according to the embodiment in the arrangement of the first optical deflection unit  2   b  and the second optical deflection unit  3   b . Furthermore, the optical deflection apparatus  20   b  is different from the optical deflection apparatus  20  in that the first swing axis Ab is configured to be substantially parallel to the first incidence plane P 1   b.    
     Example of Distortion 
     Next, distortions that occur when the image projection apparatus  100  uses the optical deflection apparatuses according to the first and second comparative examples and the present embodiment are explained. 
       FIG. 12A  is a drawing illustrating an example of distortion that occurs when the optical deflection apparatus  20   a  according to the first comparative example is used.  FIG. 12B  is a drawing illustrating an example of distortion that occurs when the optical deflection apparatus  20   b  according to the second comparative example is used.  FIG. 12C  is a drawing illustrating an example of distortion that occurs when the optical deflection apparatus  20  according to the present embodiment is used. 
     In an image  201   a  generated with the optical deflection apparatus  20   a  As illustrated in  FIG. 12A , toward the center in the X direction, the end portion at +Y side expands to +Y side, and the end portion at −Y side shrinks to +Y side. Distortion including both of the barrel type and the pincushion type in a mixed manner occurs significantly. 
     In the optical deflection apparatus  20   a , the first swing axis Aa is configured to be substantially parallel to the incidence plane P 1   a  (see  FIG. 9 ). Therefore, scanning performed by the optical deflection part  31   a  is likely to become asymmetric between the side closer to the light emitting unit  10  and the side farther from the light emitting unit  10 . This is considered to be the cause of the significant distortion. 
     In an image  201   b  generated with the optical deflection apparatus  20   b  As illustrated in  FIG. 12B , toward the center in the X direction, the end portion at +Y side expands to +Y side, and the end portion at −Y side shrinks to +Y side. Distortion including both of the barrel type and the pincushion type in a mixed manner occurs significantly. 
     In the optical deflection apparatus  20   b , the first swing axis Ab is configured to be substantially parallel to the first incidence plane P 1   b  (see FIG.  11 ). Therefore, scanning performed by the optical deflection part  21   b  is likely to become asymmetric between the side closer to the light emitting unit  10  and the side farther from the light emitting unit  10 . This is considered to be the cause of the significant distortion. 
     In contrast, in the optical deflection apparatus  20  according to the present embodiment, the first swing axis A is configured to be substantially perpendicular to the first incidence plane P 1  (see  FIG. 7 ). Therefore, scanning performed by the first optical deflection part  21  is less likely to become asymmetric between the side closer to the light emitting unit  10  and the side farther from the light emitting unit  10 . 
     As a result, as illustrated in  FIG. 12C , in the image  201  generated with the optical deflection apparatus  20 , distortion is reduced, and the image  201  becomes a non-distorted rectangular image. 
     &lt;Effects of Optical Deflection Apparatus  20 &gt; 
     Next, the effects of the optical deflection apparatus  20  are explained. 
     Conventionally, an image projection apparatus projects a two-dimensional image onto a scan-target surface using an optical deflection apparatus that deflects, at a reflection surface, light emitted by a light emitting unit. 
     However, when the optical deflection apparatus that deflects light by swinging the reflection surface in two directions perpendicular to each other is used, distortion may become significant as illustrated in, for example, the image  201   a  according to the first comparative example. 
     Also, it may be considered to employ a configuration including the first optical deflection part that deflects light by swinging the first reflection surface about the first swing axis and the second optical deflection part that deflects light by swinging the second reflection surface about the second swing axis crossing the first swing axis. 
     In this case, however, when the first swing axis is configured to be substantially parallel to the first incidence plane including the central axis of the light incident on the first reflection surface and the central axis of the light deflected by the first reflection surface, distortion may become significant as illustrated in, for example, the image  201   b  according to the second comparative example. 
     It may be considered to correct distortion by applying image processing such as changing the magnification rates in the height and width directions of original image data in order to reduce the distortion caused by the optical deflection apparatus. However, due to the image processing, the resolution of the image may decrease, the angle of view of the projected image may decrease, or moiré (interference fringes) may occur in the projected image. 
     For example, Japanese Patent No. 5492765 discloses a configuration including a first deflector that deflects light into a first direction and a scanning optical system provided between the first deflector and a scan-target surface in order to reduce TV distortion and trapezoidal distortion of the projected image. 
     However, in the configuration of Japanese Patent No. 5492765, an optical deflection apparatus such as a first deflector is provided to be inclined with respect to the scanning optical system, and this may complicate the configuration and the adjustment of the image projection apparatus. 
     In contrast, the optical deflection apparatus  20  according to the present embodiment includes the first optical deflection part  21  that deflects the incident laser light L 1  incident on the first reflection surface  22  by swinging the first reflection surface  22  about the first swing axis A. In addition, the optical deflection apparatus  20  according to the present embodiment includes the second optical deflection part  31  that deflects the reflected laser light L 2  reflected by the first reflection surface  22  by swinging the second reflection surface  32  about the second swing axis B crossing the first swing axis A. 
     Furthermore, the first swing axis A is substantially perpendicular to a first incidence plane P 1  that includes the incidence central axis L 10  of the incident laser light L 1  incident on the first reflection surface  22  and the reflection central axis L 20  of the reflected laser light L 2  reflected by the first reflection surface  22 . The second swing axis B is substantially perpendicular to the second incidence plane P 2  including the reflection central axis L 20  of the reflected laser light L 2  incident on the second reflection surface  32  and the output central axis L 30  of the output laser light L 3  reflected by the second reflection surface  32 . 
     According to this configuration, scanning performed by the first optical deflection part  21  is less likely to become asymmetric between the side closer to the light emitting unit  10  and the side farther from the light emitting unit  10 . Furthermore, scanning performed by the second optical deflection part  31  is less likely to become asymmetric between the side closer to the first reflection surface  22  and the side farther from the first reflection surface  22 . 
     As a result, the distortion of the projected image  201  can be reduced. The effect of reducing the distortion can be obtained by simply optimizing the arrangement of the first optical deflection part  21  and the second optical deflection part  31 , and therefore, in the optical deflection apparatus, the mechanism for reducing the distortion of the projected image  201  can be simplified. 
     In the present embodiment, although, for example, the first swing axis A is substantially perpendicular to the first incidence plane P 1  and the second swing axis B is substantially perpendicular to the second incidence plane P 2 , the present invention is not limited thereto. Any configuration may be adopted so long as the first swing axis A crosses the first incidence plane P 1  and the second swing axis B crosses the second incidence plane P 2 . However, when the angle between the first swing axis A and the first incidence plane P 1  is closer to 90 degrees (i.e., the first swing axis A is perpendicular to the first incidence plane P 1 ) and the angle between the second swing axis B and the second incidence plane P 2  is closer to 90 degrees (i.e., the second swing axis B is perpendicular to the second incidence plane P 2 ), the effect of reducing the distortion increases, and therefore, it is preferable that the angle between the first swing axis A and the first incidence plane P 1  is closer to 90 degrees (i.e., the first swing axis A is preferably perpendicular to the first incidence plane P 1 ) and the angle between the second swing axis B and the second incidence plane P 2  is closer to 90 degrees (i.e., the second swing axis B is preferably perpendicular to the second incidence plane P 2 ). 
     Furthermore, in the present embodiment, image processing for correcting the distortion is not performed on the original image data, and therefore, the configuration of the image projection apparatus can be simplified due to the omission of a computation device for performing the image processing, and in addition, the decrease of the resolution and the decrease of the angle of view of the image that would otherwise be caused by the image processing can be alleviated, and an occurrence of moiré can be alleviated. 
     In the image projection apparatus  100  according to the present embodiment, an image is projected by laser light scanned by the optical deflection apparatus  20  without using the scanning optical system. Therefore, the distortion can be alleviated by employing such a simple configuration without using a scanning optical system. 
     Note that the optical deflection apparatus  20  can be applied to an image projection apparatus using a scanning optical system. In this case, complicated arrangement and adjustment such as inclining the optical deflection apparatus  20  with respect to the scanning optical system are unnecessary, and therefore, the configuration of the image projection apparatus can be simplified. 
     In the present embodiment, the scan center laser light  63  passing through the center of the scan angle range η 1  of scanning performed by the first optical deflection part  21  is incident on the second reflection surface  32  from the direction substantially perpendicular to the second swing axis B. 
     According to this configuration, even in a case where the reflected laser light L 2  is scanned by the first optical deflection part  21 , the second incidence plane P 2 , formed by the scanned reflected laser light L 2 , and the second swing axis B are brought closer to such a state that the second incidence plane P 2  and the second swing axis B are perpendicular to each other. Therefore, the mechanism for alleviating the distortion of the image  201  can be simplified. 
     In the present embodiment, the first optical deflection part  21  deflects the incident laser light L 1  incident on the first reflection surface  22 , so that the incident laser light L 1  is scanned in the direction along the second swing axis B on the second reflection surface  32 . According to this configuration, the second swing axis B can be configured to cross the second incidence plane P 2  in a preferable manner. 
     In the present embodiment, the inclination of the second swing axis B with respect to the first reflection surface  22  that is not swinging is 25.5 degrees or more and 34.5 degrees or less. The inclination of the first swing axis A with respect to the second reflection surface  32  that is not swinging is 30.5 degrees or more and 39.5 degrees or less. 
     According to this configuration, the first swing axis A can be configured to cross the first incidence plane P 1  in a preferable manner, and also, the second swing axis B can be configured to cross the second incidence plane P 2  in a preferable manner. 
     Although the embodiment has been described above, the present invention is not limited to the above-described embodiment, and various modifications and changes can be made without departing from the subject matter described in the claims. 
     In this case, for applications such as a head-up display or a head-mounted display, a hologram optical system may be used. The hologram optical system diffracts the light incident on a diffractive optical element (DOE) to allow a user to visually recognize a real image or a virtual image. 
     If there is distortion when the scanned light is incident on the DOE, the incidence angle of the scanned light to the DOE deviates from a desired angle, and the quality of the real image or the virtual image seen by the user may decrease. 
     The optical deflection apparatus and the image projection apparatus according to the present embodiment can reduce the distortion in a preferable manner, and therefore, the scanned light can be configured to be incident at the desired angle, and the reduction in the quality of the real image or the virtual image seen by the user using the hologram optical system can be alleviated. Therefore, the optical deflection apparatus and the image projection apparatus according to the present embodiment can be particularly preferably applied to applications using the hologram optical system. 
     The numbers such as ordinal numbers and quantities used in the explanation of the embodiment are all shown as examples to specifically explain the techniques related to the present disclosure, and the present invention is not limited to the numbers shown in the examples. Also, the connection relationships between components are shown as examples to specifically explain the techniques of the present disclosure, and the connection relationships that achieve the function of the present disclosure are not limited thereto.