Patent Publication Number: US-9843778-B2

Title: Image display device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a Continuing Application based on International Application PCT/JP2014/003681 filed on Jul. 10, 2014, which, in turn, claims the priority from Japanese Patent Application No. 2013-162682 filed on Aug. 5, 2013, the entire disclosure of these earlier applications being herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to an image display device capable of allowing an observer to observe an image. 
     BACKGROUND 
     As a technology of deflecting light by a phased array, it has been known to emit laser light which has been shifted in phase from a single mode fiber array (see, for example, Non-patent Literature (NPL) 1). It has also been known to properly shift the phase of laser light emitted from vertical cavity surface emitting lasers (VCSELs) in a VCSEL array to thereby deflect a laser beam emitted from the VCSEL array (see, for example, Patent Literature (PTL) 1). Further, it has been known to use liquid crystal on silicon (LCOS) to deflect light (see, for example, PTL 2). 
     CITATION LIST 
     Patent Literature 
     PTL 1: U.S. Pat. No. 5,777,312A 
     PTL 2: U.S. Pat. No. 7,397,980B 
     Non-patent Literature 
     NPL 1: Hughes and Ghatak, “Phased Array Optical Scanning”, Jul. 1, 1979, p. 2098, Applied Optics, vol. 18, No. 13, Feb. 22, 1995. 
     SUMMARY 
     Technical Problem 
     According to the technology disclosed in NPL 1, the single mode fibers are varied in length so as to emit phase-shifted laser light, in which the length of each of the single mode optical fibers is temporally fixed, meaning that it can deflect light only by a certain angle. The technology disclosed in PTL 1 relates to a barcode reader, where nothing is disclosed about a specific method of shifting the phase of light or about the scanning of light in two-dimensional directions. The technology disclosed in PTL 2 relates to an optical switch (Reconfigurable Optical Add/Drop Multiplexer (ROADM)), where nothing is disclosed about the scanning of light in two-dimensional directions. 
     Solution to Problem 
     The disclosed image display device has: a light source part for emitting coherent light; and a plurality of phase shift elements arranged in two-dimensional directions, the device including a phase shift part for scanning, in two-dimensional directions, the wave front of coherent light from the light source part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is for illustrating the principle of the disclosed image display device; 
         FIG. 2  is a sectional view schematically illustrating a configuration of a main part of the image display device according to Embodiment 1; 
         FIG. 3  illustrates an exemplary arrangement of VCSELs in a VCSEL array; 
         FIG. 4  illustrates another exemplary arrangement of VCSELs in a VCSEL array; 
         FIG. 5  illustrates another configuration example of the phase shift elements; 
         FIG. 6  is for illustrating an operation of KTN crystal; 
         FIG. 7  illustrates a circuit configuration of a phase shift part; 
         FIG. 8  is for illustrating an operation of the phase shift part; 
         FIG. 9  is for illustrating an example of how an optical beam is shifted by the phase shift part; 
         FIG. 10  is a schematic diagram illustrating phase difference control carried out by the phase shift part, which is viewed from the observation plane side; 
         FIG. 11  is for illustrating another example of how an optical beam is shifted by the phase shift part; 
         FIG. 12  is a sectional view schematically illustrating a configuration of a main part of the image display device according to Embodiment 2; 
         FIG. 13  illustrates an example of an arrangement of VCSELs in a VCSEL array; 
         FIG. 14  is a schematic illustration of a section taken along the line III-III of  FIG. 13 ; 
         FIG. 15  is a schematic illustration of a section taken along the line IV-IV of  FIG. 13 ; 
         FIG. 16  is a schematic illustration of a section taken along the line V-V of  FIG. 13 ; and 
         FIG. 17  is a sectional view schematically illustrating a configuration of a main part of the image display device according to Embodiment 3. 
     
    
    
     DETAILED DESCRIPTION 
     Explained first with reference to  FIG. 1  is the principle of an image display apparatus disclosed herein, which is followed by the description of Embodiments. 
     As illustrated in  FIG. 1 , when an observer has observed an observation plane  2 , a parallel light flux L 1  from the observation plane  2  is incident through a pupil of an eyeball  3 , and the light flux L 1  forms an image at a position P 1  on a retina  5  by means of a crystalline lens  4 . A parallel light flux L 2  to be incident from the observation plane  2  at an angle different from that of the parallel light flux L 1  forms an image at a position P 2  different from the position P 1  on the retina  5 . In other words, when light fluxes from the observation plane  2  are incident at different angles on the eyeball  3 , the respective light fluxes form images at different positions on the retina  5 . 
     An example of the disclosed image display device emits light provided by sequential pixels of an image to be displayed, as a parallel light flux from the observation plane, that is, as light from infinity, by two-dimensionally deflecting the light by a phased array in accordance with the pixel position. This configuration allows an observer to observe the image. 
     In the following, Embodiments of the disclosed device are described with reference to the drawings. 
     Embodiment 1 
       FIG. 2  is a sectional view schematically illustrating a configuration of a main part of the disclosed image display device according to Embodiment 1. An image display device  100  of  FIG. 2  has a light source part  200  and a phase shift part  300  to act as an observation plane. The light source part  200  includes, for example, a vertical cavity surface emitting laser (VCSEL) array  202  having a plurality of VCSELs  201 . The VCSEL array  202  may have a publicly-known configuration disclosed in, for example, JP 2005-45243 A, and has a bottom mirror  203  and an active layer  204  shared in common, and a top mirror  205  for each VCSEL  201 . The VCSEL array  202 , which is configured as described above with the bottom mirror  203  formed in common, is capable of synchronize the phase of laser light emitted from VCSELs  201  so as to emit the light as coherent light.  FIG. 2  is an abridged illustration of the configuration of the VCSEL array  202  for the sake of clarity of the drawing. 
     In the VCSEL array  202 , the VCSELs  201  have laser emission ports  206  for emitting laser light, which are arranged in the x-y axis plane in two-dimensional directions, for example, as illustrated in  FIG. 3 or 4 , at a pitch of the wavelength level of the emitted laser light.  FIGS. 3 and 4  each are a partial plan view of the VCSEL array  202  as viewed from the line I-I of  FIG. 2 . In  FIG. 3 , the laser emission ports  206  are arranged as being staggered at a half pitch of the array pitch in the x-axis direction and the y-axis direction. In  FIG. 4 , the laser emission ports  206  are arranged in square lattice in the x-axis direction and the y-axis direction. The laser emission ports  206  illustrated in  FIGS. 3 and 4  are circular in shape, which, however, may be in an arbitrary shape such as rectangular and hexagonal. In  FIGS. 2 to 4 , the z-axis direction is perpendicular to the x-axis and y-axis directions, and indicates a direction in which laser light from the VCSELs  201  is emitted. The shape of the laser emission port and the x-, y-, and z-axes are similarly configured in other Embodiments. 
     Referring to  FIG. 2 , the phase shift part  300  is arranged on the laser light emission side of the VCSEL array  202  as being optically coupled thereto. The phase shift part  300  has a plurality of phase shift elements  301  associated with the respective VCSELs  201  of the VCSEL array  202 . The phase shift elements  301  may be configured by using publicly-known electro-optical elements which vary in refractive index depending on the applied voltage, such as, for example, potassium tantalate niobate (KTN) crystals, lithium niobate (LN) crystals, and liquid crystals. In below, description is given of a KTN crystal  302  as the elctro-optical element. 
     The phase shift element  301  has a regional electrode part  303  bonded thereto on the incident side of light from the VCSELs  201  and a transparent common electrode  304  disposed on the emission side of light as being commonly bonded to the respective phase shift elements  301 . The regional electrode part  303  may be configured by including, for example, a transparent regional electrode and a thin film transistor (TFT) as a switching element connected to the regional electrode. Formed on the regional electrode part  303  side are X-axis wiring line  305  and Y-axis wiring line  306  for selecting the phase shift elements  301 . 
     The X-axis wiring line  305  and the Y-axis wiring line  306  are connected to an X-axis line drive circuit and a Y-axis line drive circuit to be described later, so that the X-axis wiring line  305  is driven by the X-axis line drive circuit and the Y-axis wiring line  306  is driven by the Y-axis line drive circuit. The X-axis line drive circuit and the Y-axis line drive circuit may be configured to drive the phase shift elements  301  by a passive matrix system, but may preferably be configured to drive the elements  301  by an active matrix system. 
     Referring to  FIG. 2 , the phase shift element  301  is configured by forming, on a single plate of the KTN crystal  302 , the regional electrode parts  303  associated with the respective VCSELs  201 . Without being limited to the configuration of  FIG. 2 , the phase shift element  301  may be configured, as illustrated in  FIG. 5  for example, by forming the regional electrode parts  303  on the KTN crystal  302  divided in units of the Y-axis wiring lines  306 . Alternatively, although not shown, the phase shift element  301  may be configured by forming the regional electrode parts  303  on the KTN crystal  302  divided in units of the X-axis electrode wiring lines. The regional electrode part  303  may be formed exclusively of a regional electrode as long as, for example, a switching element may be formed outside the optical path of the phase shift element  301 . In such case, the switching element does not necessarily need to be TFT. 
     Here, in the phase shift element  301  having the KTN crystal  302  illustrated in  FIG. 6 , when a voltage V is applied between the regional electrode  307  and the common electrode  304 , the Kerr effect generates a refractive index profile in the application direction (z-axis direction) of the voltage V. The refractive index variation δn(z) in the z-axis direction in this case is represented by Expression (1) below. In Expression (1), n 0  represents the refractive index, ε 0  represents the permittivity of vacuum, ε r  represents the relative permittivity, d represents the thickness in the z-axis direction of the KTN crystal  302 , and z represents the distance from the regional electrode  307  in the z-axis direction. 
     
       
         
           
             
               
                 
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     When the voltage V is applied to the phase shift element  301 , the phase change Δp of light transmitting through between the regional electrode  307  and the common electrode  304  is represented by Expression (2) below. In Expression (2), λ represents the wavelength of the transmitted light. 
     
       
         
           
             
               
                 
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     Next, referring to  FIGS. 7 to 11 , description is given of a case where the phase shift part  300  drives the phase shift elements  301  by an active matrix system. The following description assumes a case where the VCSEL array  202  is arranged in square as illustrated in  FIG. 4 . Further assumed is a case where the regional electrode part  303  of each of the phase shift elements  301  has the regional electrode  307  and a TFT  308  formed therein. As illustrated in  FIG. 7 , the X-axis wiring lines  305  are connected to an X-axis line drive circuit  310  and the Y-axis wiring lines  306  are connected to a Y-axis line drive circuit  311 . 
     First, referring to  FIG. 7 , description is given of a configuration of a drive circuit of the phase shift element  301  associated with each of the VCSELs  201  in the VCSEL array  202 . The actual circuit may additionally include electronic components for the purpose of improving the SN ratio and increasing speed; however,  FIG. 7  illustrates a circuit equivalent to the drive circuit of the phase shift element  301 . The KTN crystal  302 , which functions as a dielectric, is represented as a capacitor “C”. The regional electrode  307  is denoted by reference symbol “E”, while the common electrode  304  on the opposite side is indicated by a downward arrow. 
     The regional electrode E is connected to a drain D of the TFT  308 , while a source S of the TFT  308  is connected to a corresponding one of the Y-axis wiring lines  306 , i.e., data lines, so as to be applied with a required voltage by the Y-axis line drive circuit  311 . The TFT  308  has a gate G connected to a corresponding one of the X-axis wiring lines  305 , i.e., scanning lines. To hold a voltage to be applied to the KTN crystal C, a storage capacitor Cs is formed between the regional electrode E and the X-axis wiring line  305  in the next stage. In  FIG. 7 , for the clarity of the drawing, components associated with one of the phase shift elements  301  are mainly denoted by the reference symbols. 
       FIG. 7  illustrates only 3×3 of the phase shift elements  301  (regional electrodes E), which are taken out from the entire array. In practice, the VCSEL array is composed of multiple VCSELs and includes the same number of the regional electrodes E as the VCSELs. The Y-axis line drive circuit  311  applies a voltage according to voltage data, via the Y-axis wiring line  306 , to the regional electrode E of the relevant KTN crystal C, while the X-axis line drive circuit  310  applies a control voltage for write-in scanning, via the X-axis wiring line  305 , to the gate G of the relevant TFT  308 . 
     Next, referring to  FIG. 8 , description is given of an active matrix drive of the regional electrode E. The X-axis line drive circuit  310  applies a write-in control voltage Vs to the X-axis wiring lines  305  sequentially from the above (scanning). At a current time t 0 , the X-axis wiring line  305  in the middle is applied with the control voltage Vs. When the control voltage Vs is applied to the gates G of the TFTs  308 , all the TFTs  308  connected to this X-axis wiring line  305  are all turned on. Then, electric charges are injected into the regional electrodes E connected to the drains D of the TFTs  308 , with the result that the regional electrodes E has the same potential as that of the Y-axis wiring line  306 . In this manner, the regional electrode E on each of the VCSELs will be applied with a voltage which is to be applied to the KTN crystal C. 
     Specifically, the voltage data at the time t 0  is V 4 , V 5 , V 6  sequentially from the Y-axis wiring line  306  on the left, while the regional electrodes E along the X-axis wiring line  305  in the middle where the TFTs  308  are turned on each have potentials of V 4 , V 5 , V 6 , respectively. At a time previous to the time t 0 , or the time when the control voltage Vs is applied to the X-axis wiring line  305  on the above, the voltages V 1 , V 2 , and V 3  are applied to the Y-axis wiring line  306 , and the voltages V 1 , V 2 , and V 3  are applied to the relevant regional electrodes E. The voltage applied to the regional electrodes E is held by the storage capacitor Cs. 
     As described above, the X-axis wiring lines  305  are sequentially scanned from top to bottom, so that data on voltage to be applied to KTN, which is being sent to the Y-axis wiring line  306 , is written into the regional electrodes E. 
     Next, referring to  FIG. 9 , description is given of how the phase shift part  300  deflects a light flux. Light from the VCSELs  201  in the VCSEL array  202  is emitted as plane waves of equiphase, which, however, approximates to spherical waves due to diffraction along with advancement of the wave. Then, these substantially spherical waves are made incident on the phase shift part  300 . When a desired voltage is applied to the regional electrode E of each of the phase shift elements of the phase shift part  300 , light emitted from the phase shift elements of the phase shift part  300  forms substantially spherical waves which have undergone phase change. The phase shift elements of the phase shift part  300  emit spherical waves having a phase difference form an envelope EV according to Huygens&#39; principle, as the phase shift elements are arranged at a pitch of the wavelength level. Specifically, light emitted from the VCSEL array  202  forms, as a whole, a single plane wave advancing in the direction of the arrow. 
     Here, a relation of Expression (3) below is established, where p i  represents the arrangement pitch of the phase shift elements, λ represents the wavelength of light emitted from VCSELs  201 , Φ represents the phase difference among the phase shift elements, and ω is the emission angle of the plane wave from the phase shift part  300 :
 
sin ω=λΦ/πp i   (3)
 
     Accordingly, as illustrated in  FIG. 9 , when phase differences Φ (for example, Φ1 to Φ7) is generated according to Expression (3) above, the light flux from the VCSEL array  202  may be deflected. The size of the phase difference to be given may properly be controlled, so as to continuously change the deflection direction of the light flux, which makes it possible to scan a light flux by a so-called phased array. 
       FIG. 10  is a schematic diagram illustrating phase difference control carried out by the phase shift part  300  of  FIG. 9 , which is viewed from the observation plane side. As illustrated in  FIG. 10 , when the phase shift elements  301  in the respective rows in the x-axis direction are given a phase difference that sequentially increases or decreases and the phase shift elements  301  in the respective columns in the y-axis direction are given the same phase difference, a light flux may be deflected in the x-axis direction. On the contrary, when the phase shift elements  301  in the respective rows in the y-axis direction are given a phase difference that sequentially increases or decreases and the phase shift elements  301  in the respective columns in the x-axis direction are given the same phase difference, a light flux may be deflected in the y-axis direction. Data in the x-direction and in the y-direction may be mixed so as to deflect light in the x-direction and the y-direction simultaneously. 
     Accordingly, light may be continuously deflected through a phased array so as to raster scan the light flux emitted from the VCSEL array  202 . The light intensity of the VCSEL array  202  may be modulated in accordance with the raster scan, so as to display an image. Alternatively, a light intensity modulator may be disposed in the optical path from the VCSEL array  202  to the observer, so as to display an image. In this manner, the observer may observe the phase shift part  300 , to thereby observe a virtual image of a two-dimensional image. 
     As illustrated in  FIG. 11 , the phase differences Φ1 to Φ7 may be controlled so as to make the envelope EV as a spherical wave. In this case, as indicated by the solid line of  FIG. 11 , a spherical wave may be emitted in such a manner that the sphere has the center thereof positioned toward the back of the device, that is, positioned forward relative to the VCSEL array  202  when viewed from the observer, so that the observer can clearly see the image even when focusing at a finite distance. Further, as indicted by the broken line of  FIG. 11 , a spherical wave may be emitted in such a manner that the sphere has the center thereof positioned behind the observer, which allows for even a far-sighted observer to clearly observe an image. In this case, a screen may be installed so as to project an image thereon, allowing the device to be used as a projector. 
     In the following, description is given of specific Examples. When the VCSELs of the VCSEL array  202  are arranged in square as illustrated in  FIG. 4 , at a pitch of 1.5 μm between the VCSELs, with the size of the observation plane, i.e., the size of an opening (pupil) being 100 mm×50 mm, the number of VCSELs is obtained as 66,667×33,333. Therefore, in the case of driving the elements through the active matrix system of  FIG. 7 , the number of the X-axis wiring lines  305  becomes 33,333, which means that Vs signal may be output sequentially from the above for 33,333 times in order to rewrite all the regional electrodes at once. Here, as illustrated in  FIG. 10 , in order to control the deflection direction of light in all the phase shift elements of the phase shift part  300  so as to display a screen of SVGA (pixel number 800×600) at a frame rate of 30 fps, the rewriting rate may be set to 480,000×30 Hz=14.4 MHz, and the transmission timing of voltage data to the Y-axis wiring lines  306  may be set to 14.4 MHz×33,333=479 GHz. In this case, the width of the Vs signal, that is, the switching speed of the TFT  308  becomes 2 ps. 
     The deflection of light flux may not be limitedly controlled by all the phase shift elements of the phase shift part  300 , and may be controlled by dividing the phase shift part  300 . The sub-divided regions in this case each may preferably be of, for example, on the order of 0.5 mm×0.5 mm to several mm×several mm so as not to be affected by the spread due to diffraction. In this case, the VCSELs of different regions do not need to be synchronized in phase, and the light fluxes between the sub-divided regions are incoherent to one another. In the case where the region is of 0.5 mm×0.5 mm, the number of VCSELs is obtained as 333×333. Further, the transmission timing of voltage data to the Y-axis wiring line  306  is obtained as 14.4 MHz×333=4.8 GHz, and the width of the Vs signal, that is, the switching speed of the TFT  308  becomes 0.2 ns. Accordingly, as compared to the former case of controlling the deflection by all the phase shift elements, the X-axis line drive circuit  310  and the Y-axis line drive circuit  311  may be configured with ease. 
     Embodiment 1 enables the following configurations. 
     &lt;In the VCSEL Array  202  Arranged as Illustrated in  FIG. 3 &gt; 
     Pitch between the phase shift elements=pitch between VCSELs=
         2.4 μm in the x-axis direction,   1.2 μm in the y-axis direction       

     Thickness d of KTN crystal: 1 μm 
     Voltage applied to KTN crystal: 0 to 4.18 V (phase difference 0 to λ) 
     Wavelength (λ) of light emitted from VCSEL array: 640 nm 
     Scanning maximum angle (half angle):
         18.75° in the x-axis direction,   15.5° in the y-axis direction       

     Observation plane area: 100 mm×50 mm 
     Frame rate: 30 fps 
     Number of X-axis wiring lines=the number of scanning lines: 600 to 1080. 
     &lt;In the VCSEL Array  202  Arranged as Illustrated in  FIG. 4 &gt; 
     Pitch between the phase shift elements =pitch between VCSELs =
         1.5 μm in the x-axis direction,   1.5 μm in the y-axis direction       

     Thickness d of KTN crystal: 1 μm 
     Voltage applied to KTN crystal: 0 to 4.18 V (phase difference 0 to λ) 
     Wavelength (λ) of light emitted from VCSEL array: 640 nm 
     Scanning maximum angle (half angle):
         25° in the x-axis direction,   25° in the y-axis direction       

     Observation plane area: 100 mm×50 mm 
     Frame rate: 30 fps 
     Number of X-axis wiring lines=the number of scanning lines: 600 to 1080. 
     Embodiment 2 
       FIG. 12  is a sectional view schematically illustrating a configuration of a main part of the image display device according to Embodiment 2. The image display device  130  of  FIG. 12  is for displaying a color image, and different in configuration of the light source part from the image display device  100  of Embodiment 1. The components similar to those of Embodiment 1 are denoted by the same reference symbols to omit the description thereof. 
     In Embodiment 2, the light source part  230  includes, for example: a VCSEL array  232 R having a plurality of VCSELs  231 R for emitting red laser light (R); a VCSEL array  232 G having a plurality of VCSELs  231 G for emitting green laser light (G); and a VCSEL array  232 B having a plurality of VCSELs  231 B for emitting blue laser light (B). The VCSEL arrays  232 R,  232 G, and  232 B are each configured by including, similarly to the VCSEL array  202  explained in Embodiment 1, a bottom mirror  233  and an active layer  234  each being shared in common, the active layer  234  being associated with the wavelength of the laser light to be emitted, and a top mirror  235  for each VCSEL.  FIG. 12  is an abridged illustration of the configuration of each of the VCSEL arrays  232 R,  232 G, and  232 B for the clarity of the drawing. Further, the illustration of the X-axis wiring lines and the Y-axis wiring lines in the phase shift part  300  is omitted. 
     In the VCSEL arrays  232 R,  232 G, and  232 B, the VCSELs  231 R,  231 G, and  231 B each have laser emission ports  236 R,  236 G, and  236 B, respectively, which are arranged in two-dimensional directions on an x-y axis plane at a pitch of the wavelength level, as illustrated in, for example,  FIG. 13 .  FIG. 13  is a part of a plan view of the VCSEL arrays  232 R,  232 G, and  232 B viewed from the line II-II of  FIG. 12 . Specifically, rows in the x-axis direction each have a pattern in which R row, B row, B row, and G row are repeated in the stated order, and rows in the y-axis direction each have a pattern in which a column of alternately-arranged B and G and a column of alternately-arranged R and B are repeated. The pitch of the laser emission ports of the same color and the pitch of the laser emission ports adjacent to each other may be defined, for example, as illustrated in  FIG. 13 . That is, the laser emission ports of the same color may be arranged at a pitch of 2 μm in the x-axis direction and at a pitch of 2.3 μm in the y-axis direction, and the laser emission ports adjacent to each other may be arranged at a pitch of 1 μm in the x-axis direction and at a pitch of 1.15 μm in the y-axis direction. 
     As shown in  FIG. 14  schematically illustrating a section taken along the line of  FIG. 13 , the VCSEL array  232 B is optically coupled, on the laser emission port  236 B side, to the phase shift part  300  configured similarly to that of Embodiment 1. As shown in  FIG. 15  schematically illustrating a section taken along the line IV-IV of  FIG. 13 , the VCSEL array  232 G is optically coupled, on the laser emission port  236 G side, to the phase shift part  300  via a waveguide  237 . Similarly, as shown in  FIG. 16  schematically illustrating a section taken along the line V-V of  FIG. 13 , the VCSEL array  232 R is optically coupled, on the laser emission port  236 R side, to the phase shift part  300  via a waveguide  238 . The phase shift part  300  has a plurality of phase shift elements  301  associated with the VCSELs  231 R,  231 G, and  231 R of the VCSEL arrays  232 R,  232 G, and  232 B. 
     As is apparent from  FIG. 13 , the image display device  130  of Embodiment 2 has an increased number of VCSELs  231 B for emitting blue laser light so as to reduce the pitch of the VCSELs  231 B adjacent to each other, for the following reason. The emission angle ω becomes smaller when the wavelength λ is shorter, as can be understood from Expression (3), and thus, the VCSELs  231 B emitting blue laser light of short wavelength λ are increased in number so as to be arranged at a smaller pitch, to thereby obtain a desired emission angle ω. It may of course be possible to change the pitches in the x-axis direction and the y-axis direction to be different from each other depending to the field angle in the x-axis direction and the y-axis direction. 
     The VCSEL arrays  232 R,  232 G, and  232 B of respective colors are turned on sequentially for each color or all at once, depending on the color information on the pixel to be displayed. The phase shift part  300  scans, similarly as explained in Embodiment 1, the emitted light in two-dimensional directions by a phased array, depending on the position of the pixel to be displayed. With this configuration, the observer may view the phase shift part  300 , to thereby observe a color image. 
     Embodiment 2 enables the following configuration. 
     Wavelengths: R; 640 nm, G; 530 nm, B; 450 nm 
     Pitch between the phase shift elements=pitch between VCSELs=as shown in  FIG. 13 , 
     Thickness d of KTN crystal: 1 μm 
     Voltage applied to KTN crystal: 0 to 4.18 V (phase difference 0 to λ) 
     Scanning maximum angle (half angle):
         15.4° in the x-axis direction,   11.3° in the y-axis direction       

     Observation plane area: 200 mm×100 mm 
     Frame rate: 30 fps 
     Number of X-axis wiring lines=the number of scanning lines: 600 to 1080 
     Embodiment 3 
       FIG. 17  is a sectional view schematically illustrating a configuration of a main part of the image display device according to Embodiment 3. The image display device  160  of  FIG. 17  is for displaying a color image, and different in configuration of the light source part from the image display device  100  of Embodiment 1. The components similar to those of Embodiment 1 are denoted by the same reference symbols to omit the description thereof. 
     In Embodiment 3, the light source part  260  includes, for example: a laser diode  261 R for emitting red laser light (R); a laser diode  261 G for emitting green laser light (G); a laser diode  261 B for emitting blue laser light (B); three collimator lenses  262 ,  263 ,  264 ; two dichroic mirrors  265 ,  266 ; and a beam expander  267 . The red laser light emitted from the laser diode  261 R is converted into parallel light through the collimator lens  262  and sequentially passes through the dichroic mirrors  265  and  266 , before the light flux thereof is expanded by the beam expander  267  and caused to incident, as parallel light, onto the phase shift part  300 . The green laser light emitted from the laser diode  261 G is converted into parallel light through the collimator lens  263  and reflected by the dichroic mirror  265  to be synthesized coaxially with the optical path of the red laser light and then pass through the dichroic mirror  266 , before the light flux thereof is expanded by the beam expander  267  and caused to incident, as parallel light, onto the phase shift part  300 . The blue laser light emitted from the laser diode  261 B is converted into parallel light by the collimator lens  264 , reflected by the dichroic mirror  266  to be synthesized coaxially with the optical paths of the red laser light and the green laser light, before the light flux thereof is expanded by the beam expander  267  and caused to incident, as parallel light, onto the phase shift part  300 . 
     The laser diodes  261 R,  261 G, and  261 B of respective colors are turned on sequentially or all at once, depending on the color information on the pixel to be displayed. The phase shift part  300  is configured by having a plurality of phase shift elements  301  arranged in two-dimensional directions at a pitch of the wavelength level, and as in Embodiment 1, scans the emitted light in two-dimensional directions by a phased array, depending on the position of the pixel to be displayed. With this configuration, the observer may view the phase shift part  300 , to thereby observe a color image. 
     The present disclosure is not limited to Embodiments above, and may be subjected to various modifications and alterations without departing from the gist of the disclosure. For example, in displaying a color image, the light sources are not limited to the three colors of RGB, and may further be configured, for example, to emit light of wavelengths of four or more colors with the addition of a yellow light source. Further, in Embodiments above, the refractive index variation resulting from electro-optical crystal has been used as the phase shift; however, a refractive index variation caused by carrier plasma effect may also be used. 
     REFERENCE SIGNS LIST 
       100 ,  130 ,  160  image display device 
       200 ,  230 ,  260  light source part 
       201 ,  231 R,  231 G,  231 B surface emitting laser (VCSEL) 
       202 ,  232 R,  232 G,  232 B VCSEL array 
       206 ,  236 R,  236 G,  236 B laser emission port 
       261 R,  261 G,  261 B laser diode 
       265 ,  266  dichroic mirror 
       267  beam expander 
       300  phase shift part 
       301  phase shift element 
       302  KTN crystal 
       303  regional electrode part 
       304  common electrode 
       305  X-axis wiring line 
       306  Y-axis wiring line 
       308  TFT 
       310  X-axis line drive circuit 
       311  Y-axis line drive circuit