Patent Publication Number: US-9836023-B2

Title: Apparatus and method for generating wide-angle coherent light and display apparatus using wide-angle coherent light

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Korean Patent Application No. 10-2013-0058513, filed on May 23, 2013, and Korean Patent Application No. 10-2013-0132351, filed on Nov. 1, 2013, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     Example embodiments of the following description relate to a method and apparatus for generating coherent light at a wide angle, and a display apparatus using the coherent light. 
     2. Description of the Related Art 
     Three-dimensional (3D) display technologies are applied to various image display fields, for example, movies, televisions (TVs), mobile phones, and the like. A purpose of 3D display, ultimately, is to enable a person to experience a 3D effect as if he or she is in a real environment and accordingly, research is being conducted on a large variety of technologies including, for example, a stereo scheme, a multi-view scheme, and the like. 
     However, since a viewpoint-based imaging technology uses only information on light two-dimensionally (2D) projected in a predetermined point in a space, all 3D light information may not be represented, which may cause issues such as unnatural 3D representation, visual fatigue during viewing of 3D images, and the like. 
     A holography is representatively used as a technology of restoring 3D spatial light information to the form of real light. Holography may restore light in a space, based on interference, that is, a wavelike nature of light. The concept of a hologram was initially proposed by Dennis Garbor in 1948, however, a holographic display has yet to be commercialized. 
     SUMMARY 
     The foregoing and/or other aspects are achieved by providing a coherent light generation apparatus including a backlight unit to generate parallel light, and a coherent light generator to focus the parallel light onto a focal point, and to generate coherent light so that a hologram is formed based on interference of light propagated from the focal point. 
     The coherent light generator may be a lens to focus the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of optical paths through which the parallel light travels in two media with different refractive indices. 
     The coherent light generation apparatus may further include a pixel. The coherent light generator may be placed in a rear side of a surface on which the pixel is placed, and may focus the parallel light passing through the pixel onto the focal point. 
     The coherent light generation apparatus may not include a slit. 
     The coherent light generation apparatus may further include a plurality of pixels, and the coherent light generator may be formed for each of the plurality of pixels. 
     The coherent light generation apparatus may further include a pixel. The coherent light generator may be located in a front side of a surface on which the pixel is placed, and may focus the parallel light onto the focal point before the parallel light passes through the pixel. 
     The lens may include at least one of a convex lens and a concave lens. 
     The coherent light generator may include a phase modulator to change a refractive index of a central portion of an optical axis and a refractive index of a peripheral portion of the optical axis so that the refractive indices are different from each other, and to focus the parallel light onto the focal point based on a phase difference caused by a position of an optical path through which the parallel light travels. 
     The coherent light generator may include a phase modulating grating to focus the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of a plurality of different optical paths through which the parallel light travels. 
     The coherent light generator may include an amplitude modulating grating to focus the parallel light onto the focal point, based on an amplitude difference, by blocking a part of a plurality of optical paths through which the parallel light travels. 
     The light propagated from the focal point may have a wide angle of at least 15°. The light propagated from the focal point may have a wide angle of at least 30°. The light propagated from the focal point may have a wide angle of at least 60°. 
     The coherent light generation apparatus may further include a plurality of pixels. Each of the plurality of pixels may have a width of at least 10 micrometers (μm). 
     The foregoing and/or other aspects are achieved by providing a coherent light generation method, including generating parallel light, and focusing the parallel light onto a focal point and generating coherent light so that a hologram is formed, based on interference of light propagated from the focal point. 
     The focusing may include focusing, by a lens, the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of optical paths through which the parallel light travels in two media with different refractive indices. 
     The focusing may include changing, by a phase modulator, a refractive index of a central portion of an optical axis and a refractive index of a peripheral portion of the optical axis so that the refractive indices are different from each other, and focusing the parallel light onto the focal point based on a phase difference caused by a position of an optical path through which the parallel light travels. 
     The focusing may include focusing, by a phase modulating grating, the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of a plurality of different optical paths through which the parallel light travels. 
     The focusing may include focusing, by an amplitude modulating grating, the parallel light onto the focal point, based on an amplitude difference, by blocking a part of a plurality of optical paths through which the parallel light travels. 
     The foregoing and/or other aspects are achieved by providing a display apparatus using coherent light, including a backlight unit to generate parallel light, a spatial light modulator to modulate a phase or an amplitude of the parallel light passing through a plurality of pixels, the spatial light modulator including the plurality of pixels, a coherent light generator to focus the parallel light, having the modulated phase or the modulated amplitude, onto a focal point, and to generate coherent light for each of the plurality of pixels so that the parallel light is propagated from the focal point, and a display unit to display a three-dimensional (3D) image in a space, based on interference of the wide-angle coherent light generated for each of the plurality of pixels. 
     The foregoing and/or other aspects are achieved by providing a coherent light generating apparatus that includes a pixel disposed on a planar surface, a backlight unit to generate coherent and collimated light of a single wavelength that is parallel to the planar surface on which the pixel is disposed, and a coherent light generator to focus the parallel light onto a focal point and to generate coherent light, wherein the coherent light generator is disposed at a side of the planar surface to correspond to the pixel. 
     The foregoing and/or other aspects are achieved by providing a display apparatus that includes a plurality of pixels disposed in a grid-like pattern on a planar surface, a backlight unit to generate coherent and collimated light of a single wavelength that is parallel to the planar surface on which the pixels are disposed, a plurality of coherent light generators to focus the parallel light onto a focal point to generate coherent light, wherein each of the coherent light generators is positioned at a side of the planar surface to correspond to one of the plurality of pixels, and a display unit to display a three-dimensional (3D) image based on interference of the coherent light generated for each of the plurality of pixels. 
     Additional aspects of example embodiments will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  illustrates a block diagram of an example of a wide-angle coherent light generation apparatus according to example embodiments; 
         FIG. 2  illustrates a diagram of an example in which a lens is used as a coherent light generator according to example embodiments; 
         FIG. 3  illustrates a diagram of an example in which a phase modulator is used as a coherent light generator according to example embodiments; 
         FIG. 4  illustrates a diagram of an example in which a phase modulating grating is used as a coherent light generator according to example embodiments; 
         FIG. 5  illustrates a diagram of an example in which an amplitude modulating grating is used as a coherent light generator according to example embodiments; 
         FIG. 6  illustrates a block diagram of another example of a wide-angle coherent light generation apparatus according to example embodiments; 
         FIG. 7  illustrates a block diagram of a display apparatus using a wide-angle coherent light according to example embodiments; 
         FIG. 8  illustrates a diagram of an example of a structure of a display apparatus using a wide-angle coherent light according to example embodiments; 
         FIGS. 9 and 10  illustrate diagrams of other examples of a structure of a display apparatus using a wide-angle coherent light according to example embodiments; and 
         FIG. 11  illustrates a flowchart of a wide-angle coherent light generation method according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Example embodiments are described below to explain the present disclosure by referring to the figures. 
     A hologram may be generated based on interference of coherent light. The term “coherent light” may refer to light that optically causes interference, and may typically refer to light having the same wavelength, that is, light of a single wavelength. To control the interference, light phase information may be required to be recognized in advance. 
     Typically, to simultaneously generate a plurality of coherent lights, a slit may be used. A micro-display using a liquid crystal on silicon (LCoS) technology is frequently used in hologram experiments and the like. A micro-display with two million pixels in a size of 0.7 inch may be currently implemented. The micro-display may have a pixel width of about 8 micrometers (μm), and an angle of diffraction of 3.9°. The micro-display may be insufficient to be used as a commercial display in terms of a size and a light generation angle. 
     To implement a hologram in a wide viewing angle, an active rendering technology through tracking of a user&#39;s eyes may be used. Such a display may have a relatively low specification, for example, about fifteen million pixels. The active rendering display may provide a viewing angle of 15° in a 20-inch screen through eye tracking, despite an angle of diffraction of about 0.2°. However, use of the display is limited to a single person, and a luminance is still low. 
     As described above, a large amount of research is being conducted to implement a hologram on a large screen and with a wide angle. However, since devices implemented until now use a large amount of pixel resources, it may be difficult to apply the devices as a display. 
     Light may behave as an electromagnetic wave due to a temporal and spatial variation in an electromagnetic field, and may be generated by a change in movement of electrons. Accordingly, light may include information regarding a wavelength, an amplitude, and a phase that are characteristics of a wave. Because light is typically generated by a plurality of electrons at the same time, light may have a group property. Accordingly, light may be represented as a result of combination of a large number of waves with different wavelengths, different amplitudes, and different phases. 
     Holography may be described as a technique that represents light in space through constructive interference and destructive interference of a plurality of waves in a predetermined position. To represent a hologram, coherent light enabling mutual interference may be required. For example, light with a single wavelength may be used to represent a hologram, due to coherence of the light. 
       FIG. 1  illustrates a block diagram of an example of a wide-angle coherent light generation apparatus according to example embodiments. 
     The wide-angle coherent light generation apparatus of  FIG. 1  may include, for example, a backlight unit  110 , and a coherent light generator  130 . 
     The backlight unit  110  may generate light that is parallel to a surface on which a pixel  120  has been placed. For example, the backlight unit  110  may generate light with a single wavelength. To generate the parallel light, the backlight unit  110  may use a variety of different light sources, for example, a light emitting diode (LED), and the like. In an embodiment, the backlight unit  110  may generate coherent light or collimated light, or both. 
     The coherent light generator  130  may focus the parallel light generated by the backlight unit  110  onto a focal point  140 , and may thereby generate coherent light at a wide angle. The coherent light generator  130  may correspond to, for example, a variety of optical devices with various shapes that are configured to focus parallel light onto a single focal point. 
     The coherent light generator  130  may be located at a rear side of the surface on which the pixel  120  has been placed, and may focus light passing through the pixel  120  onto the focal point  140 . For example, the coherent light generator  130  may be located on a surface opposite the surface at which the backlight unit  110  is disposed. 
     In an embodiment, the coherent light generator  130  may be, for example, a lens. The lens may focus the parallel light generated by the backlight unit  110  onto the focal point  140 , based on a phase difference caused by a difference between lengths of optical paths through which the parallel light travels in two media with different refractive indices. 
     For example, based on a shape of a lens, lengths of optical paths through which parallel light travels may be different from each other. Based on a difference between the lengths of the optical paths, phases of parallel light that is simultaneously incident on the lens may be different from each other. Based on a difference between the phases, the parallel light may be focused onto a single focal point, and may be propagated from the focal point at the same angle as an angle at which the parallel light is incident on the lens. The propagated light may indicate coherent light, and may be used to generate a hologram through constructive interference and destructive interference. 
     The lens may be either a convex lens or a concave lens. A focal point of the convex lens may be placed at a rear side of the convex lens, with respect to a direction in which light travels. A focal point of the concave lens may be placed at a front side of the concave lens, with respect to a direction in which light travels. 
     In another embodiment, the coherent light generator  130  may be, for example, a phase modulator. The phase modulator may change a refractive index of a central portion of an optical axis and a refractive index of a peripheral portion of the optical axis so that the refractive indices may be different from each other, and may focus the parallel light generated by the backlight unit  110  onto the focal point  140  based on a phase difference caused by a position of an optical path through which the parallel light travels. 
     For example, the phase modulator may enable a refractive index of a central portion of an optical axis to be different from a refractive index of a peripheral portion of the optical axis. Based on a difference between the refractive indices, phases of parallel light that is simultaneously incident on the phase modulator may be different from each other. Based on a difference between the phases, the parallel light may be focused onto a single focal point, and may be propagated from the focal point at the same angle as an angle at which the parallel light is incident on the phase modulator. The propagated light may indicate coherent light, and may be used to generate a hologram through interference. 
     In another embodiment, the coherent light generator  130  may be, for example, a phase modulating grating. The phase modulating grating may focus the parallel light onto the focal point  140 , based on a phase difference caused by a difference between lengths of a plurality of different optical paths through which the parallel light travels. 
     For example, based on a shape of a phase modulating grating, lengths of optical paths through which parallel light travels may be different from each other. Based on a difference between the lengths of the optical paths, phases of parallel light that is simultaneously incident on the phase modulating grating may be different from each other. Based on a difference between the phases, the parallel light may be focused onto a single focal point, and may be propagated from the focal point at the same angle as an angle at which the parallel light is incident on the phase modulating grating. The propagated light may indicate coherent light, and may be used to generate a hologram through interference. 
     The coherent light generator  130  may be, for example, an amplitude modulating grating. The amplitude modulating grating may focus the parallel light onto the focal point  140 , based on an amplitude difference, by blocking a part of a plurality of optical paths through which the parallel light travels. 
     For example, the amplitude modulating grating may partially block the travel of parallel light and accordingly, amplitudes of light passing through the amplitude modulating grating may be different from each other. Based on a difference between the amplitudes, the parallel light may be focused onto a single focal point, and may be propagated from the focal point at the same angle as an angle at which the parallel light is incident on the amplitude modulating grating. The propagated light may indicate coherent light, and may be used to generate a hologram through interference. 
     A focal point onto which parallel light is focused by the coherent light generator  130  may be calculated by Equation 1 below:
 
 f= 2 /p  cot(θ/2)  [Equation 1]
 
     In Equation 1, f denotes a focal point, p denotes a width of a pixel, and θ denotes a spatial angle of coherent light propagated from a focal point. When light is focused onto a focal point and propagated by a coherent light generator that will be further described below, coherent light may be formed at a wide spatial angle. As shown in Equation 1, the spatial angle θ may be set to at least 15°, at least 30°, or at least 60°, by adjusting the width p and the focal point f. Additionally, a light generation apparatus with the spatial angle θ of at least 15°, at least 30°, or at least 60° through adjustment of the focal point f, despite the width p being limited to a few μm or at least 10 μm, may be implemented. 
       FIG. 2  illustrates a diagram of an example in which a lens is used as a coherent light generator according to example embodiments. 
     Referring to  FIG. 2 , a backlight unit  210  may generate parallel waves  211 ,  213 ,  215  and  217 , namely, light that is parallel to a surface on which a pixel  220  has been placed. In an embodiment, the backlight unit  210  may generate coherent light or collimated light, or both. A lens  230  may be located at a rear side of the pixel  220 . Light passing through the pixel  220  may be focused onto a focal point  240 , by passing through the lens  230 . Light  250  passing through the focal point  240  may be propagated at a wide angle θ. 
     In box  270  showing light passing through the lens  230 , a refraction index of a portion  271  of the lens  230  may be different from a refractive index of air  273 , and lengths of optical paths through which light travels may be different from each other, which may cause a phase difference. Based on the phase difference, the light passing through the lens  230  may be focused onto a single focal point, for example, the focal point  240 . 
     In a box  260  showing the focal point  240  onto which the light passing through the lens  230  is focused, the light may be focused onto the focal point  240  at the wide angle θ, and may be propagated at the wide angle θ. The propagated light may be used to form a hologram through interference. 
     The lens  230  may include, for example, any and all lenses enabling light to be focused onto the focal point  240 . Light passing through the pixel  220  may be refracted by the lens  230 , may be focused onto the focal point  240 , and may continue to be propagated. 
     Light incident on a surface of the lens  230  may be propagated at speeds of the light that is reduced in inverse proportion to a refractive index of the lens  230 . The lens  230  may have a spherical surface or a parabolic surface. Accordingly, a phase of light far from a center of an optical axis may become faster due to a short optical path passing through the lens  230 , and a phase of light in the center of the optical axis may become slower due to a long optical path passing through the lens  230 . 
     Light incurring a phase change while passing through the lens  230  may travel towards the focal point  240 , and circular wave fronts of the light may be formed. The light may be propagated while maintaining the circular wave fronts, despite passing through the focal point  240 . In the focal point  240 , light may have a single phase, and may be propagated with a single wavelength and accordingly, coherence may be maintained and light may be propagated at a wide angle. For example, when lenses with the same shape are arranged for each pixel, coherent light with the same phase may be generated at each focal point, and may be propagated at a wide angle. 
     By controlling a wide-angle coherent light, a hologram image may be generated in a desired position through constructive interference and destructive interference. 
       FIG. 3  illustrates a diagram of an example in which a phase modulator is used as a coherent light generator according to example embodiments. 
     Referring to  FIG. 3 , a backlight unit  310  may generate parallel wave  311 , namely, light that is parallel to a surface on which a pixel  320  has been placed. A phase modulator  330  may be located in a rear side of the pixel  320 , that is, in a right side of the pixel  320 . Light passing through the pixel  320  may be focused onto a focal point  340 , by passing through the phase modulator  330 . Light  350  passing through the focal point  340  may be propagated at a wide angle θ. 
     In a box  370  showing light passing through the phase modulator  330 , a portion  371  of the phase modulator  330  that is close to an optical axis  331  may be different in a refractive index n(x) from a portion  373  of the phase modulator  330  that is far from the optical axis  331 , which may cause a phase difference. Based on the phase difference, the light passing through the phase modulator  330  may have circular wave fronts  375 ,  377  and  379 , and may be focused onto a single focal point, for example, focal point  340 . 
     In a box  360  showing focal point  340  onto which the light passing through the phase modulator  330  is focused, the light may be focused onto focal point  340  at wide angle θ, and may be propagated at wide angle θ. 
     The phase modulator  330  may have different refractive indices based on a central portion of the optical axis  331 . In the example of  FIG. 2 , light may be focused using the lens  230 , based on the phase difference caused by the difference between the lengths of the optical paths in two media with different refractive indices. In the example of  FIG. 3 , a refractive index of the central portion of the optical axis  331 , and a refractive index of a peripheral portion of the optical axis  331  may be continuously changed, despite the same absolute lengths of optical paths, and accordingly the light passing through the phase modulator  330  may have different phases based on a position. 
     The phase modulator  330  may be implemented, for example, using a holographic optical element (HOE). 
       FIG. 4  illustrates a diagram of an example in which a phase modulating grating is used as a coherent light generator according to example embodiments. 
     Referring to  FIG. 4 , a backlight unit  410  may generate parallel wave  411 , namely, light that is parallel to a surface on which a pixel  420  has been placed. A phase modulating grating  430  may be located at a rear side of the pixel  420 , that is, at a right side of the pixel  420 . Light passing through the pixel  420  may be focused onto a focal point  440 , by passing through the phase modulating grating  430 . Light  450  passing through the focal point  440  may be propagated at a wide angle θ. The phase modulating grating  430  may be generated in a form of sawteeth, for example. 
     In a box  470  showing light passing through the phase modulating grating  430 , a concave portion  471  of the phase modulating grating  430  may result in a different optical path length than a convex portion  473  of the phase modulating grating  430 , which may cause a phase difference. Based on the phase difference, the light passing through the phase modulating grating  430  may be focused onto a single focal point, for example, the focal point  440 . 
     In a box  460  showing the focal point  440  onto which the light passing through the phase modulating grating  430  are focused, the light may be focused onto the focal point  440  at the wide angle θ, and may be propagated at the wide angle θ. 
     The phase modulating grating  430  may be fabricated with high precision using an etching scheme, or other scheme and accordingly, may be implemented with uniform characteristics in a large area. 
       FIG. 5  illustrates a diagram of an example in which an amplitude modulating grating is used as a coherent light generator according to example embodiments. 
     Referring to  FIG. 5 , light  520  may be focused onto a focal point, by passing through an amplitude modulating grating  510 . The light  520  passing through the focal point may be propagated at a wide angle θ. 
     The light  520  may pass through a part of the amplitude modulating grating  510 , or may not pass through another part of the amplitude modulating grating  510 . Based on whether the light  520  passes through the amplitude modulating grating  510 , or not, the amplitude of the light  520  may be different. Based on a difference between the amplitude, light passing through the amplitude modulating grating  510  may be focused onto a single focal point. 
       FIG. 6  illustrates a block diagram of another example of a wide-angle coherent light generation apparatus according to example embodiments. 
     The wide-angle coherent light generation apparatus of  FIG. 6  may include, for example, a backlight unit  610  and a coherent light generator  620 . 
     The backlight unit  610  may generate light that is parallel to a surface on which a pixel  630  has been placed. For example, the backlight unit  610  may generate light with a single wavelength. To generate the parallel light, the backlight unit  610  may use various light sources, for example, an LED, and the like. 
     The coherent light generator  620  may focus the parallel light generated by the backlight unit  610  onto a focal point  640 , and may generate coherent light at a wide angle. The coherent light generator  620  may correspond to, for example, various optical devices with various shapes that are configured to focus parallel light onto a single focal point. For example, coherent light generator  620  may correspond to a lens, a phase modulator, a phase modulating grating, or an amplitude modulating grating. 
     The coherent light generator  620  may be located at a front side of the surface on which the pixel  630  has been placed, and may focus the parallel light onto the focal point  640 , before the parallel light passes through the pixel  630 . 
       FIG. 7  illustrates a block diagram of a display apparatus using a wide-angle coherent light according to example embodiments. 
     The display apparatus of  FIG. 7  may include, for example, a backlight unit  710 , a spatial light modulator  720 , a coherent light generator  730 , and a display unit  740 . 
     The backlight unit  710  may generate light that is parallel to a surface on which a plurality of pixels are placed. In an embodiment, the backlight unit  710  may generate coherent light or collimated light, or both. The backlight unit  710  may generate light with a single wavelength. To generate the parallel light, the backlight unit  710  may use various light sources, for example, an LED, and the like. 
     The spatial light modulator  720  may include a plurality of pixels, and may modulate a phase or an amplitude of parallel light passing through the plurality of pixels. The spatial light modulator  720  may be located for each of pixels. The spatial light modulator  720  may modulate a phase or an amplitude of light passing through a pixel. 
     The phase or the amplitude modulated by the spatial light modulator  720  may be reflected on coherent light at a wide angle by the coherent light generator  730 , and may be used as a source to restore a 3D image in a space by the display unit  740 . 
     The coherent light generator  730  may focus the parallel light that has the modulated phase or the modulated amplitude onto a focal point, and may generate coherent light at the wide angle. 
     In an embodiment, the coherent light generator  730  may be, for example, a lens. The lens may focus the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of optical paths through which the parallel light travels in two media with different refractive indices. The lens may be either a convex lens, or a concave lens. 
     In another embodiment, the coherent light generator  730  may be, for example, a phase modulator. The phase modulator may change a refractive index of a central portion of an optical axis and a refractive index of a peripheral portion of the optical axis so that the refractive indices may be different from each other, and may focus the parallel light onto the focal point based on a phase difference caused by a position of an optical path through which the parallel light travels. 
     In another embodiment, the coherent light generator  730  may be, for example, a phase modulating grating. The phase modulating grating may focus the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of a plurality of different optical paths through which the parallel light travels. 
     In another embodiment, the coherent light generator  730  may be, for example, an amplitude modulating grating. The amplitude modulating grating may focus the parallel light onto the focal point, based on an amplitude difference, by blocking a part of a plurality of optical paths through which the parallel light travels. 
     The display unit  740  may display a 3D image in space, based on interference of coherent light generated at a wide angle for each of the plurality of pixels. For example, the display unit  740  may display a 3D image on a hologram surface, using coherent light generated at a wide angle for each pixel. The display unit  740  may include, for example, a liquid crystal display (LCD), a thin film transistor-LCD (TFT-LCD), an organic LED (OLED), a flexible display, and the like, however, there is no limitation thereto. 
       FIG. 8  illustrates a diagram of an example of a structure of a display apparatus using a wide-angle coherent light according to example embodiments. 
     The display apparatus of  FIG. 8  may include, for example, a backlight unit  810 , a display panel  820 , and an optical unit  830 . 
     The backlight unit  810  may generate parallel light that is parallel to the display panel  820 . 
     The display panel  820  may be used as a spatial light modulator, and may have a structure enabling modulation of a phase or an amplitude of light. The display panel  820  may be configured with pixels in a lattice or grid-like pattern. 
     In a box  840  showing an enlarged portion of the display panel  820 , the display panel  820  may include a transistor  841 , a pixel  845  and an electrode  843  in a structure of a black matrix. The transistor  841  may include, for example, a TFT, and the pixel  845  may include, for example, an indium tin oxide (ITO) film. 
     In a box  850  showing a portion of the optical unit  830 , a coherent light generator  851  may be disposed so as to correspond to the pixel  845 . That is, the coherent light generator  851  may be located along a planar surface of the pixel  845  so that light passing through the pixel  845  may be focused onto a focal point. The coherent light generator  851  may include, for example, one or more of a lens, a phase modulator, a phase modulating grating, and an amplitude modulating grating, as described above in  FIGS. 2 through 5 . The coherent light generator  851  may be disposed at a front side of the pixel  845 . Conversely, the coherent light generator  851  may be disposed at a rear side of the pixel  845  of the display panel  820 . In either embodiment, the optical axis of the coherent light generator  851  may be generally aligned at the center of the pixel  845  of the display panel  820 . In another embodiment the optical axis may be disposed with an amount of offset from the center of the pixel for directing the generated coherent light to a specific position in a space. In yet another embodiment, when the coherent light generator  851  is located in front of the pixel  845  of the display panel  820 , it is recommended to minimize the gap between the coherent light generator  851  and the pixel  845  of the display panel  820  to reduce the light diffraction effect at the pixel. In still another embodiment, when the coherent light generator  851  is located at the rear of the pixel  845  of the display panel  820 , it is recommended to locate the display panel  820  at the focal plane of the pixel  845  of the coherent light generator  851  to prevent the loss of light by any light blocking mask between pixels. 
     In  FIG. 9 , a lens may be used as a coherent light generator. A lens may disposed so as to correspond to each pixel of a spatial light modulator. 
       FIGS. 9 and 10  illustrate diagrams of other examples of a structure of a display apparatus using a wide-angle coherent light according to example embodiments. 
       FIG. 9  illustrates an example of arrangement of coherent light generators  931 ,  933 ,  935 , and  937 . The coherent light generators  931 ,  933 ,  935 , and  937  may be arranged at a front side of a display panel  920 . The coherent light generators  931 ,  933 ,  935 , and  937  may be disposed so as to correspond to pixels  921 ,  923 ,  925 , and  927  of the display panel  920 , respectively. A phase or an amplitude of parallel light  910  may be modulated in the display panel  920 . The parallel light  910  with the modulated phase or the modulated amplitude may pass through the coherent light generators  931 ,  933 ,  935 , and  937 , may be focused onto focal points, and may be propagated at wide angles from the focal points, respectively. 
       FIG. 10  illustrates an example of arrangement of coherent light generators  1021 ,  1023 ,  1025 , and  1027 . The coherent light generators  1021 ,  1023 ,  1025 , and  1027  may be arranged at a rear side of a display panel  1030 . The coherent light generators  1021 ,  1023 ,  1025 , and  1027  may be disposed so as to correspond to pixels  1031 ,  1033 ,  1035 , and  1037  of the display panel  1030 , respectively. Parallel light  1010  may pass through the coherent light generators  1021 ,  1023 ,  1025 , and  1027 , and may be focused onto focal points on the display panel  1030 . A phase or an amplitude of the parallel light  1010  may be modulated in the display panel  1020 , and the parallel light  1010  with the modulated phase or the modulated amplitude may be propagated at wide angles from the focal points, respectively. 
       FIG. 11  illustrates a flowchart of a wide-angle coherent light generation method according to example embodiments. 
     Referring to  FIG. 11 , in  1110 , a wide-angle coherent light generation apparatus may generate light that is parallel to a surface on which a pixel has been placed. For example, the wide-angle coherent light generation apparatus may generate light with a single wavelength. To generate the parallel light, the wide-angle coherent light generation apparatus may use various light sources, for example, an LED, and the like. 
     In  1120 , the wide-angle coherent light generation apparatus may focus the parallel light onto a focal point, and may generate coherent light at a wide angle, based on light propagated from the focal point. 
     By using a lens, the wide-angle coherent light generation apparatus may focus the parallel light onto the focal point based on a phase difference caused by a difference between lengths of optical paths through which the parallel light travels in two media with different refractive indices. 
     By using a phase modulator, the wide-angle coherent light generation apparatus may change a refractive index of a central portion of an optical axis and a refractive index of a peripheral portion of the optical axis so that the refractive indices may be different from each other, and may focus the parallel light onto the focal point based on a phase difference caused by a position of an optical path through which the parallel light travels. 
     By using a phase modulating grating, the wide-angle coherent light generation apparatus may focus the parallel light onto the focal point, based on a phase difference caused by a difference between lengths of a plurality of different optical paths through which the parallel light travels. 
     By using an amplitude modulating grating, the wide-angle coherent light generation apparatus may focus the parallel light onto the focal point, based on an amplitude difference, by blocking a part of a plurality of optical paths through which the parallel light travels. 
     As described above, according to example embodiments, by using an optical device, a wide-angle coherent light generation apparatus may enable light generated in each pixel to have a wide viewing angle. 
     Additionally, according to example embodiments, a wide-angle coherent light generation apparatus may generate coherent light at a wide angle, using an optical device, while maintaining a pixel width at an existing commercial display level, for example, at least 100 μm. 
     Furthermore, according to example embodiments, to represent a hologram image, a wide-angle coherent light generation apparatus may generate coherent light at a wide angle, even in a pixel having a relatively great width, using an optical device, and may be widely utilized in a field to represent a 3D image, for example, a holographic display, holographic printing, and the like. 
     The above-described example embodiments may be recorded in non-transitory computer-readable media including program instructions to implement various operations embodied by a computer. The media may also include, alone or in combination with the program instructions, data files, data structures, and the like. The program instructions recorded on the media may be those specially designed and constructed for the purposes of example embodiments, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of non-transitory computer-readable media include magnetic media such as hard disks, floppy disks, and magnetic tape; optical media such as CD ROM discs and DVDs; magneto-optical media such as optical discs; and hardware devices that are specially configured to store and perform program instructions, such as read-only memory (ROM), random access memory (RAM), flash memory, and the like. The non-transitory computer-readable media may also be a distributed network, so that the program instructions are stored and executed in a distributed fashion. The program instructions may be executed by one or more processors. The non-transitory computer-readable media may also be embodied in at least one application specific integrated circuit (ASIC) or Field Programmable Gate Array (FPGA), which executes (processes like a processor) program instructions. Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter. The above-described devices may be configured to act as one or more software modules in order to perform the operations of the above-described example embodiments, or vice versa. 
     Any one or more of the software modules described herein may be executed by a dedicated hardware-based computer or processor unique to that unit or by a hardware-based computer or processor common to one or more of the modules. The described methods may be executed on a general purpose computer or processor or may be executed on a particular machine such as the coherent light generation apparatus described herein. 
     Although example embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these example embodiments without departing from the principles and spirit of the disclosure, the scope of which is defined by the claims and their equivalents.