Patent Publication Number: US-9417502-B2

Title: Acousto-optic device having wide diffraction angle, optical scanner, light modulator, and display apparatus using the acousto-optic device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of U.S. application Ser. No. 13/585,293, filed Aug. 14, 2012, which claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2011-0085149, filed on Aug. 25, 2011, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to acousto-optic devices having a wide range of diffraction angle, optical scanners, light modulators, and display apparatuses using the acousto-optic devices, and, for example, to acousto-optic devices capable of increasing a diffraction angle range or adjusting diffraction angle characteristics of an output light by using a strong anisotropic refractive index that generates around a photonic band gap of a photonic crystal, optical scanners, light modulators, and display apparatuses using the acousto-optic devices. 
     2. Description of Related Art 
     The acousto-optic effect serves to regularly change a refractive index of light in a medium by changing degrees of compression and rarefaction of the medium using sonic waves or ultrasonic waves. The acousto-optic effect may enable the medium to function as a phase grating. Thus, light that is incident to the medium may be diffracted according to the acousto-optic effect. 
     In addition, the medium that diffracts the incident light according to the acousto-optic effect is generally referred to as an acousto-optic medium. An intensity of light diffracted by the acousto-optic medium and angle at which the light is diffracted by the acousto-optic medium may vary respectively depending on intensity and frequency of sound waves. Therefore, an acousto-optic device, in which a sound wave generator (e.g., an ultrasonic wave generator) is mounted on a surface of the acousto-optic medium, may be applied in a light modulator to modulate an amplitude of the light, or an optical scanner to deviate the light. 
     However, a natural acousto-optic medium may be limited with respect to optical anisotropy and acousto-optic transformation rates. Therefore, acousto-optic devices using the natural acousto-optic medium may be limited with respect to the diffraction angle of the output light. That is, in related acousto-optic devices using the natural acousto-optic medium, a width of a range of the diffraction angle is insufficient to provide adequate modulation or deviation of the output light. 
     Therefore, when related acousto-optic devices are used in optical scanners, light modulators, displays, and other similar systems, an additional optical system is necessary in order to compensate for the limited diffraction angle range. The inclusion of the additional optical system may increase the size of the above-referenced systems or serve to degrade resolution in the above-referenced systems. Accordingly, there is a need for developing acousto-optic devices having increased diffraction angle ranges. Research is actively being conducted involving the structuring of the acousto-optic medium in various shapes within acousto-optic devices. 
     SUMMARY 
     In one general aspect, there is provided an acousto-optic device, including a core layer having a periodic photonic crystal structure in which unit cells of predetermined patterns are repeated, a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from a refractive index of the core layer, a second clad layer on a second surface of the core layer, the second surface being opposite the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer, and a sound wave generator configured to apply surface acoustic waves (SAW) to the core layer, the first clad layer, the second clad layer, or any combination thereof. The core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material. 
     The general aspect of the acousto-optic device may further provide that the acousto-optic material includes ZnO, ZnS, AlN, Al 2 O 3 , LiNbO 3 , TiO 2 , Si, SrTiO 3 , or any combination thereof. 
     The general aspect of the acousto-optic device may further provide that the first clad layer, the second clad layer, or a combination thereof is air. 
     The general aspect of the acousto-optic device may further provide that the sound wave generator is disposed on a surface of the core layer, the first clad layer, the second clad layer, or any combination thereof. 
     The general aspect of the acousto-optic device may further provide that the core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes a piezoelectric material as the sound wave generator. 
     The general aspect of the acousto-optic device may further provide that the sound wave generator is on a side surface of the acousto-optic device. 
     The general aspect of the acousto-optic device may further provide that the periodic photonic crystal structure includes a periodic structure in which two or more materials having different dielectric constants are regularly arranged in a two-dimensional (2D) or a three-dimensional (3D) structure. 
     The general aspect of the acousto-optic device may further provide that the first and second clad layers have periodic photonic crystal structures with equal periodicity to the photonic crystal structure of the core layer. 
     The general aspect of the acousto-optic device may further provide that the core layer includes dielectric particles arranged in a regular period structure, and air is filled between the dielectric particles. 
     The general aspect of the acousto-optic device may further provide that the core layer includes a dielectric substrate with dielectric particles arranged in the periodic photonic crystal structure. 
     The general aspect of the acousto-optic device may further provide that the dielectric particles are formed of air or a dielectric material, the dielectric material having a refractive index that is different from a refractive index of the dielectric substrate. 
     The general aspect of the acousto-optic device may further provide that a region of the core layer in which an angular distribution of the refractive index becomes flat is at certain frequencies and wave vectors of lights around a photonic bandgap. 
     The general aspect of the acousto-optic device may further provide that the core layer has an anisotropic refractive index distribution of a polygonal shape, in which refractive indices toward its vertexes are different from refractive indices toward an intermediate portion of sides of the refractive index distribution. 
     The general aspect of the acousto-optic device may further provide that incident light proceeds to a vertex of the refractive index distribution of the core layer, and the SAW proceeds along a region where the refractive index distribution of the core layer is flat. 
     In another general aspect, there is provided an optical scanner, including a first acousto-optic device configured to diffract and/or deflect light in a first direction, a second acousto-optic device configured to diffract and/or deflect light in a second direction that is perpendicular to the first direction, and light-coupling device that makes light incident to the first acousto-optic device. Each of the first and second acousto-optic devices includes a core layer having a periodic photonic crystal structure in which unit cells of predetermined patterns are repeated, a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from a refractive index of the core layer, a second clad layer on a second surface of the core layer, the second surface being opposite the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer, and a sound wave generator configured to apply surface acoustic waves (SAW) to the core layer, the first clad layer, the second clad layer, or any combination thereof. The core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material. 
     The general aspect of the optical scanner may further provide a substrate including the first and second acousto-optic devices, the first and second acousto-optic devices being adjacent to each other. 
     The general aspect of the optical scanner may further provide that the sound wave generator of the first acousto-optic device is on the substrate, and the sound wave generator of the second acousto-optic device is on an upper surface of the second acousto-optic device. 
     In yet another general aspect, there is provided a two-dimensional (2D)/three-dimensional (3D) switchable image display apparatus, including a display panel, and an acousto-optic device array on a front surface of the display panel, the acousto-optic device array being configured to diffract and/or deflect images displayed on the display panel, the acousto-optic device array including acousto-optic devices, each of the acousto-optic devices including a core layer having a periodic photonic crystal structure in which unit cells of predetermined patterns are repeated, a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from a refractive index of the core layer, a second clad layer on a second surface of the core layer, the second surface being opposite the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer, and a sound wave generator configured to apply surface acoustic waves (SAW) to the core layer, the first clad layer, the second clad layer, or any combination thereof. The core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material. 
     The general aspect of the 2D/3D switchable image display apparatus may further provide that a height of each of the acousto-optic devices is equal to a height of one or more pixel rows of the display panel. 
     The general aspect of the 2D/3D switchable image display apparatus may further provide that each of the acousto-optic devices extends in a transverse direction, and is arranged along a longitudinal direction. 
     The general aspect of the 2D/3D switchable image display apparatus may further provide that each of the acousto-optic devices corresponds to one or more pixel rows of the display panel. 
     In still another general aspect, there is provided a holographic display apparatus, including a light source configured to provide light, an acousto-optic device array including a plurality of acousto-optic devices, each of the acousto-optic devices being configured to diffract and/or deflect the light provided from the light source, each of the acousto-optic devices including a core layer having a periodic photonic crystal structure in which unit cells of predetermined patterns are repeated, a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from a refractive index of the core layer, a second clad layer on a second surface of the core layer, the second surface being opposite the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer, and a sound wave generator configured to apply surface acoustic waves (SAW) to the core layer, the first clad layer, the second clad layer, or any combination thereof, and a projection optical system configured to project the light diffracted by the acousto-optic device array. The core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes an acousto-optic material. 
     The general aspect of the holographic display apparatus may further provide that each of the acousto-optic devices extends in a transverse direction, and is arranged along a longitudinal direction. 
     The general aspect of the holographic display apparatus may further provide that the acousto-optic devices generate hologram rows in a horizontal direction of a hologram image, and each of the acousto-optic devices corresponds respectively to one or more of the horizontal hologram rows. 
     In an additional general aspect, there is provided an acousto-optic device, including a core layer including an acousto-optic material, the core layer having a periodic photonic crystal structure in which unit cells of predetermined patterns are repeated, the core layer being configured to generate a region at certain frequencies and wave vectors of lights around a photonic bandgap in which an angular distribution of a refractive index becomes flat, and a sound wave generator configured to provide surface acoustic waves (SAW) along the flat region of the angular distribution of the refractive index in the core layer. Incident light proceeding toward a vertex of the angular distribution of the refractive index is diffracted along the flat region of refractive index distribution toward an adjacent vertex. 
     The additional general aspect of the acousto-optic device may further provide a first clad layer on a first surface of the core layer, the first clad layer having a refractive index that is different from the refractive index of the core layer, and a second clad layer on a second surface of the core layer, the second surface being opposite the first surface, the second clad layer having a refractive index that is different from the refractive index of the core layer. The sound wave generator is further configured to apply the SAW to the core layer, the first clad layer, the second clad layer, or any combination thereof. The core layer, the first clad layer, the second clad layer, or any combination thereof to which the SAW are applied includes the acousto-optic material. 
     Other features and aspects may be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional view illustrating an acousto-optic device according to an example embodiment. 
         FIG. 2  is a schematic perspective view illustrating an example of a photonic crystal structure of a core layer in the acousto-optic device shown in  FIG. 1 . 
         FIG. 3  is a schematic plan view illustrating a photonic crystal structure of a core layer in an acousto-optic device according to another example embodiment. 
         FIGS. 4 and 5  are diagrams illustrating examples of equifrequency contours of wavevectors in the wavevector space, which are related to refractive index distribution contours for propagating lights along a core layer having a periodic structure. 
         FIG. 6  is a diagram illustrating an example of a principle of using refractive index surfaces generated from the equifrequency contours illustrated in  FIG. 4  to increase a diffraction angle range. 
         FIG. 7  is a schematic perspective view illustrating operations of an acousto-optic device according to an example embodiment. 
         FIG. 8  is a schematic perspective view illustrating an example of an optical scanner including the acousto-optic devices of the example embodiments. 
         FIG. 9  is a schematic diagram illustrating an example of a two-dimensional (2D)/three-dimensional (3D) convertible image display apparatus including the acousto-optic devices of the example embodiments. 
         FIG. 10  is a schematic diagram illustrating an example of a holographic display apparatus including the acousto-optic devices of the example embodiments. 
     
    
    
     Throughout the drawings and the detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the systems, apparatuses and/or methods described herein will be suggested to those of ordinary skill in the art. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
       FIG. 1  is a schematic cross-sectional view illustrating an acousto-optic device  10  according to an example embodiment. Referring to  FIG. 1 , the acousto-optic device  10  includes a core layer  11 , a first clad layer  12 , and a second clad layer  13 . The first clad layer  12  and the second clad layer  13  are disposed respectively on an upper surface and a lower surface of the core layer  11 . A refractive index of the core layer  11  is different from refractive indices of the first and second clad layers  12 ,  13 . For example, the refractive index of the core layer  11  may be greater or less than the refractive indices of the first and second clad layers  12 ,  13 . In this structure, light incident to the acousto-optic device  10  is captured between the first and second clad layers  12 ,  13 , and proceeds along the core layer  11 . Therefore, the acousto-optic device  10  may function as a waveguide of the incident light. 
     As noted above, the refractive index of the core layer  11  is to be different from the refractive indices of the first and second clad layers  12 ,  13 . While there is no limitation in selecting materials forming the core layer  11  and the first and second clad layers  12 ,  13 , the core layer  11 , the first clad layer  12 , the second clad layer  13 , or any combination thereof may be formed of an acousto-optic material having an acousto-optic effect. When the core layer  11 , the first clad layer  12 , the second clad layer  13 , or any combination thereof is formed of acousto-optic material, a local density of the acousto-optic device  10  may be changed in various forms, for example, repeatedly changed corresponding to compression and rarefaction of sound waves applied to the acousto-optic device  10 . The acousto-optic material may be, for example, ZnO, ZnS, AlN, Al 2 O 3 , LiNbO 3 , TiO 2 , Si, or SrTiO 3 . In addition, the first clad layer  12 , the second clad layer  13 , or a combination thereof may be formed of air. 
     In addition, the acousto-optic device  10  includes one or more sound wave generators  14 ,  15 ,  16 , which may apply source waves to the core layer  11 , the first clad layer  12 , the second clad layer  13 , or any combination thereof. For example, the sound wave generators  14 ,  15 ,  16  may be electroacoustic modulators that generate surface acoustic waves (SAW) such as ultrasonic waves according to applied electric signals. Although the sound wave generators  14 ,  15 ,  16  are disposed on surfaces of the core layer  11 , the first clad layer  12 , and the second clad layer  13  in  FIG. 1 , respectively, the sound wave generators may be disposed on the core layer  11 , the first clad layer  12 , the second clad layer  13 , or any combination thereof. 
     The core layer  11 , the first clad layer  12 , the second clad layer  13 , or any combination thereof may function as a sound wave generator if formed of a piezoelectric material. For example, if the first clad layer  12  is formed of the piezoelectric material, when a voltage is applied to the first clad layer  12 , the first clad layer  12  may vibrate and generate SAW. Otherwise, only one sound wave generator may be disposed adjacent to a side surface of the acousto-optic device  10 . 
     According to the acousto-optic device  10 , the core layer  11  may have a two-dimensional (2D) or a three-dimensional (3D) regular photonic crystal structure. The photonic crystal may be a periodic structure in which two or more materials having different dielectric constants (or refractive indices) are arranged regularly. For example, the photonic crystal may be a periodic structure having a periodicity of a submicron or less (e.g., a wavelength of light or less). The photonic crystal may transmit, reflect, or absorb almost 100% of light of a certain wavelength band. In general, wavelength bands of light along certain directions that may not transmit through the photonic crystal are referred to as photonic bandgap. The photonic crystals having the photonic bandgap are applied in various fields. The first and second clad layers  12 ,  13  may have the same periodicity with that of the photonic crystal structure of the core layer  11 . However, the core layer  11  may have the photonic crystal structure while the first and second clad layers  12 ,  13  do not have the photonic crystal structure. 
       FIG. 2  is a schematic perspective view illustrating an example of a photonic crystal structure of the core layer  11  in the acousto-optic device  10  shown in  FIG. 1 . Referring to  FIG. 2 , the core layer  11  includes a dielectric substrate  11   a  with dielectric particles  11   b  being vertically oriented therein. For example, when the core layer  11  is formed of the acousto-optic material, the dielectric substrate  11   a  may include the acousto-optic material. 
     In  FIG. 2 , the dielectric particles  11   b  of the dielectric substrate  11   a  are oriented perpendicularly to a surface of the dielectric substrate  11 . The dielectric particles  11   b  of the dielectric substrate  11   a , as illustrated in  FIG. 2 , extend completely through the dielectric substrate  11   a . However, the dielectric particles  11   b  of the dielectric substrate  11   a  are not limited to or may stop short of extending completely through the dielectric substrate  11   a . Further, the dielectric particles  11   b  may be formed of air or a dielectric material having a refractive index that differs from that of the dielectric substrate  11   a . In addition, the dielectric particles  11   b  of the dielectric substrate  11   a  are arranged in a periodic structure in which square pattern unit cells are repeatedly arranged. 
     In another example embodiment, the dielectric substrate  11   a  may be formed of air. In this example, the dielectric particles  11   b  may be formed of a dielectric material that is not air (e.g., the acousto-optic material). That is, the core layer  11  may include dielectric poles or particles (e.g., the acousto-optic material) arranged between the first and second clad layers  12 ,  13  in the regular periodic structure, and air between the dielectric poles or particles. 
     In addition, in  FIG. 2 , the dielectric substrate  11   a  has dielectric particles  11   b  that are cylindrical. However, the dielectric particles  11   b  may have variable width that varies depending on a height. That is, a width of an intermediate portion of the dielectric particles  11   b  may be greater or less than widths at opposite end portions of the dielectric particles  11   b . Further, the dielectric particles  11   b  may be conical. Moreover, the dielectric particles  11   b  may have polygonal cross-sections, such as triangular or square cross-sections, as well as the circular cross-section. 
     The photonic crystal structure of the core layer  11  shown in  FIG. 2  is an example, and the photonic crystal periodic structure may have various designs. For example,  FIG. 3  is a schematic plan view illustrating a 2D photonic crystal structure of the core layer  11  in the acousto-optic device  10  according to another example embodiment. 
     Referring to  FIG. 3 , the core layer  11  may have a periodic structure in which hexagonal pattern unit cells are repeatedly arranged. Beside the periodic structures shown in  FIGS. 2 and 3 , other various types of periodic structures may be used. For example, in replacement of the cylindrical dielectric particles  11   b , dielectric materials having hexahedron or spherical shapes may be regularly arranged in the dielectric substrate  11   a . In addition,  FIGS. 2 and 3  only show a 2D photonic crystal periodic structure; however, the core layer  11  may be designed to have a 3D photonic crystal periodic structure (that is, a structure having periodicities in transverse, longitudinal, and height directions). 
     The core layer  11  having 2D or 3D photonic crystals may be designed so that a region may be generated around the photonic bandgap in which an angular distribution of the refractive index becomes flat. For example,  FIG. 4  is a diagram illustrating an example of equifrequency contours of wavevectors (k(ω)) of the lights flowing through the core layer  11  having the photonic crystal periodic structure shown in  FIG. 3 . When the contour distribution of the wavevector is divided by a wavenumber in the air (that is, 2π/λ, where λ denotes wavelength of light in air), the contour distribution of the wavevector may be converted into refractive index distribution contours (i.e., index surface). In  FIG. 4 , the hexagonal dashed line denotes one unit cell (i.e., the first Brillouin zone) in a wavevector space for the photonic crystal structure shown in  FIG. 3 . In  FIG. 3 , ┌, M, and K denote main points of the wavevectors that represent symmetry. Referring to  FIG. 4 , the angular distribution of the refractive index becomes circular around the center (┌) of the unit cell in the wavevector space. This means that an isotropic refractive index characteristic is shown around the center (┌) of the unit cell, that is, the refractive index is constant in any direction. On the other hand, the refractive index distribution is nearly hexagonal around a boundary of the unit cell (near the photonic bandgap), as denoted by a solid line. That is, six regions are generated around the boundary of the unit cell in which the angular distribution of the refractive index becomes flat. As a result, the refractive index of a wavevector at a vertex (K) of the unit cell and the refractive index of a wavevector at a center (M) in each side of the unit cell greatly differ from each other. 
     In addition,  FIG. 5  is a diagram illustrating an example of contour distribution (k(ω)) of wavevectors of the light flowing through the core layer  11  having the photonic crystal periodic structure shown in  FIG. 2 . As described above, the contour distribution of the wavevector may be converted into the refractive index distribution by the directions by being divided by the wavenumber in air. Referring to  FIG. 5 , in the photonic crystal periodic structure shown in  FIG. 2 , the isotropic refractive index characteristics, that is, the refractive index, is constant in any direction around the center (┌) of the unit cell in the wavevector space is generated. The anisotropic refractive index distribution of square shape is generated around the boundary of the unit cell. In addition to the hexagonal and square anisotropic refractive index distributions shown in  FIGS. 4 and 5 , the core layer  11  may have various polygonal anisotropic distributions of the refractive index according to the design of the photonic crystal structure. 
     A range of diffraction angle of the light incident to the core layer  11  having the periodic photonic crystal structure may be greatly changed by using anisotropic refractive index distribution.  FIG. 6  is a diagram illustrating an example of a principle of using the example refractive index distribution in  FIG. 4  to increase a diffraction angle range. Referring to  FIG. 6 , in an isotropic structure in which the refractive index is constant in every direction, a maximum range of the diffraction angle of the light is θ 1 , even if the refractive index is regularly changed in the medium by changing the degrees of compression and rarefaction in the medium using ultrasonic waves. However, in the photonic crystal structure having a highly anisotropic refractive index distribution, when the incident light proceeds toward a vertex of the refractive index distribution, a SAW, such as an ultrasonic wave, is provided that proceeds along the flat region of the refractive index distribution. As a result, the light may be greatly diffracted. For example, the light may be diffracted within an angle range of θ 2  along the photonic bandgap region toward another adjacent vertex. 
       FIG. 7  is a schematic perspective view illustrating an example of operations of the acousto-optic device  10 .  FIG. 7  shows one sound wave generator  20  that is disposed on a side surface of the acousto-optic device  10  for convenience of description. However, the sound wave generators  14 ,  15 , and  16  illustrated in  FIG. 1  may be used. Referring to  FIG. 7 , when light L is incident to the acousto-optic device  10  along an x direction, the sound wave generator  20  applies a SAW, such as an ultrasonic wave, to the acousto-optic device  10  in a direction that does not coincide with the preceding direction of the light L, for example, in a y direction. Here, a periodic structure of the photonic crystals in the core layer  11  may be oriented so that the incident light L may proceed toward a vertex region of the refractive index distribution in the core layer  11 . In addition, the sound wave generator  20  may be disposed so that the SAW may proceed along the flat region of the refractive index distribution in the core layer  11 . 
     Then, the incident light L is diffracted. As a result, 0th-order diffracted light beam L 0  and 1st-order diffracted light beam L 1  is output. According to the acousto-optic device  10  of the example embodiment, when the SAW is applied to the acousto-optic device  10 , the light may be greatly diffracted while proceeding along the core layer  11  due to the highly anisotropic refractive index of the core layer  11 , because a diffraction angle range that satisfies constructive interference is increased. Therefore, the acousto-optic device  10  may provide a wider diffraction angle range than that of the related acousto-optic device. 
     Here, the diffraction angle may be defined as a difference between angles of the 0th-order diffracted light (i.e., just transmitted) beam L 0  and the 1st-order diffracted light beam L 1  by the acousto-optic device  10 . The diffraction angle of the light and the intensity of the diffracted light may be controlled by the frequency and intensity of the SAW. In addition, the frequency and the intensity of the SAW may be determined by a magnitude and a frequency of an electric signal applied to the sound wave generator  20 . Therefore, the diffraction of the light in the acousto-optic device  10  may be controlled by controlling the electric signal applied to the sound wave generator  20 . 
     The acousto-optic device  10  may be applied in various fields. For example, since the acousto-optic device  10  may adjust the intensity of the 0th-order diffracted light beam according to the diffraction degree of the light, the acousto-optic device  10  may perform as a light modulator of the 0th-order diffracted light. Since the incident light is not diffracted when the sound wave is not applied to the acousto-optic device  10 , the incident light may transmit through the acousto-optic device  10  without a loss. However, when the incident light is diffracted by applying the sound wave to the acousto-optic device  10 , 1st-order or other higher-order diffracted light beams are generated. As a result, the intensity of the 0th-order diffracted light beam transmitting through the acousto-optic device  10  is reduced. In addition, if more energy is allocated to the 1st-order or other higher-order diffracted lights according to the diffracted degree, the intensity of the 0th-order diffracted beam may be further reduced. Therefore, the acousto-optic device  10  may function as a light modulator that modulates the amplitude of the 0th-order diffracted light beam. 
     In addition, the acousto-optic device  10  may be applied as an optical scanner that deflects the incident light at a predetermined angle by changing the diffraction angle of the 1st-order diffracted light beam. For example, when the acousto-optic device  10  having the wide range of diffraction angle is used in the optical scanner, an operating range (i.e., scanning range) of the optical scanner may be increased. As a result, the configuration of the optical system used in the optical scanner may be simplified. For example, an additional optical system that is used to increase the diffraction angle range in related optical scanners might not be necessary. 
       FIG. 8  is a schematic perspective view illustrating an example of an optical scanner  100  including the acousto-optic device  10  of the example embodiment. Referring to  FIG. 8 , the optical scanner  100  may include a substrate  110 , a first acousto-optic device  131  disposed in the substrate  110 , a second acousto-optic device  132  disposed in the substrate  110  to be adjacent to the first acousto-optic device  131 , a light-coupling device  120  making the light incident to the first acousto-optic device  131 , a first sound wave generator  131   a  providing the first acousto-optic device  131  with SAW, and a second sound wave generator  132   a  providing the second acousto-optic device  132  with SAW. 
     Although not shown in  FIG. 8 , similarly to the acousto-optic device  10  shown in  FIG. 1 , the first and second acousto-optic devices  131 ,  132  may respectively include a core layer having the photonic crystal structure, and clad layers on upper and lower portions of the core layer. In  FIG. 8 , the first sound wave generator  131   a  is disposed on the substrate  110  and the second sound wave generator  132   a  is disposed on the second acousto-optic device  132 ; however, the present embodiment is not limited thereto. Locations of the first and second sound wave generators  131   a ,  132   a  may be selected appropriately in consideration of the desired direction of the SAW. For example, the first sound wave generator  131   a  may be disposed on a side surface of the substrate  110  or an upper surface of the acousto-optic device  131 . Likewise, the second sound wave generator  132   a  may be disposed on an upper surface or a side surface of the substrate  110 . 
     In addition, a refraction lens is used as the light-coupling device  120  in  FIG. 8 ; however, various optical devices may be used as the light-coupling device  120 . For example, a prism, a diffraction grating layer, a Fresnel lens, or a micro-lens array may be used as the light-coupling device  120 . 
     As an example, the first acousto-optic device  131  may be disposed so that the incident light may be deflected in a horizontal direction, and the second acousto-optic device  132  may be disposed so that the incident light may be deflected in a vertical direction. That is, as shown in  FIG. 8 , the light incident to the first acousto-optic device  131  through the light-coupling device  120  may be deflected in the horizontal direction. Then, the light deflected in the horizontal direction may be deflected in the vertical direction by the second acousto-optic device  132 . Further, the light deflected in the vertical direction may then be output. Therefore, the optical scanner  100  may perform a scanning of the incident light in the horizontal direction, the vertical direction, or a combination thereof within a predetermined angle range by modulating the magnitude and frequency of alternating current (AC) voltage applied to the first and second sound wave generators  131   a ,  132   a . In the example shown in  FIG. 8 , the optical scanner  100  includes two acousto-optic devices  131 ,  132 ; however, the optical scanner  100  may include one acousto-optic device that scans the light only in the horizontal or vertical direction, or a plurality of acousto-optic devices scanning the light in a direction. The optical scanner  100  may be applied in a laser image projection apparatus or a laser printer. 
     In addition, the acousto-optic device  10  described above may be applied to a 2D/3D switchable image display apparatus. For example,  FIG. 9  is a schematic diagram illustrating an example of a two-dimensional (2D)/three-dimensional (3D) convertible image display apparatus including a plurality of the acousto-optic devices  10  of the example embodiments. Referring to  FIG. 9 , acousto-optic devices  210  having the same height as those of one or more pixel rows of a display panel  200  and extending in a transverse direction may be arranged on a surface of the display panel  200  to form an array along a longitudinal direction. Then, each of the acousto-optic devices  210  may deflect an image displayed by respectively corresponding pixel rows of the display panel  200  in a predetermined direction. 
     For example, if sound waves are not applied to the acousto-optic medium in the acousto-optic devices  210 , the image displayed by each of the pixels of the display panel  200  is not deflected and transmitted through the array of the acousto-optic devices  210 . In this case, as shown in a left side of  FIG. 9 , the 2D/3D switchable display apparatus may operate in a 2D display mode. On the other hand, in a multi-viewpoint display mode or a 3D display mode, each of the acousto-optic devices  210  may deflect the image displayed from each of the pixels to generate beams in a plurality of directions. For example, a portion of the acousto-optic devices  210  may deflect the image to a right eye of a viewer, and another portion of the acousto-optic devices  210  may deflect the image to a left eye of the viewer. As an another example, at a certain moment of a frame time, the acousto-optic devices  210  may deflect the image to a right eye of a viewer, and at another moment of a frame time, the acousto-optic devices  210  may deflect the image to a left eye of a viewer. Then, as shown in the right side of  FIG. 9 , the viewer may see 3D images. 
     The acousto-optic device  10  may be applied to a holographic 3D display apparatus.  FIG. 10  is a schematic diagram illustrating an example of a holographic 3D display apparatus  300  including the acousto-optic device  10  of the example embodiments. For example, as shown in  FIG. 10 , the holographic 3D display apparatus  300  includes a light source  310 , an array of a plurality of acousto-optic devices  320 , and a projection optical system  330 . The light source  310  may be an array of a plurality of laser beams such as red, green and blue colors. In addition, the array of the plurality of acousto-optic devices  320  may be formed by manufacturing a plurality of acousto-optic devices extending in a transverse direction, and arranging the plurality of acousto-optic devices  320  to form an array along a longitudinal direction. Here, the acousto-optic devices  320  generate hologram rows in the horizontal direction. Each of the acousto-optic devices  320  may correspond to one or more hologram rows in a hologram image displayed by the holographic 3D display apparatus  300 . The hologram rows diffracted by the plurality of acousto-optic devices  320  may be projected on a predetermined space by the projection optical system  330  to generate the 3D image. 
     A number of examples have been described above. Nevertheless, it will be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the following claims.