Patent Publication Number: US-9842876-B2

Title: Color separation element array, image sensor including the color separation element array, and image pickup apparatus including the color separation element array

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a Continuation Application of U.S. patent application Ser. No. 14/738,396 filed Jun. 12, 2015, which claims priority from Korean Patent Application No. 10-2014-0072294, filed on Jun. 13, 2014, in the Korean Intellectual Property Office. The disclosures of the above-listed applications are incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     1. Field 
     The present disclosure relates to a color separation element array, an image sensor including the color separation element array, and an image pickup apparatus including the color separation element array, and more particularly, to a color separation element array that may improve a color separation efficiency at an edge portion thereof where light is obliquely incident, and to an image sensor and an image pickup apparatus using the color separation element array. 
     2. Description of the Related Art 
     Color display devices or color image sensors display an image of various colors or detect a color of incident light by using a color filter. An RGB color filter method, in which, for example, a green filter is arranged at two pixels of four pixels and a blue filter and a red filter are arranged in the other two pixels, is most widely employed by a currently used color display device or color image sensor. In addition to the RGB color filter method, a CYGM color filter method may be employed in which color filters of cyan, yellow, green, and magenta, which are complementary colors, are respectively arranged at four pixels. 
     However, a color filter may have a low light use efficiency because the color filter absorbs light of other colors except for filtered light. For example, when an RGB color filter is in use, only ⅓ of the incident light is transmitted and the other portion, that is, ⅔, of the incident light is absorbed. Accordingly, the light use efficiency may be about 33%. Accordingly, for the color display device or a color image sensor, most of a light loss is generated in the color filter. 
     Recently, to improve the light use efficiency of the color display device or color image sensor, a color separation element is being used instead of the color filter. The color separation element may separate colors of the incident light by using the diffraction or refraction characteristics of a light that varies according to a wavelength of the light. The colors separated by the color separation element may be transferred to pixels corresponding to the transferred colors. Accordingly, use of the color separation element may achieve a higher light use efficiency as compared to a case of using the color filter. 
     SUMMARY 
     One or more exemplary embodiments include a color separation element array, an image sensor including the color separation element array, and an image pickup apparatus including the color separation element array. 
     Additional aspects 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 presented exemplary embodiments. 
     According to an aspect of an exemplary embodiment, a color separation element array includes a plurality of color separation elements arranged in two dimensions and separating an incident light according to a wavelength such that, of the incident light, a light of a first wavelength is directed to a first direction and a light of a second wavelength that is different from the first wavelength is directed to a second direction that is different from the first direction, in which each of the plurality of color separation elements includes a first element and a second element that are sequentially arranged according to a traveling direction of the incident light, and the first element and the second element of at least one of the plurality of color separation elements are shifted with respect to each other. 
     The first and second elements of at least two of the color separation elements may be shifted with respect to each other differently. 
     The first element and the second element of one of the plurality of the color separation elements arranged in a center area of the color separation element array may be arranged such that center portions of the first element and the second element are aligned with each other, and the first element and the second element of each of the plurality of the color separation elements arranged in an area other than the center area of the color separation element array may be arranged to be shifted from each other. 
     The first element may be further shifted toward the center area of the color separation element array than the second element 
     A shift distance between the first element and the second element may increase as a distance from the center area of the color separation element array increases. 
     The first element and the second element may be symmetrically shifted with respect to the center area of the color separation element array, and the first element and the second element of the plurality of the color separation elements may be shifted to be aligned to fit to a traveling direction of light that is obliquely incident. 
     The color separation element array may further include a transparent dielectric layer, in which the plurality of color separation elements are buried in the transparent dielectric layer, and a refractive index of the first element and a refractive index of the second element are greater than that of the transparent dielectric layer. 
     The refractive index of the first element and refractive index of the second element may be identical to each other. 
     The refractive index of the first element and refractive index of the second element may be different from each other. 
     Each of the plurality of color separation element may further include a third element that is arranged following the second element along the traveling direction of the incident light. 
     A width of the second element may be smaller than a width of the first element, and a width of the third element may be smaller than the width of the second element. 
     According to another aspect of an exemplary embodiment, an image sensor includes a pixel array including a plurality of pixels arranged in two dimensions and detecting light, and a color separation element array including a plurality of color separation elements arranged in two dimensions and separating an incident light according to a wavelength such that light of different wavelengths are incident on different pixels, in which each of the plurality of color separation elements includes a first element and a second element that are sequentially arranged according to a traveling direction of the incident light, and the first element and the second element of at least one of the plurality of color separation elements are shifted with respect to each other. 
     The first element and the second element of one of the plurality of the color separation elements arranged in a center area of the color separation element array may be arranged such that center portions of the first element and the second element are aligned with each other, and the first element and the second element of each of the plurality of the color separation elements arranged in an area other than the center area of the color separation element array may be arranged to be shifted from each other. 
     The first element may be further shifted toward the center area of the color separation element array than the second element 
     A shift distance between the first element and the second element may increase as a distance from the center area of the color separation element array increases. 
     The first element and the second element may be symmetrically shifted with respect to the center area of the color separation element array, and the first element and the second element of the plurality of the color separation elements may be shifted to be aligned to fit to a traveling direction of light that is obliquely incident. 
     According to another aspect of an exemplary embodiment, an image pickup apparatus includes an objective lens, and an image sensor converting a light focused by the objective lens to an electric image signal, in which the image sensor includes a pixel array including a plurality of pixels arranged in two dimensions and detecting light, and a color separation element array including a plurality of color separation elements arranged in two dimensions and separating an incident light according to a wavelength such that light of different wavelengths are incident on different pixels, each of the plurality of color separation elements includes a first element and a second element that are sequentially arranged according to a traveling direction of the incident light, and the first element and the second element of at least one of the plurality of color separation elements are shifted with respect to each other. 
     The first element and the second element of one of the plurality of the color separation elements arranged in a center area of the color separation element array may be arranged such that center portions of the first element and the second element are aligned with each other, and the first element and the second element of each of the plurality of the color separation elements arranged in an area other than the center area of the color separation element array may be arranged to be shifted from each other. 
     The first element may be further shifted toward the center area of the color separation element array than the second element, a shift distance between the first element and the second element increases as a distance from the center area of the color separation element array may increase, and the first element and the second element may be symmetrically shifted with respect to the center area of the color separation element array. 
     The first element and the second element of the plurality of the color separation elements may be shifted to be aligned to fit to a traveling direction of a chief light that passes through the objective lens. 
     The image sensor may further include a transparent dielectric layer arranged on a surface of the pixel array, and the plurality of color separation elements may be buried in the transparent dielectric layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will become more apparent by describing certain exemplary embodiments with reference to the accompanying drawings, in which: 
         FIG. 1  is a cross-sectional view schematically illustrating an image pickup apparatus including a color separation element array and an image sensor according to an exemplary embodiment; 
         FIG. 2  is a plan view exemplarily illustrating a positional relationship between pixels of an image sensor and color separation elements; 
         FIG. 3  is a cross-sectional view exemplarily illustrating a pixel structure of the image sensor of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view exemplarily illustrating another pixel structure of the image sensor of  FIG. 2 ; 
         FIG. 5A  is a cross-sectional view exemplarily illustrating a positional relationship between a first element and a second element of a color separation element when a light is perpendicularly incident on an image sensor; 
         FIGS. 5B and 5C  are cross-sectional views exemplarily illustrating in detail a positional relationship between the first element and the second element of the color separation element when a light is obliquely incident on the image sensor; 
         FIGS. 6A and 6B  are cross-sectional views illustrating a change in the positions of the first element and the second element of the color separation element according to a change in a light incident angle; 
         FIGS. 7A, 7B, 8A, 8B, 9A, and 9B  are cross-sectional views exemplarily illustrating color separation elements according to various exemplary embodiments; 
         FIG. 10  is a plan view exemplarily illustrating shift forms of first elements and second elements according to the positions of a plurality of color separation elements in the image sensor; and 
         FIG. 11  is a graph exemplarily showing color separation efficiency according to a change in a light incident angle. 
     
    
    
     DETAILED DESCRIPTION 
     Certain exemplary embodiments are described in greater detail below with reference to the accompanying drawings. 
     In the following description, like drawing reference numerals are used for like elements, even in different drawings. The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. However, it is apparent that the exemplary embodiments can be practiced without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. 
     A color separation element array, an image sensor including the color separation element array, and an image pickup apparatus including the color separation element array are described in detail with reference to the accompanying drawings. In the following descriptions, like reference numerals refer to like elements. In the drawings, the size of each element is exaggerated for clarity and convenience of explanation. Also, in the following description of a layer structure, when a layer is described to exist “on” or “above” another layer, the layer may exist directly on or indirectly above the other layer, or a third layer may be interposed therebetween. 
       FIG. 1  is a cross-sectional view schematically illustrating an image pickup apparatus  200  and an image sensor  100  including a color separation element array according to an exemplary embodiment. Referring to  FIG. 1 , the image pickup apparatus  200  according to the present exemplary embodiment may include an objective lens  210  and the image sensor  100  for converting light focused by the objective lens  210  to an electric image signal. The image sensor  100  may include a pixel array  110  having a plurality of pixels detecting light and arranged in two dimensions (2D), and the color separation element array having a plurality of color separation elements  130  arranged in 2D. The image sensor  100  may further include a transparent dielectric layer  120  arranged on a surface of the pixel array  110 . The color separation elements  130  may be buried in the transparent dielectric layer  120 . 
     The color separation elements  130  are arranged at a light incident side of the pixel array  110  and each separate the incident light according to the wavelength of the incident light such that light of different wavelengths may be incident on different pixels. The color separation elements  130  may separate colors by changing traveling paths of light according to the wavelengths of the light by using the diffraction or refraction characteristics of the light that vary according to the wavelengths. For example, the color separation elements  130  are formed in various shapes such as a rod shape having a transparent symmetric or asymmetric structure or a prism shape having an inclined surface, which are well known, and a variety of designs may be available according to a desired spectrum distribution of an exit light. Light use efficiency may be increased by using the color separation elements  130  to optimize a spectrum distribution of light incident on the respective pixels to fit to the pixels. A positional relationship between the pixels of the image sensor  100  and the color separation elements  130  may be variously designed according to the color separation characteristics of the color separation elements  130 . 
     For example,  FIG. 2  is a plan view exemplarily illustrating a positional relationship between the pixels of the image sensor  100  and the color separation elements  130 . Referring to  FIG. 2 , the image sensor  100  may include the pixel array  110  having a plurality of photodetector pixels Px 1 , Px 2 , and Px 3  arranged in the form of a 2D matrix having a plurality of rows and columns. For example, as illustrated in  FIG. 2 , only the first pixels Px 1  may be arranged in a first pixel row P 1 , and the second pixels Px 2  and the third pixels Px 3  may be alternately arranged in a second pixel row P 2  that is adjacent to the first pixel row P 1 . The first pixel row P 1  and the second pixel row P 2  may be alternately arranged in a vertical direction. The color separation elements  130  may be arranged facing the second pixels Px 2  in the second pixel row P 2 . 
       FIG. 3  is a cross-sectional view exemplarily illustrating a structure of the first pixel Px 1  arranged in the first pixel row P 1  of the image sensor  100  of  FIG. 2 . Referring to  FIG. 3 , the first pixel Px 1  may include a light sensing layer  111 , a color filter layer  112  arranged on a light incident surface of the light sensing layer  111 , the transparent dielectric layer  120  arranged on the color filter layer  112 , and a micro lens  141  arranged on the transparent dielectric layer  120  to focus the incident light on the light sensing layer  111 . The light sensing layer  111  converts the incident light to an electric signal according to the intensity of the incident light. In such a structure, the incident light may be focused by the micro lens  141  on the light sensing layer  111  by passing through the transparent dielectric layer  120  and the color filter layer  112 . The color filter layer  112  may include a first color filter CF 1  that transmits only a light in a first wavelength band of the incident light. Accordingly, the first pixel Px 1  may detect only the light in the first wavelength band. 
       FIG. 4  is a cross-sectional view exemplarily illustrating a structure of the second and third pixels Px 2  and Px 3  arranged in the second pixel row P 2  of the image sensor  100  of  FIG. 2 . Referring to  FIG. 4 , the second pixel row P 2  may include the light sensing layer  111 , a color filter layer  112  arranged on a light incident surface of the light sensing layer  111 , the transparent dielectric layer  120  arranged on the color filter layer  112 , the color separation elements  130  arranged in the transparent dielectric layer  120  of the second pixel Px 2 , and a micro lens  142  arranged on the transparent dielectric layer  120  to focus the incident light on the color separation elements  130 . The color filter layer  112  may include a second color filter CF 2  that is arranged in the second pixel Px 2  to transmit only a light in a second wavelength band and a third color filter CF 3  arranged in the third pixel Px 3  to transmit only a light in a third wavelength band. The color separation elements  130  may be buried in the transparent dielectric layer  120  and may be fixed by being surrounded by the transparent dielectric layer  120 . 
     In the above structure, while passing through the color separation elements  130 , the light focused by the micro lens  142  may be separated into a light C 2  of a second wavelength band and a light C 3  of a third wavelength band by the color separation elements  130 . The color separation elements  130  may be designed, for example, to change a traveling direction of the light C 3  of the third wavelength band of the incident light into two inclined lateral directions without changing a traveling direction of the light C 2  of the second wavelength band. Then, the light C 2  of the second wavelength band may pass through the color separation elements  130  and may be incident on the light sensing layer  111  of the second pixel Px 2  disposed directly under the color separation elements  130 . On the other hand, after passing through the color separation elements  130 , the light C 3  of the third wavelength band may be incident on the light sensing layer  111  of each of the third pixels Px 3  disposed at the opposite sides of the second pixel Px 2 . 
     In the example illustrated in  FIGS. 2 to 4 , in the first color filter CF 1  of the first pixel Px 1 , only about 33% of the incident light is transmitted and arrives at the light sensing layer  111  as in a pixel structure of the related art. In contrast, in the second color filter CF 2  of the second pixel Px 2  and the third color filter CF 3  of the third pixel Px 3 , since a ratio of a color corresponding to each of the color filters CF 2  and CF 3  is high, transmissivity of light increases compared to the pixel structure of the related art. Accordingly, light use efficiency in the second pixel Px 2  and the third pixel Px 3  may be increased. For example, the first wavelength band may be green, the second wavelength band may be blue, and the third wavelength band may be red. In other words, the first pixel Px 1  may be a green pixel, the second pixel Px 2  may be a blue pixel, and the third pixel Px 3  may be a red pixel. 
     The structure of the pixel array  110  of the image sensor  100  and the characteristics of the color separation elements  130  illustrated in  FIGS. 2 to 4  are a mere example to help understanding and are not limited to the exemplary embodiment illustrated in  FIGS. 2 to 4 . A variety of color separation characteristics may be selected according to the design of the color separation elements  130 . A variety of structures of the pixel array  110  may be selected according to the color separation characteristics of the color separation elements  130 . Also, a part or the entire of the micro lenses  141  and  142  and the color filters CF 1 , CF 2 , and CF 3  may be omitted according to the design. 
     Referring back to  FIG. 1 , the objective lens  210  focuses an image of an object (not shown) on the image sensor  100 . When the image sensor  100  is accurately located on a focal plane of the objective lens  210 , a light starting from at a certain point of the object arrives at a certain point on the image sensor  100  by passing through the objective lens  210 . For example, a light starting from a certain point A on an optical axis OX passes through the objective lens  210  and then arrives at a center of the image sensor  100  on the optical axis OX. Also, light starting from any one of points B, C, and D located out of the optical axis OX travels across the optical axis OX by the objective lens  210  and arrives at a point in a peripheral portion of the image sensor  100 . For example, a light starting from the point B located above the optical axis OX arrives at a lower peripheral portion of image sensor  100 , crossing the optical axis OX, and a light starting from the point C located under the optical axis OX arrives at an upper peripheral portion of the image sensor  100 , crossing the optical axis OX. Also, a light starting from the point D located between the optical axis OX and the point B arrives at a position between the lower peripheral portion and the center of image sensor  100 , crossing the optical axis OX. 
     Accordingly, the light starting from the different points A, B, C, and D are incident on the image sensor  100  at different incident angles according to the distance between the points A, B, C, and D and the optical axis OX. An incident angle of a light incident on the image sensor  100  is typically defined to be a chief ray angle (CRA). A chief ray (CR) denotes a light ray starting from a point of the object and arriving at the image sensor  100  by passing through a center of the objective lens  210 . The CRA denotes an angle formed by the CR with respect to the optical axis OX. The CRA of the light starting from the point A on the optical axis OX is 0° and the light is perpendicularly incident on the image sensor  100 . The CRA increases as the starting point is farther from the optical axis OX. 
     From the viewpoint of the image sensor  100 , the CRA of the light incident on the center portion of the image sensor  100  is 0° and the CRA of the incident light gradually increases toward the edge of the image sensor  100 . For example, the CRA of the light starting from each of the points B and C and arriving at the outermost edge of the image sensor  100  is the largest, whereas the CRA of the light starting from the point A and arriving at the center of the image sensor  100  is 0°. The CRA of the light starting from the point D and arriving at a position between the center and the edge of the image sensor  100  is greater than 0° and less than the CRA of the light starting from each of the points B and C. 
     However, the color separation elements  130  generally have a structure having directivity. Due to the directivity, the color separation elements  130  efficiently operate with respect to the light perpendicularly incident on the color separation elements  130 . However, if the incident angle increases over a certain angle, the color separation efficiency of the color separation elements  130  is drastically lowered. Accordingly, when the color separation elements  130  having the same structure are arranged in the entire area of the image sensor  100 , the quality of an image may be more degraded as a distance from the center portion of the image sensor  100  increases. 
     The color separation element array according to the present exemplary embodiment may include the color separation elements  130  that are configured to efficiently perform color separation even at the edge of the image sensor  100 . For example, each of the color separation elements  130  may include a first element  130   a  and a second element  130   b  that are sequentially arranged in the direction of the optical axis OX or a traveling direction of the incident light. The first element  130   a  and the second element  130   b  of the color separation elements  130  may be shifted by different degrees according to the positions of the color separation elements  130  in the image sensor  100 . For example, the first element  130   a  and the second element  130   b  of the color separation element  130  at the center portion of the image sensor  100  may be arranged such that the center portions, e.g., center lines, of the first element  130   a  and the second element  130   b  may be aligned with each other. The first element  130   a  and the second element  130   b  of the color separation element  130  arranged in an area other than the center portion of the image sensor  100  may be shifted with each other. For example, a shift distance between the first element  130   a  and the second element  130   b  as a distance from the center portion of the image sensor  100  increases. The first element  130   a  and the second element  130   b  of the color separation element  130  arranged at the outermost edge of the image sensor  100  may be shifted to the greatest extent with respect to each other. 
       FIG. 5A  is a cross-sectional view exemplarily illustrating a positional relationship between the first element  130   a  and the second element  130   b  of the color separation element  130  when a light is perpendicularly incident on the image sensor  100 .  FIGS. 5B and 5C  are cross-sectional views exemplarily illustrating in detail a positional relationship between the first element  130   a  and the second element  130   b  of the color separation element  130  when a light is obliquely incident on the image sensor  100 . 
     Referring to  FIG. 5A , when the incident light is perpendicularly incident on the image sensor  100 , the first element  130   a  and the second element  130   b  of the color separation element  130  are not shifted with each other. In this case, the first element  130   a  and the second element  130   b  of the color separation element  130  may be aligned along a center line (not shown) of a pixel facing the color separation element  130  such that the center portions of the first element  130   a  and the second element  130   b  may be matched with each other. In contrast, referring to  FIGS. 5B and 5C , when the incident light is obliquely incident on the image sensor  100 , the first element  130   a  and the second element  130   b  of the color separation element  130  may be shifted with each other. The first element  130   a  and the second element  130   b  of the color separation element  130  may be shifted to be aligned with the traveling direction of a light that is obliquely incident. For example, as illustrated in  FIG. 5B , when the incident light is obliquely incident from the left side, the first element  130   a  may be relatively further shifted to the left compared to the second element  130   b . Also, as illustrated in  FIG. 5C , when the incident light is obliquely incident from the right side, the first element  130   a  may be relatively further shifted to the right compared to the second element  130   b . A relative shift distance “d” of the first element  130   a  and the second element  130   b  gradually increases as the incident angle of the incident light increases, that is, the CRA increases. 
     As described above, when the incident light is perpendicularly incident, the color separation elements  130  may be aligned along the center line of a pixel facing the color separation element  130 . However, when the incident light is obliquely incident, the first and second elements  130   a  and  130   b  are relatively shifted with each other according to a direction in which a light is incident.  FIGS. 6A and 6B  are cross-sectional views illustrating a change in the positions of the first element  130   a  and the second element  130   b  of the color separation element  130  according to a change in a light incident angle. 
     For example, when the incident angle is θ 1  as illustrated in  FIG. 6A , the incident light may be refracted from a surface of the transparent dielectric layer  120  to travel inside the transparent dielectric layer  120  at an inclined angle of α 1 . Then, the second element  130   b  may be moved in the direction toward the incident light such that the light C 2  of the second wavelength band exiting from the second element  130   b  accurately travels toward the center portion of the light sensing layer  111  of a pixel corresponding to the light C 2  and the light C 3  of the third wavelength band travel toward the center portion of the light sensing layer  111  of a pixel corresponding to the light C 3 . The first element  130   a  is further shifted with respect to the second element  130   b  in the direction toward the incident light such that the first element  130   a  and the second element  130   b  are arranged to match the inclined angle α 1 . As a result, the first element  130   a  may be moved by D 1  from the center line of a pixel facing the color separation element  130 . 
     The inclined angle α 1  in which a light travels inside the transparent dielectric layer  120  may be calculated by the Snell&#39;s law. For example, an equation that n1×sin θ1=n2×sin α1 is established, where “n1” is an external refractive index of the image sensor  100  and “n2” is an average refractive index of the transparent dielectric layer  120  and the color separation elements  130 . The average refractive index n2 is calculated considering a volume ratio of the transparent dielectric layer  120  and the color separation elements  130 . Since the incident angle θ 1  may correspond to the CRA, the angle α at which the first and second elements  130   a  and  130   b  of the color separation elements  130  at a particular position of the image sensor  100  are aligned may satisfy an equation that n1×sin(CRAi)=n2×sin α, where “CRAi” is the CRA at an i-th position. 
     On the other hand, when the incident angle is θ 2  that is greater than θ 1  as illustrated in  FIG. 6B , the incident light is refracted on the surface of the transparent dielectric layer  120  and travels inside the transparent dielectric layer  120  at an inclined angle α 2  that is greater than the inclined angle α 1 . Then, a degree that the first element  130   a  and the second element  130   b  are shifted in a direction toward the incident light may be increased compared to the case in  FIG. 6A . As a result, the first element  130   a  may be shifted by D 2  that is greater than D 1  from the center line of a corresponding pixel such that the first element  130   a  and the second element  130   b  are arranged to match the inclined angle α 2 . 
       FIGS. 7A to 9B  are cross-sectional views exemplarily illustrating the color separation elements  130  according to various exemplary embodiments. First, referring to  FIGS. 7A and 7B , the first element  130   a  and the second element  130   b  of the color separation element  130  may be arranged to be separated from each other by a predetermined gap g. Although  FIGS. 5A to 5C  illustrate that the first element  130   a  and the second element  130   b  closely contact to each other, the structure thereof is not limited thereto. As illustrated in  FIGS. 7A and 7B , the first element  130   a  and the second element  130   b  may be arranged to be separated from each other. The gap between the first element  130   a  and the second element  130   b  may be less than or equal to about 50 or 100 nm. 
     Also, referring to  FIGS. 8A and 8B , the color separation element  130  may further include a third element  130   c . The third element  130   c  may be arranged following the second element  130   b  in the traveling direction of the incident light. When the incident light is perpendicularly incident, the first to third elements  130   a ,  130   b , and  130   c  of the color separation element  130  may be aligned along the center line of a corresponding pixel such that the center portions of the first to third elements  130   a ,  130   b , and  130   c  are matched with one another as illustrated in  FIG. 8A . In contract, when the incident light is obliquely incident, the first to third elements  130   a ,  130   b , and  130   c  of the color separation element  130  may be shifted with respect to one another as illustrated in  FIG. 8B . A relative shift distance d 1  between the first element  130   a  and the second element  130   b  may be the same as or different from a relative shift distance d 2  between the second element  130   b  and the third element  130   c . The shift distance d 1  and the shift distance d 2  may be variously selected according to an incident angle of the incident light and a wavelength band to be separated. Although  FIGS. 8A and 8B  exemplarily illustrates that the color separation element  130  includes three elements, that is, the first to third elements  130   a ,  130   b , and  130   c , the color separation element  130  may include four or more elements that are sequentially arranged in a traveling direction of the incident light. 
     The widths of the first to third elements  130   a ,  130   b , and  130   c  of the color separation element  130  may be the same as or different from one another. For example, the width of the first element  130   a  located at the foremost of the traveling direction of the incident light may be the largest and the width of the third element  130   c  located at the rearmost of the traveling direction of the incident light may be the smallest. The width of the second element  130   b  may be smaller than that of the first element  130   a  and larger than that of the third element  130   c . As the widths of the first to third elements  130   a ,  130   b , and  130   c  gradually decrease along the traveling direction of the incident light, the use of a material of the color separation elements  130  may be reduced while the color separation efficiency is maintained or improved. 
     On the other hand, the first to third elements  130   a ,  130   b , and  130   c  of the color separation element  130  may be formed of a material having a higher refractive index than the refractive index of a surrounding portion. For example, the refractive indices of the first to third elements  130   a ,  130   b , and  130   c  may be higher than the refractive index of the transparent dielectric layer  120 . For example, the transparent dielectric layer  120  may be formed of SiO 2  or siloxane-based spin-on glass (SOG), the first to third elements  130   a ,  130   b , and  130   c  may be formed of a material having a high refractive index, such as, TiO 2 , SiN 3 , ZnS, ZnSe, and Si 3 N 4 . Although the first to third elements  130   a ,  130   b , and  130   c  may have the same refractive index, different refractive indices may be selected to improve the color separation efficiency according to the incident angle of the incident light and a wavelength band to be separated. 
     Although  FIGS. 8A and 8B  illustrate that the first to third elements  130   a ,  130   b , and  130   c  closely contact one another, as illustrated in  FIGS. 9A and 9B , the first to third elements  130   a ,  130   b , and  130   c  may be arranged to be separated from one another. A gap g 1  between the first element  130   a  and the second element  130   b  may be the same or different from a gap g 2  between the second element  130   b  and the third element  130   c . The gaps g 1  and g 2  may be selected based on the incident angle of the incident light and the shift distances d 1  and d 2  between the first to third elements  130   a ,  130   b , and  130   c , such that the first to third elements  130   a ,  130   b , and  130   c  are arranged to match the travelling direction of the incident light. For example, both the gaps g 1  and g 2  may be selected to be less than or equal to about 50 or 100 nm. 
       FIG. 10  is a plan view exemplarily illustrating shift forms of first elements and second elements according to the positions of a plurality of color separation elements in the image sensor  100 . Referring to  FIG. 10 , since a first element  131   a  and a second element of the color separation element are arranged to be overlapped with each other at the center portion of the image sensor  100 , only the first element  131   a  is seen whereas the second element covered by the first element  131   a  is not seen. Also, first elements  132   a ,  133   a ,  134   a ,  135   a ,  136   a ,  137   a ,  138   a , and  139   a  and second elements  132   b ,  133   b ,  134   b ,  135   b ,  136   b ,  137   b ,  138   b , and  139   b  of the color separation elements located at a peripheral portion of the image sensor  100  are shifted with each other in a direction x and a direction y. Since a z-axis in  FIG. 10  is the same direction as the optical axis OX, the first elements  132   a ,  133   a ,  134   a ,  135   a ,  136   a ,  137   a ,  138   a , and  139   a  and the second elements  132   b ,  133   b ,  134   b ,  135   b ,  136   b ,  137   b ,  138   b , and  139   b  may be shifted in a direction perpendicular to the optical axis OX. 
     For example, the first element  132   a  and the second element  132   b  located in the upper area of the image sensor  100  are shifted in a direction −y; the first element  133   a  and the second element  133   b  located in the lower area of the image sensor  100  are shifted in a direction +y; and the first element  134   a  and the second element  134   b  located at the left area of the image sensor  100  are shifted in a direction +x. The first element  138   a  and the second element  138   b  located in the lower right area of the image sensor  100  are shifted in the direction +y and a direction −x. As illustrated in  FIG. 10 , the first elements  132   a ,  133   a ,  134   a ,  135   a ,  136   a ,  137   a ,  138   a , and  139   a  of the color separation elements arranged in a peripheral portion of the image sensor  100  are further shifted toward the center area compared to the second elements  132   b ,  133   b ,  134   b ,  135   b ,  136   b ,  137   b ,  138   b , and  139   b . The first elements  132   a ,  133   a ,  134   a ,  135   a ,  136   a ,  137   a ,  138   a , and  139   a  and the second elements  132   b ,  133   b ,  134   b ,  135   b ,  136   b ,  137   b ,  138   b , and  139   b  may be symmetrically shifted with respect to the center area of the image sensor  100 . For example, the first elements  131   a ,  132   a ,  133   a ,  134   a ,  135   a ,  136   a ,  137   a ,  138   a , and  139   a  and the second elements  132   b ,  133   b ,  134   b ,  135   b ,  136   b ,  137   b ,  138   b , and  139   b  of the color separation elements may be shifted to be aligned with a traveling direction in the transparent dielectric layer  120  of the CR that passed through the objective lens  210 . 
       FIG. 11  is a graph exemplarily showing color separation efficiency according to a change in a light incident angle. In the graph of  FIG. 11 , curved lines indicated by A, B, and C denote color separation efficiencies when the first element and the second element are shifted according to the incident angle of the incident light, whereas curved lines indicated by A′, B′, and C′ denote color separation efficiencies when the first element and the second element are not shifted regardless of the incident angle of the incident light. The curved lines A and A′ denote color separation efficiencies of blue and red, the curved lines B and B′ denote color separation efficiencies of green, and the curved lines C and C′ denote average color separation efficiencies of the entire colors. As it may be seen from the graph of  FIG. 11 , the total average efficiencies C and C′ for both cases of shifting and not shifting the first element and the second element are similar to each other. However, when the first element and the second element are not shifted, as the incident angle increases, the color separation efficiencies of blue and red decrease much and the color separation efficiency of green increases much. Accordingly, color distortion may greatly occur in the peripheral portion of the image sensor  100 . In contrast, when the first element and the second element are shifted, a change in the color separation efficiency according to a change in the incident angle is not generated much. Accordingly, uniform color characteristics may be obtained through the entire area of the image sensor  100 . 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.