Patent Publication Number: US-8120834-B2

Title: Optical property altering apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present document incorporates by reference the entire contents of Japanese priority document, 2009-050576 filed in Japan on Mar. 4, 2009. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical property altering apparatus. 
     2. Description of the Related Art 
     In general, imaging apparatuses, such as compact digital cameras and monitoring cameras are among devices employing small lenses include. In such imaging apparatuses, a given lens in the optical system is moved along the optical axis, or if digital processing is possible, captured image data is digitally processed and image expansion/reduction processing is executed. Image focusing is typically performed by the movement of a focusing lens. Further, aberration occurs in a lens as a consequence of refractive index differences related to optical wavelength. Thus in an effort to eliminate aberration, the curved surface of a given lens in the optical system is formed to into an aspheric surface derived from a polynomial expression. 
     However, for zoom and focus functions provided in conventional imaging apparatuses, a lens is mechanically moved and thus, as a result of mechanical instability, optical axis deviation, optical axis, tilt, lens tilt, etc. occur and consequently, is linked to deterioration of the image quality. Furthermore, there is a problem of differences among elements as a cumulative result of manufacture tolerances. On the other hand, problems arise even if an aspheric lens is employed. For example, if the aspheric lens is fabricated by a glass mold, high precision fabrication technology is required. Further, if an aspheric surface is created by a compound lens, an aspheric shape must be formed on a glass lens using, for example, a UV curable resin, inviting additional fabrication steps. 
     On the other hand, telescopes provided at observatories and the like are devices that employ large lenses. The Subaru Telescope at an observatory in Hawaii is a classic example. This telescope is a large reflecting telescope, whose most important element, the primary mirror, is said to have a 14 nm planar grind tolerance, extremely high planar precision. Furthermore, the primary mirror is fabricated to be thin for weight reduction and from a back side, is supported by 261 actuators to sequentially correct distortion of the primary mirror resulting from orientation. With respect to atmospheric distortion, a prism having a structure substantially identical to that of the primary mirror is inserted into the optical path and the prism is deformed in such a way to negate the distortion and facilitate the sequential correction. 
     However, with such telescopes achieving high resolution by a single primary mirror, the primary mirror must have extremely high planar precision and thus, an apparatus that corrects distortion of such a primary mirror must be uniquely fabricated according to the properties of the primary mirror, making versatility extremely low. If atmospheric distortion is corrected by a technique similar to that for correcting distortion of the primary mirror, additional optical elements such as a prism for correction become necessary and, luminance and saturation of that amount alone decrease. Further, if the number of optical elements increases, the rate of failure increases. 
     To solve such problems, the development of “plasmonic metamaterials” (metamaterials) is in progress. A metamaterial is an element that achieves optical property improvement and has an optical property that does not conventionally exist. For example, Tanaka, Takuo, et al in “Design of Plasmonic Metamaterials in the Visible Light Region”, Optical Society of Japan, Kogaku Journal, Vol. 6, No. 10, 2007, pp. 584-589, discloses an attempt to create an element having a negative refractive index by creating a fine structure on a surface of an optical element and by using the dielectric constant of the material used for the structure and unique permeability obtained from the arrangement of the structure. Further, Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, 2006-301345, and 2005-260965, for example, propose technology that improves optical properties using a metamaterial. 
     To solve the above problem associated with the small lens, demand exists for a means to change the focal length of an optical system without the movement of an optical element. Further, demand exists for provision of a function that by an optical element obtains an effect equivalent to an aspheric lens. 
     However, the technologies disclosed in the above patent documents fail to solve the problems associated with the above conventional technologies. That is, the technologies disclosed in Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, and 2006-301345 respectively involve setting, in advance, the refractive index to become a given value (negative refractive index) to design and fabricate an element, making the refractive index unchangeable after fabrication. Hence, variation of the focal length of an optical system is impossible without moving an optical element. Further, since a uniform refractive index distribution is imparted for an optical element, for example, it cannot be said that an effect equivalent to an aspheric lens will be achieved by making the refractive index distribution non-uniform. 
     Further, the technology disclosed in Japanese Patent Application Laid-Open Publication No. 2005-260965 is able to vary the refractive index. However, this technology is limited to use in a radio wave area and merely switches between a common property and a property as that of a metameterial and hence, the above problems associated with a small lens are not solved. 
     On the other hand, to solve the above problems associated with a large lens, it is preferable for optical system distortion and atmospheric distortion to be addressed using an optical element facilitating versatility. 
     However, the technologies disclosed in the above patent documents fail to solve the problems associated with the conventional technologies. That is, the technologies disclosed in Japanese Patent Application Laid-Open Publication Nos. 2007-226033, 2007-256929, and 2006-301345 respectively involve setting, in advance, the refractive index to become a given value (negative refractive index) to design and fabricate an element, making the refractive index unchangeable after fabrication. Hence, the refractive index cannot be changed in real-time and thus, in particular, distortion resulting from a difference in orientation cannot be corrected as circumstances dictate. Further, since the refractive index cannot be changed in real-time, atmospheric distortion cannot be corrected. 
     The technology disclosed in Japanese Patent Application Laid-Open Publication No. 2005-260965 can vary the refractive index. However, this technology is limited to use in a radio wave area and merely switches between a common property and a property as that of a metameterial and hence, cannot correct optical element distortion and atmospheric distortion. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to at least solve the above problems in the conventional technologies. 
     An optical property altering apparatus according to one aspect of the present invention includes an optical property altering element formed by inductors that are smaller than a wavelength of visible light, mutually connected by connecting lines, and arranged in a single plane; a photoconductor that is excited by incident light and generates alternating current of a frequency identical to that of the incident light; and an amplifying circuit that amplifies the alternating current generated by the photoconductor and supplies the amplified alternating current to the optical property altering element, where the optical property altering element, through supply of the alternating current from the amplifying circuit, arbitrarily alters its refractive index. 
     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic depicting a fundamental structure of the metamaterial; 
         FIG. 2  is a diagram of a configuration of an optical property altering apparatus according to a first embodiment; 
         FIG. 3  is a diagram of an arrangement example of a photoconductor, an amplifying circuit, and the optical property altering element; 
         FIG. 4  is a diagram of an arrangement example of the photoconductor and the optical property altering element; 
         FIG. 5  is a diagram of another example of a configuration of the optical property altering element; 
         FIG. 6  is a diagram of an example of a configuration of the optical property altering element formed by plural layers; 
         FIG. 7  is a diagram of a configuration of an optical property altering apparatus according to a second embodiment; and 
         FIG. 8  is a diagram of an example of a configuration of the optical property altering element. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the accompanying drawings, exemplary embodiments according to the present invention are explained in detail below. 
     An optical property altering apparatus according to the present invention includes an optical property altering element that is formed using a metamaterial that artificially produces a negative refractive index. First, a mechanism of the metamaterial will be described. 
       FIG. 1  is a schematic depicting a fundamental structure of the metamaterial. As depicted in  FIG. 1 , a metamaterial  100  is formed by magnetic field generating coils (nanocoils)  101  (inductors) that are smaller than a wavelength of visible light, connected by connecting lines  102 , and arranged in plural in a single plane. This is a fundamental structure of the metamaterial. The magnetic field generating coils  101  may be formed in any number of layers. The metamaterial  100  generates a demagnetizing field with respect to light, i.e., is a material having a negative refractive index.
 
 N =(∈μ) 1/2  
 
     Where, N is the refractive index, ∈ is the dielectric constant of the material, and μ is permeability. 
     Conventionally, a material of μ&lt;0 has not commonly existed. For example, glass which is widely used in the formation of optical elements has values of ∈&gt;0, μ&gt;0, and N&gt;0. Further, for materials having ∈&lt;0, such as silver, N is an imaginary number. This demonstrates that electromagnetic waves including light cannot be transmitted. 
     Here, if the magnetic field generating coils  101 , which are made of silver and are smaller than a wavelength of light, are arranged on a glass surface, the magnetic field generating coils  101  generate a magnetic field by the magnetic field accompanying light (and the resonance vibration of free electrons on the surface of the silver). The generated magnetic field moves in a direction contrary to and is larger than the magnetic field accompanying light; the apparent permeability at the glass surface is μ&lt;0. Further, for silver, the material from which the magnetic field generating coils  101  are made, ∈&lt;0 and hence, the apparent dielectric constant at the glass surface is ∈&lt;0. Thus, a material (metamaterial) having N&lt;0 is created. 
     Since the value of permeability μ changes according to the magnitude of the current in the magnetic field generating coils  101 , if a current can be forced through the magnetic field generating coil  101  externally, the value of N can also be varied. According to a trial calculation of the Independent Administrative Institution Rikagaku Kenkyujo (RIKEN), to change the permeability g, the current for one of the magnetic field generating coils  101 , assuming 3 [V] is applied to the magnetic field generating coil  101 , is 1.6×10 −12  [A]. Thus, if the magnetic field generating coil  101  is arranged in a single layer on a φ 20  optical element, overall a current of approximately 2.6×10 −4  [A] is required. 
     Here, for example, the metamaterial  100  is assumed to be uniformly distributed on a lens of φ 20 , having radii of curvature of a first and a second surface respectively 100 mm, and a surface separation of 2 mm. The shape of the magnetic field generating coil  101  is the shape and quality proposed by RIKEN. 
     Assuming that the frequency of light incident to the element is 700 THz, according to the Drude Model, the dielectric constant ∈ of the magnetic field generating coil  101  is: 
     
       
         
           
             
               
                 
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     Where, ωp is plasma frequency and ω is angular frequency. Further, the value of ωp is referenced from p. 585 of the publication by Tanaka, Takuo, et al cited above. 
     If current is not applied particularly to the magnetic field generating coils  101 , according to the publication by Tanaka, Takuo, et al cited above, the permeability μ of the element is −1 and thus, the refractive index N of the element is:
 
 N =(∈μ) 1/2 ≈20
 
     Where, the focal length of the element is 0.27 mm. 
     Here, for example, with excitation caused by the incidence of light, if with respect to current flowing through the magnetic field generating coil  101 , a current of 6.4×10 −12  [A] flows in a successive direction, permeability μ becomes approximately −2 and the focal length of the element becomes 0.19 mm. On the other hand, if a current of 1.2×10 −12  [A] flows in the reverse direction, permeability μ becomes approximately −0.5 and the focal length of the element becomes 0.41 mm, i.e., the refractive index can be varied according to the magnitude and direction of the current supplied to the element. 
     The present invention includes an optical element (optical property altering element) that using the metamaterial  100 , alters its refractive index, where current is applied to the optical property altering element and by a change in the magnitude of the current or direction, etc., the refractive index of the optical property altering element is altered. By this configuration, a zoom lens function can be implemented without moving the optical property altering element. Further, the optical property altering element is formed by independent units of the metamaterial  100  and by supplying currents of different magnitudes to each unit of metamaterial  100 , the refractive index distribution in the optical property altering element can be made non-uniform, and thereby, an effect equivalent to an aspheric lens is achieved. 
     The following 4 elements contribute to the implementation of the present invention. 
     (1) Arrangement of a photoconductor (photoconductor coil) that induces resonance optically and generates an alternating current. 
     (2) Arrangement of an amplifying unit (amplifying circuit) that amplifies the alternating current. 
     (3) Arrangement of a means (metamaterial) to generate a demagnetizing field with respect to light. 
     (4) Connection of the 3 elements above. 
     Exemplary embodiments of optical property altering apparatus according to the present invention are explained in detail below. 
       FIG. 2  is a diagram of a configuration of the optical property altering apparatus according to a first embodiment. This optical property altering apparatus  200  includes a photoconductor  201 , an amplifying circuit  202 , and an optical property altering element  203 . 
     The photoconductor  201  is formed by a photoconductor coil that similar to the magnetic field generating coil  101  depicted in  FIG. 1 , is smaller than a wavelength of visible light. The photoconductor  201  is excited by the incidence of light and generates an alternating current of a frequency identical to that of the incident light. 
     The amplifying circuit  202  amplifies the alternating current generated by the photoconductor  201  and supplies the amplified alternating current to the optical property altering element  203 . The amplifying circuit  202  includes an operational amplifier  202   a  and a variable resistor  202   b . By varying the resistance of the variable resistor  202   b , the magnitude of the alternating current supplied to the optical property altering element  203  can be varied. The resistance of the variable resistor  202   b  is variable external to the optical property altering apparatus  200 . Although an example of current amplification by the operational amplifier  202   a  is given, current amplification may be performed by another means. 
     The optical property altering element  203  is formed using the metamaterial  100  depicted in  FIG. 1 , i.e., is formed by the magnetic field generating coils  101 , which are smaller than a wavelength of visible light, connected by connecting lines  102 , and arranged in plural in a single plane. The optical property altering element  203  is fabricated using nanotechnology such as photolithography. Further, in general, the optical property altering element  203  is used arranged on a surface (of an optical element) through which light is transmitted. 
     In the optical property altering apparatus  200 , the photoconductor  201 , by receiving light, generates an alternating current of a frequency equivalent to that of the light received; the amplifying circuit  202  amplifies the alternating current generated by the photoconductor  201  and supplies the amplified alternating current to the optical property altering element  203 ; and consequently, the optical property altering element  203  can alter its refractive index for light having a frequency equivalent to that of the alternating current supplied thereto (i.e., light identical to the light received by the photoconductor  201 ). 
     In the optical property altering apparatus  200 , the resistance of the variable resistor  202   b  in the amplifying circuit  202  can be arbitrarily varied. Consequently, the magnitude of the current supplied to the optical property altering element  203  is varied and thus, its refractive index for light transmitted through the optical property altering element  203  can be arbitrarily altered. Further, since the photoconductor  201  can generate alternating current, the direction of the current supplied to the optical property altering element  203  can also be changed. Hence, by changing the direction of current supplied to the optical property altering element  203 , its refractive index for light transmitted through the optical property altering element  203  can be altered. 
     Even if the direction of the magnetic field of the magnetic field generating coil  101  forming the optical property altering element  203  and that of photoconductor coil forming the photoconductor  201  are inversed, the magnitude of current supplied to the magnetic field generating coil  101  is amplified by the amplifying circuit  202  and thus, as the magnetic field of the photoconductor coil is cancelled, no trouble occurs. 
     As described, in the optical property altering apparatus  200 , through the incidence of light to the apparatus, current is generated and the refractive index is altered. Hence, to efficiently convert the refractive index, it is preferable for the conditions of the light incident to the photoconductor  201  and to the optical property altering element  203  to be identical. Therefore, preferably the photoconductor  201 , the amplifying circuit  202 , and the optical property altering element  203  are arranged in close proximity to one another. 
       FIG. 3  is a diagram of an arrangement example of the photoconductor  201 , the amplifying circuit  202 , and the optical property altering element  203 . As depicted in  FIG. 3 , the photoconductor coil forming the photoconductor  201 , the amplifying circuit  202 , and the magnetic field generating coils  101  forming the optical property altering element  203  are arranged in close proximity to one another, preferably. In this case, it is preferable for the photoconductor  201 , the amplifying circuit  202 , and the optical property altering element  203  to be arranged on a surface (of an optical element) through which light is transmitted. Concerning the relative positions of the photoconductor  201  and the optical property altering element  203 , the photoconductor  201  may be arranged outside an effective diameter of the optical property altering element  203  or within the effective diameter of the optical property altering element  203 . 
       FIG. 4  is a diagram of an arrangement example of the photoconductor  201  and the optical property altering element  203 .  FIG. 4  depicts an example in which the photoconductor  201  is arranged in a band-like shape outside the effective diameter of the optical property altering element  203  that is formed into a circular shape. Through such an arrangement, the conditions of the light incident to the photoconductor  201  and the optical property altering element  203  become identical. 
     As described, according to the first embodiment, the refractive index of the optical property altering element  203  can be arbitrarily altered. Here, if alternating current uniformly flows through all of the magnetic field generating coils  101  forming the optical property altering element  203 , the refractive index distribution in the optical property altering element  203  becomes uniform. Further, if the magnitude of the current flowing through all of the magnetic field generating coils  101  is uniform, the refractive index uniformly changes and thus, the focal length can be varied. That is, the optical property altering apparatus  200  of the optical property altering element  203  can implement the function of conventional zoom and focus mechanisms. Consequently, driving units for zoom mechanisms, focus mechanisms, etc. equipped in conventional imaging apparatuses become unnecessary, facilitating a simpler configuration and reductions in noise, vibration, and weight. 
     Further, since electrical signals directly become zoom and focus control signals without passing through a driving mechanism, trouble such as response delay, overshooting, etc. can be resolved. If a filter that transmits only light of a given wavelength is provided ahead of (on a side where light is incident to) the photoconductor  201 , refractive index control specific to light of the given wavelength is enabled. 
     The optical property altering element  203  may be arranged on a surface of an optical element having a planar shape or on a surface of a lens. In the case of arrangement on a surface of a lens, the inherent refractive index of the lens is regarded as a reference and by causing the refractive index to change by the optical property altering element  203 , application to a wide variety of uses is possible. Further, by selecting material of ∈&lt;0 or a material of ∈&gt;0 and fabricating the magnetic field generating coil  101 , further application to various uses becomes possible. 
     On the other hand, by configuring the optical property altering element  203  such that alternating current flows through only a portion of the magnetic field generating coils  101  forming the optical property altering element  203 , the refractive distribution in the optical property altering element  203  becomes non-uniform, i.e., only the refractive index of a portion of the optical property altering element  203  is controlled. Consequently, an effect equivalent to an aspheric lens is achieved. 
     To achieve an effect equivalent to an aspheric lens, the metamaterial  100  forming the optical property altering element  203  may be characteristically arranged such that different refractive indexes are generated in the element. 
       FIG. 5  is a diagram of another example of configuration for the optical property altering element  203 . In this example, on a surface (of an optical element) through which light is transmitted (not depicted), independent units of the metamaterial  100  are formed in circular bands having an identical center (circular bands  203   a ,  203   b ,  203   c ,  203   d , and  203   e ) to form the optical property altering element  203 . The circular bands  203   a ,  203   b ,  203   c ,  203   d , and  203   e  are supplied alternating currents from mutually independent amplifying circuits (not depicted), respectively. By varying the resistance of variable resistors incidental to the independent the amplifying circuits, currents of differing magnitudes can be respectively supplied to the circular bands  203   a ,  203   b ,  203   c ,  203   d , and  203   e , thereby enabling the refractive indices of the circular bands  203   a ,  203   b ,  203   c ,  203   d , and  203   e , respectively, to be set to differ thereamong and to achieve an effect equivalent to an aspheric lens. 
     In  FIG. 5 , an example is depicted in which a function equivalent to that of an aspheric lens is achieved by the optical property altering element  203 . However, another configuration may be employed. For example, the optical property altering element  203  may be formed in plural layers along the direction of the optical axis. 
       FIG. 6  is a diagram of an example of a configuration of the optical property altering element  203  formed by plural layers. In this example, sequentially, a first layer  203   f , a second layer  203   g  and a third layer  203   h  are overlapped to form the optical property altering element  203 . The first layer  203   f , the second layer  203   g , and the third layer  203   h  are formed by independent units of metamaterial  100 , respectively. The first layer  203   f , the second layer  203   g , and the third layer  203   h  are supplied alternating currents from independent amplifying circuits (not depicted), respectively. By varying the resistance of variable resistors incidental to the independent amplifying circuits, currents of differing magnitudes can be supplied to the first layer  203   f , the second layer  203   g , and the third layer  203   h , thereby enabling the refractive indices of the first layer  203   f , the second layer  203   g , and the third layer  203   h , respectively, to be set to differ thereamong and cause the refractive index distribution in the optical property altering element  203  to become non-uniform and thus, achieve an effect equivalent to an aspheric lens. 
     As described, by forming the optical property altering element  203  in mutually independent circular bands or layers, refractive index distribution can be made uniform or non-uniform by a single unit of the optical property altering element  203 . Hence, it becomes possible to implement a function of a spherical lens and an aspheric lens by a single unit of the optical property altering element  203 . By equipping the optical property altering apparatus  200  having such characteristics in an imaging apparatus, an aspheric lens becomes unnecessary, thereby making fabrication and inspection of an aspheric lens unnecessary and simplifying the manufacturing process of the imaging apparatus. 
     When the optical property altering apparatus  200  according to the first embodiment is used, if the optical refractive index distributions for zoom position and focus position are known, the refractive index of each of the circular bands or layers forming the optical property altering element  203  can be altered according to the zoom position or focus position to consistently achieve ideal optical performance. In other words, by altering the refractive index of the circular bands or layers according to zoom or focus position, a lens that consistently achieves optimal refractive index distribution by dynamic variation can be provided. 
     Although description has been given presuming primarily the handling of light of wavelengths in the visible spectrum, if the quality of the magnetic field generating coils  101  and, the frequency and phase of the alternating current thereto are changed, theoretically, with any magnetic field, the refractive index can be altered. 
     According to the first embodiment, an example of an optical property altering apparatus primarily direct to small imaging apparatuses has been described. A second embodiment describes an optical property altering apparatus suitable for large optical systems like astronomical telescopes at observatories. 
       FIG. 7  is a diagram of a configuration of an optical property altering apparatus according to the second embodiment.  FIG. 7  depicts installation in a large telescope. An optical property altering apparatus  700  includes an optical property altering element  701 , a frequency/phase detecting unit  702 , a distortion detecting unit  703  and a power source  704 . 
     The optical property altering element  701  is formed using the metamaterial  100  depicted in  FIG. 1 , i.e., is formed by the magnetic field generating coils  101 , which are smaller than a wavelength of visible light, connected by connecting lines  102 , and arranged in plural in a single plane. The optical property altering element  701  is fabricated using nanotechnology such as photolithography. Further, the optical property altering element  701  is arranged on a surface of an optical element of an astronomical telescope. The optical property altering element  701  alters its refractive index for light having the same frequency/phase as the alternating current supplied thereto. The frequency/phase detecting unit  702  detects the frequency and the phase of a light beam from a collimating mirror  706  collimating light incident to a primary mirror.  FIG. 7  depicts an example in which the frequency/phase detecting unit  702  detects the frequency and the phase of a light beam at a mirror  707  that changes the optical path of the light beam from the collimating mirror  706 . The distortion detecting unit  703  detects image distortion caused by optical element distortion at an imaging plane  708  or caused by atmospheric distortion. The power source  704  supplies alternating current to the optical property altering element  701 . The power source  704  is capable of generating alternating currents of a frequency up to a THz level. The reasoning for this is that for observation using astronomical telescopes, observation is not limited to visible light and for example, high frequency radiation may be observed. Hence, to alter the refractive index of a high frequency light beam, high frequency current is necessary. 
     In the example depicted in  FIG. 7 , if the refractive index is to be altered for light having the frequency and the phase detected by the frequency/phase detecting unit  702 , for example, the power source  704  may supply to the optical property altering element  701 , alternating current of the frequency and the phase detected by the frequency/phase detecting unit  702 , thereby enabling refractive index control specific to light of a given frequency/phase. 
     In astronomical telescopes, image distortion occurs as a consequence of distortion of internal optical elements (especially the primary mirror  705 ) and atmospheric distortion. Hence, if the distortion detecting unit  703  detects image distortion at the imaging plane  708 , the frequency/phase detecting unit  702  detects the frequency and the phase of the light causing the distortion, and the power source  704  supplies to the optical property altering element  701 , alternating current of the frequency and the phase detected by the frequency/phase detecting unit  702  to thereby alter the refractive index for light having the frequency and the phase causing the image distortion and thus, correct the image distortion. 
     Similar to the first embodiment, in the second embodiment, if configuration is such that only a portion of the magnetic field generating coils  101  forming the optical property altering element  701  are supplied alternating current, the refractive index distribution in the optical property altering element  701  becomes non-uniform, i.e., only the refractive index of a portion of the optical property altering element  701  is controlled. Consequently, an effect equivalent to an aspheric lens is achieved and more precise correction of image distortion can be implemented. 
     On the other hand, for astronomical telescopes installed at observatories, since faint light must be detected, highly precise image formation is required. Hence, highly precise refractive index control is required of the optical property altering element  701  and thus, it is preferable for finer settings of the refractive index to be possible at the optical property altering element  701 . 
       FIG. 8  is a diagram of an example of a configuration of the optical property altering element  701 . The optical property altering element  701  is formed by arranging plural independent grids  701   a  on a surface (of an optical element) through which light is transmitted. Each grid  701   a  is formed of the metamaterial  100  depicted in  FIG. 1 . Further, alternating current differing in magnitude, frequency, etc. is supplied to the grids  701   a , respectively from the power source  704 . Thus, the refractive index can be set for each grid  701   a . And, at the same time, refractive index control specific to light of a given frequency can be executed for the grids  701   a , respectively. If refractive index control is executed for light transmitted through the grids  701   a  overall, light in the visible light region to the ultraviolet/infrared region can be handled. Further, refractive index control may be executed for only a portion of the grids  701   a . Although in  FIG. 8 , grids  701   a  are depicted to have a square shape, the shape of the grids  701   a  is not limited hereto and may be, for example, a pentagonal or hexagonal shape. The grids  701   a  on a planar surface may be arranged at a distance less than the wavelength of the light transmitted therethrough. Further, the grids  701   a  may be formed in plural layers, in which case, adjacent layers may be independent of one another. Thus, finer refractive index control can be executed. 
     As described, according to the optical property altering apparatus  700  of the second embodiment, the grids  701   a  forming the optical property altering element  701  are independent and control the refractive index. Therefore, image distortion caused by distortion of large optical elements in a telescope or caused by atmospheric distortion can be simultaneously corrected. Further, correction of distortion specific to light of a specific frequency is possible. Additionally, distortion correction can be executed without moving the optical property altering element  70 , thereby preventing deviation of the optical axis as a result of moving the optical property altering element  701 . Since a unit for moving the optical property altering element  701  becomes unnecessary, the size of the apparatus can be reduced. The grids  701   a  forming the optical property altering element  701  are independent and control the refractive index and thus, the optical property altering element  701  has a function equivalent to that of an aspheric lens and consequently, it is not necessary to impart complicated curvatures to the shape of the optical property altering element  701 . 
     The optical property altering element  701  may be arranged on a surface of an optical element having a planar shape or on a surface of a lens. Here, if the optical property altering apparatus  700  according to the second embodiment is applied to a telescope, it is preferable for the optical property altering element  701  to be arranged on an optical element other than the one of the largest diameter and if possible, to be arranged on the optical element having the smallest diameter. Thus, the optical property altering apparatus  700  can be easily installed in a telescope, i.e., unlike conventional technology where an image distortion correcting unit is provided for a large element whose shape differs according to telescope, the optical property altering element  701  is applicable as a universal optical element and thus, irrespective of the type of telescope, can be easily adopted and by merely providing the optical property altering element  701  at an existing telescope facility, distortion correction can be implemented. Although the example depicted in  FIG. 7  is an example of application of the optical property altering apparatus  700  to a reflecting telescope, the optical property altering apparatus  700  is additionally applicable to refracting telescopes. 
     If the optical property altering apparatus  700  is applied to a telescope, since distortion correction is executed by the optical property altering element  701 , high precision processing of large diameter optical elements such as the primary mirror  705  becomes unnecessary. For example, if configuration is such that a rib is provided, whereby a large optical element is thin overall with only a designated portion being relatively thick, a large amount of distortion would be expected near the rib. However, in this case, since the pattern of distortion can be predicted in advance, based on information concerning the predicted pattern of distortion, refractive index control of the optical property altering element  701  is executed and thus, image distortion can be easily corrected. 
     Similar to the first embodiment, according to the optical property altering apparatus  700  of the second embodiment, if the quality of the magnetic field generating coils  101  and, the frequency and the phase of the alternating current supplied thereto are changed, theoretically, with any magnetic field, the refractive index can be altered. 
     Although in the second embodiment, an example is given of the optical property altering element  701  being applied to a telescope having large optical elements, the optical property altering element  701  is additionally applicable to small imaging apparatuses, such as digital cameras, single lens reflex camera, monitoring cameras, and mobile phone cameras, having small optical elements. Application of the optical property altering element  701  to small imaging apparatuses enables more complex refractive index control and images of high resolution. 
     As described, according to the optical property altering apparatus of the present invention, the refractive index of an optical element can be arbitrarily altered. Consequently, without moving an optical element, the focal length of the optical system can be varied enabling magnification. Furthermore, since the optical property altering apparatus can make the refractive index distribution non-uniform, the optical element can be imparted with a function equivalent to that of an aspheric lens. 
     According to the present invention, by merely supplying the optical property altering element with alternating current, the function of an aspheric lens can be implemented and thus, by ON/OFF control of the alternating current supplied to the optical property altering element, functions of a spherical lens and an aspheric lens can be implemented. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.