Patent Publication Number: US-11391970-B2

Title: Reflective spatial light modulator, optical observation device, and light irradiation device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a reflective spatial light modulator, an optical observation device, and a light irradiation device. 
     BACKGROUND ART 
     For example, Patent Literature 1 and Patent Literature 2 disclose electro-optical elements. These electro-optical elements include a substrate, a KTN (KTa 1-x Nb x O 3 ) layer of a ferroelectric substance laminated on the substrate, a transparent electrode disposed on a front surface of the KTN layer, and a metal electrode disposed on a back surface of the KTN layer. KTN exhibits four crystal structures depending on a temperature and is utilized as an electro-optical element when it has a perovskite-type crystal structure. Such a KTN layer is formed on a seed layer which is formed on a metal electrode. 
     CITATION LIST 
     Patent Literature 
     [Patent Literature 1] Japanese Unexamined Patent Publication No. 2014-89340 
     [Patent Literature 2] Japanese Unexamined Patent Publication No. 2014-89341 
     SUMMARY OF INVENTION 
     Technical Problem 
     Patent Literature 1 and Patent Literature 2 disclose that conductivity is applied to a seed layer by adding a conductive substance to the seed layer. In this case, a metal electrode and a KTN layer are electrically connected to each other. Therefore, an electric field can be applied to the KTN layer. However, in such a configuration, there is concern that if charge is injected into the KTN layer from the metal electrode, the modulation accuracy may not become stable due to the behavior of electrons inside a KTN crystal. Particularly, if conductivity is applied to a seed layer when a plurality of metal electrodes of an electro-optical element are formed in an array shape, there is concern that electrical signals input to the plurality of metal electrodes may become mixed and the modulation accuracy may not become stable. 
     An object of an embodiment is to provide a reflective spatial light modulator, a light irradiation device, and an optical observation device, in which mixing of electrical signals input to a plurality of electrodes can be curbed and modulation accuracy can become stable. 
     Solution to Problem 
     According to an aspect, there is provided a reflective spatial light modulator modulating input light and outputting modulated modulation light. The reflective spatial light modulator includes a perovskite-type electro-optic crystal having an input surface to which the input light is input and a rear surface opposing the input surface, and having a relative dielectric constant of 1,000 or higher; a light input/output unit being disposed on the input surface of the electro-optic crystal and having a first electrode through which the input light is transmitted; a light reflection unit including a substrate on which a plurality of second electrodes are disposed, being disposed on the rear surface side of the electro-optic crystal, and reflecting the input light toward the light input/output unit; and a drive circuit applying an electric field between the first electrode and the plurality of second electrodes. The light input/output unit includes a first charge injection curbing layer formed on the input surface, and the first charge injection curbing layer has a dielectric material in a cured product made of a non-conductive adhesive material such that injection of charge into the electro-optic crystal from the first electrode is curbed. The light reflection unit includes a second charge injection curbing layer formed on the rear surface, and the second charge injection curbing layer has a dielectric material in a cured product made of a non-conductive adhesive material such that injection of charge into the electro-optic crystal from the plurality of second electrodes is curbed. 
     In addition, according to another aspect, there is provided an optical observation device including a light source outputting the input light, the reflective spatial light modulator described above, an optical system irradiating a target with modulation light output from the spatial light modulator, and a photodetector detecting light output from the target. 
     In addition, according to still another aspect, there is provided a light irradiation device including a light source outputting the input light, the reflective spatial light modulator described above, and an optical system irradiating a target with modulation light output from the spatial light modulator. 
     According to the reflective spatial light modulator, the light irradiation device, and the optical observation device described above, input light is transmitted through the light input/output unit and is input to the input surface of the electro-optic crystal. This input light can be reflected by the light reflection unit disposed on the rear surface of the electro-optic crystal and can be output from the light input/output unit. At this time, an electrical signal is input between the first electrode provided in the light input/output unit and the plurality of second electrodes provided on the substrate. Accordingly, an electric field is applied to the electro-optic crystal having a high relative dielectric constant, and thus the input light can be modulated. In this reflective spatial light modulator, the non-conductive first charge injection curbing layer is formed on the input surface of the electro-optic crystal, and the non-conductive second charge injection curbing layer is formed on the rear surface of the electro-optic crystal. Accordingly, injection of charge into the electro-optic crystal from the first charge injection curbing layer and the second charge injection curbing layer is curbed. Particularly, since the second charge injection curbing layer is formed, an electrical signal input to each of the plurality of second electrodes is unlikely to spread, and mixing between electrical signals is curbed. Therefore, the modulation accuracy can become stable. 
     In addition, in the aspect, the light reflection unit further includes a plurality of third electrodes being formed on a surface of the second charge injection curbing layer on a side opposite to the rear surface and corresponding to the plurality of respective second electrodes, and a plurality of bumps being disposed such that the plurality of second electrodes and the plurality of third electrodes corresponding to the plurality of second electrodes are electrically connected to each other. In this configuration, when an electric field is applied to the electro-optic crystal, an electric field can be individually applied to the plurality of third electrodes. Therefore, mixing of electrical signals input to a plurality of electrodes can be curbed, and thus the modulation accuracy can become more stable. 
     In addition, in the aspect, the substrate includes a pixel region in which the plurality of second electrodes are disposed and a surrounding region surrounding the pixel region. The second charge injection curbing layer has a first region facing the pixel region and a second region surrounding the first region. A content of the dielectric material in the second region is lower than a content of the dielectric material in the first region. In this configuration, the second region allows a substrate to be fixed to the rear surface of the electro-optic crystal with an adhesive force greater than that of the first region. Accordingly, falling-off of a substrate from the electro-optic crystal is curbed. 
     In addition, in the aspect, a boundary between the first region and the second region coincides with a boundary between the pixel region and the surrounding region when viewed in an input direction of the input light. In this configuration, the electro-optic crystal and the substrate can be more firmly bonded to each other. 
     In addition, in the aspect, a boundary between the first region and the second region is positioned on a side outward from an edge of a boundary between the pixel region and the surrounding region when viewed in an input direction of the input light. In this configuration, the first region can be reliably disposed between the electro-optic crystal and the pixel region. 
     In addition, in the aspect, the light input/output unit may further include a transparent substrate having a first surface to which the input light is input and a second surface serving as a surface on a side opposite to the first surface, and the first electrode may be disposed on the second surface of the transparent substrate. In such a spatial light modulator, even when the electro-optic crystal is formed to be thin in an optical axis direction, the electro-optic crystal can be protected by the transparent substrate from an external impact or the like. 
     In addition, in the aspect, when the relative dielectric constant of the electro-optic crystal is ε xtl , a thickness of the electro-optic crystal from the input surface to the rear surface is d xtl , a sum of thicknesses of the first charge injection curbing layer and the second charge injection curbing layer is d ad , and a ratio V xtl /V smax  of V xtl  indicating a voltage applied to the electro-optic crystal in order to perform phase modulation or retardation modulation of input light by 2π radians to V smax  indicating a maximum voltage of an application voltage generated by the drive circuit is R s , a relative dielectric constant ε ad  of the first charge injection curbing layer and the second charge injection curbing layer including the dielectric material may be indicated by Expression 1. In this case, a voltage sufficient for performing phase modulation or retardation modulation of input light by 2π radians can be applied to the electro-optic crystal. 
     
       
         
           
             
               
                 
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     In addition, in the aspect, the first electrode may be formed on the whole surface of the input surface. For example, when a plurality of first electrodes are provided in a manner corresponding to the plurality of second electrodes, it is difficult to positionally align the first electrodes and the second electrodes with each other. In the foregoing configuration, there is no need to positionally align the first electrode and the second electrodes with each other. 
     In addition, in the aspect, the light reflection unit may further include a plurality of third electrodes disposed on the rear surface of the electro-optic crystal in a manner of facing the plurality of second electrodes. According to this configuration, the plurality of third electrodes can prevent spreading of an electrical signal transferred as an electric line of force. 
     In addition, in the aspect, in the light reflection unit, the input light may be reflected by the plurality of third electrodes. Moreover, in the aspect, in the light reflection unit, the input light may be reflected by the plurality of second electrodes. According to these configurations, there is no need to separately provide a reflection layer or the like on the second electrode side. 
     In addition, in the aspect, the electro-optic crystal may be a KTa 1-x Nb x O 3  (0≤x≤1) crystal, a K 1-y Li y Ta 1-x Nb x O 3  (0&lt;x&lt;1 and 0≤y≤1) crystal, or a PLZT crystal. According to this configuration, an electro-optic crystal having a high relative dielectric constant can be easily realized. 
     In addition, in the aspect, the reflective spatial light modulator may further include a temperature control element for controlling a temperature of the electro-optic crystal. According to this configuration, modulation accuracy can become more stable by maintaining a uniform temperature in the electro-optic crystal. 
     Advantageous Effects of Invention 
     According to the reflective spatial light modulator, the light irradiation device, and the optical observation device of the embodiment, mixing of electrical signals input to a plurality of electrodes can be curbed, and thus the modulation accuracy can become stable. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a configuration of an optical observation device according to an embodiment. 
         FIG. 2  is a cross-sectional view showing a spatial light modulator used in the optical observation device in  FIG. 1 . 
         FIG. 3  is a view showing a relationship between crystal axes, a traveling direction of light, and an electric field in retardation modulation. 
         FIG. 4  is a view for describing an electrode of the spatial light modulator in  FIG. 2 . 
         FIG. 5  is a cross-sectional view along V-V in  FIG. 2 . 
         FIG. 6  is a cross-sectional view showing a spatial light modulator according to another embodiment. 
         FIG. 7  is a cross-sectional view along VII-VII in  FIG. 6 . 
         FIG. 8  is a cross-sectional view showing a spatial light modulator according to another embodiment. 
         FIG. 9  is a cross-sectional view showing a spatial light modulator according to another embodiment. 
         FIG. 10  is a cross-sectional view showing a spatial light modulator according to another embodiment. 
         FIG. 11  is a block diagram showing a configuration of a light irradiation device according to the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be specifically described with reference to the drawings. For the sake of convenience, there are cases in which the same reference signs are applied to elements which are substantially the same and description thereof is omitted. 
     First Embodiment 
       FIG. 1  is a block diagram showing a configuration of an optical observation device according to an embodiment. For example, an optical observation device  1 A is a fluorescence microscope for capturing an image of an observation target. The optical observation device  1 A acquires an image of a specimen (target) S by irradiating a front surface of the specimen S with input light L 1  and capturing an image of detection light L 3  such as fluorescence or reflected light output from the specimen S in response to the irradiation. 
     For example, the specimen S which becomes an observation target is a sample such as a cell or an organism including a fluorescent material such as a fluorescent dye or fluorescent protein. In addition, the specimen S may be a sample such as a semiconductor device or a film. The specimen S emits the detection light L 3  such as fluorescence, for example, when irradiation with light (excitation light or illumination light) having a predetermined wavelength region is performed. For example, the specimen S is accommodated inside a holder having transmitting properties with respect to at least the input light L 1  and the detection light L 3 . For example, this holder is held on a stage. 
     As shown in  FIG. 1 , the optical observation device  1 A includes a light source  10 , a collimator lens  11 , a polarization element  12 , a polarization beam splitter  13 , a spatial light modulator  100 , a first optical system  14 , a beam splitter  15 , an objective lens  16 , a second optical system  17 , a photodetector  18 , and a control unit  19 . 
     The light source  10  outputs the input light L 1  including a wavelength for exciting the specimen S. For example, the light source  10  emits coherent light or incoherent light. Examples of a coherent light source include a laser light source such as a laser diode (LD). Examples of an incoherent light source include a light emitting diode (LED), a super luminescent diode (SLD), and a lamp system light source. 
     The collimator lens  11  collimates the input light L 1  output from the light source  10  and outputs the collimated input light L 1 . The polarization element  12  allows the input light L 1  to be selectively transmitted therethrough in accordance with a polarization component. For example, the polarization element  12  allows S-wave light of the input light L 1  to be transmitted therethrough. The polarization beam splitter  13  reflects the input light L 1  transmitted through the polarization element  12  toward the spatial light modulator  100 . The spatial light modulator  100  is a spatial light modulator performing phase modulation or retardation modulation of the input light L 1  output from the light source  10 . The spatial light modulator  100  modulates the input light L 1  input through the collimator lens  11  and outputs modulated modulation light L 2  toward the polarization beam splitter  13 . At this time, the spatial light modulator  100  outputs the modulation light L 2  by rotating a polarization surface of the input light L 1  by 90 degrees. For this reason, the modulation light L 2  output from the spatial light modulator  100  is transmitted through the polarization beam splitter  13  and is optically guided to the first optical system  14 . The spatial light modulator  100  in the present embodiment is constituted as a reflective type. The spatial light modulator  100  is electrically connected to a controller  21  of the control unit  19  and constitutes a spatial light modulation unit. Driving of the spatial light modulator  100  is controlled by the controller  21  of the control unit  19 . Details of the spatial light modulator  100  will be described below. Using the spatial light modulator  100 , 1) a position of an irradiation location can be limited, 2) the position of the irradiation location can be moved, 3) a plurality of irradiation locations can be formed at the same time, and 4) a phase of irradiation light can be controlled. 
     The first optical system  14  optically joins the spatial light modulator  100  and the objective lens  16  to each other. Accordingly, the modulation light L 2  output from the spatial light modulator  100  is optically guided to the objective lens  16 . For example, the first optical system  14  is a lens, which concentrates the modulation light L 2  from the spatial light modulator  100  at a pupil of the objective lens  16 . 
     The beam splitter  15  is an optical element for separating the modulation light L 2  and the detection light L 3  from each other. For example, the beam splitter  15  allows the modulation light L 2  having an excitation wavelength to be transmitted therethrough and reflects the detection light L 3  having a fluorescent wavelength. In addition, the beam splitter  15  may be a polarization beam splitter or may be a dichroic mirror. Depending on optical systems (for example, the first optical system  14  and the second optical system  17 ) in front of and behind the beam splitter  15  or the kind of an applied microscope, the beam splitter  15  may reflect the modulation light L 2  and may allow the detection light L 3  having a fluorescent wavelength to be transmitted therethrough. 
     The objective lens  16  concentrates the modulation light L 2  modulated by the spatial light modulator  100 , irradiates the specimen S with the concentrated light, and optically guides the detection light L 3  emitted from the specimen S in response to the irradiation. For example, the objective lens  16  is configured to be able to be moved along an optical axis by a driving element such as a piezo-actuator or a stepping motor. Accordingly, a concentration position of the modulation light L 2  and a focal position for detecting the detection light L 3  can be adjusted. 
     The second optical system  17  optically joins the objective lens  16  and the photodetector  18  to each other. Accordingly, an image of the detection light L 3  optically guided from the objective lens  16  is formed by the photodetector  18 . The second optical system  17  has a lens  17   a  for forming an image of the detection light L 3  from the objective lens  16  on a light receiving surface of the photodetector  18 . 
     The photodetector  18  captures an image of the detection light L 3  which is optically guided by the objective lens  16  and of which an image is formed on the light receiving surface. For example, the photodetector  18  is an area image sensor such as a CCD image sensor or a CMOS image sensor. 
     The control unit  19  includes a computer  20  which includes a control circuit such as a processor, an image processing circuit, a memory, and the like; and the controller  21  which includes a control circuit such as a processor, a memory, and the like and is electrically connected to the spatial light modulator  100  and the computer  20 . For example, the computer  20  is a personal computer, a smart device, a microcomputer, a cloud server, or the like. The computer  20  controls operation of the objective lens  16 , the photodetector  18 , and the like and executes various kinds of control using the processor. In addition, the controller  21  controls a phase modulation quantity or a retardation modulation quantity in the spatial light modulator  100 . 
     Next, the spatial light modulator  100  will be described in detail.  FIG. 2  is a cross-sectional view showing a spatial light modulator. The spatial light modulator  100  is a reflective spatial light modulator modulating the input light L 1  and outputting the modulated modulation light L 2 . As shown in  FIG. 2 , the spatial light modulator  100  includes an electro-optic crystal  101 , a light input/output unit  102 , a light reflection unit  107 , and a drive circuit  110 . In the present embodiment, the thickness of the electro-optic crystal  101  in an optical axis direction may be 50 μm or smaller, for example. 
     The electro-optic crystal  101  exhibits a plate shape having an input surface  101   a  to which the input light L 1  is input, and a rear surface  101   b  opposing the input surface  101   a . The electro-optic crystal  101  has a perovskite-type crystal structure and utilizes an electro-optical effect such as a Pockels effect or a Kerr effect for changing a refractive index. The electro-optic crystal  101  having a perovskite-type crystal structure is an isotropic crystal which belongs to a point group m3m of a cubic crystal system and of which a relative dielectric constant is 1,000 or higher. For example, the relative dielectric constant of the electro-optic crystal  101  can have a value within a range of approximately 1,000 to 20,000. Examples of such an electro-optic crystal  101  include a KTa 1-x Nb x O 3  (0≤x≤1) crystal (which will hereinafter be referred to as □ a KTN crystal □), a K 1-y Li y Ta 1-x Nb x ) 3  (0≤x≤1 and 0≤y≤1) crystal, and a PLZT crystal. Specifically, BaTiO 3 , K 3 Pb 3 (Zn 2 Nb 7 )O 27 , K(Ta 0.65 Nb 0.35 )P 3 , Pb 3 MgNb 2 O 9 , Pb 3 NiNb 2 O 9 , and the like are included. In the spatial light modulator  100  of the present embodiment, a KTN crystal is used as the electro-optic crystal  101 . Since a KTN crystal is in an m3m point group of a cubic crystal system, modulation is performed using a Kerr effect instead of a Pockels effect. For this reason, phase modulation can be performed by inputting light in a manner of being parallel or perpendicular to crystal axes of the electro-optic crystal  101  and applying an electric field in the same direction. In addition, retardation modulation can be performed when two arbitrary crystal axes are rotated about the remaining axis by an angle other than 0° and 90°.  FIG. 3( a )  is a perspective view showing a relationship between the crystal axes, a traveling direction of light, and an electric field in retardation modulation, and  FIG. 3( b )  is a plan view showing each of the axes. The example in  FIG. 3  shows a case in which the crystal is rotated by an angle of 45°. When the axes X 2  and X 3  are rotated by 45° about the axis X 1  and new axes X 1 ′, X 2 ′, and X 3 ′ are set, retardation modulation can be performed by inputting light in a manner of being parallel or perpendicular to these new axes. In  FIG. 3 , an electric field is applied in an applying direction  1102  of a crystal  1104 . A propagation direction  1101  of the input light L 1  becomes parallel to the applying direction  1102  of an electric field. In this case, Kerr coefficients used for modulation of the input light L 1  become g 11 , g 12 , and g 44 . 
     The relative dielectric constant of a KTN crystal is likely to be affected by the temperature. For example, the relative dielectric constant becomes approximately 20,000 which is the largest at a temperature in the vicinity of −5° C., and the relative dielectric constant falls to approximately 5,000 at a temperature near 20° C. which is a normal temperature. Here, the electro-optic crystal  101  is controlled such that it has a temperature in the vicinity of −5° C. by a temperature control element P such as a Peltier element, for example. 
     The light input/output unit  102  has a first electrode  103 , a transparent substrate  104 , a transparent electrode  105 , an adhesive layer  106 , and an adhesive layer (first charge injection curbing layer)  119 . The first electrode  103  is disposed on the input surface  101   a  side of the electro-optic crystal  101 . For example, the first electrode  103  is a transparent electrode formed of indium tin oxide (ITO), and the input light L 1  is transmitted therethrough. In the present embodiment, the first electrode  103  is formed on the whole surface on the input surface  101   a  side. The input light L 1  is transmitted through the first electrode  103  and is input to the inside of the electro-optic crystal  101 . 
     For example, the transparent substrate  104  is formed of a material such as glass, quartz, or plastic in a flat plate shape. The transparent substrate  104  has a first surface  104   a  to which the input light L 1  is input, and a second surface  104   b  which is a surface on a side opposite to the first surface  104   a  and faces the input surface  101   a  of the electro-optic crystal  101 . The transparent electrode  105  is an electrode formed on the whole surface of the second surface  104   b  of the transparent substrate  104 , and the input light L 1  is transmitted therethrough. For example, the transparent electrode  105  can be formed on the second surface  104   b  of the transparent substrate  104  by performing vapor deposition of ITO. 
     The adhesive layer  106  causes the first electrode  103  formed in the electro-optic crystal  101  and the transparent electrode  105  formed in the transparent substrate  104  to adhere to each other. For example, the adhesive layer  106  is formed of an epoxy-based adhesive, and the input light L 1  is transmitted therethrough. For example, conductive members  106   a  such as metal spheres are disposed inside the adhesive layer  106 . The conductive members  106   a  come into contact with both the first electrode  103  and the transparent electrode  105  and electrically connect the first electrode  103  and the transparent electrode  105  to each other. For example, the conductive members  106   a  are disposed in four corners of the adhesive layer  106  in a plan view. 
     The adhesive layer  119  is disposed between the first electrode  103  and the input surface  101   a  and bonds the first electrode  103  and the electro-optic crystal  101  to each other. The adhesive layer  119  of the present embodiment has a first region  119   a  forming the center thereof and a second region  119   b  surrounding an outer circumference of the first region  119   a . The first region  119   a  has fine particles of a dielectric material in a cured product made of a non-conductive adhesive material and includes no conductive material. The term non-conductive is not limited to properties of having no conductivity and includes highly insulating properties and properties of having high electrical resistivity. That is, the first region  119   a  has high insulating properties (high electrical resistivity) and ideally has no conductivity. 
     For example, an adhesive material can be formed using an optically colorless and transparent resin such as an epoxy-based adhesive. For example, the dielectric material can have a relative dielectric constant of the same degree as that of the electro-optic crystal  101 , which is within a range of approximately 100 to 30,000. The dielectric material may be a powder having a particle size equal to or smaller than the wavelength of the input light L 1  and can have a particle size within a range of approximately 50 nm to 3,000 nm, for example. Scattering of light can be curbed by reducing the particle size of the dielectric material. When scattering of light is taken into consideration, the particle size of the dielectric material may be 1,000 nm or smaller and may also be 100 nm or smaller. The dielectric material may be a powder of the electro-optic crystal  101 . The proportion of the dielectric material in a mixture of an adhesive material and a dielectric material may be approximately 50%. For example, the first region  119   a  exhibits a rectangular shape in a plan view. 
     The second region  119   b  is constituted of a non-conductive adhesive material. That is, differing from the first region  119   a , the second region  119   b  includes no dielectric material such as a powder of the electro-optic crystal  101 . For example, the adhesive material can be formed using an optically colorless and transparent resin such as an epoxy-based adhesive. The second region  119   b  may include a dielectric material as in the first region. In such a case, the proportion of the dielectric material in a mixture of an adhesive material and a dielectric material is smaller than the proportion thereof in the first region  119   a . For example, the first region  119   a  exhibits a rectangular frame shape in a plan view. 
     The first region  119   a  can be formed by coating the input surface  101   a  of the electro-optic crystal  101  or the first electrode  103  with a mixture of an adhesive material and a dielectric material. In addition, the second region  119   b  can be formed by coating the input surface  101   a  of the electro-optic crystal  101  or the first electrode  103  with an adhesive material. 
     The light reflection unit  107  is disposed on the rear surface  101   b  side of the electro-optic crystal  101  and reflects the modulation light L 2  toward the input/output unit. This light reflection unit  107  includes a CMOS substrate (substrate)  108  and an adhesive layer (second charge injection curbing layer)  109 . The CMOS substrate  108  is fixed to a substrate  112  such as an organic substrate including a glass epoxy (epoxy resin having a glass fiber sheet as a core material) substrate, or a ceramic substrate with an adhesive layer  111  therebetween, for example. The CMOS substrate  108  includes second electrodes  108   a  which are a plurality of pixel electrodes facing the rear surface  101   b  of the electro-optic crystal  101 . The second electrodes  108   a  can reflect the input light L 1  propagated inside the electro-optic crystal  101  toward the light input/output unit  102 . For example, the second electrodes  108   a  are formed of a material such as a metal (aluminum or the like). As shown in  FIG. 4 , in the light reflection unit  107  in the present embodiment, the plurality of second electrodes  108   a  formed to have a rectangular shape in a plan view are disposed in a two-dimensional array. A length W 1  in a transverse direction and a length W 2  in a vertical direction of the second electrode  108   a  can be formed to be the same length, for example. Second electrodes  108   a  adjacent to each other are disposed with gaps S 1  and S 2  therebetween.  FIGS. 2 and 4  schematically show the spatial light modulator  100 . For the sake of simplification of description, an example in which the second electrodes  108   a  are disposed in a 4×4 array is described. The CMOS substrate  108  may function as a drive circuit applying an electric field between the first electrode  103  and the second electrodes  108   a.    
     Each of the plurality of second electrodes  108   a  is provided with a corresponding driving switch  108   b . An arbitrary voltage can be controlled for each of the second electrodes  108   a  using these switches  108   b.    
     The adhesive layer  109  fixes the CMOS substrate  108  to the rear surface  101   b . The adhesive layer  109  of the present embodiment has a first region  109   a  forming the center thereof and a second region  109   b  surrounding an outer circumference of the first region  109   a . The configuration of the adhesive layer  109  is similar to that of the adhesive layer  119  described above. The first region  109   a  has a configuration similar to that of the first region  119   a , and the second region  109   b  has a configuration similar to that of the second region  119   b.    
     The first region  109   a  can be formed by coating the rear surface  101   b  of the electro-optic crystal  101  or the CMOS substrate  108  with a mixture of an adhesive material and a dielectric material. In addition, the second region  109   b  can be formed by coating the rear surface  101   b  of the electro-optic crystal  101  or the CMOS substrate  108  with an adhesive material. 
     The drive circuit  110  is electrically connected to the first electrode  103  and is connected to the CMOS substrate  108 , thereby being electrically connected to each of the plurality of second electrodes  108   a . In the present embodiment, the transparent substrate  104  on the second surface  104   b  side is formed to have a larger size in a plan view than the input surface  101   a  of the electro-optic crystal  101 . For this reason, in a state in which the electro-optic crystal  101  is supported by the transparent substrate  104 , a part of the transparent electrode  105  formed in the transparent substrate  104  becomes an exposed portion  105   a  exposed to the outside. The drive circuit  110  is electrically connected to this exposed portion  105   a  and the CMOS substrate  108 . That is, since the drive circuit  110  is electrically connected to the first electrode  103  with the transparent electrode  105  and the conductive members  106   a  therebetween, an electric field can be applied between the first electrode  103  and the second electrodes  108   a.    
     The drive circuit  110  is controlled by the control unit  19 . The drive circuit  110  inputs an electrical signal between the first electrode  103  and the second electrodes  108   a . Accordingly, an electric field is applied to the electro-optic crystal  101  and the adhesive layers  109  and  119  disposed between the first electrode  103  and the second electrodes  108   a . In this case, a voltage applied by the drive circuit  110  is distributed to the electro-optic crystal  101  and the adhesive layers  109  and  119 . Therefore, when a voltage applied to the electro-optic crystal  101  is V xtl , a voltage applied to the adhesive layers  109  and  119  is V ad , the relative dielectric constant of the electro-optic crystal  101  is ε xtl , the thickness of the electro-optic crystal  101  from the input surface  101   a  to the rear surface  101   b  is d xtl , the relative dielectric constant of the adhesive layers  109  and  119  is ε ad , and the sum of the thicknesses of the adhesive layers  109  and  119  is d ad , a voltage ratio R between a voltage applied between the first electrode  103  and the second electrodes  108   a  and a voltage applied to the electro-optic crystal  101  is expressed by the following Expression (2). For the sake of simplification of description, the adhesive layer  109  and the adhesive layer  119  are formed of materials having the same relative dielectric constant. 
     
       
         
           
             
               
                 
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     In this manner, a voltage applied to the electro-optic crystal  101  depends on the relative dielectric constant ε ad  and the thicknesses d ad  of the adhesive layers  109  and  119 . For example, the spatial light modulator  100  in the present embodiment has a modulation performance of outputting the modulation light L 2  obtained by modulating the input light L 1  by one wavelength. In this case, the relative dielectric constant ε ad  of the adhesive layers  109  and  119  is obtained as follows. First, the upper limit for a voltage applied to the CMOS substrate  108  by the drive circuit  110  is determined in order to avoid a breakdown of a CMOS circuit. Here, the maximum voltage of an application voltage generated by the drive circuit  110  is referred to as V smax . In addition, it is assumed that when V xtl  is added to the electro-optic crystal  101  and V ad  is added to the adhesive layers  109  and  119  respectively, the modulation light L 2  modulated by one wavelength is output. At this time, V xtl &lt;V xtl +V ad ≤V smax  is established. Therefore, when a voltage ratio V xtl /V smax  between V xtl  and V smax  is R s , there is a need for the voltage ratio R and the voltage ratio R s  to satisfy the relationship of the following Expression (3). In this case, a voltage sufficient for performing phase modulation of the input light L 1  by 2π radians can be applied to the electro-optic crystal  101 .
 
R s &lt;R  (3)
 
     Further, from Expression (2) and Expression (3), the relative dielectric constant ε ad  and the thicknesses d ad  of the adhesive layers  109  and  119  satisfy the following Expression (4). 
     
       
         
           
             
               
                 
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     From this Expression (4), the relative dielectric constant of the adhesive layers  109  and  119  is obtained. That is, when Expression (4) is transformed into an expression related to the relative dielectric constant of the adhesive layers  109  and  119 , the following Expression (1) is derived. 
     
       
         
           
             
               
                 
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     When the relative dielectric constant of the adhesive layers  109  and  119  satisfies Expression (1), an electric field sufficient for performing modulation of the input light L 1  by one wavelength can be applied to the electro-optic crystal. 
     In addition, when a parameter in indicated by the following Expression (5) is defined using the relative dielectric constant ε ad  of the adhesive layers  109  and  119 , the thicknesses d ad  of the adhesive layers  109  and  119 , the relative dielectric constant ε xtl  of the electro-optic crystal  101 , and the thickness d xtl  of the electro-optic crystal  101 , it is preferable that the parameter in satisfy m&gt;0.3. In addition, it is more preferable that the parameter in satisfy m&gt;3. 
     
       
         
           
             
               
                 
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     Subsequently, a relationship between the adhesive layer  109 , the adhesive layer  119 , and the CMOS substrate  108  will be described. In the present embodiment, since the adhesive layer  109  and the adhesive layer  119  exhibit configurations similar to each other, the adhesive layer  109  will be representatively described here.  FIG. 5  is a cross-sectional view along V-V in  FIG. 2 . As shown in  FIG. 5 , the CMOS substrate  108  includes a pixel region  108   c  and a surrounding region  108   d  surrounding the pixel region  108   c . The pixel region  108   c  is a region in which the plurality of second electrodes  108   a  (refer to  FIGS. 2 and 4 ) are disposed and which exhibits a rectangular shape as an example. The surrounding region  108   d  exhibits a rectangular frame shape. The first region  109   a  of the adhesive layer  109  faces the pixel region  108   c  and exhibits a rectangular shape in a plan view. The second region  109   b  of the adhesive layer  109  surrounds the first region  109   a  and exhibits a rectangular frame shape in a plan view. A boundary between the first region  109   a  and the second region  109   b  is positioned on a side outward from an edge of a boundary between the pixel region  108   c  and the surrounding region  108   d  in a plan view. That is, when viewed in an input direction of the input light L 1 , the first region  109   a  exhibits a rectangular shape larger than the pixel region  108   c . The second region  109   b  is disposed between the surrounding region  108   d  and the rear surface  101   b  of the electro-optic crystal  101 . 
     According to the spatial light modulator  100  described above, the input light L 1  is transmitted through the first electrode  103  of the light input/output unit  102  and is input to the input surface  101   a  of the electro-optic crystal  101 . This input light L 1  can be reflected by the light reflection unit  107  disposed on the rear surface  101   b  of the electro-optic crystal  101  and can be output from the light input/output unit  102 . At this time, an electrical signal is input between the first electrode  103  provided in the light input/output unit  102  and the plurality of second electrodes  108   a  provided on the CMOS substrate  108 . Accordingly, an electric field is applied to the electro-optic crystal  101  having a high relative dielectric constant, and thus the input light L 1  can be modulated. 
     In this reflective spatial light modulator  100 , the non-conductive adhesive layer  119  is formed on the input surface  101   a  of the electro-optic crystal  101 , and the non-conductive adhesive layer  119  is formed on the rear surface  101   b  of the electro-optic crystal  101 . 
     Accordingly, injection of charge into the electro-optic crystal  101  from the adhesive layer  109  and the adhesive layer  119  is curbed. Particularly, since the adhesive layer  109  is formed, an electrical signal input to each of the plurality of second electrodes  108   a  is unlikely to spread, and mixing between electrical signals is curbed. Therefore, the modulation accuracy can become stable. 
     In the configuration of the present embodiment, the higher the relative dielectric constant of the adhesive layers  109  and  119 , the easier it is to apply a voltage to the electro-optic crystal  101 . For this reason, it is desirable that the content of the dielectric material in the adhesive layers  109  and  119  be high. However, if the content of the dielectric material is increased, an adhesive force in the adhesive layer deteriorates. In the present embodiment, the content of the dielectric materials in the second regions  109   b  and  119   b  are lower than the content of the dielectric materials in the first regions  109   a  and  119   a.    
     For this reason, the second regions  109   b  and  119   b  allow the CMOS substrate  108  and the first electrode  103  to be fixed to the electro-optic crystal  101  with an adhesive force greater than that of the first regions  109   a  and  119   a.    
     The boundary between the first region  109   a  and the second region  109   b  is positioned on the side outward from the edge of the boundary between the pixel region  108   c  and the surrounding region  108   d  when viewed in the input direction of the input light. The area of the first region  109   a  in a plan view can be larger than the area of the pixel region  108   c . For this reason, positional alignment between the pixel region  108   c  and the first region  109   a  can be easily performed. 
     The first electrode  103  is formed on the whole surface of the input surface  101   a . For example, when a plurality of first electrodes  103  are provided in a manner corresponding to the plurality of second electrodes  108   a , it is difficult to positionally align the first electrodes  103  and the second electrodes  108   a  with each other. In the foregoing configuration, there is no need to positionally align the first electrode  103  and the second electrodes  108   a  with each other. 
     In the light reflection unit  107 , since the input light L 1  is reflected by the plurality of second electrodes  108   a , there is no need to separately provide a reflection layer or the like on the second electrodes  108   a  side. 
     In addition, since the temperature control element P for controlling the temperature of the electro-optic crystal  101  is provided, a uniform temperature can be maintained in the electro-optic crystal  101 . Accordingly, modulation accuracy can become more stable. The temperature control may be performed by the temperature control element P targeting not only the electro-optic crystal  101  but also the spatial light modulator  100  in its entirety including the CMOS substrate  108  and the like. 
     In addition, in the spatial light modulator  100 , phase modulation or retardation modulation can be performed more favorably by forming the electro-optic crystal  101  to be thin in the optical axis direction. When the electro-optic crystal  101  is formed to be thin in this manner, there is concern that the electro-optic crystal  101  may be damaged due to an impact or the like from the outside. In the present embodiment, the input surface  101   a  side of the electro-optic crystal  101  is supported by the transparent substrate  104 , and thus the electro-optic crystal  101  is protected from an external impact or the like. 
     Second Embodiment 
     Subsequently, a spatial light modulator  200  according to the present embodiment will be described. Points differing from the first embodiment will be mainly described. The same reference signs are applied to elements or members which are the same, and detailed description thereof will be omitted. 
       FIG. 6  is a cross-sectional view showing the spatial light modulator  200  according to the present embodiment. As shown in  FIG. 6 , the reflective spatial light modulator  200  includes the electro-optic crystal  101 , a light input/output unit  202 , a light reflection unit  207 , and the drive circuit  110 . 
     The light input/output unit  202  has the first electrode  103 , the transparent substrate  104 , the transparent electrode  105 , the adhesive layer  106 , and an adhesive layer (first charge injection curbing layer)  219 . The adhesive layer  219  is disposed between the first electrode  103  and the input surface  101   a  and bonds the first electrode  103  and the electro-optic crystal  101  to each other. The adhesive layer  219  of the present embodiment has a first region  219   a  forming the center thereof and a second region  219   b  surrounding an outer circumference of the first region  219   a . The first region  219   a  can be formed of a material having a composition similar to that of the first region  119   a . In addition, the second region  219   b  can be formed of a material having a composition similar to that of the second region  119   b.    
     The light reflection unit  207  has the CMOS substrate  108  and an adhesive layer (second charge injection curbing layer)  209 . The adhesive layer  209  has a first region  209   a  forming the center thereof and a second region  209   b  surrounding an outer circumference of the first region  209   a . The configuration of the adhesive layer  209  is similar to that of the adhesive layer  219  described above. The first region  209   a  has a configuration similar to that of the first region  219   a , and the second region  209   b  has a configuration similar to that of the second region  219   b.    
     Subsequently, a relationship between the adhesive layer  209 , the adhesive layer  219 , and the CMOS substrate  108  will be described. Since the adhesive layer  209  and the adhesive layer  219  exhibit configurations similar to each other, the adhesive layer  209  will be representatively described here.  FIG. 7  is a cross-sectional view along VII-VII in  FIG. 6 . As shown in  FIG. 7 , the first region  209   a  of the adhesive layer  209  faces the pixel region  108   c  and exhibits a rectangular shape in a plan view. The second region  209   b  of the adhesive layer  209  surrounds the first region  209   a  and exhibits a rectangular frame shape in a plan view. A boundary between the first region  209   a  and the second region  209   b  coincides with the boundary between the pixel region  108   c  and the surrounding region  108   d  in a plan view. That is, as in  FIG. 7 , when viewed in the input direction of the input light L 1 , the first region  209   a  overlaps the pixel region  108   c . For this reason, in  FIG. 7 , the hidden line indicating the pixel region  108   c  overlaps the boundary between the first region  209   a  and the second region  209   b , and therefore it is not depicted. The second region  209   b  is disposed between the surrounding region  108   d  and the rear surface  101   b  of the electro-optic crystal  101 . 
     In the present embodiment, since the area of the second region  109   b  in a plan view can be increased, the electro-optic crystal  101  and the CMOS substrate  108  can be more firmly bonded to each other. In addition, the electro-optic crystal  101  and the first electrode  103  can be more firmly bonded to each other. 
     Third Embodiment 
     Subsequently, a spatial light modulator  300  according to the present embodiment will be described. Points differing from the first embodiment will be mainly described. The same reference signs are applied to elements or members which are the same, and detailed description thereof will be omitted. 
       FIG. 8  is a cross-sectional view showing the spatial light modulator  300  according to the present embodiment. As shown in  FIG. 8 , the reflective spatial light modulator  300  includes the electro-optic crystal  101 , the light input/output unit  102 , a light reflection unit  307 , and the drive circuit  110 . The CMOS substrate  108  constituting the light reflection unit  107  is fixed to the substrate  112 . 
     The light reflection unit  307  includes the CMOS substrate  108 , the adhesive layer  109 , a plurality of third electrodes  308 , and a plurality of bumps  309 . The CMOS substrate  108  is fixed to the substrate  112 . The plurality of third electrodes  308  are disposed on the rear surface  101   b  side of the electro-optic crystal  101 . In the present embodiment, similar to the plurality of second electrodes  108   a , the adhesive layer  109  formed on the rear surface  101   b  is disposed in a two-dimensional manner. In this case, the adhesive layer  109  can be formed of the same material as that of the first region  109   a . The third electrodes  308  can reflect the input light L 1  propagated inside the electro-optic crystal  101  toward the light input/output unit  102 . For example, the third electrodes  308  are metal electrodes and can be formed of aluminum or the like. In the present embodiment, the plurality of third electrodes  308  formed to have a rectangular shape in a plan view are disposed in a two-dimensional manner corresponding to the plurality of second electrodes  108   a . The plurality of second electrodes  108   a  and the plurality of third electrodes  308  face each other. The third electrodes  308  can be formed on a surface of the adhesive layer  109  on a side opposite to the electro-optic crystal  101  by performing vapor deposition of aluminum or the like using a mask pattern. 
     The plurality of bumps  309  are formed in the same number as the second electrodes  108   a  and the third electrodes  308 . The plurality of bumps  309  electrically connect the plurality of second electrodes  108   a  and the plurality of third electrodes corresponding to these second electrodes  108   a  to each other in one-to-one correspondence. For example, the bumps  309  can be formed of gold (Au), a soldering material, or the like. Between the adhesive layer  109  and the CMOS substrate  108 , a space between bumps  309  adjacent to each other and a space between third electrodes  308  adjacent to each other may be a gap, for example, or may be filled with an insulating substance. 
     In this configuration, when an electric field is applied to the electro-optic crystal, an electric field can be individually applied to a plurality of third electrodes. In addition, since the adhesive layer  109  is disposed in a two-dimensional manner, an influence on adjacent pixels can be reduced. Therefore, mixing of electrical signals input to a plurality of electrodes can be curbed, and thus the modulation accuracy can become more stable. 
     Fourth Embodiment 
     Subsequently, a spatial light modulator  400  according to the present embodiment will be described. Points differing from the first embodiment will be mainly described. The same reference signs are applied to elements or members which are the same, and detailed description thereof will be omitted. 
       FIG. 9  is a cross-sectional view showing the spatial light modulator  400  according to the present embodiment. As shown in  FIG. 9 , the reflective spatial light modulator  400  includes the electro-optic crystal  101 , a light input/output unit  402 , the light reflection unit  107 , and the drive circuit  110 . The CMOS substrate  108  constituting the light reflection unit  107  is fixed to the substrate  112 . 
     The light input/output unit  402  is constituted of the first electrode  103  and the adhesive layer  119 . That is, the light input/output unit  402  does not have the transparent substrate  104 , the transparent electrode  105 , and the adhesive layer  106 . In the present embodiment, the drive circuit  110  is connected to the first electrode  103  and the CMOS substrate  108 . As an example, the first electrode  103  can be formed by performing vapor deposition of ITO with respect to the cured adhesive layer  119  which is bonded to the input surface  101   a  of the electro-optic crystal  101 . In this configuration, the adhesive layer  119  is disposed not for adhesion between the electro-optic crystal  101  and the first electrode  103  but to mainly curb injection of charge into the electro-optic crystal  101  from the first electrode  103 . For this reason, the adhesive layer  119  shown in the example includes the first region  119   a  and the second region  119   b . For example, the second region  119   b  may have a composition similar to the composition of the first region  119   a.    
     Fifth Embodiment 
     Subsequently, a spatial light modulator  500  according to the present embodiment will be described. Points differing from the first embodiment will be mainly described. The same reference signs are applied to elements or members which are the same, and detailed description thereof will be omitted. 
       FIG. 10  is a cross-sectional view showing the spatial light modulator  500  according to the present embodiment. As shown in  FIG. 10 , the reflective spatial light modulator  500  includes the electro-optic crystal  101 , the light input/output unit  202 , a light reflection unit  507 , and the drive circuit  110 . 
     The light reflection unit  507  includes the CMOS substrate  108 , the adhesive layer  109 , and auxiliary electrodes (fourth electrodes)  509 . The CMOS substrate  108  is fixed to the substrate  112 . A plurality of auxiliary electrodes  509  are disposed on the rear surface  101   b  of the electro-optic crystal  101 . The auxiliary electrodes  509  functions as a mirror reflecting the input light L 1  propagated inside the electro-optic crystal  101  toward the light input/output unit  102 . For example, the auxiliary electrodes  509  are metal electrodes and can be formed of aluminum or the like. Similar to the second electrodes  108   a  formed on the CMOS substrate  108 , the auxiliary electrodes  509  are disposed in a two-dimensional manner. That is, the auxiliary electrodes  509  and the second electrodes  108   a  face each other in one-to-one correspondence. 
     The plurality of auxiliary electrodes  509  are formed on the rear surface  101   b  side of the electro-optic crystal  101  in a manner of facing the plurality of second electrodes  108   a . The auxiliary electrodes  509  are positioned in an electrostatic field formed by the first electrode  103  of the electro-optic crystal  101  on the input surface  101   a  side and the second electrodes  108   a . For this reason, an electrostatic field is generated between the first electrode  103  and the auxiliary electrodes  509  and between the auxiliary electrodes  509  and the second electrodes  108   a  due to electrostatic induction. That is, the auxiliary electrodes  509  function as electrostatic lenses for preventing spreading of an electrical signal transferred as an electric line of force. Accordingly, in the adhesive layer  109  and the electro-optic crystal  101 , spreading of an electrical signal (that is, an electric line of force) input from the drive circuit  110  can be curbed drastically. Therefore, mixing of input electrical signals can be further curbed, and thus the modulation accuracy can become stable with higher resolution. 
     Hereinabove, the embodiments have been described in detail with reference to the drawings. However, specific configurations are not limited to these embodiments. 
     For example, in the foregoing embodiments, the optical observation device  1 A including a spatial light modulator has been exemplified, but the embodiments are not limited thereto. For example, the spatial light modulator  100  may be mounted in a light irradiation device  1 B.  FIG. 11  is a block diagram showing a configuration of a light irradiation device. The light irradiation device  1 B has the light source  10 , the collimator lens  11 , the polarization element  12 , the polarization beam splitter  13 , the spatial light modulator  100 , the first optical system  14 , and the control unit  19  including the computer  20  and the controller  21 . In this configuration, the specimen S is irradiated with the modulation light L 2  output from the spatial light modulator  100  by the first optical system  14 . Using the spatial light modulator  100 , 1) a position of an irradiation location can be limited, 2) the position of the irradiation location can be moved, 3) a plurality of irradiation locations can be formed at the same time, and 4) a phase of irradiation light can be controlled. 
     In addition, the fifth embodiment has shown a configuration in which the auxiliary electrodes  509  formed of a metal reflect the input light L 1 , but the embodiments are not limited thereto. For example, the auxiliary electrodes  509  may be transparent electrodes or may be formed of a transparent film such as ITO, for example. In this case, the input light L 1  can be transmitted through the auxiliary electrodes and can be reflected by the second electrodes  108   a.    
     In addition, the configurations of the foregoing embodiments can be diverted to each other unless there is any particular contradiction or problem. In the adhesive layer  109  and the adhesive layer  119  shown in the third embodiment to the fifth embodiment, the boundary between the first region and the second region is positioned on the side outward from the edge of the boundary between the pixel region  108   c  and the surrounding region  108   d . For example, the adhesive layer  109  and the adhesive layer  119  may have a configuration in which the boundary between the first region and the second region coincides with the boundary between the pixel region  108   c  and the surrounding region  108   d.    
     In addition, an example in which the first region  109   a  is formed on the whole surface of the first region has been described, but the embodiments are not limited thereto. For example, the first region  109   a  may be disposed in a two-dimensional manner corresponding to the second electrodes  108   a.    
     REFERENCE SIGNS LIST 
       1 A Optical observation device 
       1 B Light irradiation device 
       100  Spatial light modulator (reflective spatial light modulator) 
       101  Electro-optic crystal 
       101   a  Input surface 
       101   b  Rear surface 
       102  Light input/output unit 
       103  First electrode 
       107  Light reflection portion 
       108  CMOS substrate (substrate) 
       108   a  Second electrode 
       109  Adhesive layer 
       110  Drive circuit 
       509  Auxiliary electrode (third electrode) 
     L 1  Input light 
     L 2  Modulation light