Patent Publication Number: US-2021191165-A1

Title: Light modulator, optical observation device, and light irradiation device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a 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 
     An electro-optical element as described above has a configuration in which a KTN layer is interposed between a pair of electrodes. In addition, the pair of electrodes are formed entirely throughout a front surface and a back surface of the KTN layer. For this reason, there is concern that when an electric field is applied to the KTN layer, an inverse piezoelectric effect or an electrostrictive effect may increase and stable light modulation may not be able to be performed. In addition, there is concern that if charge is injected into a KTN layer from a metal electrode, the modulation accuracy may not become stable due to the behavior of electrons inside a KTN crystal. 
     An object of the present disclosure is to provide a light modulator, an optical observation device, and a light irradiation device, in which stable light modulation can be performed. 
     Solution to Problem 
     According to an aspect, there is provided a light modulator modulating input light and outputting modulated modulation light. The 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 first optical element being disposed on the input surface side of the electro-optic crystal and having a first electrode through which the input light is transmitted; a second optical element being disposed on the rear surface side of the electro-optic crystal and having a second electrode through which the input light is transmitted; and a drive circuit applying an electric field between the first electrode and the second electrode. The first electrode is disposed alone on the input surface side. The second electrode is disposed alone on the rear surface side. At least one of the first electrode and the second electrode partially covers the input surface or the rear surface. A propagation direction of the input light and an applying direction of the electric field in the electro-optic crystal are parallel to each other. At least one of the first optical element and the second optical element includes a charge injection curbing layer for curbing injection of charge into the electro-optic crystal. 
     According to another aspect, there is provided a light modulator modulating input light and outputting modulated modulation light. The 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 first optical element being disposed on the input surface side of the electro-optic crystal and having a first electrode through which the input light is transmitted; a second optical element having a second electrode disposed on the rear surface side of the electro-optic crystal and reflecting the input light toward the input surface; and a drive circuit applying an electric field between the first electrode and the second electrode. The first electrode is disposed alone on the input surface side. The second electrode is disposed alone on the rear surface side. At least one of the first electrode and the second electrode partially covers the input surface or the rear surface. A propagation direction of the input light and an applying direction of the electric field in the electro-optic crystal are parallel to each other. At least one of the first optical element and the second optical element includes a charge injection curbing layer for curbing injection of charge into the electro-optic crystal. 
     In addition, according to another aspect, there is provided an optical observation device including a light source outputting the input light, the light modulator described above, an optical system irradiating a target with modulation light output from the light modulator, and a photodetector detecting light output from the target. 
     In addition, according to another aspect, there is provided a light irradiation device including a light source outputting the input light, the light modulator described above, and an optical system irradiating a target with modulation light output from the light modulator. 
     According to the light modulator, the optical observation device, and the light irradiation device described above, the input light is transmitted through the first electrode of the first optical element and is input to the input surface of the perovskite-type electro-optic crystal. This input light can be output after being transmitted through the second optical element disposed on the rear surface of the electro-optic crystal or can be output after being reflected by the second optical element. At this time, an electric field is applied between the first electrode provided in the first optical element and the second electrode provided in the second optical element. Accordingly, an electric field can be applied to the electro-optic crystal having a high relative dielectric constant, and the input light can be modulated. In this light modulator, one first electrode and one second electrode are disposed, and at least one of the first electrode and the second electrode partially covers the input surface or the rear surface. In this case, an inverse piezoelectric effect or an electrostrictive effect occurs in a part in which the first electrode and the second electrode face each other, but an inverse piezoelectric effect or an electrostrictive effect does not occur around the part. For this reason, a portion around the part in which the first electrode and the second electrode face each other functions as a damper. Accordingly, compared to a case in which the input surface and the rear surface are entirely covered by the electrodes, an inverse piezoelectric effect and an electrostrictive effect can be curbed, and occurrence of resonance or the like is curbed. In addition, since a charge injection curbing layer for curbing injection of charge into the electro-optic crystal is formed, behavior of electrons inside the electro-optic crystal can become stable. Therefore, stable light modulation can be performed. 
     In addition, in the aspect, the light modulator may further include a transparent substrate having a first surface facing the second optical element and a second surface serving as a surface on a side opposite to the first surface. The transparent substrate may be output the input light transmitted through the second optical element. In addition, in the aspect, the light modulator may further include a substrate having a first surface facing the second optical element. In such light modulators, even when the electro-optic crystal is formed to be thin in an optical axis direction, the electro-optic crystal can be protected from an external impact or the like. 
     In addition, the charge injection curbing layer may be formed in each of a part between the input surface and the first electrode and a part between the rear surface and the second electrode. According to this configuration, injection of charge into the electro-optic crystal from both the first electrode and the second electrode is curbed. 
     In addition, in the aspect, at least an area (μm 2 ) of one of the first electrode and the second electrode may be 25d 2  or smaller when a thickness (μm) of the electro-optic crystal in the electric field applying direction of the electro-optic crystal is d. In such a light modulator, an inverse piezoelectric effect or an electrostrictive effect can be effectively reduced. 
     In addition, in the aspect, the area of the first electrode may be larger or smaller than the area of the second electrode. In this case, positional alignment between the first electrode and the second electrode can be easily performed. 
     In addition, in the aspect, the light modulator may further include a third electrode being electrically connected to the first electrode, and a fourth electrode being electrically connected to the second electrode. The third electrode and the fourth electrode may be disposed not to overlap each other with the electro-optic crystal interposed therebetween. 
     In addition, in the aspect, the first optical element may have the third electrode being electrically connected to the first electrode, and an insulation unit being disposed between the third electrode and the input surface and reducing an electric field generated in the third electrode. The drive circuit may apply an electric field to the first electrode via the third electrode. Since the third electrode is provided for connection with the drive circuit, the size or the position of the first electrode can be designed freely. At this time, an influence of an electric field generated in the third electrode on the electro-optic crystal can be curbed by the insulation unit. 
     In addition, in the aspect, one optical element may have a light reduction unit covering the input surface around the first electrode and reducing light input to the input surface from parts around the first electrode. In this case, the light reduction unit may be a reflection layer reflecting the light. In addition, the light reduction unit may be an absorption layer absorbing the light. In addition, the light reduction unit may be a blocking layer blocking the light. Accordingly, input of light from a part on the input surface where the first electrode is not formed can be curbed. 
     In addition, in the aspect, a dielectric multilayer film reflecting the input light may be provided in the second electrode. According to this configuration, the input light can be efficiently reflected. 
     In addition, in the aspect, the second electrode may reflect the input light. According to this configuration, 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≤x≤1 and 0&lt;y&lt;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 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. 
     Effects of Invention 
     According to the light modulator, the optical observation device, and the light irradiation device of the embodiment, an inverse piezoelectric effect or an electrostrictive effect can be curbed, and stable light modulation can be performed. 
    
    
     
       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 view schematically showing a light modulator according to a first embodiment. 
         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 schematically showing a light modulator according to a second embodiment. 
         FIG. 5  is a view schematically showing a light modulator according to a third embodiment. 
         FIG. 6  is a view schematically showing a light modulator according to a fourth embodiment. 
         FIG. 7  is a view schematically showing a light modulator according to a fifth embodiment. 
         FIG. 8  is a view schematically showing a light modulator according to a sixth embodiment. 
         FIG. 9  is a view schematically showing a light modulator according to a seventh embodiment. 
         FIG. 10  is a view schematically showing a light modulator according to an eighth embodiment. 
         FIG. 11  is a view schematically showing a light modulator according to a ninth embodiment. 
         FIG. 12  is a view schematically showing a light modulator according to a tenth embodiment. 
         FIG. 13  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  11 , a concentration lens  12 , a 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  11  outputs the input light L 1  including a wavelength for exciting the specimen S. For example, the light source  11  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 concentration lens  12  concentrates the input light L 1  output from the light source  11  and outputs the concentrated input light L 1 . The light modulator  100  is disposed such that a propagation direction of the input light L 1  and a direction of an applied electric field are parallel to each other. Therefore, in the light modulator  100 , the propagation direction of the input light L 1  and the applying direction of an electric field in an electro-optic crystal  101  become parallel to each other. The light modulator  100  is a light modulator modulating the phase or retardation (phase difference) of the input light L 1  output from the light source  11 . The light modulator  100  modulates the input light L 1  input from the concentration lens  12  and outputs modulated modulation light L 2  toward the first optical system  14 . In the present embodiment, the light modulator  100  is constituted as a transmitting type. However, a reflective light modulator may be used in the optical observation device  1 A. The light modulator  100  is electrically connected to a controller  21  of the control unit  19  and constitutes a light modulator unit. Driving of the light modulator  100  is controlled by the controller  21  of the control unit  19 . Details of the light modulator  100  will be described below. 
     The first optical system  14  optically joins the light modulator  100  and the objective lens  16  to each other. Accordingly, the modulation light L 2  output from the light modulator  100  is optically guided to the objective lens  16 . For example, the first optical system  14  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 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 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 light modulator  100 . 
     Next, the light modulator  100  will be described in detail.  FIG. 2  is a view schematically showing a light modulator. The light modulator  100  is a transmitting-type light modulator modulating the input light L 1  and outputting the modulated modulation light L 2 . As shown in  FIG. 2 , the light modulator  100  includes the electro-optic crystal  101 , a light input unit (first optical element)  102 , a light output unit (second optical element)  106 , and a drive circuit  110 . In  FIG. 2( a ) , the electro-optic crystal  101 , the light input unit  102 , and the light output unit  106  of the light modulator  100  are shown in a cross section. In addition,  FIG. 2( b )  is a view of the light modulator  100  viewed from the light input unit  102  side, and  FIG. 2( c )  is a view of the light modulator  100  viewed from the light output unit  106  side. 
     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 O 3  (0≤x≤1 and 0&lt;y&lt;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 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 X2 and X3 are rotated by 45° about the axis X1 and new axes X1′, X2′, and X3′ are set, retardation modulation can be performed by inputting light in a manner of being parallel or perpendicular to these new axes. In  FIG. 4 , 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. 
     As shown in  FIG. 2 , the light input unit  102  includes a transparent electrode (first electrode)  103 , a charge injection curbing layer  121 , an intermediate layer  120 , a connection electrode (third electrode)  104 , and an insulation unit  105 . 
     The transparent electrode  103  is disposed on the input surface  101   a  side of the electro-optic crystal  101 . For example, the transparent electrode  103  is formed of indium tin oxide (ITO) and allows the input light L 1  to be transmitted therethrough. That is, the input light L 1  is transmitted through the transparent electrode  103  and is propagated toward the electro-optic crystal  101 . In the present embodiment, for example, the transparent electrode  103  exhibits a rectangular shape in a plan view and partially covers the input surface  101   a . In addition, the area (μm 2 ) of the transparent electrode  103  may be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (μm). The transparent electrode  103  is formed alone at a place substantially at the center on the input surface  101   a  and is distanced from a circumferential edge on the input surface  101   a . For example, such a transparent electrode  103  can be formed through vapor deposition of ITO using a mask pattern. 
     The charge injection curbing layer  121  is formed between the transparent electrode  103  and the input surface  101   a . For example, the charge injection curbing layer  121  has the same size as the transparent electrode  103  and exhibits a rectangular shape in a plan view. For example, the charge injection curbing layer  121  has 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 charge injection curbing layer  121  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 dielectric material has no Pockels effect. As an example, the proportion of the dielectric material in a mixture of an adhesive material and a dielectric material may be approximately 50%. For example, the charge injection curbing layer  121  can be formed by coating the input surface  101   a  of the electro-optic crystal  101  with a mixture of an adhesive material and a dielectric material. The charge injection curbing layer  121  need only be formed in a manner corresponding to the transparent electrode  103 , and there is no need to form the charge injection curbing layer  121  on the whole surface of the input surface  101   a.    
     In addition, the charge injection curbing layer  121  may be formed of a dielectric material such as SiO 2 , HfO 2 , BaTiO 3 , BST ((Ba, Sr)TiO 3 ), STO (SrTiO 3 ), SrTa 2 O 6 , Sr 2 Ta 2 O 7 , ZnO, Ta 2 O 5 , SiO 2 , PZT (Pb(Zr, Ti)O 3 , PZTN (Pb(Zr, Ti)Nb 2 O 8 , PLZT ((Pb, La)(Zr, Ti)O 3 , SBT (SrBi 2 Ta 2 O 9 ), SBTN (SrBi 2 (Ta, Nb) 2 O 9 , or BTO (Bi 4 Ti 3 O 12 ). 
     The intermediate layer  120  is formed on the input surface  101   a . In the present embodiment, the intermediate layer  120  comes into contact with the charge injection curbing layer  121  and is formed equally to an end edge on one side beyond the charge injection curbing layer  121  on the input surface  101   a . For example, the height of the intermediate layer  120  may be approximately the same as the height of the charge injection curbing layer  121 . For example, the intermediate layer  120  may be formed of the same adhesive material as the adhesive material constituting the charge injection curbing layer  121 . In addition, similar to the charge injection curbing layer  121 , the intermediate layer  120  may be a mixture of an adhesive material and a dielectric material. Moreover, the intermediate layer  120  may be an insulation film formed of SiO 2 , HfO 2 , or the like. 
     The insulation unit  105  is formed on the intermediate layer  120 . In the present embodiment, the insulation unit  105  comes into contact with the transparent electrode  103  and is formed equally to an end edge on one side beyond the transparent electrode  103  on the intermediate layer  120 . For example, the insulation unit  105  is formed to have a height lower than the height of the transparent electrode  103 . For example, the insulation unit  105  is an insulation film formed of SiO 2 , HfO 2 , or the like. The connection electrode  104  is formed on the insulation unit  105 . That is, the insulation unit  105  is disposed between the intermediate layer  120  and the connection electrode  104 . Accordingly, since most of an electric field generated in the connection electrode  104  is applied to the insulation unit, the insulation unit  105  has a thickness to an extent that an electric field applied to the electro-optic crystal  101  is disregarded. When the intermediate layer  120  and the insulation unit  105  are formed of the same material, the intermediate layer  120  and the insulation unit  105  can be formed integrally. 
     The connection electrode  104  is electrically connected to the transparent electrode  103 . The connection electrode  104  has a thin wire-shaped lead portion  104   a  of which one end is electrically connected to the transparent electrode  103 , and a main body portion  104   b  which has a rectangular shape in a plan view and is electrically connected to the other end of the lead portion  104   a . For example, the area of the main body portion  104   b  is larger than that of the transparent electrode  103 . In addition, for example, the main body portion  104   b  extends to the circumferential edge on the input surface  101   a . In the present embodiment, one side  104   c  of the main body portion  104   b  exhibiting a rectangular shape coincides with the circumferential edge on the input surface  101   a  of the electro-optic crystal  101 . Similar to the transparent electrode  103 , the connection electrode  104  may be formed of a transparent material such as ITO. In addition, other than a transparent material, the connection electrode  104  may be formed of other conductive materials not allowing the input light L 1  to be transmitted therethrough. For example, the connection electrode  104  can be formed by performing vapor deposition of ITO on the insulation unit  105  using a mask pattern. 
     As shown in  FIG. 2( c ) , the light output unit  106  includes a transparent electrode (second electrode)  107 , a charge injection curbing layer  123 , an intermediate layer  122 , a connection electrode (fourth electrode)  108 , and an insulation unit  109 . 
     The transparent electrode  107  is disposed on the rear surface  101   b  side of the electro-optic crystal  101 . Similar to the transparent electrode  103 , the transparent electrode  107  is formed of ITO, for example, and the input light L 1  is transmitted therethrough. That is, the input light L 1  which has been input to the inside of the electro-optic crystal  101  and subjected to phase modulation or retardation modulation can be output from the transparent electrode  107  as the modulation light L 2 . In the present embodiment, for example, the transparent electrode  107  exhibits a rectangular shape in a plan view and partially covers the rear surface  101   b . In addition, the area (μm 2 ) of the transparent electrode  107  may be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (μm). The transparent electrode  107  is formed alone at a place substantially at the center on the rear surface  101   b  and is distanced from a circumferential edge on the rear surface  101   b . In addition, in a plan view, the area of the transparent electrode  107  is formed to be larger than that of the transparent electrode  103 . In addition, the center of the transparent electrode  107  and the center of the transparent electrode  103  substantially coincide with each other in an optical axis direction. For this reason, when viewed in the optical axis direction, the transparent electrode  103  is entirely accommodated on the inward side of the transparent electrode  107 . 
     The charge injection curbing layer  123  is formed between the transparent electrode  107  and the rear surface  101   b . For example, the charge injection curbing layer  123  has the same size as the transparent electrode  107  and exhibits a rectangular shape in a plan view. For example, the charge injection curbing layer  123  can be formed of the same material as that of the charge injection curbing layer  121 . 
     The intermediate layer  122  is formed on the rear surface  101   b . In the present embodiment, the intermediate layer  122  comes into contact with the charge injection curbing layer  123  and is formed equally to an end edge on one side beyond the charge injection curbing layer  123  on the rear surface  101   b . For example, the height of the intermediate layer  122  may be approximately the same as the height of the charge injection curbing layer  123 . For example, the intermediate layer  122  can be formed of the same material as that of the intermediate layer  120 . 
     The insulation unit  109  is formed on the intermediate layer  122 . In the present embodiment, the insulation unit  109  comes into contact with the transparent electrode  107  and is formed equally to an end edge on one side beyond the transparent electrode  107  on the intermediate layer  122 . For example, the insulation unit  109  is formed to have a height lower than the height of the transparent electrode  107 . For example, the insulation unit  109  is an insulation film formed of an insulator such as SiO 2  or HfO 2 . The connection electrode  108  is formed on the insulation unit  109 . That is, the insulation unit  109  is disposed between the intermediate layer  122  and the connection electrode  108 . Accordingly, the insulation unit  109  insulates an electric field generated in the connection electrode  108 . 
     The connection electrode  108  is electrically connected to the transparent electrode  107 . The connection electrode  108  has a thin wire-shaped lead portion  108   a  of which one end is electrically connected to the transparent electrode  107 , and a main body portion  108   b  which has a rectangular shape in a plan view and is electrically connected to the other end of the lead portion  108   a . For example, the area of the main body portion  108   b  is larger than that of the transparent electrode  107 . In addition, for example, the main body portion  108   b  extends to the circumferential edge on the rear surface  101   b . In the present embodiment, one side  108   c  of the main body portion  108   b  exhibiting a rectangular shape coincides with the circumferential edge on the rear surface  101   b  of the electro-optic crystal  101 . In addition, the one side  108   c  of the main body portion  108   b  does not have to coincide with a surrounding portion on the rear surface  101   b  of the electro-optic crystal  101 . Similar to the transparent electrode  107 , the connection electrode  108  may be formed of a transparent material such as ITO. In addition, other than a transparent material, the connection electrode  108  may be formed of other conductive materials not allowing the input light L 1  to be transmitted therethrough. For example, the connection electrode  108  can be formed by performing vapor deposition of ITO on the insulation unit  109  using a mask pattern. For example, the area of the main body portion  108   b  may be substantially the same as the area of the main body portion  104   b  of the light input unit  102 . In addition, the area of the main body portion  108   b  may be smaller than the area of the front surface of the transparent electrode  107 . 
     The drive circuit  110  applies an electric field between the transparent electrode  103  and the transparent electrode  107 . In the present embodiment, the drive circuit  110  is electrically connected to the connection electrode  104  and the connection electrode  108 . The drive circuit  110  inputs an electrical signal to the connection electrode  104  and the connection electrode  108  and applies an electric field between the transparent electrode  103  and the transparent electrode  107 . Such a drive circuit  110  is controlled by the control unit  19 . 
     The drive circuit  110  inputs an electrical signal between the transparent electrode  103  and the transparent electrode  107 . Accordingly, an electric field is applied to the electro-optic crystal  101  and the charge injection curbing layers  121  and  123  disposed between the transparent electrode  103  and the transparent electrode  107 . In this case, a voltage applied by the drive circuit  110  is distributed to the electro-optic crystal  101  and the charge injection curbing layers  121  and  123 . Therefore, when a voltage applied to the electro-optic crystal  101  is V xtl , a voltage applied to the charge injection curbing layers  121  and  123  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 charge injection curbing layers  121  and  123  is ε ad , and the sum of the thicknesses of the charge injection curbing layers  121  and  123  is d ad , a voltage ratio R between a voltage applied between the transparent electrode  103  and the transparent electrode  107  and a voltage applied to the electro-optic crystal  101  is expressed by the following Expression (1). For the sake of simplification of description, the charge injection curbing layer  121  and the charge injection curbing layer  123  are assumed to be formed of materials having the same relative dielectric constant. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   R 
                   = 
                   
                     
                       
                         V 
                         xtl 
                       
                       
                         
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                           xtl 
                         
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                           ad 
                         
                       
                     
                     = 
                     
                       
                         
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                         · 
                         
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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 charge injection curbing layers  121  and  123 . For example, in the present embodiment, the light modulator  100  has a modulation performance of outputting the input light L 1  obtained by modulating the modulation light L 2  by one wavelength. In this case, the relative dielectric constant ε ad  of the charge injection curbing layers  121  and  123  is obtained as follows. First, 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 charge injection curbing layers  121  and  123  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 1  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 (2). 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   (2)
 
     Further, from Expression (1) and Expression (2), the relative dielectric constant ε ad  and the thicknesses d ad  of the charge injection curbing layers  121  and  123  satisfy the following Expression (3). 
     
       
         
           
             
               
                 
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                     Math 
                     . 
                     
                         
                     
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     From this Expression (3), the relative dielectric constant of the charge injection curbing layers  121  and  123  is obtained. That is, when Expression (3) is transformed into an expression related to the relative dielectric constant of the charge injection curbing layers  121  and  123 , the following Expression (4) is derived. 
     
       
         
           
             
               
                 
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     When the relative dielectric constant of the charge injection curbing layers  121  and  123  satisfies Expression (4), 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 charge injection curbing layers  121  and  123 , the thicknesses d ad  of the charge injection curbing layers  121  and  123 , the relative dielectric constant ε xtl  of the electro-optic crystal  101 , and the thickness d 1  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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     According to the light modulator  100  described above, the input light L 1  is transmitted through the transparent electrode  103  of the light input unit  102  and is input to the input surface  101   a  of the perovskite-type electro-optic crystal  101 . This input light L 1  is output after being transmitted through the light output unit  106  disposed on the rear surface  101   b  of the electro-optic crystal  101 . At this time, an electric field is applied between the transparent electrode  103  provided in the light input unit  102  and the transparent electrode  107  provided in the light output unit  106 . Accordingly, an electric field is applied to the electro-optic crystal  101  having a high relative dielectric constant, and the input light L 1  can be modulated. In this light modulator  100 , the transparent electrode  103  partially covers the input surface  101   a . In addition, it is preferable that the area (μm 2 ) of the transparent electrode  103  be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (μm). In addition, the transparent electrode  107  partially covers the rear surface  101   b . The area of the transparent electrode  107  (μm 2 ) may be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (μm). In this case, an inverse piezoelectric effect or an electrostrictive effect occurs in a part in which the transparent electrode  103  and the transparent electrode  107  face each other, but an inverse piezoelectric effect or an electrostrictive effect does not occur around the part. For this reason, a portion around the part in which the transparent electrode  103  and the transparent electrode  107  face each other functions as a damper. Accordingly, compared to a case in which the input surface  101   a  and the rear surface  101   b  are entirely covered by the electrodes, an inverse piezoelectric effect or an electrostrictive effect can be curbed, and occurrence of resonance or the like is curbed. In addition, since a charge injection curbing layer for curbing injection of charge into the electro-optic crystal is formed, behavior of electrons inside the electro-optic crystal can become stable. Therefore, stable light modulation can be performed. 
     In addition, since the area of the transparent electrode  103  is formed to be smaller than the area of the transparent electrode  107 , positional alignment between the transparent electrode  103  and the transparent electrode  107  can be easily performed. 
     In addition, the light input unit  102  has the connection electrode  104  which is electrically connected to the transparent electrode  103 , and the insulation unit  105  which blocks an electric field generated in the connection electrode  104 . In addition, the drive circuit  110  applies an electric field between the transparent electrode  103  and the transparent electrode  107  via the connection electrode  104 . In this manner, since the connection electrode  104  is provided for connection with the drive circuit  110 , the size, the position, or the like of the transparent electrode  103  can be designed freely. At this time, an influence of an electric field generated in the connection electrode  104  on the electro-optic crystal  101  can be curbed by the insulation unit  105 . Similarly, even in the light output unit  106 , the size, the position, or the like of the transparent electrode  107  can be designed freely. In addition, an influence of an electric field generated in the connection electrode  108  on the electro-optic crystal  101  can be curbed. 
     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 light modulator  100  in its entirety. 
     Second Embodiment 
     A light modulator  200  according to the present embodiment differs from the light modulator  100  of the first embodiment in that a light input unit  202  has a light reduction unit. Hereinafter, 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. 4  is a view schematically showing the light modulator  200 . The light modulator  200  includes the electro-optic crystal  101 , the light input unit  202 , the light output unit  106 , and the drive circuit  110 . In  FIG. 4( a ) , the electro-optic crystal  101 , the light input unit  202 , and the light output unit  106  of the light modulator  200  are shown in a cross section. In addition,  FIG. 2( b )  is a view of the light modulator  200  viewed from the light input unit  202  side. 
     As shown in  FIG. 4 , the light input unit  202  includes the transparent electrode  103 , the connection electrode  104 , the insulation unit  105 , the charge injection curbing layer  121 , the intermediate layer  120 , an intermediate layer  124 , and a light reduction layer  205 . 
     The intermediate layer  124  is formed on a surface of the input surface  101   a  excluding a part in which the charge injection curbing layer  121  (transparent electrode  103 ) and the intermediate layer  120  (insulation unit  105 ) are formed. That is, the whole surface of the input surface  101   a  is covered by the charge injection curbing layer  121 , the intermediate layer  120 , and the intermediate layer  124 . For example, a material for forming the intermediate layer  124  may be the same as the material for forming the intermediate layer  120 . 
     The light reduction layer  205  is formed on the whole surface of the intermediate layer  124 . The light reduction layer  205  curbs transmitting of the input light L 1  into the electro-optic crystal  101 . For example, the light reduction layer is formed of a material such as a black resist obtained by dispersing carbon in an epoxy-based UV cured resin. 
     In the present embodiment, the insulation unit  105  is formed of a material not allowing the input light L 1  to be transmitted therethrough. Examples of such a material include a black resist or the like obtained by dispersing carbon in an epoxy-based UV cured resin. In this manner, the input surface  101   a  is covered by the light reduction layer  205  and the insulation unit  105  around the transparent electrode  103 . The light reduction layer  205  and the insulation unit  105  reduce light input to the input surface  101   a  from a part other than the transparent electrode  103 . That is, the light reduction layer  205  and the insulation unit  105  constitute a light reduction unit  207 . Since such a light reduction unit  207  is included, interference or the like of the input light L 1  with different light inside the electro-optic crystal  101  can be curbed. The light reduction unit  207  may be any of a reflection layer formed with a layer reflecting light, an absorption layer formed with a layer absorbing light, and a blocking layer formed with a layer blocking light. In addition, when the light reduction layer  205  and the insulation unit  105  are formed of the same material, the light reduction layer  205  and the insulation unit  105  may be formed integrally. 
     Third Embodiment 
     A light modulator  300  according to the present embodiment differs from the light modulator  100  of the first embodiment in a configuration of a light output unit  306 . Hereinafter, 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. 5  is a view schematically showing the light modulator  300 . The light modulator  300  includes the electro-optic crystal  101 , the light input unit  102 , the light output unit  306 , and the drive circuit  110 . In  FIG. 5 , the electro-optic crystal  101 , the light input unit  102 , and the light output unit  306  of the light modulator  300  are shown in a cross section. 
     The light output unit  306  includes a transparent electrode (second electrode)  307  and a charge injection curbing layer  323 . The transparent electrode  307  is disposed on the rear surface  101   b  side of the electro-optic crystal  101 . Similar to the transparent electrode  103 , the transparent electrode  307  is formed of ITO, for example, and the input light L 1  is transmitted therethrough. That is, the input light L 1  which has been input to the inside of the electro-optic crystal  101  and subjected to phase modulation or retardation modulation can be output from the transparent electrode  307  as the modulation light L 2 . In the present embodiment, the transparent electrode  307  is formed on the whole surface on the rear surface  101   b  side. 
     The charge injection curbing layer  323  is formed between the transparent electrode  307  and the rear surface  101   b . That is, the charge injection curbing layer  323  is formed on the whole surface of the rear surface  101   b . For example, the charge injection curbing layer  323  can be formed of the same material as that of the charge injection curbing layer  123 . 
     The drive circuit  110  is electrically connected to the connection electrode  104  and the transparent electrode  307  and applies an electric field between the transparent electrode  103  and the transparent electrode  307 . 
     Fourth Embodiment 
     A light modulator  400  according to the present embodiment differs from the light modulator  300  of the third embodiment in having the light input unit  202  in place of the light input unit  102 . Hereinafter, points differing from the third 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 view schematically showing the light modulator  400 . The light modulator  400  includes the electro-optic crystal  101 , the light input unit  202 , the light output unit  306 , and the drive circuit  110 . In  FIG. 6 , the electro-optic crystal  101 , the light input unit  202 , and the light output unit  306  of the light modulator  400  are shown in a cross section. 
     As shown in  FIG. 6 , the light input unit  202  includes the transparent electrode  103 , the connection electrode  104 , the insulation unit  105 , the charge injection curbing layer  121 , the intermediate layer  120 , the intermediate layer  124 , and the light reduction layer  205 . Further, similar to the second embodiment, the light reduction layer  205  and the insulation unit  105  constitute the light reduction unit  207 . Accordingly, input of the input light L 1  to the input surface  101   a  from parts other than the transparent electrode  103  can be curbed. The light reduction unit  207  may be any of a reflection layer formed with a layer reflecting light, an absorption layer formed with a layer absorbing light, and a blocking layer formed with a layer blocking light. In addition, when the light reduction layer  205  and the insulation unit  105  are formed of the same material, the light reduction layer  205  and the insulation unit  105  may be formed integrally. In addition, the drive circuit  110  is electrically connected to the connection electrode  104  and the transparent electrode  307  and applies an electric field between the transparent electrode  103  and the transparent electrode  307 . 
     Fifth Embodiment 
     A light modulator  500  according to the present embodiment differs from the light modulator  100  of the first embodiment in shape of an electro-optic crystal  501 . Hereinafter, 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. 7  is a view schematically showing the light modulator  500 . The light modulator  500  includes the electro-optic crystal  501 , the light input unit  102 , the light output unit  106 , and the drive circuit  110 . In  FIG. 7( a ) , the electro-optic crystal  501 , the light input unit  102 , and the light output unit  106  of the light modulator  500  are shown in a cross section. In addition,  FIG. 7( b )  is a view of the light modulator  500  viewed from the light input unit  102  side, and  FIG. 7( c )  is a view of the light modulator  500  viewed from the light output unit  106  side. 
     As shown in  FIG. 7 , the electro-optic crystal  501  exhibits a plate shape having an input surface  501   a  to which the input light L 1  is input and a rear surface  501   b  opposing the input surface  501   a . The electro-optic crystal  501  is made of the same material as that of the electro-optic crystal  101  of the first embodiment and is a KTN crystal, for example. 
     In the present embodiment, the shapes of the light input unit  102  and the light output unit  106  are the same as the shapes of those of the first embodiment, whereas the electro-optic crystal  501  is formed to have a compact shape compared to the electro-optic crystal  101  of the first embodiment. Accordingly, the transparent electrode  103  and the transparent electrode  107  are disposed in a manner of being displaced to one side (lower side in  FIGS. 7( b ) and 7( c ) ) from the centers on the input surface  101   a  side and the rear surface  101   b  side, respectively. In the shown example, a circumferential edge of the transparent electrode  103  is distanced from a circumferential edge of the input surface  501   a . On the other hand, one side  107   a  of the transparent electrode  107  exhibiting a rectangular shape coincides with the circumferential edge on the rear surface  101   b.    
     Sixth Embodiment 
     A light modulator  600  according to the present embodiment differs from the light modulator  100  of the first embodiment in configurations of a light input unit  602  and a light output unit  606 . Hereinafter, 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 view schematically showing the light modulator  600 . The light modulator  600  includes the electro-optic crystal  101 , the light input unit  602 , the light output unit  606 , and the drive circuit  110 . In  FIG. 8 , the electro-optic crystal  101 , the light input unit  602 , and the light output unit  606  of the light modulator  600  are shown in a cross section. 
     As shown in  FIG. 8 , the light input unit  602  includes the transparent electrode  103 , the charge injection curbing layer  121 , an intermediate layer  620 , an insulation unit  605 , and a transparent connection electrode  604 . The intermediate layer  620  is formed on the whole surface of the input surface  101   a  excluding a position where the charge injection curbing layer  121  is formed. A material for forming the intermediate layer  620  may be the same as the material for forming the intermediate layer  120 . 
     The insulation unit  605  is formed on the whole surface of the intermediate layer  620 . For example, the insulation unit  605  is an insulation film formed of an insulator such as SiO 2  or HfO 2 . In addition, the insulation unit  605  may further have properties of not allowing the input light L 1  to be transmitted therethrough. In this case, the insulation unit  605  can function as a light reduction unit. In the present embodiment, the insulation unit  605  is formed to have a height substantially the same as the height of the transparent electrode  103 . 
     The transparent connection electrode  604  is formed on the whole surface of the front surfaces of the transparent electrode  103  and the insulation unit  605 . Accordingly, the transparent connection electrode  604  is electrically connected to the transparent electrode  103 . The input light L 1  is input to the transparent electrode  103  from the transparent connection electrode  604  side. For this reason, the transparent connection electrode  604  is formed of a material through which the input light L 1  is transmitted. Similar to the transparent electrode  103 , the transparent connection electrode  604  may be formed of ITO, for example. 
     The light output unit  606  includes the transparent electrode  107 , the charge injection curbing layer  123 , an intermediate layer  622 , an insulation unit  609 , and a transparent connection electrode  608 . The intermediate layer  622  is formed on the whole surface of the rear surface  101   b  excluding a position where the charge injection curbing layer  123  is formed. A material for forming the intermediate layer  622  may be the same as the material for forming the intermediate layer  120 . The insulation unit  609  is formed on the whole surface of the intermediate layer  620 . For example, the insulation unit  609  is an insulation film formed of an insulator such as SiO 2  or HfO 2 . In addition, the insulation unit  609  may further have properties of not allowing the input light L 1  to be transmitted therethrough. In this case, the insulation unit  609  can function as a light reduction unit. In the present embodiment, the insulation unit  609  is formed to have a height substantially the same as the height of the transparent electrode  107 . 
     The transparent connection electrode  608  is formed on the whole surface of the front surfaces of the transparent electrode  107  and the insulation unit  609 . Accordingly, the transparent connection electrode  608  is electrically connected to the transparent electrode  107 . The modulation light L 2  is output from the transparent electrode  107  via the transparent connection electrode  608 . For this reason, the transparent connection electrode  608  is formed of a material through which the modulation light L 2  is transmitted. Similar to the transparent electrode  107 , the transparent connection electrode  608  may be formed of ITO, for example. 
     The drive circuit  110  is electrically connected to the transparent connection electrode  604  and the transparent connection electrode  608  and applies an electric field between the transparent electrode  103  and the transparent electrode  107 . 
     Seventh Embodiment 
     A light modulator  700  according to the present embodiment differs from the light modulator  600  of the sixth embodiment in that the electro-optic crystal  101  is supported by a transparent substrate  713 . Hereinafter, points differing from the sixth 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 view schematically showing the light modulator  700 . The light modulator  700  includes the electro-optic crystal  101 , the light input unit  602 , the light output unit  606 , and the drive circuit  110 . In  FIG. 9 , the electro-optic crystal  101 , the light input unit  602 , and the light output unit  606  of the light modulator  700  are shown in a cross section. In the present embodiment, the thickness of the electro-optic crystal  101  in the optical axis direction can be 50 μm or smaller, for example. 
     The rear surface  101   b  side of the electro-optic crystal  101  is supported by the transparent substrate  713  through which the modulation light L 2  is transmitted. For example, the transparent substrate  713  is formed of a material such as glass, quartz, or plastic in a flat plate shape. The transparent substrate  713  has an output surface (second surface)  713   b  outputting the modulation light L 2  and an input surface (first surface)  713   a  serving as a surface on a side opposite to the output surface  713   b  and facing the light output unit  606  formed on the electro-optic crystal  101 . A transparent electrode  715  formed of ITO, for example, is formed on the input surface  713   a  of the transparent substrate  713 . The transparent electrode  715  is formed on the whole surface of the input surface  713   a . The transparent electrode  715  can be formed by performing vapor deposition of ITO on the input surface  713   a  of the transparent substrate  713 . 
     The transparent connection electrode  608  formed in the electro-optic crystal  101  and the transparent electrode  715  formed on the transparent substrate  713  are adhered to each other by a transparent adhesive layer  717 . For example, the transparent adhesive layer  717  is formed of an epoxy-based adhesive, and the modulation light L 2  is transmitted therethrough. For example, conductive members  717   a  such as metal spheres are disposed inside the transparent adhesive layer  717 . The conductive members  717   a  come into contact with both the transparent connection electrode  608  and the transparent electrode  715  and electrically connect the transparent connection electrode  608  and the transparent electrode  715  to each other. For example, the conductive members  717   a  are disposed at four corners of the transparent adhesive layer  717  in a plan view. 
     In the present embodiment, the input surface  713   a  side of the transparent substrate  713  is formed to have a larger size than the rear surface  101   b  of the electro-optic crystal  101  in a plan view. For this reason, in a state in which the electro-optic crystal  101  is supported by the transparent substrate  713 , a part of the transparent electrode  715  formed on the transparent substrate  713  becomes an exposed portion  715   a  exposed to the outside. The drive circuit  110  is electrically connected to this exposed portion  715   a  and the transparent connection electrode  604 . That is, the drive circuit  110  is electrically connected to the transparent electrode  107  via the transparent electrode  715 , the conductive members  717   a , and the transparent connection electrode  608  and is electrically connected to the transparent electrode  103  via the transparent connection electrode  604 . Accordingly, the drive circuit  110  can apply an electric field between the transparent electrode  103  and the transparent electrode  107 . 
     In such a light modulator  700 , 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, since the electro-optic crystal  101  is supported by the transparent substrate  713 , the electro-optic crystal  101  is protected from an external impact or the like. 
     Eighth Embodiment 
     A light modulator  800  according to the present embodiment differs from the light modulator  100  of the first embodiment in being a reflective light modulator. When a reflective light modulator is used, it is possible to use an optical element such as a beam splitter which optically guides the input light L 1  to the light modulator and optically guides the modulation light L 2  modulated by the light modulator to the first optical system  14 . Hereinafter, 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 view schematically showing the light modulator  800 . The light modulator  800  is a reflective light modulator modulating the input light L 1  and outputting the modulated modulation light L 2 . As shown in  FIG. 10 , the light modulator  800  includes the electro-optic crystal  101 , a light input/output unit (first optical element)  802 , a light reflection unit (second optical element)  806 , and the drive circuit  110 . In  FIG. 10 , the electro-optic crystal  101 , the light input/output unit  802 , and the light reflection unit  806  of the light modulator  800  are shown in a cross section. In the present embodiment, the thickness of the electro-optic crystal  101  in the optical axis direction can be 50 μm or smaller, for example. 
     The rear surface  101   b  side of the electro-optic crystal  101  is supported by a substrate  813 . The substrate  813  is formed to have a flat plate shape. The substrate  813  has a first surface  813   a  facing the light reflection unit  806  bonded to the electro-optic crystal  101 , and a second surface  813   b  serving as a surface on a side opposite to the first surface  813   a . An electrode  815  is formed on the first surface  813   a  of the substrate  813 . The electrode  815  is formed on the whole surface of the first surface  813   a.    
     The light input/output unit  802  includes a transparent electrode (first electrode)  803 , the charge injection curbing layer  121 , the intermediate layer  620 , the connection electrode (third electrode)  104 , the insulation unit  105 , and the light reduction layer  205 . The transparent electrode  803  is disposed on the input surface  101   a  side of the electro-optic crystal  101 . The transparent electrode  803  is formed of ITO, for example, and the input light L 1  is transmitted therethrough. That is, the input light L 1  is transmitted through the transparent electrode  803  and is input to the inside of the electro-optic crystal  101 . In the present embodiment, the transparent electrode  803  is formed at a place at the center on the input surface  101   a  side and partially covers the input surface  101   a . The area (μm 2 ) of the transparent electrode  803  may be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (pin). For example, the transparent electrode  803  exhibits a rectangular shape in a plan view. That is, the transparent electrode  803  is distanced from the circumferential edge on the input surface  101   a . For example, such a transparent electrode  803  can be formed by performing vapor deposition of ITO on the input surface  101   a  of the electro-optic crystal  101  using a mask pattern. 
     The charge injection curbing layer  121  is formed between the transparent electrode  803  and the input surface  101   a . For example, the charge injection curbing layer  121  has the same size as the transparent electrode  803  and exhibits a rectangular shape in a plan view. 
     The light reflection unit  806  includes a transparent electrode (second electrode)  807 , the charge injection curbing layer  123 , the intermediate layer  622 , the connection electrode (fourth electrode)  108 , the insulation unit  109 , and a dielectric multilayer film  809 . The transparent electrode  807  is disposed on the rear surface  101   b  side of the electro-optic crystal  101 . In the present embodiment, the transparent electrode  807  is formed at a place at the center on the rear surface  101   b  side and partially covers the rear surface  101   b . The area (μm 2 ) of the transparent electrode  807  may be 25d 2  or smaller when the thickness of the electro-optic crystal  101  in the electric field applying direction is d (unit of μm). For example, the transparent electrode  807  exhibits a rectangular shape in a plan view. That is, the transparent electrode  807  is distanced from the circumferential edge on the rear surface  101   b . Similar to the transparent electrode  803 , the transparent electrode  807  is formed of ITO, for example, and the input light L 1  is transmitted therethrough. That is, the input light L 1  which has been input to the inside of the electro-optic crystal  101  and subjected to phase modulation or retardation modulation can be transmitted through the transparent electrode  807  as the modulation light L 2 . In the present embodiment, the dielectric multilayer film  809  capable of efficiently reflecting light is provided on the front surface of the connection electrode  108  which is provided in the transparent electrode  807 . In this case, the connection electrode  108  is a transparent electrode. The connection electrode  108  and the dielectric multilayer film  809  reflect the modulation light L 2  transmitted through the transparent electrode  807  toward the transparent electrode  803  formed on the input surface  101   a . For example, the dielectric multilayer film  809  can be formed by performing vapor deposition of a material such as a substance (Ta 2 O 5 ) having a high refractive index or a substance (SiO 2 ) having a low refractive index on the front surface of the transparent electrode  807 . In addition, the connection electrode  108  can also serve as a reflection electrode so as to reflect the modulation light L 2 . In this case, the dielectric multilayer film  809  is not necessary. 
     The charge injection curbing layer  123  is formed between the transparent electrode  807  and the rear surface  101   b . For example, the charge injection curbing layer  123  has the same size as the transparent electrode  807  and exhibits a rectangular shape in a plan view. 
     The connection electrode  108  formed in the electro-optic crystal  101  and the electrode  815  formed on the substrate  813  are adhered to each other by an adhesive layer  817 . For example, the adhesive layer  817  is formed of an epoxy-based adhesive. For example, conductive members  817   a  such as metal spheres are disposed inside the adhesive layer  817 . The conductive members  817   a  come into contact with both the connection electrode  108  and the electrode  815  and electrically connect the connection electrode  108  and the electrode  815  to each other. For example, the conductive members  817   a  are disposed at four corners of the adhesive layer  817  in a plan view. In addition, the electrode  815  has an exposed portion  815   a  which is a part thereof exposed to the outside. The drive circuit  110  is electrically connected to this exposed portion  815   a  and the connection electrode  104 . 
     In addition, when viewed in the optical axis direction, the area of the transparent electrode  807  is formed to be smaller than the transparent electrode  803 . Further, the center of the transparent electrode  807  and the center of the transparent electrode  803  substantially coincide with each other in the optical axis direction. In this case, for example, even when the input light L 1  is inclined with respect to the reflection surface of the dielectric multilayer film  809 , the reflected modulation light L 2  easily passes through the transparent electrode  803 . In addition, as shown in  FIG. 10 , even when a beam waist is set to the reflection surface of the dielectric multilayer film  809 , the input light L 1  and the modulation light L 2  easily pass through the transparent electrode  803 . In addition, in the present embodiment, since the electro-optic crystal  101  is supported by the substrate  813 , the electro-optic crystal  101  is protected from an external impact or the like, similar to the seventh embodiment. 
     Ninth Embodiment 
     A light modulator  900  according to the present embodiment differs from the light modulator  100  of the first embodiment in having a light output unit  906  instead of the light output unit  106 . Hereinafter, 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. 11  is a view schematically showing the light modulator  900 . The light modulator  900  includes the electro-optic crystal  101 , the light input unit  102 , the light output unit  906 , and the drive circuit  110 . In  FIG. 11( a ) , the electro-optic crystal  101 , the light input unit  102 , and the light output unit  906  of the light modulator  900  are shown in a cross section. In addition,  FIG. 11( b )  is a view of the light modulator  900  viewed from the light input unit  102  side, and  FIG. 11( c )  is a view of the light modulator  900  viewed from the light output unit  906  side. 
     The light output unit  906  includes the transparent electrode  107 , the charge injection curbing layer  123 , a connection electrode  908 , an intermediate layer  922 , and an insulation unit  909 . Similar to the connection electrode  108  in the first embodiment, the connection electrode  908  is connected to the transparent electrode  107  and the drive circuit  110 . Similar to the intermediate layer  122  in the first embodiment, the intermediate layer  922  is disposed on the rear surface  101   b . Similar to the insulation unit  109  in the first embodiment, the insulation unit  909  is formed on the intermediate layer  922  and is disposed between the intermediate layer  922  and the connection electrode  908 . 
     Positions where the connection electrode  104 , the insulation unit  105 , and the intermediate layer  120  are disposed on the input surface  101   a  and positions where the connection electrode  908 , the insulation unit  909 , and the intermediate layer  122  are disposed on the rear surface  101   b  are in directions opposite to each other with respect to the transparent electrode  103  and the transparent electrode  107  when viewed in a direction along the optical axis. For this reason, the connection electrode  104 , the insulation unit  105 , and the intermediate layer  120 ; and the connection electrode  908 , the insulation unit  909 , and the intermediate layer  122  are displaced from each other when viewed in a direction along the optical axis and are disposed not to overlap each other with the electro-optic crystal  101  interposed therebetween. According to such a light modulator  900 , effects of the insulation unit can be further enhanced. The insulation units  105  and  909  are not necessarily essential. 
     Tenth Embodiment 
     A light modulator  1000  according to the present embodiment differs from the light modulator  100  of the first embodiment in further including transparent substrates  125  and  126 . Hereinafter, 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. 12  is a view schematically showing the light modulator  1000 . The light modulator  1000  includes the electro-optic crystal  101 , the light input unit  102 , the light output unit  106 , the drive circuit  110 , the transparent substrate  125 , and the transparent substrate  126 . 
     For example, the transparent substrate  125  is formed of a material such as glass, quartz, or plastic in a flat plate shape. The transparent substrate  125  has an input surface  125   a  to which the input light L 1  is input and an output surface  125   b  serving as a surface on a side opposite to the input surface  125   a  and facing the input surface  101   a  of the electro-optic crystal  101 . The transparent electrode  103  is formed and the connection electrode  104  is formed on the output surface  125   b . The transparent substrate  125  protrudes beyond the end edge of the electro-optic crystal  101  in one direction intersecting the optical axis direction. Accordingly, in the present embodiment, a part of the connection electrode  104  formed on the transparent substrate  125  becomes an exposed portion  104   d  exposed to the outside. The drive circuit  110  is electrically connected to this exposed portion  104   d.    
     For example, the transparent substrate  126  is formed of a material such as glass, quartz, or plastic in a flat plate shape. The transparent substrate  126  has an output surface  126   a  outputting the modulation light L 2  and an input surface  126   b  serving as a surface on a side opposite to the output surface  126   a  and facing the rear surface  101   b  of the electro-optic crystal  101 . The transparent electrode  107  is formed and the connection electrode  108  is formed on the input surface  126   b . The transparent substrate  126  protrudes beyond the end edge of the electro-optic crystal  101  in one direction intersecting the optical axis direction. Accordingly, in the present embodiment, a part of the connection electrode  108  formed on the transparent substrate  126  becomes an exposed portion  108   d  exposed to the outside. The drive circuit  110  is electrically connected to this exposed portion  108   d . That is, the drive circuit  110  is electrically connected to the transparent electrode  103  with the connection electrode  104  therebetween and is electrically connected to the transparent electrode  107  with the connection electrode  108  therebetween. 
     Also in the second embodiment to the tenth embodiment described above, similar to the first embodiment, occurrence of resonance or the like is curbed, and stable light modulation can be performed. 
     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 light modulator has been exemplified, but the embodiments are not limited thereto. For example, the light modulator  100  may be mounted in a light irradiation device  1 B.  FIG. 13  is a block diagram showing a configuration of a light irradiation device. The light irradiation device  1 B has the light source  11 , the concentration lens  12 , the light modulator  100 , the first optical system  14 , and a control unit including the computer  20  and the controller  21 . In this configuration, the first optical system  14  irradiates the specimen S with the modulation light L 2  output from the light modulator  100 . 
     In the first embodiment to the seventh embodiment, the ninth embodiment, and the tenth embodiment described above, usage examples in which the input light L 1  is input from a light input unit and the modulation light L 2  is output from a light output unit have been described, but the embodiments are not limited thereto. For example, the input light L 1  may be input from a light output unit of the light modulator, and the modulation light L 2  may be output from a light input unit. In such a usage method, for example, the transparent electrode  103  corresponds to the second electrode, and the transparent electrode  107  having an area larger than that of the second electrode corresponds to the first electrode. In addition, in this case, for example, in the light modulator  200 , a light reduction unit may be formed in the light output unit  106  on a side to which the input light L 1  is input. 
     In addition, in the eighth embodiment, a configuration in which light is reflected by the dielectric multilayer film  809  formed on the front surface of the transparent electrode  807  has been exemplified, but the embodiment is not limited thereto. For example, an electrode may reflect input light by using an electrode which can reflect light in place of the transparent electrode  807 . For example, input light may be reflected by an electrode formed of aluminum. According to such a configuration, there is no need to separately provide a reflection layer or the like on the second electrode side. 
     In addition, the configurations in the foregoing embodiments may be partially combined or substituted. For example, in the second embodiment to the eighth embodiment, the electro-optic crystal and the like may be subjected to temperature control by the temperature control element P similar to the electro-optic crystal  101  in the first embodiment. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 A Optical observation device 
               1 B Light irradiation device 
               100  Light modulator 
               101  Electro-optic crystal 
               101   a  Input surface 
               101   b  Rear surface 
               102  Light input unit (first optical element) 
               103  Transparent electrode (first electrode) 
               104  Connection electrode (third electrode) 
               105  Insulation unit 
               106  Light output unit (second optical element) 
               107  Transparent electrode (second electrode) 
               110  Drive circuit 
               207  Light reduction unit 
               809  Dielectric multilayer film 
             L 1  Input light 
             L 2  Modulation light 
             P Temperature control element