JPH10239718A - Light control element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light control element reducing the drive voltage to about 10V, and improving the drive speed to 500MHz or above. SOLUTION: In the light control element provided with an optical waveguide 2 consisting of an epitaxial or orientation property ferroelectric thin film with an electro-optical effect, a conductive or semiconductive upper electrode 3 provided being in contact with the optical waveguide 2, a lower part electrode 1 provided opposite to an upper electrode 3 holding the optical waveguide 2 between them and a voltage application means 7 applying a voltage between the upper part electrode 3 and the lower part electrode 1, generating an area having a different diffractive index in the optical waveguide 2 and controlling a light beam made incident on the optical waveguide 2 according to the voltage, a contact electrode 5 connected with the voltage application means 7 and upper part electrode 2 and having the area larger than the upper part electrode 2 is formed on an intermediate insulation layer 4 formed on the optical waveguide 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control device which functions as a waveguide type optical switching element, optical deflection element, or the like formed of a thin film, which is used for coherent optical communication utilizing an electro-optic effect or a laser printer. Related to the element.

[0002]

2. Description of the Related Art Light control elements include those utilizing an acousto-optic effect and those utilizing an electro-optic effect.
The light control element using the electro-optic effect is Pb _1-x La
_x (Zr _1-y Ti _y ) _{1-x / 4} O ₃ (PLZT), LiNb
By applying an electric field to a ferroelectric material such as O ₃ or KNbO ₃ , the refractive index in the optical waveguide is changed. Several such light control elements have been conventionally proposed. For example,
"A. Yariv, OpticalElectroni
cs, 4th ed. (New York, Rine
Hart and Winston, 1991) pp.
336-339. Discloses a prism type light deflecting element.

[0003] Also, "Q. Chen, et al.,
J. Lightwave Tech. vol. 12 (1
994) pp. 1401 ”and JP-A-62-47627 show a prism-type domain inversion light deflection element and a prism-type electrode light deflection element using a LiNbO ₃ single crystal wafer prepared with a Ti diffusion type optical waveguide or a proton exchange type optical waveguide. Have been. Further, Japanese Patent Application Laid-Open No. 5-134275 discloses a light control element for deflecting coherent light by a pair of prism electrodes forming a predetermined electric field in a partial region of an electro-optic crystal.
No. 3 discloses a light control element that performs polarization separation and switching of light by forming a loaded clad layer and a prismatic electrode on an electro-optic crystal.

[0004]

However, in such a bulk element using ceramic or single crystal, it is difficult to reduce the size of the light control element, and only a device having a considerably high driving voltage can be obtained. Was. In addition, LiN prepared from a Ti diffusion type optical waveguide and a proton exchange type optical waveguide were manufactured.
A prism type domain inversion light deflection element or a prism type electrode light deflection element using a bO ₃ single crystal wafer is made of LiN.
The drive voltage is increased because an electrode interval of about 0.5 mm, which is substantially equal to the thickness of the bO ₃ single crystal wafer, is required. Such a prism type domain inversion light deflecting element or prism type electrode light deflecting element requires a driving voltage of about 600 V in order to obtain a deflection angle of about 0.5 °. There is such a problem.

The present inventors have proposed a method of forming a driving voltage by forming an optical waveguide, which is an epitaxial or oriented ferroelectric thin film having an electro-optical effect, on a lower electrode made of a conductive or semiconductive single crystal substrate. Was found to be able to be reduced to 10 V or less, and was filed as Japanese Patent Application No. 7-176939.

In a light control element utilizing the electro-optic effect,
Compared with the light control element using the acousto-optic effect, there is no limitation due to the movement time of the phonon, so the switching time should be on the order of picoseconds and should be extremely fast. However, in the above-described invention, since the ferroelectric thin film as the optical waveguide is sandwiched between the upper electrode and the lower electrode, the capacitance formed between the upper electrode and the lower electrode is smaller than the area of the upper electrode. It increases proportionally, and the high speed inherent to the light control element utilizing the electro-optic effect is impaired. For this reason, in order to perform ultra-high-speed switching, it is necessary to reduce the capacitance formed between the upper electrode and the lower electrode by reducing the area of the upper electrode. For example, for driving at 500 MHz, the area of the upper electrode is desirably 10 ⁻⁵ cm ² or less.

However, if the area of the upper electrode is set to this order, it becomes difficult to connect the wiring to an external voltage supply circuit by a wire bonding technique. This is because the upper electrode to be wire-bonded must have an area of about 10 ⁻⁴ cm ² in order to connect the wiring to an external voltage supply circuit by the wire bonding technique.

To increase the area for wire bonding, there is a method of providing a contact electrode separately from the upper electrode. The contact electrode is an electrode for directly performing wire bonding, and has a sufficient area for directly performing wire bonding. The contact electrode is electrically connected to an upper electrode for forming an electric field in the optical waveguide that causes an electro-optic effect between the contact electrode and the lower electrode. The contact electrode is typically formed directly on the thin film optical waveguide other than the upper electrode, and applies a voltage supplied from a voltage driving circuit through a bonded wire to the upper electrode. However, if the contact electrode is formed directly on the thin-film optical waveguide, the contact electrode has a relatively large capacitance between the lower electrode and the contact electrode because the area of the contact electrode is larger than the area of the upper electrode. As a result, problems such as a decrease in control speed and a loss of power occur.

An object of the present invention is to provide a light control element in which a drive voltage is reduced and an operation speed is improved.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical waveguide made of an epitaxial or oriented ferroelectric thin film having an electro-optical effect, and a conductive or semiconductive upper portion formed in contact with the optical waveguide. An electrode, and a lower electrode provided opposite to the upper electrode with the optical waveguide interposed therebetween, and applying a voltage between the upper electrode and the lower electrode to generate a region having a different refractive index in the optical waveguide. An optical control element for controlling a light beam in an optical waveguide according to a voltage, wherein an intermediate insulating layer formed on the optical waveguide on the upper electrode side and a contact connected to the upper electrode and formed on the intermediate insulating layer This is achieved by a light control element comprising: an electrode;

As a ferroelectric thin film constituting an optical waveguide,
ABO ₃ type perovskite type oxides include, for example, BaTiO ₃ , Pb as tetragonal, orthorhombic or pseudo-cubic.
_{TiO 3, Pb 1-x La} x (Zr y Ti 1-y) 1-x / 4O 3 (x
PZT, PLT, PLZT), Pb
(Mg _1/3 Nb _2/3 ) O ₃ , KNbO _3, etc., a ferroelectric material represented by a hexagonal system such as LiNbO ₃ , LiTaO _3, etc., and a tungsten bronze type oxide, Sr _x Ba
Preferred are _1-x Nb ₂ O ₆ and Pb _x Ba _1-x Nb ₂ O ₆ .
In addition, Bi ₄ Ti ₃ O ₁₂ , Pb ₂ KNb ₅ O ₁₅ , K ₃
Li ₂ Nb ₅ O ₁₅ and further substituted derivatives thereof can also be applied as a ferroelectric thin film.

[0012] Ferroelectric thin films made of these substances are formed by electron beam evaporation, flash evaporation, ion plating,
Rf-magnetron sputtering, ion beam sputtering, laser ablation, MB
It is produced by a vapor phase growth method selected from E, CVD, plasma CVD, MOCVD and the like, and a solid phase growth method of a thin film produced by a wet process such as a sol-gel method and a MOD method.

Here, the optical waveguide constituted by the ferroelectric thin film has, for example, a prism-shaped polarization domain inversion portion having two sides that are not parallel to each other, and applies a voltage between the upper electrode and the lower electrode. By doing so, different refractive indexes are generated in the polarization domain inversion portion of the prism shape and the other portion. Further, in such an optical waveguide, the upper electrode has a prism-shaped pattern having two sides that are not parallel to each other, and by applying a voltage between the upper electrode and the lower electrode, a portion having a different refractive index corresponding to this electrode pattern is formed. It may be generated.

As a specific material constituting the upper electrode, a metal such as Pt or Al or a transparent oxide such as ITO having a smaller refractive index than the optical waveguide is preferable. When a cladding layer having a smaller refractive index than the optical waveguide is provided between the optical waveguide and the upper electrode, an arbitrary material can be used for the upper electrode. However, from the viewpoint of driving voltage, it is desirable to use a transparent oxide such as ITO.

The lower electrode is preferably formed of a conductive or semiconductive single crystal substrate, or a conductive or semiconductive epitaxial or oriented thin film. As the lower electrode, Nb-doped SrTiO ₃ , Al-doped ZnO, In ₂
O ₃ , RuO ₂ , BaPbO ₃ , SrRuO ₃ , YBa ₂ C
_{u 3 O 7-x, SrVO} 3, LaNiO 3, La 0.5 Sr 0.5 C
An oxide such as oO ₃ is desirable, but Pd, Pt, Al,
Metals such as Au and Ag can also be used. These conductive or semiconductive single-crystal substrates, or conductive or semiconductive epitaxial or oriented thin films,
It is selected according to the crystal structure of the ferroelectric thin film. The resistivity of a conductive or semiconductive thin film or a single crystal substrate used as an upper electrode or a lower electrode is 10 ⁻⁶ Ω.
A range of about cm to about 10 ³ Ωcm is effective, but it can be used as an upper electrode or a lower electrode if the resistivity of the voltage drop is negligible. Depending on the deflection speed or the modulation speed, an upper electrode material or a lower electrode material having an appropriate carrier mobility can be selected.

As the contact electrode, Ti, Cr, M
o, Cu, W, Ni, Ta, Ga, In, Al, Pd,
Metals such as Pt, Au, Ag, Ti-Al, Al-C
It is preferable to use an alloy such as u, TiN, Ni—Cr, or a laminate of these.

The intermediate insulating layer has a relative dielectric constant epsilon _r of less than 10, preferably is suitable as less than 4. Also,
The resistivity ρ of the intermediate insulating layer is preferably at least 10 ¹⁰ Ω · cm. Examples of such a material include organic compounds such as polyimide and polycarbonate, SiO ₂ , Si ₃ N ₄ , A
An inorganic compound such as l ₂ O ₃ can be used. The intermediate insulating layer is preferably transparent to prevent absorption of guided light, but may be opaque. For example, when a polyimide resin is used for the intermediate layer, the microfabrication is excellent when photolithography is used, and the insulation resistance is strong. When an organic compound is used, the intermediate insulating layer is formed by spinner coating, vapor deposition, or CVD, and when an inorganic compound is used, the intermediate insulating layer is formed by vapor deposition, sputtering, CVD, spinner coating, or the like.

The thickness of the intermediate insulating layer is from 0.01 μm to 10
It may be in the range of 0 μm, but preferably 0.1 μm to 10 μm.
μm. By forming such an intermediate insulating layer between the optical waveguide and the contact electrode, the interval between the contact electrode and the lower electrode can be isolated. Therefore,
Even if the area of the contact electrode is increased, the capacitance formed between the lower electrode and the upper electrode is negligibly small compared to the capacitance formed between the upper electrode and the lower electrode. Therefore, according to the present invention, by forming a contact electrode having a large area, an area for wire bonding is ensured, and even if the area of the contact electrode is increased, the capacitance formed between the contact electrode and the lower electrode is increased. Is small, the speed of the device can be increased.

The light source may be a laser that oscillates a single laser beam or a laser array formed on a single substrate that oscillates a plurality of laser beams, and may be a gas laser such as He-Ne. And AlG
A compound semiconductor laser such as aAs or a laser array thereof is used. The oscillated laser light is introduced into the optical waveguide by a method such as prism coupling, butt coupling (or end coupling), grating coupling, and evanescent field coupling.

As a thin film lens, a mode index lens, a Luneburg lens, a geodesic lens, a Fresnel lens, a grating lens and the like are suitable. Emission means include end face emission, prism
Suitable are couplers, grating couplers, focusing couplers, SAW grating couplers, and the like. By using such a configuration, it is possible to easily realize wire bonding to a light control element that can be driven at high speed without loss of power.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A light control device according to a first embodiment of the present invention will be described with reference to FIGS. The light control element according to the present embodiment is an optical deflection element that deflects a laser beam incident on a thin film waveguide within a predetermined angle range. FIG. 1 is a cross-sectional view of an optical deflecting element according to the present embodiment.
FIG. 2 shows a top view. Here, FIG.
It is sectional drawing in A 'cross section.

As shown in FIGS. 1 and 2, the optical deflection element according to the present embodiment has a resistivity of 5 mΩ · cm to 500 mΩ.
Cm of Nb-doped SrTiO ₃ (100) single-crystal conductive substrate 1 onto epitaxial PLZT (12/4
0/60) The thin film optical waveguide 2 is grown. This PLZT
The layer has a thickness d _w = 600 nm, ε _w = 1300, r =
It has a characteristic of 120 × 10 ⁻¹² m / V. PLZT
The layer is formed by solid phase epitaxial growth using a sol-gel method.

First, anhydrous lead acetate Pb (CH ₃ COO) ₂ ,
Lanthanum isopropoxide La (OiC
₃ H ₇ ) ₃ , zirconium isopropoxide Zr (O-
_{i-C 3 H 7) 4} , and titanium isopropoxide Ti
(OiC ₃ H ₇ ) ₄ was used as a starting material, dissolved in 2-methoxyethanol, distilled for 6 hours, refluxed for 18 hours, and finally reached a PLB concentration of 0.6 M PLZ.
A precursor solution for T (12/40/60) is obtained. further,
This precursor solution is spin-coated on a substrate. All of the above operations are performed in an N ₂ atmosphere.

Next, in a humidified O ₂ atmosphere at 10 ° C./sec.
After the temperature was raised at c and maintained at 350 ° C., the temperature was maintained at 650 ° C. Finally, the power of the electric furnace was turned off and cooled. Thus, a first-layer PLZT thin film having a thickness of about 100 nm is formed by solid phase epitaxial growth. By repeating this process five more times, an epitaxial PLZT thin film having a total thickness of 600 nm can be obtained. This epitaxial P
The crystallographic relationship of the LZT thin film is PLZT (100) // N
b-SrTiO ₃ (100) and the in-plane orientation is PLZ
T [001] // Nb-SrTiO ₃ [001].

An upper electrode formed by stacking 40 triangles having a bottom of 25 μm and a height of 6.8 μm made of an ITO transparent conductive oxide thin film having a resistivity of about 1 mΩ · cm and a thickness of about 100 nm on the PLZT thin film optical waveguide. The electrode array 3 is manufactured. An intermediate insulating layer 4 made of polyimide and having a thickness of 500 nm is formed on the electrode array 3, and a contact hole is formed on the electrode array 3 by a photolithography process. Next, a conductive layer is formed on the entire surface including the contact hole by CV.
After the deposition by the method D, the plug 30 is formed by etching back and leaving the conductive layer only in the contact hole. The plug 30 is typically W. Next, the contact electrode 5 that contacts the plug 30 is formed on the intermediate insulating layer 4. The contact electrode 5 is composed of a composite layer, and the first layer is T
i, and the upper portion is covered with Au or Pt having an area of 4 × 10 ⁻⁸ m ² . An Au wire is bonded on the contact electrode 5 to connect the contact electrode 5 to the voltage driving circuit 7 together with the opposite electrode 6 made of In formed on the back surface of the substrate.

After collimating the laser beam 8 to a width of 2 mm using a laser diode having a wavelength of 780 nm and an output of 20 mW as a light source, the PLZT thin-film optical waveguide 2 is formed.
It is introduced by a hemi-grating 9. Since the PLZT thin film optical waveguide 2 has a higher refractive index than the ITO transparent conductive oxide thin film and the Nb-doped SrTiO ₃ (100) single crystal substrate 1, the laser beam is confined in the PLZT thin film optical waveguide 2. The incident laser beam is ITO
It is deflected by applying a voltage between the thin film triangular electrode array 3 and the Nb-doped SrTiO ₃ single crystal electrode 1. Then, the deflected laser beam is emitted from the end face 10. The laser beam emitted by controlling the deflection can be applied to, for example, exposing a photosensitive member through an optical system such as an F / θ lens.

Here, the laser polarization using the electro-optic effect is considered.
The direction angle θ is r for electro-optic constant, V for applied voltage,
The film thickness of the path is d and the refractive index is n₀, The length of the prism electrode
l and height D, θ = 1 / 2D · rn₀ ^Three(V / d) (1) In the case of the present embodiment, the deflection angle is
When the degree is calculated, the deflection angle θ is 1.2 at an applied voltage of 1 V.
7 mrad. In addition, the area is 3.4 × 10^-9m ^TwoNo electricity
Capacitance by pole array 3 is 15pF, area 4 × 10^-8m^Two
Of the contact electrode 5 is 0.52 pF,
The capacitance of the contact electrode 5 can be almost ignored. These contents
The limit operation speed calculated from the quantity value is 650 MHz.
Therefore, high-speed modulation is possible. Meanwhile, the contact electrode
5 has a sufficiently large area so that the wire
Bonding can be performed.

Next, a light control element according to a second embodiment of the present invention will be described with reference to FIGS. The light control element according to the present embodiment is also a light deflecting element as in the first embodiment. FIG. 3 is a sectional view of the light deflecting element, and FIG. 4 is a top view thereof. The optical deflecting element according to the present embodiment is different from the optical deflecting element according to the first embodiment in that the materials of the single crystal substrate and the intermediate insulating layer are different, the optical waveguide is an oriented thin film, There is a difference in that a prism is used as the introducing means.

In this embodiment, as shown in FIGS. 3 and 4, a sapphire (0001) single crystal substrate 1 having an insulating property is used.
9 on which (0001) highly-oriented Al-doped Z having a resistivity of about 1 mΩ · cm by Rf magnetron sputtering.
An nO conductive thin film 20 is grown, and (00)
01) A highly oriented LiNbO ₃ thin film optical waveguide 21 was grown. On the LiNbO ₃ thin film optical waveguide 21, an upper electrode is formed by chaining 100 triangles having a base of 10 μm and a height of 6.8 μm of an ITO transparent conductive oxide thin film having a resistivity of about 1 mΩ · cm and a film thickness of about 100 nm. Electrode array 22
Is prepared. The CVD is performed on the triangular electrode array 22.
An intermediate insulating layer 23 made of SiOx and having a thickness of 1 μm is formed by a method, and a contact hole is formed by a photolithography process.

Next, a conductive plug 31 is formed in the contact hole by reflow sputtering. In the present embodiment, the material of the plug is Al. Then, Au or P having a size of 200 μm × 100 μm is
The t contact electrode 24 is formed. As a result, the contact electrode 24 is connected to the electrode array 22 via the plug 31. An Au wire is bonded on the contact electrode 24 and connected to the voltage driving circuit 26. On the other hand, the opposite electrode 25 is formed on the Al-doped ZnO conductive thin film 20 exposed by partially etching the LiNbO ₃ thin film 21. The opposite electrode 25 is connected to the voltage driving circuit 26 together with the contact electrode 24.

As a light source for the laser beam incident on the LiNbO3 thin film optical waveguide 21, a wavelength of 780 nm and an output of 2
0mW dual spot laser diode
Use an array. Two generated laser beams 2
7 is collimated to a width of 2 mm and introduced into the LiNbO ₃ thin film optical waveguide 21 via the prism 28. LiNb
Since the O ₃ thin film optical waveguide 21 has a higher refractive index than the ITO transparent conductive oxide thin film and the Al-doped ZnO conductive thin film 20, the laser beam is confined in the LiNbO ₃ thin film optical waveguide 21. The incident laser beam is deflected by applying a voltage between the prism-shaped ITO electrode array 22 and the Al-doped ZnO electrode 20 to generate different refractive indexes in the prism portion and other portions. The two deflected laser beams are emitted through the prism 29.

In the light deflecting element according to the present embodiment,
Using Expression (1), the deflection angle θ is 6.78 mrad at an applied voltage of 0.5 V. The capacitance of the electrode array 22 having an area of 3.4 × 10 ⁻⁹ m ² is 15 pF and the area is 2 × 10 ⁻⁸ m.
^The capacitance of the ^second contact electrode 24 is 0.81 pF, and the capacitance of the contact electrode 24 can be ignored. Since the area of the contact electrode 24 is sufficiently large, wire bonding can be facilitated. Also, the contact electrode 2
4 has a sufficiently small capacity, and a critical operating speed of 700
A good high-speed operation of MHz can be realized.

Next, a light deflecting element as a comparative example to the light deflecting elements according to the first and second embodiments will be described with reference to a sectional view of FIG. 5 and a top view of FIG. This comparative example employs the same material and the light introducing method as the optical deflecting element according to the first embodiment, but the contact electrode 14 is formed directly on the optical waveguide 12 together with the electrode array 13. The difference is that there is no insulating layer.

As in the first embodiment, Nb-doped Sr
Thickness d _w = solid phase epitaxial growth on TiO ₃ (100) single crystal conductive substrate 11 by sol-gel method
600 nm, ε _w = 1300, r = 120 × 10−12
m / V epitaxial PLZT (12/40/60)
A thin film optical waveguide 12 is grown. On this PLZT thin-film optical waveguide, the resistivity is about 1 mΩ · cm, and the film thickness is about 100 n.
25 μm of ITO transparent conductive oxide thin film
m, an electrode array 13 in which forty triangles having a height of 6.8 μm are arranged and a contact electrode 14 of 200 μm × 200 μm.
Is prepared. An Au wire is bonded on the contact electrode 14 and connected to the voltage drive circuit 16 together with the opposite electrode 15 made of In formed on the back surface of the substrate. Wavelength 78
A laser beam 17 is collimated to a width of 2 mm using a laser diode of 0 nm and output of 20 mW as a light source, and then introduced into the PLZT thin film optical waveguide 12 through a grating 18.

In the case of this comparative example, the area is 3.4 × 10 ⁻⁹ m ^2.
The capacitance of the electrode array 13 is 15 pF and the area is 4 × 10
^The capacitance of the contact electrode 14 of ^-8 m ² is 177 pF. The reason why the capacitance due to the contact electrode is extremely large as compared with the above embodiment of the present invention is that the contact electrode is formed directly on the optical waveguide 12. And
The calculated limit operation speed becomes 10 MHz, and operation at high speed becomes impossible.

[0036]

As described above, according to the present invention, by providing the intermediate insulating layer interposed between the optical waveguide and the contact electrode, it is possible to prevent a large capacitance from being formed by the contact electrode having a large area. The limit operation speed of the light control element can be greatly improved. In addition, by providing an intermediate insulating layer interposed between the optical waveguide and the contact electrode, a contact electrode having a large area can be formed without lowering the limit operation speed of the light control element, and the bonding operation can be facilitated. it can. Therefore, according to the present invention, in the thin film waveguide type light control element, the driving voltage is reduced to about 10 V, and
The driving speed can be increased to 500 MHz or more.

Further, according to the present invention, it is possible to provide a light control element which solves the problems of the drive voltage and the operation speed, so that the size, cost, efficiency, speed, noise, etc. can be reduced. Provides laser beam deflecting elements that can be used in laser printers, digital copiers, and facsimile machines that can operate, and optical deflecting elements that cover a wide range of optoelectronics, including optical disc pickups and optical switches for optical communications and optical computers. It is possible to do.

[0038]

[Brief description of the drawings]

FIG. 1 is a sectional view of a light control element according to a first embodiment of the present invention.

FIG. 2 is a top view of the light control element according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a light control element according to a second embodiment of the present invention.

FIG. 4 is a top view of a light control element according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view of a light control element according to a comparative example.

FIG. 6 is a top view of a light control element according to a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 11 Conductive single crystal substrate 2, 12, 21 Thin film optical waveguide 3, 13, 22 Electrode array 4, 23 Intermediate insulating layer 5, 14, 24 Contact electrode 6, 15 Opposite electrode 7, 16, 26 Voltage drive circuit 8 , 17, 27 Laser beam 9, 18 Grating 19 Insulating single crystal substrate 20 Conductive thin film 28, 29 Prism 30, 31 Plug

Claims (6)

[Claims] 1. An optical waveguide comprising an epitaxial or oriented ferroelectric thin film having an electro-optical effect, a conductive or semiconductive upper electrode formed in contact with the optical waveguide, and A lower electrode provided so as to face the upper electrode, and applying a voltage between the upper electrode and the lower electrode to generate a region having a different refractive index in the optical waveguide; In a light control element that controls a light beam in an optical waveguide according to the voltage, an intermediate insulating layer formed on the optical waveguide on the upper electrode side, connected to the upper electrode, and on the intermediate insulating layer A light control element comprising: a formed contact electrode. 2. The light control element according to claim 1, wherein said upper electrode is an oxide having a refractive index smaller than said optical waveguide. 3. The light control device according to claim 1, wherein a cladding layer having a smaller refractive index than said optical waveguide is formed between said optical waveguide and said upper electrode. element. 4. The light control element according to claim 1, wherein the lower electrode is a conductive or semiconductive single crystal substrate;
Alternatively, the light control element is the conductive or semiconductive epitaxial or oriented thin film, and is an oxide having a smaller refractive index than the optical waveguide. 5. The light control element according to claim 1, wherein the dielectric constant of the intermediate insulating layer is less than 10. 6. The light control element according to claim 1, wherein the resistivity of the intermediate insulating layer is 10 ¹⁰ Ω · cm or more.