JPH06160788A - Optical modulator - Google Patents

Abstract

PURPOSE:To provide the optical modulator which is low in driving voltage and is small in light insertion loss. CONSTITUTION:An optical waveguide forming substrate 1 formed with optical waveguides 2 having an electrooptical effect and an electrode forming substrate 3 formed with a film-like superconducting electrode 4 consisting of an oxide superconductor are so fixed in proximity that the optical waveguides 2 and the electrode 4 face each other. The distance between the optical waveguides 2 and the oxide superconducting electrode 4 is set at <=20mum. The surface of the optical waveguides 2 in proximity to the oxide superconducting electrode 4 is so formed as to come into contact with a material having the light refractive index lower than the light refractive index of the optical waveguides 2 or atm. layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external optical modulator in optical communication, and more particularly to an optical modulator having a modulation electrode composed of an oxide superconductor.

[0002]

2. Description of the Related Art With the increase in transmission speed and the increase in capacity of optical communication systems, it is necessary to increase the frequency of optical modulation, and high-frequency optical modulation methods have been studied. This method is roughly classified into a direct modulation method using a semiconductor laser and LiNbO.
₃ (hereinafter LN) can be classified into an external modulation method by an optical modulator using an electro-optic crystal. The direct modulation method using a semiconductor laser modulates the oscillating laser light itself with high frequency,
It is a method of extracting modulated laser light, and its frequency limit has been extended to ten and several GHz at present, but there is an unavoidable problem of frequency chirping. Frequency chirping is a phenomenon in which the frequency spreads during intensity modulation, and is particularly problematic in the high frequency range. Therefore, an external modulation method without frequency chirping is being reviewed. For the prior art in this field, for example, O plus
E, July 1991, p. 104, etc.

Conventionally, in a typical LN optical modulator used in an external modulation method, when performing modulation using a high frequency for speeding up and large capacity, new problems cannot be avoided. It was It is the modulation efficiency (degree of modulation)
Is low, the propagation loss is large, and a large modulation power (modulator driving voltage) is required. In particular, the latter problem is a major obstacle to the construction of an optical communication system because a high voltage control element for driving must be newly developed and the reliability of the high voltage control system is low. However, in the optical modulators reported to date, the reduction of the driving voltage and the improvement of the modulation efficiency that have been realized have not yet reached a satisfactory level. That is, further reduction of the driving voltage and high modulation efficiency are required in order to put the optical modulator using the external modulation method into practical use and popularization.

Therefore, it is necessary to reduce the surface resistance of the optical modulator electrode to suppress high frequency propagation loss. Therefore, the present inventors have previously proposed an optical modulator in which a superconducting film is formed on an electro-optic crystal as a modulation electrode. FIG. 7 is a sectional view showing a conventional optical modulator. In the figure, 1 is an optical waveguide forming substrate, 2 is an optical waveguide formed on the optical waveguide forming substrate 1, 4 is an electrode, and an electro-optical effect is obtained by a film forming method such as a vapor deposition method, a sputtering method or a chemical vapor deposition method. It is an oxide superconducting film formed on the substrate 1 on which the optical waveguide 2 having is formed.

[0005]

In a conventional optical modulator, a substrate 1 on which an optical waveguide 2 having an electro-optical effect is formed is formed by a film forming method such as a vapor deposition method, a sputtering method or a chemical vapor deposition method. Even if the oxide superconducting film 4 is formed, the expected performance improvement in light modulation may not be obtained. The possible causes are as follows. That is, in any of the above thin film forming methods, the substrate temperature is set to 500 to 9 during film formation.
Since it is held at a high temperature of 00 ° C. for several hours, the elements in the optical waveguide 2 are evaporated or react with the elements in the superconducting film 4. For this reason, it was confirmed using an optical intensity measuring instrument and an infrared camera that the optical propagation loss of the optical waveguide 2 was increased and the number of propagation modes was changed.

The present invention has been made in order to solve the above problems, and it is possible to obtain an optical modulator which can be driven at a low voltage and has a small optical insertion loss by using a superconducting conductive electrode having a low propagation loss of high frequency. It is an object.

[0007]

According to a first aspect of the present invention, there is provided an optical modulator comprising: an optical waveguide forming substrate on which an optical waveguide having an electro-optic effect is formed; and an electrode forming substrate on which an oxide superconducting electrode is formed. The optical waveguide forming substrate and the electrode forming substrate are fixed in close proximity so that the surface on which the optical waveguide is formed and the surface on which the electrode is formed face each other.

The optical modulator according to the invention of claim 2 is
In addition to the invention of claim 1, the distance between the optical waveguide and the oxide superconducting electrode is fixed in close proximity to 20 μm or less.

The optical modulator according to the invention of claim 3 is
In addition to the first aspect of the invention, the surface of the optical waveguide adjacent to the oxide superconducting electrode is in contact with a substance having a lower photorefractive index than the optical waveguide or the atmosphere layer.

[0010]

In the optical modulator configured as described above, the optical waveguide can be manufactured without passing through the high temperature process of 500 ° C. or higher required for forming the high temperature superconducting thin film, so that the optical loss hardly increases. In addition, since a single crystal substrate such as MgO suitable for epitaxial growth of a high temperature superconductor can be used as the superconducting substrate, the superconducting characteristics are improved and the surface resistance is lowered compared with the case of forming the substrate on the conventional LN substrate. improves.

In addition to this, since the distance between the optical waveguide and the oxide superconducting electrode is close to 20 μm or less, the electric field generated by the electrode becomes as high as possible.

Furthermore, since the surface of the optical waveguide adjacent to the oxide superconducting electrode is in contact with a substance having a lower photorefractive index than the optical waveguide or the atmospheric layer, the optical insertion loss is suppressed to a small value.

[0013]

【Example】

Example 1. 1 is a sectional view showing an optical modulator according to Embodiment 1 of the present invention. In the figure, 1 is an optical waveguide forming substrate, 2 is an optical waveguide formed on the optical waveguide forming substrate 1, 3 is an electrode forming substrate, 4 is an electrode formed on the electrode forming substrate 3, 5
Is an adhesive layer, for example, an ultraviolet curable resin. Also, FIG.
[Fig. 3] is a plan view showing an electrode shape according to the first embodiment, showing a shape from above. In the figure, 8 is a modulation signal input unit, and 9 is a modulation signal terminating unit. FIG. 3 is a plan view of the optical modulator according to the first embodiment seen through from above. In the figure, 6 is an optical input unit and 7 is an optical output unit.

X as an optical waveguide 2 having an electro-optical effect
A cut-and-y-propagating Ti diffusion LN waveguide was prepared and used. In this preparation, first, on one surface of the optical waveguide forming substrate 1 made of LN crystal whose both surfaces are optically polished, a width of 6 μm and a film thickness of 50 n are formed.
After the Ti thin film of m was formed by the electron beam evaporation method and the lift-off method, it was heat-treated in an argon atmosphere at 1050 ° C. for 10 hours to diffuse Ti into LN. As shown in the top view of FIG. 3, the optical waveguide 2 has a length of 20 mm and a width of 40 mm.
A μm Mach-Zehnder interference portion 2a is provided.

A MgO single crystal was used for the superconducting electrode forming substrate 3. In the superconducting electrode 4, first, a Y—Ba—Cu—O-based superconducting thin film having a metal element ratio of Y, Ba, and Cu of about 1: 2: 3.
The film was formed by the reactive vapor deposition method so as to have the following structure and then processed into the electrode shape by the wet etching method using dilute nitric acid. Here, for the superconducting thin film, a partially ozoned oxygen gas is introduced from the nozzle near the substrate, and the substrate temperature is set to 700.
The film was formed under the conditions of ℃, vapor deposition rate of 4 nm / min and film thickness of 0.5 μm. The electrode shape is center line width 30μ as shown in Fig.2.
A traveling wave electrode of a coplanar type having a gap width of about 40 m to about 110 m was used. In order to achieve impedance matching with the modulation power source, the size of the gap width was adjusted according to each structure of the optical modulator described below. The LN substrate 1 had a width of 6 mm and a length of 40 mm, and the MgO substrate 3 had a width of 10 mm and a length of 20 mm. Since the substrates 1 and 3 having different widths and lengths are used as described above, the optical waveguide 2 and the light input portion 6 of the electrode 4 can be formed by adhering the substrates in the arrangement as shown in FIG.
Since there is a portion that cannot be bonded to the light output portion 7, connection between the electrode 4 and the connector and connection between the optical waveguide 2 and the optical fiber become easy.

The optical waveguide forming substrate 1 and the electrode forming substrate 3 are
Bonding was performed as follows using a mask aligner and an ultraviolet curable resin. First, the optical waveguide forming substrate 1 is bonded to the lower side of the plain glass mask with an organic material. At this time, a transparent organic material that is softened at about 70 ° C. is used, and the organic waveguide is bonded so that the optical waveguide 2 side faces downward. Next, the electrode forming substrate 3 on which the ultraviolet curable resin has been dropped is placed on the substrate stage of the mask aligner with the electrode 4 side facing up. The ultraviolet curable resin used here has a photorefractive index of 1.5 to 1.7, and
The refractive index of the diffused LN optical waveguide is smaller than about 2.3.
Since the optical waveguide forming substrate 1 is double-sided optical polished, the optical waveguide 2 and the electrode 4 can be aligned with each other by using an optical microscope of a mask aligner. As shown in FIG. 3, the two substrates 1 and 3 are brought into close contact with each other so that the center line of the superconducting electrode 4 is sandwiched along the Mach-Zehnder interference portion 2a of the optical waveguide 2, and ultraviolet rays are irradiated to cure and bond the resin. The thickness of the ultraviolet curable resin 5 sandwiched between the two substrates 1 and 3 thus bonded together is 2 μm as a result of observing the cross section with an electron microscope.
It was about. Optical fibers were connected to the optical input section 6 and the optical output section 7 on the end face of the optical waveguide 2 of this optical modulator, and connectors were connected to the modulated signal input section 8 and the modulated signal terminal section 9.

As a comparative example, a modulator having exactly the same structure as the above modulator (hereinafter A) and using Al as an electrode material (hereinafter B) was prepared. Further, an optical modulator in which the electrode 4 is directly formed on the LN substrate 1 having the conventional structure as shown in FIG. 7 and using a YBCO superconducting film as the electrode 4 (hereinafter, C).
And, the one using the Al electrode (hereinafter, D) was also prepared. The B and D Al electrodes were formed by processing a high-vacuum-deposited Al film with a thickness of 3 μm by a lithographic process without heating the substrate. The electrodes were all coplanar transmission line type as shown in FIG.

The above optical modulators A to D were cooled to the temperature of liquid nitrogen, and the half-wave voltage and the shape of the modulated light output when a rectangular pulse of 100 ps was input as the optical insertion loss were measured. The results are shown in Table 1 and FIG. A semiconductor laser having a wavelength of 1.3 μm was used as a light source, and a polarizer was used on the output side to detect only TE mode guided light. Table 1 is A ~
FIG. 4 shows the optical insertion loss (dB) and the half-wave voltage (V) in the D optical modulator. In FIG. 4, the horizontal axis represents time (ps),
It is a graph which shows the characteristic in the optical modulator of AD when the vertical axis is a light intensity (arbitrary unit).

[0019]

[Table 1]

The optical insertion loss of these optical modulators is A, B,
D is almost the same as 6 to 7 dB, while C is 2
It was extremely large at 2 dB or more. It is considered that in C, since the optical waveguide 2 was exposed to the process of forming the YBCO superconducting thin film, deterioration occurred. The half-wave voltage is the first embodiment.
It was found that A was the lowest, and driving at low voltage was possible. Further, as shown in FIG. 4, the waveform of the output modulated light has larger rounding at the rising and falling of Al electrodes B and D, as compared with A and C using the superconducting conductive electrode. This is a result of the effect that the superconducting electrode has smaller propagation loss and smaller frequency dispersion.

In the optical modulator A of this embodiment, the distance between the optical waveguide and the electrode is 2 μm, but the distance is 5 μm.
Optical modulators of 10 μm and 20 μm were also manufactured. These half-wave voltages are 8.1V, 11.2V, 1
It was 6.5V. Therefore, when the distance between the optical waveguide forming substrate 1 and the electrode forming substrate 3 is 20 μm or more, the optical waveguide 2
It was found that, since the electric field from the electrode 4 was extremely small, the light modulation efficiency was significantly reduced. It is considered that the relationship between this interval and the half-wave voltage also depends on the electrode shape.
It was confirmed that the effect of using the low-loss superconducting electrode 4 becomes smaller when the flat electrode exceeds 20 μm.

As described above, in the optical modulator according to this embodiment, the optical waveguide is required for forming the high temperature superconducting thin film.
Since it can be manufactured without going through a high temperature process of 00 ° C. or higher, there is almost no increase in optical loss. Also, MgO suitable for epitaxial growth of high-temperature superconductors on the superconducting substrate
Since a single crystal substrate such as that described above can be used, the superconducting characteristics are improved as compared with the case where it is formed on a conventional LN substrate, and the modulation efficiency is improved due to the effect of reducing the surface resistance.

Example 2. FIG. 5 is a plan view showing an electrode shape according to the second embodiment of the present invention. In this embodiment, as an optical waveguide 2 having an electro-optical effect, x-propagation T is formed on one surface of a z-cut, LN substrate 1 whose both surfaces are optically polished.
An i-diffused LN waveguide was created and used. The optical waveguide was a simple straight line. Further, a 0.5 μm thick MgO film was vapor-deposited on the surface on which the optical waveguide 2 was formed. The electrodes were Er-Ba with a thickness of 0.6 μm on one surface of the MgO substrate 3 which was optically polished.
A -Cu-O (hereinafter EBCO) based superconducting film 4 was formed by a sputtering method, and this was processed into a resonance type superconducting electrode composed of a coplanar transmission line as shown in FIG. The shorting strap portion 10 is made of S having a thickness of 0.3 μm.
It was composed of an iO ₂ film and an Al film with a thickness of 1 μm, and was formed by processing by vapor deposition and the lift-off method.

The optical waveguide forming substrate 1 and the electrode forming substrate 3 are
As in Example 1, the mask aligner and the ultraviolet curable resin 5 were used for adhesion. First, the optical waveguide forming substrate 1 is bonded to the lower side of the plain glass mask with an organic material. As this organic material, a transparent material that softens at about 70 ° C. is used, and the organic waveguide 2 is adhered so that the optical waveguide 2 side faces downward. Next, the electrode forming substrate 3 on which the ultraviolet curable resin 5 having a smaller optical refractive index than the optical waveguide 2 is dropped is placed on the substrate stage of the mask aligner so that the electrodes 4 face upward. The linear optical waveguide 2 is a superconducting resonance electrode 4
The two substrates 1 and 3 are brought into close contact with each other along the edge portion of the center line of, and ultraviolet rays are irradiated to cure the resin to form the adhesive layer 5. Optical fibers were connected to the optical input section 6 and the optical output section 7 on the end face of the optical waveguide 2 of this optical modulator, and a high frequency connector was connected to the modulated signal input section 8 and the modulated signal terminal section 9.

As a comparative example, a modulator having exactly the same structure as the above modulator (hereinafter P) and using Al as the material of the electrode 4 (hereinafter Q) was prepared. Further, an optical modulator in which a buffer layer is formed on the LN substrate 1 having a conventional structure and the electrode 4 is formed thereon, which uses an EBCO superconducting film as an electrode (hereinafter, R) and an Al electrode are used. A thing (hereinafter S) was also created. The R and S buffer layers have the same thickness as P, 0.5
It was a MgO film of μm. The P and R Al electrodes were formed by a method of processing a high-vacuum deposited Al film with a thickness of 3 μm by a lithographic process without heating the substrate. All electrodes were of a resonance type composed of a coplanar transmission line as shown in FIG.

These optical modulators were cooled to the temperature of liquid nitrogen, and the reflection characteristics of the electrodes were evaluated using a network analyzer. Table 2 shows the resonance frequency (GHz), the reflection loss (dB), and the Q value. The resonance frequency was about 10 GHz, but the reflection loss and Q value were P and R using the superconducting electrode compared to Q and S using the Al electrode.
Was a big value. This is A, where the superconducting electrode is normally conductive.
It is considered that the conductor loss at 10 GHz is smaller than that of the 1-electrode. Especially for P, since the MgO substrate suitable for forming superconductivity was used, it is considered that the loss of the electrode portion was extremely small, and the Q value was 480, which was extremely large.

[0027]

[Table 2]

Next, the optical insertion loss (dB) and the optical modulation characteristic were evaluated. The light insertion loss was measured by using a semiconductor laser having a wavelength of 1.3 μm as a light source and comparing the intensities of the input light and the output light with an optical power meter. The light modulation characteristics are
The modulation microwave of the resonance frequency was input from the connector, the modulated light was passed through a Fabry-Perot interferometer having a reflectance of 99%, and the modulation depth was evaluated.
From the result, the modulation power (mW) for changing the phase of πrad was calculated. The results are shown in Table 3. R
Although the buffer layer is formed on the optical waveguide, a small amount of L is left from the optical waveguide during the high temperature superconducting thin film formation process.
Since i ions diffuse into the buffer layer and the superconducting electrode,
The refractive index changed and the optical loss increased to 18.8 dB. On the other hand, it was confirmed that P having the structure of this embodiment can realize a small optical insertion loss and a low modulation power.

[0029]

[Table 3]

Example 3. It was often observed that when the optical waveguide forming substrate 1 and the electrode forming substrate 3 were directly adhered by the ultraviolet curable resin 5, the insertion loss of TM mode light was increased. This tendency was observed especially when the close contact between the optical waveguide 2 and the electrode 4 was enhanced. It is speculated that the cause is that the electric field of the TM mode light in the optical waveguide 2 is scattered in the electrode 4 because the optical waveguide 2 and the electrode 4 are too close to each other.
It is well known that when a substance having a light refractive index larger than that of the optical waveguide 2 or a conductor such as the electrode 4 contacts, the attenuation of the TM mode light increases. Therefore, the optical waveguide forming substrate 1 and the superconducting electrode forming substrate 3 were fixed in close proximity to each other so that a substance having a lower photorefractive index than the optical waveguide 2 or the atmosphere layer was in contact with the surface of the optical waveguide 2.

As a third embodiment, a superconducting electrode 4 and an optical waveguide 2
An optical modulator X in which an atmospheric layer was formed between and an optical modulator Y in which an electrode 4 and an optical waveguide 2 were in close contact with each other were manufactured as a comparative example. 6A and 6B are cross-sectional views showing X and Y.
In the figure, 11 is an atmospheric layer and 12 is a resist. As the superconducting electrode forming substrate 3, MgO is used as in the first embodiment.
A single crystal substrate having YBCO electrodes formed thereon was used.
As the optical waveguide forming substrate 1, as in the second embodiment, z-c
Although one linear Ti diffusion optical waveguide was formed on the LN of ut, the MgO film was not formed on the optical waveguide formation substrate 1 unlike Example 2.

As a procedure for forming the optical modulator X, first, a resist film 12 having a constant film thickness is left on a portion of the optical waveguide forming substrate 1 where the optical waveguide 2 is not formed by a lithography process. Then, the optical waveguide forming substrate 1 and the electrode forming substrate 3 were adhered by the same method as in Example 2. In addition,
The Ti-diffused LN optical waveguide 2 used had a protrusion of about 50 nm with respect to the surface of the LN substrate.
Thickness is about 1.2 μm
And Further, the substrate 1 and the substrate 3 were closely adhered to each other, and the ultraviolet curable resin 5 was made so as not to come into contact with the optical waveguide 2. Also in Comparative Example Y, when the optical waveguide 2 and the electrode 4 were sufficiently adhered, the ultraviolet curable resin 5 was carefully adhered so as not to be sandwiched therebetween.

With respect to the prototyped optical modulator, the same optical insertion loss (dB) as in Example 1 and the modulation voltage (V) using the pulse voltage were evaluated. However, since the phase of the light is modulated, the modulated light was detected through the Fabry-Perot interferometer. The results are shown in Table 4. In each case, the superconducting electrode having a low loss is used in the same manner, so that the voltage for modulating the phase of light by πrad is low. The reason why the value of Y was slightly lower than that of Example X is considered to be that the distance of Y between the electrode 4 and the optical waveguide 2 was smaller and the electric field density of the modulation microwave in the optical waveguide 2 was increased. . However, in Y, since the optical waveguide 2 and the electrode 4 were in close contact with each other, the optical insertion loss became a large value and it was found that there was a problem in practical use. Therefore, as in this embodiment, the atmospheric layer 11 is formed on the optical waveguide 2.
It has been found that the formation of is effective in suppressing the optical insertion loss to a small value.

[0034]

[Table 4]

In the third embodiment, since the resist 12 on the optical waveguide 2 is removed, the atmospheric layer 11 is in contact with the optical waveguide 2. However, even if the resist 12 is not removed, it has been confirmed that the effect is obtained when the optical refractive index of the resist 12 is smaller than that of the optical waveguide 2. Further, it has been confirmed that if the optical refractive index is smaller than that of the optical waveguide 2, good characteristics can be obtained even if an inorganic material is used. That is, if the surface of the optical waveguide 2 adjacent to the oxide superconducting electrode 4 is in contact with a substance having a lower photorefractive index than the optical waveguide 2 or the atmosphere layer, the optical insertion loss can be suppressed to a small value.

Although the above embodiment is a case of a Y-Ba-Cu-O type or Er-Ba-Cu-O type superconducting electrode, another superconducting electrode whose forming process temperature is 500 ° C. or higher, for example, Bi. A -Sr-Ca-Cu-O system or the like may be used, and the same effect as that of the above-mentioned embodiment is exhibited.

Further, among the optical waveguides having an electro-optical effect, those whose optical propagation characteristics are deteriorated by a high temperature process, for example, an organic material having a nonlinear optical effect may be used.
The same effect as that of the above embodiment is exhibited.

Further, the oxide superconducting electrode 4 may have another planar electrode shape such as a strip line or a micro strip as long as a part thereof is close to the optical waveguide 2.
In particular, if the distance between the electrode 4 and the optical waveguide 2 is 20 μm or less, the same good effect as that of the above-mentioned embodiment is exhibited.

Further, the electrode forming substrate and the optical waveguide forming substrate may be fixed mechanically by using a screw or the like without using the adhesive layer 5, and the same effect as that of the above embodiment is exhibited.

Even if a dielectric film or the like is formed on one or both of the substrates before the electrode forming substrate 3 and the optical waveguide forming substrate 1 are bonded together, the distance between the electrode and the optical waveguide is 20 μm.
As long as it is m or less, the same effect as that of the above-mentioned embodiment is exhibited.

[0041]

As described above, according to the invention of claim 1, the optical waveguide forming substrate having the optical waveguide having the electro-optical effect is formed, and the electrode forming substrate having the oxide superconducting electrode is formed. By fixing the optical waveguide forming substrate and the electrode forming substrate in close proximity so that the surface on which the optical waveguide is formed and the surface on which the electrode is formed face each other, it is possible to drive at a low voltage and to reduce the optical insertion loss. There is an effect that the optical modulator can be obtained.

According to the invention of claim 2, claim 1
In addition to the above invention, by fixing the optical waveguide and the oxide superconducting electrode in close proximity to each other so that the distance between them is 20 μm or less, there is an effect that an optical modulator capable of increasing the electric field generated by the electrode can be obtained.

According to the invention of claim 3, claim 1
In addition to the invention described above, by making the surface of the optical waveguide close to the oxide superconducting electrode in contact with a substance having a lower photorefractive index than that of the optical waveguide or the atmospheric layer, it is possible to suppress the optical loss to a small value. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an optical modulator according to a first embodiment of the present invention.

FIG. 2 is a plan view showing an electrode shape of the optical modulator according to the first embodiment.

FIG. 3 is a plan view of the optical modulator according to the first embodiment seen through from above.

FIG. 4 is a graph showing the time change of the intensity of the output modulated light in the optical modulators of Example 1 and the comparative example.

FIG. 5 is a plan view showing an electrode shape of an optical modulator according to a second embodiment.

FIG. 6 is a sectional view showing an optical modulator according to a third embodiment of the present invention and a comparative example.

FIG. 7 is a sectional view showing a conventional optical modulator.

[Explanation of symbols]

 1 Optical Waveguide Forming Substrate 2 Optical Waveguide 3 Electrode Forming Substrate 4 Oxide Superconducting Electrode 5 Adhesive Layer 11 Atmosphere Layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisao Watai 8-1-1 Tsukaguchihonmachi, Amagasaki City Mitsubishi Electric Corporation

Claims (3)

[Claims] 1. An optical waveguide forming substrate on which an optical waveguide having an electro-optical effect is formed, and an electrode forming substrate on which an oxide superconducting electrode is formed, wherein the surface on which the optical waveguide is formed and the electrode are formed. An optical modulator in which the optical waveguide formation substrate and the electrode formation substrate are fixed in close proximity to each other so that the surfaces facing each other face each other. 2. The optical modulator according to claim 1, wherein the optical waveguide and the oxide superconducting electrode are fixed in proximity to each other at a distance of 20 μm or less. 3. The surface of the optical waveguide adjacent to the oxide superconducting electrode is in contact with a substance having a lower photorefractive index than that of the optical waveguide or the atmospheric layer.
An optical modulator according to the item.