JPH09171035A - Optical waveguide type voltage sensor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the reliability of withstand voltage characteristics for a voltage higher than a measuring voltage by forming first and second electrodes, respectively, on the upper and lower surface sides of a substrate. SOLUTION: Resist is applied to the surface of an LiNbO3 substrate 1 and exposed to form a resist pattern where the resist is removed from the part for forming a first electrode 3. Al is then deposited thereon and the resist pattern is removed along with the Al deposited thereon thus forming a first electrode 3 of desired shape. Similarly, Al is deposited entirely on the underside of substrate 1 thus forming a second electrode 4. Subsequently, a polarization maintaining fiber 5 and a single mode optical fiber 6 are connected, respectively, with the input and output sides of an optical waveguide. This structure protects the electrodes 3, 4 against breakdown even when a voltage high than measuring voltage is applied between them thus enhancing the reliability of withstand voltage characteristics for a voltage higher than the measuring voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical waveguide type voltage sensor and its manufacturing method. More specifically, it is an optical waveguide voltage sensor for high voltage that can be used for power system monitoring and a method for manufacturing the same, and an optical waveguide voltage sensor having high reliability of withstand voltage characteristics against a voltage higher than a measurement voltage and the same. Regarding manufacturing method.

[0002]

2. Description of the Related Art FIG. 7 is an external perspective view showing an optical voltage sensor disclosed in, for example, Japanese Patent Publication No. 3-46806 as an example of a conventional optical voltage sensor. In FIG. 7, 1 is a substrate, 12 is an optical waveguide, 7 is an electrode, and 18 is a signal source.

The operation will be described based on the conventional photovoltage sensor shown in FIG. First, laser light is input to the optical waveguide 12. The input laser light is split into two at the Y branch, then propagates through the linear waveguide, and is coupled again at the Y branch. Signal source 1 by means of electrode 7 on optical waveguide 12
When the measuring voltage from 8 is applied, a phase difference proportional to the measuring voltage is given between the two light beams divided by the electro-optic effect, so that the light beams re-combined at the Y branch are caused by this phase difference. Interference occurs. FIG. 8 shows the relationship between the voltage applied to the electrodes (measurement voltage) and the output light intensity. In FIG. 8, Vπ represents the applied voltage when the output light intensity is 0 a.u. Thus, the intensity of the light emitted from the end of the optical waveguide changes depending on the applied voltage due to the interference.
The optical voltage sensor measures the voltage by utilizing such a change, and the voltage can be obtained from the measured intensity of the emitted light.

In Japanese Patent Publication No. 3-46806, there is an electrode structure in which voltages opposite to each other are applied to two optical waveguides in order to increase the measurement voltage sensitivity of the optical voltage sensor. Even if it is applied only to the optical waveguide, the same effect is produced.

[0005]

In general, a voltage sensor for measuring a high voltage used in a power system requires a withstand voltage equal to or higher than a measurement voltage in consideration of a lightning impulse or the like. However, the conventional optical voltage sensor as described above has a problem that it cannot obtain a withstand voltage higher than the measured voltage. The conventional optical voltage sensor aims to detect a weak electric field,
It is necessary to increase the sensitivity to the measurement voltage. Therefore,
By increasing the distance between the electrodes as much as possible to increase the strength of the electric field applied to the optical waveguide, or by adopting an electrode structure in which the two optical waveguides are applied with opposite voltages as shown in the above example. , The sensitivity was improved.
Therefore, when a high voltage is applied between the electrodes, there is a problem that the substrate material or the electrodes are destroyed due to the narrow electrode gap.

The present invention has been made to solve the above problems, and the reliability of the withstand voltage characteristics with respect to a voltage higher than the measured voltage is not destroyed even if a high voltage is applied between the electrodes. It is an object of the present invention to provide an optical waveguide type voltage sensor having high efficiency and a manufacturing method thereof.

[0007]

An optical waveguide type voltage sensor of the present invention comprises a substrate having an electro-optical effect, an optical waveguide provided on the upper surface of the substrate, and a voltage for applying the voltage to the optical waveguide. An optical waveguide type voltage sensor using an optical modulator composed of first and second electrodes, wherein the first electrode is formed on the upper surface side of the substrate and the second electrode is on the lower surface side of the substrate. It is characterized in that it is formed.

The optical waveguide has a branch interference type structure having two branch portions, and the first electrode is formed on one of the two optical waveguides divided at the branch interference portion. It is preferable that a voltage can be applied to one of the optical waveguides in a direction perpendicular to the surface of the substrate.

The shape between the two branched portions of the optical waveguide is asymmetrical with respect to the straight line connecting the incident-side branched portion and the output-side branched portion of the optical waveguide. This is preferable because a phase difference can be provided between the two optical waveguides in between.

It is preferable that at least one of the first electrode and the second electrode has a rounded corner so that the electric field formed between the first and second electrodes is concentrated. It is preferable because it can be prevented.

The substrate is a lithium niobate (LiNbO ₃ ) crystal cut by a plane perpendicular to the Z-axis direction of the crystal, and the incident light on the optical waveguide is the vibration direction of the electric field component of the light. Is preferably TE polarized light lying in a horizontal plane, because an optical waveguide type voltage sensor can be formed without providing a buffer layer between the substrate and the first electrode.

The buffer layer is a layer provided to reduce the absorption of light incident on the optical waveguide into the first electrode formed on the substrate and attenuation thereof.

The material of the first electrode is aluminum (A
l), and the shape of the first electrode is such that the ratio a (a = d / W) between the thickness d and the width W of the electrode is 0.04 ≦ a ≦.
It is preferable that it is 0.2 because the electrode can be easily formed.

The fact that an insulating layer is inserted between the first electrode and the optical waveguide means that a voltage higher than the measurement voltage is applied between the first and second electrodes. However, both electrodes are not destroyed, and the reliability of the withstand voltage characteristics with respect to a voltage higher than the measurement voltage can be improved, which is preferable.

It is preferable that the surface of the substrate is dry-etched after the optical waveguide is formed on the substrate, because discharge on the surface of the substrate can be prevented.

The manufacturing method of the optical waveguide type voltage sensor of the present invention is as follows.
(A) a step of forming a titanium (Ti) film on the substrate,
(B) a step of forming a resist pattern matching the shape of the optical waveguide by applying a resist on the Ti film, exposing it, and developing it; and (c) using the resist pattern as a mask to form the Ti film. Dry etching to form a Ti film conforming to the shape of the optical waveguide; and (d) removing the resist pattern.
(E) a step of diffusing Ti provided as the titanium film on the substrate into the inside of the substrate, (f) a step of dry etching the surface of the substrate, and (g) applying a resist on the upper surface side of the substrate. And then exposing to form a resist pattern from which the resist in the portion forming the first electrode has been removed, and (h) forming a metal film on the resist pattern and the substrate, and removing the resist. The method is characterized by comprising a step of forming a first electrode at a desired position and (i) a step of forming a metal film on the lower surface side of the substrate to form a second electrode.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, an optical waveguide type voltage sensor is manufactured by forming a pair of electrodes on the upper surface side and the lower surface side of a substrate. In comparison with the case where a pair of electrodes are formed on the same surface, the distance between the electrodes is longer and the substrate material or the electrodes are less likely to be damaged even when a high voltage is applied. Further, the shape of the branch interference portion of the optical waveguide is asymmetrical with respect to the straight line connecting the branch portion on the incident side of the optical waveguide and the branch portion on the outgoing side of the optical waveguide. In other words, the lengths of the two optical waveguides are different (a difference in optical path length occurs) between the branch portions on both the incident side and the output side (branch interference portion). Due to the optical path length difference, a phase difference occurs between the two laser beams split at the branching portion before reaching the branching portion on the emission side.
In the present invention, the optical path length difference between the two optical waveguides in the branch interference portion is set to ¼ wavelength, and the modulation operation is performed at a position of π / 2 where the output light intensity that changes by drawing a sine wave has good linearity. The optical waveguide was formed so as to shift the points. Further, by rounding the corners of the electrodes, it is possible to prevent damage to the substrate material or the electrodes due to concentration of an electric field, and to increase the thickness of the electrodes, it is possible to suppress disconnection of the electrodes. Further, by inserting an insulating layer under the electrode, the withstand voltage is increased, and the surface layer of the substrate after diffusion is removed by dry etching to suppress discharge on the substrate surface.

Therefore, since the withstand voltage of the substrate material and the electrodes can be increased, an optical waveguide type voltage sensor having a high withstand voltage characteristic for a voltage higher than the measured voltage, which is used for monitoring the power system, is provided. be able to.

An optical waveguide type voltage sensor of the present invention and a method for manufacturing the same will be described below with reference to the accompanying drawings.
Note that the present invention is not limited to the following embodiments.

[0020]

【Example】

[Embodiment 1] FIG. 1 is a perspective explanatory view showing an embodiment of an optical waveguide type voltage sensor of the present invention, and FIG. 2 is an AA line in FIG.
It is sectional explanatory drawing which showed the cross section in the line. 1 and 2, 1 is a LiNbO ₃ substrate, 2 is a branch interference type optical waveguide, 3 is a first electrode, 4 is a second electrode, and 5 is a polarization-maintaining fiber. Yes, 6 is a single mode optical fiber. The polarization plane preserving fiber 5 is an optical fiber capable of emitting laser light incident from one end of the optical fiber from the other end of the optical fiber without changing the polarization plane of the laser light. . In this embodiment, the TE-polarized light whose oscillation direction of the electric field of the laser light is in the horizontal plane is the polarization-maintaining fiber 5
And is incident on the branch interference type optical waveguide 2. The single-mode optical fiber 6 is an optical fiber that can propagate only one mode of laser light.

Next, a manufacturing process of the optical waveguide type voltage sensor in this embodiment will be described. The substrate was made of LiNbO ₃ with a thickness of 0.5 mm cut along a plane perpendicular to the Z axis direction of the crystal.
The substrate 1 was used. On the LiNbO ₃ substrate 1, a thickness of 600 ~
A Ti film (not shown) of 800 Å was formed, and a resist was patterned in the shape of the branch interference type optical waveguide 2 using a chromium mask. Branch interference type optical waveguide 2
The shapes of the branch interference portions of the branch interference type optical waveguide 2 are the incident side branch portion (the portion indicated by C in FIG. 1) and the branch interference type optical waveguide 2 the emission side branch portion (the portion indicated by D in FIG. 1). By making it asymmetric with respect to the straight line connecting
2 propagating separately in each of the two optical waveguides
The optical path length difference of 1/4 wavelength is provided between the optical waveguides at the branching portion D so that a phase difference is generated between the two laser beams. Next, after removing the Ti film other than the branch interference type optical waveguide 2 portion by a dry etching method, the remaining resist is removed, and diffusion is performed at a temperature of 1000 to 1100 ° C. in an oxygen atmosphere into which water vapor has been introduced to branch. The interference type optical waveguide 2 was produced. Further, the surface of the substrate 1 was etched for several minutes by the dry etching method. The first electrode 3 was formed by a lift-off method on one optical waveguide of the branch interference type manufactured by such a method. In this example, first, a resist was applied on the surface of the LiNbO ₃ substrate 1 and exposed to light to form a resist pattern in which the resist in the portion where the first electrode 3 was formed was removed. Further, an Al film is formed as a metal film, and finally the resist pattern is removed to remove A on the resist pattern.
The 1 film was removed, and the first electrode 3 having a desired shape was formed.
The lift-off method is, as described above, a method of removing the Al film on the resist pattern at the same time of removing the resist pattern and leaving the Al film so as to have a desired shape. In order to prevent the concentration of the electric field, the pattern of the first electrode 3 has a shape with rounded corners so that the radius of curvature is about 1 μm to 4 μm, and the cross section of the first electrode 3 has a width of about 8 μm and a thickness. Is a rectangle of 0.3 μm. An Al film is also formed on the entire lower surface of the substrate, and the second electrode 4 is formed.
Was prepared. After producing the first and second electrodes 3 and 4, the polarization-maintaining fiber 5 was connected to the input side of the optical waveguide and the single-mode optical fiber 6 was connected to the output side. The polarization-maintaining fiber 5 was connected by adjusting the direction so that the vibration direction of the electric field incident on the optical waveguide was in the horizontal plane.

TE polarized light of a laser beam having a wavelength of 1.3 μm is incident on the optical waveguide type voltage sensor manufactured by the above procedure, and a signal generator (not shown) is provided between the first and second electrodes 3 and 4. The voltage of the optical waveguide type voltage sensor was evaluated by applying a voltage from (1) and measuring the intensity of the output light at that time using a light receiver. FIG. 3 shows the experimental results according to this example. The horizontal axis represents the AC applied voltage to the electrodes, and the vertical axis represents the modulation degree. Here, the output voltage of the light receiver is composed of an amplitude component and a bias component, and the modulation factor is a value obtained by dividing the amplitude component by the bias component in the output voltage of the light receiver at the time of measurement. From FIG. 3, it can be seen that the voltage can be measured in the range of at least 0 to 15V. The voltage at which the electrodes were damaged when an AC voltage was applied between the electrodes was 1.4 kV in this case, and an optical waveguide type voltage sensor having a high withstand voltage was obtained.

[Embodiment 2] In this embodiment, the materials of the first and second electrodes, the shape of the second electrode, the manufacturing method and shape of the optical waveguide (see FIGS. 1 and 2), etc. are the same as those in Embodiment 1. Using the same conditions as described above, an optical waveguide voltage sensor was manufactured by changing only the cross-sectional shape of the second electrode into a rectangle having a width of about 8 μm and a thickness of 0.7 μm. As a result of evaluating the optical waveguide type voltage sensor under the same conditions as in Example 1, the voltage at which the electrodes were damaged was 1.6 kV, and the withstand voltage was further improved as compared with Example 1.

[Third Embodiment] FIG. 4 is a sectional view showing an optical waveguide type voltage sensor according to the present embodiment. In FIG. 4, 1
Is a LiNbO ₃ substrate, 2 is a branch interference type optical waveguide, 3 is a first electrode, 4 is a second electrode,
Reference numeral 5 is a polarization-maintaining fiber, 6 is a single-mode optical fiber, and 8 is an insulating film. In this example, first, the branch interference type optical waveguide 2 having the same shape as that of Example 1 was produced on the LiNbO ₃ substrate 1 by the method shown in Example 1. After that, a SiO ₂ film was formed as an insulating film 8 on the surface of the LiNbO ₃ substrate 1 by a sputtering method. The thickness of the insulating film 8 was 0.2 μm. After the insulating film 8 is formed, the second electrode 3 is formed on one optical waveguide of the branched interference type optical waveguide 2 divided into two by using the same method as in Example 1 again, and then LiNbO 2 is formed. ₃ The second electrode 4 was formed on the lower surface side of the substrate 1, and the optical waveguide type voltage sensor of this example was evaluated under the same conditions as in Example 1. The measurement voltage of this example was 0 to 6 V, which was similar to that of Example 1, but the voltage at which the electrode was damaged was further improved to 1.6 kV.

[Comparative Example 1] FIG. 5 is a perspective explanatory view showing an optical waveguide type voltage sensor of Comparative Example 1, and FIG. 6 is a sectional view taken along line BB in FIG.
It is sectional explanatory drawing which showed the cross section in the line. In this comparative example, two electrodes 7 are formed in the same plane. The distance between the two electrodes 7 is 12 μm. The same conditions as in Example 1 were used for the other two electrodes, the material, the method for manufacturing the branched interference type optical waveguide 2, and the like. The optical waveguide voltage sensor of Comparative Example 1 was evaluated under the same conditions as in Example 1, and as a result, the electrode 7 was broken when an AC voltage of about 350 V was applied between the two electrodes 7. The measurement voltage range of the optical waveguide type voltage sensor of this comparative example is 0 to 4 V, which is almost the same as that of the example 1, but the withstand voltage is low.

[Comparative Example 2] Similar to Comparative Example 1, Example 1
Based on the manufacturing method of 1), only the electrode shape was manufactured in the same plane. In this comparative example, electrodes having an interval of 18 μm were manufactured. The optical waveguide voltage sensor of Comparative Example 2 was evaluated under the same conditions as in Example 1, and as a result, the electrodes were damaged when an AC voltage of about 400 V was applied between the electrodes. The measured voltage range of the optical waveguide type voltage sensor of this comparative example is 0 to 6 V, which is almost the same as that of the example 1, but the withstand voltage is low.

The optical waveguide type voltage sensor according to the present invention is more excellent than that of the optical waveguide type voltage sensors of Comparative Example 1 and Comparative Example 3.
The withstand voltage is about 5 to 4.5 times higher.

In the present invention, a 0.5 mm thick LiNbO ₃ substrate cut along a plane perpendicular to the Z-axis direction of the crystal is used as the substrate of the optical waveguide type voltage sensor, and a film is formed by the sputtering method. Using a Ti film having a thickness of about 650Å, Ti is diffused into the substrate at 1050 ° C. for 6 hours in an oxygen atmosphere in which Ti is introduced into the substrate to form an optical waveguide. Al of about 0.7 μm
Is preferable, and Al having a thickness of about 0.7 μm is used as the second electrode in terms of improving reliability of withstand voltage characteristics.

[0029]

The optical waveguide type voltage sensor of the present invention includes a substrate having an electro-optical effect, an optical waveguide provided on the upper surface side of the substrate, and first and first optical waveguides for applying a voltage to the optical waveguide. 2 electrodes, the first electrode is formed on the upper surface side of the substrate, and the second electrode is formed on the lower surface side of the substrate. Therefore, the measurement is performed between the first and second electrodes. Even when a voltage higher than the voltage is applied, both electrodes are not destroyed, and the reliability of the withstand voltage characteristics with respect to the voltage higher than the measurement voltage can be increased.

The optical waveguide type voltage sensor of the present invention has a branch interference type structure in which the optical waveguide has two branch portions, and the first electrode is one of two optical waveguides divided at the branch interference portion. Since it is formed on one of the optical waveguides, a voltage can be applied to the one optical waveguide in a direction perpendicular to the surface of the substrate.

In the optical waveguide type voltage sensor of the present invention, the shape between the two branched portions of the optical waveguide is asymmetric with respect to the straight line connecting the incident side branched portion and the output side branched portion of the optical waveguide. Since it is a mold, a phase difference can be provided between the two optical waveguides between the two branch portions.

In the optical waveguide type voltage sensor of the present invention, since at least one of the first electrode and the second electrode has a rounded corner, the first and second electrodes are provided.
The electric field formed between the electrodes can be prevented from being concentrated, and damage to the substrate and the both electrodes can be prevented.

In the optical waveguide type voltage sensor of the present invention, the substrate is an L cut by a plane perpendicular to the Z-axis direction of the crystal.
A buffer layer is provided between the substrate and the first electrode because it is an iNbO ₃ crystal and the incident light to the optical waveguide is TE polarized light in which the vibration direction of the electric field component of the light is in the horizontal plane. It is possible to form an optical waveguide type voltage sensor without using it.

In the optical waveguide type voltage sensor of the present invention, the material of the first electrode is Al, and the shape of the first electrode is the ratio a (a = a = a) of the thickness d and the width W of the electrode. d / W)
Since 0.04 ≦ a ≦ 0.2, the electrode can be easily formed.

In the optical waveguide type voltage sensor of the present invention, since the insulating layer is inserted between the first electrode and the optical waveguide, the voltage between the first and second electrodes is higher than the measured voltage. Both electrodes are not destroyed even when a high voltage is applied, and the reliability of the withstand voltage characteristics with respect to a voltage higher than the measurement voltage can be improved.

In the optical waveguide type voltage sensor of the present invention, since the surface of the substrate is dry-etched after the optical waveguide is formed on the substrate, discharge on the surface of the substrate can be prevented.

The manufacturing method of the optical waveguide type voltage sensor of the present invention is as follows.
(A) a step of forming a Ti film on the substrate; and (b) a resist pattern is formed on the Ti film by applying a resist, exposing it, and developing it to form a resist pattern that matches the shape of the optical waveguide. A step of: (c) dry etching the Ti film using the resist pattern as a mask to form a Ti film having a shape that matches the shape of the optical waveguide; and (d)
A step of removing the resist pattern; (e) a step of diffusing Ti provided as the Ti film on the substrate into the inside of the substrate; (f) a step of dry etching the surface of the substrate; A step of applying a resist on the upper surface side of the substrate and exposing the resist to form a resist pattern in which the resist in the portion where the first electrode is to be formed is removed;
Forming a metal film on the resist pattern and the substrate and removing the resist to form a first electrode at a desired position; (i) forming a metal film on the lower surface side of the substrate; Since it comprises the step of forming the electrodes, the both electrodes are not destroyed even when a voltage higher than the measurement voltage is applied between the first and second electrodes, and the withstand voltage against the voltage higher than the measurement voltage. The reliability of the characteristics can be increased.

[Brief description of the drawings]

FIG. 1 is a perspective explanatory view showing an embodiment of an optical waveguide type voltage sensor of the present invention.

FIG. 2 is a cross-sectional explanatory view taken along the line AA of FIG.

FIG. 3 is a diagram showing a relationship between applied voltage and modulation degree of the optical waveguide type voltage sensor of the present invention.

FIG. 4 is a sectional explanatory view showing another embodiment of the optical waveguide type voltage sensor of the present invention.

5 is a perspective explanatory view showing an optical waveguide type voltage sensor of Comparative Example 1. FIG.

6 is a cross-sectional explanatory view taken along the line BB of FIG.

FIG. 7 is a perspective explanatory view showing a conventional optical waveguide type voltage sensor.

FIG. 8 is a diagram showing a relationship between an applied voltage and an output light intensity of the optical waveguide type voltage sensor.

[Explanation of symbols]

1 LiNbO ₃ substrate, 2 branch interference type optical waveguide, 3
First electrode, second electrode, 5 polarization-maintaining fiber, 6 single mode optical fiber.

Claims (9)

[Claims] 1. An optical modulator comprising a substrate having an electro-optical effect, an optical waveguide provided on the upper surface side of the substrate, and first and second electrodes for applying a voltage to the optical waveguide. An optical waveguide type voltage sensor used, comprising:
Is formed on the upper surface side of the substrate, and the second electrode is formed on the lower surface side of the substrate. 2. The optical waveguide has a branch interference type structure having two branch portions, and the first electrode is formed on one of the two optical waveguides divided at the branch interference portion. An optical waveguide type voltage sensor according to claim 1. 3. The shape between the two branched portions of the optical waveguide is asymmetrical with respect to a straight line connecting the incident-side branched portion and the outgoing-side branched portion of the optical waveguide. Optical waveguide type voltage sensor. 4. The optical waveguide voltage sensor according to claim 2, wherein at least one of the first electrode and the second electrode has a shape with rounded corners. 5. The substrate is a lithium niobate crystal cut in a plane perpendicular to the Z-axis direction of the crystal, and the incident light to the optical waveguide has a horizontal plane in which the vibration direction of the electric field component of the light is horizontal. 5. The optical waveguide type voltage sensor according to claim 1, wherein the TE polarized light is inside. 6. The material of the first electrode is aluminum, and the shape of the first electrode is such that the ratio a between the thickness d and the width W of the electrode is 0.04 ≦ a ≦ 0.2. The optical waveguide type voltage sensor according to claim 5, wherein 7. The optical waveguide type voltage sensor according to claim 5, wherein an insulating layer is inserted between the first electrode and the optical waveguide. 8. The optical waveguide type voltage sensor according to claim 5, wherein the surface of the substrate is dry-etched after the optical waveguide is formed on the substrate. 9. The method of manufacturing an optical waveguide type voltage sensor according to claim 1, wherein: (a) a step of forming a titanium film on the substrate; and (b) applying a resist on the titanium film, Exposing and developing to form a resist pattern that matches the shape of the optical waveguide; and (c) dry etching the titanium film using the resist pattern as a mask to form titanium that matches the shape of the optical waveguide. A step of forming a film, (d) a step of removing the resist pattern, (e) a step of diffusing titanium provided as the titanium film on the substrate into the substrate, and (f) a surface of the substrate. A step of dry etching; and (g) a step of applying a resist on the upper surface side of the substrate and exposing it to form a resist pattern in which the resist in the portion where the first electrode is formed is removed. And (h) a step of forming a metal film on the resist pattern and the substrate and removing the resist to form a first electrode at a desired position,
(I) A method of manufacturing an optical waveguide type voltage sensor, which comprises the step of forming a metal film on the lower surface side of the substrate to form a second electrode.