JP2004212136A - Electric field sensing device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric field sensing device in which the optical bias point in its photoelectric field sensor head is optimized, and to provide a method of manufacturing the sensing device. <P>SOLUTION: This electric field sensing device is provided with the photoelectric field sensor head 31 constituted by forming metallic electrodes and Mach-Zehnder interferometer type branched optical waveguides on a substrate composed of an electrooptic crystal, optical fibers 32 and 33, and a laser light soruce 301. This device is also provided with a photodetector 302. The wavelength of the laser light source 301 is selected so that the phase difference between light rays having passed through the branched optical waveguides may become a prescribed value when no electric field is impressed upon the metallic electrodes. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electric field sensing device for measuring an electric field using an electro-optic effect, and in particular, to an electric field sensing device using an interference type optical waveguide suitable for measuring a small space, high accuracy, high sensitivity, and high frequency electric field. And its manufacturing method.
[0002]
[Prior art]
An optical electric field sensor and an electric field sensing device using an interference type optical waveguide utilizing the electro-optic effect have the following features. That is, since the electric field to be measured is not disturbed because it has almost no metal part, the detection signal is transmitted through an optical fiber so that it is not affected by induction or electric noise on the way, and the electro-optic effect of the crystal is used. , High-speed response is possible and the detection signal can be transmitted as it is with little loss, no power supply is required for the sensor part, and the optical waveguide and antenna electrode are integrated and there is no power supply, so miniaturization is achieved. Is easy. Due to such characteristics, the optical electric field sensor is used for electric field measurement in the EMC field.
[0003]
First, the optical electric field sensor head used in the electric field sensing device will be described. FIG. 2 is a schematic perspective view showing the structure of a general optical electric field sensor head. Light incident from the optical fiber 12 passes through the optical waveguide 21 on the LiNbO ₃ single crystal substrate 11, and is branched into two branch optical waveguides 22a and 22b. At that time, in the one branch optical waveguide 22a, when an electric field is applied by the metal electrodes (antenna electrodes) 23m and 23n, the refractive index changes.
[0004]
On the other hand, there is no change in the refractive index of the branch optical waveguide 22b due to the electric field. The light propagating through each branch optical waveguide is multiplexed in the optical waveguide 24, but the amplitude of the multiplexed light changes as shown in FIG. 3 due to the phase difference caused by the difference in the refractive index between the two optical paths. I do. FIG. 3A shows a case where there is almost no phase difference between the two branched lights, and FIG. 3B shows a case where there is a phase difference of 1/4 wavelength between the two branched lights. Since the square of the amplitude is the light intensity, the light intensity changes due to the phase difference between the two optical paths. Thereafter, the light is coupled to the optical fiber 13 via the optical waveguide 24 and emitted.
[0005]
Generally, in an optical electric field sensor head, even when an electric field is not applied, the multiplexing is performed by intentionally shifting the optical path length of the branch optical waveguide or adjusting the refractive index of a part of the branch optical waveguide. A phase difference is generated in the light at the time of use. In many cases, the phase difference between the branched light beams is used such that the phase difference is about １ ／ or ／ wavelength.
[0006]
FIG. 4 shows the relationship (modulation curve) between the applied electric field and the intensity of the emitted light when a phase difference of ３ wavelength is generated. Point A when no electric field is applied is called an optical bias point. In this case, the intensity of light changes according to the applied electric field. When an AC electric field is applied, the emitted light is intensity-modulated according to the applied AC electric field.
[0007]
In the conventional electric field sensing device using the optical electric field sensor head as described above, the electric field sensing device is configured by combining a laser light source having a fixed wavelength, a photodetector, and an optical fiber.
[0008]
When actually manufacturing an optical electric field sensor head, in order to control the phase difference of light passing through the branch optical waveguide when no electric field is applied, that is, to control the optical bias point, strict control of the optical path length and optical control are required. Precise control of the refractive index of the waveguide is required, which has been a very difficult process in practice.
[0009]
Therefore, conventionally, an optical electric field sensor head is manufactured, and an optical bias point that is inappropriate is discarded, or a stress is applied to a part of the optical waveguide to change the refractive index, and the optical bias point is post-adjusted. Things have been done.
[0010]
For example, the following Patent Document 1 discloses a technique for adjusting an optical bias point by applying an external force from a side surface of an optical waveguide.
[0011]
[Patent Document 1]
JP-A-6-337385
In an element using a reflection type optical waveguide, the angle of a reflection mirror is changed to adjust an optical bias point afterward. For example, it is as disclosed in the following Patent Document 2.
[0013]
[Patent Document 2]
JP-A-10-260328
[Problems to be solved by the invention]
If the optical electric field sensor head having an inappropriate bias point is discarded, and only the optical electric field sensor head having the target optical bias point is selected and used, the cost is greatly increased. Further, when adjustment is performed after applying a stress to a part of the optical waveguide, a problem remains with time. Further, the method of changing the angle of the reflection mirror to adjust the optical bias point afterward cannot be applied to the transmission type optical electric field sensor head.
[0015]
Therefore, the present invention provides an electric field sensing device that optimizes a difference in optical path length in a state where an electric field of a branch optical waveguide is not applied in an optical electric field sensor head of an electric field sensing device, that is, optimizes an optical bias point, and a method of manufacturing the same. The task is to provide
[0016]
[Means for Solving the Problems]
In order to solve the above problems, an electric field sensing device according to the present invention includes an optical electric field sensor head formed by forming a metal electrode and a Mach-Zehnder interferometer type branch optical waveguide on an electro-optic crystal substrate, an optical fiber, and a laser. An electric field sensing device including a light source and a photodetector, wherein a wavelength of the laser light source is such that a phase difference of light passing through the branch optical waveguide in a state where an electric field is not applied to the metal electrode is a predetermined value. Is selected.
[0017]
Further, the electro-optic crystal is a LiNbO ₃ single crystal, and the branch optical waveguide can be formed by diffusing Ti ions on the electro-optic crystal substrate.
[0018]
Further, the method for manufacturing an electric field sensing device according to the present invention includes an optical electric field sensor head formed by forming a metal electrode and a Mach-Zehnder interferometer type branch optical waveguide on an electro-optic crystal substrate, a laser light source, and a photodetector. A method of measuring the optical bias point of the obtained optical electric field sensor head, and changing the wavelength of the laser light source according to a difference between the target optical bias point and the method. Adjusting the optical bias point.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0020]
First, Ti ions were thermally diffused on a LiNbO ₃ single crystal substrate to form an optical waveguide of a Mach-Zehnder interferometer type, and optical fibers for input and output were connected to manufacture an optical electric field sensor head of the present embodiment. .
[0021]
FIG. 5 is a diagram showing the relationship (modulation curve) between the intensity of the applied electric field and the intensity of the emitted light when an electric field is applied to the manufactured optical electric field sensor head. The wavelength of the laser light source used at this time is 1530 nm. is there. The point on the modulation curve corresponding to the optical bias point, ie, the phase difference of the light passing through the branch optical waveguide with no electric field applied, is point B, where a phase difference of about 118 ° It occurs during light passing through the wave path.
[0022]
Incidentally, the optimum value of the target optical bias point differs depending on the application of the electric field sensing device, but the target optical bias point is assumed to be 90 ° ± 10 °.
[0023]
Therefore, the wavelength of the laser light source was set to 1542 nm in order to adjust the difference between the optical bias points of minus 28 degrees. FIG. 6 shows a relationship (modulation curve) between the intensity of the applied light and the intensity of the emitted light when an electric field is applied to the optical electric field sensor head at this wavelength. The optical bias point was 89 °, and the optical bias point could be easily adjusted within the target range.
[0024]
Using this optical electric field sensor, an electric field sensing device of the present embodiment was manufactured.
[0025]
FIG. 1 is a schematic diagram illustrating an electric field sensing device according to the present embodiment. 31 is an optical electric field sensor head, 32 and 33 are optical fibers, 34 is a laser light source head, 35 is a laser light source drive circuit, 36 is a photodetector, 37 is an O / E conversion amplifier, and 39 is an electric signal output terminal. The laser light source 301 includes a laser light source head 34, a laser light source drive circuit 35, and a power supply unit 38, and the photodetector 302 includes a photodetector 36, an O / E conversion amplifier 37 supplied with power from the power supply unit 38, and Consists of
[0026]
By the way, in actual production, the wavelength change of the laser light source is performed as follows. Once the optical bias point of the optical electric field sensor head is adjusted to the target value by changing the wavelength of the tunable laser light source, it is not necessary to readjust the wavelength later. Therefore, after determining the wavelength for providing the optimum optical bias point, the light source is replaced by a fixed wavelength semiconductor laser that is distributed on the market in increments of 1 nm.
[0027]
In the present embodiment, a LiNbO ₃ single crystal is used as the substrate crystal of the light modulating unit. However, for example, when a LiTaO ₃ single crystal is used, optical damage due to laser light can be reduced. Further, instead of the Ti diffusion waveguide, an H ⁺ exchange waveguide can be used.
[0028]
Further, in the present embodiment, the optical electric field sensor head having the transmission type branch optical waveguide has been described, but the present invention is also applicable to an electric field sensing device using the optical electric field sensor head having the reflection type branch optical waveguide. It is clear that it is effective.
[0029]
Furthermore, in the present embodiment, the metal electrode formed on the substrate of the electro-optic crystal functions as both an antenna for detecting an electric field to be measured and a modulation electrode, but the antenna is provided outside the substrate. Obviously, it may be.
[0030]
【The invention's effect】
As described above, according to the present invention, an optical bias point, which is a bias point on a modulation curve corresponding to a phase difference of light that has passed through a branch optical waveguide in a state where an electric field is not applied in an optical electric field sensor head, can be easily determined. An adjustable electric field sensing device and a method for manufacturing the same can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an electric field sensing device according to an embodiment of the present invention.
FIG. 2 is a schematic perspective view showing the structure of a general optical electric field sensor head.
FIG. 3 is a diagram showing the amplitude of light when two branched lights are combined. FIG. 3A shows a case where there is almost no phase difference between two branched lights, and FIG. 3B shows a case where there is a phase difference of 1/4 wavelength between the two branched lights.
FIG. 4 is a diagram showing a modulation curve when a branch optical waveguide has a phase difference of ／ wavelength.
FIG. 5 is a diagram showing a modulation curve at a wavelength of 1530 nm in the obtained optical electric field sensor head.
FIG. 6 is a diagram showing a modulation curve after adjusting the wavelength of a laser light source according to the present invention.
[Explanation of symbols]
11 LiNbO ₃ single crystal substrate 12, 13 Optical fiber 21, 24 Optical waveguide 22a, 22b Branch optical waveguide 23m, 23n Metal electrode 31 Optical electric field sensor head 32, 33 Optical fiber 34 Laser light source head 35 Laser light source drive circuit 36 Photodetector 37 O / E conversion amplifier 38 Power supply unit 39 Electric signal output terminal 301 Laser light source 302 Photodetector

Claims (4)

An electric field sensing device comprising an optical electric field sensor head formed by forming a metal electrode and a Mach-Zehnder interferometer type branched optical waveguide on an electro-optic crystal substrate, an optical fiber, a laser light source, and a photodetector, The electric field sensing device according to claim 1, wherein a wavelength of the laser light source is selected such that a phase difference of light passing through the branch optical waveguide becomes a predetermined value when an electric field is not applied to the metal electrode. The electro-optical crystal is a LiNbO ₃ single crystal, the branched optical waveguides, the electric field sensing system according to claim 1, characterized by being formed by diffusing Ti ions in the electro-optical crystal substrate. 3. The electric field sensing device according to claim 1, wherein the laser light source is a semiconductor laser. A method for manufacturing an electric field sensing device, comprising: an optical electric field sensor head formed by forming a metal electrode and a Mach-Zehnder interferometer type branch optical waveguide on an electro-optic crystal substrate; a laser light source; and a photodetector. Measuring the optical bias point at a predetermined wavelength of the obtained optical electric field sensor head, and changing the wavelength of the laser light source according to the difference between the target optical bias point and the optical bias point. Optimally adjusting the electric field sensing device.

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