JPH0943288A - Electric field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable photoelectric field sensor. SOLUTION: This electric field sensor includes a receiving antenna 1, an electric field sensor head 2, an incoming optical fiber 3 and an outgoing optical fiber 4, a light source 5 and a photo detector 6. The electric field sensor head 2 has a substrate 7, an optical waveguide 8 and a modulation electrode 9. The waveguide 8 has an incoming optical waveguide 10, two phase shift optical waveguides 11 and an outgoing optical waveguide 12. The modulation electrode is formed near at least one of the two phase shift optical waveguides 11 and moreover, has a high resistance conductive film 16 formed on the surface of the substrate 7 so as not to be connected to the optical waveguide 8 and the modulation electrode 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric field sensor used for measuring the electric field strength of radiated electromagnetic waves and the like.

[0002]

2. Description of the Related Art As an example of an optical modulator constituting an electric field sensor, an optical waveguide having a structure in which incident light is split into two and then combined is formed on an optical crystal substrate having an electro-optical effect. The modulation electrode is arranged near each of the two branched optical waveguides. The natural or forcibly generated electric field is transmitted to the electrode through the antenna section and causes phase modulation in the light propagating in the optical waveguide near the electrode due to the electro-optic effect. The lights combined after this interfere with each other to cause intensity modulation, and thus have the feature that the light intensity corresponding to the strength of the electric field can be obtained. The output light intensity due to the applied voltage to the optical modulator is a trigonometric function, where the horizontal axis represents the applied voltage and the vertical axis represents the output light intensity. The optical modulator used for the electric field sensor is preferably located at the midpoint of the straight line portion between the maximum value and the minimum value of the output light intensity when the voltage applied to the modulation electrode is 0V. At such an optical bias position, even a slight voltage change significantly appears as a light intensity change, which leads to an improvement in the sensitivity of the electric field sensor.

[0003]

In the conventional electric field sensor, a LiNbO ₃ crystal substrate is often used as an optical modulator. This LiNbO ₃ crystal substrate has a pyroelectric effect and changes its refractive index due to changes in the external environment temperature and electric charges accumulated between the modulation electrodes, and thus changes the optical bias position. That is, the characteristics are such that a DC voltage is applied to the modulation electrode. Such a change in the optical bias position not only deteriorates the sensitivity of the electric field sensor as described above, but also the generated electric charge is unstable, so that the change does not subside even during measurement, and accurate electric field strength measurement cannot be performed. There is a problem. Therefore, a method of forming a conductive film on the surface of the substrate is conceivable, but frequency resonance may occur due to the conductive film being formed directly on the modulation electrode portion near the optical waveguide.

An object of the present invention is to provide a highly reliable optical electric field sensor in which fluctuations in the optical bias point due to changes in temperature environment are significantly reduced.

[0005]

In order to solve the above problems, the present invention provides a receiving antenna that receives an input signal, and the intensity of light that is transmitted by the receiving antenna according to the electric field strength of the input signal. An electric field sensor head configured to change, an incident optical fiber and an outgoing optical fiber connected to the electric field sensor head, and a light source connected to one end of the incident optical fiber to emit light to the incident optical fiber. An electric field sensor that receives transmitted light from the electric field sensor head via the emission optical fiber and detects the transmitted light, wherein the electric field sensor head includes a substrate and an incident optical fiber. It has an optical waveguide and a modulation electrode formed on the surface of the substrate so as to be connected to each other, and the optical waveguide is an incident optical waveguide formed on one end of the surface of the substrate. A path, two phase shift optical waveguides formed so as to be branched from the incident optical waveguide and having a refractive index varying according to the strength of an electric field, and the two phase shift optical waveguides connected to the emission optical fiber and joined together. And an emission optical waveguide formed on the other end of the surface of the substrate, the modulation electrode is formed in the vicinity of at least one of the two phase shift optical waveguides, and the optical waveguide and the modulation are provided. A high resistance conductive film is formed on the surface of the substrate so as not to connect to the electrodes.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a front view showing a first embodiment of the present invention. FIG. 2 is an enlarged perspective view showing a main part of the first embodiment of the present invention. As shown in FIGS. 1 and 2,
The electric field sensor of the present invention comprises a receiving antenna 1, an electric field sensor head 2, an incident optical fiber 3, and an outgoing optical fiber 4.
And a light source 5 and a photodetector 6.

The receiving antenna 1 receives an input signal. The electric field sensor head 2 includes the reception antenna 1
It is connected to the. The electric field sensor head 2 is configured to receive the input signal from the receiving antenna 1 and to change the intensity of the transmitted light according to the electric field intensity. The incident optical fiber 3 and the outgoing optical fiber 4 are connected to the electric field sensor head 2. The light source 5
Is connected to one end of the incident optical fiber 4 and emits light to the incident optical fiber 3. The photodetector 6 transmits the transmitted light from the electric field sensor head 2 to the emission optical fiber 4
The transmitted light is detected by receiving the light through.

The electric field sensor head 2 has a substrate 7, an optical waveguide 8 and two modulation electrodes 9. The optical waveguide 8 has an incident optical waveguide 10, two phase shift optical waveguides 11 and an outgoing optical waveguide 12. The incident optical waveguide 10 is formed at one end of the surface of the substrate 7 so as to be connected to the incident optical fiber 3. The two phase shift optical waveguides 11 are the same as the incident optical waveguides 1.
It is formed on the surface of the substrate 7 so as to branch from 0, and the refractive index changes according to the strength of the electric field. The output optical waveguide 12 is connected to the output optical fiber 4 and
The two phase shift optical waveguides 11 are formed at the other end of the surface of the substrate 7 so as to merge. The modulation electrode 9
Are formed in the vicinity of the two phase shift optical waveguides 11. The receiving antenna 1 is connected to the electrode pad 13 of the modulation electrode 11 via a lead wire 14.

The substrate 7 is composed of a lithium niobate single crystal plate cut out perpendicularly to the c-axis. On the substrate 7, titanium is diffused to form the incident optical waveguide 10, the phase shift optical waveguide 11 and the outgoing optical waveguide 12. The incident light from the incident optical fiber 3 is incident on the incident optical waveguide 10 and then split into two phase shift optical waveguides 11. When the receiving antenna 1 receives an input signal, a voltage is induced in the modulation electrode 9 by this input signal, and electric field components in opposite directions in the depth direction are generated in the two phase shift optical waveguides 11.

As a result, the two phase shift optical waveguides 11
A phase difference corresponding to the magnitude of the applied electric field is generated between the lights propagating through the two phase shift optical waveguides 11 due to the change in the refractive index due to the electro-optic effect, and the lights are merged to form the output optical waveguide 12. The light intensity changes due to the interference when the light is combined with each other to form emitted light. That is, the intensity of the outgoing light emitted to the outgoing optical fiber 12 changes according to the applied electric field intensity, and the intensity of the applied electric field can be measured by measuring the change in the optical intensity with the photodetector 6. .

The electric field sensor head 2 further includes an electric insulator plate 15 formed so as to cover the modulation electrode 9 without coming into contact with the optical waveguide 8, and a surface of the substrate 7 and the electric insulator plate 15. It has a high resistance conductive film 16 formed so as not to contact the optical waveguide 8. The electric insulator plate 15 is made of, for example, a ceramic plate, and the electrode pad 1
3 is exposed a little and adhered by an adhesive.
The high resistance conductive film 16 is formed of a Cr thin film having a thickness of, for example, about 100 angstroms.

It should be noted that the high-resistance conductor 16 may be formed on the surface of the substrate 7 so as not to connect the film optical waveguide 8 and the modulation electrode 9 without providing the electric insulator plate 15. Further, a lead wire connecting the receiving antenna and the modulation electrode may be connected to the high resistance conductive film.

[0014]

According to the present invention, the charge generated in the substrate can be short-circuited in the crystal axis direction to be neutralized.
A highly reliable optical electric field sensor can be provided by significantly reducing the fluctuation of the optical bias point due to the change of the temperature environment.

[Brief description of drawings]

FIG. 1 is a front view showing one embodiment of the present invention.

FIG. 2 is an enlarged perspective view showing a main part of one embodiment of FIG.

[Explanation of symbols]

 1 reception antenna 2 electric field sensor head 3 incident optical fiber 4 emission optical fiber 5 light source 6 photodetector 7 substrate 8 optical waveguide 9 modulation electrode 10 incident optical waveguide 11 phase shift optical waveguide 12 emission optical waveguide 13 electrode pad 14 lead wire 15 Electrical insulation board 16 High resistance conductive film

Claims (3)

[Claims] 1. A receiving antenna for receiving an input signal, an electric field sensor head configured to change the intensity of light passing therethrough according to the electric field strength of the input signal received by the receiving antenna, and the electric field sensor. An incident optical fiber and an outgoing optical fiber connected to the head, a light source connected to one end of the incident optical fiber to radiate light to the incident optical fiber, and transmitted light from the electric field sensor head through the outgoing optical fiber. In the electric field sensor, the electric field sensor head comprises a substrate and an optical waveguide formed on the surface of the substrate so as to be connected to the incident optical fiber. A modulation electrode, and the optical waveguide is formed so as to branch from the incident optical waveguide formed at one end of the surface of the substrate and the incident optical waveguide. The two phase shift optical waveguides whose refractive index changes according to the strength of the field, and the two phase shift optical waveguides connected to the emission optical fiber and formed on the other end of the surface of the substrate so as to merge. An emission optical waveguide, the modulation electrode is formed in the vicinity of at least one of the two phase shift optical waveguides, and further formed on the surface of the substrate so as not to be connected to the optical waveguide and the modulation electrode. An electric field sensor having a high resistance conductive film. 2. The electric field sensor according to claim 1, wherein:
The electric field sensor head further includes an electric insulator plate formed so as to cover the modulation electrode without coming into contact with the optical waveguide, and surfaces of the substrate and the electric insulator plate formed so as not to come into contact with the optical waveguide. Electric field sensor having a high resistance conductive film. 3. The electric field sensor according to claim 1 or 2, wherein a lead wire connecting the receiving antenna and the modulation electrode is connected to the high resistance conductive film.