JPH10206476A - Electric field sensor - Google Patents

Abstract

(57) [Problem] To provide an electric field sensor which is easy to adjust so that a weak electric field can be received, and has excellent reliability and durability. SOLUTION: A receiving antenna 5 for receiving an input signal, a sensor head 1 configured so that incident light changes and emits according to the electric field strength of the input signal, and a sensor head 1
, A light source 7 for light incident on the sensor head 1, a photodetector 8 for detecting light emitted from the sensor head 1, the sensor head 1 and the light source 7
And an optical fiber connecting the photodetector 8, an impedance conversion circuit 4 between the coaxial cable 6 and the sensor head 1, and the impedance conversion circuit 4 and the modulation electrode of the sensor head 1 constitute a series resonance circuit. An electric field sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to the field of communication and EMC.
The present invention relates to an electric field sensor used for measuring characteristics of radio waves and electromagnetic noise in a field or the like.

[0002]

2. Description of the Related Art Information devices and communication devices such as computers,
Many electrical devices, such as FA devices such as robots, and controllers such as automobiles and railways, always have a risk of being affected by malfunctions and the like due to external electromagnetic noise. EM
In the field of C, it is important to accurately measure the external electromagnetic environment, the magnitude of the noise that affects it, and the noise that it generates.

In the measurement of the electric field intensity, the electric field intensity is converted into the light intensity change by using an optical element configured so that the intensity of the incident light changes and emits according to the applied electric field intensity. Electric field sensors for detection have been developed.

FIG. 4 shows a configuration diagram of a conventional electric field sensor, and FIG. 5 shows an explanatory diagram of a configuration of a conventional sensor head. As shown in FIG. 4, the sensor head 1 (FIG. 5) attached to the balun 16 near the element of the receiving antenna 5
Is substantially integrated with the receiving antenna 5.

[0005] The incident light from the light source 7 to the sensor head 1 through the incident optical fiber 2 such as a single mode fiber enters the incident optical waveguide 12, where the energy is split into two phase shift optical waveguides 13. , Outgoing optical waveguide 1
Merge at 4. When an electric field is applied, a voltage is induced on the modulation electrode 15 by the receiving antenna, and electric field components in the two phase-shifted optical waveguides 13 are generated in opposite directions in the depth direction.

As a result, a phase difference occurs between the two light waves according to the magnitude of the applied electric field, and the intensity of the outgoing light emitted from the end of the outgoing optical waveguide 14 changes according to the applied electric field intensity.

[0007]

The electric field sensor integrated with the receiving antenna has a problem in that the receivable level is limited with respect to a weak electric field and it is difficult to change the configuration of the receiving antenna. In addition, since it is exposed to the harsh natural environment, there are problems to be solved for its reliability and durability.

An object of the present invention is to solve the above-mentioned conventional problems, that is, to provide an electric field sensor which is easily adjusted so as to be able to receive a weak electric field and which is excellent in reliability and durability. It is in.

[0009]

According to the present invention, there is provided a receiving antenna for receiving an input signal, a sensor head configured so that incident light changes and emits according to the electric field intensity of the input signal, and a sensor head. A coaxial cable for connecting the receiving antenna, a light source for light incident on the sensor head, a photodetector for detecting light emitted from the sensor head, an optical fiber for connecting the sensor head to the light source and the photodetector, a coaxial cable and The electric field sensor has an impedance conversion circuit between the sensor heads, and the impedance conversion circuit and the modulation electrode of the sensor head form a series resonance circuit.

Further, according to the present invention, the sensor head may include at least one of a branch interference type optical waveguide formed on a crystal substrate exhibiting an electro-optic effect, and two phase shift optical waveguides of a branch interference type optical waveguide. This is an electric field sensor including a modulation electrode disposed near a phase shift optical waveguide.

Further, the present invention is an electric field sensor comprising a plurality of polarization electrodes, wherein the modulation electrode is divided in the light traveling direction and capacitively coupled.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of an electric field sensor according to the present invention. FIG. 2 is a configuration diagram of a sensor head used in the electric field sensor of the present invention. FIG. 3 is an equivalent circuit diagram of the electric field sensor.

As shown in FIG. 1, a coaxial cable 6 and an impedance conversion circuit 4 are sequentially connected to a receiving antenna 5 and connected to a modulation electrode of the sensor head 1 to form an electric field sensor. The sensor head 1 is installed underground or indoors. Further, a light source 7 and a photodetector 8 are connected to the sensor head 1.

Next, as shown in FIG.
In the figure, an incident optical waveguide 12, two phase-shift optical waveguides 13 branched from the incident optical waveguide 12, and an exit where these two phase-shift optical waveguides 13 join on a substrate 11 of a lithium niobate crystal of a z-plate. An optical waveguide 14 is formed.

Further, as a buffer layer for preventing light absorption, the entire surface of the substrate 11 is coated with a SiO ₂ film, and then a modulation electrode 15 is formed on the phase shift optical waveguide 13.
Are formed. The modulation electrode 15 has a structure divided into four in the light traveling direction, and has a capacitance of 3 pF. Further, the incident optical waveguide 12 and the output optical waveguide 14 include:
The input optical fiber 2 and the output optical fiber 3 are respectively connected.

In FIG. 3, R is the resistance component of the coaxial cable, V is the reception voltage component of the receiving antenna, and the inductance L and the capacitance C constitute the impedance conversion circuit 4 shown in FIG. L ₁ , C ₁ , and R ₁ are the inductance, capacitance, and resistance components, respectively, of the modulation electrode 15 of the sensor head 1 shown in FIG. The impedance conversion circuit 4 and the modulation electrode 15 constitute a series resonance circuit. The impedance conversion circuit 4 may be formed on the substrate 11 of the sensor head 1.

In this embodiment, even when the coaxial cable 6 of 50Ω is used, the modulation electrode 15 of the sensor head 1 is used.
And the impedance of the closed circuit constituted by the impedance conversion circuit 4 is about 10Ω, so that a decrease in Q can be prevented. Further, as compared with the case where an impedance conversion transformer is used, not only low loss, but also a simple circuit using L and C, and easy adjustment can be achieved.

As a result of examining the electric field detection sensitivity using the electric field sensor according to the present embodiment, the sensitivity is improved as compared with the conventional electric field sensor, and the light detection at the electric field strength of 80 dBμV with respect to the electric wave of 500 MHz is performed. The detection signal output of the detector 8 is
What was conventionally 55 dBμV has been greatly improved to 75 dBμV.

The configuration in which the sensor head 1 is separated from the receiving antenna 5 increases the degree of freedom of the configuration of the receiving antenna 5, and has an advantage that it can cope with a weak reception electric field.

Further, since the degree of freedom for the installation environment of the sensor head 1 is increased and the sensor head 1 can be protected from a severe natural environment, reliability and durability including temperature characteristics can be measured as a measurement system. An electric field sensor with sufficient characteristics is realized.

[0022]

As described above, according to the present invention, by using the impedance conversion circuit and forming the sensor head and the resonance circuit, it is easy to adjust so that a weak electric field can be received, and An electric field sensor with excellent reliability and durability was provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electric field sensor according to the present invention.

FIG. 2 is a configuration diagram of a sensor head used in the electric field sensor of the present invention.

FIG. 3 is an equivalent circuit diagram of the electric field sensor.

FIG. 4 is a configuration diagram of a conventional electric field sensor.

FIG. 5 is an explanatory diagram of a sensor head including a conventional transmission type waveguide element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Sensor head 2 Incident optical fiber 3 Outgoing optical fiber 4 Impedance conversion circuit 5 Receiving antenna 6 Coaxial cable 7 Light source 8 Photodetector 11 Substrate 12 Incident optical waveguide 13 Phase shift optical waveguide 14 Emitting optical waveguide 15 Modulation electrode 16 Balun L, L ₁ inductance component C, C ₁ capacitance component R, R ₁ resistance component

Claims (3)

[Claims] 1. An electric field sensor in which incident light is modulated into the intensity of emitted light in accordance with the intensity of an applied electric field. A sensor head configured to emit light in accordance with the electric field strength of the input signal, a coaxial cable connecting the sensor head and the receiving antenna, a light source of light incident on the sensor head, and the sensor A light detector for detecting light emitted from the head, an optical fiber connecting the sensor head, the light source and the light detector, and an impedance conversion circuit between the coaxial cable and the sensor head; An electric field sensor, wherein a circuit and a modulation electrode of the sensor head form a series resonance circuit. 2. A branch interference optical waveguide formed on a crystal substrate exhibiting an electro-optic effect, and a phase shift optical waveguide of at least one of two phase shift optical waveguides of the branch interference optical waveguide. 2. The device according to claim 1, further comprising a modulation electrode disposed near the wave path.
An electric field sensor according to any of the preceding claims. 3. The electric field sensor according to claim 1, wherein the modulation electrode is composed of a plurality of divided electrodes that are divided in a light traveling direction and are capacitively coupled.