JP3435588B2 - Electric field sensor - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electric field sensor for detecting an electromagnetic wave propagating in a space or measuring an electric field strength of the electromagnetic wave.

[0002]

2. Description of the Related Art Many electric devices such as information devices such as computers, communication devices, FA devices such as robots, control devices such as automobiles and trains are always at risk of being affected by malfunctions due to electromagnetic noise from the outside. I have it. For this reason, in the EMC field, it is important to accurately measure the magnitude of noise that affects the external electromagnetic environment and influence, and the noise generated by itself.

Conventionally, in the above-mentioned measurement of electromagnetic noise, a device (hereinafter, referred to as device (a)) which receives an ordinary antenna and guides it to a measuring instrument by a coaxial cable, and a signal received by the antenna are used. A device that detects and converts it into an optical signal and guides it to the measuring device with an optical fiber (hereinafter referred to as (b) device), using an optical element configured to change the intensity of transmitted light according to the applied electric field intensity There are used three types of devices (hereinafter referred to as (c) device) for converting a change in electric field intensity into a change in light intensity and connecting the optical element, a light source and a photodetector connected to a measuring instrument with an optical fiber. .

Of these, the measurement using the device (a) is the most general, but the presence of an electric cable such as a coaxial cable may disturb the electric field distribution, or noise may be mixed in the middle of the cable. Because of problems, it is desired to develop a device (b) and a device (c) using an optical fiber.

Here, the device (b) is for amplifying a signal detected by a diode, adding it to a light emitting diode, converting it into an optical signal and guiding it to an optical detector by an optical fiber. Since an electric circuit and a battery are required, there is a problem that a metal part of a certain size is present and the shape becomes large, and there is a problem that the response speed is slow.

On the other hand, the device (c) uses a crystal having an electro-optical effect as an optical element for converting an electric field intensity into a change in intensity of transmitted light. The element structure is as follows: the light emitted from the optical fiber is made into parallel light by a lens and passed through a crystal with a small antenna attached, the polarization state is changed by the electric field in the crystal, and the intensity is changed by an analyzer, then again. There are a bulk type element which is coupled to an optical fiber and a waveguide type element which constitutes the above optical element by an optical waveguide provided on a crystal. Usually, the waveguide type element is 1
Higher detection sensitivity than 0 times.

As an example of an electric field sensor using a bulk type element, there is one disclosed in Japanese Patent Laid-Open No. 4-285866 (hereinafter referred to as Reference Example 1).

This is to improve the sensitivity by changing the resonance frequency of the sensor rod by inserting an impedance element between the sensor rod and the electrode of the optical modulator.

Further, as an electric field sensor using a waveguide type element, there is a conventional one as shown in FIG. 10 (hereinafter referred to as reference example 2). Here, FIG. 10 is a partially cutaway front view showing a main part of an electric field sensor using a conventional waveguide type element. This electric field sensor includes an electric field receiving antenna 101,
A light source (not shown) that emits light, and an incident optical fiber 103 that is connected to the light source and transmits the light emitted by the light source.
And the electric field receiving antenna 101 and the incident optical fiber 10
3, an electric field sensor head 102 configured to change the intensity of light incident through the incident optical fiber 103 according to the electric field intensity of an input signal received by the electric field receiving antenna 101, An output optical fiber 104 that is connected to the electric field sensor head 102 and that transmits the transmitted light that has transmitted through the electric field sensor head 102, and a photodetector that detects a change in the light intensity of the transmitted light transmitted by the emission optical fiber 104. (Not shown).

Here, the electric field sensor head 102 is
The substrate 105, the incident optical waveguide 106 formed on the substrate 105 so as to be connected to the incident optical fiber 103, and the refractive index of which changes according to the strength of the electric field of the input signal received by the electric field receiving antenna 101. In addition, the two phase shift optical waveguides 107a and 107b formed on the substrate 105 so as to be branched from the incident optical waveguide 106 and the two phase shift optical waveguides 107a and 107b connected to the emission optical fiber 104 merge. 2 is formed in the vicinity of both the output optical waveguide 108 formed on the substrate 105 and the two phase shift optical waveguides 107a and 107b so as to be connected to the electric field receiving antenna 101.
It consists of one modulation electrode 109a and 109b.

The substrate 105 is composed of a lithium niobate single crystal plate cut out perpendicularly to the c-axis of the crystal.
The incident optical waveguide 10 is formed by diffusing titanium on the substrate 105.
6 and two phase shift optical waveguides 107a and 107b
And the output optical waveguide 108 are formed.

In this electric field sensor, the incident light transmitted through the incident optical fiber 103 is incident on the incident optical waveguide 106, and then the two phase shift optical waveguides 107a and 107a.
The energy is divided into 07b. Here, a voltage is induced in the two modulation electrodes 109a and 109b by the input signal received by the electric field receiving antenna 101, and in the two phase shift optical waveguides 107a and 107b in the depth direction, that is, in the plane of the drawing. Electric field components opposite to each other are generated in the direction perpendicular to. As a result, in the two phase shift optical waveguides 107a and 107b, the refractive index changes due to the electro-optic effect, and the two phase shift optical waveguides are provided between the light waves propagating through the two phase shift optical waveguides 107a and 107b. 107a and 10
A phase difference corresponding to the magnitude of the electric field generated in each of 7b occurs, and when two light waves having the phase difference merge and combine in the emission optical waveguide 108, interference occurs and the light intensity changes. That is, the intensity of the outgoing light emitted to the outgoing optical fiber 104 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.

[0013]

However, in the case of the electric field sensor using the waveguide type element of the second reference example, although the electric field distribution is not disturbed by the presence of the electric cable and noise is not mixed, the minimum detectable electric field strength is (A) It is inferior to the device, that is, the electric field sensor that leads to the measuring instrument by the coaxial cable using the antenna by about one digit.

Generally, in order to increase the sensitivity of the antenna, the effective length h is set by increasing the element length of the antenna.
Although the method of increasing e is adopted, the radiation resistance of the antenna increases when the element length of the antenna is increased and the length approaches the wavelength of the received radio wave. Here, a half-wavelength dipole antenna will be described as an example of an antenna often used for receiving radio waves. The radiation resistance ra of this antenna is 73
Ω, and the reactance Xa is inductive 42 Ω.
When such an antenna is connected to the modulation electrode 109 having the combined resistance re, the combined reactance Le, and the combined capacitance Ce as shown in FIG. 3B, the radiation resistance r of the antenna is
Power is consumed and sensitivity is lost due to a and the combined resistance re of the modulation electrode 109, and it is difficult to realize high sensitivity.

In order to receive radio waves over a wide frequency range with one antenna, the antenna must have a wide band. An example of such an antenna is a short dipole antenna. This short dipole antenna has a characteristic that it is capacitive and its radiation resistance can be made small by making the antenna element sufficiently shorter than the wavelength of the radio wave to be received, and since there is no resonance of the antenna element, it can cover a wide frequency range. A flat characteristic, that is, a wide band of the antenna can be obtained. When this antenna is connected to the modulation electrode 109 as shown in FIG. 3C, the sensitivity is determined by the ratio of the combined capacitance Ce of the modulation electrode 109 and the capacitance C generated in the antenna. That is, if the combined capacitance Ce of the modulation electrode 109 is smaller than the capacitance C of the antenna, high sensitivity can be obtained. However, if the combined resistance re of the modulation electrode 109 is large, there is a problem that the combined resistance re consumes power and lowers the sensitivity.

These problems also apply to the electric field sensor of the first reference example. Furthermore, the reference example 1
It is intended to obtain a desired resonance frequency by changing the resonance frequency of the sensor rod, and the modulation electrode is not taken into consideration. However, in reality,
The modulation electrode also affects the resonance frequency of the entire antenna, and there is a problem that the desired resonance frequency cannot be obtained unless the influence of the modulation electrode on the resonance frequency is taken into consideration.

It is an object of the present invention to provide an electric field sensor using a waveguide type element, which can improve the sensitivity by setting the resonance frequency of the entire antenna to a desired resonance frequency. is there.

[0018]

In order to solve the above-mentioned problems, the present invention provides an electric field sensor as described below.

That is, according to the present invention, an electric field receiving antenna, a light source for emitting light, an incident optical fiber connected to the light source for transmitting light emitted by the light source, the electric field receiving antenna, and An electric field sensor head connected to the incident optical fiber and configured so that the intensity of light incident through the incident optical fiber changes according to the electric field intensity of an input signal received by the electric field receiving antenna; An emission optical fiber connected to a sensor head for transmitting transmitted light transmitted through the electric field sensor head, and a photodetector for receiving the transmitted light via the emission optical fiber and detecting a change in light intensity of the transmitted light. An electric field sensor comprising:
The electric field sensor head includes a substrate, an incident optical waveguide formed on the substrate so as to be connected to the incident optical fiber, and the electric field receiving head formed on the substrate so as to be branched from the incident optical waveguide. Two phase shift optical waveguides whose refractive index changes according to the electric field strength of the input signal received by the antenna, and formed on the substrate so as to join the two phase shift optical waveguides connected to the output optical fiber. In an electric field sensor including an outgoing optical waveguide and a modulation electrode formed near at least one of the two phase shift optical waveguides, a resonance circuit formed by the modulation electrode and the electric field receiving antenna further includes: The modulation voltage
Fewer paths connecting the pole and the electric field receiving antenna
And insert it on one side to improve sensitivity at the desired resonance frequency.
An electric field sensor is obtained which is provided with a resonance correction circuit . With such a configuration, the Q value of the resonance circuit is 2 or more.
To obtain sufficient sensitivity at the desired resonance frequency.
Can be improved.

Further, according to the present invention, an electric field receiving antenna, a light source for emitting light, an incident optical fiber connected to the light source for transmitting light emitted by the light source, the electric field receiving antenna, and An electric field sensor head connected to the incident optical fiber and configured so that the intensity of light incident through the incident optical fiber changes according to the electric field intensity of an input signal received by the electric field receiving antenna; An emission optical fiber connected to a sensor head for transmitting transmitted light transmitted through the electric field sensor head, and a photodetector for receiving the transmitted light via the emission optical fiber and detecting a change in light intensity of the transmitted light. An electric field sensor comprising:
The electric field sensor head includes a substrate, an incident optical waveguide formed on the substrate so as to be connected to the incident optical fiber, and the electric field receiving head formed on the substrate so as to be branched from the incident optical waveguide. Two phase shift optical waveguides whose refractive index changes according to the electric field strength of the input signal received by the antenna, and formed on the substrate so as to join the two phase shift optical waveguides connected to the output optical fiber. In the electric field sensor including the emitting optical waveguide and the modulation electrode formed near at least one of the two phase shift optical waveguides, the modulation electrode and the electric field receiving antenna form a resonance circuit. By setting the thickness of the modulation electrode to 1 μm or more, the resistance of the modulation electrode is reduced, and the Q value of the resonant circuit is set to 2 or more to improve the sensitivity. Electric field sensor, wherein Rukoto is obtained.

Further, according to the present invention, in the electric field sensor, wherein the modulation electrode is formed in the vicinity of both of the two phase shift optical waveguides, the modulation electrode is a light traveling direction. And the divided electrodes that are divided by are capacitively coupled to each other,
The composite capacitance of the modulation electrode is reduced to reduce the Q of the resonance circuit.
By increasing the value, an electric field sensor characterized by improving the sensitivity can be obtained.

Further, according to the present invention, an electric field receiving antenna, a light source for emitting light, an incident optical fiber connected to the light source for transmitting the light emitted by the light source, the electric field receiving antenna, and An electric field sensor head connected to the incident optical fiber and configured so that the intensity of light incident through the incident optical fiber changes according to the electric field intensity of an input signal received by the electric field receiving antenna; An emission optical fiber connected to a sensor head for transmitting transmitted light transmitted through the electric field sensor head, and a photodetector for receiving the transmitted light via the emission optical fiber and detecting a change in light intensity of the transmitted light. An electric field sensor comprising:
The electric field sensor head includes a substrate, an incident optical waveguide formed on the substrate so as to be connected to the incident optical fiber, and the electric field receiving head formed on the substrate so as to be branched from the incident optical waveguide. Two phase shift optical waveguides whose refractive index changes according to the electric field strength of the input signal received by the antenna, and formed on the substrate so as to join the two phase shift optical waveguides connected to the output optical fiber. In the electric field sensor including the outgoing optical waveguide and the modulation electrode formed near both of the two phase shift optical waveguides, the modulation electrode and the electric field receiving antenna form a resonance circuit, The modulation electrodes are divided in the light traveling direction, and the divided electrodes thus divided are capacitively coupled to each other to reduce the combined capacitance of the modulation electrodes. By increasing the Q value of the resonance circuit, the electric field sensor, characterized in that to improve the sensitivity obtained.

Further, according to the present invention, in any one of the electric field sensors, the electric field receiving antenna is a low radiation resistance antenna to reduce the radiation resistance of the electric field receiving antenna, and the resonance circuit. An electric field sensor characterized by improving the sensitivity can be obtained by increasing the Q value of.

According to the present invention, in any one of the above electric field sensors, the electric field sensor further comprises at least one of a director and a reflector coupled to the electric field sensor. Thus, an electric field sensor characterized by concentrating radio waves and improving sensitivity can be obtained.

[0025]

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an electric field sensor according to a first embodiment of the present invention will be described with reference to the drawings. First
As shown in FIG. 1, the electric field sensor according to the embodiment of the present invention is connected to the electric field receiving antenna 1, a light source 6 that emits light, and the light source 6, and is an incident device that transmits the light emitted by the light source 6. The optical fiber 4 and the optical fiber 4 are configured so that the intensity of light incident through the incident optical fiber 4 changes according to the electric field intensity of the input signal received by the electric field receiving antenna 1. 1 and an incident optical fiber 4, an electric field sensor head 3, an outgoing optical fiber 5 that is connected to the electric field sensor head 3 and that transmits the transmitted light that has passed through the electric field sensor head 3, and is transmitted through the outgoing optical fiber. The light detector 7 detects a change in the light intensity of the transmitted light.

Here, as shown in FIG. 2, the electric field sensor head 3 includes a substrate 8, an incident optical waveguide 9 formed on the substrate 8 so as to be connected to the incident optical fiber 4, and an electric field strength. Two phase shift optical waveguides 10a and 10b formed on the substrate 8 so as to be branched from the incident optical waveguide 9 and two phase shifts connected to the outgoing optical fiber 5 Optical waveguides 10a and 10
The exiting optical waveguide 11 formed on the substrate 8 so that b merges with each other, and the two modulation electrodes 12a and 12b formed near both the two phase shift optical waveguides 10a and 10b.
Consists of.

A resonance correction circuit 2 is connected to the path connecting the modulation electrode 12a and the electric field receiving antenna 1. Further, the electric field receiving antenna 1 and the resonance correction circuit 2
Are modulated electrodes 12a, 12a,
It is connected to 12b.

The resonance correction circuit 2 corrects the resonance frequency of the resonance circuit composed of the electric field receiving antenna 1 and the two modulation electrodes 12a and 12b. That is, for example, the resonance frequency of the resonance circuit formed by the electric field receiving antenna 1 and the two modulation electrodes 12a and 12b when the resonance correction circuit 2 is not inserted is 800 MHz,
If the desired resonance frequency is 500 MHz,
By adding an inductance of 48 nH as the resonance correction circuit 2 to the resonance circuit composed of the electric field receiving antenna 1 and the two modulation electrodes 12a and 12b, a desired resonance frequency of 500 MHz can be obtained. Therefore, the electric field receiving antenna 1 and the two modulation electrodes 12a,
If the resonance frequency of the resonance circuit formed by 12b matches the frequency of the radio wave intended for reception, it is not necessary to use it.

Further, the resonance correction circuit 2 may be inserted in one of the paths connecting the two modulation electrodes 12a and 12b and the electric field receiving antenna 1 for the above-mentioned reason, and it is not always necessary to use two. It does not have to be connected to both of the paths connecting the two modulation electrodes 12a and 12b and the electric field receiving antenna 1. In addition, the resonance correction circuit 2
2 is inserted only in the path connecting the modulation electrode 12a and the electric field receiving antenna 1 in FIG. 2, but may be inserted only in the path connecting the modulation electrode 12b and the electric field receiving antenna 1, It may be inserted in both the path connecting the modulation electrode 12a and the electric field receiving antenna 1 and the path connecting the modulation electrode 12b and the electric field receiving antenna 1. Further, the resonance correction circuit 2 may have any desired effect, and may be composed of only a capacitor, only an inductor, or a combination of a capacitor and an inductor, and is not limited to the present embodiment.

Here, the substrate 8 is composed of a lithium niobate single crystal plate cut out perpendicularly to the c-axis. Titanium is diffused on the substrate 8 to form an incident optical waveguide 9, two phase shift optical waveguides 10a and 10b, and an outgoing optical waveguide 11. In this electric field sensor, the incident light transmitted by the incident optical fiber 4 is incident on the incident optical waveguide 9, and thereafter, the energy is split into two phase shift optical waveguides 10a and 10b. Here, a voltage is induced in the two modulation electrodes 12a and 12b by the input signal received by the electric field receiving antenna 1, and the two phase shift optical waveguides 10a and 10b have a depth direction, that is, in the figure. Electric field components in mutually opposite directions are generated in the direction perpendicular to the paper surface. As a result, in the two phase shift optical waveguides 10a and 10b, the refractive index changes due to the electro-optical effect, and the two phase shift optical waveguides 1
Between the optical waves propagating through 0a and 10b, a phase difference corresponding to the magnitude of the electric field generated in each of the two phase shift optical waveguides 10a and 10b occurs, and the two optical waves having the phase difference occur. When they merge and are coupled in the emission optical waveguide 11, interference occurs and the light intensity changes.
That is, the intensity of the emitted light emitted to the outgoing optical fiber 5 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 7.

Here, the electric field sensor in the first embodiment has two modulation electrodes 12a, 12b in the resonance circuit composed of the two modulation electrodes 12a, 12b, the electric field receiving antenna 1, and the resonance correction circuit 2. Each film thickness of 12b is set to 1 μm or more, and two modulation electrodes 12a and 12b are provided.
The Q value of the resonance circuit is set to a certain value or more by reducing the combined resistance of the above.

An equivalent circuit of the resonance circuit in the electric field sensor of the first embodiment is shown in FIG. 3 (a).
In this resonance circuit, the radiation impedance of the electric field receiving antenna 1 was Za (= ra + jXa), and the open circuit voltage of the antenna was V (= E · he). further,
The inductance of the resonance correction circuit 2 is Lp, and the combined resistance of the modulation electrode 12 (means the combination of the two modulation electrodes 12a and 12b. (The same applies below)) is re.
And the combined inductance is Le and the combined capacitance is Ce.
And Here, E is the electric field strength (V / m), and he is the effective length.

The electric field sensor according to the first embodiment of the present invention amplifies the voltage applied to the modulation electrode 12,
The resonance electrode is configured by the modulation electrode 12 and the reactance component generated in the electric field receiving antenna 1, and the sensitivity is increased by increasing the Q value of the resonance circuit.

In general, the resonance frequency f of the resonance circuit is determined by the reactance component Xa of the radiation impedance Za of the electric field receiving antenna 1 and the combined inductance Le of the modulation electrode 12.
And the combined capacity Ce. Here, the impedance of Le is sufficiently smaller than that of Ce and can be ignored. If the resonance correction circuit is connected, the reactance component of the resonance correction circuit (here,
The frequency is determined including the inductance Lp).
It should be noted that the Q value indicating the goodness of the resonance circuit has a frequency f, a capacitance component C (mainly Ce in this embodiment), and a resistance component R.
(In the present embodiment, if it is mainly ra + re), in the case of a series resonance circuit, it is expressed by Q = 1 / (2πfCR) (Definition by Basics of Electricity and Electronics Ohmsha Co., Ltd., January 1992) It

Therefore, in the first embodiment of the present invention, in order to enhance the sensitivity, the two modulation electrodes 12a and 12a are formed.
b) It was decided to increase the Q value by increasing the film thickness of both. Here, the relationship between the combined resistance of the modulation electrode 12 and the film thickness of each of the two modulation electrodes 12a and 12b is shown in FIG.
It is represented by a curve as shown in. As can be seen from FIG. 4, by setting the film thickness of the two modulation electrodes 12a and 12b to 1 μm or more, the combined resistance of the modulation electrodes 12 can be suppressed to a small value, that is, the Q value can be increased. ,
Thereby, the sensitivity can be improved.

(Second Embodiment) Next, the second embodiment of the present invention will be described.
The electric field sensor according to the embodiment will be described with reference to FIG.

Also in the electric field sensor of the second embodiment, the substrate 8 made of a lithium niobate single crystal plate cut out perpendicularly to the c-axis was used.

In the electric field sensor according to the second embodiment of the present invention, the modulation electrode 12a is the phase shift optical waveguide 10a.
12a1, 12a2, in the traveling direction of light at
12a3 and 12a4 are divided into four, and similarly, the modulation electrode 12b includes 12b1, 12b2, 12b3,
And 12b4. Furthermore, the divided electrodes 12a1, 12a2, 12a3, 12a that have been divided.
4, 12b1, 12b2, 12b3, 12b4 are capacitively coupled to each other. The electric field receiving antenna 1 is a low radiation resistance antenna. In the electric field sensor according to the second embodiment, the combined capacitance Ce of the modulation electrode 12 is reduced, and the radiation resistance ra of the electric field receiving antenna 1 is reduced to increase the Q value of the resonance circuit. To increase the sensitivity of.

In the electric field sensor of the second embodiment, the two modulation electrodes 12a and 12b are each divided into four, but may be divided into five, six, etc. It is not limited.

Since the method of capacitive coupling of the divided electrodes is determined by the plane orientation of the crystal used as the substrate, when a crystal cut out in another plane orientation is used, it is suitable for the crystal. There is no limitation to this embodiment as long as capacitive coupling is performed.

The electric field receiving antenna 1 shown in FIG. 5 is an 8JK beam antenna according to the invention of Jiyon Claus, which is one of low radiation resistance antennas.
This 8JK beam antenna is constructed in the basic form shown in FIG. 6, and the elements 1a of L = λ / 2 dipoles (half-wavelength dipole antennas) are normally arranged in parallel at narrow intervals of about w = λ / 8, and have opposite phases. The principle is that the element 1a is excited by the opposite phase.
The radiation resistance becomes lower and smaller as the interval w of is reduced. Where λ is the wavelength of the radio wave.

The electric field sensor of the present invention may be provided with a director or a reflector such as a Yagi antenna. In this case, the sensitivity of the electric field sensor can be increased by concentrating radio waves.

Although the electric field sensors of the first and second embodiments have been described using the two modulation electrodes 12a and 12b, the modulation electrodes are not necessarily the two phase shift optical waveguides 10a and 10b. It does not have to be in the vicinity of both, and it may be provided only in the vicinity of either one of the phase shift optical waveguides.

(Third Embodiment) As a third embodiment of the present invention, as shown in FIG. 7, the electric field sensor of the present invention is used in a television relay broadcasting station or the like in which a transmission point and a reception point are separated. An example used in a transmission / reception transmission system will be described. This transmission / reception transmission system has the same components as those of the first embodiment shown in FIG. Further, this transmission / reception transmission system includes a photoelectric conversion circuit 14 that restores the light from the outgoing optical fiber 5 to the original RF signal, a compensation circuit 15 that receives light leaked from the photoelectric conversion circuit 14, and a compensation circuit 1.
Receives RF signal that passed 5 and IF signal (intermediate frequency signal)
It has a conversion amplifier circuit 16 for converting into. Furthermore, the conversion amplification circuit 16 converts the converted IF signal (intermediate frequency signal).
To the broadcaster.

As described above, according to the third embodiment of the present invention, since the optical signal can be directly modulated by the weak RF signal, the receiving side does not need a power source.

(Fourth Embodiment) As a fourth embodiment of the present invention, an electric field sensor of the present invention as shown in FIG. 8 is used for insulation of equipment to which high frequency and high voltage are applied. An example will be described.

In order to reduce the cost, the STL reception parabolic antenna 1b is often attached to the medium-wave antenna 17 of about 100 m as shown in FIG. The electric field sensor head 3 is grounded via the pole gap 18. Further, a medium wave transmitter 19 is connected to a connection point between the electric field sensor head 3 and the pole gap 18. Here, in general, a high frequency and a high voltage are applied to the medium-wave antenna 17, and a large insulation duplexer is used between the medium-wave antenna 17 and the STL receiver. However, in the fourth embodiment using the electric field sensor of the present invention, it is possible to eliminate the need for an insulation duplexer and reduce the cost.

(Fifth Embodiment) As a fifth embodiment of the present invention, as shown in FIG. 9, an example in which the electric field sensor of the present invention is used as a countermeasure against lightning damage on a wired line will be described. In the fifth embodiment of the present invention, the electric field sensor head 3 includes an external wired circuit 20 via an arrester 21 and a terminating resistor 22.
Connected with. As described above, when the electric field sensor according to the present invention is used, the transmission and reception can be electrically separated, so that it is possible to prevent the receiving side device from being damaged by lightning or the like.

[0050]

EXAMPLES Next, examples for confirming the effects of the present invention will be described.

The embodiment of the present invention is an electric field sensor having an electric field sensor head 3 of the type shown in FIG.

Here, the substrate 8 is formed of a lithium niobate crystal plate (Z plate). Titanium is diffused on this substrate 8 to form an incident optical waveguide 9 and two phase shift optical waveguides 10.
a and 10b, and the output optical waveguide 11 were formed.
Further, the entire surface is coated with a silicon dioxide (SiO ₂ ) film as a buffer layer for preventing absorption of light, and a pair of modulation electrodes 12a and 12b are formed in the regions corresponding to the two phase shift optical waveguides 10a and 10b. Was formed. The two modulation electrodes 12a and 12b are made of Au,
In order to set the combined resistance re of the modulation electrode 12 to 5Ω or less, the film thickness of each of the two modulation electrodes 12a and 12b was set to 1 μm. Also, two modulation electrodes 12a and 12b
Each of the two phase shift optical waveguides 10a and 10
The composite capacitance Ce of the modulation electrode 12 was set to be about 3 pF by dividing the light traveling direction in b into four.

When the combined resistance re and combined capacity Ce of the modulation electrode 12 were measured by a network analyzer,
The synthetic resistance re was 5Ω (500 MHz), and the synthetic capacitance Ce was 3 pF. Also, as the electric field receiving antenna 1,
An 8JK beam antenna having a distance w = λ / 10 between the elements 1a and a length L = λ / 2 of the element 1a was prepared (see FIG.
), The radiation resistance ra of the antenna was 5Ω when measured with a network analyzer.

The resonance correction circuit 2 and the 8JK beam antenna which is the electric field receiving antenna 1 were connected to the two modulation electrodes 12a and 12b of the electric field sensor head 3 and the electric field detection sensitivity was examined. The detection signal output of the photodetector 7 when the electric field intensity was 80 dBμV / m was 75 dBμV.

Further, in order to compare with the electric field sensor of the present invention, an electric field sensor having a conventional structure was prepared (see FIG. 10).
Here, the structure of the modulation electrode is a single electrode and the film thickness is 10
An electric field sensor having a conventional structure was prepared by using the same material and method except that the antenna was 00 × 10 ⁻¹⁰ m and the electric field receiving antenna was a half-wavelength dipole.

Therefore, when the combined resistance re and the combined capacitance Ce of the modulation electrodes of the electric field sensor head of this conventional structure were measured by a network analyzer, the combined resistance re was obtained.
Is 50 Ω (500 MHz), the combined capacitance Ce is 12 pF, and the radiation resistance ra of the half-wave dipole antenna is
Was 73Ω.

In contrast to this conventional electric field sensor, the light source 6
The measurement conditions of the photodetector 7 and the like are exactly the same as those of the embodiment of the present invention, and the electric field detection sensitivity is measured to be 500 MH.
With respect to the radio wave of z, the detection signal output of the photodetector 7 when the electric field strength was 80 dBμV / m was 55 dBμV.

As described above, the electric field sensor of the embodiment of the present invention has a higher sensitivity of 20 dB than the electric field sensor of the conventional structure.

As a result of combining the electric field sensor manufactured according to this example with the Yagi antenna provided with a director of 20 elements, a further sensitivity increase of 10 dB or more was observed.

Needless to say, when the frequency can be adjusted by the electric field receiving antenna and the modulation electrode, the resonance correction circuit is not necessary as described above.

[0061]

As described above, according to the present invention, the Q value of the resonance circuit can be increased, that is, the voltage applied to the modulation electrode formed near the shift optical waveguide can be amplified. This can increase the sensitivity.

Further, the combination of the electric field sensor head of the present invention and the Yagi antenna provided with a multi-element director can further enhance the sensitivity.

Further, if the electric field sensor of the present invention is used as a transmission / reception signal transmission system of a television relay broadcasting station in which transmission / reception points are separated, power supply to the receiving station side is not required, and therefore, it is possible to completely electrically complete the transmission. You can separate the sending and receiving points,
Greatly effective in preventing lightning damage.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a front view showing a main part of the first embodiment of the present invention.

FIG. 3A is a circuit diagram showing an equivalent circuit of a resonance circuit including an electric field receiving antenna and an electric field sensor head in the first embodiment of the present invention. (B) In the conventional example, it is a circuit diagram showing an equivalent circuit of a resonance circuit when a half-wavelength dipole antenna is used as the antenna. (C) In the conventional example, it is a circuit diagram showing an equivalent circuit of a resonance circuit when a short dipole antenna is used as the antenna.

FIG. 4 is a diagram showing the relationship between the film thickness of the modulation electrode and the resistance of the electric field sensor head in the first embodiment of the present invention.

FIG. 5 is a front view showing a main part of a second embodiment of the present invention.

FIG. 6 is a perspective view showing an electric field receiving antenna according to a second embodiment of the present invention.

FIG. 7 is a block diagram showing a third embodiment of the present invention.

FIG. 8 is a block diagram showing a fourth embodiment of the present invention.

FIG. 9 is a block diagram showing a fifth embodiment of the present invention.

FIG. 10 is a front view showing a main part of a conventional electric field sensor.

[Explanation of symbols]

1 Electric field receiving antenna 2 Resonance correction circuit 3 Electric field sensor head 4 incident optical fiber 5 Output optical fiber 6 light source 7 Photodetector 8 substrates 9 Incident optical waveguide 10a Phase shift optical waveguide 10b Phase shift optical waveguide 11 Output optical waveguide 12 Modulation electrode 12a modulation electrode 12b Modulation electrode 12a1 split electrode 12a2 split electrode 12a3 split electrode 12a4 split electrode 12b1 split electrode 12b2 split electrode 12b3 split electrode 12b4 split electrode 13 electrode pads

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuro Sato 6-7-1, Koriyama, Taihaku-ku, Sendai-shi, Miyagi Tokin Co., Ltd. Japan Broadcasting Corporation Broadcasting Center Broadcasting Center (72) Inventor Nakasho 2-2, Jinnan, Shibuya-ku, Tokyo Japan Broadcasting Corporation Broadcasting Center (72) Inventor Tadashi Ishikawa 2-2-1, Jinnan, Shibuya-ku, Tokyo Japan Within the Broadcasting Corporation Broadcasting Center (56) Reference JP 5-2043 (JP, A) JP 1-284826 (JP, A) JP 2-93423 (JP, A) JP 62-265619 ( JP, A) JP-A-52-95144 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01R 29/08 G01R 15/00-17/22

Claims (5)

(57) [Claims] 1. An electric field receiving antenna, a light source for emitting light, an incident optical fiber connected to the light source for transmitting light emitted by the light source, and connected to the electric field receiving antenna and the incident optical fiber. And an electric field sensor head configured to change the intensity of light incident through the incident optical fiber according to the electric field intensity of an input signal received by the electric field receiving antenna, and connected to the electric field sensor head. An electric field sensor comprising: an outgoing optical fiber that transmits transmitted light that has passed through an electric field sensor head; and a photodetector that receives the transmitted light via the outgoing optical fiber and detects a light intensity change of the transmitted light. The electric field sensor head may include a substrate, an incident optical waveguide formed on the substrate so as to be connected to the incident optical fiber, and branched from the incident optical waveguide. Two phase shift optical waveguides formed on the substrate and having a refractive index that changes according to the electric field strength of an input signal received by the electric field receiving antenna; and two phase shift optical waveguides connected to the output optical fiber are provided. An electric field sensor comprising an emission optical waveguide formed on the substrate so as to merge and a modulation electrode formed in the vicinity of at least one of the two phase shift optical waveguides, wherein the modulation electrode and the electric field receiving member are provided. The resonance circuit formed by the antenna further includes the modulation electrode and the electric field receiving antenna.
Insert into at least one of the paths connecting
An electric field sensor comprising a resonance correction circuit for improving sensitivity at a resonance frequency . 2. A method according to claim 1, wherein the modulating electrode has a thickness
Electric field sensor, characterized in that a least 1μm to. 3. The method of claim 1, wherein the modulation electrode, before
Formed near both of the two phase shift optical waveguides,
Moreover, the divided electrodes are divided in the light traveling direction, and the divided electrodes are capacitively coupled to each other .
And an electric field sensor. Wherein any one of claims 1 to 3
In the field sensor, wherein the electric field sensor, wherein the electric field receiving antenna is a low radiation resistance antenna. 5. to any one of claims 1 to 4
In the field sensor, wherein the electric field sensor further out of the waveguide and a reflector coupled to the electric field sensor, the electric field sensor characterized in that it comprises at least one.