JPH11202010A - Optical electric field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical electric field sensor which enables its reliability increase and high-sensitivity electric field measurement as well. SOLUTION: A sensor head is fitted with a directional coupling type 3 dB coupler 22, and a photodetector 4 is composed of two photoelectric converters 5 and an arithmetic circuit 6. Two output lights of a directional coupling type 3 dB coupler 22 strike the two photoelectric converters 5, respectively. The output signal lights of the photoelectric converters 5 are insulted to the arithmetic circuit 6, and one output signal light of the photoelectric converters 5 by an output signal light of a smaller one out of the optical biases of the two output signal lights of the directional coupling type 3 dB coupler 22 is outputted selectively. Along with it, the intensity of emitted light of a light source 3 is controlled so that the intensity of the said optical bias may be constant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical electric field sensor used for measuring characteristics of electromagnetic noise or relaying broadcast waves in the EMC field, and more particularly to an optical waveguide type optical electric field sensor.

[0002]

2. Description of the Related Art FIG. 4 is an explanatory view of a conventional optical electric field sensor. FIG. 4A is a block diagram of the optical electric field sensor.
(B) is an explanatory view of a sensor head used for the optical electric field sensor.

As shown in FIG. 4A, a conventional optical electric field sensor uses a sensor head 11 from a light source 3 through an optical fiber 7.
Incident light guided to the antenna 2 is intensity-modulated by an electric field of the surrounding environment captured by the antenna 2 to become outgoing light. The emitted light is guided by the optical fiber 8 to the photoelectric converter 5 as a photodetector, and is output from the output end 9 as an electric signal.

In the recent detection of electromagnetic noise, FIG.
As shown in FIG. 2, incident light from a light source introduced into a sensor head by an optical fiber 7 is captured by an antenna 2 and intensity-modulated by an electric field intensity applied to a modulation electrode 26 to become emission light. In many cases, a sensor head which is a type optical waveguide element is used.

In a conventional sensor head, as shown in FIG. 4B, a modulation electrode 26 and a phase shift optical waveguide 24 are formed on a substrate 21 so that an electric field generated by the modulation electrode 26 is orthogonal to the phase shift optical waveguide 24. It is provided so that. Further, one end of the phase shift optical waveguide 24 and the incident optical waveguide 23 are connected, and the other end of the phase shift optical waveguide 24 and the output optical waveguide 25 are connected. The modulation electrode 26 is shaped so as to be capacitively coupled along the phase shift waveguide 24 and is divided into a plurality of parts. Also, the incident optical waveguide 23
, The optical fiber 7, the outgoing optical waveguide 25 and the optical fiber 8 are connected.

This optical electric field sensor detects the electric field strength in a non-contact manner, and transmits the intensity-modulated outgoing light to the photodetector by the optical fiber 8, so that the transmission line system and its surrounding environment are connected. There is no transmission and reception of noise.

The output characteristic curve of the sensor head that determines the intensity of the emitted light with respect to the electric field intensity is expressed as a sine curve, and the electric field intensity is output after being modulated into the light intensity. The amplitude of the output characteristic curve depends on the intensity of incident light from the light source.

Due to the electric field applied to the phase shift optical waveguide, the intensity of the emitted light changes around the intensity of the emitted light when no electric field is applied (hereinafter referred to as an optical bias).

For electric field detection, it is most desirable to use a sensor head whose optical bias matches the midpoint between the maximum and minimum values on the output characteristic curve (hereinafter simply referred to as the midpoint).

The reason is that the gradient of the output characteristic curve is maximum at the middle point, so that the highest sensitivity is obtained near the middle point, and that the output characteristic curve has the best linearity near the middle point. Another problem is that the electric field intensity can be measured with a small waveform distortion.

[0011]

However, the deviation of the optical bias of the sensor head due to the temperature dependence of the output characteristics cannot be actually suppressed.
The output light intensity of the sensor head varies for that. This is one cause of the unreliability of the optical electric field sensor.

There are many difficulties in manufacturing a sensor head so that the optical bias is at the midpoint of the output characteristic curve, and it may not always be realized.

Since the photodetector has an upper limit in the intensity of the incident light, the intensity of the incident light of the sensor head is increased when the incident light has a large DC component (a component of the intensity of the optical signal that does not change with time). However, there is no effect, and the intensity of the AC component (a component of the optical signal that changes with time) that is a substantial signal is low.

In the case of receiving a weak signal requiring high sensitivity, it is particularly desirable that the AC (signal) component is larger than the DC component.

Therefore, an object of the present invention is to provide a high reliability,
Another object of the present invention is to provide an optical electric field sensor capable of measuring an electric field with high sensitivity.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to a receiving antenna for receiving an electric field, a light source for light incident on a sensor head, and a light input according to a signal voltage upon input of a signal received by the receiving antenna. A sensor head that intensity-modulates and emits light, and a photodetector that receives light emitted from the sensor head and converts the light into an electric signal. The sensor head includes a directional coupling type 3 dB coupler, The photodetector is an optical electric field sensor including two photoelectric converters to which two outputs of the directional coupling type 3 dB coupler are respectively incident, and an arithmetic circuit to which an output signal of the photoelectric converter is input.

Further, according to the present invention, in the arithmetic circuit, a circuit for inverting the phase is provided in one of the paths of the output signals of the two photoelectric converters to match the phase of the output signal light,
The above-mentioned optical electric field configured to selectively output one output signal of the photoelectric converter relating to the smaller output signal light of the two output signal lights of the directional coupling type 3 dB coupler of the sensor head. It is a sensor.

Further, according to the present invention, the arithmetic circuit includes an input signal of one of the photoelectric converters, the output signal being the smaller of the two output signal lights of the directional coupling type 3 dB coupler of the sensor head. The above optical electric field sensor controls the intensity of light emitted from the light source so that the light intensity is constant.

The present invention also provides the optical electric field sensor, wherein the arithmetic circuit inverts the phase of one of the output signals of the photoelectric converters and then combines and outputs the two output signals. is there.

Further, the present invention is the above-mentioned optical electric field sensor, wherein the substrate of the sensor head is made of a material exhibiting an electro-optic effect.

Further, the present invention is the above-mentioned optical electric field sensor, wherein the substrate of the sensor head is made of lithium niobate.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view for explaining an optical electric field sensor according to the present invention, and FIG. 1A is a block diagram of the optical electric field sensor.
FIG. 1B is an explanatory diagram of a sensor head used for the optical electric field sensor. FIG. 2 is a diagram showing output characteristics corresponding to two emission ends of the sensor head and a waveform of an output signal light according to an input signal.

As shown in FIG. 1B, the sensor head 1 used in the optical electric field sensor according to the present invention has a modulation electrode 26 connected to the antenna 2, an incident optical waveguide 23, It has an optical waveguide 25 and a phase shift optical waveguide 24. Further, a directional coupling type 3 dB coupler 22 is provided.

The phase shift optical waveguide 24 and the directional coupling type 3 dB coupler 22 are provided on a substrate 21 made of an X plate of lithium niobate crystal exhibiting an electro-optic effect.
By i-diffusion, the direction of the phase shift optical waveguide is
It is formed so as to be orthogonal to the azimuth.

The incident (guided) light from the light source to the incident optical waveguide 23 of the sensor head 1 through the optical fiber 7
The light is split into two phase-shifted optical waveguides 24. The electric field detected by the receiving antenna 2 is applied to the phase shift optical waveguide 24 via the modulation electrode 26, and the two guided lights are given a phase difference, and the directional coupling type 3 dB coupler 22
And is intensity-modulated.

At the two emission ends 29 of the directional coupling type 3 dB coupler 22, the phases are inverted with respect to each other, and light intensity signals having a complementary relationship are output to the optical fiber 8.

As shown in FIG. 1A, the sensor head 1
Are incident on the two photoelectric converters 5 of the photodetector 4 via the optical fiber 8, respectively, and the optical signals are converted into electric signals again and input to the arithmetic circuit 6,
The processed signal is output to the output terminal 9. Also,
The arithmetic circuit 6 and the light source 3 are connected by a feedback circuit 10.

The output characteristic of the sensor head having the directional coupling type 3 dB coupler is expressed as a sinusoidal curve as shown in FIG. 2, and the output characteristics have a complementary relationship between the two emission ends. I have.

FIG. 2 shows a characteristic curve A and a characteristic curve B showing output characteristics of output light corresponding to two output ends of the directional coupling type 3 dB coupler, an output signal light waveform a applied to an input signal, and an output signal. The optical waveform b is shown.

In the characteristic curves shown in FIG. 2A and FIG. 2B, the directional coupling type 3 dB
The magnitude relationship between the optical biases at the two exit ends of the coupler is reversed.

In the optical electric field sensor of the present invention, when the optical bias of the characteristic curve A is lower than the optical bias of the characteristic curve B, as shown in FIG. The arithmetic circuit selectively outputs the small output signal light a1.

As shown in FIG. 2B, when the optical bias of the characteristic curve A is higher than the optical bias of the characteristic curve B, the arithmetic circuit selectively outputs the output signal light b2 having a small DC component. Output.

In the present embodiment, in order to maintain the consistency of the output signal light of the arithmetic circuit, the arithmetic circuit operates in such a manner that one of the outputs of the two photoelectric converters is inverted in phase. Was done.

Further, the arithmetic circuit unit in the photodetector includes:
Since the feedback circuit is incorporated, the intensity of the incident light from the light source can be adjusted according to the output of the arithmetic circuit, and the intensity of the incident light can be controlled so that the output level of the optical bias becomes constant. became.

The optical electric field sensor always outputs the output signal light waveform having the smaller DC component among the two outputs of the sensor head by the selection and switching functions of the arithmetic circuit, and the feedback circuit controls the light source. The output light intensity was controlled and the temperature dependence was substantially reduced.

In the optical electric field sensor according to the present embodiment, even if the optical bias is deviated, the output fluctuation of the optical electric field sensor is suppressed.

Further, even when the output characteristics of the sensor head itself have a temperature dependency, the influence of the temperature dependency is suppressed in the optical electric field sensor of the present embodiment.

The optical electric field sensor of the present invention is useful as an optical electric field sensor that suppresses the adverse effects of the optical bias of the sensor head regardless of the cause.

Next, a second embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is an explanatory view of an optical electric field sensor having another configuration according to the present invention. The configuration of the sensor head in the present embodiment is exactly the same as the sensor head described in the first embodiment, and a description thereof will be omitted.

As shown in FIG. 3, two outgoing lights from the sensor head 1 are respectively incident on two photoelectric converters 5 via an optical fiber 8, and optical signals are converted into electric signals again. It is input to the arithmetic circuit 6.

In the arithmetic circuit 6, the output signal light of the two photoelectric converters 5 is obtained by inverting the phase of one output signal light,
It is combined with the other signal and output as information indicating the electric field strength.

The configuration of the optical electric field sensor according to the present embodiment is such that half of the component to be emitted, which has been wasted as a radiation mode outside the emission optical waveguide in the conventional optical electric field sensor, is also used as a radiation mode. The mode was effectively used, and substantially double the sensitivity was achieved.

[0045]

As described above, according to the present invention, as long as a constant bias of optical bias is permitted regardless of the reason for manufacturing the sensor head or the reason accompanying a change in the installation environment, etc. Thus, an optical electric field sensor that exhibits highly sensitive and highly reliable measurement results can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating an optical electric field sensor according to the present invention. FIG. 1A is a block diagram of the optical electric field sensor, and FIG.
FIG. 4 is an explanatory diagram of a sensor head used for an optical electric field sensor.

FIG. 2 is a diagram showing output characteristics corresponding to two emission ends of a sensor head, and a waveform of an output signal light according to an input signal.

FIG. 3 is an explanatory view of an optical electric field sensor having another configuration according to the present invention.

4A and 4B are explanatory diagrams of a conventional optical electric field sensor. FIG. 4A is a block diagram of the optical electric field sensor, and FIG. 4B is an explanatory diagram of a sensor head used for the optical electric field sensor.

[Explanation of symbols]

 Reference Signs List 1 sensor head (of the present invention) 2 (receiving) antenna 3 light source 4 photodetector 5 photoelectric converter 6 arithmetic circuit 7,8 optical fiber 9 output end 10 feedback circuit 11 (conventional) sensor head 21 substrate 22 directionality Coupling type 3 dB coupler 23 Incident optical waveguide 24 Phase shift optical waveguide 25 Emitting optical waveguide 26 Modulation electrode 29 Emitting end

Claims (6)

[Claims] 1. A receiving antenna for receiving an electric field, a light source for light incident on a sensor head, a signal received by the receiving antenna, and intensity-modulated light incident on the antenna according to the voltage of the signal for emission. A sensor head is coupled with a photodetector that receives light emitted from the sensor head and converts the light into an electric signal. The sensor head is a directional coupling type 3 dB.
A coupler is provided, and the photodetector has two photoelectric converters to which two outputs of the directional coupling type 3 dB coupler are respectively incident, and an arithmetic circuit to which an output signal of the photoelectric converter is input. An optical electric field sensor comprising: 2. The arithmetic circuit according to claim 1, wherein a circuit for inverting a phase is provided in one path of the output signal lights of the two photoelectric converters to match a phase of the output signal light, and a direction of the sensor head is adjusted. 2. The configuration according to claim 1, wherein one of the two output signal lights of the sex-coupling type 3 dB coupler is output selectively from one of the photoelectric converters, the output signal being one of the smaller output signal lights. Optical electric field sensor. 3. The arithmetic circuit according to claim 2, wherein, of the two output signal lights of the directional coupling type 3 dB coupler of the sensor head, an input signal light intensity of the photoelectric converter related to a smaller output signal light is constant. 3. The optical electric field sensor according to claim 2, wherein the intensity of the emitted light from the light source is controlled so that the light intensity is controlled. 4. The arithmetic circuit according to claim 1, wherein one of the photoelectric converters is inverted in phase, and then the two output signals are combined and output. The optical electric field sensor according to claim 1. 5. The optical electric field sensor according to claim 1, wherein the substrate of the sensor head is made of a material exhibiting an electro-optic effect. 6. The optical electric field sensor according to claim 5, wherein the substrate of the sensor head is made of lithium niobate.