JPH07113824A - Electric field sensor and voltage sensor - Google Patents

Abstract

PURPOSE:To provide an electric field/voltage sensor of an optical resonator type which shows, in spite of a simple light source, a higher sensitivity than a conventional electric field/voltage sensor measuring a retardation based on the Pockels effect. CONSTITUTION:The electric field sensor measures a space electric field by detecting a change of a refractive index of an electrooptic crystal due to an electric field with the use of light. An electrooptic crystal 1 is disposed between confronting two partial transmitting mirrors 2 and 3 to constitute an optical resonator. In the electric field sensor, a light beam from a light source is made incident on from one partial transmitting mirror 2, and emitted light beams from the optical resonator corresponding to two allowed vibration light beams in the electrooptic crystal 1 are interfered with each other by an analyzer or the like, and a frequency of a beat signal corresponding to a frequency difference of the allowed vibration light beams is detected by a detecting means (photodetector, frequency detector or the like), whereby a space electric field is measured. If the electrooptic crystal is held between two confronting electrodes, the sensor is turned to a voltage sensor for measuring a potential difference between the confronting electrodes.

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 and a voltage sensor for measuring an electric field and a voltage by using an electro-optic crystal.

[0002]

2. Description of the Related Art Although the idea of measuring an electric field and a voltage by utilizing the Pockels effect of an electro-optic crystal has long been known, it is difficult to measure a weak electric field and a voltage because the electro-optic crystal has a low sensitivity to the electric field. A complicated means such as performing synchronous detection by modulating the incident light on the electro-optic crystal is required (see Japanese Patent Laid-Open No. 4-359165, etc.), and this is a problem in practical use. Therefore, the inventors of the present invention have devised an optical resonator type electric field / voltage sensor in order to increase the sensitivity of the sensor portion to electric fields and voltages using an electro-optic crystal. In this structure, mirrors are arranged on both sides of the electro-optic crystal to form an optical resonator, so that a larger intensity change and a larger phase change than those of the conventional electric field and voltage sensor can be obtained.

[0003]

However, in the optical resonator type electric field / voltage sensor, in addition to the fact that a light source for making light incident on the optical resonator has to have a narrow line width, There is a problem that the frequency must be stably operated near the resonance frequency of the optical resonator. The present invention was devised to solve such a problem, and uses a light source with higher sensitivity than an electric field / voltage sensor that measures retardation due to the conventional Pockels effect while using a simpler light source. An object is to provide a resonator type electric field sensor and a voltage sensor.

[0004]

In order to achieve the above object, the invention of claim 1 uses a light to detect a change in the refractive index of an electro-optic crystal due to an electric field, thereby measuring a spatial electric field. In the sensor, an electro-optic crystal is arranged between two facing partially transmissive mirrors to form an optical resonator, and light from a light source is made incident from one of the partially transmissive mirrors. The spatial light field is measured by interfering the light emitted from the optical resonator corresponding to one of the intrinsic polarizations and detecting the frequency of the beat signal corresponding to the frequency difference between the intrinsic polarizations. Is characterized by.

According to a second aspect of the invention, in a voltage sensor for measuring a potential difference between the electrodes by detecting a change in the refractive index of the electro-optic crystal held by the counter electrodes due to the electro-optic effect, using light. , An optical resonator is formed by disposing an electro-optic crystal sandwiched by a counter electrode between two facing partial transmission mirrors, and light from a light source is made incident from one of the partial transmission mirrors. By interfering the light emitted from the optical resonators corresponding to the two intrinsic polarizations in the crystal and detecting the frequency of the beat signal corresponding to the frequency difference between the intrinsic polarizations, the potential difference between the counter electrodes is It is characterized in that it is configured to perform measurement.

Here, the optical resonator comprises an external partial transmission mirror arranged outside the electro-optic crystal and the other partial transmission mirror provided on one surface of the electro-optic crystal, or Opposite two of electro-optic crystal
The structure is such that a partial transmission mirror is provided on one end face (claim 3).

Further, the light source for causing the light to enter the optical resonator is configured to use an LED (Light Emitting Diode) or an SLD (Super Luminecence Diode) (claim 4).

[0008]

The present invention was devised to measure electric fields and voltages with high sensitivity using an electro-optic crystal. An electric field / voltage sensor using a conventional electro-optic crystal has a retardation (2
The electric field and voltage are measured by detecting the phase difference between two intrinsic polarizations. However, in this method, the half-wave voltage of the electro-optic crystal is so high that it is difficult to measure a minute electric field or voltage. Therefore, in the present invention, as in the electric field sensor according to claim 1 and the voltage sensor according to claim 2, by using the configuration in which the electro-optic crystal is inserted into the optical resonator, a more sensitive electric field / voltage sensor is realized. did.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration, operation and operation of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram illustrating the principle of an optical resonator according to the present invention, and FIG. 2 is a schematic configuration diagram of an electric field (voltage) sensor showing an embodiment of the present invention. The electric field sensor includes a light source, a deflector, and a sensor portion ( The optical resonator), the analyzer, the light receiver, and the frequency measuring device. Hereinafter, the principle of the present invention will be described with reference to FIGS. As shown in FIG. 1, two partially transmissive mirrors 2 and 3 facing each other.
Between electro-optic crystal 1 (eg KDP, ADP, BS
O, LiNbO ₃ etc.) to form an optical resonator,
Consider a case where light is incident from one of the partial transmission mirrors 2. However, it is assumed that light having an appropriate spectrum width is used as the incident light, and that the incident light is vertically incident for simplicity. At this time, the q-th resonance frequency f _a corresponding to the two intrinsic polarizations a and b of the electro-optic crystal 1
f _{b is, f a = qc 0/2} {n 0 (d 1 + d 3) + n a d 2} ··· (1) f b = qc 0/2 {n 0 (d 1 + d 3) + n b d ₂ } It is expressed as (2). Where c ₀ is the speed of light and d ₁ , d ₂ , d ₃
Is the thickness of each region, n ₀ is the refractive index of the regions corresponding to d ₁ and d ₃ , and n _a and n _b are the respective refractive indices corresponding to the two intrinsic polarizations a and b of the electro-optic crystal. . Of the light incident on the optical resonator, the light having a frequency matching the above resonance frequency is transmitted through the optical resonator. Therefore, as shown in FIG. 2, the transmitted lights corresponding to the two unique polarizations a and b of the electro-optic crystal are made to interfere with each other by the analyzer, and the light is received by the photodetector, so that the respective intrinsic lights in the electro-optic crystal are received. refractive index n _a polarization feel, frequency corresponding to the difference between the n _b | it is possible to obtain a beat signal of | f _a -f _b.

On the other hand, the electro-optic crystal 1 inserted in the optical resonator can produce birefringence according to the electric field strength in the crystal by appropriately selecting the point group and orientation of the crystal. now,
Assuming that the refractive indices for the intrinsic polarized lights a and b are changed by Δn _a and Δn _b due to the electro-optic effect, the resonance frequencies f _a ′ and f _b ′ in the equations (1) and (2) are f _a ′ = qc _{0. / 2 {n 0 (d 1} + d 3) + (n a + Δn a) d 2} ··· (3) f b '= qc 0/2 {n 0 (d 1 + d 3) + (n b + Δn b ) d _2} ··· (4), and the frequency of the beat signal | f _a -f _b | a | f _a '
-F _b '| Since a specific relational expression holds for the change in the electric field and the refractive index in the electro-optic crystal, the change in the beat frequency is detected by the frequency measuring device as shown in FIG. 2 to measure the electric field in the crystal. It becomes possible.

Next, FIGS. 3 (a) and 3 (b) show a structural example of an optical resonator used in the voltage sensor of the present invention.
As shown in (a) and (b), when the electro-optic crystal 1 is sandwiched by the two opposing electrodes 4 and 5, a beat frequency signal corresponding to the potential difference between the electrodes can be obtained. If this optical resonator is used in the sensor portion of FIG. 2, it can be used as a voltage sensor. However, in this case, 2
The point group and orientation of the electro-optical crystal 1 and the arrangement of the electrodes 4 and 5 (vertical arrangement or horizontal arrangement) are set so that the electro-optical crystal 1 causes the birefringence as described above by the electric field formed between the electrodes. It is necessary to select it appropriately.

Although the two partial transmission mirrors 2 and 3 are provided outside the electro-optical crystal in FIGS. 1 to 3, as shown in FIG. 4, one partial transmission mirror is provided on the end surface of the electro-optical crystal. By forming it, the structure of the sensor can be simplified and miniaturized, and the loss due to reflection on the electro-optic crystal surface can be suppressed to only one side. Further, as shown in FIG. 5, it is possible to further miniaturize the sensor by forming two partial transmission mirrors on both sides of the electro-optic crystal. However, with this configuration, the characteristics of the optical resonator (width of transmitted light spectrum, finesse, etc.) and the sensitivity of the electro-optic crystal to the electric field (change in optical path length with respect to the electric field)
Will have a correlation, and there may be a case where a configuration suitable for the purpose of use cannot be obtained.

Next, in the electric field / voltage sensor of the present invention, the light source for supplying light to the optical resonator has a spectral width larger than the difference between the resonance frequencies of the optical resonators corresponding to the above two intrinsic polarizations. What you have is needed. Here, when a laser is used as the light source, the oscillation spectrum width of the laser is narrow, so that the oscillation frequency must be stably operated in the vicinity of the resonance frequency of the optical resonator, and the dynamic range for the electric field and voltage is Has the drawback of being narrowed. Therefore, as a more practical light source, LE having a wider spectrum width than a laser is used.
D (Light Emitting Diode) and SLD (Super Luminecenc)
e Diode) is possible. However, when an LED is used as a light source, there is an advantage that the sensor can be constructed at a very low cost, but the spectrum width of the beat signal frequency is widened, which may lead to a decrease in sensitivity. On the other hand, the SLD has an appropriate spectrum width and high brightness, and is therefore a light source suitable for the principle of the present invention. still,
Whichever light source is used, the coherence degree can be increased by allowing the polarizer to pass before entering the optical resonator as shown in FIG.

[0014]

As described above, in the electric field sensor according to the first aspect of the invention, an electro-optic crystal is arranged between two facing partial transmission mirrors to form an optical resonator, and the light from the light source is transmitted to one side. Of the beat signal corresponding to the frequency difference between the intrinsic polarizations by interfering the light emitted from the optical resonator corresponding to the two intrinsic polarizations in the electro-optic crystal. Since the spatial electric field is measured by the detection, the electric field sensor having a higher sensitivity than the conventional electric field sensor for detecting the retardation can be configured.

According to another aspect of the voltage sensor of the present invention, an electro-optical crystal sandwiched by a counter electrode is arranged between two facing partially transmissive mirrors to form an optical resonator, and light from a light source is used for one of the above. The frequency of the beat signal corresponding to the frequency difference between the intrinsic polarizations is detected by causing the light emitted from the optical resonator corresponding to the two intrinsic polarizations in the electro-optic crystal to interfere with each other by entering the partial transmission mirror. Thus, since the potential difference between the opposed electrodes is configured to be measured, it is possible to configure a voltage sensor with higher sensitivity than the conventional voltage sensor that detects retardation.

According to another aspect of the electric field and voltage sensor of the present invention, the optical resonator comprises an external partial transmission mirror arranged outside the electro-optical crystal and the other partial transmission mirror provided on one surface of the electro-optical crystal. Thus, the structure of the optical resonator can be simplified and miniaturized, and the loss of light inside the resonator due to reflection on the electro-optic crystal surface can be reduced. Further, by configuring the optical resonator with the partial transmission mirrors on the two opposing end faces of the electro-optic crystal, a sensor smaller than the above configuration can be configured, and the loss of light inside the resonator can be achieved. Can be suppressed.

According to the electric field / voltage sensor of the fourth aspect, by using an LED as a light source for making light incident on the optical resonator, a small and inexpensive sensor can be constructed. When the SLD is used for the sensor, a sensor having higher sensitivity than the case where the LED is used can be configured.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of an optical resonator of an electric field sensor according to the present invention.

FIG. 2 is a schematic configuration diagram of an electric field (voltage) sensor showing an embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of an optical resonator used in the voltage sensor of the present invention.

FIG. 4 is a diagram showing another configuration example of the optical resonator used in the electric field / voltage sensor of the present invention.

FIG. 5 is a diagram showing still another configuration example of the optical resonator used in the electric field / voltage sensor of the present invention.

[Explanation of symbols]

 1: electro-optic crystal 2, 3: partial transmission mirror 4, 5: electrode a, b: intrinsically polarized light

Claims (4)

[Claims] 1. In an electric field sensor for measuring a spatial electric field by detecting a change in the refractive index of the electro-optic crystal due to an electric field using light, the electro-optic crystal is provided between two facing partial transmission mirrors. The optical resonators are arranged so that light from the light source is incident from one of the partial transmission mirrors, and light emitted from the optical resonators corresponding to two intrinsic polarizations in the electro-optic crystal is caused to interfere with each other. An electric field sensor configured to measure a spatial electric field by detecting a frequency of a beat signal corresponding to a frequency difference between the intrinsic polarized lights. 2. A voltage sensor for measuring a potential difference between the electrodes by detecting a change in the refractive index of the electro-optical crystal held by the counter electrodes due to the electro-optic effect by using light, and two electrodes facing each other. The electro-optic crystal sandwiched by the counter electrodes is arranged between the partial transmission mirrors of 1 to form an optical resonator, and the light from the light source is made incident from one of the partial transmission mirrors, and By measuring the frequency of the beat signal corresponding to the frequency difference between the intrinsic polarized lights by interfering the light emitted from the optical resonator corresponding to the intrinsic polarized light, the potential difference between the counter electrodes is measured. A voltage sensor characterized by being configured. 3. The optical resonator comprises an external partial transmission mirror arranged outside the electro-optic crystal and the other partial transmission mirror provided on one surface of the electro-optic crystal, or 3. The electric field sensor according to claim 1 and the voltage sensor according to claim 2, wherein a partial transmission mirror is provided on two opposing end faces of the optical crystal. 4. An LED (Light Emitting Diode) or an LED (Light Emitting Diode) is provided in the light source for causing light to enter the optical resonator.
The electric field sensor and the voltage sensor according to any one of claims 1 to 4, wherein the electric field sensor and the voltage sensor have a configuration using an SLD (Super Luminecence Diode).