JPH06289064A - Fabry-perot resonator type electric field sensor - Google Patents

Abstract

PURPOSE:To improve the S/N ratio and measuring sensitivity of the sensor by applying a signal voltage to transparent electrodes arranged on both sides of a first electrooptical crystal and controlling an optical resonator length. CONSTITUTION:Transparent electrodes 1, 2 are provided on both sides of a first electrooptical crystal 5, and a dielectric mirror 3 is arranged between the electrode 1 and the crystal 5. A second electrical crystal 6 is disposed near the crystal 5 to constitute an optical resonator with a dielectric mirror 7 provided on one side of the crystal 6. If an incident laser light varies in its wavelength, a DC voltage is applied to the electrodes 1, 2 to vary a refractive index of the crystal 5 to control an optical resonator length, thereby turning the resonance frequency of the resonator with the frequency of the incident light. Thus, an electric field sensor having a high sensitivity can be realized. As the crystal 5, electrooptical crystal belonging to point groups 4, 4mm, 3, 3m, 6, 6mm is used, and a longitudinal modulator in which an optical axis coincides with the direction of the probe light is formed. Further, a spatially electric field can be measured by the crystal 6.

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 for measuring a spatial electric field and surface potential used for optical application measurement.

[0002]

2. Description of the Related Art Conventional methods for measuring a spatial electric field include various methods such as a method using electrostatic induction, a method using electric field force and ion motion. Recently, a method utilizing the electro-optical effect has been used as a method for evaluating a high-speed electronic device because of its high responsiveness.This method is called an electro-optical sampling method, and is a method called electro-optical sampling. This is a method of measuring an electric field by using an optical element having an optical effect as an electric field sensor for detecting a leakage electric field from an electronic device and detecting a phase change and a polarization state change of probe light due to birefringence. In this method, the electro-optic constant of the electro-optic crystal must be made large in order to increase the detection sensitivity, but in reality, no electro-optic crystal with a large electro-optic constant exists, and therefore,
It is difficult to measure a minute electric field. As a solution to such a problem, for example, Japanese Patent Application No.
-122309, there is a Fabry-Perot-resonator type electric field sensor. In this method, an electro-optic crystal is arranged inside the resonator, and when an electric field is applied to this electro-optic crystal, the intensity of transmitted light or reflected light from the resonator changes in accordance with the change in the optical path length of the resonator. The electric field can be measured by detecting the electric field.

[0003]

However, this method cannot accurately measure the electric field when the wavelength of the incident light fluctuates. Therefore, there is a problem that the incident light must be stabilized in the vicinity of the resonance frequency, and this problem hinders the practical application of the Fabry-Perot-resonator type electric field sensor. The present invention has been made in view of the above problems, and is a practical solution to the above problems by controlling the optical resonator length of the electric field sensor instead of controlling the frequency of incident light. Fabry
An object is to provide a Pero-resonator type electric field sensor.

[0004]

According to the invention of claim 1, a Fabry-Perot having an electro-optic crystal between dielectric mirrors.
In a resonator type electric field sensor, first and second transparent electrodes are arranged on both sides of a first electro-optical crystal, and a first electro-optical crystal is provided between the first transparent electrode and the first electro-optical crystal. A dielectric mirror is arranged, a second electro-optic crystal is arranged in the vicinity of the first electro-optic crystal, and a dielectric mirror is arranged on one side surface of the second electro-optic crystal. An air gap is provided between the second transparent electrode and the second electro-optic crystal, and a feedback signal voltage corresponding to wavelength fluctuation is applied to the transparent electrodes provided on both sides of the first electro-optic crystal. The refractive index of the first electro-optic crystal is changed to control the optical resonator length.

According to the second aspect of the invention, the electro-optic crystal for controlling the resonator length for applying a voltage has a point group of 4, 4 mm, 3,
It was decided to use electro-optic crystals belonging to 3 m, 6 and 6 mm.

According to the third aspect of the invention, in the Fabry-Perot-resonator type electric field sensor, the spatial electric field is measured by the second electro-optic crystal.

According to the fourth aspect of the invention, the surface potential is measured by disposing the transparent mirror on one side surface of the second electro-optic crystal and disposing the transparent electrode on the other side surface.

According to the invention of claim 5, the surface potential is measured by using the second transparent electrode provided on the first electro-optic crystal and the third transparent electrode provided on the second electro-optic crystal in common. I decided to do it.

[0009]

According to the invention of claim 1, in a Fabry-Perot resonator type electric field sensor having an electro-optic crystal between dielectric mirrors, a first and a second electro-optic crystal are provided on both sides of the first electro-optic crystal. A transparent electrode is provided, and a first dielectric mirror is provided between the first transparent electrode and the first electro-optic crystal,
A second electro-optic crystal is arranged in the vicinity of the first electro-optic crystal, a dielectric mirror is arranged on one side surface of the second electro-optic crystal, and the second transparent electrode and the second electro-optic crystal are arranged. A void is provided between the electro-optic crystals, and a transparent electrode provided on both sides of the first electro-optic crystal is applied with a feedback signal voltage corresponding to the wavelength variation, and the refractive index of the first electro-optic crystal is applied. Can be changed to control the optical resonator length.

According to the second aspect of the invention, the first electro-optic crystal has a point group of 4, 4 mm, 3, 3 m, 6, 6 mm.
It is possible to measure the electric field by utilizing the birefringence of only the second electro-optic crystal, since the one belonging to (1) is used.

According to the third aspect of the invention, a direct current voltage corresponding to the wavelength variation of the incident laser light is applied to the transparent electrode of the first electro-optical crystal to control the resonator length, and the second electrode It becomes possible to measure the spatial electric field by the electro-optic crystal.

According to the fourth aspect of the present invention, the surface potential can be measured by disposing a dielectric mirror on one side surface of the second electro-optic crystal and disposing a transparent electrode on the other side surface. Become.

According to the fifth aspect of the invention, the second transparent electrode provided on the first electro-optic crystal and the third transparent electrode provided on the second electro-optic crystal are commonly used as the second transparent electrode. It becomes possible to measure the surface potential by using the electro-optic crystal.

[00014]

EXAMPLES Examples of the present invention will be described below. The present invention, in a Fabry-Perot-resonator type electric field sensor used for high-sensitivity electric field measurement, controls the optical resonator length of the electric field sensor so that the potential and the electric field can be measured. It was done.

The Fabry-Perot resonator type electric field sensor has a structure in which an electro-optic crystal is inserted inside the resonator as shown in FIG. When an electric field is applied to this electro-optic crystal, the intensity or phase of the transmitted light or reflected light from the resonator changes according to the change in the optical path length of the resonator, and the electric field can be measured by detecting this. The Fabry-Perot resonator type electric field sensor can realize an electric field sensor having a higher mirror reflectivity and a longer resonator length to have a higher sensitivity to an electric field.

FIG. 1 shows the configuration of the present invention. FIG. 1 is a Fabry-Perot-resonator type electric field sensor placed in a spatial electric field. Transparent electrodes 1 and 2 are provided on both sides of the first electro-optic crystal 5, and a dielectric mirror 3 is provided between the transparent electrode 1 and the first electro-optic crystal 5. A second electro-optic crystal 6 is arranged near the first electro-optic crystal 5, and an optical resonator is formed by a dielectric mirror provided on one side surface of the second electro-optic crystal 6. Are configured. As a material of the first electro-optic crystal 5, for example, Li
There is NbO ₃ , and examples of the material of the second electro-optical crystal 6 include KDP and ADP.

When laser light is incident on the Fabry-Perot-resonator type electric field sensor placed in the spatial electric field in such a structure, the optical path length of the resonator changes in accordance with the intensity of the spatial electric field. The intensity or phase of the transmitted light or the reflected light from the resonator changes according to the change of the optical path length, and the electric field can be measured by detecting this. When the wavelength of the incident laser light fluctuates, a direct current voltage is applied to the transparent electrodes 1 and 2 arranged on both sides of the first electro-optic crystal to control the resonator length. As described above, another electro-optic crystal provided with electrodes in the configuration of FIG. 4 is inserted into the resonator, and a feedback signal voltage corresponding to wavelength fluctuation is applied to the electro-optic crystal to change the refractive index. It is possible to control the optical resonator length. The voltage application for controlling the resonator length may be the same as in FIG.

When selecting an electro-optic crystal for controlling the cavity length, it is necessary to prevent birefringence due to this, and as an electro-optic crystal therefor, the point groups 4, 4 mm, 3 and 3 m are used. , 6 mm, 6 mm, and 6 mm, and a vertical modulator having an optical axis aligned with the direction of the probe light is used. This is because when the electric field is applied in the optical axis direction, the refractive index ellipsoid of these crystals is isotropic regardless of the presence or absence of the electric field.

FIG. 2 shows an example in which the electric field sensor of the present invention is used as a surface potential sensor. Transparent electrodes 1 and 2 are provided on both sides of the first electro-optical crystal 5, and a dielectric mirror is provided between the transparent electrode 1 and the first electro-optical crystal 5.
3 are arranged. Further, a second electro-optic crystal 6 is arranged in the vicinity of the first electro-optic crystal 5, and an optical resonator is formed with a transparent mirror provided on one side surface of the second electro-optic crystal 6. Are configured. The difference from FIG. 1 is that the dielectric mirror 7 of the second electro-optic crystal 6 in FIG.
The point is that the transparent electrode 8 is provided on the opposite surface where is provided.
When the electro-optic crystal for electric field measurement has a vertical modulation structure in which the refractive index changes only with respect to the electric field in the same direction as the probe light, the magnitude of birefringence is determined by the voltage applied to both sides of the crystal. Therefore, the potential on the bottom face of the crystal can be measured by providing a transparent electrode on the upper surface of the crystal to form a reference for the potential. That is, this sensor can be used as a surface potential sensor. In other words, by providing a transparent electrode on the surface inside the resonator facing the dielectric mirror as shown in FIG. 2, the potential on the dielectric mirror surface of the electro-optic crystal for electric field measurement with respect to the potential of this electrode Can be measured.

Here, the voltage applied to the transparent electrodes 1 and 2 will be specifically described. A polarization beam splitter 9 is arranged after the second electro-optical crystal 6, and the laser light emitted from the second electro-optical crystal 6 is divided into transmitted light and reflected light, and each light is a photodiode. Optical sensor-11 (PD
1) and 12 (PD2) receive light, and the difference signals PD1-PD2 of the output signals of 11 and 12 are applied to the transparent electrodes 1 and 2 as a feedback signal. In this way, the resonator length can be controlled according to the frequency of incident light. Further, the output signal of PD1 can be taken out as a signal representing the electric field strength. Also in this case, the measured potential is a potential based on the transparent electrode 8.

FIG. 3 is a modification of FIG. In FIG. 3, the transparent electrode 1 and the dielectric mirror are arranged from the laser light incident side.
3, the first electro-optic crystal 5, the transparent electrode 10, the second electro-optic crystal 6, and the dielectric mirror 7 are arranged in this order. The difference from FIG. 2 is that there is no space between the transparent electrode 2 provided on the first electro-optic crystal 5 and the transparent electrode 8 provided on the second electro-optic crystal 6, and the transparent electrode is It is a common point. In general, the structure shown in FIG. 2 has a higher detection sensitivity, but in the case where the detection sensitivity does not have to be considered so much, the electric field sensor can be made compact because the void can be eliminated. Moreover, since the transparent electrode is shared, the cost can be reduced economically.

[00022]

According to the invention of claim 1, a transparent electrode is provided on the first electro-optic crystal so as to sandwich the electro-optic crystal,
A direct current voltage is applied to the transparent electrode, and a laser for probe is used.
Since the optical resonator length of the Fabry-Perot resonator is controlled so as to follow the wavelength fluctuation of the light, the optical resonator length is kept constant even if the wavelength of the laser light changes. Since it can be maintained, the SN ratio is improved and the sensitivity can be improved.

The invention according to claim 2 is characterized in that the point cloud is 4, 4 m.
Since the electro-optic crystal belonging to m, 3, 3 m, 6, and 6 mm is used, the resonator length can be controlled without causing birefringence.

According to the third aspect of the present invention, the optical resonator length can be controlled, and the spatial electric field can be measured by the second electro-optic crystal.

According to the fourth aspect of the invention, since the dielectric mirror is disposed on one side surface of the second electro-optic crystal and the transparent electrode is disposed on the other side surface, the surface potential can be measured. .

According to a fifth aspect of the present invention, the second transparent electrode provided on the first electro-optic crystal and the third transparent electrode provided on the second electro-optic crystal are made common, so that both are provided. Since there is no space between them, the device is downsized and the transparent electrode is shared, so that the cost can be reduced economically.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the invention described in claim 1.

FIG. 2 is a diagram showing an embodiment of the invention described in claim 4;

FIG. 3 is a diagram showing an embodiment of the invention described in claim 5;

FIG. 4 is a diagram showing a basic configuration of a conventional Fabry-Perot-resonator type electric field sensor having an electro-optic crystal between dielectric mirrors.

[Explanation of symbols]

 1,2,8,10 Transparent electrode 3,4,7 Dielectric mirror 5 First electro-optic crystal 6 Second electro-optic crystal 9 Polarization beam splitter-11, Voltage applying means 12,13 Optical sensor-

Claims (5)

[Claims] 1. A Fabry-Perot resonator type electric field sensor having an electro-optic crystal between dielectric mirrors, wherein first and second transparent electrodes are provided on both sides of the first electro-optic crystal. A first dielectric mirror is arranged between the first transparent electrode and the first electro-optic crystal, and a second electro-optic crystal is arranged in the vicinity of the first electro-optic crystal, A dielectric mirror is disposed on one side surface of the second electro-optic crystal, and the second mirror
An air gap is provided between the transparent electrode and the second electro-optic crystal, and a feedback signal voltage corresponding to wavelength fluctuation is applied to the transparent electrodes provided on both sides of the first electro-optic crystal. 1. A Fabry-Perot-resonator type electric field sensor, characterized in that the optical resonator length is controlled by changing the refractive index of the electro-optic crystal. 2. The electro-optic crystal for controlling the resonator length for applying a voltage is an electro-optic crystal belonging to the point group 4, 4 mm, 3, 3 m, 6, 6 mm. The described Fabry-Perot-resonator type electric field sensor. 3. The Fabry-Perot-resonator type electric field sensor according to claim 1, wherein the spatial electric field is measured by the second electro-optic crystal. 4. The surface potential is measured by disposing a dielectric mirror on one side surface of the second electro-optical crystal and disposing a transparent electrode on the other side surface of the second electro-optical crystal. Fabry-Perot-Resonator type electric field sensor-. 5. The second transparent electrode provided on the first electro-optic crystal and the third transparent electrode provided on the second electro-optic crystal are commonly used. The described Fabry-Perot-resonator type electric field sensor.