JP3159823B2 - Optical electric field measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical type electric field measuring apparatus for measuring an electric field using an electro-optic crystal, and more particularly to improvement of detection characteristics.

[0002]

2. Description of the Related Art Generally, when an electric field is applied to a substance, its optical properties change. Such a phenomenon is widely called an electro-optic effect, and for example, the Pockels effect, the Kerr effect, and the like are well known. Such an electro-optic effect is given by the following formula as the refractive index n of a substance when an electric field E is applied to the substance. n = n0 + an + bn2 +... where n0: refractive index before electric field application E: applied electric field Here, the first order coefficient a of the electric field E is called the Pockels coefficient, and the second order coefficient b is called the Kerr coefficient.

Such an electro-optic effect is remarkable, and materials used for measuring electric field intensity and the like (hereinafter referred to as electro-optic crystals) include lithium niobate (LiNbO3), lithium tantalate (LiTaO3), quartz, BSO ( Bi12Si
O20) and BGO (Bi12GeO20) crystals are known. These crystals are cut at a predetermined angle with respect to the crystal axis and shaped into a rectangular parallelepiped for use. An apparatus for measuring an electric field, a voltage, and the like by using an optical fiber for transmitting and receiving light using the Pockels effect in which the refractive index of such an electro-optic crystal is proportional to the first-order term of the electric field has been studied.

[0004] That is, when an electric field is applied to an electro-optic crystal, the refractive index of the crystal changes, thereby changing the speed of light rays passing through the crystal. On the other hand, the two polarized light components transmitted through the electro-optic crystal undergo different phase modulations according to the electric field strength applied to the electro-optic crystal. Therefore, in an apparatus for measuring such an electric field, for example, after light from a light source of monochromatic light is linearly polarized by a polarizing plate, λ
The light is transmitted through a 波長 wavelength plate to form circularly polarized light, and this light is incident on the electro-optic crystal. The light transmitted through the electro-optic crystal becomes so-called elliptically polarized light, and the direction of the major axis changes according to the electric field intensity applied to the electro-optic crystal and the length of the optical path in the electro-optic crystal. Then, when the light emitted from the electro-optic crystal is transmitted through the analyzer, only the light of the directional component corresponding to the angle of the analyzer passes, so that the intensity of the light output changes in accordance with the electric field intensity, and the intensity of the light intensity is changed. The change will correspond to the magnitude of the electric field strength.

Based on such a principle, the applicant of the present invention has filed a Japanese Patent Application No. 63-316 as an apparatus for measuring an electric field.
No. 726, "Optical DC electric field measuring apparatus" has been filed. In such an electric field measuring apparatus, for example, a monochromatic light source such as a laser diode is prepared in a measuring unit, and a light beam from this light source is guided to an electro-optic crystal of a detecting unit using an optical fiber. Then, the light beam transmitted through the electro-optic crystal is guided again to the measuring section using an optical fiber, and an optical change is detected by a light receiving element.

However, when an electric field is measured by such a device, the electro-optic crystal and the optical fiber are made of an insulator, so that electrical insulation can be easily performed, and signal transmission is performed by light. Even in an electric field, there is no influence from electromagnetic induction or external noise, and advantages such as no spark, explosion proof and good chemical resistance can be obtained. Therefore, such an electric field measuring device is expected to have a unique use in fields where safety is important, such as maintenance of high-voltage power facilities in the field of high power, and measurement of charged charges at a petroleum storage base in a complex.

FIG. 5 is a block diagram showing the basic configuration of a conventional electric field measuring device. For example, a light source driving unit 1 drives a monochromatic light source 2 and guides a light beam generated by the light source 2 to an optical fiber 3. The light guided by the optical fiber 3 enters the electro-optic crystal 7 made of, for example, quartz through the lens 4, the polarizer 5, and the wavelength plate 6. An electric field E to be measured is applied to the electrodes 8 on both sides of the electro-optic crystal 7, and the light emitted from the electro-optic crystal 7 is guided to the light receiving element 12 by the optical fiber 11 via the analyzer 9 and the lens 10. The detection signal of the light receiving element 12 is input to the electric field measuring unit 13 to obtain a measured value of the electric field, and the measured value is displayed on the display unit 14 and recorded as necessary. Then, for example, the modulation characteristics of the transmitted light as shown in FIG. 6 are obtained, and the value of the electric field E is measured from the optical change of the transmitted light obtained according to the electric field intensity, for example, the change of the light intensity. .

In such an electric field measuring apparatus, a detecting section including an electro-optical crystal or the like for applying an electric field to be measured, and an electric field measuring section for measuring an electric field intensity from an optical change generated in the detecting section are provided. It is only necessary to optically couple between them. Therefore, for example, by connecting the detection unit and the electric field measurement unit using an optical fiber that is an electrical insulator, it is possible to transmit and receive signals while maintaining high electrical insulation. Therefore, by connecting the detection section and the electric field measurement section via an optical fiber having a length that can provide sufficient electrical insulation, high voltage measurement can be performed safely.

As a light source used in such an electric field measuring apparatus, a semiconductor element which satisfies various required characteristics, such as a laser diode or a light emitting diode, is used. However, in such a light source, the amount of energy loss supplied when emitting light becomes heat, and the temperature rises until the calorific value and the heat radiation amount are balanced, and the wavelength of the light output changes according to the temperature of the light source. FIG. 7 is a graph showing an example of a deviation of the peak emission wavelength with respect to the emission wavelength λ at 25 ° C. and the temperature of the case of this type of light emitting diode. As is clear from this graph, the wavelength 85 at 25 ° C.
On the basis of 0 nm, the emission wavelength λ changes by ± 10 nm due to a temperature change of ± 35 degrees, and the rate of this change corresponds to ± 1.2% of the emission wavelength.

In such a device, the electro-optic effect of the electro-optic crystal can be expressed as a half-wave voltage Vπ. This half-wavelength voltage Vπ is a voltage necessary to change the light intensity from 0 to 1 in FIG. 6, and a crystal having a low voltage has good sensitivity, but the highest measurable voltage is limited to a lower level. Conversely, in the case of a crystal having a high half-wave voltage Vπ, the sensitivity is low, but the measurement can be performed with good linearity up to a high voltage.

The half-wavelength voltage Vπ varies according to the type of crystal, the direction of voltage application to the crystal axis, and the direction of light transmission to the crystal axis. When an electric field is applied and the light is arranged to transmit light in the Z-axis direction, it is given by the following equation. Vπ = λ / 2no3r11 · (d / L) where λ is the wavelength of the transmitted light beam, no is the ordinary refractive index, r11 is the Pockels constant d is the thickness of the crystal in the direction in which the voltage or electric field is applied, and L is the thickness of the crystal in the direction of transmitting the light beam Length As is clear from this equation, since the value of the half-wavelength voltage Vπ is proportional to the wavelength λ of the light beam, a change in the wavelength λ of the output light from the light source directly becomes an error in the measured value.

Further, when the wavelength of the output light of the light source changes as described above, there is also a problem that the optical system depending on the wavelength cannot exhibit the performance as designed. For example, when a photodiode is used as a light receiving element, this type of diode has a wavelength sensitivity characteristic as shown in FIG. 8, for example.
The light receiving sensitivity changes according to the wavelength λ of the input light. For this reason, the wavelength λ of the output light of the light source is designed so as to be in the region having the best light receiving sensitivity of the photodiode. Will decrease.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in an optical measurement of an electric field, a voltage, and the like, the wavelength of output light is maintained by maintaining a light source at a constant temperature. It is an object of the present invention to provide an optical electric field measuring apparatus capable of obtaining good detection characteristics while maintaining a constant wavelength.

[0014]

According to the present invention, a light beam from a light source is transmitted through an electro-optic crystal to which an electric field to be measured is applied, and the light is received by a light receiving element. In a device for measuring an electric field, a thermo module that thermally couples the light source and the heat-generating side of the light-receiving element to transfer heat from the light-receiving element to the light source side is provided, and the light source is kept at a constant temperature. It is characterized by comprising a temperature control unit for controlling the amount of heat transferred by the thermo module so as to maintain the temperature.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the schematic diagram of the electric field measuring apparatus shown in FIG. Note that the same members as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, reference numeral 21 denotes a thermo module for transferring heat according to a control current. FIG. 2 is a cutaway front view showing an example of the structure around the thermo module 21. The thermo module 21 thermally couples the light source 2 and the light receiving element 12 to transfer heat from the light receiving element 12 to the light source 2. To do. Then, a temperature sensor 22 is attached to the light source 2, and a detection signal of the sensor 22 is sent to a temperature control unit 23.
To control the amount of heat transfer so as to maintain the light source 2 at a constant temperature. The thermo module 21 and the like are housed in a container 24, and the light source 2 and the light receiving element 1
2 is connected to an optical fiber via an optical connector 25. In FIG. 2, reference numeral 26 denotes the light receiving element 12.
Is a preamplifier.

The thermo-module 21 is, for example, a Peltier element heat pump using a thermoelectric semiconductor as shown in FIG. That is, two types of thermoelectric semiconductors, which are the P-type element 21a and the N-type element 21b, are joined to the electrode metal 21c to form a π-type series circuit. When a current flows from the power supply 21d in the direction from the P-type and N-type N-type elements 21b to the P-type element 21a in the π-type series circuit, heat is absorbed at the upper part of the π-type and heat is generated at the lower part by the Peltier effect.
The heat is transferred from the heat absorbing side to the heat generating side. The heat absorbing side of the Peltier element is attached to the light receiving element 12 and the heat radiating side is attached to the light source 2 to transfer heat from the light receiving element 12 to the light source 2, thereby cooling the light receiving element 12 and the preamplifier 26 side. Heating and thermo module 2
1 is controlled by the temperature control unit 23,
The light source 2 is kept at a constant temperature.

With such a configuration, the electro-optic crystal 7
When an electric field E is applied to the light, the light beam transmitted through the electro-optic crystal 7 causes an optical change according to the magnitude of the applied electric field E. Therefore, the value of the applied electric field E can be measured by converting the magnitude of the optical change of the transmitted light into an electric signal by the light receiving element 12 and measuring the electric signal by the electric field measuring unit 13. Then, the light source 2 and the light receiving element 12 are thermally coupled by the thermo module 21 to transfer the heat of the light receiving element 12 to the light source 2 side, thereby cooling the light receiving element 12 and heating the light source 2. I have. And the temperature controller 2
3, the amount of heat transferred by the thermo module 21 is controlled to keep the temperature of the light source 2 at a constant temperature. Therefore, since the light source 2 is heated to a constant temperature, the wavelength λ of the output light can be maintained at a constant wavelength, and the optical system can exhibit the highest performance as designed.

On the other hand, when a photodiode is used as the light receiving element, the relationship between the ambient temperature of the photodiode and the dark current is as shown in FIG. 4, for example. That is, the dark current increases as the temperature rises, making it impossible to detect a weak signal. Therefore, it is desirable to keep the temperature as low as possible.
Thus, in the above embodiment, the temperature of the light receiving element 12 is lowered due to cooling, whereby the S / N ratio can be increased, and good detection sensitivity can be obtained.

[0019]

As described in detail above, according to the present invention, the light output wavelength of the light source can be maintained at a constant wavelength with a simple configuration, and the light receiving element can maintain a high S / N ratio. Provided is an optical-type electric field measurement device that can detect an optical change with respect to a light beam transmitted through an electro-optic crystal with high sensitivity, and thereby can measure an electric field such as an electric field and a voltage with high sensitivity and accuracy. Can be.

[0020]

[Brief description of the drawings]

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

FIG. 2 is a cutaway front view around the thermo module of the embodiment shown in FIG. 1;

FIG. 3 is a diagram for explaining the operation of the thermo module of the embodiment shown in FIG.

FIG. 4 is a graph showing a relationship between a temperature of a light receiving element and a dark current.

FIG. 5 is a block diagram illustrating an example of a conventional electric field measurement device.

6 is a graph showing a relationship between an applied voltage and transmitted light intensity of the electric field measuring device shown in FIG.

FIG. 7 is a graph showing a deviation between a case temperature of a light emitting diode and a peak light emission wavelength λ.

FIG. 8 is a graph showing the relationship between the wavelength λ of the light receiving element and the light receiving sensitivity.

[Explanation of symbols]

 2 light source 7 electro-optic crystal 12 light receiving element 21 thermo module 23 temperature controller

Claims (2)

(57) [Claims] 1. An apparatus for transmitting a light beam from a light source to an electro-optic crystal to which an electric field to be measured is applied, receiving the light beam from a light source, and measuring the electric field from an optical change due to an electro-optic effect of the transmitted light. An optical electric field measuring apparatus, comprising: a thermo module for thermally coupling a light source and a heat generating side of the light receiving element to transfer heat of the light receiving element to the light source side. 2. An optical electric field measuring apparatus according to claim 1, further comprising a temperature controller for controlling an amount of heat transferred by said thermo module so as to keep the temperature of said light source at a constant temperature.