JPH1054850A - Optical-voltage/photocurrent sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the change in resonat frequency and the deterioration of temperature characteristics by the stress caused by the difference between the expansion coefficient of a bonding agent for fixing a Pockels element and the expansion coefficient of the Pockels element and to achieve the compact configuration in an optical-voltage sensor using the Pockels element, whose quantity of transmitting light changes in correspondence with the applied voltage from a Cerminal. SOLUTION: In a concave groove 38 formed in a bottom plate 37 of a casing 36, a polarizer 32, a λ/4 plate 33 and an analyzer 35 are coupled together with a Pockels element 34 and tightened and fixed by compressing screws 45 and 46 in the optical-axis direction. Therefore, the Pockels element 34 is not bonded, the change of resonant frequency by heat is suppressed and the temperature characteristics can be improved. At the same time, the resonat frequency can be expanded to the frequency band, which can correspond to the surge current of thunderbolt. Furthermore, the compact configuration can be achieved since the Pockels element 34 is held from the direction of the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical voltage / optical current sensor which detects a change in an applied voltage or a current to be detected as a transmitted light amount change by an electro-optic effect such as a Pockels effect or a Faraday effect.

[0002]

2. Description of the Related Art Line voltages and currents can be reduced by using an electro-optic effect element that generates the Pockels effect or the Faraday effect.
An optical voltage / current sensor that is electrically insulated from the line is used.

FIG. 5 is a plan view of a typical prior art optical voltage sensor 1 with a lid removed. This optical voltage sensor 1 has a BGO (Bi ₁₂ G) as an electro-optical effect element.
using a Pockels element 2 made of eO ₂₀ ) crystal,
An input voltage from the terminals 3 and 4 is applied to the Pockels element 2, and an output signal proportional to the input voltage is generated by utilizing the fact that the amount of transmitted light of the Pockels element 2 changes in response to a voltage change. The detection is performed by a path that is electrically insulated from the terminals 3 and 4.

Accordingly, the side wall 6 of the casing 5 has
Collimators 7, 8 are mounted together with the terminals 3, 4. On the bottom plate 9, the Pockels element 2 is placed.
At the same time, a polarizer 10, a λ / 4 plate 11, an analyzer 12
And are attached. The polarizer 10 and the λ / 4 plate 1
1, the Pockels element 2, and the analyzer 12 are arranged on the optical axis 13 of the Pockels element 2.

From the light emitted from the collimator 7 arranged orthogonal to the optical axis 13, only a component having a predetermined polarization plane is extracted by the polarizer 10.
After being converted into circularly polarized light at 1, the light enters the Pockels element 2. The Pockels element 2 changes the amount of transmitted light in proportion to the input voltage. Light emitted from the Pockels element 2 is incident on the analyzer 12 and only a predetermined component of the polarization plane is extracted. The light is emitted to the collimator 8 arranged at a position orthogonal to the axis 13. Thus, an output signal electrically insulated from the terminals 3 and 4 can be obtained from the collimator 8 in proportion to the input voltage to the terminals 3 and 4.

However, in the above-described conventional optical voltage sensor 1, on the bottom plate 9 made of ceramic or the like, the Pockels element 2 made of the BGO crystal, the polarizer 10 made of PBS, the λ / 4 plate 11, and the detection plate are mounted. The photons 12 are fixed with a thermosetting or ultraviolet curable adhesive. On the other hand, since the optical voltage sensor 1 is used in connection with power transmission and distribution lines, the temperature environment in which it is used undergoes a large change, for example, from −20 ° C. to + 80 ° C. from winter to summer.

For this reason, there is a problem that a strain is generated by a stress generated in the Pockels element 2 due to a difference in expansion coefficient between the adhesive and the Pockels element 2, a refractive index in the crystal changes, and a resonance frequency changes. . In addition, there is a problem that the change in the refractive index deteriorates the ratio error characteristic with respect to the temperature change.

On the other hand, as the frequency of the applied voltage increases, the Pockels device 2 made of the BGO crystal causes resonance due to surface slip vibration. Here, when the BGO crystal is cut in the Z-axis direction and light is transmitted in the Z-axis direction,
Assuming that the size of the crystal is a × b in a plane perpendicular to the optical axis, the resonance frequency Fr can be expressed by the following equation.

[0009]

(Equation 1)

Here, C ₄₄ is the piezoelectric stiffness (BG
O is 0.291 × 10 ¹¹ N / m ² ), and ρ is specific gravity (BGO
Is 9.22 × 10 ³ Kg / m ³ ), and a and b are the lengths (m) in the X and Y axes orthogonal to the Z axis, which is the optical axis, and m and n.
Is an integer defining the vibration mode (m = n in the basic mode)
= 1).

Therefore, there is also a problem that even if an attempt is made to detect a surge current due to lightning by the optical voltage sensor 1, the detectable bandwidth is limited based on the resonance frequency Fr according to the above equation (1).

For this reason, in order to suppress a change in the resonance frequency of the Pockels element 2 due to the use of the adhesive as described above and to realize a wide-band optical voltage sensor capable of detecting the lightning surge as described above, another conventional method is used. As a technique, the present applicant has previously proposed Japanese Patent Application No. 5-166885.

FIG. 6 is a plan view of another conventional optical voltage sensor 21 with its lid removed. In addition,
The configuration in FIG. 6 is similar to the configuration in FIG. 5 described above, and corresponding portions are denoted by the same reference numerals and description thereof is omitted. In this optical voltage sensor 21, the Pockels element 2
Are sandwiched in a direction perpendicular to the optical axis 13 by sandwiching members 22 and 23 made of the same material as the polarizer 10 and the analyzer 12 and made of PBS having substantially the same expansion coefficient as the Pockels element 2. . Further, the holding member 23 abuts on the side wall 6, and the holding member 22 is pressed by a pressing member 26 pressed by pressing screws 24 and 25 screwed into screw holes formed in the side wall 6. Pressure is applied in the direction of the side wall 6.

Therefore, the Pockels element 2 is fixed without using an adhesive, and the Pockels element 2 has, for example, the aforementioned X = 2.5 (mm) and Y = 4 (m).
m) and Z = 3 (mm), the pressure is increased at an optimal pressure of 190 (gf / mm ² ), and the resonance frequency Fr is expanded to a frequency at which a lightning surge can be detected. Have been.

[0015]

In the prior art optical voltage sensor 21 as described above, the Pockels element 2 is formed by holding the Pockels element 2 with the holding members 22 and 2 having substantially the same expansion coefficient as the Pockels element 2.
3 and a large pressurizing member 26 is used.

An object of the present invention is to provide an optical voltage / current sensor that can be miniaturized.

[0017]

According to a first aspect of the present invention, there is provided an optical voltage / photocurrent sensor using an electro-optic effect element which generates a change in transmitted light quantity in proportion to an applied voltage or a current to be detected. In the sensor, a first light guide member provided at an incident end of the electro-optical effect element, and entering incident light from a direction intersecting an optical axis of the electro-optical effect element to the incident end of the electro-optical effect element A second light guide member provided at an emission end of the electro-optic effect element, and emitting light emitted from the emission end of the electro-optic effect element in a direction intersecting the optical axis of the electro-optic effect element; A pressure member for pressing and holding the first and second light guide members in the optical axis direction of the electro-optic effect element to press and hold the electro-optic effect element.

According to the above arrangement, it is not necessary to use a special intervening member between a pressing member such as a pressure screw and the electro-optical effect element in order to fix and press the electro-optical effect element. The electro-optic effect element is sandwiched and fixed and pressurized by first and second light guide members used for detecting a change in the amount of transmitted light.

Therefore, it is possible to realize a configuration that can be fixed without using an adhesive and that can perform pressurization for increasing the resonance frequency without using the holding member. Can be

According to a second aspect of the present invention, in the optical voltage / current sensor, the first light guide member converts light incident from a direction perpendicular to the optical axis into circularly polarized light, and converts the light into a circularly polarized light. A polarizer and a λ / 4 plate incident on an incident end, wherein the second light guide member extracts a component in a predetermined polarization direction of light from the exit end of the electro-optic effect element,
The analyzer is characterized by being an analyzer that emits light in a direction perpendicular to the optical axis.

According to the above arrangement, the first light guide member for guiding the incident light from the direction intersecting the optical axis of the electro-optical effect element to the electro-optical effect element, A second light guide member for guiding the emitted light in a direction intersecting with the optical axis, and a polarizer and a λ / Four plates as well as an analyzer, so that all of the optical components can be fixed without the use of adhesives.

Still further, according to the third aspect of the present invention,
In the photocurrent sensor, the electro-optic effect element and the first
The second light guide member is fitted in a concave groove formed in the bottom plate of the casing, and a deviation in a direction intersecting with the optical axis is also restricted.

According to the above configuration, the electro-optic effect element and the first and second electro-optical effect elements are formed in a pair of wall surfaces which are erected with a predetermined accuracy or in grooves such as grooves formed with a predetermined accuracy. The optical axis can be aligned simply by inserting the light guide member,
A complicated optical axis alignment operation can be eliminated.

According to a fourth aspect of the present invention, there is provided an optical voltage / current sensor, wherein a groove facing the groove is also formed on the lid of the casing.

According to the above configuration, it is possible to prevent the electro-optical effect element and the first and second light guide members from dropping out of the concave groove, and to improve vibration resistance.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described.
The following is a description based on FIGS. 1 to 4.

FIG. 1 is an exploded perspective view of an optical voltage sensor 31 according to an embodiment of the present invention, and FIG.
It is a top view in the state where 1 lid was removed. In this optical voltage sensor 31, the polarizer 32 and the λ / 4 plate 33 which are made of the BGO crystal and are the first light guide member, and the BGO
A Pockels element 34, which is made of a crystal and is an electro-optical effect element, and an analyzer 35 which is made of the BGO crystal and is a second light guide member are engraved in this order on a bottom plate 37 made of ceramic in a casing 36. The optical axis 42 is fitted into the concave groove 38. Further, from both outer sides of the polarizer 32 and the analyzer 35, via intervening members 39 and 40 made of a glass plate or the like, respectively.
Screw holes 4 formed in the side wall 41 of the casing 36
The polarizer 32, the λ / 4 plate 33, the Pockels element 34, and the analyzer 35 are pressed and held by the pressure screws 45 and 46 screwed to the grooves 3 and 44 in the groove 38 without being adhered. Have been.

Correspondingly, the cover 47 is provided with the groove 38.
Are formed opposite to the groove 48. by this,
The optical components of the polarizer 32, the λ / 4 plate 33, the Pockels element 34, and the analyzer 35 are formed by a concave groove 38 of the bottom plate 37.
Is prevented from falling off, and the vibration resistance is improved.

The pressure generated by the pressure screws 45 and 46 is as large as possible without damaging the Pockels element 34, for example, when the dimensions of the Pockels element 34 are X = 2.5 (mm) and Y = 4 (mm). ), Z = 3 (mm)
Is 190 (gf / mm ² ).

On the other hand, a pair of terminals 49 and 50 to which an input voltage for applying a voltage to the Pockels element 34 is applied are attached to the side wall 41, and a light from the optical fiber 53 facing the polarizer 32. A collimator 51 which is incident on the optical axis 42 at right angles to the optical axis 42 and a collimator 52 which faces the analyzer 35 and receives light from the analyzer 35 and enters the optical fiber 54 at right angles to the optical axis 42 are attached.

The optical voltage sensor 31 configured as described above
In FIG. 3, light incident on the optical voltage sensor 31 from a light source (not shown) via an optical fiber 53 is transmitted to a collimator 51.
At, the light is converted into parallel light and is incident on the polarizer 32. The polarization direction of the light from the collimator 51 is random. Only the light whose polarization direction is constant in the polarizer 32 is selected, emitted in the direction of the optical axis 42, and made incident on the λ / 4 plate 33. The λ / 4 plate 33 enters the Pockels element 34 as incident light as circularly polarized light.

The Pockels element 34 is connected to the terminals 49 and 5.
According to the input voltage of 0, the polarization direction of the incident light is changed and is incident on the analyzer 35. The analyzer 35 extracts only a component in a predetermined polarization direction from the incident light from the Pockels element 34 and enters the collimator 52 arranged in a direction perpendicular to the optical axis 42. Light incident on the collimator 52 is input to a light receiving element (not shown) via the optical fiber 54. The input voltage is applied only to the Pockels element 34 among the polarizer 32, the λ / 4 plate 33, the Pockels element 34, and the analyzer 35 made of BGO crystal.

In the optical voltage sensor 31 according to the present invention thus configured, the polarizer 32, the λ / 4 plate 33, and the analyzer 35 are made of a BGO crystal in order to match the expansion coefficient of the Pockels element 34, Furthermore, since these are fitted into the concave groove 38 formed in the bottom plate 37 and are also fitted into the concave groove 48 formed in the lid 47 to prevent falling off from the concave groove 38, it is possible to avoid complicated optical axis alignment. , The optical axis 42 of the optical component is cut out of the concave grooves 38 and 48, for example, with a precision of 0.1 mm.
It can be matched at about 1 μm.

The Pockels element 34 is connected to the polarizer 32.
And the λ / 4 plate 33 and the analyzer 35, and these optical components are pressed and fixed from the direction of the optical axis 42 by the pressing screws 45 and 46 and the intervening members 39 and 40.
The size can be reduced. Furthermore, the generation of stress due to the use of the adhesive as described in the related art can be prevented, the change in the resonance frequency can be suppressed, and the temperature characteristic of the ratio error can be improved to improve the resonance frequency of the Pockels element 34. Fr can be expanded to a high frequency band in which a surge current due to lightning can be detected.

FIGS. 3 and 4 are graphs showing the experimental results of the present inventor. When the temperature is changed from around -20 ° C. to around 60 ° C., when the pressure is applied to the Pockels element 34, It is a graph which shows the change of the ratio error with the case where it is not added. As is clear from these figures, the change width of the ratio error is -0.2% to + 0.5% in the case of FIG. 3 where the pressure is applied, whereas the pressure shown in FIG. If not added, -0.7% to +2.2
%. This is probably because the strain caused by the temperature of the BGO crystal is suppressed by the pressure, and the change in the refractive index of the crystal is reduced. By applying the pressure in this manner, the temperature characteristics can be improved.

In the above-described example, the voltage is detected using the Pockels element 34 whose polarization direction changes in accordance with the applied voltage as the electro-optical effect element. May be configured to use a Faraday element that detects current using the Faraday effect in which the polarization direction changes in response to a magnetic field generated by the Faraday effect.

[0037]

As described above, the optical voltage / photocurrent sensor according to the first aspect of the present invention includes an electro-optic effect element that generates a change in the amount of transmitted light in proportion to an applied voltage or a current to be detected.
A first light guide member for inputting incident light from a direction intersecting with the optical axis of the electro-optical effect element to an incident end of the electro-optical effect element, and emitting light from an output end of the electro-optical effect element; The electro-optic effect element is sandwiched by a second light guide member that emits light in a direction intersecting with the optical axis of the electro-optic effect element, and is pressed and held in the optical axis direction of the electro-optic effect element to hold and fix the electro-optic effect element. Press.

Therefore, it is possible to realize a small-sized structure that can be fixed without using an adhesive and that can perform pressurization for increasing the resonance frequency.

Further, in the optical voltage / photocurrent sensor according to the second aspect of the present invention, as described above, the first light guide member is formed by a polarizer and a λ which make incident light to the electro-optic effect element circularly polarized.
The second light guide member is an analyzer that extracts a component in a predetermined polarization direction from the light emitted from the electro-optic effect element.

Therefore, all of the optical components necessary for extracting the electro-optical effect of the electro-optical effect element as a change in the amount of transmitted light can be fixed without using an adhesive.

Further, according to the third aspect of the present invention,
As described above, the photocurrent sensor is provided with the electro-optic effect element and the first and second Optical axis alignment can be performed only by fitting the light guide member.

Therefore, complicated optical axis alignment work can be eliminated.

In the optical voltage / current sensor according to the fourth aspect of the present invention, as described above, the cover of the casing is also provided with:
A groove facing the groove is formed.

Therefore, it is possible to prevent the electro-optic effect element and the first and second light guide members from dropping out of the groove, and to improve the vibration resistance.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view of an optical voltage sensor according to an embodiment of the present invention.

FIG. 2 is a plan view of the optical voltage sensor shown in FIG. 1 with a lid removed.

FIG. 3 is a graph showing a change in a ratio error with respect to a temperature change when a pressure is applied to a Pockels element used in the optical voltage sensor.

FIG. 4 is a graph showing a change in a ratio error with respect to a temperature change when no pressure is applied to the Pockels element.

FIG. 5 is a plan view of a typical prior art light voltage sensor with the lid removed.

FIG. 6 is a plan view of another conventional optical voltage sensor with a lid removed.

[Explanation of symbols]

 Reference Signs List 31 light voltage sensor 32 polarizer (first light guide member) 33 λ / 4 plate (first light guide member) 34 Pockels element (electro-optic effect element) 35 analyzer (second light guide member) 36 casing 37 bottom plate 38 concave groove 39 interposition member 40 interposition member 41 side wall 42 optical axis 45 pressure screw 46 pressure screw 47 lid 48 concave groove 49 terminal 50 terminal 51 collimator 52 collimator

Claims (4)

[Claims] 1. A light voltage / light current sensor using an electro-optic effect element which produces a change in transmitted light quantity in proportion to an applied voltage or a current to be detected, wherein said electro-optic effect element is provided at an incident end of said electro-optic effect element. A first light guide member for inputting incident light from a direction intersecting the optical axis of the element to an incident end of the electro-optical effect element; and an electro-optical effect element provided at an output end of the electro-optical effect element. A second light-guiding member that emits light emitted from the light-emitting end in a direction intersecting the optical axis of the electro-optic effect element; And a pressure member for holding and fixing the electro-optic effect element while pressing the electro-optic effect element by applying pressure in the axial direction. 2. The first light guide member comprises a polarizer and a λ / 4 plate for converting light incident from a direction perpendicular to the optical axis to the incident end of the electro-optic effect element as circularly polarized light. The second light guide member is an analyzer that extracts a component of a predetermined polarization direction of light from the emission end of the electro-optic effect element and emits the component in a direction orthogonal to the optical axis. The optical voltage / current sensor according to claim 1, wherein: 3. The electro-optic effect element and the first and second light guide members are fitted into concave grooves formed in a bottom plate of a casing, and also restrict displacement in a direction intersecting with the optical axis. 3. An optical voltage / photocurrent sensor according to claim 1, wherein 4. An optical voltage / photocurrent sensor according to claim 3, wherein a concave groove facing the concave groove is also formed in the lid of the casing.