JPH06258352A - Photovoltaic sensor - Google Patents

Abstract

PURPOSE:To provide a photovoltaic sensor in which an SN ratio is improved and accuracy is enhanced so that sensitivity is hardly changed even when an angle of optical rotation is varied due to a temperature and temperature characteristic as a sensor is stabilized and the sensitivity is roughly constant and the output characteristic is uniform, even when existing slippage of face direction of a crystal and of axis between a polarizer or a wave plate and crystal axis and unevenness of the structures such as variety of the angle of optical rotation due to unevenness of accuracy of thickness of the crystal, by measuring at the maximum sensitivity of the sensor. CONSTITUTION:As photovoltaic sensor consists of a polarizer 3 disposed in the light proceeding direction, a one fourth wave plate 4, an electro-optical crystal element 8 having a natural optical rotation efficiency and an analyzer 7 and an electric field is applied between electrode membranes 6 provided on opposing two faces being perpendicular or parallel to the light proceeding direction and in the circumferential surface of the electro-optical crystal element 8 so that a voltage is detected. In the above voltage sensor, an input and an output faces of the electro-optical crystal element 8 is disposed perpendicular to one of the crystal axes. The electro-optical crystal element 8 is disposed in such a manner that one of the other two axes is inclined at half of angle of optical rotation determined by a penetration optical path in the direction reversed to the optical rotation direction of the electro-optical crystal element for the polarized light direction of a linearly polarized light emitted from the polarizer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical voltage sensor for detecting the voltage of an object to be measured such as a distribution line.

[0002]

2. Description of the Related Art Conventionally, in this type of optical voltage sensor, as shown in FIG. 2, light from a light source (not shown) is guided by an optical fiber 1a, collimated by a collimator lens 2a, and polarized by a polarizer 3. It is reflected or transmitted to form linearly polarized light 3a, and when this linearly polarized light is transmitted through the quarter-wave plate 4, two linearly polarized light 4a.
It is divided into a and 4b, and a phase difference of 90 ° is generated to become circularly polarized light, and when passing through the electro-optic crystal element 5, the birefringence that occurs according to the voltage applied to the electrode film 6 provided on the crystal is used. Then, optical phase modulation is performed, the light is transmitted or reflected by the analyzer 7, and the collimator lens 2b collects the light on the optical fiber 1b to detect the voltage. An electro-optical crystal element used for such an optical voltage sensor is, for example, Bi ₁₂
A cubic system such as GeO ₂₀ (abbreviated as BGO) or Bi ₁₂ S _i O ₂₀ (abbreviated as BSO) is used, and the cut surface has three crystal axes x <001>, y <010>, and z. <1
00> is cut out vertically.

[0003]

By the way, such an electro-optical crystal element has a natural optical rotatory power, and linearly polarized light rotates by an optical rotation angle Φ determined by the thickness L of the crystal. In the case of BGO, linearly polarized light 3a 'rotates counterclockwise when viewed from the light receiving side.
Becomes Therefore, the sensor sensitivity changes. Therefore, when the relationship between the rotation angle θ when the electro-optic crystal element is rotated around the crystal axis z <100> and the sensor sensitivity is measured, the vertical axis represents the sensitivity and the horizontal axis represents the crystal rotation angle θ. As shown in FIG. 3, the sensor sensitivity curve b is obtained, and the sensitivity becomes maximum when the rotation angle θ = Φ / 2. In the figure, the right side shows the crystal rotated clockwise as viewed from the light receiving side, and the left side shows the counterclockwise rotation. Since the polarization direction of the polarizer is usually aligned with the y-axis or the x-axis, the rotation angle θ of the crystal is 0.
However, the sensor sensitivity was a little low. The region in which the sensor sensitivity is lowered is a region in which the change in sensitivity is large, and the temperature change of the spontaneous optical rotation is remarkably exhibited, which causes the temperature characteristics of the entire sensor to be deteriorated. In addition, because the structural variations such as the accuracy of the plane orientation of cutting out the electro-optical crystal element and the axis deviation between the polarizer and the quarter-wave plate and the crystal axis of the electro-optical crystal element cause the rotation angle θ to vary, The variations in sensor sensitivity were increasing. It is an object of the present invention to improve the sensitivity of a sensor, eliminate variations in sensitivity, and stabilize temperature characteristics.

[0004]

In order to solve the above problems, the present invention provides a polarizer arranged in the traveling direction of light and a quarter
A wave plate, an electro-optical crystal element having a natural optical rotation, and an analyzer, which are provided on two surfaces on the peripheral surface of the electro-optical crystal element which are perpendicular to or parallel to the light traveling direction. In an optical voltage sensor for detecting a voltage by applying an electric field to the formed electrode film, the entrance and exit surfaces of the electro-optical crystal element are arranged perpendicular to one crystal axis of the electro-optical crystal element, Any one of the other two crystal axes is tilted in the direction opposite to the optical rotation direction of the electro-optic crystal element with respect to the polarization direction of the linearly polarized light emitted from the polarizer, by half the optical rotation angle determined by the transmitted optical path length. The electro-optic crystal element is arranged in the same manner.

[0005]

Therefore, the maximum point of the sensor sensitivity is used for the measurement.

[0006]

EXAMPLE The present invention will be described with reference to the example shown in FIG. The same parts as those in FIG. 2 are designated by the same reference numerals and detailed description thereof will be omitted. Reference numeral 8 denotes a BGO having a thickness L of the crystal element, crystal axes x <001>, y <010>, and z <100>, and the incident surface and the emission surface are cut out and arranged perpendicular to the crystal axis z <100>. The electro-optic crystal element is tilted and cut out in the direction opposite to the optical rotation direction of the electro-optic crystal element with respect to the polarization direction of the linearly polarized light emitted from the polarizer on the axis y <010>. The tilt amount is Φ = L × Φ ₀ , where Φ ₀ is the optical rotatory power of the electro-optical crystal element and Φ is the optical rotation angle, and the optical rotation angle Φ
It is cut out by tilting half the amount. Now, assuming that the thickness L of the BGO is 2 mm, the optical rotation power Φ _{0 of the} BGO is 10.2 deg.
/ Mm, the optical rotation angle Φ is 20.4 deg,
Half of that amount is cut out with an inclination of 10.2 deg. When a voltage of 100 V was applied to the BGO electrode film 6 thus constructed, a sensor sensitivity curve a shown in FIG. 3 was obtained. Therefore, when the linearly polarized light 3a emitted from the polarizer 3 passes through the quarter-wave plate 4, the two linearly polarized light 4a, 4a
It is divided into b and a phase difference of 90 ° is generated to become circularly polarized light. By the time the circularly polarized light passes through the optical crystal element 5, it is rotated counterclockwise by the optical rotation angle Φ when viewed from the light receiving side. On the other hand, with respect to the crystal axis, with respect to the polarization direction 3a of the polarizer 3,
Since it is tilted in the direction opposite to the optical rotation direction with a size equal to half the optical rotation angle, the sensor sensitivity takes the maximum value when the rotation angle θ is 0 ° in the sensor sensitivity curve a of FIG. In this example, the crystal was cut out so that the crystal axes y and x were inclined by Φ / 2 with respect to the normals to the upper surface and the side surface. The same effect can be obtained by tilting Φ / 2 around the axis.

[0007]

Since the configuration as described above is adopted, the sensitivity of the sensor is measured at the maximum value, so that the SN ratio is improved and the accuracy becomes high. Further, even if the optical rotation angle changes with temperature, the sensitivity hardly changes, so that the temperature characteristics of the sensor are stable. In addition, the sensitivity is almost constant even if there are structural variations such as misalignment of the crystal plane orientation, misalignment of the crystal axis with the polarizer or wave plate, and variation of the optical rotation angle due to the accuracy of the crystal thickness. The sensor has no characteristic variations.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical voltage sensor showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional optical voltage sensor.

FIG. 3 is a relationship diagram between a crystal rotation angle and sensor sensitivity.

[Explanation of symbols]

 1a, 1b Optical fiber 2a, 2b Collimator lens 3 Polarizer 4 1/4 wavelength plate 5 Electro-optical crystal element 6 Electrode film 7 Analyzer 8 Electro-optical crystal element

Claims (1)

[Claims] 1. A polarizer arranged in a light traveling direction, and 1 /
A four-wave plate and an electro-optic crystal element having a natural optical rotatory power,
Light for detecting a voltage by applying an electric field to electrode films provided on two surfaces of the electro-optical crystal element, which are arranged on the peripheral surface of the electro-optical crystal element and which face each other in the direction perpendicular to or parallel to the traveling direction of light. In the voltage sensor, the entrance and exit faces of the electro-optic crystal element are arranged perpendicular to one crystal axis of the electro-optic crystal element, and one of the other two crystal axes of the electro-optic crystal element is used as a polarizer. It is characterized by comprising an electro-optical crystal element which is arranged in a direction opposite to the optical rotation direction of the electro-optical crystal element with respect to the polarization direction of the linearly polarized light emitted from Optical voltage sensor.