JPH08220149A - Photovoltaic sensor - Google Patents

Abstract

PURPOSE: To obtain a photovoltaic sensor in which stabilized temperature characteristics are ensured for the sensitivity of the sensor. CONSTITUTION: The photovoltaic sensor comprises a polarizer 3, a quarter wavelength plate 4, an electrooptic crystal 5, and an analyzer 6 arranged sequentially along an optical path. The electrooptic crystal 5 is composed of Bi12 GeO20 or Bi12 SiO20 and a relationship κc =|(π/2)κ1/4 | is set between the temperature coefficient κc of the electrooptic crystal 5 and that κ1/4 of the quarter wavelength plate 4 by regulating the angle of rotation dependent on the thickness of the electrooptic crystal 5 and the cutting direction thereof.

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 measuring voltage with high accuracy in a field of electric power which is harsh in an electromagnetic field environment.

[0002]

2. Description of the Related Art Conventionally, this type of optical voltage sensor is constructed as shown in FIG. Light emitted from a light source (not shown) including a light emitting element such as a light emitting diode is guided by the optical fiber 1, becomes parallel light by the collimator lens 2a, and is reflected or transmitted by the polarizer 3 and then linearly polarized light 3a. Becomes This linearly polarized light 3a is a quarter wavelength plate 4
Linearly polarized light 4 shown in FIG.
A and 4b generate a phase difference of 90 degrees and become circularly polarized light. When this circularly polarized light passes through the electro-optical element 5, the optical phase modulation is performed by utilizing the birefringence generated by applying an electric field through the transparent electrodes provided on the front and back surfaces of the crystal. After that, this light is passed through the analyzer 6 to be subjected to analog modulation, condensed by the collimator lens 2b, input to a detector (not shown) via the optical fiber 1b, and the analog modulation is performed according to the degree of analog modulation. The voltage is detected (for example, Japanese Patent Publication No. 2-10383).

However, in the prior art, the change in the output characteristics of the optical voltage sensor with respect to the temperature change is large, which has been a major obstacle to highly accurate voltage measurement. For example, the conventional wound type PT (Pote)
accuracy class 1P
In order to use it in the same way as the class, it is necessary to make the ratio error 1.0% or less in the voltage range of 70% to 110% of the rated voltage. However, there is a problem that it is difficult for the current optical voltage sensor to be within this temperature range in consideration of the temperature characteristics of the ¼ wavelength plate, the electro-optic crystal and the like which are the components. It is an object of the present invention to provide a method for stabilizing the temperature characteristic of an optical voltage sensor that can obtain a stable temperature characteristic of sensor sensitivity.

[0004]

In order to solve the above problems, the present invention provides a polarizer, which is arranged in order along an optical path, 1 /
In an optical voltage sensor including a four-wave plate, an electro-optical crystal, and an analyzer, the electro-optical crystal is Bi ₁₂ GeO ₂₀ (hereinafter referred to as B ₁₂ GeO ₂₀
GO) or Bi ₁₂ SiO ₂₀ (hereinafter referred to as BSO), and the electro-optic crystal is adjusted by adjusting the optical rotation angle determined by the thickness of the electro-optic crystal and the cutting direction of the electro-optic crystal. the relationship between the temperature coefficient kappa _1/4 of the temperature coefficient kappa _c of the crystal the quarter-wave plate,
κ _c = | (π / 2) κ _1/4 |. Further, when the polarizer and the analyzer are arranged so as to be orthogonal to each other, the temperature coefficient κ _c has a positive sign. When the polarizer and the analyzer are arranged in parallel,
The sign of the temperature coefficient κ _c becomes negative.

[0005]

The optical voltage sensor, as shown in FIG.
There is a method in which the analyzer 6 is orthogonal, and a method in which the polarizer and the analyzer are parallel, but two methods of orthogonal method and parallel method will be considered. The transmitted light amount P _v (V, T) when the polarizer and the analyzer are orthogonal to each other is expressed by the following equation (1) as a function of the voltage V and the temperature T. P _{V (V,} T) = The _{(P 0/2) [1} -cos {δ (V, T) + δ 1/4 (T)}] ... (1), the polarizer and analyzer are parallel When the amount of transmitted light P
Similarly, _P (V, T) is expressed by the following equation (1) as a function of the voltage V and the temperature T. _{P P (V, T) =} (P 0/2) [1 + cos {δ (V, T) + δ 1/4 (T)}] ... (2) where, δ (V, T) is the temperature Retardation that occurs in the electro-optic crystal under the conditions of T (° C) and applied voltage V
Is. δ _1/4 (T) is the phase difference of the quarter-wave plate at the temperature T (° C.). Also, P ₀ is δ (V, T) + δ _1/4 (T) = 0 or π
Is the amount of transmitted light. In FIG. 3, the vertical axis indicates the amount of transmitted light P.
_v (V, T) and the amount of transmitted light P _P (V, T) are given by equations (1) and (2) with the horizontal axis representing the phase difference δ (V, T) + δ _1/4 (T). ) Is a summary of the relationship. As shown in FIG. 3, δ (V,
T) + δ _1/4 (T) increases, the amount of transmitted light P _v (V, T) when the polarizer and analyzer are orthogonal to each other increases, and the amount of transmitted light P _P (V, when parallel) T) decreases.

Next, the phase difference δ used in equations (1) and (2)
The temperature characteristics of (V, T) and δ _1/4 (T) and their sizes will be described. Assuming that the temperature characteristic of the phase difference δ (V, T) of the electro-optic crystal is expressed by the relationship of the temperature T and a linear expression, and its temperature coefficient is κ _c (1 / ° C), δ (V, T T) is represented by equation (3). δ (V, T) = δ ₀ (V) (1+ κ _c T) (3) where δ ₀ (V) is the phase difference of the electro-optic crystal at a temperature of zero (° C) and the applied voltage V Is a function of. Also, 1/4
The temperature characteristic of the phase difference δ _1/4 (T) of the wave plate is assumed to be represented by a linear expression of the temperature T, and its temperature coefficient is κ _1/4 (1 / ° C)
Then, δ _1/4 (T) is expressed by equation (4). δ _1/4 (T) = (π / 2) (1+ κ _1/4 T) (4) In this case, the _1/4 wave plate has a phase difference of π / 2 (at temperature zero (° C)). (Corresponding to 1/4 wavelength).

Next, the temperature characteristics of the transmitted light quantity P _v (V, T) when the polarizer and the analyzer are orthogonal to each other and the temperature characteristics of the transmitted light quantity P _P (V, T) when they are parallel to each other will be described. Amount of transmitted light P _v
(V, T) is expressed by the following equation (5) by substituting equation (3) and equation (4) into equation (1). _{P v (V, T) =} (P 0/2) [1 + sin {δ 0 (V) (1+ κ c T) + (π / 2) κ 1/4 T}] ... (5) Likewise By substituting the equations (3) and (4) into the equation (2), the transmitted light amount P _P (V, T) is represented by the following equation (6). _{P P (V, T) =} (P 0/2) [1-sin {δ 0 (V) (1+ κ c T) + (π / 2) κ 1/4 T}] ... (6) where The value of the phase difference δ ₀ (V) generated in the electro-optic crystal is usually used in the order of 10 ^-2 (rad), and κ _1/4 is 10 ^-4 in the quarter-wave plate using quartz. It is on the order of (1 / ℃). Therefore, the following expression (7) is established. ｜ δ ₀ (V) (1+ κ _c T) + (π / 2) κ _1/4 T ｜ ≪1… (7)

In the configuration in which the polarizer and the analyzer are orthogonal to each other under the condition that the formula (7) is satisfied, the transmitted light amount P _v (V, T) in the formula (5) is
It can be expressed as an approximate expression of the following Expression (8) as a function of the temperature T. _{P v (V, T) ≒} (P 0/2) [{1+ (π / 2) κ 1/4 T} + δ 0 (V) (1+ κ c T)] ... (8) Equation (8 The right side of) indicates that the temperature characteristic of the transmitted light amount P _v (V, T) can be divided into a first term that is independent of the applied voltage V and a second term that is a function of the applied voltage V. . Similarly, the transmitted light amount P _P (V,
T) is calculated from the equation (6) as a function of the temperature T by the following equation (9).
Can be expressed by an approximate expression. _{P P (V, T) ≒} (P 0/2) [{1- (π / 2) κ 1/4 T} -δ 0 (V) (1+ κ c T)] ... (9) Equation (8 ) And (9), the first term is independent of the applied voltage V and represents the influence of the temperature of the quarter-wave plate. When the polarizer and the analyzer are orthogonal and parallel, the sign of (π / 2) κ _1/4 T in this term is opposite, so there are two effects of the temperature change of the quarter-wave plate. The configuration is reversed. On the other hand, the second term on the right side of the formulas (8) and (9) is a term representing the influence of the applied voltage V. When BGO or BSO having the Pockels effect is used as the electro-optic crystal, δ ₀ (V) is applied. The voltage V increases or decreases in proportion to the first order. Comparing these two equations, it can be seen that the signs of the coefficients are opposite, and thus the phase of the amount of transmitted light differs by 180 degrees with respect to the applied voltage. It can be seen that the effects of temperature in the electro-optic crystal are equal for these two configurations, because the sign of κ _c T is equal, despite the phase inversion.

Next, the modulation degree of the optical sensor is obtained in two configurations in which the polarizer and the analyzer are orthogonal and parallel, and the temperature characteristic of the modulation degree is derived from the result. The modulation degree in this case is obtained by dividing the second term on the right side of the equations (8) and (9) by the first term. That is, the degree of modulation m _{V (V,} T) in the configuration of the polarizer and the analyzer are perpendicular is obtained by the following expression as a function of the temperature T (10). _{m V (V, T) =} {δ 0 (V) (1+ κ c T)} / {1 + (π / 2) κ 1/4 T} ... (10) Similarly, the analyzer and the polarizer Modulation degree when is parallel
_P (V, T) is obtained as a function of temperature T by the following equation (11). _{m V (V, T) =} {- δ 0 (V) (1+ κ c T)} / {1 - (π / 2) κ 1/4 T} ... (11) where they modulation m _V (V, T), represents m _{V (V,} T) and the absolute value, will be referred to as sensor sensitivity.

Next, in order to make the physical meaning clearer, the equations (10) and (11) are modified as follows. That is, it is assumed that the temperature change (π / 2) κ _1/4 T of the _quarter- wave plate is small and the condition of the following expression (12) is satisfied. | (Π / 2) κ _1/4 T | << 1, | κ _c T | << 1 (12) Under the condition that Eq. (12) holds, the sensor sensitivity in the configuration in which the polarizer and the analyzer are orthogonal to each other | m _{V (V,} T) | is the following equation (13)
Is approximated by. | M _V (V, T) | ≒ δ ₀ (V) {(1+ (κ _c- (π / 2) κ _1/4 ) T} |… (13) On the other hand, similarly, the equation (12) holds. Under the condition, the sensor sensitivity | m _P (V, T) | when the polarizer and the analyzer are parallel is approximated by the following equation (14): | m _P (V, T) | ≈δ ₀ ( V) {(1+ (κ _{c +} (π / 2) κ _1/4 ) T} | ... (14) The optical sensor sensitivity | m | normally used is | δ
₀ (V) | Therefore, as is clear from the equations (13) and (14), the sensor sensitivity obtained here is obtained by adding the {} temperature term to the normal voltage function term δ ₀ (V). Also, comparing equation (13) and equation (14),
It can be seen that the effects of the temperature characteristics of the quarter-wave plate are reversed in the two configurations.

Next, in order to reduce the temperature change of the sensor sensitivity to zero in the two configurations, it suffices that the value of {} in the temperature terms of the equations (13) and (14) becomes zero. Therefore, when the polarizer and the analyzer are orthogonal to each other, the following expression (15) may be satisfied. κ _c = (π / 2) κ _1/4 (15) On the other hand, in order to make the temperature change of the sensor sensitivity zero when the polarizer and the analyzer are parallel, the following equation (16) must hold. Good. κ _c =-(π / 2) κ _1/4 (16) Equation (15) is a condition for stabilizing the temperature characteristic of the sensor sensitivity when the polarizer and the analyzer are orthogonal to each other.
Is a condition for stabilizing the temperature characteristic of the sensor sensitivity when the polarizer and the analyzer are parallel.

In order to satisfy the equations (15) and (16), it is necessary to adjust either the temperature coefficient κ _c of the electro-optic crystal or the temperature coefficient κ _1/4 of the quarter wave plate. Here, a method of adjusting the temperature coefficient κ _c of δ ₀ (V) when BGO or BSO is used as the electro-optic crystal will be described. Therefore, first, the phase difference δ ₀ (V) corresponding to the equation (3) will be described. The voltage applied to the electro-optic crystal is V, the half-wave voltage is V _h, and the optical rotation angle determined by the thickness of the electro-optic crystal is Φ.
₀ (these are the values at 0 degrees Celsius),
Further, when the cutting direction with respect to the crystal orientation is θ, the phase difference δ ₀ (V) generated in the crystal is expressed by the following equation (17). δ ₀ (V) = (πV / V _h ) (sin Φ ₀ / Φ ₀ ) cos (Φ ₀ + 2θ) (17) Next, the temperature coefficient κ _c of the equation (3) will be described. For this reason, first, it is assumed that the half-wave voltage V _h and the optical rotation angle Φ ₀ have a temporary relationship with the temperature T, and if the respective temperature coefficients are κ _a and κ _b , the half-wave voltage V _h and the optical rotation angle. Φ ₀
Is expressed by the following equation (18). V _h (T) = V _h0 (1 + κ _a T), Φ ₀ (T) = Φ ₀ (1+ κ _b T) (18) Under the condition that equation (18) holds, Temperature coefficient κ _c
Is expressed by the following equation (19). κ _c =-(κ _a + κ _b ) + κ _b F (Φ ₀ , θ) (19) where F (Φ ₀ , θ) is a function determined by the optical rotation angle Φ ₀ and the crystal orientation θ. It is represented by the equation (20). F (Φ ₀ , θ) = (Φ ₀ / sinΦ ₀ ) {cos (2 Φ ₀ + 2θ) / cos (Φ ₀ + 2θ)}… (20) κ _a and κ _b are determined by the physical properties, so κ _In order to control _c , the value of F (Φ ₀ , θ) may be changed and designed. FIG. 4 shows the relationship between the cutting direction θ, which is the crystal orientation, and | δ (V) |
The result calculated using 7) is shown. However, the vertical axis is |
Instead of δ (V) |, the normalized sensor sensitivity | m | _n normalized by πV / V _h is used. The optical rotation angle Φ ₀ is proportional to the crystal thickness d. Further, FIG. 5 shows a result of calculating the relationship between the cutting direction θ and the temperature coefficient κ _c of the sensor sensitivity by using the equations (19) and (20). In this way, the cutting direction θ
And the crystal thickness d which is proportional to the angle of rotation Φ ₀ | δ (V)
It can be seen that | and κ _c can be adjusted. The definition of the cutting direction is shown in FIG.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 1 is an optical fiber for guiding light emitted from a light source (not shown) including a light emitting element such as a light emitting diode, 2a is a collimator lens for collimating the light from the optical fiber 1, and 3 is a polarization beam splitter. Is used as a linearly polarized light 3a by reflecting light. 4 is 1/4
In the wave plate, when the linearly polarized light 3a passes through the quarter wavelength plate 4, it becomes linearly polarized lights 4a and 4b which are orthogonal to each other, and a phase difference of 90 degrees is generated to become circularly polarized light. 5 is an electro-optical element,
When this circularly polarized light passes through the electro-optical element 5, the optical phase modulation is performed by utilizing the birefringence generated by applying an electric field through the transparent electrodes provided on the front and back surfaces of the crystal.
Reference numeral 6 is a polarizer including a polarization beam splitter.
And the analyzer 6 are orthogonal to each other, the reflected light (S
Polarized light is used, and transmitted light (P-polarized light) is used for the analyzer 6. In this case, in order to facilitate the handling of the optical voltage sensor, the transmitted light amount P _P (V, T) parallel to the polarizer 3 reflected by the analyzer 6 is condensed by the collimator lens 2b, and the optical fiber 1b is collected. It is input to a detector (not shown) via the. Amount of transmitted light that passes through the analyzer 6 and is orthogonal to the polarizer 3 P _S (V, T)
The light path is bent 90 degrees by the mirror 7, condensed by the collimator lens 2c, and input to a detector (not shown) via the optical fiber 1c.

The temperature characteristic of the optical voltage sensor thus constructed was measured by the measuring system shown in the block diagram of FIG. With this configuration, the optical voltage sensor unit and the light source unit are connected by an optical fiber, placed in separate thermostats, and the temperature of these units is controlled independently. Further, a beam splitter (BS) was inserted in the middle of the optical fiber between the light source section and the voltage sensor section, and the wavelength was measured by the spectrum analyzer. Here, in measuring the temperature characteristic of the sensitivity of the optical voltage sensor, the conditions were applied such that a constant voltage of 60 Hz and 100 V (voltage stability 0.1%) was applied to the optical voltage sensor.
Since the temperature characteristics of the optical voltage sensor are greatly affected by stress and thermal strain, special consideration was given to avoid these effects. Next, a method of processing measurement data will be described.
The temperature characteristic% m (T) of the sensitivity of the photovoltage sensor in the configuration in which the polarizer 3 and the analyzer 6 are orthogonal to each other is defined by the following formula (21). That is, it is assumed that the expression (2
Determined by calculating the% m _V (T) by 1). % m _V (T) = {| m _V (100, T) |-| m _V (100,20) |} / | m _V (100), 20) | × 100 (%)… (21) Polarizer The% m _P (T) in the configuration in which
Obtain in the same way as. However, in equation (21), | m _V (100,
Instead of T) |, use | m _P (100, T) | and add | m _V (100,
Instead of 20) |, use the measured values of | m _P (100,20) | respectively.

The validity of equations (13) and (14) was confirmed as follows. The thickness of the BGO crystal is 2 m in FIG.
The temperature characteristics when cut at m and θ = −45 degrees are shown. In this example, by keeping the temperature of the light source constant,
The emission wavelength λ was set to a constant condition for measurement. In addition, in Fig. (A),% m when measured at the same time for the same crystal
_{The characteristics of V} (T) and% m _P (T) are shown together. Thus,% m _V (T) increases with increasing temperature and% m _P (T) decreases with increasing temperature. Furthermore, the temperature characteristics of these two sensor sensitivities have a nearly linear relationship with temperature,
It can be seen that the temperature can be approximated by a linear expression like the expressions (13) and (14). On the other hand, the temperature coefficients of these two sensor sensitivities are obtained from the gradients of% m _V (T) and% m _P (T) shown in FIG. The temperature coefficients obtained from the gradients of% m _V (T) and% m _P (T) correspond to the temperature terms of the equations (13) and (14). Therefore, the following expression (22) is established. κ _c- (π / 2) κ _1/4 = -4.0 × 10 ^-4 , κ _c + (π / 2) κ _1/4 = -8.5 × 10 ^-4 … (22) From equation (22), It is possible to obtain κ _{1/4 of} the ¼ wavelength plate used in the above and the temperature coefficient κ _c of the electro-optic crystal BGO. As a result, κ _1/4 and κ _c have the values shown in the following equation (23). (π / 2) κ _1/4 = 2.25 × 10 ⁴ (1 / ° C), κ _c = -6.5 × 10 ^-4 (1 / ° C)… (23) Thus,% m _V (T) and% From m _P (T), when the temperature characteristic of the sensor sensitivity is expressed by a linear expression of temperature, the temperature coefficient κ _1/4 of the quarter-wave plate, which is a component of the optical voltage sensor, and the temperature of the electro-optic crystal BGO. The coefficient κ _c can be obtained.

[Embodiment 2] Here, F (Φ
An example in which the value of the temperature coefficient κ _c of the electro-optic crystal is adjusted by adjusting the values of ( ₀ , θ) will be shown. In order to make the temperature coefficient of the optical voltage sensor zero, the equation (15) is obtained under the condition that the polarizer and the analyzer are orthogonal to each other, and the equation (16) is obtained under the condition that they are parallel to each other.
Must be established. Therefore, here, an example in which the temperature coefficient of the electro-optic crystal is adjusted to match the temperature coefficient of the quarter-wave plate to stabilize the temperature characteristics will be described. First, in a configuration in which the polarizer and the analyzer shown in FIG. 1 are orthogonal to each other, a BGO crystal is used as an electro-optical crystal in order to stabilize the temperature characteristics of the optical voltage sensor, the thickness thereof is 4 mm, and the cutting direction is θ = −. The temperature coefficient was adjusted to 20 degrees and the temperature coefficient κ _c was adjusted to the value shown in the following formula (24). κ _c = -2.25 × 10 ^-4 (1 / ℃) (24) Measured in the configuration in which the polarizer and the analyzer are orthogonal to each other in Fig. 8 (b).
The measurement result of% m _V (T) is shown. In the orthogonal configuration, the temperature change of the optical voltage sensor could be made almost zero in this way. Fig. 8 (b) also shows an example of% m _P (T) for the configuration in which the analyzer and the polarizer were measured in parallel under these conditions.
Are also shown. The temperature gradient in this case has a negative magnitude theoretically, and its temperature coefficient,% m _P (T), has a gradient of 2κ _c .

[Embodiment 3] Next, an example will be described in which the polarizer and the analyzer are parallel to each other and the temperature characteristics of the sensor sensitivity are stabilized. In this case, BGO was similarly used as the electro-optic crystal. However, the thickness is 4 mm and the cutting direction is θ =
The temperature coefficient of the electro-optic crystal was adjusted to 0 °, and the temperature coefficient of the electro-optic crystal was adjusted according to the following formula (25). κ _c = 2.25 × 10 ⁴ (1 / ℃)… (24) Fig. 8 (c) shows the temperature characteristics% m when the polarizer and analyzer are parallel.
Indicates _P (T). Thus, by selecting the temperature coefficient of the electro-optic crystal as the value of the equation (25), it was possible to suppress the temperature change of the optical voltage sensor in the parallel configuration this time. On the other hand,% m _V in the configuration in which a polarizer and an analyzer was measured simultaneously in this condition is perpendicular (T), the temperature characteristic is positive, yet as its value either apparent from equation (8), the 2Kappa _c It was confirmed by this example that a close value was obtained.

[0018]

As described above, according to the present invention, the temperature characteristics of the electro-optical crystal of the optical voltage sensor can be adjusted to the ¼ wavelength plate by optimally adjusting the thickness and crystal orientation of the electro-optical crystal. Since the temperature variation of the optical voltage sensor is suppressed to be small by making the temperature characteristic coincide with the temperature characteristic, the optical voltage sensor having stable temperature characteristic can be provided. Further, since the temperature characteristics of the optical voltage sensor can be stabilized by adjusting only the design condition of the electro-optic crystal, there is an effect that it can be performed without adding new parts.

[Brief description of drawings]

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

FIG. 2 is an explanatory view showing the operation of the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing the relationship between the amount of transmitted light and the phase difference according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a cutting direction and sensor sensitivity according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing the relationship between the cutting direction and the temperature coefficient of the electro-optic crystal in the example of the present invention.

FIG. 6 is an explanatory diagram showing a cutting direction of the electro-optic crystal according to the example of the present invention.

FIG. 7 is a block diagram showing a configuration of a measuring apparatus according to an embodiment of the present invention.

FIG. 8 is an explanatory diagram showing temperature characteristics of the optical voltage sensor according to the embodiment of the present invention.

FIG. 9 is an explanatory diagram showing an operation of a conventional example.

[Description of Reference Signs] 1 optical fiber, 2a, 2b, 2c collimator lens, 3 polarizer, 4 1/4 wavelength plate, 5 electro-optic crystal,
6 analyzers, 7 mirrors

Claims (3)

[Claims] 1. A polarizer arranged in order along an optical path, 1 /
An optical voltage sensor comprising a four-wave plate, an electro-optic crystal, and an analyzer, wherein the electro-optic crystal is Bi ₁₂ GeO ₂₀ or B.
i ₁₂ SiO ₂₀ and adjusting the optical rotation angle determined by the thickness of the electro-optic crystal and the cutting direction of the electro-optic crystal to obtain the temperature coefficient κ _c of the electro-optic crystal and the ¼ An optical voltage sensor characterized in that the relationship with the temperature coefficient κ _1/4 of the wave plate is κ _c = | (π / 2) κ _1/4 |. 2. The photovoltage sensor according to claim 1, wherein the temperature coefficient κ _c has a positive sign when the polarizer and the analyzer are arranged orthogonally to each other. 3. The temperature coefficient κ _c has a negative sign when the polarizer and the analyzer are arranged in parallel.
The optical voltage sensor described.