JPH0743397B2 - Optical DC transformer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical transformer, and more particularly to an optical DC transformer suitable for measuring a DC current and voltage.

[Conventional technology]

A conventional optical current / voltage sensor is, for example, as shown in FIG. 9 as an optical current sensor, a light source 1, an optical fiber 2, a polarizer 3, and a Faraday cell having a magneto-optical effect such as lead glass. 4, an analyzer 5, and optical fibers 6,7
And the opto-electric conversion circuits 8 and 9 and the arithmetic circuit 10.

In such an optical current sensor, the optical polarization plane is rotated by the magneto-optical effect corresponding to the magnetic field H generated by the measured current, and the polarization plane of the incident light I ₀ is only θ as compared with the case where the magnetic field H is not present. Rotate. This emitted light is divided into two polarization components orthogonal to each other, and further passed through opto-electric conversion circuits 8 and 9 to obtain outputs V ₁ and V ₂ . When k ₁ and k ₂ are proportional constants, the following equations (1) and (2) are obtained.

V ₁ = k ₁ I ₀ (1 + sin2θ) …… (1) V ₂ ＝ k ₂ I ₀ (1-sin2θ) …… (2) Now, if it is possible to adjust k ₁ = k ₂ by some method, , The following equation (3) is obtained.

In the range of sin2θ << 1, sin2θ≈2θ, and an output proportional to the Faraday rotation angle θ, that is, an output V proportional to the conductor current can be obtained.

Since this detection method uses the equation (3), it can be detected even if the measured quantity is a direct current.

However, in general, the light emission source 1, the optical fiber 2, the polarizer 3, the Faraday cell 4, the analyzer 5, the optical fibers 6 and 7, the opto-electric conversion circuit
In the optical transmission parts such as 8, 9 and the like, it is very difficult to maintain the state of k ₁ = k ₂ because the transmission characteristic of the amount of light changes due to temperature characteristics and changes over time. When k ₁ ≠ k ₂ , the error of the numerator V ₁ −V _{2 in} the equation (3) significantly increases, and there is a drawback that the error in detecting the direct current increases. Since the formula (3) is used also in the measurement of the DC voltage, there are similar drawbacks.

[Problems to be Solved by the Invention]

As an attempt to improve this point and measure a DC voltage / electric field, as described in JP-A-57-141562, a light intensity signal obtained by superimposing a constant amplitude AC on a constant DC level is used. After application to the applied voltage sensor and conversion of the emitted light into an electric signal, it is divided into two signals, a signal obtained by removing only the AC signal component from this electric signal and a signal obtained by obtaining only the AC signal component. It is also considered to obtain the ratio of the direct current component and the alternating current component in the incident light and calculate the difference between the two, in addition to obtaining the signal ratio. That is, since the fluctuation of the light quantity in the optical transmission path is expressed in the same proportion as the direct current component and the alternating current component contained in the original light emission intensity, attention is paid to the fact that the ratio can be regarded as almost constant in the optical transmission path. The ratio is used to correct the detection signal from the sensor.

However, in this method, there is no consideration for the modulation component due to the Pockels effect in the sensor being superimposed on the AC component of the light emitted from the sensor, and there is a drawback that the error is very large when measuring the DC voltage. is there.

Further, as described in JP-A-59-0888665, a method of correcting the detection signal using the AC component included in the emitted light from the optical applied magnetic sensor is also considered,
There is a drawback that measurement cannot be performed if the amount of alternating current contained in the measured direct current is small. Further, there is a drawback that the measurement error increases when the frequency of the AC current included in the DC current to be measured increases, and the response speed as a sensor is very slow when the frequency of the AC current is low.

An object of the present invention is to provide a light amount variation in an optical transmission path,
It is an object of the present invention to provide an optical applied current / voltage transformer capable of correcting the fluctuation in an arithmetic circuit and measuring a DC current or a DC voltage with high accuracy and stability.

[Means for Solving the Problems]

The present invention applies a constant AC magnetic field or AC electric field from the outside to the sensor itself, divides the light emitted from the sensor into at least two optical signals, and converts each optical signal into an electrical signal,
Each electric signal is divided into an AC signal component and a component from which the AC signal has been removed, and the component from which the AC signal has been removed is corrected by the AC signal component so that the detection error due to the temperature characteristics, aging, etc. is constantly corrected. It is the one.

That is, in order to achieve the above object, the present invention provides a light emitting source that emits a certain level of light, a polarizer that polarizes the emitted light, and a sensor that applies a magneto-optical effect or an electro-optical effect to the polarized light. An analyzer disposed in the optical path emitted from the sensor; an opto-electric conversion circuit for converting at least two optical signals emitted from the analyzer into electric signals; and an electric signal applied to the sensor. In the optical DC transformer including an arithmetic circuit for obtaining the strength of a magnetic field or an electric field, the sensor includes means for generating a constant AC magnetic field or AC electric field in the sensor, and the arithmetic circuit includes Means for obtaining only the AC component from the electric signal, means for obtaining the ratio of each AC component, means for obtaining each electric signal from which the AC component has been removed, ratio of each AC component and the AC Means for obtaining the product of one of the electric signals with the component removed, means for obtaining the difference between the product and the other electrical signal of which the AC component has been removed, and the other electrical signal with the product and the AC component removed The present invention proposes an optical DC transformer provided with a means for obtaining the sum of the above and a means for obtaining the strength of the magnetic field or the electric field using the ratio of the difference and the sum.

The present invention also provides that the sensor includes means for generating a constant AC magnetic field or AC electric field in the sensor, the arithmetic circuit determining only the AC component from each electric signal, and the AC component. Means for obtaining each electrical signal with the removed, a means for obtaining each ratio of the electrical signal with the AC component removed and the AC component corresponding to each optical signal, and a means for obtaining the difference between the signals of each ratio, The present invention proposes an optical DC transformer provided with means for obtaining the sum of the signals of the respective ratios and means for obtaining the strength of the magnetic field or the electric field using the ratio of the difference and the sum.

The sensor having the magneto-optical effect is specifically composed of a Faraday cell, and the AC magnetic field generating means includes a coil wound around at least a part of the Faraday cell to generate a constant AC magnetic field, and a coil. An AC power supply for supplying AC power is included.

The sensor having the magneto-optical effect may be a Faraday cell sandwiched in a gap of a core with a gap, in which case the alternating magnetic field generating means is wound around at least a part of the core with a gap. A coil for generating a constant AC magnetic field and an AC power supply for supplying AC power to the coil are included.

The sensor having the magneto-optical effect may be a plurality of Faraday cells including cells to which a magnetic field to be measured is applied, and the Faraday cells may be coupled by an optical waveguide capable of preserving the plane of polarization.

On the other hand, when the sensor having the electro-optical effect is composed of a Pockels cell to which an electric field to be measured is applied, the AC electric field generating means includes means for applying an AC electric field to the other part of the Pockels cell. .

The sensor having the electro-optical effect may also be a plurality of Pockels cells including cells to which the electric field to be measured is applied, and the Pockels cells may be coupled by an optical waveguide capable of preserving the plane of polarization.

More specifically, the means for obtaining the signal with the AC component removed consists of a low-pass filter, the means for obtaining only the AC component comprises a bandpass filter and a rectifier circuit, and the means for obtaining the AC component ratio consists of a divider. The means for obtaining the product of the ratio of each of the AC components and the one electric signal from which the AC component has been removed comprises a multiplier.

The means for obtaining the ratio between the signal from which the AC component has been removed and the signal containing only the AC component also comprises a divider.

[Action]

Consider an optical magnetic sensor. The amount of light incident on the sensor is J _0, and the rotation angle of the Faraday cell due to the measured current is θ _i . If the frequency of the AC magnetic field applied to the Faraday cell is f, ω = 2πf, and the rotation angle in the Faraday cell due to this AC magnetic field is θ _f sin ωt, the two polarization components orthogonal to each other at the exit end are V ₁ = k ₁ J ₀ {1 + sin (2θ _i + 2θ _f sin ωt)} ……
(4) V ₂ = k ₂ J ₀ {1-sin (2θ _i + 2θ _f sin ωt)} ......
(5) _If both 2θ _i and 2θ _f are sufficiently smaller than π / 2, V ₁ = k ₁ J ₀ (1 + 2θ _i + 2θ _f sinωt) = k ₁ J ₀ (1 + 2θ _i ) + k ₁ J ₀ 2θ _f sinωt ...... ( 6) V ₂ = k ₂ J ₀ (1-2θ _i ) −k ₂ J ₀ 2θ _f sin ωt (7) is obtained. k ₁ and k ₂ are proportional constants including fluctuations in the amount of light in the optical transmission path. Since the second term on the right side of the equations (6) and (7) is a signal containing only an AC component, it is possible to extract k ₁ and k ₂
The ratio of is required. If only the AC component is removed from the equations (6) and (7), V ₁ ′ = k ₁ · J ₀ (1 + 2θ _i ) ... (8) V ₂ ′ = k ₂ · J ₀ (1-2θ _i ) ... … (9). When the ratio of k ₁ and k ₂ is calculated, (8),
By adding the correction to k ₁ and k ₂ in equation (9),
Proportional coefficients k ₁ and k ₂ in equations (8) and (9) can be made almost the same,
Similar to the expressions (1) to (3), an output proportional to the Faraday rotation angle θ _i can be obtained. Since the measured magnetic field is proportional to this rotation angle θ _i , the measured magnetic field is obtained.

Moreover, if the ratio of the first term and the second term of the equation (6) is taken and the ratio of the first term and the second term of the equation (7) is taken and the difference between them is taken, the output proportional to the Faraday rotation angle is obtained. Is obtained.

On the other hand, also in the optical electric field sensor, if the phase difference in the Pockels cell due to the measured electric field is Γ _i and the phase difference in the Pockels cell due to the AC electric field is Γ _f sin ωt, then V ₁ = k ₁ ′ as in the optical electric field sensor. J ₀ {1 + sin (Γ _i + Γ _f sin ωt)} …… (1
0) V ₂ = k ₂ ′ J ₀ {1-sin (Γ _i + Γ _f sin ωt)} …… (1
1) _If both Γ _i and Γ _f are sufficiently smaller than π / 2, V ₁ = k ₁ ′ J ₀ (1 + Γ _i + Γ _f sinωt) = k ₁ J ₀ (1 + Γ _i ) + k ₁ ′ J ₀ Γ _f sinωt ... (12) V ₂ = k ₂ ′ J ₀ (1-Γ _i ) −k ₂ ′ J ₀ Γ _f sin ωt (13) is obtained. That is, similar to the photovoltage sensor, an output proportional to the phase difference Γ _i is obtained, and the measured electric field is proportional to the phase difference Γ _i , so the measured electric field is obtained.

〔Example〕

The first embodiment of the optical DC transformer according to the present invention will be described below.
This will be described with reference to the drawings and FIG.

As shown in FIG. 1, the optical DC transformer of this embodiment has
The light emitting source 1, the optical fiber 2, the polarizer 3, the Faraday cell 4, the analyzer 5, the optical fibers 6 and 7, the opto-electric conversion circuits 8 and 9, the arithmetic circuit 10, and the AC power source 20. , A coil 21 for generating an alternating magnetic field. Details of the arithmetic circuit 10 will be described later with reference to FIG.

The light emitting source 1 emits light with a constant output by a light emitting diode, a laser diode, or the like. After being guided to the optical fiber 2, this light is linearly polarized by the polarizer 3 and enters the Faraday cell 4. In the Faraday cell 4, a Faraday rotation θ _i proportional to the magnetic field generated by the current flowing through the conductor 15 and a Faraday rotation θ _f sin ωt proportional to the AC magnetic field applied from the outside by the coil 21 are generated. AC power supply 20
The frequency f (ω = 2πf) of 1 may be selected to be a value sufficiently larger than the frequency of the AC component included in the measured current or measured magnetic field. Light from Faraday cell 4
Is divided into two polarization components Ip and Is which are orthogonal to each other by the analyzer 5 placed at the exit end of the light and is transmitted by the optical fibers 6 and 7 and then enters the opto-electric conversion circuits 8 and 9 to generate an electrical signal. Is converted to. At this time, with respect to the P-polarized plane at the exit end,
If the polarizer 3 is installed so as to obtain linearly polarized light,
The following equation is obtained as the two polarization components Ip and Is.

Ip = kp · I ₀ · {1 + sin (2θ _i + 2θ _f sin ωt)} ...
… (14) Is ＝ ks ・ I ₀・ {1-sin (2θ _i + 2θ _f sin ωt)}…
(15) Here, kp and ks are proportional constants, and generally, including I ₀ , fluctuate with time. If 2θ _i and 2θ _f are selected to be sufficiently smaller than π / 2, Ip = kp · I ₀ (1 + 2θ _i + 2θ _f sinωt) (16) Is = ks · I ₀ (1-2θ _i + 2θ _f sin ωt) ... (17) is obtained.

Such two polarization components Ip and Is are guided to the opto-electric conversion circuits 8 and 9 in FIG. 1 and detected by the arithmetic circuit 10 as the Faraday rotation angle θ _i proportional to the measured current or magnetic field. . The calculation method will be described with reference to FIG.

The two optical signals Ip and Is are converted into electric signals by the opto-electric conversion circuits 8 and 9, and then branched as input signals to the two signal processing circuits. One passes through the bandpass filters 101 and 102 and is rectified by the rectifier circuits 103 and 104. The pass frequencies of the band pass filters 101 and 102 are made to match the frequency of the AC power supply 20. Only the AC component is output at this time, and Ip (AC) = k ′ · kp · I ₀ · 2θ _f sinωt …… (18) Is (AC) = k ′ · ks · I ₀ · 2θ _f sin ωt ... (19) is obtained. Therefore, the divider 107 causes Ip (AC) and Is (A
Find the ratio of C), To get On the other hand, the other signal branched as an input signal to the two signal processing circuits passes through the low pass filters 105 and 106. The cutoff frequency of this low-pass filter is selected to be sufficiently lower than the frequency of the AC power supply 20 and higher than the frequency contained in the magnetic field to be measured. At this time, the low-pass filter 10
The output signal of 5,106 is Ip (DC) = k ″ · kp · I ₀ (1 + 2θ _i ) …… (21) Is (DC) = k ″ · ks · I ₀ (1-2θ _i ) …… (22) Becomes In this Is (DC), Ip (AC) / Is (AC) = kp / ks
= Kps is multiplied by the multiplier 108, kps × Is (DC) = (kp / ks) · k ″ · ks · I ₀ (1-2
θ _i ) = k ″ · kp · I ₀ (1-2 θ _i ) ... (2
3) get Based on Ip (DC) and this kps · Is (DC), using the subtractor 109, the adder 110, and the divider 111, by calculating the equation (24), The Faraday rotation angle θ _i proportional to the measured current or the measured magnetic field is obtained. The arithmetic circuit has a feature that the Faraday rotation angle θ _i can be obtained without removing the DC signal.

Another embodiment of the calculation method for detecting the Faraday rotation angle θ _i will be described with reference to FIG. In FIG. 3, the two optical signals Ip and Is detected by the configuration of FIG. 1 are converted into electric signals by the opto-electric conversion circuits 8 and 9 and then input to the two signal processing circuits, respectively. It is branched as a signal.
One of the signals passes through the low pass filters 105 and 106.
The cutoff frequency of this low-pass filter is selected based on the same idea as described above. At this time, the equations (21) and (22) are obtained as the output signals from the low-pass filters 105 and 106. On the other hand, the respective other signals branched as inputs to the two signal processing circuits pass through bandpass filters 101 and 102,
It is rectified by the rectifier circuits 103 and 104. The currency frequency of the bandpass filter is selected in the same way as above. The signal output at this time is only the AC component.
Equation (19) is obtained. The four signals thus obtained are used as input signals for the dividing circuits 112 and 113, and Ip (DC) / Ip (AC) = (k ″ / k ′) (1 + 2θ _i ) / (2θ _f sin ωt).
(25) Is (DC) / Is (AC) = (k ″ / k ′) (1-2θ _i ) / (2θ _f sin ωt) ……
Get (26). Based on this Ip (DC) / Ip (AC) and Is (DC) / Is (AC), a subtracter 114, an adder 115, and a divider 116 are used to obtain (2
By calculating formula 7), The Faraday rotation angle θ _i proportional to the measured current or the measured magnetic field is obtained. The arithmetic circuit has a feature that the Faraday rotation angle θ _i can be obtained without removing the DC signal.

Another embodiment of the present invention is shown in FIG. In the present embodiment, the iron core with a gap is formed so as to surround the conductor 15 through which the measured current flows.
16 is arranged, and the optical applied magnetic field sensor having the polarizer 3, the Faraday cell 4, and the analyzer 5 is placed in the gap portion. An AC magnetic field generating coil 21 from an AC power supply 20 is wound around at least a part of the iron core 16 to flow the AC magnetic field in the iron core. At this time, the magnetic flux generated in the iron core is formed by superposing the magnetic flux generated by the current flowing in the conductor 15 and the magnetic flux generated by the AC power supply. Therefore, the light emitting source 1
When the light from the light passes through the polarizer 3 and enters the Faraday cell 4, the emitted light undergoes Faraday rotation. As a result, the output of the analyzer 5 is Ip = kp ₁ · I ₀ {1 + sin (2θ _i + 2θ _f sin ωt)} ...
(28) Is = ks ₁ · I ₀ {1-sin (2θ _i + 2θ _f sin ωt)} ……
(29) Here, θ _i is the Faraday rotation angle generated by the magnetic field corresponding to the measured current flowing through the conductor, and θ _f is the Faraday rotation angle generated by the alternating magnetic field. This Ip, Is
Is the same as the equations (14) and (15). By using Ip and Is in the same manner as above, the rotation angle θ _i proportional to the measured current can be detected.

Another embodiment of the present invention is shown in FIG. Faraday cell 4
The AC magnetic field generating coil 21 is wound around at least a part of. The light linearly polarized through the polarizer 3 undergoes Faraday rotation under the influence of the magnetic field H to be measured and the AC magnetic field while traveling while reciprocally reflecting through the Faraday cell 4. As a result, the output of the analyzer 5 is Ip · kp ₂ · I ₀ {1 + sin (2θ _h + 2θ _f sin ωt)} ...
(30) Is ・ ks ₂・ I ₀ {1-sin (2θ _h ＋ 2θ _f sin ωt)} ……
(31) θ _h is the Faraday rotation angle generated by the measured magnetic field H. These Ip and Is are the same as the above equations (14) and (15), and the rotation angle θ _h proportional to the magnetic field to be measured can be detected by the same calculation as above.

Another embodiment of the present invention is shown in FIG. Faraday cell 4
Is divided into at least two or more parts, and the two are connected by an optical waveguide 17 capable of holding a polarization plane so that a magnetic field generated by a current to be measured is applied to one Faraday cell 4 and an AC power source 20 is applied to the other Faraday cell 4A. The AC magnetic field generating coil 21 is wound around. The light linearly polarized by the polarizer 3 is subjected to Faraday rotation θ _f sin ωt by passing through one Faraday cell 4A, and the other Faraday cell 4 while maintaining its polarization state by the optical waveguide 17 capable of holding the polarization plane. Incident on. The Faraday cell 4 receives the Faraday rotation θ _i corresponding to the magnetic field generated by the measured current. As a result, the output of the analyzer 5 is Ip = kp ₃ · I ₀ {1 + sin (2θ _i + 2θ _f sin ωt)} ...
(32) Is = ks ₃ · I ₀ {1-sin (2θ _i + 2θ _f sin ωt)} ……
(33) These Ip and Is are the same as those in the equations (16) and (17), and the Faraday rotation angle θ _i proportional to the measured current or the measured magnetic field can be detected by the same calculation as above.
If the optical waveguide 17 that holds the plane of polarization is, for example, optical glass or a spatial transmission line, placing the Faraday cell 4 in the high potential portion and the Faraday cell 4A in the ground potential portion can maintain the insulation therebetween. It will be easy.

FIG. 7 shows another embodiment of the present invention, that is, an example of an optical voltage transformer. An electric field from the AC power supply 20 is applied to a part of the Pockels cell 11, and a measured electric field E _DC is applied to the other part. The light linearly polarized by the polarizer 3 is a quarter wavelength plate 1
Circularly polarized light passes through 2. This circularly polarized light is Pockels cell 1
While passing through 1, a phase difference Γ _f sin ωt due to the AC electric field and a phase difference Γ _i due to the electric field to be measured E _DC are generated. Therefore, the output of the analyzer 5 at the exit end is Ip = kp ₄ · I ₀ {1 + sin (Γ _i + Γ _f sin ωt)} (3
4) Is = ks ₄ · I ₀ {1-sin (Γ _i + Γ _f sin ωt)} …… (3
5) These Ip and Is are Γ _i instead of 2θ _i and Γ instead of 2θ _{f in} the equations (14) and (15).
_It just substitutes _f . Therefore, the phase difference Γ _i proportional to the electric field to be measured can be detected by performing the same calculation as above.

FIG. 8 shows another embodiment of the present invention, that is, an example of an optical voltage transformer. The Pockels cell 11 is divided into at least two or more parts, and the two are connected by an optical waveguide 17 capable of holding the polarization plane, and one of the Pockels cells 11 has a measured electric field E _DC.
And an AC electric field from the AC power supply 20 is applied to the other Pockels cell 11A. The light linearly polarized by the polarizer 3 passes through the quarter-wave plate 12 and becomes circularly polarized light. While this circularly polarized light passes through the Pockels cell 11A, a phase difference Γ _f sin ωt is generated by the AC electric field, and is incident on the other Pockels cell 11 while keeping the polarization plane by the optical waveguide 17 capable of holding the polarization plane. In the Pockels cell 11, a measured electric field E _DC causes a phase difference Γ _i . As a result, the output of the analyzer 5 is Ip = kp ₅ · I ₀ {1 + sin (Γ _i + Γ _f sin ωt)} (3
6) Is = ks ₅ · I ₀ {1-sin (Γ _i + Γ _f sin ωt)} …… (3
7) These Ip and Is are obtained by substituting Γ _i for 2θ _i and Γ _f for 2θ _{f in} the equations (14) and (15). Therefore, if the calculation is performed in the same manner as described above, the phase difference Γ _i proportional to the measured electric field E _DC can be detected.

〔The invention's effect〕

According to the present invention, it is possible to constantly correct the detection error of the DC current or the DC voltage due to the temperature characteristics or the change over time in the optical transmission path, so that the high-precision measurement of the DC current or the DC voltage can be stably performed for a long period of time. It is possible.

Furthermore, according to the present invention, not only direct current but also alternating current / voltage can be similarly measured.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of an optical current transformer according to the present invention, FIG. 2 is a block diagram showing a configuration of an embodiment of an arithmetic circuit used in the embodiment of FIG. 1, and FIG. FIG. 1 is a block diagram showing the configuration of another embodiment of the arithmetic circuit used in the embodiment of the present invention, FIG. 4, FIG. 5, and FIG. 6 show the configuration of another embodiment of the optical current transformer according to the present invention. Figure, Figure 7,
FIG. 8 is a diagram showing a configuration of an embodiment of an optical voltage transformer according to the present invention, and FIG. 9 is a diagram showing a configuration of an example of a conventional optical current transformer. 1 ... Emitting light source, 2 ... Optical fiber, 3 ... Polarizer, 4,
4A ... Faraday cell, 5 ... Analyzer, 6,7 ... Optical fiber, 8,9 ... Optical-electric conversion circuit, 10 ... Operation circuit, 11,11A ... Pockels cell, 12 ... 1 /
4 wave plate, 15 ... conductor, 16 ... iron core with gap, 17 ... optical director,
20 …… AC power supply, 21 …… AC magnetic field generating coil, 101,102 …… Band pass filter, 103,104 …… Rectifier circuit, 105,106 …… Low-pass filter, 107,111,112,113 …… Divider, 108 …… Multiplier, 109,114 …… Subtractor, 110, 115 ... Adder.

Claims (9)

[Claims] 1. A light emitting source that emits light of a certain level, a polarizer that polarizes the emitted light, a sensor that gives a magneto-optical effect or an electro-optical effect to the polarized light, and an emission optical path of the sensor. An arranged analyzer, an opto-electric conversion circuit that converts at least two optical signals emitted from the analyzer into electric signals, and the strength of the magnetic field or electric field applied to the sensor from the electric signals. In an optical DC transformer including an arithmetic circuit to be sought, the sensor includes means for generating a constant AC magnetic field or AC electric field in the sensor, and the arithmetic circuit includes only the AC component from each of the electric signals. And a means for obtaining the ratio of the AC components,
A means for obtaining each electric signal from which the AC component has been removed, a means for obtaining the product of the ratio of each AC component and one electrical signal from which the AC component has been removed, and the other of which the product and the AC component have been removed Means for obtaining the difference between the electric signal, means for obtaining the sum of the product and the other electric signal from which the AC component has been removed, and the strength of the magnetic field or electric field using the ratio of the difference and the sum An optical DC transformer characterized by comprising: 2. A light emitting source which emits a certain level of light, a polarizer which polarizes the emitted light, a sensor which gives a magneto-optical effect or an electro-optical effect to the polarized light, and an emission optical path of the sensor. An arranged analyzer, an opto-electric conversion circuit that converts at least two optical signals emitted from the analyzer into electric signals, and the strength of the magnetic field or electric field applied to the sensor from the electric signals. In an optical DC transformer including an arithmetic circuit to be sought, the sensor includes means for generating a constant AC magnetic field or AC electric field in the sensor, and the arithmetic circuit includes only the AC component from each of the electric signals. And a means for obtaining each electrical signal from which the AC component has been removed, and a respective ratio between the electrical signal from which the AC component has been removed and the AC component, which corresponds to each optical signal. A step, a means for obtaining the difference between the signals of the respective ratios, a means for obtaining the sum of the signals of the respective ratios, and a means for obtaining the strength of the magnetic field or the electric field using the ratio of the difference and the sum. An optical DC transformer characterized by: 3. The optical DC transformer according to claim 1, wherein the sensor having a magneto-optical effect is a Faraday cell, and the AC magnetic field generating means is provided in at least a part of the Faraday cell. An optical DC transformer comprising: a coil wound around to generate a constant AC magnetic field; and an AC power supply for supplying AC power to the coil. 4. The optical DC transformer according to claim 1, wherein the sensor having a magneto-optical effect comprises a Faraday cell sandwiched by a gap of a core with a gap, and the AC magnetic field generating means. An optical DC transformer comprising: a coil that is wound around at least a part of the iron core with a gap to generate a constant AC magnetic field; and an AC power supply that supplies AC power to the coil. 5. The optical DC transformer according to claim 1, wherein the sensor having a magneto-optical effect comprises a plurality of Faraday cells including a cell to which a magnetic field to be measured is applied. The generating means includes a coil wound around at least a part of the Faraday cell other than the cell to which the magnetic field to be measured is applied to generate a constant AC magnetic field, and an AC power supply that supplies AC power to the coil. An optical DC transformer, characterized in that the Faraday cells are coupled by an optical waveguide capable of preserving the wavefront. 6. The optical DC transformer according to claim 1, wherein the sensor having an electro-optical effect is a Pockels cell to which an electric field to be measured is applied, and the AC electric field generating means. An optical DC transformer, comprising means for applying an AC electric field to the other part of the Pockels cell. 7. The optical DC transformer according to claim 1, wherein the sensor having an electro-optical effect is composed of a plurality of Pockels cells including cells to which an electric field to be measured is applied. The generating means includes means for applying a constant AC electric field to a Pockels cell other than the cell to which the electric field to be measured is applied, and the Pockels cells are coupled by an optical waveguide capable of preserving the plane of polarization. Optical DC transformer. 8. The optical DC transformer according to claim 1, wherein the means for obtaining the signal with the AC component removed comprises a low-pass filter, and the means for obtaining only the AC component has a bandpass filter and a rectifier. A circuit, the means for obtaining the ratio of the AC components is a divider, and the means for obtaining the product of the ratio of the AC components and one of the electric signals from which the AC components have been removed is a multiplier. A characteristic optical DC transformer. 9. The optical DC transformer according to claim 2, wherein the means for obtaining the signal with the AC component removed comprises a low-pass filter, and the means for obtaining only the AC component has a bandpass filter and a rectifier. An optical DC transformer, comprising a circuit, and means for obtaining a ratio of the signal from which the AC component has been removed and the signal having only the AC component is composed of a divider.