JP2011214959A - Optical fiber current sensor and electric current measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently reduce temperature dependence of a current measured value and particularly to enable removal of the dependence of high order on a temperature change, in an optical fiber current sensor and an electric current measurement method which are provided for measuring the current by using the Faraday effect.SOLUTION: The optical fiber current sensor includes a sensor fiber 11, a polarization separating element 13 which separates emission light from the sensor fiber 11 into two polarization components of which the polarization planes intersect each other at right angles, and a signal processing part 15 which converts the two separated polarization components into a first signal and a second signal respectively by photoelectric conversion and computes a Faraday rotation angle by substituting the ratio S1 between DC and AC components of the first signal and the ratio S2 between DC and AC components of the second signal into an operational expression. As for the operational expression, equations of the ratio S1 and the ratio S2 expressed respectively as functions of the Faraday rotation angle and the temperature are made simultaneous equations wherein the Faraday rotation angle and the temperature are unknown, and the equations are solved about the Faraday rotation angle.

Description

  The present invention relates to an optical fiber current sensor and a current measurement method for measuring current using a Faraday effect in which a polarization plane of light propagating in an optical fiber is rotated by a magnetic field.

In recent years, an optical fiber current sensor using an optical fiber as a sensor has attracted attention as a current measuring device for monitoring power facilities and the like.
In this optical fiber current sensor, the current is measured using the Faraday effect in which the polarization plane of light propagating in the magnetic medium rotates in proportion to the magnitude of the magnetic field in the propagation direction. An optical fiber is also a kind of magnetic medium. When linearly polarized light is incident on an optical fiber used as a sensor and placed near a conductor through which a current to be measured flows, that is, a magnetic field source, the optical fiber is polarized to linearly polarized light in the optical fiber by the Faraday effect. Wavefront rotation (Faraday rotation) is given. At this time, since a magnetic field proportional to the current is generated, the rotation angle of the plane of polarization (Faraday rotation angle) due to the Faraday effect is proportional to the magnitude of the current to be measured. Therefore, the magnitude of the current can be obtained by measuring the Faraday rotation angle. This is the principle of the optical fiber current sensor.

  In order to measure the Faraday rotation angle, a technique is adopted in which light output from an optical fiber is received by a photodiode or the like and converted into an electrical signal, and the obtained electrical signal is subjected to predetermined signal processing. However, when the environmental temperature of the place where the optical fiber current sensor is installed changes, the optical bias, which is the operating point when measuring the Faraday rotation angle, changes, or the physical property value gives the sensitivity of the Faraday effect in the optical fiber. The Verde constant fluctuates. And under these influences, the Faraday rotation angle obtained by the above signal processing has an error, and as a result, temperature measurement is dependent on the measured current value and correct measurement cannot be performed. Will occur.

  In response to such problems, the present inventor has proposed an optical fiber current sensor in which the signal processing method is improved to reduce the temperature dependence of the current measurement value (see Patent Document 1).

JP 2009-122095 A

  However, in the signal processing used in the optical fiber current sensor of Patent Document 1, it is possible to remove the component (primary component) that changes in proportion to the amount of temperature fluctuation from the temperature dependence of the current measurement value. However, the high-order (second-order or higher) dependence on the temperature change remained without being removed. For this reason, when the temperature change increases, the error of the measured current value also increases. Thus, conventionally, there remains room for further reducing the temperature dependence of the current measurement value.

  The present invention has been made in view of the above points, and an object of the present invention is to sufficiently reduce the temperature dependence of a current measurement value in an optical fiber current sensor and a current measurement method that measure current using the Faraday effect. In particular, to remove the high-order dependence on the temperature change.

  The present invention has been made to solve the above-described problems, and propagates linearly polarized light to a sensor fiber and imparts it to the linearly polarized light by a magnetic field generated by a current to be measured flowing through a conductor installed in the vicinity of the sensor fiber. By detecting the Faraday rotation angle, the optical fiber current sensor for measuring the measured current separates the sensor fiber and the light emitted from the sensor fiber into two polarization components whose polarization planes are orthogonal to each other. The polarization separation means and the two polarization components separated by the polarization separation means are converted into a first signal and a second signal by photoelectric conversion, respectively, and the ratio S1 of the direct current component to the alternating current component of the first signal and the first signal Signal processing means for calculating the Faraday rotation angle by substituting the ratio S2 of the DC component and AC component of the two signals into an arithmetic expression. The equation is an equation obtained by solving the equation of the ratio S1 and the equation of the ratio S2 respectively expressed as a function of the Faraday rotation angle and the temperature with respect to the Faraday rotation angle as a simultaneous equation having the Faraday rotation angle and the temperature as unknowns. It is characterized by.

  In the present invention, the arithmetic expression used by the signal processing means for calculating the Faraday rotation angle is an expression obtained by eliminating the temperature variable from the simultaneous equations of the ratio S1 and the ratio S2. Therefore, since the Faraday rotation angle is calculated using an arithmetic expression that does not include a temperature variable, high-order dependence on the temperature change does not remain, and the obtained Faraday rotation angle and the current obtained from this Faraday rotation angle The temperature dependence of measured values can be eliminated in principle.

In the optical fiber current sensor, the Faraday rotation angle at the reference temperature of the sensor fiber is φ ₀ , the temperature change from the reference temperature is T, the temperature dependence coefficient of the optical bias is α, and the sensor fiber Where the temperature dependence coefficient of the Faraday rotation angle at β is β, the equation of the ratio S1 is S1 = 2 · (1 + β · T) · φ ₀ / (1 + α · T), and the equation of the ratio S2 is S2 = −2 · (1 + β · T) · φ ₀ / (1−α · T), and the arithmetic expression is φ ₀ = S 1 · S 2 / {(β / α−1) · S 1 + (β / α + 1) -S2}.

  According to the present invention, the measured current value is obtained by using the temperature dependence coefficient α of the optical bias that is a known constant, the temperature dependence coefficient β of the Faraday rotation angle in the sensor fiber, and the ratios S1 and S2 that are values obtained by the measurement. Can be sought.

In the optical fiber current sensor, the Faraday rotation angle at the reference temperature of the sensor fiber is φ ₀ , the temperature change from the reference temperature is T, the temperature dependence coefficient of the optical bias is α, and the sensor fiber When the temperature dependence coefficient of the Faraday rotation angle at β is β, the equation of the ratio S1 is S1 = 2 · (1 + β · T) · cos (α · T) · φ ₀ / (1 + sin (α · T)) And the equation of the ratio S2 is S2 = −2 · (1 + β · T) · cos (α · T) · φ ₀ / (1−sin (α · T)), and the arithmetic expression is φ ₀ = S1 · S2 / {(S2−S1) · (1 + A · β / α) · cosA}, A = sin−1 {(S1 + S2) / (S2−S1)}.

  According to the present invention, the measured current value is obtained by using the temperature dependence coefficient α of the optical bias that is a known constant, the temperature dependence coefficient β of the Faraday rotation angle in the sensor fiber, and the ratios S1 and S2 that are values obtained by the measurement. Can be sought. Moreover, since the equations of the ratios S1 and S2 are derived without using approximation in the derivation process, the current measurement value can be obtained with high accuracy.

  In the present invention, the linearly polarized light is propagated to the sensor fiber, and the Faraday rotation angle given to the linearly polarized light is detected by a magnetic field generated by a current to be measured flowing through a conductor installed in the vicinity of the sensor fiber. In the current measurement method for measuring the current to be measured, a process of separating the outgoing light from the sensor fiber into two polarization components whose polarization planes are orthogonal to each other, and the two separated polarization components by photoelectric conversion, respectively The Faraday rotation by substituting the DC signal / AC component ratio S1 of the first signal and the DC signal / AC component ratio S2 of the first signal and the ratio S2 of the DC signal / AC component of the second signal into an arithmetic expression. A process of calculating an angle, and the calculation formula is expressed by the equation of the ratio S1 and the ratio S2 respectively expressed as a function of the Faraday rotation angle and the temperature. The equations, characterized in that it is an expression obtained by solving for the Faraday rotation angle as simultaneous equations to unknown Faraday rotation angle and temperature.

  According to the present invention, in the optical fiber current sensor and the current measurement method for measuring current using the Faraday effect, the temperature dependence of the current measurement value is sufficiently reduced by removing the high-order dependence on the temperature change. This makes it possible to perform accurate current measurement.

It is a block diagram of the reflection type optical fiber current sensor by the 1st Embodiment of this invention. It is a graph showing the characteristic of the electric signals P1 and P2 obtained with a light receiving element. It is a block diagram of the transmission type optical fiber current sensor by embodiment (modification) of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
FIG. 1 shows a configuration diagram of a reflective optical fiber current sensor according to a first embodiment of the present invention.
In the figure, the optical fiber current sensor includes a sensor fiber 11, an optical circulator 12, a polarization separation element 13, a Faraday rotator 14, and a signal processing unit 15. The signal processing unit 15 includes light receiving elements 151A and 151B, band pass filters BPF1 and BPF2, low pass filters LPF1 and LPF2, division units 152A and 152B, and a calculation unit 153 (CPU).

  The sensor fiber 11 is arranged so as to circulate around the conductor 100 such as a power transmission line through which the current I to be measured flows. As the sensor fiber 11, a lead glass fiber, which is an optical fiber having a characteristic that the Verde constant that determines the magnitude of the Faraday effect is preferably large can be used. A Faraday rotator 14 is attached to one end of the sensor fiber 11, and a reflecting portion (mirror) 111 is formed at the other end by vapor deposition of a metal thin film. The Faraday rotator 14 and the polarization separation element 13, and the polarization separation element 13 and the optical circulator 12 are connected by optical fibers. The optical circulator 12 transmits light supplied from the light source 21 through the light transmission fiber 22 to the sensor fiber 11 side. Connected in the direction you want. The signal processing unit 15 has two light receiving elements 151A and 151B as input units, and one light receiving element 151A is connected to a terminal through which light transmitted from the sensor fiber 11 side of the optical circulator 12 is output by the light receiving fiber 16A. The other light receiving element 151B is connected to the polarization separating element 13 by the light receiving fiber 16B.

  With respect to the thus configured optical fiber current sensor, light emitted from the light source 21 is incident on the polarization separation element 13 via the light transmission fiber 22 and the optical circulator 12. This light is converted into linearly polarized light in which the vibration direction of the electric field is aligned in one direction (the principal axis direction of the polarization separation element 13) by the polarization separation element 13, and is incident on the Faraday rotator 14. The Faraday rotator 14 includes a permanent magnet and a ferromagnetic garnet that is a ferromagnetic crystal that is magnetically saturated by the permanent magnet. The Faraday rotator 14 imparts a 22.5 degree one-way Faraday rotation to light passing through the ferromagnetic garnet. . The linearly polarized light that has passed through the Faraday rotator 14 is incident on the sensor fiber 11, undergoes Faraday rotation by a magnetic field generated around the current I to be measured flowing through the conductor 100, and the plane of polarization of the linearly polarized light passes through the sensor fiber 11. It rotates by the Faraday rotation angle proportional to the magnitude of the magnetic field.

  The light propagating through the sensor fiber 11 is further reflected by the reflecting portion 111, passes through the circulation portion again, undergoes Faraday rotation, and enters the Faraday rotator 14. By passing through the Faraday rotator 14 again, another Faraday rotation of 22.5 degrees is given, so that the Faraday rotator 14 gives a total of 45 degrees Faraday rotation in a reciprocating manner. That is, in this optical fiber current sensor, the optical bias is set to 45 degrees. The light that has passed through the Faraday rotator 14 is guided again to the polarization separation element 13 and separated into two polarization components whose polarization directions are orthogonal to each other (the main axis direction of the polarization separation element 13 and a direction perpendicular thereto). One of the separated lights is received by the light receiving element 151A via the optical circulator 12 and the light receiving fiber 16A, and is converted into an electric signal P1 proportional to the light intensity. The other light is received by the light receiving element 151B via the light receiving fiber 16B and converted into an electric signal P2 proportional to the light intensity.

  Here, it is assumed that the measured current I measured by the present optical fiber current sensor is an alternating current (only an alternating current component). At this time, the Faraday effect felt by the light in the sensor fiber 11 also reflects this alternating current, and the electric signals P1 and P2 both contain a direct current component and an alternating current component (see FIG. 2).

  The electric signal P1 from the light receiving element 151A is input to the band pass filter BPF1 and the low pass filter LPF1. The band pass filter BPF1 extracts the AC component contained in the electric signal P1 and outputs it to the dividing unit 152A, and the low pass filter LPF1 extracts the DC component contained in the electric signal P1 and outputs it to the dividing unit 152A. Division unit 152A outputs to signal processing unit 153 a signal S1 representing the ratio of the AC component to the DC component obtained by dividing the input AC component by the DC component.

  The electric signal P2 from the light receiving element 151B is input to the band pass filter BPF2 and the low pass filter LPF2. Similarly to the above, the band pass filter BPF2 and the low pass filter LPF2 extract the AC component and the DC component included in the electric signal P2, respectively, and output them to the dividing unit 152B. Division unit 152B outputs a signal S2 representing the ratio of the AC component to the DC component obtained by dividing the input AC component by the DC component to operation unit 153.

  The calculation unit 153 converts the two input signals S1 and S2 into digital values, and substitutes the converted values into an arithmetic expression f (S1, S2) or g (S1, S2) described later, The Faraday rotation angle given in the sensor fiber 11 is calculated. In addition, the calculation unit 153 calculates the value of the current I to be measured from the obtained Faraday rotation angle. It is assumed that the above arithmetic expression is stored in advance in a predetermined storage unit (memory such as RAM).

Next, the detailed operation principle of the signal processing unit 15 will be described using mathematical expressions.
FIG. 2 is a graph showing characteristics of electric signals P1 and P2 (light intensity of received light) obtained by the light receiving elements 151A and 151B. In this graph, the horizontal axis represents the Faraday rotation angle θ received by the linearly polarized light incident on the sensor fiber 11, and the vertical axis represents the signal intensity P of each electrical signal. As described above, the light intensity of the light reaching each of the two light receiving elements 151A and 151B includes the Faraday rotation angle θ given by the sensor fiber 11 and the Faraday rotation angle given by the Faraday rotator 14, that is, the optical bias. It depends on the value. In general, considering the case where the optical bias has an error of δ from its set value of 45 degrees, the electric signals P1 (θ) and P2 (θ) are given by the following equations (1a) and (1b) as a function of θ. It is done.
P1 (θ) = 1 + sin (2δ + 2θ) (1a)
P2 (θ) = 1−sin (2δ + 2θ) (1b)

  Here, since the measured current I is an alternating current composed only of an alternating current component, the Faraday rotation imparted to the linearly polarized light in the sensor fiber 11 by this measured current I is about the angle 0 degrees. It will vibrate at a frequency. The amplitude of this vibration is φ. Further, in the figure, a time change of the Faraday rotation angle caused by the alternating current I to be measured is represented by a curve C.

When the Faraday rotation angle changes along the curve C as −φ → 0 → φ, the electric signal P1 obtained by the light receiving element 151A sequentially changes as follows.
P1 (−φ) = 1 + sin (2δ−2φ)
→ P1 (0) = 1 + sin (2δ)
→ P1 (φ) = 1 + sin (2δ + 2φ)
In this way, the electric signal P1 obtained corresponding to the AC measured current I becomes a signal that vibrates at the same frequency as the measured current I, as indicated by the curve P1 in the figure. This signal has a DC component magnitude P1 (0) = 1 + sin (2δ), and the amplitude of the AC component {P1 (φ) −P1 (−φ)} / 2 = {sin (2δ + 2φ) −sin (2δ). -2φ)} / 2. In the region where the error δ of the optical bias and the amplitude φ of the Faraday rotation by the sensor fiber 11 are sufficiently small (δ, φ << 1), the direct current component P1 _DC and the alternating current component P1 _AC of the electric signal P1 when the measured current I is measured. Can be represented by the following equations (2a) and (2b), respectively.
P1 _DC = P1 (0) ≈1 + 2δ (2a)
P1 _AC = {P1 (φ) −P1 (−φ)} / 2≈2φ (2b)
The above equations (2a) and (2b) are signals output from the bandpass filter BPF1 and the lowpass filter LPF1, respectively.

Similarly, when the Faraday rotation angle changes with time along the curve C as −φ → 0 → φ, the electric signal P2 obtained by the light receiving element 151B sequentially changes as follows.
P2 (−φ) = 1−sin (2δ−2φ)
→ P2 (0) = 1−sin (2δ)
→ P2 (φ) = 1−sin (2δ + 2φ)
In this way, the electric signal P2 obtained corresponding to the AC measured current I becomes a signal that vibrates at the same frequency as the measured current I, as indicated by the curve P2 in the figure. This signal has a DC component magnitude P2 (0) = 1−sin (2δ), and the amplitude of the AC component {P2 (−φ) −P2 (φ)} / 2 = {sin (2δ + 2φ) −sin. (2δ−2φ)} / 2. Similarly, in the region where δ, φ << 1 holds, the direct current component P2 _DC and the alternating current component P2 _AC of the electric signal P2 when the measured current I is measured are expressed by the following equations (3a) and (3b), respectively. Can do.
P2 _DC = P2 (0) ≈1-2δ (3a)
P2 _AC = − {P2 (−φ) −P2 (φ)} / 2≈−2φ (3b)
However, the negative sign of the alternating current component P2 _AC is obtained by considering that the alternating current component P2 _AC phase are inverted. The above equations (3a) and (3b) are signals output from the bandpass filter BPF2 and the lowpass filter LPF2, respectively.

Here, the magnitude of the Faraday rotation imparted in the sensor fiber 11 changes according to a change in the environmental temperature due to the Verde constant of the sensor fiber 11 having temperature dependence. Further, the optical bias due to the Faraday rotator 14 also changes in accordance with the change in environmental temperature due to the temperature dependence of the Verde constant of the ferromagnetic garnet. Considering this, it is assumed that the amplitude φ of the Faraday rotation by the sensor fiber 11 and the error δ of the optical bias have temperature dependence expressed by the following equations (4a) and (4b).
δ = αT / 2 (4a)
φ = (1 + βT) φ ₀ (4b)
Where α and β are respective temperature dependence coefficients (known constants), T is the amount of temperature change from a reference temperature (for example, 20 ° C.), and φ ₀ is the amplitude of the Faraday rotation angle at the reference temperature.

  From the above equations (2a), (2b), (3a), (3b), (4a), (4b), the signals S1 and S2 input to the calculation unit 153 are expressed by the following equations (5a), (5b), respectively. It is represented by

Thus, the signals S1 and S2 can be expressed as functions of the Faraday rotation angle and temperature, respectively. In the above formulas (5a) and (5b), α and β are known constants, S1 and S2 are known values obtained by measurement, and the unknowns are two of φ ₀ and T. Therefore, when equations (5a) and (5b) are solved for φ ₀ as simultaneous equations, the following equation (6) is obtained.

By substituting S1, S2, α, β into this arithmetic expression f (S1, S2), the Faraday rotation angle φ ₀ is obtained, and from this Faraday rotation angle φ ₀ , the following equation φ ₀ = V · I The value of the measurement current I is obtained. However, V is the Verde constant of the sensor fiber 11 at the same reference temperature as described above. The arithmetic unit 153 thus calculates the Faraday rotation angle and the value of the current to be measured using the arithmetic expression f (S1, S2). Since the equation f (S1, S2) does not include a temperature variable, the obtained Faraday rotation angle and the measured current value do not depend on temperature in principle.

  Therefore, according to the optical fiber current sensor of the present embodiment, the temperature dependence of the current measurement value can be sufficiently reduced, and thereby accurate current measurement can be performed.

(Second Embodiment)
In the above-described embodiment, approximation is taken in assuming the conditions of δ, φ << 1 when deriving the equations (2a), (2b), (3a), (3b). In the present embodiment, the exact values of the Faraday rotation angle and the current to be measured are calculated without performing such approximation. Note that this embodiment has the same configuration and operation as those of the above-described embodiment except for differences in mathematical expressions described below.

  When approximation is not used, the equations of the signals S1 and S2 corresponding to the above equations (5a) and (5b) are expressed as follows.

Similar to the embodiment described above, equation (7a), and solving for ₀ phi as simultaneous equations (7b), the following equation is obtained (8).

In the present embodiment, the arithmetic unit 153, the calculation formula g (S1, S2) to the S1, S2, alpha, by substituting the beta, calculates the Faraday rotation angle phi _0. As in the above-described embodiment, since the equation g (S1, S2) does not include a temperature variable, the obtained Faraday rotation angle and the current measurement value calculated from the Faraday rotation angle are in principle the temperature. It will not depend. In addition, since the arithmetic expression g (S1, S2) does not include approximation, the accuracy of measurement can be improved.

  As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to

  The optical fiber current sensor is not limited to the reflective type, and the present invention can also be applied to a transmission type optical fiber current sensor. As shown in FIG. 3, the transmission type optical fiber current sensor includes a polarization separation element 13 and a signal processing unit 15 on the side opposite to the light source 21 of the sensor fiber 11, and linearly polarized light incident on the sensor fiber 11. Is configured to pass through the sensor fiber 11 and enter the polarization separation element 13. In the transmission type optical fiber current sensor, in place of the Faraday rotator 14 used in the reflection type optical fiber current sensor, a polarizer that transmits only a component in which the vibration direction of the electric field is one direction out of the incident light, or the transmission. The optical bias may be set using a wave plate that rotates the plane of polarization of linearly polarized light by a predetermined angle. In this case, the error δ of the optical bias is caused by these polarizers and wave plates. The principle explained is the same.

  DESCRIPTION OF SYMBOLS 11 ... Sensor fiber 12 ... Optical circulator 13 ... Polarization separation element 14 ... Faraday rotator 15 ... Signal processing part 16 ... Light receiving fiber 21 ... Light source 22 ... Light transmission fiber 151 ... Light receiving element 152 ... Dividing part 153 ... Calculation part

Claims (4)

The linearly polarized light is propagated to the sensor fiber, and the measured current is measured by detecting the Faraday rotation angle given to the linearly polarized light by the magnetic field generated by the measured current flowing through the conductor installed in the vicinity of the sensor fiber. In the optical fiber current sensor
The sensor fiber;
Polarization separation means for separating the outgoing light from the sensor fiber into two polarization components whose planes of polarization are orthogonal to each other;
The two polarization components separated by the polarization separation means are converted into a first signal and a second signal by photoelectric conversion, respectively, a ratio S1 of the direct current component to the alternating current component of the first signal and a direct current component of the second signal And a signal processing means for calculating the Faraday rotation angle by substituting the AC component ratio S2 into an arithmetic expression,
The calculation formula is an equation obtained by solving the equation of the ratio S1 and the equation of the ratio S2 respectively expressed as a function of the Faraday rotation angle and the temperature with respect to the Faraday rotation angle as a simultaneous equation with the Faraday rotation angle and the temperature being unknown. An optical fiber current sensor. When the Faraday rotation angle at the reference temperature in the sensor fiber is φ ₀ , the temperature change from the reference temperature is T, the temperature dependency coefficient of the optical bias is α, and the temperature dependency coefficient of the Faraday rotation angle in the sensor fiber is β ,
The equation for the ratio S1 is
S1 = 2 · (1 + β · T) · φ ₀ / (1 + α · T)
And
The equation for the ratio S2 is
S2 = −2 · (1 + β · T) · φ ₀ / (1−α · T)
And
The arithmetic expression is
φ ₀ = S1 · S2 / {(β / α-1) · S1 + (β / α + 1) · S2}
The optical fiber current sensor according to claim 1, wherein When the Faraday rotation angle at the reference temperature in the sensor fiber is φ ₀ , the temperature change from the reference temperature is T, the temperature dependency coefficient of the optical bias is α, and the temperature dependency coefficient of the Faraday rotation angle in the sensor fiber is β ,
The equation for the ratio S1 is
S1 = 2 · (1 + β · T) · cos (α · T) · φ ₀ / (1 + sin (α · T))
And
The equation for the ratio S2 is
S2 = −2 · (1 + β · T) · cos (α · T) · φ ₀ / (1-sin (α · T))
And
The arithmetic expression is
φ ₀ = S1 · S2 / {(S2−S1) · (1 + A · β / α) · cosA},
A = sin-1 {(S1 + S2) / (S2-S1)}
The optical fiber current sensor according to claim 1, wherein The linearly polarized light is propagated to the sensor fiber, and the measured current is measured by detecting the Faraday rotation angle given to the linearly polarized light by the magnetic field generated by the measured current flowing through the conductor installed in the vicinity of the sensor fiber. In the current measurement method to
Separating the outgoing light from the sensor fiber into two polarization components whose planes of polarization are orthogonal to each other;
Converting the two separated polarization components into a first signal and a second signal by photoelectric conversion, respectively;
A step of calculating the Faraday rotation angle by substituting the DC component / AC component ratio S1 of the first signal and the DC component / AC component ratio S2 of the second signal into an arithmetic expression;
The calculation formula is an equation obtained by solving the equation of the ratio S1 and the equation of the ratio S2 respectively expressed as a function of the Faraday rotation angle and the temperature with respect to the Faraday rotation angle as a simultaneous equation with the Faraday rotation angle and the temperature being unknown. A current measuring method characterized by being.

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