JP3148579B2 - Optical fiber current / magnetic field sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber current / magnetic field sensor for measuring a current / magnetic field using a magneto-optical element having a Faraday effect and a natural optical rotation, and more particularly to minimizing an output error due to a change in temperature. .

[0002]

2. Description of the Related Art FIG. 8 is a block diagram showing a conventional optical fiber current / magnetic field sensor disclosed in Japanese Patent Publication No. 24665/1992, for example. In the figure, reference numeral 1 denotes a light source using a light emitting diode (LED). Reference numeral 2 denotes a polarizer that directly converts light from the light source 1 into polarized light. Reference numeral 3 denotes a magneto-optical element having a Faraday effect and a natural optical rotation, and uses an oxide crystal Bi ₁₂ GeO ₂₀ element (hereinafter abbreviated as a BGO element). . When the linearly polarized light from the polarizer 2 passes through the BGO element, the plane of polarization rotates in proportion to the length of the optical path due to natural rotation, and the length of the optical path and the strength of the magnetic field acting in parallel to the optical path due to the Faraday effect. Rotate in proportion to. Reference numeral 4 denotes an analyzer that modulates the intensity of light in accordance with the rotation angle of the plane of polarization of the linearly polarized light in the magneto-optical element 3. Reference numeral 5 denotes an electric symbol corresponding to the intensity obtained by photoelectrically converting the linearly polarized light from the analyzer 4. Optical receiver for detecting
Reference numerals a and 10b denote a first optical fiber and a second optical fiber connecting the light source 1 and the polarizer 2, and the analyzer 4 and the optical receiver 5, respectively.

The conventional optical fiber current / magnetic field sensor is constructed as described above. The length of the optical path of the magneto-optical element 3 is such that the circuit angle of the plane of polarization of linearly polarized light is 4 due to its natural optical rotation.
The value at which the sensitivity of 5 ° is maximized is selected. In this way, each optical axis of the polarizer 2 and the analyzer 4 is geometrically set to 45.
It is equivalent to forming an angle of relatively 45 ° even if it is not arranged at ゜. The light emitted from the light source 1 is an optical fiber 10
a, and is incident on the polarizer 2 and converted into linearly polarized light. The linearly polarized light emitted from the polarizer 2 is incident on the magneto-optical element 3, and the plane of polarization is rotated by 45 ° due to natural optical rotation, and further rotated in proportion to the strength of a magnetic field acting in parallel to the optical path due to the Faraday effect. I do. Rotation angle Δψ of this polarization plane
Is H, the Verde constant of the magneto-optical element 3 is V, the natural optical rotation of the magneto-optical element 3 is θ, and the magneto-optical element 3 is
Where L is the length of the optical path of

[0004]

(Equation 1)

The Verde constant of the BGO element is 4 to 5 times the Verde constant of lead glass, which is well known as a transparent material having a Faraday effect, so that the sensitivity is good. The sensitivity is maximized by selecting such that the rotation angle of the polarization plane due to natural optical rotation is 45 °, that is, θL in Expression 1 is π / 4. The linearly polarized light emitted from the magneto-optical element 3 enters the analyzer 4 and undergoes light intensity modulation corresponding to the rotation angle of the polarization plane rotated by the magneto-optical element 3. The linearly polarized light emitted from the analyzer 4 propagates through the optical fiber 10b, enters the optical receiver 5, is photoelectrically converted, and is detected as an electric signal corresponding to the intensity of the linearly polarized light, that is, the strength H of the magnetic field. This allows the strength of the magnetic field to be measured, and if the magnetic field is due to current,
The magnitude of the current can be measured.

[0006]

The conventional optical fiber current / magnetic field sensor is constructed as described above.
Is selected so that the sensitivity is maximized when the rotation angle of the plane of polarization of linearly polarized light is 45 ° due to its natural optical rotation, and the optical axes of the polarizer 2 and the analyzer 4 become 45 ° to each other. However, there is a problem to be solved such that when the temperature changes, the Verdet constant and the natural optical rotation of the magneto-optical element 3 greatly change, and the rotation angle of the polarization plane changes to increase the output error.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and modulates the rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of a magneto-optical element and the Faraday effect to the intensity of light by an analyzer. The primary objective is to obtain an optical fiber current / magnetic field sensor that minimizes the output error by minimizing the effect of temperature changes on the sensitivity when performing the operation. It is a second object of the present invention to obtain an optical fiber current / magnetic field sensor in which the length of the optical path at which the sensitivity is maximum when the rotation angle of the linearly polarized light is 45 ° is optimized in relation to the wavelength of the light from the light source. Also, by using a BGO element as the magneto-optical element, it is possible to minimize the output error when the sensitivity of the rotation plane of the polarization plane due to the natural optical rotation becomes 45 °, and to increase the sensitivity. A third object of the present invention is to obtain a magnetic field sensor. Similarly, it is intended to obtain an optical fiber current / magnetic field sensor capable of minimizing an output error and arbitrarily increasing sensitivity by using a BGO element as a magneto-optical element. The fourth purpose.

[0008]

An optical fiber current / magnetic field sensor according to the present invention transmits light from a light source through a first optical fiber, enters a polarizer, converts the light into linearly polarized light, and has a natural optical rotation and Faraday Incident on the magneto-optical element with the effect,
The intensity of light corresponding to the angle of rotation of the plane of polarization of the magneto-optical element is incident on the analyzer by rotating the plane of polarization of the linearly polarized light by 45 ° by its natural optical rotation and further by rotating the plane of polarization by a predetermined angle by the Faraday effect. Performs modulation, transmits the emitted linearly polarized light through the second optical fiber, enters the optical receiver, detects an electrical signal corresponding to the intensity of the linearly polarized light by photoelectric conversion, and acts in parallel with the optical path of the magneto-optical element. When measuring the strength of a magnetic field, the optical axes of the polarizer and analyzer are perpendicular to each other when the natural optical rotation of the magneto-optical element and the temperature coefficients of the Verde constant are the same sign, and the polarization is used when the sign is different. The optical axes of the detector and the analyzer are made parallel to each other.

In the same optical fiber current / magnetic field sensor as described above, the optical axes of the polarizer and the analyzer are made parallel to each other by using an oxide crystal BGO element as the magneto-optical element.

In the same optical fiber current / magnetic field sensor as described above, the light source has a light wavelength of 800 nm and 900 nm.
The light wavelength of the light source λ (nm) and the length L (mm) of the optical path of the magneto-optical element are L = 0.0092λ−
3.42.

Next, in the same optical fiber current / magnetic field sensor as described above, a magneto-optical element is formed by combining an odd number of dextrorotatory BGO elements and levorotatory BGO elements having the same optical path length. The rotation angle of the plane of polarization of the linearly polarized light due to the natural optical rotation of 45 ° is set to 45 °.

In the same optical fiber current / magnetic field sensor as described above, a magneto-optical element is formed by combining one dextrorotatory BGO element and one levorotatory BGO element having different optical path lengths. The rotation angle of the plane of polarization of the linearly polarized light due to the natural optical rotation of 45 ° is set to 45 °.

[0013]

In the present invention, the optical axes of the polarizer and the analyzer are made perpendicular to each other when the natural optical rotation power and the temperature coefficient of the Verde constant of the magneto-optical element have the same sign. Since the axes are parallel to each other, the effect of temperature change on the sensitivity when the angle of rotation of the plane of polarization of linearly polarized light due to the natural optical rotation of the magneto-optical element and the Faraday effect is modulated by the analyzer to the light intensity is reduced. .

Further, an oxide crystal BGO is used for the magneto-optical element.
Since the optical axes of the polarizer and analyzer are parallel to each other using the element, the angle of rotation of the plane of polarization of linearly polarized light due to the natural optical rotation of the magneto-optical element and the Faraday effect is modulated by the analyzer to the light intensity. The effect of temperature change on the sensitivity of the device is reduced.

Further, the light source has a light wavelength of 800 nm and 9 nm.
Using a light emitting diode between 00 nm and a BGO element for the magneto-optical element, the wavelength λ (nm) of light from the light source and the length L (mm) of the optical path of the magneto-optical element are L = 0.0092.
Since the relationship is λ-3.42, the relationship between the optical path length of the magneto-optical element and the wavelength of the light from the light source that maximizes the sensitivity is optimized.

Next, dextrorotatory BGO with the same optical path length
An odd number of BGO elements and BGO elements with left-handed rotation are combined to form a magneto-optical element, and the rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of the magneto-optical element is set to 45 °. And the sensitivity increases.

Then, dextrorotatory BG having different optical path lengths
The O-element and the left-handed BGO element are combined one by one to form a magneto-optical element, and the rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of the magneto-optical element is set to 45 °, so that the change in temperature that affects the sensitivity And the sensitivity is arbitrarily increased.

[0018]

【Example】

Embodiment 1 FIG. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 1, 5, 10a, and 10b are the same as those described with reference to FIG. 12
Is a polarizer that converts the light from the light source 1 into linearly polarized light. 13 is a magneto-optical element having a Faraday effect and a natural optical rotation. The optical path length is such that the rotation angle of the polarization plane due to the natural optical rotation is 45 °. It is the maximum value. Reference numeral 14 denotes an analyzer that modulates the intensity of light in accordance with the rotation angle of the plane of polarization of linearly polarized light emitted from the magneto-optical element 13.

In this embodiment, when the Verdet constant of the magneto-optical element 13 and each temperature coefficient of the natural optical rotation have the same sign, the optical axes of the polarizer 12 and the analyzer 14 are perpendicular to each other. Make their optical axes parallel to each other. With this arrangement, the Verdet constant of the magneto-optical element 13 and the temperature coefficients of the natural optical rotation cancel each other, and the output error with respect to a change in temperature is minimized.

Next, the reason will be described. Light source 1
Is transmitted through the optical fiber 10a, and the polarizer 1
2 and is converted into linearly polarized light. The linearly polarized light emitted from the polarizer 12 is incident on the magneto-optical element 13, the polarization plane is rotated by 45 ° due to natural optical rotation, and furthermore, due to the Faraday effect, in proportion to the strength of the magnetic field acting in parallel to the optical path. Rotate. The linearly polarized light emitted from the magneto-optical element 13 enters the analyzer 14 and undergoes light intensity modulation corresponding to the rotation angle of the plane of polarization of the magneto-optical element 13. The linearly polarized light emitted from the analyzer 14 propagates through the optical fiber 10b, enters the optical receiver 5, and is photoelectrically converted.
It is detected as an electric signal corresponding to the strength of the magnetic field. Thereby, the strength of the magnetic field can be measured.

When the optical axes of the polarizer 12 and the analyzer 14 are perpendicular to each other, the electric field vector components Ex and Ey of the intensity of the linearly polarized light modulated by the analyzer 14 are transmitted from the magneto-optical element 13 to the analyzer 14. The intensity of the magnetic field is H, the intensity of the magnetic field is H, the Verdet constant of the magneto-optical element 13 is V, its natural optical rotation is θ, and the length of its optical path is L. It is represented by

[0022]

(Equation 2)

The intensity I of the linearly polarized light is obtained by equation (3).

[0024]

(Equation 3)

If VHL is very small in Equation 3, Equation 3 becomes approximately Equation 4.

[0026]

(Equation 4)

In the equation (4), (1-COS2θL) / 2 is a component which is not affected by the magnetic field, and VHL sin2θL
Is a component affected by the magnetic field. The former is represented by Idc, the latter by Iac, and the sensitivity η when the light intensity is modulated by the analyzer 14 with the magnetic field acting parallel to the optical path of the magneto-optical element 13 as an alternating magnetic field is defined by η = Iac / Idc. 5 is obtained.

[0028]

(Equation 5)

Next, when the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other, the sensitivity η when the light intensity is modulated by the analyzer 14 is calculated by the same equation.

[0030]

(Equation 6) In Equations 5 and 6, H represents the effective value of the intensity of the alternating magnetic field.

Since the rotation angle of the polarization plane due to the natural optical rotation of the magneto-optical element 13 is 45 °, θL = 45 in equations (5) and (6).
゜, Equation 7 is obtained.

[0032]

(Equation 7)

Next, the effect of the change in temperature on the sensitivity η when the light intensity is modulated by the analyzer 14 will be described.
The temperature characteristic of the magneto-optical element 14 can be considered with respect to the Verde constant, the natural optical rotation, and the length of the optical path.
Since it is negligible, it is not considered here. The temperature characteristics of the Verdet constant and spontaneous optical rotation of the magneto-optical element 14 are represented by temperature t, and the value of the Verdet constant at the temperature t by
(T), the value of the natural optical rotation at the temperature t is θ (t), the value of the Verdet constant at the operating center temperature is Vo, the value of the natural optical rotation at the operating center temperature is θo, the temperature coefficient of the Verdet constant is α, The temperature coefficient of the optical rotation is β, and the temperature difference between the operating center temperature and the temperature is Δt.

[0034]

(Equation 8)

[0035]

(Equation 9)

When the optical axes of the polarizer 12 and the analyzer 14 are perpendicular to each other, the sensitivity η (t) when the light intensity is modulated by the analyzer 14 at the temperature t is given by the following equations (5), (8) and (9). Equation 10 is approximately obtained.

[0037]

(Equation 10)

Further, since θoL = 45 °, Expression 10 becomes Expression 11.

[0039]

[Equation 11]

From equation 11, the temperature coefficient of sensitivity η (t) is α−
(Π / 2) β, which causes an output error.

When the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other, the temperature coefficient of the sensitivity 7 (t) is α + (π / 2) β, similarly calculated.

From these results, the temperature coefficient of sensitivity when the light intensity is modulated by the analyzer 14 is determined by the polarizer 12 and the analyzer 14.
Even if the optical axes are perpendicular to each other and parallel, not only the temperature coefficient of the Verdet constant and the natural optical rotation,
It can be seen that it is also affected by the rotation angle θoL of the polarization plane due to natural optical rotation. The temperature coefficient of sensitivity α- (π / 2) when the optical axes of the polarizer 12 and the analyzer 14 are perpendicular to each other.
From β and the temperature coefficient of sensitivity α + (π / 2) β when the optical axes are parallel to each other, the polarizer 12 and the analyzer 14
It can also be seen that the sign of the temperature coefficient of natural optical rotation is reversed depending on whether the optical axes are perpendicular or parallel to each other.

The value and the sign of the temperature coefficient α of the Verdet constant and the temperature coefficient β of the natural optical rotation power are determined depending on what kind of oxide crystal is used for the magneto-optical element 13, and α and β have the same sign. Then, the polarizer 12 and the analyzer 14
When the optical axes are perpendicular to each other, the temperature coefficient of sensitivity decreases and the output error is minimized. If α and β have different signs, the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other. In some cases, the temperature coefficient of sensitivity is reduced and the output error is minimized.

Embodiment 2 FIG. The second embodiment uses a BGO element for the magneto-optical element 13 of the first embodiment, and thus has the same configuration as that of FIG. FIG. 2 is a temperature characteristic diagram showing the relationship between the temperature and the rate of change of the Verde constant of the BGO element;
FIG. 3 is a dispersion characteristic diagram showing the relationship between the wavelength of light and the natural optical rotation of the BGO element. FIG. 4 is a graph showing the temperature and output when the ambient temperature of the optical fiber current / magnetic field sensor is changed from -20 ° C. to + 60 ° C. FIG. 4 is a characteristic curve diagram showing a relationship between an error and an elapsed time during measurement, in which a broken line indicates temperature and a solid line indicates error. FIG. 5 is a characteristic diagram showing the relationship between the wavelength of light and the length of the optical path where the rotation angle of the polarization plane due to the natural optical rotation of the BGO element is 45 °.

In the second embodiment, an oxide crystal BGO element is used for the magneto-optical element 13, and the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other. The temperature coefficient β of the natural rotatory power of the BGO element can be calculated, for example, by referring to the IEICE Technical Committee on Sensor Technology, “Improving the accuracy of optical fiber voltage sensors” (Document number ST-
92-19, December 10, 1992), and β = −250 ppm / ° C. The temperature coefficient α of the Verde constant of the BGO element is α = 165 ppm / ° C. by the calculation based on FIG. As described above, in the case of the BGO element, α and β have different signs, so that the temperature coefficient of sensitivity decreases when the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other as described in the first embodiment. Output error is minimized. When the temperature coefficient α + (π / 2) β in this case is calculated, it is -228 ppm / ° C. By the way, polarizer 1
When the temperature coefficient α- (π / 2) β of the sensitivity when the optical axes of the sample 2 and the analyzer 14 are perpendicular to each other is calculated, 558 ppm
/ ° C and the output error increases.

Using a BGO element as the magneto-optical element 13 and an optical fiber current / magnetic field sensor in which the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other, the ambient temperature is reduced by -2.
The output error when changing from 0 ° C. to + 60 ° C. was actually measured. FIG. 4 shows the result. The output error is ± 1.04% for a temperature range of 80 ° C., and the temperature coefficient of the output error is −260 ppm / ° C., which is a calculated value of −228 ppm / ° C. It turned out to be close.

Embodiment 3 FIG. In the second embodiment, the magneto-optical element 13
A BGO element made of an oxide crystal is used as the light source, but the length of the optical path where the rotation angle of the plane of polarization of the linearly polarized light due to its natural optical rotation becomes 45 ° changes with the wavelength of the light of the light source 1. The inventors of the present application have made the light source 1 have a light whose central wavelength is
This relationship was confirmed by experiments using a light emitting diode of 0 nm, and the results shown in FIG. 5 were obtained. In the third embodiment, when the wavelength of light of the light source 1 is between 800 nm and 900 nm,
The purpose of the present invention is to optimize the relationship between the length of an optical path where the rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of the BGO element is 45 ° and the wavelength of the light. From FIG. 5, the length L (mm) of the optical path of the BGO element and the wavelength λ (mm) of the light have the relationship of Expression 12.

[0048]

(Equation 12)

Therefore, for example, if the wavelength of light is 850n
m, the length of the optical path where the rotation angle of the plane of polarization of the linearly polarized light due to the natural optical rotation of the BGO element is 45 ° is 4.4 mm.
become.

FIG. 6 is a block diagram showing a fourth embodiment of the present invention. In FIG. 6, 1, 5, 10a, 10b, 12,
14 is the same as that described with reference to FIG. Reference numeral 23 denotes a magneto-optical element having a Faraday effect and a natural optical rotation, comprising two right-rotating BGO elements 23a and one left-rotating BGO element 23b, all having the same optical path length.

There is a correspondence between the optical path length of the magneto-optical element 23 and the sensitivity, and the sensitivity increases as the optical path length increases. As is clear from the description of the first embodiment, the magneto-optical element 2
3. The rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of 3 is 45.
The sensitivity also increases when it is an odd multiple of ゜ (see Equation 6). However, since the rotation angle of the polarization plane affects the temperature coefficient of sensitivity, if it becomes an odd multiple of 45 °, the temperature coefficient of sensitivity also increases. The output error increases and the output error increases. In the fourth embodiment, the magneto-optical element 23 is composed of a combination of two dextrorotatory BGO elements 23a and one levorotatory BGO element 23b, and the rotation angle of the plane of polarization of linearly polarized light due to their natural optical rotation. 45
The temperature coefficient of sensitivity is set to be small, and the error is minimized to increase the sensitivity.

In the fourth embodiment, the magneto-optical element 23 is composed of two dextrorotatory BGO elements 23a and one levorotatory BGO element 2a.
3b, and the lengths of the optical paths are the same. Therefore, the length of the optical path for the natural optical rotation of the magneto-optical element 23 is the length of the optical path of one dextrorotatory BGO element 23a. The optical path length for the effect is 2
Dextrorotatory BGO elements 23a and one dextrorotatory BGO
The sum of the lengths of the respective optical paths of the element 23b, that is, three times the length of the optical path of a single right-handed (left-handed) BGO element 23a (23b). Accordingly, the rotation angle of the polarization plane due to natural optical rotation is 45 °, and when the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other, the temperature coefficient of sensitivity is small and the output error with respect to a change in temperature is minimized. Then, the rotation angle of the polarization plane due to the Faraday effect increases, and the sensitivity increases.

In the third embodiment, the light wavelength of the light source 1 is 800 nm and 900 nm by using a BGO element for the magneto-optical element 13.
In the description above, the optimization of the relationship between the optical path length and the light wavelength at which the rotation angle of the plane of polarization of linearly polarized light due to the natural optical rotation of the BGO element becomes 45 ° is described. BGO element 23a with dextrorotatory (levorotary) even with 4
By optimizing the relationship between the optical path length and the light wavelength at which the rotation angle of the plane of polarization of the linearly polarized light due to the natural optical rotation of (23b) becomes 45 °, two dextrorotatory BGO elements 23a and one The magneto-optical element 23 composed of the combination of the left-handed BGO element 23b is also optimized.

FIG. 7 is a block diagram showing a fifth embodiment of the present invention. In FIG. 7, 1, 5, 10a, 10b, 12,
14 is the same as that described in the first embodiment. 33
Is a magneto-optical element having a Faraday effect and a natural optical rotation, and is configured by combining one right-handed BGO element 33a and one left-handed BGO element 33b having different optical path lengths.

In the fifth embodiment, the magneto-optical element 33 is composed of a dextrorotatory BGO element 33a having a different optical path length and a levorotatory BG element.
O elements 33b are combined one by one, the rotation angle of the plane of polarization of linearly polarized light due to their natural optical rotation is set to 45 °, the temperature coefficient of sensitivity is reduced, the output error is minimized, and the sensitivity is arbitrarily increased. Things.

In the fourth embodiment, the optical path length for the Faraday effect of the magneto-optical element 23 is the sum of the optical path lengths of two right-handed BGO elements 23a and one left-handed BGO element 23b. That is, one dextrorotatory (levorotary) BGO
The length of the optical path of the element 23a (23b) is three times as long as
If the magneto-optical element 23 is composed of an odd number of combinations of the right-handed BGO element 23a and the left-handed BGO element 23b, the optical path length for the Faraday effect is one right-handed (left-handed). The sensitivity is increased stepwise by being an odd multiple of the optical path length of the BGO element 23a (23b). However, in the fifth embodiment, since the magneto-optical element 33 is configured by combining one dextrorotatory BGO element 33a and one dextrorotatory BGO element 33b having different optical path lengths, the optical path length for the Faraday effect is increased. The sensitivity can be arbitrarily selected, and thus the sensitivity can be arbitrarily increased.

In the fifth embodiment, the magneto-optical element 33
The length of the optical path for the natural rotation is L ₁ (mm), and the length of the optical path of the BGO element 33a is dextrorotatory.
L ₁ -L ₂ its element 33b as L ₂ (mm) (m
m). According to the description in the third embodiment, for example, if the wavelength of the light from the light source 1 is 850 (nm), the rotation angle of the polarization plane of the linearly polarized light due to the natural optical rotation of the magneto-optical element 33 is 4.
The length L ₁ -L ₂ of the optical path which becomes 5 ° is optimized at 4.4 (mm). Therefore, the difference between the lengths of the respective optical paths of the right-handed BGO element 33a and the left-handed BGO element 33b is 4.4.
(Mm), the length of each optical path can be arbitrarily selected, and the length L ₁ + L ₂ of the optical path for the Faraday effect of the magneto-optical element 33 increases, and the sensitivity increases arbitrarily. The temperature coefficient of sensitivity is exactly the same as that described in the second embodiment, and becomes smaller when the optical axes of the polarizer 12 and the analyzer 14 are parallel to each other, and the output error is minimized.

[0058]

As described above, according to the present invention,
The light from the light source is transmitted through the first optical fiber, enters the polarizer, changes to linearly polarized light, and then enters the magneto-optical element having natural optical rotation and the Faraday effect. The linearly polarized light is rotated by 45 ° by the optical rotation, and furthermore, the linearly polarized light is rotated by a predetermined angle by the Faraday effect, enters the analyzer, modulates the intensity of light corresponding to the rotation angle of the polarization plane in the magneto-optical element, and emits the linearly polarized light. Is transmitted through a second optical fiber, is incident on an optical receiver, detects an electrical signal corresponding to the intensity of linearly polarized light by photoelectric conversion, and measures the intensity of a magnetic field acting in parallel to the optical path of the magneto-optical element. In the fiber current / magnetic field sensor, when the natural optical rotation of the magneto-optical element and the temperature coefficient of the Verde constant have the same sign, the optical axes of the polarizer and the analyzer are perpendicular to each other. The optical axes of the photons The effect of temperature changes on sensitivity when the angle of rotation of the plane of polarization of linearly polarized light due to the natural optical rotation of the magneto-optical element and the Faraday effect is modulated by the analyzer to light intensity is reduced. Is minimized.

Further, in the same optical fiber current / magnetic field sensor, the optical axes of the polarizer and the analyzer are made parallel to each other by using an oxide crystal BGO element as the magneto-optical element. And the output error is minimized.

Further, in the same optical fiber current / magnetic field sensor, a light emitting diode whose light wavelength is between 800 nm and 900 nm is used as a light source, and a BG is used as a magneto-optical element.
Using the O element, the wavelength λ (nm) of the light from the light source and the length L (mm) of the optical path of the magneto-optical element are L = 0.0092λ-3.42.
The relationship between the optical path length of the magneto-optical element and the wavelength of light from the light source that maximizes the sensitivity is optimized.

Next, in the same optical fiber current / magnetic field sensor, an odd number of dextrorotatory BGO elements and levorotatory BGO elements having the same optical path length are combined to form a magneto-optical element. Since the rotation angle of the plane of polarization of linearly polarized light due to natural optical rotation is 45 °, the effect of temperature change on sensitivity is reduced, and output error is minimized.
Sensitivity increases.

Then, in the same optical fiber current / magnetic field sensor, a dextrorotatory BGO element and a dextrorotatory BGO element having different optical path lengths are combined one by one to form a magneto-optical element. Since the rotation angle of the plane of polarization of the linearly polarized light due to the optical rotation is set to 45 °, the influence of the temperature change on the sensitivity is reduced, the output error is minimized, and the sensitivity is arbitrarily increased.

[Brief description of the drawings]

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

FIG. 2 is a temperature characteristic diagram showing a relationship between a temperature and a rate of change of a Verde constant.

FIG. 3 is a dispersion characteristic diagram showing the relationship between the wavelength of light and the natural optical rotation.

FIG. 4 is a characteristic curve diagram showing a relationship between temperature, output error, and elapsed time.

FIG. 5 is a characteristic diagram showing a relationship between the wavelength of light and the length of an optical path at which a rotation angle of a polarization plane due to natural optical rotation becomes 45 °.

FIG. 6 is a configuration diagram showing a fourth embodiment of the present invention.

FIG. 7 is a configuration diagram showing a fifth embodiment of the present invention.

FIG. 8 is a configuration diagram showing a conventional optical fiber current / magnetic field sensor.

[Explanation of symbols]

1: light source, 5: optical receiver, 10a: first optical fiber,
10b: second optical fiber, 12: polarizer, 13: magneto-optical element, 14: analyzer, 23: magneto-optical element, 23
a: right-handed BGO element, 23b: left-handed BGO element, 33: magneto-optical element, 33a: right-handed BGO element, 33b: left-handed BGO element.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-107273 (JP, A) JP-A-63-182573 (JP, A) JP-A-61-243380 (JP, A) JP-A-2- 38880 (JP, A) JP-A-3-37584 (JP, A) JP-A-61-250574 (JP, A) JP-A-61-250573 (JP, A) JP-A-1-312483 (JP, A) JP-A-61-250572 (JP, A) JP-A-58-140716 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 15/24 G01R 33/032 G02F 1/09 505

Claims (5)

(57) [Claims] 1. A light from a light source is transmitted through a first optical fiber, is incident on a polarizer, is changed to linearly polarized light, and is incident on a magneto-optical element having natural optical rotation and a Faraday effect. The polarization plane is rotated by 45 ° by the natural optical rotation, and linearly polarized light rotated by a predetermined angle by the Faraday effect is incident on the analyzer to modulate the intensity of light corresponding to the rotation angle of the polarization plane in the magneto-optical element. Then, the emitted linearly polarized light is transmitted through the second optical fiber, is incident on the optical receiver, detects an electric signal corresponding to the intensity of the linearly polarized light by photoelectric conversion, and a magnetic field acting in parallel with the optical path of the magneto-optical element. In the optical fiber current / magnetic field sensor for measuring the strength of the optical fiber, the natural optical rotation of the magneto-optical element and the respective temperature coefficients of the Verdet constant have the same sign, and the optical axes of the polarizer and the analyzer are perpendicular to each other. , For different signs Is an optical fiber current, wherein the optical axes of the polarizer and the analyzer are parallel to each other.
Magnetic field sensor. 2. An oxide crystal of Bi ₁₂ Ge is used for a magneto-optical element.
Optical fiber current and the magnetic field sensor according to claim 1, characterized in that the parallel to the optical axes of the polarizer and analyzer using O ₂₀ device. 3. The light source has light wavelengths of 800 nm and 900 n.
m, and a light wavelength λ (n) of the light source using a Bi ₁₂ GeO ₂₀ element as a magneto-optical element.
3. The optical fiber current / magnetic field sensor according to claim 2, wherein m) and a length L (mm) of an optical path of the magneto-optical element have a relationship of L = 0.0092λ-3.42. 4. A dextrorotatory Bi ₁₂ GeO having the same optical path length.
_A magneto-optical element is formed by combining an odd number of Bi ₁₂ GeO ₂₀ elements with ₂₀ elements of levorotation, and the rotation angle of the plane of polarization of linearly polarized light by the natural optical rotation of the magneto-optical element is set to 45 °. The optical fiber current / magnetic field sensor according to claim 2. 5. A dextrorotatory Bi ₁₂ Ge having different optical path lengths.
The O ₂₀ device and levorotatory Bi ₁₂ GeO ₂₀ combined one by one to constitute the magneto-optical element, and characterized in that 45 ° rotation angle of the polarization plane of linearly polarized light by the natural optical activity of the magneto-optical element The optical fiber current / magnetic field sensor according to claim 2 or 3, wherein