JPH11183737A - Optical fiber and optical fiber type measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to measure a large current and to attain highly accurate measurement. SOLUTION: Laser beam from a light source is transmitted by a transmitting optical fiber 5, linearly polarized by a polarizer 4 and made incident upon and optical fiber 3. Core glass of the fiber 3 consists of high lead glass of which photo elastic constant at transmission wavelength is substantially zero and Verdet's constant is <5.8×10<-6> rad/A. Light made incident upon the fiber 3 undergoes, while passing through the fiber 3 rotation of the polarization plane in proportion to a current allowed to flow into a conductor 1 by a magnetic field formed by the current, and is projected. The outgoing light is passed through a 1/2 wavelength plate 6 and divided into two arthogonally polarized components, T, R by an analyser 7 and a prism 8, respective polarized components T, R are sent to a signal processing part through respective light receiving fibers 9, 10 and the current value of a current allowed to flow into the conductor 1 is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber and an optical fiber type measuring device for measuring a magnetic field or a current for generating a magnetic field, and particularly to a measuring device capable of measuring a large current.
The present invention relates to an optical fiber and an optical fiber type measuring device capable of performing highly accurate measurement.

[0002]

2. Description of the Related Art Conventionally, as a current measuring device for obtaining the magnitude of a magnetic field from a Faraday rotation angle by utilizing the Faraday effect of an optical fiber and measuring a current generating the magnetic field, a device shown in FIG. It has been known. As shown in the figure, an optical fiber 42 having a Faraday effect is wound around a conductor 41 on which a current measurement is performed, and light emitted from a light source 43 is converted into linearly polarized light by a polarizer 44 to be converted into light. The light enters the fiber 42. While propagating through the optical fiber 42, the incident light is emitted after being rotated by a polarization plane proportional to the current I due to the Faraday effect due to the magnetic field generated by the current I flowing through the conductor 41. The outgoing light is separated into two orthogonal polarization components (signal light T and signal light R) by an analyzer (polarizing beam splitter) 45, and the photodiode 4
The electrical signals I _T and I _R that have been photoelectrically converted by the photoelectric conversion units 6 and 47 are input to the signal processing unit 48.

When no current flows through the conductor 41, that is, when the Faraday rotation angle is zero, the direction of the polarization plane is set to be 45 ° with respect to the axis of the analyzer 45. If the angle is θ, sin2θ =
(I _T -I _R) / there is relationship (I _T + I _R), the signal processing unit 48 in the input I _T, the Faraday rotation angle θ is determined from I _R. If the Verdet constant of the optical fiber 42 is V and the number of turns of the optical fiber 42 around the conductor 41 is N, there is a relationship of θ = VNI, and the current I is obtained from this.

If the X axis is the vibration direction of the electric field of the signal light T and the Y axis is the vibration direction of the electric field of the signal light R, and an alternating current flows through the conductor 41, the polarization plane becomes as shown in FIG. ,
It swings right and left around a 45 ° straight line (polarization plane when the current is zero) 50. When the current flowing through the conductor 41 increases and the Faraday rotation angle exceeds 45 °, as shown in FIG. 6, two polarization planes (straight lines 51 and 52) symmetric with respect to the X-axis to the Y-axis become currents. Since the measurement cannot be distinguished, the measurable range is up to a Faraday rotation angle of 45 °.

[0005] Further, as an optical fiber of this kind, a quartz glass fiber or a high lead glass fiber (Japanese Patent Publication No. 6-50363) is known.

[0006]

However, although the silica glass fiber has a small Verdet constant, the absolute value of the photoelastic constant is large, and birefringence is induced when an external force or the like is applied to the fiber. The rotation angle is affected, and it is difficult to perform highly accurate measurement.

On the other hand, the above-mentioned high lead glass fiber has a small photoelastic constant and has good polarization plane holding characteristics against external force and the like. However, since the Verdet constant is large, the rated current (47
kArms) (2 × 2 of rated current)
^When a large current corresponding to ^1/2 times (135 kA) flows, the Faraday rotation angle exceeds 45 °, and it is difficult to measure a large current. In the current measurement so far, it has been sufficient if the rated overcurrent of 23 kA corresponding to the rated current of 8 kArms can be measured. In the future, however, it will be necessary to measure a large current of 135 kA or even 178 kA with high accuracy.

The present invention has been made to solve the above problems, and has as its object to provide an optical fiber and an optical fiber type measuring apparatus capable of measuring a large current and realizing a highly accurate measurement. .

[0009]

In order to achieve the above object, an optical fiber according to the present invention is an optical fiber having at least a core and a clad, wherein the core has substantially a photoelastic constant at a wavelength of transmission light. It is made of glass having a specific zero and a Verdet constant of 5.8 × 10 ⁻⁶ rad / A or less.

The inventor of the present invention measures a large current using long wavelength light whose Verdet constant becomes small as light transmitted through a glass fiber because the Verdet constant is approximately inversely proportional to the square of the wavelength of transmitted light. Tried that. However, the holding characteristic of the polarization plane against external force or the like deteriorates, the output becomes unstable, and high-precision measurement cannot be realized. Investigation of the cause revealed that the photoelastic constant of glass had wavelength dependence, and that the absolute value of the photoelastic constant increased when the wavelength of the transmitted light was changed. For example, with high lead glass, it was found that the photoelastic constant increased (there was a positive dependence) as the wavelength increased (see FIG. 3). For accurate measurement of a small photoelastic constant, a measurement method by the optical heterodyne method (Hiroyuki Takawa, Norihiro Umeda: “Measurement of photoelastic constant by frequency stable transverse Zeeman laser”, Optics, 20 (1991) 112-114) The photoelastic constant and refractive index of glass at a desired transmission wavelength were measured with high accuracy.

As described above, since the photoelastic constant of glass has wavelength dependence, simply increasing the wavelength of transmitted light decreases the Verdet constant but increases the absolute value of the photoelastic constant. . Therefore, in the present invention, the photoelastic constant at each wavelength is measured accurately, the refractive index of the glass becomes substantially zero, and the glass composition is adjusted so that the refractive index of the core glass becomes the value. Thus, the optical fiber has a photoelastic constant at a transmission wavelength of substantially zero.

In the present invention, a glass having a photoelastic constant of substantially zero means a photoelastic constant of ± 1 × 10 ⁻¹ (nm / c).
m) / (kgf / cm ² ) or less (note that
This value is two orders of magnitude smaller than the photoelastic constant of quartz glass).
More preferably, the photoelastic constant is ± 1 × 10 ^-2 (nm / c
m) / (kgf / cm ² ) or less.

The Verde constant is 5.8 × 10 ^-6 rad.
The reason for setting to / A or less is to make it possible to measure an accident current such as a lightning strike without causing the Faraday rotation angle to exceed 45 ° even when a rated overcurrent of 135 kA flows. If the change in the Faraday rotation angle is tracked and detected, it is possible to measure a large current whose Faraday rotation angle exceeds 45 °, but this is not preferable because the signal processing system becomes complicated. Furthermore, the rated overcurrent 178 kA corresponding to the maximum current that can flow when a failure occurs in the power system (63 kArm at the rated current)
Even if s) flows, it is preferable to set the Verdet constant to 4.4 × 10 ⁻⁶ rad / A or less in order to enable measurement of the fault current without the Faraday rotation angle exceeding 45 °.

In the above-mentioned optical fiber of the present invention, 5-28 wt% of SiO ₂ and B ₂ O ₃ are used as the glass component of the core.
The 0-10 wt%, 0-5 wt% of Al ₂ O _3, Na ₂ O
+ K ₂ O the 0.3~2.5wt%, 69.5~ the PbO
83.7 wt%, As ₂ O ₃ + Sb ₂ O ₃ is 0 to 0.5 wt%
%, However, the _{SiO 2 + B 2 O 3 +} Al 2 O 3 16~28
By using the one containing wt%, an optical fiber having a photoelastic constant of substantially zero can be easily obtained. In addition, wavelength 1.
If an optical fiber for transmitting light of 55 μm is used, compared with an optical fiber for the 850 nm band conventionally used,
The Verdet constant can be reduced, which is suitable for measuring a large current.
Note that it is preferable to use light having a wavelength of 1.55 μm, because a general-purpose light source (eg, a long-wavelength semiconductor light source) and a photodetector can be used.

An optical fiber type measuring apparatus according to the present invention is an optical fiber type measuring apparatus for measuring a magnetic field or a current for generating a magnetic field from a change in a polarization plane of light emitted from an optical fiber due to the Faraday effect. As a fiber,
The optical fiber of the present invention is used.

Further, the optical fiber type measuring device of the present invention comprises:
An optical fiber type measurement device for measuring current from a change in polarization plane due to the Faraday effect of light emitted from an optical fiber, wherein the core of the optical fiber is made of glass whose photoelastic constant is substantially zero. And the range of the measurable current is 135 kA. Furthermore, the maximum current that can flow when a failure occurs in the power system is 17
Those containing 8 kA in the measurable current range are preferred.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of an optical fiber type measuring device according to the present invention.

In FIG. 1, reference numeral 1 denotes a conductor such as a transmission line through which a current to be measured flows, and the conductor 1 extends through a bobbin 2 in a direction perpendicular to the drawing. An optical fiber 3 wrapped around the bobbin 2 for measuring current by the Faraday effect is wound around the bobbin 2.

The optical fiber 3 is made of high lead glass, and has a core glass composition of ₅ to 28% by weight of SiO ₂ and B ₂ O
₃ 0-10 wt%, 0-5 wt% of Al ₂ O _3, Na ₂ O
+ K ₂ O the 0.3~2.5wt%, 69.5~ the PbO
83.7 wt%, As ₂ O ₃ + Sb ₂ O ₃ is 0 to 0.5 wt%
%, However, the _{SiO 2 + B 2 O 3 +} Al 2 O 3 16~28
What contains wt% (hereinafter referred to as FR glass) is used. The optical fiber 3 is a single mode fiber for 1.55 μm transmission, and has a photoelastic constant of ± 1 × 10 ⁻¹ (nm / cm) / (kgf) at a wavelength of 1.55 μm.
/ Cm ² ) or less and the Verdet constant is 5.8 × 10
^-6 rad / A or less of core glass.

A light transmitting fiber 5 is optically connected to the incident end of the optical fiber 3 via a polarizer 4. A polarization-maintaining fiber is used as the light transmitting fiber 5 in order to keep the polarization direction of the laser light from the light source incident on the polarizer 4 constant and stabilize the intensity of the light incident on the optical fiber 3. Further, an analyzer (polarization beam splitter or the like) 7 for separating the output light into two orthogonal polarization components (signal light T and signal light R) is provided at the output end of the optical fiber 3. The analyzer 7 is installed such that the direction of the plane of polarization of linearly polarized light emitted from the optical fiber 3 is at 45 ° with respect to the axis of the analyzer 7 when no current flows through the conductor 1. In addition, the inclination of the polarization plane when the current is zero is set to 45.
In order to adjust the angle to °, a half-wave plate 6 is provided between the exit end of the optical fiber 3 and the analyzer 7.

Of the two polarization components separated by the analyzer 7, the signal light T is directly connected from the analyzer 7 to the receiving fiber 9, while the signal light R is totally reflected twice by the prism 8, Optically connected to the light receiving fiber 10. Multi-mode fibers are used for the light receiving fibers 9 and 10 so that the light receiving fibers 9 and 10 can be efficiently coupled with the signal lights T and R. A signal processing unit of a current measuring device (not shown) is provided on the emission end side of the light receiving fibers 9, 10, and the light intensity of the signal lights T and R is converted into an electric signal by a light receiving element of the signal processing unit. The current flowing through the conductor 1 is calculated. The optical fiber 3, which optically detects the current of the conductor 1,
The detection unit of the current measuring device including the polarizer 4, the analyzer 7, and the like is housed in the module 11.

The laser light from the light source is transmitted to a light transmitting fiber 5.
, And is converted into linearly polarized light by the polarizer 4 and enters the optical fiber 3. The light that has entered the optical fiber 3 is emitted while undergoing rotation of the polarization plane proportional to the current by the magnetic field generated by the current flowing through the conductor 1 while passing through the optical fiber 3. The emitted light passes through a half-wave plate 6 for adjusting the plane of polarization, and is then split into two orthogonal polarization components T and R by an analyzer 7 and a prism 8, and the respective polarization components T and R are respectively received. The current value sent to the signal processing unit via the fibers 9 and 10 and flowing through the conductor 1 is obtained.

As the optical fiber 3, a fiber for 1.55 μm having a refractive index of the core of 1.86195 and a refractive index of the cladding of 1.85829 was prepared using the above-mentioned FR glass. For comparison, an FR-based glass was used, and the core had a refractive index of 1.85316 and the clad had a refractive index of 1.84.
A 974 0.85 μm fiber was prepared. FR-based glass used in optical fiber manufacturing, specifically, as a glass batch material, 21.5～24.35Wt the SiO ₂
%, Na ₂ O 0.2 wt%, K ₂ O 0.5 wt%, P
74.65 to 77.5 wt% of bO and 0.1 of As ₂ O ₃
wt% and 0.2 wt% of Sb ₂ O ₃ were prepared. In addition, a jacket layer (or an over cladding layer) may be provided on the outer periphery of the cladding as the optical fiber 3. In this case, the jacket layer contains an absorbent that absorbs light of a transmission wavelength to absorb the cladding mode light. It may be removed. In addition, the above refractive index is d of yellow helium.
The refractive index n _d for the spectral line (wavelength 587.56 nm).

Table 1 shows that, when the above-mentioned fiber makes one round around a conductor, the rated overcurrent (23 kA) of the related art, the rated overcurrent (135 kA) and the rated overcurrent (178 kA) of the present invention are considered. The measured values of the Faraday rotation angle at each wavelength and the results of the Verdet constant calculated from the measured values are shown. The numerical value of the wavelength of 1.3 μm is a calculated value obtained from the above measurement results.

[0025]

[Table 1] From Table 1, when measured with light at a wavelength of 1.55 μm, the Faraday rotation angle is within 45 ° even at the rated overcurrent of 135 kA, and it is possible to measure the maximum current that can flow when a failure occurs in the power system due to lightning strike or the like. Become. in this way,
By increasing the wavelength of the light transmitted through the optical fiber, the dynamic range of the measurement current can be increased. Note that F
Since the R-based glass is diamagnetic, there is no temperature dependence of the magnetic susceptibility, so that the Faraday rotation angle does not depend on the temperature and the temperature stability of current measurement is excellent.

Since the cross section of the core of the optical fiber is not a perfect circle and the materials of the core and the clad are different, an internal stress is generated due to a difference in coefficient of thermal expansion, and it is difficult to completely eliminate birefringence. Further, birefringence is also induced by disturbances such as bending, twisting, vibration, temperature, and pressure when mounting the optical fiber. Therefore, in order to obtain a high-sensitivity and high-precision optical fiber for current measurement, it is useful to use glass that is unlikely to cause birefringence and birefringence induced by disturbances specific to these optical fibers. It can be seen that most of the birefringence is proportional to the photoelastic constant C as shown below.

Birefringence due to residual stress: β _S β _S = (2π / λ) · CT Bend induced birefringence: β _B β _B = (π / λ) · C · E · (r / R) ² twist induced _{birefringence: β t β t = 2C ·} (G / n) · Φ t pressure induced _{birefringence: β P β P = (8} / λ) · C · (F C / r · L) thermal stress birefringence Refraction: β _T β _T = C · (α · E / (1−ν _P )) · f where λ: wavelength, T: residual stress, R: bending radius, r:
Radius of fiber, E: Young's modulus, G: rigidity, n: refractive index of core glass, Φ _t : torsion of fiber, L: length of fiber to which compressive force F _C is applied, α: coefficient of linear expansion, f :
A shape-dependent coefficient, ν _P : Poisson's ratio.

For example, taking only the pressure-induced birefringence β _P from the above equation, a quartz glass fiber normally used as a sensing fiber has a photoelastic constant of 3.4 (nm).
/ Cm) / (kgf / cm ² ), and a birefringence value of 149 is applied to a fiber of 125 μm in diameter and 1.55 μm in wavelength band made of quartz glass only by applying a load of 1 g to a length of 1 mm of the fiber. ° / m. Therefore, it cannot be used in the standard measurement example in which the measurement is performed within 45 °, and the birefringence value is greatly different due to a slight change in load for fixing the fiber, so that it is difficult to measure with high accuracy. On the other hand, in the present invention, the photoelastic constant is ± 1 ×
Since it is within 10 ⁻¹ (nm / cm) / (kgf / cm ² ), the birefringence value under the above conditions is reduced to 4.3 ° / m or less, which is a range where measurement can be sufficiently performed.

However, it has now been found that the photoelastic constant of glass has wavelength dependence, and that the absolute value of the photoelastic constant changes when the wavelength of the transmitted light is changed. for that reason,
When the wavelength of the transmission light is changed, there is a problem how to make the absolute value of the photoelastic constant at that wavelength close to zero. Therefore, a measurement method using the optical heterodyne method (Hiroyuki Takawa, Norihiro Umeda: "Measurement of photoelastic constant by frequency stable transverse Zeeman laser", Optics, 20
Using (1991) 112-114), the photoelastic constant and refractive index of glass at each transmission wavelength were measured with high accuracy. Next, this measuring method will be described using a photoelasticity measuring device shown in FIG.

In the measurement in FIG. 2, a compressive stress is applied to the columnar or disk-shaped sample 20 in the diametrical direction, and the resulting retardation (birefringence phase difference) Δ is measured. The laser light from the frequency-stable transverse Zeeman laser 21 is transmitted through the half-wave plate 22, the sample 20, and the analyzer 23, detected by the photoelectric detector 24, and the electric signal detected by the photoelectric detector 24 is converted into an electric signal. Input to the phase meter 27. The electric phase meter 27 outputs a phase difference signal between an electric signal from the photoelectric detector 24 and a beat signal (reference signal) for stabilizing control of the laser 21, and this phase difference signal is output from the A / D converter 28a.
Is converted into digital data, and is taken into the computer 29. Further, the amount of load applied to the sample 20 by the pressurizing device 25 is detected by the load cell 26, converted to digital by the A / D converter 28 b, and taken into the computer 29. The laser 21 has a wavelength of 632.8.
The measurement device was constructed using a He-Ne laser with a wavelength of 1.523 μm and a new wavelength of 1.523 μm.

The light emitted from the frequency stable transverse Zeeman laser 21 is composed of two linearly polarized light components having slightly different frequencies and orthogonal to each other. Two respective x-direction vibration direction of the polarized light component (direction of the transverse magnetic field), when the y-direction, these vibration components E _x, E _y can be expressed as follows. _{E x = a x cosωt E y} = a y cos (ωt + 2πf b t) where, a _x, a _y is the amplitude of the x and y components, omega is the optical frequency of the x component, f _b is the x and y components Is the frequency difference.

When the fast axis of the sample 20 is matched with the x-direction component, the phase difference of the y-direction component is delayed by Δ, and when this passes through the analyzer 23 having an azimuth of 45 °, the transmitted light intensity I becomes Become like ^{_{I = a x 2 + a y}} 2 + 2a x a y cos (2πf b t + Δ) above equation, cosine signal at the signal frequency f _b which is incident on the photoelectric detector 24, the retardation delta of its phase sample 20
Changes depending on

The laser 21 is applied in the diameter direction of the cylindrical sample 20.
A compressive load is applied in a direction of 90 degrees with respect to the magnetic field given to the sample, the resulting retardation of the sample 20 is measured, and the photoelastic constant C is calculated by the following equation. C = πD · Δ / 8P where D is the diameter of the cylindrical sample 20, Δ is the retardation at the center of the cylindrical sample 20, and P is the compression load.

When the half-wave plate 22 and the analyzer 23 are rotated with the rotation angles synchronized at a ratio of 1: 2, the direction of polarization can be changed without affecting the cosine signal of the frequency f _b. Can be. When the phase difference is measured while rotating the half-wave plate 22 and the analyzer 23, the phase difference when one of the two orthogonal polarization directions coincides with the fast axis (F axis) of the sample 20 is the largest. Therefore, a phase difference change component that changes by four periods for one rotation of the half-wave plate 22 is obtained. The amplitude of this component and the initial phase amount are respectively equal to those of Sample 2
Δ of 0 is twice the azimuth of the F axis.

[0035] To express the state of the birefringence vector, the magnitude of the vector delta, twice the F axis azimuth θ as a direction of the vector defines the distortion vector H (Note that under the vector A A It is written with a line). The size and orientation of the residual strain H _R and synthetic distortion (composite value of the load strain and residual strain caused by the load) H _S in a state where the sample does not give a load, respectively R _R, theta _R and R _S, theta _Assuming that _S , the load distortion H _L is obtained as follows. _{H L = H S - H R} = (H Lx, H Ly) Here, the H _Lx and H _Ly, x components of the respective load strain H _L, is represented as follows in the y component. _{H Lx = R S cosΘ S -R} R cosΘ R H Ly = R S sinΘ S -R R sinΘ R

In this manner, the positive or negative of the photoelastic constant can be determined from the F-axis azimuth of the load strain obtained by removing the residual strain. If the photoelastic constant is positive, the azimuth (9
0 °) is in a dense state and has a large refractive index.
The axial direction is 0 °. On the other hand, if the photoelastic constant is negative,
Since the refractive index in the same direction as the load becomes smaller due to the influence of the polarization of the cation, the F-axis direction becomes 90 °.

In order to improve the reliability of the measurement, in the actual measurement, the birefringence amount is measured at several points while changing the load, the load is linearly approximated by the least squares method, and the light is obtained from the slope of the obtained straight line. Find the elastic constant.

Using the above photoelasticity measuring apparatus, 1.523
The measurement of the photoelastic constant at a wavelength of 632.8 nm in μm was performed on samples of FR glass having variously changed refractive indexes ( _nd ). FIG. 3 plots the measured values. As shown in the figure, the refractive index and the photoelastic constant of the FR glass were in good agreement with the regression line. The regression line 31 has a wavelength of 6
For the 32.8 nm measurement, the regression line 3
2 is for the measured value at a wavelength of 1.523 μm.
Also, in the same sample, it was found that the photoelastic constant increased as the wavelength was increased, and that the photoelastic constant had a positive dependence on the wavelength. (In the case of a flint optical glass having a relatively low refractive index, The photoelastic constant has a negative dependence on wavelength). In addition, as shown in FIG. 3, it was found that the photoelastic constant had a negative dependency on the refractive index.

By extrapolating to a wavelength of 1.55 μm based on the regression lines 31 and 32 by the least squares method at a wavelength of 632.8 nm and 1.523 μm, a photoelastic constant C [(nm / cm) at a wavelength of 1.55 μm is obtained. ) /
(Kgf / cm ^2)] dependence on the refractive index n _d of is given by the following equation. C = 23.331-12.52 × n _d From this equation, the transmission wavelength 1.55 .mu.m, target of photoelastic constant ^{± 1 × 10 -1 (nm /} cm) / (kgf / cm
² ) The refractive index n _d of the core glass satisfying the following is 1.863.
It became clear that it was 10 ± 0.00800.

The refractive index n at which the photoelastic constant C for an arbitrary wavelength λ _x becomes zero can be expressed by the following equation, assuming that the linearity is satisfied from the measured data at 632.8 nm and 1.523 μm. . n = 1.82525 + 0.013525 × λ _x This makes it possible to design a glass satisfying zero photoelastic constant at an arbitrary wavelength with respect to the FR glass. Also, F
When the photoelastic constant and refractive index of the glass at each wavelength are measured in the same manner as described above for the glass other than the R-based glass, the refractive index at which the photoelastic constant for the glass at any wavelength is zero is obtained Thus, it is possible to manufacture an optical fiber having a very small photoelastic constant at the transmission wavelength.

[0041]

As described in detail above, according to the present invention,
Since the knowledge that the photoelastic constant of glass has wavelength dependence was obtained, it became possible to manufacture an optical fiber in which the photoelastic constant at a desired transmission light wavelength was substantially zero, Good polarization surface retention properties against
Highly accurate measurement can be realized. In addition, long-wavelength light that is effective in reducing the Verdet constant can be used for transmission light while maintaining the photoelastic constant substantially at zero, making it possible to measure large currents equivalent to the rated overcurrent. Become.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an optical fiber type measuring device according to the present invention.

FIG. 2 is a schematic configuration diagram showing a photoelasticity measuring device for measuring a photoelastic constant of glass.

3 is a diagram showing measured values obtained by measuring photoelastic constants at different wavelengths for various FR glass samples having different refractive indices using the photoelasticity measuring device of FIG.

FIG. 4 is a configuration diagram showing a conventional optical fiber type current measuring device.

FIG. 5 is a diagram showing a change in a polarization plane when an alternating current is measured by a current measuring device.

FIG. 6 is a diagram for explaining a problem when the polarization plane exceeds a Faraday rotation angle of 45 ° in the current measurement device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Conductor 3 Optical fiber 4 Polarizer 5 Transmitting fiber 6 1/2 wavelength plate 7 Analyzer 8 Prism 9 and 10 Receiving fiber

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI G01R 15/24 G01R 33/032 // G01R 33/032 15/07 B (72) Inventor Toshiharu Yamashita 2-7-7 Nakaochiai, Shinjuku-ku, Tokyo No. 5 in Hoya Corporation

Claims (5)

[Claims] 1. An optical fiber having at least a core and a clad, wherein the core has a photoelastic constant of substantially zero at a wavelength of transmission light and a Verdet constant of 5.8 × 10 ^-6 rad.
An optical fiber comprising a glass of / A or less. 2. A glass component of the core, wherein SiO ₂ is 5-28 wt%, B ₂ O ₃ is 0-10 wt%, Al ₂ O ₃ is 0-5 wt%, and Na ₂ O + K ₂ O is 0.3-0.3 wt%. 2.5wt
%, 69.5-83.7% by weight of PbO, As ₂ O ₃ + S
b ₂ O ₃ is 0 to 0.5 wt%, provided that SiO ₂ + B ₂ O ₃
+ Al ₂ O ₃ of claim 1, wherein the optical fiber which is characterized in that it contains 16~28wt%. 3. The optical fiber according to claim 1, wherein the optical fiber is for transmitting light having a wavelength of 1.55 μm. 4. An optical fiber type measuring apparatus for measuring a magnetic field or a current for generating a magnetic field based on a change in a polarization plane of light emitted from an optical fiber due to a Faraday effect, wherein the optical fiber is An optical fiber type measuring apparatus using the optical fiber according to any one of the preceding claims. 5. An optical fiber type measuring apparatus for measuring a current based on a change in a polarization plane of light emitted from an optical fiber due to a Faraday effect, wherein a core of the optical fiber has a photoelastic constant of substantially zero. Made of glass and has a measurable current range of 13
An optical fiber type measuring device comprising 5 kA.