JPH0980135A - Optical magnetic field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the Fresnel reflection loss and the combination loss of a magneto-optical sensor and at the same time reduce time required for adjusting a light axis. SOLUTION: Semispherical lenses 11 and 12 where an outer-periphery surface consists of spherical surfaces 11a and 12a and planes 11b and 12b including the curvature center of the spherical surfaces are arranged in a light path. Polarization separation films 13 and 14 are vapor-deposited in the semispherical lenses 11 and 12. The semispherical lenses 11 and 12 are used instead of a lens and a polarization beam splitter in a conventional light magnetic field sensor, thus the number of optical parts can be reduced and Fresnel reflection loss and combination loss can also be reduced for that amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical magnetic field sensor for measuring magnetic field strength by using the Faraday effect of a magneto-optical element. The present invention particularly relates to a transmission line for supplying electric power, a distribution line, a substation facility (hereinafter, referred to as “cubicle”)
An optical magnetic field sensor that detects the magnitude of the current by measuring the strength of the magnetic field generated around the electric wire such as GIS (GAS INSULATED SWITCH GEAR), and a light that measures a general static magnetic field, AC magnetic field, etc. Magnetic field sensor.

[0002]

2. Description of the Related Art A current sensor for detecting an abnormality by measuring the magnitude of a current flowing through a power transmission line or a distribution line, which is a power transportation route from a power plant to a consumer, or a cubicle, G
As a current sensor used in the IS, a transformer type sensor has been conventionally used. However, this transformer type current sensor has various problems such as large size, large weight, and low insulation. For this reason, in recent years, instead of the transformer-type current sensor, an optical magnetic field sensor having advantages such as high withstand voltage, high insulation, non-contact, small size and light weight, and no need for a power source or electric circuit on the high voltage side is used. It has become. The optical magnetic field sensor measures a magnetic field generated around a conductor (for example, a transmission line) by a current flowing through the conductor by using the Faraday effect of a magneto-optical material, and obtains a current value from the value of the magnetic field. It is a thing.

FIG. 4 shows the basic structure of a conventional optical magnetic field sensor for measuring current. The light emitted from the light source 1 passes through the optical fiber 2, is converted into parallel light by the first lens 3, and then is converted into parallel light by the first polarization beam splitter (hereinafter, “PBS”).
Incident) 4. In the PBS 4, light is split into linearly polarized light of S polarization component and P polarization component. Only the S-polarized component has its optical path bent 90 degrees and enters the half-wave plate 5. This half-wave plate 5 is an S plate formed in PBS 4.
It is used to rotate the polarization plane of the polarization component by 45 degrees to maximize the sensitivity of the optical magnetic field sensor. Light is
After passing through the half-wave plate 5, it passes through the magneto-optical element 6.
When the light passes through the magneto-optical element 6, the light is rotated according to the strength of the magnetic field to be measured and is incident on the second PBS 7. PBS
In 7, the light has a light intensity corresponding to the intensity of the magnetic field to be measured, the optical path is bent again by 90 degrees, and the light is focused on the optical fiber 9 by the second lens 8. After this, the light
It is guided to the detector 10 by the optical fiber 9 and photoelectrically converted.

A light emitting diode is generally used as the light source 1. A laser diode having a high light emission intensity and a strong directivity can be used as the light source 1, but when a laser diode is used, the light emitted from the laser diode is substantially linearly polarized light, and when passing through the optical fiber 2, When a stress change occurs in the optical fiber 2, the plane of polarization becomes unstable and the intensity of the light passing through the PBS 4 fluctuates. Therefore, as the light source 1, a light emitting diode that emits unpolarized light is suitable.

[0005]

The optical magnetic field sensor used for current measurement of transmission lines and distribution lines, current transformers for measuring instruments in GIS and cubicles is required to have high sensitivity. Materials of the magneto-optical element 6 which is a component of the optical magnetic field sensor include lead glass, diamagnetic materials such as ZnSe, BGO, and BSO, or paramagnetic materials. Overall low. For this reason, a magnetic garnet having high magnetic sensitivity and high mass productivity or a more highly sensitive Bi-substituted magnetic garnet is used as the magneto-optical element 6.
It is considered to be used as a material for.

Generally, it is necessary to minimize the insertion loss of the optical magnetic field sensor and increase the S / N ratio at the time of photoelectric conversion by the photodetector. However, Fresnel reflection loss occurs in each of the optical elements such as the lens, the PBS, the half-wave plate, and the magneto-optical element located between the input and output fibers,
There is a limit to the reduction of the insertion loss of the optical magnetic field sensor.

Although optical axis alignment between the optical elements such as the optical fiber, the lens and the PBS is an indispensable task for realizing low insertion loss, the more the number of elements, the more time and effort it takes to align the optical axes. Therefore, it is one of the factors that hinder the improvement of productivity.

The present invention has been made in view of the above problems in the conventional optical magnetic field sensor, and an object of the present invention is to provide an optical magnetic field sensor with low loss and high productivity.

[0009]

[MEANS FOR SOLVING THE PROBLEMS] Insertion loss due to Fresnel reflection loss occurring in each optical element is reduced, and
Reducing the effort of optical axis alignment between the optical elements can be achieved by reducing the number of optical elements. Focusing on this point, the present invention replaces each of the first lens 3 and the PBS 4 and the second lens 8 and the PBS 7 in the conventional optical magnetic field sensor shown in FIG. We are trying to reduce the number.

That is, the optical magnetic field sensor according to the present invention is
The light emitted from the light source has a first lens, a first polarization separation film provided on a light-transmitting body having an incident interface and an outgoing interface, a half-wave plate, a magneto-optical element, a transparent interface having an incident interface and an outgoing interface. In a magneto-optical sensor that outputs via a second polarization separation film and a second lens provided on the optical body, the first polarization separation film and the first polarization separation film provided on the first lens and the light transmitting body, and A hemispherical lens is arranged instead of the second lens and the second polarization separation film provided on the translucent body, and the hemispherical lens is composed of a spherical surface and a plane including a center of curvature of the spherical surface. An outer peripheral surface is formed, a polarization separation film is provided on the plane, and the hemispherical lens is arranged so that the light enters from the spherical surface.

The hemispherical lens used in the optical magnetic field sensor according to the present invention has a shape obtained by dividing the spherical lens in half, and its outer peripheral surface is composed of a spherical surface and a plane including the center of curvature of the spherical surface. ing. On the plane of this hemispherical lens, there is provided a polarization separation film made of a dielectric multilayer film that functions as a polarizer when unpolarized light having a single wavelength enters at an angle of 45 degrees. As a result, a hemispherical lens (lens 3 or 8 in FIG. 4) and a PBS (PBS 4 in FIG. 4) are formed.
Alternatively, the two functions of 7) can be provided, and as a result, the number of optical elements forming the optical magnetic field sensor can be reduced.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an optical magnetic field sensor according to the present invention. In the optical magnetic field sensor according to the present embodiment, hemispherical lenses 11 and 12 are arranged instead of the lens 3 and the PBS 4 and the lenses 8 and PBS 7 in the conventional optical magnetic field sensor shown in FIG.

The hemispherical lenses 11, 12 are spherical surfaces 11a, 1
An outer peripheral surface is formed of 2a and planes 11b and 12b including the center of curvature of the spherical surface, and the planes 11b and 12b are coated with polarization separation films 13 and 14 each made of a dielectric multilayer film. The hemispherical lenses 11 and 12 receive the light from the spherical surfaces 11a and 12a, and then the polarized light separating film 1
It is arranged to reach 3,14. The polarization separation films 13 and 14 are PBS of the optical magnetic field sensor shown in FIG.
It is the same as the polarization separation film used in Nos. 4 and 7.

Light emitted from a light source 1 composed of a light emitting diode is condensed by an optical fiber 2 and emitted from the optical fiber 2 at a spread angle of 10 degrees or less. This emitted light passes through the center 11c of the spherical surface 11a of the hemispherical lens 11,
Further, the light is incident on the hemispherical lens 11 so as to be incident on the plane 11b at an incident angle of 45 degrees. The P-polarized light component of the incident light that has entered the hemispherical lens 11 and has reached the flat surface 11b is transmitted through the polarization separation film 13 without being reflected at all, but the S-polarized light component is included in each of the dielectric multilayer films constituting the polarization separation film 13. It partially reflects on the boundary surface of the dielectric film, and finally reflects with a reflectance of 98% or more.

The reflected S-polarized component becomes parallel light and is emitted from the hemispherical lens 11. The emitting direction is 90 degrees with respect to the incident direction. After that, the parallel light passes through the half-wave plate 5 and the magneto-optical element 6 to rotate the plane of polarization according to the magnetic field strength of the magnetic field to be measured, and further passes through the hemispherical lens 12 provided with the polarization separation film 14. As a result, the light intensity changes according to the magnetic field intensity. Thereafter, the light is collected by the optical fiber 9, guided to the detector 10, and photoelectrically converted. The optical magnetic field sensor having the above-described configuration according to the present embodiment has a reduced Fresnel reflection loss as compared with the conventional optical magnetic field sensor shown in FIG. 4, as described below.

Fresnel reflection loss occurs when light passes through an interface where the refractive index changes. In the optical magnetic field sensor according to the present embodiment, since the hemispherical lenses 11 and 12 also serve as the lenses 3 and 8 and the PBSs 4 and 7 in the optical magnetic field sensor shown in FIG. 4, the conventional optical magnetic field shown in FIG. There are four fewer interfaces that cause Fresnel reflection loss compared to the sensor. That is, since the input / output interfaces of the hemispherical lenses 11 and 12 correspond to the input / output interfaces of the lenses 3 and 8 of the optical magnetic field sensor shown in FIG. 4, the optical magnetic field sensor shown in FIG. This means that the four input / output interfaces of PBS 4 and 7 in the sensor are omitted. Fresnel reflection loss is also reduced due to the reduction in the number of input / output interfaces.

The hemispherical lenses 11 and 12, the lenses 3 and 8 (see FIG. 4), and the PBSs 4 and 7 (see FIG. 4) all have a refractive index of 1.
Assuming that it is made of the representative optical glass of No. 5, the insertion loss is reduced by about 0.7 dB by using the optical magnetic field sensor according to this embodiment.

Further, in the optical magnetic field sensor according to this embodiment, the hemispherical lenses 11, 12 are the lenses 3, 8 and PB.
Since the functions of S4 and S7 are provided, it is not necessary to separately provide the PBS, and the distance between the two hemispherical lenses 11 and 12 can be made shorter than before. The lenses 3 and 8 are used to convert diffused light into parallel light, or convert parallel light into focused light, but it is impossible to convert diffused light into completely parallel light. Therefore, if the distance between the lenses can be shortened, the coupling loss due to incomplete parallel light can be reduced.

Further, the conventional optical magnetic field sensor has lenses 3, 8 and PBSs 4, 7, between two optical fibers 2, 9.
It had six optical components, the half-wave plate 5 and the magneto-optical element 6, and required a considerable amount of time to adjust the optical axis.
On the other hand, in the optical magnetic field sensor according to the present embodiment, since it is not necessary to dispose the PBS, the number of optical components between the two optical fibers 2 and 9 is 4, and the time required for adjusting the optical axis is reduced. Can be shortened accordingly.

[0020]

EXAMPLE A comparative experiment between the optical magnetic field sensor according to the present embodiment and a conventional optical magnetic field sensor will be described below. First,
The optical magnetic field sensor according to this embodiment was manufactured as follows. A multi-component glass optical fiber having a core diameter of 200 μm was used as the optical fibers 2 and 9, and a hemispherical lens 11 and 12 having a diameter of 2 mm and a material of BK7 was used. Hemispherical lens 1
The polarization separation film 1 made of a dielectric multilayer film that allows the P-polarized component to pass therethrough but reflects the S-polarized component when light is incident on the planes 11a and 12a of 1 and 12 at an incident angle of 45 degrees.
3,14 were vapor-deposited. The thickness of the half-wave plate 5 is 1.0
mm optical synthetic quartz, and the magneto-optical element 6 was a Bi-substituted magnetic garnet film.

The optical magnetic field sensor is assembled by using the hemispherical lens 11,
The optical fibers 2 and 9, the hemispherical lenses 11 and 12, the half-wave plate 5 and the magneto-optical element 6 were adhered to a holder so that the interval of 12 was 5.0 mm. The time required for adhering the optical fibers 2 and 9, the hemispherical lenses 11 and 12, the half-wave plate 5 and the magneto-optical element 6 to the holder and adjusting the optical axis was 32 minutes per optical magnetic field sensor.

The insertion loss of the optical magnetic field sensor according to this embodiment manufactured in this manner was 9.9 dB. Here, the insertion loss is the difference between the light intensity measured by the detector 10 and the light intensity measured by the detector 10 when the optical fiber 2 is directly connected to the detector 10.

An alternating magnetic field of 50 Hz 700 [Oe]
When the ratio error and the phase angle when the value is changed to 35 [Oe] as the rated effective magnetic field are measured with respect to the optical magnetic field sensor according to the present embodiment, as shown in FIGS. In the effective magnetic field range of up to 700 [Oe], it was very small and almost zero.

Here, the ratio error R is (output from photodetector when rated effective magnetic field is applied) / (rated effective magnetic field) = K0,
When (output from the photodetector when a measurement effective magnetic field is applied) / (measurement effective magnetic field) = K, it is expressed by the following equation. R = (K0 / K-1) × 100 That is, the output of the photodetector and the magnitude of the magnetic field to be measured should have a linear relationship, but due to various factors, the output of the photodetector has a linear relationship. It may deviate. This deviation rate is the ratio error. Further, the phase angle refers to a phase difference between the phase of the magnetic field to be measured and the output phase of the photodetector.

On the other hand, the conventional optical magnetic field sensor was manufactured as follows. As the optical fibers 2 and 9, the half-wave plate 5 and the magneto-optical element 6, the same ones as in the above embodiment were used. The lenses 3 and 8 were made of BK7, and spherical lenses having a diameter of 2 mm were used. The PBSs 4 and 7 were made of BK7 and 2 mm square.

Optical fibers 2 and 9, lenses 3 and 8, and PBS so that the distance between PBS 4 and 7 is 5.0 mm.
4, 7 and the half-wave plate 5 and the magneto-optical element 6 were bonded to a common holder to assemble an optical magnetic field sensor as shown in FIG. The time required for adhering these eight optical components and adjusting the optical axis was 46 minutes per optical magnetic field sensor. Also,
The insertion loss of the conventional optical magnetic field sensor measured in the same manner as in the above-described embodiment was 11.6 dB.

As described above, this experiment proves that the optical magnetic field sensor according to the present embodiment is improved over the conventional optical magnetic field sensor in terms of both insertion loss and assembly time of the optical magnetic field sensor.

[0028]

According to the optical magnetic field sensor of the present invention, it is possible to reduce Fresnel reflection loss and coupling loss by using a hemispherical lens instead of the conventional lens and PBS, and The time required for the axis adjustment can be shortened, and the productivity of the optical magnetic field sensor can be improved.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a basic configuration of an embodiment of an optical magnetic field sensor according to the present invention.

FIG. 2 is a graph showing a result of measuring a ratio error of the optical magnetic field sensor according to the present invention in a rated effective magnetic field of 700 [Oe].

FIG. 3 is a graph showing the results of measuring the phase angle of the optical magnetic field sensor according to the present invention in a rated effective magnetic field of 700 [Oe].

FIG. 4 is a schematic diagram showing a basic configuration of a conventional optical magnetic field sensor.

[Explanation of symbols]

 1 Light source 2,9 Optical fiber 3,8 Lens 4,7 PBS 5 Half-wave plate 6 Magneto-optical element 10 Detector 11,12 Hemispherical lens 13,14 Polarization separation film

Claims (1)

[Claims] 1. A first polarization separation film, a half-wave plate, a magneto-optical element, an incident interface, which is provided on a translucent body having light emitted from a light source, and which has a first lens, an incident interface, and an outgoing interface. In the optical magnetic field sensor which outputs through the second polarization separation film and the second lens provided on the light-transmitting body having the emission interface, the first lens and the first lens provided on the light-transmitting body are provided. A hemispherical lens is arranged instead of the polarization separation film and the second polarization separation film provided on the second lens and the translucent body, and the hemisphere lens has a spherical surface and a center of curvature of the spherical surface. An outer peripheral surface is formed from a plane including a plane, a polarization separation film is provided on the plane, and the hemispherical lens is arranged so that the light enters from the spherical surface. Optical magnetic field sensor.