JPH0980137A - Light magnetic field sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light magnetic field sensor with a low insertion loss and a high productivity. SOLUTION: A light magnetic field sensor comprise a light source 1, a first optical fiber 2, a first lens, a first polarizer 5, a magnetic optical element 6, a second polarizer 7, a second lens, a second optical fiber 10, and a detector 11. The first and second lenses are constituted of semispherical lenses 12 and 13 where an outer-periphery surface is formed by a spherical surface and a plane including the curvature center of the spherical surface.

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 utilizing the Faraday effect of a magneto-optical element, and more particularly to a power transmission line and a distribution line for supplying electric power and a power receiving and transforming facility. (Hereinafter referred to as cubicle), GIS (GAS INSULATED SWITCH GEAR), or other optical magnetic field sensor that detects the magnitude of the current by measuring the strength of the magnetic field generated around the wire, and general static magnetic fields and AC magnetic fields. The present invention relates to an optical magnetic field sensor for measuring.

[0002]

2. Description of the Related Art Conventionally, a current sensor for detecting an abnormality by measuring the magnitude of a current flowing through a transmission line or a distribution line, which is a transportation route of electric power from a power plant to a consumer, a cubicle, a G
As the current sensor used in the IS, a transformer type has been used. However, since the transformer-type current sensor has various problems such as large size, heavy weight, and poor insulation properties, recently, a magnetic field (current) sensor has been replaced with such a transformer-type current sensor. Plans for use are in progress.

The principle of the optical magnetic field sensor is that a magnetic field generated around a conductor such as a power transmission line is measured by utilizing the Faraday effect of a magneto-optical material, and the magnetic field is flowed from the measured magnetic field to the magnetic field. The characteristic of the optical magnetic field sensor is that it has high withstand voltage, high insulation, non-contact, small size and light weight, and does not require a power supply or electric circuit on the high voltage side. it can.

The basic structure of a conventional optical magnetic field sensor having such characteristics will be described with reference to FIG. The light emitted from the light source 1 is collimated by the lens 3 through the optical fiber 2 and is then bent 90 degrees in the optical path by the total reflection triangular prism 4, and is linearly polarized by the polarizer 5. It is incident on the element 6. The linearly polarized light, when passing through the magneto-optical element 6, is a magnetic field to be measured (hereinafter, abbreviated as magnetic field)
According to the intensity of the light, passes through the polarizer 7, and becomes a light intensity corresponding to the strength of the magnetic field and enters the total reflection triangular prism 8, where the optical path is bent again by 90 degrees, and the lens 9 Is focused on the optical fiber 10. The light collected here is guided to the photodetector 11 and photoelectrically converted.

Here, a light emitting diode is generally used as the light source 1. Although it is possible to use a laser diode having a high emission intensity and a strong directivity for the light source 1,
The laser light emitted from the laser diode is substantially linearly polarized light, and the polarization plane of the light changes due to the stress-induced birefringence generated in the optical fiber 2 when the light passes through the optical fiber 2, and the polarizer There is a problem that the intensity of the light passing through 5 becomes unstable. Therefore, a light emitting diode which emits unpolarized light is used as the light source 1.

As a material of the magneto-optical element 6 used in the optical magnetic field sensor thus constructed, lead glass, Zn
There are diamagnetic materials such as Se, BGO and BSO, or paramagnetic materials, but their magnetic sensitivity is generally low. However, recently, as mentioned above, current measurement of transmission lines and distribution lines,
A plan to use the optical magnetic field sensor for the current transformers for measuring instruments in the GIS and the cubicle is being actively promoted, and the optical magnetic field sensor is required to have higher sensitivity, smaller size, and lower price. Therefore, from such a viewpoint, a magnetic garnet having high mass productivity and high magnetic sensitivity, and a magnetic field sensor using a highly sensitive Bi-substituted magnetic garnet have been developed.

[0007]

By the way, in the above-mentioned optical magnetic field sensor, it is necessary to increase the S / N ratio after photoelectric conversion by the photodetector. For that purpose, insertion loss in each optical element is required. It is important to make it as small as possible (the insertion loss here means the reflection loss at the interface of each optical element, excluding the unavoidable loss due to light absorption and diffraction of each optical element). .
However, since the Fresnel reflection loss occurs in each of the optical elements such as the lens located between the optical fibers, the total reflection triangular prism, the polarizer, and the magneto-optical element, there is a limit to the reduction of the insertion loss. Also, adjusting the optical axis between the optical elements of the optical fiber, the lens, and the triangular prism for total reflection is an essential task to achieve low insertion loss, but this is a factor that hinders the improvement of the productivity of the optical magnetic field sensor. It is one.

In view of the above-mentioned problems of the prior art, an object of the present invention is to provide an optical magnetic field sensor with low insertion loss and high productivity.

[0009]

In order to achieve the above object, an optical magnetic field sensor according to the present invention comprises a light source, a first optical fiber, a first lens, a first polarizer, a magneto-optical element and a second optical fiber. In an optical magnetic field sensor including a polarizer, a second lens, a second optical fiber and a detector, the first lens and the second lens each have a spherical surface and a plane including a center of curvature of the spherical surface. It is characterized by being constituted by a hemispherical lens having an outer peripheral surface formed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The hemispherical lens used in the optical magnetic field sensor of the present invention has a shape obtained by dividing a spherical lens in half, and the outer peripheral surface of the lens is a spherical surface and a plane including the center of curvature of this spherical surface. It is formed from and. Therefore, when the light enters through the center of curvature of the spherical surface of the hemispherical lens, the light is reflected at the center of curvature of the spherical surface and has the same focal length as the spherical lens of the same diameter and the same material. At that time, if the angle of incidence of light on a plane including the center of curvature of the spherical surface of the hemispherical lens satisfies the condition of total reflection, the incident light does not suffer loss even if a reflecting film is not provided on this plane. Is reflected. For example, if such a hemispherical lens is made of optical glass having a refractive index of 1.42 or more, total reflection occurs when the incident angle of light on the plane of the hemispherical lens is 45 degrees. Therefore, the hemispherical lens thus configured can have two functions of a lens and a total reflection prism.

A hemispherical lens 12 having such a function,
The optical magnetic field sensor of the present invention shown in FIG. 1 is configured using 13. As described above, the optical magnetic field sensor of the present invention is configured by using the lens and the hemispherical lenses 12 and 13 having the functions of the total reflection prism. That is, the optical magnetic field sensor of the present invention comprises the lens 3 and the total reflection triangular prism 4 and the lens 9 which constitute the conventional optical magnetic field sensor shown in FIG.
And a hemispherical lens 1 instead of the total reflection triangular prism 8.
2 and 13 are used. Fresnel reflection occurs when light passes through an interface where the refractive index changes, but in the optical magnetic field sensor of the present invention, there are four fewer interfaces that cause Fresnel reflection loss than in the conventional example shown in FIG. ing. Specifically, considering that the input / output interfaces of the hemispherical lenses 12, 13 in the magnetic field sensor of the present invention correspond to the input / output interfaces of the lenses 3, 9, the total reflection triangular prisms 4, 8 are used in the optical magnetic field sensor of the present invention. It is possible to omit a total of four input / output interfaces included in. Such a hemispherical lens 1
2, 13, lenses 3, 9 and total reflection triangular prisms 4, 8
However, assuming that the optical magnetic field sensor of the present invention is used in place of the conventional optical magnetic field sensor, it is possible to obtain an insertion loss of 0.7.
It is improved by (dB).

Further, in the optical magnetic field sensor of the present invention, since the hemispherical lenses 12 and 13 have the functions of both the lens and the total reflection prism as described above, the total reflection triangular prisms 4 and 8 can be omitted. Therefore, the distance between the two lenses (hemispherical lenses) can be made shorter than before. A lens is used to convert diffused light into parallel light and parallel light into convergent 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, in the conventional optical magnetic field sensor, as shown in FIG. 4, a lens 3 is provided between two optical fibers 2 and 10.
It includes seven optical components including 9, total reflection triangular prisms 4 and 8, polarizers 5 and 7, and magneto-optical element 6, and it took a considerable time to adjust the optical axis. On the other hand, in the optical magnetic field sensor of the present invention, since the lenses 3 and 9 and the total reflection triangular prisms 4 and 8 are omitted, the number of optical components becomes 5,
Assembly time can also be shortened.

The present invention will be described below with reference to specific examples.

In the optical magnetic field sensor of the present invention shown in FIG. 1, optical fibers 2 and 10 are multi-component glass optical fibers having a core diameter of 200 μm, and hemispherical lenses 12 and 13 are 2 mm in diameter and made of a material BK7. Using. Wavelength 850
nm has a refractive index of 1.51 with respect to BK7.
The critical angle for total internal reflection at the interface between K7 and air is 42 degrees. Therefore, with respect to the plane of the hemispherical lenses 12, 13, 45
The incident light is totally reflected. Further, polarizing glass having a thickness of 1.0 mm is used for the polarizers 5 and 7, and Bi is used for the magneto-optical element 6.
A substituted magnetic garnet film was used. The magneto-optical element 6 and the polarizers 5 and 7 were previously bonded and integrated with a high transmittance adhesive.

The optical magnetic field sensor is assembled by using the hemispherical lens 12,
As shown in FIG. 1, the optical fibers 2 and 10, the hemispherical lenses 12 and 13 and the integrated optical element are adhered to a common holder so that the interval of 13 is 5.0 mm.
It was constructed as shown in. At this time, the time required for bonding the five optical components (hemispherical lens 12, polarizer 5, magneto-optical element 6, polarizer 7, and hemispherical lens 13) and adjusting the optical axis was about 30 minutes.

The characteristic evaluation results of the optical magnetic field sensor thus configured are as follows. Here, the insertion loss of the magnetic field sensor has the configuration shown in FIG.
The difference between the light intensity measured by 1 and the light intensity measured by the photodetector 11 when the optical fiber 2 shown in FIG. 1 was directly connected to the photodetector 11 was defined as the insertion loss. The insertion loss of the optical magnetic field sensor of the present invention measured by this method is 9.9.
It was (dB).

Further, the ratio error and the phase angle when the alternating magnetic field 700 (Oe) of 50 Hz was changed to 35 (Oe) as the rated effective magnetic field were measured for the optical magnetic field sensor of the present invention. The output of the photodetector and the magnitude of the magnetic field to be measured should originally have a linear relationship, but the output from the photodetector may deviate from this line due to various factors, and this deviation rate is called the ratio error. That is, (output from photodetector when rated effective magnetic field is applied) / (rated effective magnetic field) value is K ₀ , (output from photodetector when rated effective magnetic field is applied) / (measured effective magnetic field) value Is K, the relative error R is expressed as R = (K ₀ / K−1) × 100. The phase angle means the phase difference between the phase of the magnetic field to be measured and the output phase of the photodetector. The ratio error and the phase difference measured by the optical magnetic field sensor of the present invention are shown in FIG.
As shown in FIG. 3, it was very small and almost zero in the entire effective magnetic field range of 35 to 700 (Oe).

Here, in order to show the advantage of the optical magnetic field sensor according to the present invention, the result of the same measurement as the above in the conventional optical magnetic field sensor is shown below. In FIG. 4, the optical fibers 2 and 10 and the optical element in which the magneto-optical element 6 and the polarizers 5 and 7 are bonded and integrated are the same as those used in the optical magnetic field sensor of the present invention. I used one. or,
The lenses 3 and 9 are spherical lenses made of BK7 and having a diameter of 2 mm, and the total reflection triangular prisms 4 and 8 are made of BK7 and have an optical path size of 2 mm square. The distance between the total reflection triangular prisms 4 and 8 should be 5.0 mm, and
The optical fibers 2 and 10, the lenses 3 and 9, the total reflection triangular prisms 4 and 8 and the integrated optical element are bonded to a common holder to form the optical magnetic field sensor shown in FIG. At this time, the time required for bonding the seven optical components (lens 3, total reflection triangular prism 4, polarizer 5, magneto-optical element 6, polarizer 7, total reflection triangular prism 8 and lens 9) and adjusting the optical axis. Was approximately 44 minutes. Further, the insertion loss in the conventional optical magnetic field sensor evaluated similarly to the optical magnetic field sensor of the present invention was 11.6 (dB).

[0020]

As described above, since the optical magnetic field sensor according to the present invention is constructed by using the hemispherical lens, Fresnel reflection loss and coupling loss between the optical elements can be reduced. Further, the optical magnetic field sensor of the present invention can shorten the time required for the optical axis adjustment in the manufacturing process, and can markedly improve the productivity.

[Brief description of drawings]

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

FIG. 2 is a graph showing a result of measuring a specific error in the optical magnetic field sensor of the present invention in a rated effective magnetic field of 700 (Oe).

FIG. 3 is a graph showing a result of measuring a phase angle in the optical magnetic field sensor of the present invention in a rated effective magnetic field of 700 (Oe).

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

[Explanation of symbols]

 1 light source 2,10 optical fiber 3,9 lens 4,8 total reflection triangular prism 5,7 polarizer 6 magneto-optical element 11 photodetector 12,13 hemispherical lens

Claims (1)

[Claims] 1. A light source, a first optical fiber, a first lens, a first polarizer, a magneto-optical element, a second polarizer, and a second polarizer.
In the optical magnetic field sensor including the lens, the second optical fiber, and the detector, the first lens and the second lens each have an outer peripheral surface formed by a spherical surface and a plane including a center of curvature of the spherical surface. An optical magnetic field sensor comprising a hemispherical lens.