JPH0695049A - Magneto-optical field sensor - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in the characteristics of sensor output at the time of a high temp. and to enable current measurement with a good sensitivity regardless of temp. conditions for use by constituting two polarizers provided on the incident side and exit side of a magneto-optical element of polarizing glass plates. CONSTITUTION:Optical fibers 1 and 7 consist respectively of multimode fibers and lenses 2 and 6 consist of convex lenses. The polarizers 3 and 5 consist of the polarizing glass plate The magneto-optical element 4 consists of (YbTb)3 Fe5O12 and is constituted of total reflection prisms 8 and 9 to be used for bending the propagation direction of light at a right angle. The exit light passes the polarizer 3, the magneto-optical element 4 and the polarizer 5 and is then made incident on the photodetecting side optical fiber 7. The performance assurance temp. of the polarizing glass plates is as high as about 400 deg.C and the magneto-optical sensor operates well at the temp. at which the sensor is used as a current sensor or below. The thickness of the polarizing glass plates is as thin as <=1mum and since optical parts, such as half wavelength plates, are not needed and, therefore, the number of the parts decreases and the sensor is additionally miniaturized.

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 by measuring a magnetic field generated around a power transmission / distribution line. , An optical magnetic field sensor for detecting the magnitude of the current.

[0002]

2. Description of the Related Art An optical magnetic field sensor that measures the magnetic field strength by utilizing the Faraday effect of a magneto-optical element is small in size, has excellent insulating properties, and is resistant to electromagnetic noise. It has begun to be used as a current sensor to detect anomalies in substations, power transmission lines, distribution lines, etc., which are electric power transmission routes from a consumer to a consumer, and detect abnormalities in these routes.

FIG. 2 shows the basic structure of an optical magnetic field sensor. In the figure, light emitted from a light source (not shown) such as a laser diode or a light emitting diode propagates in the optical fiber 1 and is emitted from its emission end 1a. The light exits and becomes linearly polarized light through the lens 2 and the polarizer 3 and enters the magneto-optical element 4. Then, when passing through the magneto-optical element 4, it receives an optical rotation effect according to the strength of the magnetic field to be measured (hereinafter, simply referred to as “magnetic field”), passes through the polarizer 5, and has an intensity corresponding to the strength of the magnetic field. Then, the light is further focused by the lens 6 on the incident end 7a of the optical fiber 7. The light incident on the optical fiber 7 propagates in the fiber, is guided to a photodetector (not shown), and is photoelectrically converted. here,
Polarizing beam splitters are usually used as the polarizer 3 and the polarizer 5, and the incident surfaces of these are arranged with an inclination of 45 degrees with respect to the optical axis. In this case, the measurement magnetic field and the optical path are parallel.

Further, FIG. 3 shows an actual manufacturing structure of the optical magnetic field sensor. This is based on the basic configuration described above.
A polarization beam splitter is used as the polarizers 3 and 5, and a half-wave plate 10 for arranging these two polarization beam splitters in the same plane and a total semi-reflection prisms 8 and 9 for converting the traveling direction of light are used. Each of them is arranged in the optical path.

[0005]

However, when the optical magnetic field sensor having such a structure is used as a current sensor,
The current sensor is required to operate well even at operating temperatures reaching up to + 100 ° C as the environment resistance characteristic, whereas the upper limit of the performance guarantee temperature of the above polarization beam splitter is only + 80 ° C, and therefore the environment resistance is high. There was a problem that it was inferior to. Further, when the polarization beam splitter is used as the polarizer as described above, due to the structural restriction that the polarization beam splitter is a cubic body and the optical characteristic that another optical component such as a half-wave plate is required. There is a problem that it is difficult to miniaturize the sensor.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a small-sized optical magnetic field sensor having excellent environment resistance. Is.

[0007]

In the optical magnetic field sensor according to the present invention, the light emitted from the lens provided immediately after the emission end of the optical fiber on the light source side is received after passing through the polarizer, the magneto-optical element and the polarizer. In the optical magnetic field sensor in which the light is incident on the light receiving side optical fiber by a lens provided immediately before the incident end of the side optical fiber, the two polarizers are polarizing glass plates.

[0008]

The performance guarantee temperature of the polarizing glass plate is as high as about 400 ° C., and it works well under the temperature environment where the optical magnetic field sensor is used as a current sensor. In addition, the thickness of the polarizing beam splitter is about 3 mm, whereas the thickness of the polarizing glass plate is sufficiently thin as 1 mm or less, and since the polarizing glass plate does not require an optical component such as a half-wave plate, the number of components is reduced. , The sensor can be made smaller.

[0009]

EXAMPLES Below, based on FIG. 1, shown in FIG. 2 and FIG.
The same reference numerals are used for the same members as in the conventional example, and
An example will be described. The optical magnetic field sensor of the present invention is shown in FIG.
Although it has the basic configuration described above, Fig. 1 further embodies it.
It was done. That is, the optical fiber 1 and the optical fiber 7
The lens 2 and lens are
S 6 are convex lenses, and the polarizers 3 and 5 are
Magneto-optical element 4 (YbTb)
₃Fe _FiveO₁₂And bend the direction of light at a right angle
By the total reflection prism 8 and the total reflection prism 9 for
Composed. Further, in the figure, 11 is a wavelength of 0.85 μm
, A light source composed of a light emitting diode for generating
It is a photodetector consisting of a photodiode.

The optical magnetic field sensor of the present invention is constructed as described above. Next, with respect to concrete tests and results performed on this optical magnetic field sensor, a similar test is shown in FIG. 3 as a comparative example. A description will be given together with the results obtained when the conventional optical magnetic field sensor is used. In the test on the conventional optical magnetic field sensor, the same light source and photodetector as shown in FIG. 1 were used.

First, the optical magnetic field sensor is set to 50 Hz, 40 Oe.
-30 ℃ ～ + 80 ℃ under the condition that AC magnetic field is applied
The sensitivity of the sensor output at this time was measured. As a result, in both the optical magnetic field sensor according to the present invention and the conventional optical magnetic field sensor, the variation in sensitivity was within ± 1%, both showed good characteristics, and no difference in characteristics was observed.

Next, after the optical magnetic field sensor was left to stand at a high temperature of + 120 ° C. for 2000 hours at high temperature, the insertion loss in which the characteristic deterioration was remarkable was measured. As a result, the conventional optical magnetic field sensor had an insertion loss of 9 dB before the test, but increased to 12 dB after the test. This is due to deterioration of the polarization beam splitter. On the other hand, in the optical magnetic field sensor according to the present invention, an increase in insertion loss was not observed before and after the test and was constant at 9 dB.

[0013]

As described above, since the optical magnetic field sensor according to the present invention uses the polarizing glass plate as the polarizer, there is no deterioration in the characteristics of the sensor output at the time of high temperature use, and good sensitivity is obtained regardless of the operating temperature conditions. It is suitable as a current sensor that requires current measurement in. Further, the number of parts constituting the sensor is small, and the sensor can be made smaller.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a basic configuration of a conventional optical magnetic field sensor.

FIG. 3 is a diagram showing a configuration in actual manufacture of a conventional optical magnetic field sensor.

[Explanation of symbols]

 1, 7 ... Optical fiber 2, 6 ... Lens 3, 5 ... Polarizer 4 ... Magneto-optical element 8, 9 ... Total reflection prism 10 ... Half-wave plate 11 ... Light emitting diode 12 ... Photodiode

Claims (1)

[Claims] 1. Light emitted from a lens provided immediately after the exit end of the light source side optical fiber is passed through a polarizer, a magneto-optical element, and a polarizer, and then by a lens provided immediately before the entrance end of the light receiving side optical fiber. In the optical magnetic field sensor which is made incident on the light receiving side optical fiber, the two polarizers are polarizing glass plates.