JPS6057276A - Magnetic field measuring device - Google Patents

Abstract

PURPOSE:To measure a magnetic field with high sensitivity by dividing an incident light into two linear polarized lights by a polarizer, placing two magneto- optical elements and analyzers having a prescribed direction to the linear polarized light, and detecting output light. CONSTITUTION:An incident light of a light generating means 6 is divided into tow linear polarized lights by a polarizer 2, a linear polarized light direction of the first linear polarized light and the first analyzer 3a is made orthogonal, and the first magneto-optical element 1a is placed between them. The linear polarized light direction of the second linear polarized light and the second analyzer 3b is inclined by 45 deg., and the second magneto-optical element 1b is placed between them, and a magneto-optical converting part is constituted, and it is placed in a magnetic field, and an output light is detected by detecting means 7a, 7b. As for an output light P1, the shot noise in a low magnetic field area drops and the high sensitivity is obtained as shown in the figure. Also, the polarity of the magnetic field is discriminated by an output light P2. Therefore, the sensitivity is raised by >=10 times when comparing with a conventional device.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an apparatus for observing Faraday rotation by a magneto-optical element, detecting the entire magnetic field, and measuring the strength of the magnetic field.

Conventional Structure and Problems Recently, a method that fully utilizes the Faraday effect, which is one of the magneto-optical effects, has been proposed as a method for measuring magnetic field strength. Because it uses light as a medium, it has good insulation properties, does not interfere with electromagnetic induction noise, etc.It is useful for measuring high voltages and large currents in power transmission equipment.

There is an application to current measurement of welding machines.

FIG. 1 shows a diagram of the principle of a magnetic field measurement method using Faraday sound effects. In FIG. 1, a magneto-optical element 1 is placed in a magnetic field H. Light that has been linearly polarized by a polarizer 2 (indicated by an arrow) is passed through this magneto-optical element 1 .

Due to the Faraday effect, the plane of polarization undergoes rotation in proportion to the magnetic field strength H. Its rotation angle is indicated by θ. The rotated polarized light passes through an analyzer 3 whose transmission polarization direction is different from that of the polarizer 2 by 45 degrees, and the magnitude of the rotation angle θ is converted into a change in the amount of light. The optical output at that time is expressed by the following equation.

PoH(””K (1+5in2θ) (1) where θ
=VH1, Pou□ is the optical output, is a proportionality constant, θ is the Faraday rotation angle [degrees], and ■ is the Weerde constant, which is in the unit [o/cm・00] and measures the sensitivity of the magneto-optical element. It shows. This configuration has been well known for a long time, but one of the factors that determines the sensitivity of a magnetic field measurement device, which has the disadvantage of having a large amount of noise in the photoreceiver, is the noise in the photoreceiver. The sources are broadly divided into dark current, which is thermal noise that exists even when no light is irradiated, and shot noise, which occurs when light is irradiated. FIG. 2 shows the optical output of equation (1) according to the conventional configuration. With this configuration, even in the case of H=O, the light is still being irradiated onto the receiver, producing shot noise, and this noise is the main cause of determining the limit of measurement sensitivity. Above the optical input level, shot noise becomes dominant as a noise source.

OBJECTS OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a magnetic field measuring device with high sensitivity and excellent reliability.

Structure of the Invention The present invention includes a polarizer that separates incident light into first and second orthogonal linearly polarized light, and first and second analyzers, and the first linearly polarized light of the polarizer and the The linear polarization directions of the first analyzer are orthogonal to each other, the first magneto-optical element is entirely disposed between them, and the second linear polarization direction of the polarizer and the linear polarization direction of the second analyzer are different from each other. a magneto-optic converter in which a second magneto-optical element is arranged between the magneto-optic converters; three optical transmission paths provided at both ends of the magneto-optic converter; and a light generator for inputting light into the first optical transmission path. and detection means for respectively detecting the output of the light that the incident light passes through the magneto-optic converter and is guided to the second and third optical transmission paths,
By arranging the magneto-optical conversion section in a magnetic field, the magnetic field strength is detected by the detection section.

DESCRIPTION OF EMBODIMENTS In the present invention, an optical arrangement with low shot noise is used to measure the magnetic field strength, and an optical arrangement with a conventional structure is used to determine the direction of the magnetic field, thereby achieving high sensitivity and excellent reliability. All equipment provided. The present invention will be explained below using examples. FIG. 3 shows an embodiment of the present invention.

In the drawings, reference numerals 1-a and 1-b denote magneto-optical elements, which are made of Zn5e in this embodiment, and both end surfaces are parallel mirror polished. 2 is a polarizer that separates light into two linearly polarized lights, and here a Wollaston prism is used. 3-a is an analyzer installed so that the transmitted polarization direction is perpendicular to the first linear polarization direction separated by the polarizer 2; 3-b is polarizer 2
The analyzer is installed so that the transmitted polarization direction is tilted by 46 degrees with respect to the second linear polarization direction that is polarized by .

As analyzers 3-a and 3-b, polarization separation plates made of T102 crystal, which has good temperature characteristics and excellent mechanical strength, were used. Magneto-optical elements 1-a, 1-b, polarizer 2
．． A magneto-optical converter consisting of analyzers 3-a and 3'-b is placed in the magnetic field H. 4-a, 4-b.

4'-C are rod lenses, and lens 4-a
The lenses 4-b and 4-c are for converting the light incident on the magneto-optic converter into parallel rays, and the lenses 4-b and 4-c are for condensing the light that has passed through the magneto-optic converter.

6-a, 5-b, and 5-c are optical fibers that form the entire optical transmission path. 6 is 6-a [incident light generating means. 7-a and 7-b are means for detecting the light output transmitted through the magneto-optical converter.

7-a, light output P1 entering 7-b. P2 changes as shown in FIG. 4 depending on the magnetic field strength. Since the polarizer and analyzer are orthogonal to each other, the optical output P1 is PloC(1-cos2θ)
Therefore, when H=O, P1=0, and as the magnetic field strength increases, the optical output P1 also increases. Therefore, shot noise was reduced especially in the low magnetic field region where sensitivity is required, and higher sensitivity was achieved. However, when the polarity of the magnetic field is reversed, the optical output is not reversed, and the direction of the magnetic field cannot be determined. The optical output P2 is P2oc (1+Sln 2θ) because the polarizer and the analyzing consonant are arranged at 46°.

In this case, for a reversal of the polarity of the magnetic field, the optical output is reduced by the magnetic field H
increases or decreases with respect to the light amount = 0.

Therefore, the polarity of the magnetic field can be determined based on the optical output P2, and since the optical outputs P1 and P2 are synchronized, the polarity of the optical output P1 can be easily determined.

In this embodiment, the light generating means 6 has a wavelength of 0.8μ.
A light emitting diode with m.

Silicon PIN 7 is attached to the light receiver of the light detection means 7-b and 7-a.
Otodiode was used. In this case, compared to the conventional method, it was possible to suppress the noise to less than -0, and the sensitivity was improved by more than 10 times.

In this example, Zn5ef magneto-optical element 1-
a, 1-b, but ferromagnetic garnet crystal 1
Any material having a magneto-optical effect, such as diamagnetic glass or paramagnetic glass, may be used. Furthermore, although a Wollaston prism is used for the polarized light 2, a Rochon prism, a polarization separation plate using a single plate of birefringent material, or a polarization beam splitter using a dielectric multilayer film may also be used. Also analyzer 3-a, 3-b
Although a polarization splitter plate was used in this example, a Wollaston prism, a Rochon prism, a polarization beam splitter, or a Glanmon prism may also be used.

Furthermore, although a silicon PIN photodiode was used as a light receiver, a Ge photodiode was used instead.

I”n Ga A s P or In Ga A
A quaternary or ternary III-V photodiode such as S may also be used.

Effects of the Invention As is clear from the above description, the magnetic field measuring device of the present invention provides highly sensitive measurement capability, and its industrial value is limited despite its reliability.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of a conventional magnetic field measuring device using the Faraday effect, Fig. 2 is a diagram explaining the optical output of the conventional magnetic field measuring device, and Fig. 3 is an example of an embodiment of the present invention. FIG. 4 is a diagram illustrating the optical output in one embodiment of the present invention. 1a, 1-b...Magneto-optical element, 2...
・Polarizer, 3-a, 3-b---analyzer, 4
-a, 4-b, 4-〇...Selfoc lens, 5-a, 5-b. 5-C...Optical fiber, 6...
...Light generation means, 7-a, 7-b... Light detection means. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 - K 10F f'out = K (a + δbt12θ) Figure 3

Claims (1)

[Claims] It has a polarizer that separates the incident light into first and second orthogonal linearly polarized lights, and first and second analyzers; The linear polarization directions of the photons are orthogonal to each other, and a first magneto-optical element is disposed therebetween, and the second linear polarization direction of the polarizer and the linear polarization direction of the second analyzer are all different from each other. a magneto-optic converter in which all magneto-optical elements are arranged; three optical transmission paths provided at both ends of the magneto-optic converter; a light generating means for inputting light into the first optical transmission path; transmitting the magneto-optic converter and guided to the second and third optical transmission paths, the magneto-optic converter is arranged in a magnetic field, and the magnetic field is A magnetic field measuring device characterized in that intensity is detected by the detection section.