JPH0228574A - Optical magnetic field sensor - Google Patents

Abstract

PURPOSE:To reduce the size of the sensor and to reduce the thickness of a signal transmission part by applying a bias which has a 45 deg. angle of rotation to polarized light which passes through a Faraday effect element while a magnetic field to be measured is zero. CONSTITUTION:A polarizer 3, the Faraday effect element 1, and a reflecting mirror 2 are aligned in this order coaxially with the optical axis of a lens 5 which is coupled with a terminal of a single-core optical fiber 6 and an annular permanent magnet 4 is arranged surrounding the Faraday effect element 1 and polarizer 3. Then the light projected from the optical fiber 6 is collimated by the lens 5 into parallel light, which becomes linear polarized light by passing through the polarizer 3. The linear polarized light is applied with the bias at 45 deg. by the permanent magnet 4 while travels forward and backward once in the Faraday effect element 1, so the light passes through an analyzer 3 while having its plane of polarization at the angle obtained by adding the bias with the 45 deg. angle based upon the magnetic field intensity of the permanent magnet 4 to the angle of rotation of the plane of polarization based upon the intensity of the external magnetic field to be measured, and the light enters an optical fiber 6 through the lens 5. Consequently, measurement data on the intensity of the external magnetic field to be measured is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical magnetic field sensor using a Faraday effect element.

[Prior Art] When color-polarized light travels through a substance that is subject to a magnetic field, the plane of polarization rotates, and this rotation is proportional to the strength of the magnetic field.

Magnetic field sensors using elements that significantly produce such a Faraday effect, such as elements such as BSO single crystal and Zn5e polycrystal, have been developed.

FIG. 4 shows the configuration of an optical magnetic field sensor using the Faraday effect element as described above. In the figure, there are two polarizers, 22
is a Faraday effect element, and 23 is an analyzer. A polarizer 21 is arranged on a straight line so as to polarize light, for example in the vertical direction, a Faraday effect element 22 is arranged on this, and an analyzer 23 is placed on the opposite side of the polarizer 21 with the Faraday effect element 22 in between. The polarization direction is rotated by 45'' with respect to the polarizer 21.

In the Faraday effect element 22, the length of the crystal through which light passes is Q, the magnetic field strength that reaches the element 22 in the direction in which the light passes is H1, the rotation angle of the polarization plane of polarized light is θ, and Ve is the Verdet constant. The rotation angle of the plane of polarization is expressed by the following equation.

θ=Ve-H-ρ...0) The light from the light source receives linear polarization at the polarizer 21, and undergoes rotation of the plane of polarization at the Faraday effect element 22 due to the magnetic field H.
Analyzer 23 with an analyzer angle of 45@ with respect to polarizer 21
pass through.

If Po is the intensity of the light passing through the analyzer 23 when the magnetic field to be measured is zero, and P is the intensity of the light passing through the analyzer 23 when there is a magnetic field to be measured, then P is the following formula % formula % , the rotation angle θ is sufficiently smaller than 45″″.

Substituting equation (1) into equation (2), P = Po (1+ 5in2Ve -H-Q)
...-(3).

Here, since an analyzer angle of 45° is given between the polarizer 21 and the analyzer 23, it is expressed by the above equation (3), and in this form, when the magnetic field is zero, the analyzer angle is Since the transmitted light passing through 23 is found, it is easy to calculate 5in2θ, that is, α
It is possible to extract an output that changes depending on the magnitude of one constant magnetic field.

In order to take out 5 in 2θ in this way, instead of the above configuration, a configuration using an optical rotator 24 as shown in FIG. 5 may be adopted. Polarizer 21. 45° rotator 24. Faraday effect element 22. Analyzers 23 are arranged in order. The optical rotator 24 rotates the plane of polarization of the light linearly polarized by the polarizer 21 by 45 degrees, and is made of, for example, a single crystal of BSO. While the polarized light rotated by 45 degrees passes through the Faraday effect element 22 , the plane of polarization is rotated by the magnetic field, and the polarized light is transmitted through the analyzer 23 . In this configuration, the polarizer 21 and analyzer 23 are arranged so that their polarization directions are parallel to each other.

In this configuration, when the magnetic field is zero, the intensity of light passing through the analyzer 23 is Po, and when the magnetic field is added and the polarization plane is rotated by θ, the intensity P of the light passing through the analyzer 23 is calculated by the following formula. It is expressed as

P=Po(1+5in2θ)=Po(1+5in2Ve-H-Q)
-(4) In this way, the polarizer and analyzer are set at an angle of 45° to each other, but if you use one with a 45° angle, the rotation of the plane of polarization due to the magnetic field to be measured The angle can be easily determined, and the magnitude of the magnetic field H can be determined from this rotation angle. If this magnetic field is caused by a line current, the line current value can be measured.

[Problems to be Solved] As explained above, according to the conventional configuration, as a light path, ■ a high-light optical fiber (not shown), ■ a polarizer,
■A path that passes through a Faraday effect element, ■a polarizer and an analyzer with an analyzer angle of 45'', or a polarizer and a 45° optical rotator, and ■an optical fiber for light output, or in the reverse order. However, it is not possible to share optical fibers for people to use the lights.
Two optical fibers are always required.

For this reason, there is a limit to reducing the size of this type of sensor, and the optical fiber must have two cores, which has been an obstacle to reducing the diameter of the signal transmission section.

[Means for Solving the Problems] In order to solve the above problems, the present invention connects a magnetic field sensor with a single-core optical fiber for both light input and output. In order to input and output light using a single gate using an optical fiber, a reflective mirror is placed at the position where the polarized light turns back, and while the polarized light travels back and forth within the magnetic field sensor, the polarization plane is adjusted to 45 degrees, which is necessary for measurement. In addition to this, the polarization plane is rotated by an external magnetic field to be measured to emit light.

Those using magnets shown in ``Sensor'' are applicable.

[Structure of the invention] The present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing the principle of the present invention. A polarizer 3. The Faraday effect element 19 and the reflecting mirror 2 are arranged in this order. The reflective mirror may be a reflective film.

Said Faraday effect element 1. An annular permanent magnet 4 is arranged surrounding the polarizer 3. The permanent magnet 4 used as the magnetic field applying section forms a magnetic field in the same direction as the optical path at its annular center, and when there is no external magnetic field to be measured, the polarized light is generated by the Faraday effect element as described below. When reciprocating from 1 to 1, it is possible to generate a magnetic field strength that causes a bias of 45'' angle rotation in the plane of polarization.

The light exiting the optical fiber 6 becomes parallel light by the lens 5, and becomes linearly polarized light by passing through the polarizer 3. Furthermore, by passing through the Faraday effect element 1, if the permanent magnet 4 were not present, the polarization plane is rotated by the magnetic field exerted by the external magnetic field to be measured and reflected by the reflection mirror 2, and the polarization is reflected by the Faraday effect element 1 again. The polarized light is rotated and enters the lens 5, but during one round trip inside the Faraday effect element 1, this polarized light is biased by an angle of exactly 45@ by the permanent magnet 4, so that the polarized light is biased by an angle of exactly 45@ It passes through the analyzer 3 with a polarization plane that is the rotation angle of the polarization plane due to the magnetic field strength plus a 45° bias due to the magnetic field strength of the permanent magnet 4, passes through the analyzer 3, passes through the lens 5, and enters the optical fiber 6.

In other words, according to the present magnetic field sensor, external measured magnetic field strength measurement data can be obtained during the round trip in which light enters from a single optical fiber, is reflected by a reflection mirror, and is emitted to the optical fiber.

To measure the magnetic field using the magnetic field sensor, an optical signal detection device as shown in FIG. 3 is used.

As shown in the figure, an optical splitter 9 is coupled to the light emitting element 8, an optical fiber 6 is coupled to the optical splitter 9, and the magnetic field sensor 11 shown in FIG. 1 is coupled to the terminal of the optical fiber 6. A light receiving element 10 is arranged with respect to the optical splitter 8 .

As understood from the previous embodiment, the light from the light emitting element 8 passes through the optical splitter 9, passes through the optical fiber 6, travels back and forth to the magnetic field sensor (2), and the light that reaches the optical splitter 9 is split in two directions. The signals are branched, one of which is input to the light receiving element IO and converted into an electrical signal, resulting in a total of C1ff1.

FIGS. 2(A), 2(B), and 2(C) show embodiments of the present invention. Components that are the same as those in the embodiment of FIG. 1 are designated by the same reference numerals.

(a) In the optical magnetic field sensor shown in the figure, an annular permanent magnet 4 whose upper and lower surfaces are magnetized to S and H is arranged surrounding a polarizer 3 with a Faraday effect element 1 in between. A permanent magnet 4' is arranged outside the reflection mirror 2 at the other end, with the polarity opposite to the magnetic polarity of the annular permanent magnet 4 as a reflection.

This magnet configuration allows biasing precisely along the polarization path within the Faraday effect element 1 to the required polarization angle of 45°.

(b) The figure shows the magnetic pole configuration of the permanent magnet 4 used in the one shown in FIG.

(c) The one shown in the figure uses an electromagnet or an air-core coil port instead of using a permanent magnet. When an electromagnet or an air-core coil is used, the adjustment of the magnetic field that generates a bias of 45'' rotation angle of the plane of polarization by reciprocating the Faraday effect element is facilitated by controlling the energization of the coil. Not only permanent magnets but also electromagnets and air-core coils can be used.

[Effects of the Invention] According to the present invention, one polarizer can be used as an analyzer, and only one optical fiber is required, making it possible to miniaturize the optical magnetic field sensor and reduce the diameter of the signal transmission section.

[Brief explanation of the drawing]

FIG. 1 shows a diagram of the principle of the present invention, and FIG. 2 (A). (b) and (c) show examples. FIG. 3 shows an optical signal detection device. 4 and 5 show conventional magnetic field sensors. DESCRIPTION OF SYMBOLS 1... Faraday effect element, 2... Reflection mirror or reflective film, 3... Polarizer, 4.4'... Permanent magnet,
5... Lens, 6... Optical fiber, 7... Optical polarizer, 8... Light emitting element, 9... Optical splitter, 1G... Light receiving element, Sumire ■... Magnetic field sensor, ! 2...Electromagnet or air-core coil. Santu Kaizu Answer 4 22 () 75 Day Effect Deep Moat)) %5 Figure

Claims (3)

[Claims] (1) An optical magnetic field sensor for passing polarized light through a Faraday effect element and measuring the intensity of a magnetic field to be measured across the Faraday effect element based on a rotation angle of a plane of polarization of the polarized light, wherein the magnetic field sensor is A polarizer, a Faraday effect element, and a reflecting mirror are provided in this order from the light side, and the polarized light from the polarizer passes through the Faraday effect element, is reflected by the mirror, and passes back through the Faraday effect element again to produce the While reaching the polarizer, the magnetic field to be measured is zero,
An optical magnetic field sensor comprising a magnetic field applying section that applies a bias of a rotation angle of 45 degrees to the polarized light passing through the Faraday effect element. (2) The optical magnetic field sensor according to claim (1), wherein the magnetic field applying section is a permanent magnet. (3) The optical magnetic field sensor according to claim (1), wherein the magnetic field applying section is an electromagnet or an air-core coil.