JPH02291985A - Magnetic field sensor - Google Patents

Abstract

PURPOSE:To enable highly accurate measurement of an intensity of a magnetic field within an ultrafine pipe by rotating a polarization plane of light polarized linearly according to the intensity of magnetic field with a Faraday rotation element. CONSTITUTION:When a light source 10 emits light, the light from the light source 10 is transmitted through an optical fiber 11 and reaches a selfoc lens 15. The light is converted into a parallel light with the selfoc lens and polarized linearly with the subsequent polarizer 14 to be incident into a garnet element 13 as Faraday rotation element. Under such a condition, when a magnetic field H is applied to the garnet element 13, the garnet element 13 rotates a polariza tion plane of the light incident according to an intensity of a magnetic field. The light thus rotated is converted to an intensity of light with an analyzer 16 and condensed with the subsequent selfoc lens 11 to be sent to an optical fiber 18. The light is transmitted through the optical fiber 18 to reaches a meas uring device 19. The measuring device 19 converts the light incident into an voltage signal with a photoelectric transducer to determine the intensity of magnetic field from a voltage signal level thereof.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to magnetic field sensors.

(Prior Art) A magnetic field sensor is composed of a probe and a measuring element provided at the tip of the probe, and the shape of this measuring element can be roughly divided into flat type and axial type. 7 and 8 are configuration diagrams of such a magnetic field sensor,
FIG. 7 shows a magnetic sensor composed of a probe 1 and a flat type n1 constant element 2, and FIG. 8 shows a magnetic sensor composed of a probe 3 and an axial type dPj constant element 4. Here, germanium Hall generators are used for both the 71?3 constant elements 2 and 4. When measuring the magnetic field strength, in the case of a magnetic sensor with a flat measuring element 2, the probe 1 is inserted so that the Hall generator is arranged perpendicularly to the magnetic field H, and also with the axial measuring element 4.
In a magnetic field sensor having a magnetic field H, the probe 3 is inserted so that the Hall generator is arranged parallel to the magnetic field H.

By the way, in order to determine the magnetic field/j degree inside the small-diameter vibrator, the axial type measuring element 4 is better than the flat type ΔIII constant element 2 because the magnetic field strength inside the small-diameter vibrator can be determined by using the axial type measuring element 4. This is advantageous for determining allJ.

Therefore, in a magnetic field sensor having an axial type ΔP1 constant probe 4, the diameter of the probe 3 is determined by the size of the measuring element 4. Specifically, the diameter of probe 3 is φ5llllI
It is about 1. Therefore, the diameter of the vibrator is less than φ5, for example, the ultra-thin diameter φ1! When it comes to llII, the bulb 3
cannot be inserted into the vibrator, and it becomes impossible to constant the magnetic field aP1 inside the ultra-thin vibrator.

(Problems to be Solved by the Invention) As described above, it has been difficult to determine the magnetic field strength inside the ultra-thin vibrator.

Therefore, one object of the present invention is to provide a magnetic field sensor that can measure the magnetic field strength inside an extremely thin pipe with high precision.

[Details of the Invention] (Means for Solving the Problems) The present invention provides a light source, an extremely thin first optical transmission line for transmitting light from the light source, and one end connected to the first optical transmission line. a hollow casing formed to have approximately the same diameter as the first optical transmission path;
A Faraday rotation element placed inside the housing, an optical system placed inside the housing that uses the light from the light source as mourning light, and a linear polarization of the light transmitted through the optical system placed inside the housing. A linear polarizing element, a detection optical element disposed inside the housing and set at a polarization angle shifted by a predetermined angle with respect to the polarization angle of the linear polarizing element, and emitting light that has passed through the Faraday rotation element; a condensing optical system configured to condense the light that has passed through the detection optical element; an ultra-thin second transmission line connected to the other end of the housing and transmitting the light detected by the detection optical element;
The present invention is a magnetic field sensor that attempts to achieve the above object by being equipped with an Illl constant device that determines the magnetic field intensity from the amount of light transmitted through the second optical transmission line.

(Function) By providing such a means, the light from the light source is transmitted through the ultra-thin first optical transmission path and is transmitted to the optical system inside the casing, which is formed to have approximately the same diameter as the first optical transmission path. converted into prison light,
The light is linearly polarized by the i-line polarizing element and sent to the Faraday rotation element, where the plane of polarization of the linearly polarized light is rotated in accordance with the magnetic field strength. Then, the light whose polarization plane has been rotated by this Faraday rotation element is projected by an exposed optical element and transmitted through an ultra-thin second transmission line to the 'AFl constant device. A strong magnetic field is required.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of a magnetic field sensor, and FIG. 2 is a partial block diagram of the same sensor. The light source 10 includes a light emitting diode (L
ED) is used, and this light source 10 is connected to an extremely thin fiber 11 having a diameter of, for example, φ1 am. A hollow casing, ie, a copper vib 12, is connected to the other end of the optical fiber 11, and the copper vibe 12 is formed to have approximately the same diameter as the optical fiber 11. As shown in FIG. 2, a garnet element 13 as a Faraday rotation element is disposed in the hollow interior of the copper vibe 12 at the center thereof. Furthermore, the optical fiber 11 seen from the garnet element 13 in the hollow interior of the copper pipe 12
A polarizer 14 and a self-neck lens 15 are arranged on the side. Further, an analyzer 16 and a self-occurring lens 17 are disposed on the opposite side of the tip fiber 11 when viewed from the garnet element 13. The angle of polarization of the analyzer 16 is shifted by 45'' with respect to the polarization plane of the polarizer 14.Then, on the side where the SELFOC lens 17 is placed inside the copper vibe 12, an ultra-fine optical fiber is installed. 18
is connected to the optical fiber 18, and an a-1 regulator 19 is connected to the other end of the optical fiber 18. This one measuring device has the function of receiving light transmitted through the optical fiber 18 and determining the magnetic field strength from the amount of received light.

Next, as above! The operation of the magnetic field sensor that has been increased by +1 will be explained.

When the light source 10 emits light, the light from the front source 10 is transmitted through the front fiber 11 and reaches the self-cleaning lens 15. This self-occurring lens 15 converts the light into parallel light, which is then converted into a straight line by a polarizer 14 and enters the garnet element 13 . When a magnetic field H is applied to the garnet element 13 in this state, the garnet element 13 rotates the plane of polarization of the incident light in accordance with the strength of the magnetic field, as shown in FIG.

Here, the Verdet constant of the garnet cord 13 is v1, the thickness of the garnet element 13 in the axial direction is p1, the garnet element 13
When the magnetic field applied to is H, the rotation angle ψ of the polarization plane of light in the garnet element 13 becomes ψ-VH-,Q. The light whose polarization plane has been rotated by this garnet element 13 is converted into a pre-intensity by an analyzer 16, and then condensed by a Selfox lens 17 and sent to an optical fiber 18. However, this light is transmitted through the optical fiber 18
is transmitted and reaches the measuring device 19. This jl determiner 19 converts the incident light into a voltage signal using an optical ra conversion element, and determines the magnetic field strength from this tonic pressure level. This method of determining the magnetic field strength applies the fact that the voltage signal level and the magnetic field strength are in a proportional relationship as shown in FIG.

Note that since the polarization planes of the polarizer 14 and the analyzer 16 are shifted by 45 degrees, the output voltage of the photoelectric conversion element in the measuring device 19 is determined by the rotation of the polarization plane of the light in the Garnet element 13, as shown in FIG. The detection sensitivity of the magnetic field strength becomes high in a range Q centered around the angle ψ of 45°.

In this way, in the above-mentioned embodiment, the ultra-fine tip fiber 11 includes a polarizer 14, a Garnet Soto element 13, and an analyzer 1.
In this configuration, a copper vibe 12 having approximately the same diameter as the optical fiber 11.18 in which the fiber 6 is disposed inside is connected, and a flFj constant The diameter of the pipe 12 can be approximately the same as that of the ultra-fine optical fiber 11.18, specifically, the diameter of the copper pipe 12 can be approximately φ1 w. Therefore, the magnetic field strength inside the vibrator whose diameter is on the order of millimeters can be easily determined as AI1. Further, since external influences are canceled by the polarizer 14 and the analyzer 16, it is not affected by disturbances such as magnetic fields and electric fields.

Furthermore, since it has the sensitivity shown in Figure 5, the magnetic field strength can be adjusted with high precision. 1-1 can be determined. In addition, a polarizer 14 and an analyzer 16
Since Selfox lenses 15 and 17 are arranged on each optical fiber 11 and 18 side, optical loss is small.

Note that the present invention is not limited to the above-mentioned embodiment, and may be modified without departing from the spirit thereof. For example, as shown in FIG. 6, a thin film 20 such as a Polaroid film that acts as a polarizer may be formed on both sides of the garnet element 13, and a thin film 21 such as a Polaroid film that acts as an analyzer may be formed on each side of the garnet element 13. With this configuration, the space between each optical fiber 11 and 18 becomes narrower, making it possible to eliminate the Selfox lens and further reducing optical loss. Further, the light source is not limited to a light emitting diode, but a laser diode, a HeNe laser, or the like may be used.

Effects of the Invention J As described in detail above, according to the present invention, a magnetic field sensor capable of measuring the magnetic field strength inside an ultra-thin vibrator with high precision can be provided.

[Brief explanation of drawings]

1 to 5 are diagrams for explaining one embodiment of a magnetic field sensor according to the present invention, and FIG. 1 is an overall configuration diagram;
Figure 2 is a diagram of the internal configuration of the copper vibe, Figure 3 is a schematic diagram showing the action of the garnet rotating element, Figures 4 and 5 are
Diagram 6 for explaining the calculation effect of magnetic field strength in the measuring device
The figure is a configuration diagram showing a modification of the present invention, and FIGS. 7 and 8 are configuration diagrams of a conventional magnetic field sensor. 10... Light source, 11.18... Optical fiber 12.
・・Copper pipe, 13・・Garnet rotating element, 14・
...Polarizer, 15.17...Selfoc lens, 1
6...Analyzer, 19...4-j meter. Applicant's agent Patent attorney Takeshi Suzue 7 3 Mei Ku 7 Ku 2) 8 2} 4

Claims (1)

[Claims] A light source, an ultra-thin first optical transmission line for transmitting light from the light source, and a hollow housing having one end connected to the first optical transmission line and having approximately the same diameter as the first optical transmission line. , a Faraday rotation element disposed inside the housing, and an optical system disposed inside the housing that converts light from the light source into parallel light;
a linear polarizing element arranged inside the casing and linearly polarizing the light transmitted through the optical system; a detection optical element that detects the light that has passed through the Faraday rotary element; a condensing optical system that is arranged inside the housing and that collects the light that has passed through the detection optical element; and a condensing optical system that is connected to the other end of the housing. A magnetic field sensor comprising: an ultrathin second optical transmission path that transmits the light detected by the detection optical element; and a measuring device that determines magnetic field strength from the amount of light transmitted through the second optical transmission path. .