JPH06100642B2 - Optical applied magnetic field sensor - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an optical magnetic field sensor for detecting the strength of a magnetic field by utilizing the Faraday effect.

[Technical background of the invention]

The principle of detecting the strength of a magnetic field by using the Faraday effect and an optical magnetic field sensor based on the principle are well known.

FIG. 4 shows an example of the configuration of a conventional magnetic field sensor for optical application, the basic configuration of which is a polarizer 3 in which an optical fiber 1a is coupled through a rod lens 2a and an incident light is guided, and this polarizer. 3 and a Faraday element 5 adhered to the Faraday element 3 and an analyzer 4 which guides the emitted light, which is adhered to the Faraday element 5 and polarized, to an optical fiber 1b coupled through a rod lens 2b. In this case, a magneto-optical material having a large Verdet constant is used as the Faraday element 5. Many of the polarizer 3 and the analyzer 4 utilize dichroism, and generally have a structure in which a polyvinyl film containing a large amount of iodine called polaroid is sandwiched between two pieces of glass having a small Verdet constant. ing.

Here, the Faraday effect is a phenomenon in which the plane of polarization of emitted light rotates when a magnetic field is applied in the same direction as the traveling direction of this light while linearly polarized light is incident on the magneto-optical material. The angle is proportional to the magnitude of the magnetic field. That is, this can be expressed by the equation: = V · L · H (1)

Here, V is the Verdet constant, L is the length of the Faraday element along the magnetic field direction, H is the strength of the magnetic field, and the rotation angle of the polarization plane.

[Problems of background art] By the way, in the above-mentioned conventional optical applied magnetic field sensor, since the strength of the measured magnetic field is often in the range of several kilogausses, a material having a large Verdet constant is used as the Faraday element. The rotation angle is increased and the applied magnetic field H is measured from the above formula (1). in this case,
As described above, the polarizer and analyzer have a structure in which a polyvinyl film is sandwiched between two pieces of glass with a small Verdet constant, so it is almost ignored for measurement magnetic field strengths of up to several kilogauss. be able to.

However, when the strength of the measured magnetic field is, for example, 10 kilogauss or more, even if a polarizer and an analyzer made of a material having a small Verdet constant are used, they still have a function as a magneto-optical substance exhibiting the Faraday effect. Inevitably, the rotation angle of the plane of polarization generated in the polarizer and analyzer becomes large.
This means that when the magnetic field strength is calculated from the above formula (1) for a single Faraday element, it does not show an accurate value.

As described above, in the conventional optical magnetic field sensor, when the magnetic field strength is calculated by using two or more kinds of materials such as a Faraday element having a large Verdet constant, a polarizer having a small Verdet constant, and an analyzer, a polarizer or an analyzer is used. Since the rotation angle generated in 1 is ignored, an error will inevitably occur. Further, since it is necessary to use a Faraday element having a long element length in order to perform accurate measurement even in a low magnetic field, there is a drawback that the sensor itself becomes large and the spatial resolution deteriorates.

[Object of the Invention]

The present invention has been made to eliminate the above drawbacks.
It is an object of the present invention to provide an optical applied magnetic field sensor which can improve the detection accuracy of the magnetic field strength regardless of the magnitude of the magnetic field and can improve the spatial resolution in a small size.

[Summary of the Invention] In order to achieve the above object, the present invention provides a polarizer in which a polarizing film is interposed between two prisms made of a material having the same Verdet constant, and a polarizer made of the same material as the polarizer. The analyzer with the analysis film interposed between the polarizing film and the analysis film
The incident light is guided to the polarizer through an optical transmission path, and the P-polarized light and the S-polarized light separated by the analysis film are provided for the polarizer.
The polarized light is guided to each of the optical transmission lines as outgoing light. Therefore, in such an optical applied magnetic field sensor, the prisms existing between the polarizing film and the analyzing film have the same Verdet constant without inserting a Faraday element between the polarizer and the analyzer. Since it is made of a material, the Faraday effect can be generated in this portion.

Example of Invention

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a principle configuration of an optical magnetic field sensor according to the present invention. That is, according to the present invention, as shown in FIG. 1, two right-angle prisms 14a and 14b, which are the same as the polarizer 13 in which a polaroid film 13c is inserted as a polarization film and adhered between the inclined surfaces of the two right-angle prisms 13a and 13b. An analyzer 1 in which a polaroid film 14c is interposed as an analysis film and adhered between the inclined surfaces of
In order to prevent the influence of the change in the intensity of incident light, the polarizing film 4 and the analyzing film 4 are configured to be bonded in a positional relationship different from each other by 45 degrees. in this case,
The two right-angle prisms 13a, 13b and 14a, 14b, which are the constituent elements of the polarizer 13 and the analyzer 14, are made of a material such as BK glass having the same Verdet constant. Then, unpolarized incident light 11 is applied to the polarizer 13 through an optical transmission line.
Further, a is guided to the analyzer 14, and P-polarized light 11b and S-polarized light 11c separated by the light-analyzing film are guided to the optical transmission line as emitted lights. In FIG. 1, the polarizing film of the polarizer 13 and the analyzing film of the analyzer 14 are not in a positional relationship different from each other by 45 degrees, but this is because the Faraday element length can be clearly understood. The polarizer 13 and the analyzer 14 are shown so as to be parallel to each other.

Next, the operation of the optical applied magnetic field sensor having the above-described principle configuration will be described.

When the incident light 11a is guided to the polarizer 13 and reaches the point P in the figure, the P-polarized light 11e and S
It is separated into polarized light 11e. Both the P-polarized light 11e and the S-polarized light 11e are linearly polarized light, and the plane of polarization of the P-polarized light 11e rotates in a magnetic field, and when it reaches the point Q in the figure of the analyzer 14, the P-polarized film 14c between C and D in the figure again causes P-polarization. It is separated into polarized light 11b and S polarized light 11c.

Here, the rotation angle of the plane of polarization can be calculated by measuring the intensities of the P-polarized light 11b and the S-polarized light 11c as emitted light. And the Faraday element length L is PQ in Fig. 1.
The space corresponds to this. In this case, the Verdet constant V is determined by the materials of the two right angle prisms 13a and 14b of ΔABC and ΔCBD that sandwich the polaroid films 13c and 14c. Therefore, the magnetic field strength H can be calculated by substituting the rotation angle, the Faraday element length L, and the Verdet constant V described above into the above equation (1).

In this way, in this sensor, two polarizers 13a, 13b and 14a, 14b made of the same material are used, and the polarizer 13 and the analyzer are
A Faraday element can be made into these polarizers by simply constructing 14
Since it is possible to obtain the Faraday effect by the Verdet constant of the material of the right-angle prism without interposing between the analyzer 14 and the analyzer 14, it is possible to measure the magnetic field strength extremely accurately, The size can be reduced and the spatial resolution can be improved.

FIG. 2 shows a concrete example of the optical applied magnetic field sensor based on the above-mentioned principle configuration. In FIG. 2, the polarizer 13 and the analyzer 14 are the same as those of the configuration shown in FIG. 1, but here the polarizing film and the analyzing film 45
It is shown as an original configuration in which the adhesive is placed in different positional relationships. Reference numeral 12a is an optical fiber that guides incident light, and this optical fiber 12a is coupled to the polarizer 13 via a rod lens 15a. Reference numeral 16a is a right-angle prism which is adhered to the surface of the analyzer 14 from which S-polarized light is emitted and which changes the optical path of S-polarized light in the same direction as the emission direction of P-polarized light. Reference numerals 12b and 12c are optical fibers for guiding the P-polarized light and the S-polarized light emitted from the analyzer 14 to a measurement unit (not shown). The optical fiber 12b is the analyzer 1
4, coupled via a rod lens 15b, and also an optical fiber
12c is coupled to the right-angle prism 16a via a rod lens 15c.

Therefore, with such a configuration, the P-polarized light and the S-polarized light separated by the analysis film of the analyzer 14 can be guided to the side opposite to the incident light side.

FIG. 3 shows a specific embodiment different from that of FIG. 2, and the same parts as those of FIG. 2 are designated by the same reference numerals. In FIG. 3, a right-angle prism 16b is adhered to the surface of the analyzer 14 from which P-polarized light is emitted, and an optical fiber 12b is coupled to the right-angle prism 16b via a rod lens 15c, and the emitted light is changed to incident light. The right-angle prism 16a is adhered to the surface of the analyzer 14 from which the S-polarized light is emitted, and the optical fiber 12c is attached to the right-angle prism 16a through the rod lens 15b so that the emitted light is also the same as the incident light. It is designed to be guided in the direction.

Therefore, with such a configuration, both P-polarized light and S-polarized light emitted from the analyzer 14 can be guided in the same direction as the incident side, so that the measurement object cannot be measured on the side opposite to the incident light side. In case it would be very convenient.

In addition, the present invention is not limited to the configurations shown in FIG. 2 and FIG. 3 as long as it is based on the above-described principle configuration, and various modifications can be implemented.

〔The invention's effect〕

As described above, according to the present invention, a polarizer having a polarizing film interposed between two prisms made of a material having the same Verdet constant, and an analyzer film formed between the two prisms made of the same material as the polarizer. Since the analyzer and the polarization plane of the light emitted from the polarizer and the polarization plane of the light emitted from the analyzer are arranged in a 45 degree positional relationship with each other and are bonded together, the Faraday element is interposed. It is possible to generate the Faraday effect required for magnetic field strength by using a prism made of a material having the same Verdet constant that exists between the polarizing film and the analyzer film, and separate the analyzer with the analyzer film. Since the extracted P-polarized light and S-polarized light are extracted and their light intensities are used, the optical applied magnetic field sensor can improve the detection accuracy of the magnetic field intensity regardless of the magnitude of the magnetic field and can improve the spatial resolution in a small size. Can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the principle of an optical applied magnetic field sensor according to the present invention, and FIGS. 2 and 3 are configurations showing concrete different embodiments based on the principle configuration shown in FIG. FIG. 4 and FIG. 4 are configuration diagrams for explaining a conventional optical applied magnetic field sensor. 11a …… incident light, 11b …… P polarized light, 11c …… S polarized light, 13…
… Polarizer, 14 …… Analyzer, 13a, 13b, 14a, 14b …… Right-angle prism, 13c, 14c …… Polaroid film.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Susumu Yoshizawa No. 1 in Toshiba Fuchu factory, Fuchu-shi, Tokyo (72) Inventor Soichiro Hayashi No. 1 in Toshiba-machi, Fuchu, Tokyo Tokyo Fuchu factory ( 72) Inventor Mikiyuki Ono 1-5-1, Kiba, Koto-ku, Tokyo Inside the Fukagawa Plant, Fujikura Electric Wire Co., Ltd. (72) Inventor Yoshio Kikuchi, 1440, Rokuzaki, Sakura City, Chiba Prefecture Inside the Sakura Factory of Fujikura Electric Wire Co. Inventor Asawa Tanaka 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Line Co., Ltd.

Claims (3)

[Claims] 1. An optical applied magnetic field sensor for detecting the strength of a magnetic field using the Faraday effect, a polarizer having a polarizing film interposed between two prisms made of a material having the same Verdet constant, and the polarizer. And an analyzer in which an analysis film is inserted between two prisms of the same material as above, the polarization plane of the light emitted from the polarizer and the polarization plane of the light emitted from the analyzer are arranged in a 45 ° positional relationship with each other. The incident light is guided to the polarizer through an optical transmission path, and the P-polarized light and the S-polarized light separated by the analysis film are emitted to the analyzer as outgoing lights. An optical magnetic field sensor characterized by being guided to a road. 2. The optical applied magnetic field sensor according to claim 1, wherein the P-polarized light and the S-polarized light separated by the analysis film are guided to the incident light side. 3. The optical applied magnetic field sensor according to claim 1, wherein the P-polarized light and the S-polarized light separated by the analysis film are guided to the side opposite to the incident light side. .