JPH03238377A - Magnetic sensor - Google Patents

Abstract

PURPOSE:To achieve a smaller size of a sensor with a shorter optical length of a sensor element by using a thin glass polaroid plate as polarizer and analyzer while magnetic garnet with a large Verdet's constant is employed for a Faraday element. CONSTITUTION:This sensor has a polarizer 3, a Faraday element 4 and an analyzer 5 arranged in the order. At least one of the polarizer 3 and the analyzer 5 comprises a glass polaroid plate and the element 4 is composed of garnet as given by a formula of A3B5O12(wherein A is composed of, for example, one or a plurality of elements selected from a rare earth element, Bi and Pb. B is, for example, Fe alone or additional one or more elements selected from A, Ga, In, Co, Ge and Sc). Light emitted from a collimation lens 2 is turned to a linearly polarized light and as passing through the element 4 to which a magnetic field H is applied, a polarizing plane thereof rotates by an angle theta. Then, the light passes through the glass polaroid plate with an optical axis 5a inclined to the optical axis 3a of the glass polaroid plate. The transmission light is introduced to a photo detector to be converted into an electrical signal for computation thereby calculating the intensity of the magnetic field H.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a magnetic sensor that uses the Faraday effect to measure magnetic fields and currents.

[Conventional technology]

One type of magnetic sensor utilizes the Faraday effect, in which the plane of polarization of linearly polarized light rotates when light passes through a substance to which a magnetic field is applied in the direction of magnetic lines of force. FIG. 2 shows an example of a magnetic sensor. This magnetic sensor has a polarizer 13, a Faraday element 14g, and an analyzer 15 arranged in this order. The polarizer 13 is connected to a light source (not shown) through a collimating lens 2 and an optical fiber 1, and the analyzer 15 is connected to a photodetector (not shown) through a collimating lens 6 and an optical fiber 7. The polarizer 13 has a polarization direction in the direction of arrow 13a, and the analyzer 15 has a polarization direction in the direction of arrow 15a. When the light emitted from the collimating lens 2 through the optical fiber cable l passes through the polarizer 13, the tip axis 13
It becomes linearly polarized light with only a component parallel to a. When this linearly polarized light passes through the Faraday element 14 to which a magnetic field H is applied, it becomes linearly polarized light whose plane of polarization has been rotated by θ, and the analyzer 15
pass through. The optical axis of the analyzer 15 is the optical axis 13 of the polarizer 13
Since it is tilted with respect to a, the amount of light passing through the analyzer 15 is
It is determined by the rotation angle θ of polarized light. The rotation angle θ is the formula θ
= V-H-J2 (V is the Verdet constant, and F is the element length of the Faraday element), which is proportional to the magnetic field strength H. The strength H of the magnetic field can be calculated by guiding it to a photodetector (not shown), converting it into an electrical signal, and performing calculations.

[Problem to be solved by the invention]

Such magnetic sensors are required to be as small as possible. However, the magnetic sensor shown in FIG.
Since a polarizing prism is used in the analyzer 15, the optical path length becomes long, and the effective beam diameter is small compared to the size of the sensor. The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a compact magnetic sensor whose element has a short optical path length.

[Means to solve the problem]

A magnetic sensor of the present invention, which has been made to achieve the above object, will be explained using FIG. 1 corresponding to an embodiment. As shown in the figure, in the magnetic sensor of the present invention, a polarizer 3, a Faraday element 4, and an analyzer 5 are arranged in this order. At least one of the polarizer 3 and the analyzer 5 is made of a glass polarizing plate, and the Faraday element 4 has the formula As5so+□
Consisting of garnet indicated by . A in the formula A3B60□ is composed of one or more elements selected from, for example, rare earth elements, Bi, and Pb. B is composed of, for example, Fe alone, or a plurality of elements selected from Al, Ga, In, Co, Ge, and Sc and Fe. A polarizing plate in which silver crystals are oriented on the surface of a glass plate is used as the glass polarizing plate. It is desirable that the polarizer 3, the Faraday element 4, and the analyzer 5 have a disk shape.

[Effect]

The magnetic sensor of the present invention uses a thin glass polarizing plate as the polarizer 3 and the analyzer 5, and uses a large magnetic garnet with a Verdet constant as the Faraday element 4, so that the optical path is shortened and the lens generates light. collimation is easy. Furthermore, since the polarizer 3, Faraday element 4, and analyzer 5 are formed in a disk shape centered on the optical path, the ratio of the effective beam diameter to the outer diameter of the magnetic sensor is large.

【Example】

The present invention will be explained in detail below. FIG. 1 shows a magnetic sensor of the present invention. This sensor has a polarizer 3, a Faraday element 4, and an analyzer 5 connected in this order. The polarizer 3 is connected to a light source (not shown) via a rod-shaped collimating lens 2 and an optical fiber l, and the analyzer 5 is connected to a photodetector (not shown) via a collimating lens 6 and an optical fiber 7. has been done. The polarizer 3 and the analyzer 5 are glass polarizing plates (manufactured by Corning, Polar Core 78612) having a thickness of 0.2 m+a and having silver crystals oriented on the glass surface. This is processed into a disk shape of 1.8 mmφ and used. The Faraday element 4 has the formula (GdBil s (FeG
A garnet single crystal with a thickness indicated by al sO + t (1,04+ am is processed into a disk shape of 1.8++a◆). When the light emitted from the collimating lens 2 passes through the glass polarizing plate 3, The Faraday element 4 becomes linearly polarized light with only a component parallel to its tip axis 3a, and a magnetic field H is applied to it.
When passing through, the plane of polarization rotates by an angle θ. The linearly polarized light whose plane of polarization has been rotated passes through the glass polarizing plate 5 whose optical axis 5a is inclined with respect to the optical axis 3a of the glass polarizing plate 3. The transmitted light is guided to a photodetector (not shown) through a conomete lens 6 and an optical fiber 7, and is converted into an electrical signal and subjected to calculation to calculate the strength H of the magnetic field. In the magnetic sensor of this embodiment, the effective beam diameter through which light can pass is 1.6+++aφ. On the other hand, the diameter of the glass polarizing plates 3 and 5 and the Faraday element 4 is 1.8 m.
mφ, the ratio of the effective beam diameter to the outer diameter of the magnetic sensor is 0.89, and it can be seen that the cross sections of the glass polarizing plates 3 and 5 and the Faraday element 4 constituting the magnetic sensor are effectively utilized. Further, the optical path length of the transmitted light was 0.5 mm. On the other hand, the conventional magnetic sensor shown in FIG.
dBi) x fFeGal sO+ 2 denoted by t
0X O, (14ma+ garnet single crystal is used. In this structure, the effective beam diameter that can transmit light is 1.61φ, and the polarization beam splitter is 13 and 15.
Since the diameter of the circle inscribed in the Faraday element 14 and perpendicular to the optical path is 2.83r++a$, the ratio of the effective beam diameter to the inscribed circle of the magnetic sensor is 0.57. The optical path length passing through the polarizing beam splitters 13 and 15 and the Faraday element 14 was 4.1 mm. As described above, the magnetic sensor according to the embodiment of the present invention has an optical path length of about 178 mm and an outer diameter of about 171.6 mm, compared to the conventional magnetic sensor described using FIG. The volume has been reduced to 1/26. [Effects of the Invention] As explained in detail above, the magnetic sensor of the present invention has a short optical path length of the polarizing element, and the cross section of each polarizing element is used as an optical path with high area efficiency, so that it is different from conventional magnetic sensors. It is significantly smaller than the previous model. It is also easy to process.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of the magnetic sensor of the present invention;
FIG. 2 is a perspective view showing a conventional magnetic sensor. l・7−・・Optical fiber 2・6・・・Collimator lens 3・5−・・Glass polarizing plate 4・14・・Faraday element

Claims (1)

[Claims] 1. In a magnetic sensor in which a polarizer, a Faraday element, and an analyzer are arranged in this order, at least one of the polarizer and the analyzer is made of a glass polarizing plate, and the Faraday element has the formula A_2B_5O_1_2 (A is a rare earth element). Element, Bi,
One or more elements selected from Pb, B is Fe alone or one or more elements selected from Al, Ga, In, Co, Ge, Sc and Fe), and is characterized by consisting of a garnet single crystal. magnetic sensor. 2. The magnetic sensor according to claim 1, wherein the glass polarizing plate is a polarizing plate in which silver crystals are oriented on the surface of a glass plate. 3. The magnetic sensor according to claim 1, wherein at least one of the polarizer, Faraday element, and analyzer is formed into a disk shape.