JPS6080779A - Magnetic field sensor - Google Patents

Abstract

PURPOSE:To obtain inexpensively a magnetic field sensor which has high sensitivity and small temp. dependency in a large amt. by using a polycrystal of II-VI group compds. semiconductor as a magnetooptic material having a Faraday effect. CONSTITUTION:Both opposite end faces of a polycrystal 1 of II-VI group compds. semiconductor as a magnetooptic material are optically polished and dichromatic plastic polarizing elements 2, 3 of which the passing directions of polarized light have 45 deg. gradient with each other are provided thereon. Lenses 6, 7 are so used that the light emitted from an optical fiber 4 is effectively condensed to an optical fiber 5. The polycrystalline body formed by a vapor growth method of the II-VI group compds. semiconductor (ZnSe, ZnTe, CdSe, ZnO, etc.), for example, ZnSe, has the Faraday rotation power equiv. to that of a single crystal and the temp. stability is rather excellent with the polycrystal.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a magnetic field sensor that applies the Faraday effect in which the plane of polarization of light rotates in response to a magnetic field, and is a practical magnetic field sensor that has both high cost performance and mass productivity. We aim to provide the following.

Conventional configuration and its problems In a magnetic field sensor that combines a magneto-optical material with a Faraday effect and a pair of polarizing elements, a material with a large Verdet constant and a small light absorption coefficient is used as the magneto-optic material. is advantageous.

Conventionally, magnetic garnet, lead glass, and Faraday rotation glass have been mainly considered as materials that meet this condition. However, each of these has its own problems, and does not necessarily fully meet the wide range of performance requirements for magnetic field sensors. Regarding magnetic garnet, although it has a large Faraday rotation ability, since it is a ferromagnetic material, it has a magnetic saturation phenomenon, and problems with reproducibility such as hysteresis characteristics and Barkhausen phenomenon have been pointed out. Furthermore, since the absorption of light with a wavelength of 1 μm or less is large, it is necessary to use a germanium photodiode with large noise as a light receiving element, and the low signal-to-noise ratio is also a major drawback. In addition, the Faraday rotation ability usually has a large temperature dependence, and unless this is corrected, sufficient 6
4I] Consistent accuracy cannot be obtained.

As for lead glass, the Faraday rotation power is small, and even at wavelength 0' and 633 pm, it is 16×1odeq10e@C1
It is of the order of n. In addition, the Faraday rotation ability of the 7 Arade single rotation crow is 4.5 x 10 d at a wavelength of 0.6331 tm.
eg 10e-tm, which is larger than lead glass, but because it has very high temperature dependence, the accuracy is low unless temperature correction is made like magnetic garnet.

OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic field sensor that is highly sensitive to magnetic fields and has low temperature dependence at low cost and in a large quantity.

Structure of the Invention As a structure therefor, the present invention includes a first polarizing element, a magneto-optical material having a Faraday effect, and a second polarizing element.

Description of Examples Zn5e, which is collectively called n-vt group compound semiconductor,
Single crystals such as ZnTeCdSe and ZnO are known to have a large Faraday rotation ability based on interband transitions. However, the crystal growth technology for obtaining large quantities of these single crystals has not yet been established, and is still difficult to obtain for industrial use, and is expensive. In the process of investigating a growth method that would allow mass production of n-vt group compound semiconductors, the present inventor discovered that even a polycrystalline material produced by vapor phase growth can have properties comparable to those of a single crystal. For example, in the case of Zn5e, the Faraday rotation power in a single crystal is 3.4 × 10 degloe -c
m (λ=O, Q2, am), its temperature change rate is ±1% from 20 to 120°C, whereas in polycrystalline materials, the Faraday rotation ability is 3. lX1O-3d e g
10e-cm (λ=0.82pm) and 6.0X
10 degloe-m (λ-0, 63 μm), the rate of change due to temperature was ±0.3% from 20 to 120° C., and the polycrystalline one had better temperature stability. Furthermore, polycrystalline Zn5e is in large demand as a material for infrared rays, a manufacturing method has been established, and it is much cheaper than lead glass.

FIG. 1 is a front view of polycrystalline Zn5e produced by vapor phase growth. In the figure, 1 is n-v as a magneto-optical material.
It is a polycrystal of an i-group compound semiconductor, and both opposing end faces are optically polished.

Polarizing elements 2 and 3 whose polarized light passing directions have an inclination of 45° to each other are provided on both polished end faces. In the case of this example 1, dichroic plastic polarizing plates were used for the polarizing elements 2 and 3. The reason for this is firstly that polycrystalline Zn5e is relatively brittle compared to single-crystal Zn5e, and when bonded to a hard polarizing element made of calcite or titanium dioxide, the difference in adhesive stress and coefficient of thermal expansion causes Crank may occur due to the stress generated.Secondly, polarizing elements themselves made of materials such as calcite and titanium dioxide are expensive and difficult to obtain in large quantities. 4 and 5 are optical fibers, and lenses 6.7 are used so that the light emitted from the optical fiber 4 is effectively focused on the optical fiber 6. 8 and 9 are ceraminocticops, which are used to firmly bond the optical fiber 4.6.

A specific example will be described in which Zn5e is used as the II-Vl group compound semiconductor polycrystal in the above structure.

Zn5e is manufactured using a vapor phase growth method, and its length in the light transmission direction is 5.
I used something that I indulged in. The dichroic glass polarizing element used was HN38 (thickness Ooam) manufactured by Polaroid, and the lens was a self-focusing rod lens with a pitch of %. The optical fiber is a step index type glass fiber with a core diameter of SOOμm, and the light emitting element has a wavelength of 0.
．． A 66 μm visible LED and a St PIN photodiode were used as the light receiving element.

Excluding the -6 dB polarization loss, the insertion loss was -6 dB, the received light power was 1 μ4 or more, and the incident light to noise ratio was 72 dE with a bandwidth of 10 KHz, which is sufficient for practical use.

The minimum detection sensitivity of the magnetic field sensor in this example was 1 oersted, which was in good agreement with the calculated results. Furthermore, the temperature characteristics also matched the measurement results of a single Zn5e polycrystalline substance within a measurement error.Effects of the InventionThe magnetic field sensor of the present invention has the following effects.

(1) High magnetic sensitivity and good temperature characteristics.

(2) magneto-optical material, polarizing element 2 light emitting element, light receiving element,
Since both optical fibers are easily available and inexpensive general-purpose products, they are suitable for mass production and can be supplied at low cost.

(3) Even if the magneto-optical material is a polycrystalline material produced by vapor phase growth, since the polarizing element to be bonded is made of plastic, it is less likely to be damaged by thermal stress, etc., and is highly reliable.

[Brief explanation of drawings]

FIG. 1 is a wavelength characteristic diagram of the Faraday rotation ability of polycrystalline Zn5e used in an example of the present invention, and FIG. 2 is a sectional view of the magnetic field sensor of the present invention. 1... magneto-optical material (polycrystal of II-Vl group compound semiconductor), 2, 3... polarizing element, 4, 5... optical fiber, 6, 7... lens, 8, 9... ...Ceramic chief. Figure 1: Carious surface (k), 2 y

Claims (1)

Scope of Claims: (1) A first polarizing element, a magneto-optical material having a Faraday effect, and a second polarizing element are sequentially optically coupled, and the magneto-optical material is a polycrystalline N-VT compound semiconductor. A magnetic field sensor using (2) A magnetic field sensor according to claim (1) using dichroic plastic polarizing plates as the first and second polarizing elements. Growth