JP3148024B2 - Reflection type optical magnetic field sensor head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical magnetic field sensor head utilizing the Faraday effect of a bismuth-substituted magnetic garnet film. More specifically, the present invention relates to an improvement in a reflection-type optical magnetic field sensor head for detecting the strength of a magnetic field that is small, lightweight, and can be easily mass-produced in a magnetic field sensor for detecting the strength of a magnetic field. .

[0002]

2. Description of the Related Art At present, many industrial devices and consumer devices generally used generally have a rotating device such as a motor or a gear and a rotating portion. Due to the advancement of science and technology and the growing public interest and demand for energy conservation, the operation control of industrial equipment, for example, aircraft and ships, and consumer equipment, for example, rotating equipment and devices such as passenger cars Attempts have been made to implement the method with higher accuracy and higher precision.

As one of the concrete methods for responding to social demands for protection of the global environment and energy saving, in order to realize more advanced and highly accurate operation control of rotating equipment and devices, first, accurate rotation must be performed. Speed [number] continuously,
And they must be able to know immediately. In order to know the exact rotation speed [number] of the rotating device / device, a highly reliable tachometer / measuring device capable of instantly measuring the accurate rotation speed must be provided. However, it can still meet this social demand. More specifically, it is small, lightweight, highly accurate, easy to handle and can withstand long-term continuous use in harsh environments with high temperatures and vibration. A possible and inexpensive measuring device has not been provided. In order to respond to the international social demands for global environmental protection and energy saving, it is necessary to develop high-performance measuring devices that can quickly respond to social demands, and provide them inexpensively and in large quantities. There is.

[0004] As a method for measuring the rotational speed [number], a method using electromagnetic induction [sensor technology, 1986, 12
Monthly, p. 68) and a method using an optical magnetic field sensor utilizing the Faraday effect of a magneto-optical material (Applied Optics, Vol. 28, No. 11, p. 1992 (1.
989)].

The method using electromagnetic induction has already been used for measuring and measuring the rotational speed [number] of an aircraft or an automobile engine. However, the tachometer using electromagnetic induction has a serious drawback in that the transmission line (cable) between the measurement terminal and the device main body is susceptible to electromagnetic noise and is inferior in reliability. In addition, since electric circuits are used, flammable substances such as organic solvents, that is, facilities that handle hazardous materials,
In other words, there is a serious problem that explosion-proof measures must be taken at hazardous material factories and hazardous material handling sites.

A method using an optical magnetic field sensor utilizing the Faraday effect of a magneto-optical material is such that when a permanent magnet [magnetic field] approaches the optical magnetic field sensor, the polarization plane of the magneto-optical material in the optical magnetic field sensor changes the magnetic field [magnet]. It uses the fact that it rotates depending on the presence or absence. That is, the rotation of the plane of polarization of light transmitted through the magneto-optical material in the optical magnetic field sensor is converted into a change in light intensity, and the rotation is detected and counted to measure the rotation speed [number] [National Technical Report (N
ational Technical Report), Vol.29, No.5, P70 (1983)
].

The optical magnetic field sensor includes a transmission type and a reflection type. Due to the nature of the components, the transmission type is arranged so that the directions of signal light incidence and transmission are aligned.
Since they must be arranged, there are restrictions on their installation locations, and they cannot be installed or adopted depending on the purpose of use and the installation locations.

[0008] A reflection type optical magnetic field sensor has been proposed as a configuration for improving the drawbacks of the transmission type optical magnetic field sensor [
56-55811, Tokuhei 3-22595]. In the reflection type optical magnetic field sensor proposed here, the input optical fiber and the output optical fiber of the signal light are on the same side of the Faraday rotator, in other words, the output optical fiber is the input optical fiber. The Faraday rotator is disposed and installed at the tip of the optical magnetic field sensor in the same direction as the fiber, in other words, the Faraday rotator. Therefore, the reflection type optical magnetic field sensor has a feature that it can be installed in a contaminated and narrow space where the installation space is narrow and a transmission type optical magnetic field sensor cannot be installed. But,
The reflection-type optical magnetic field sensor proposed by Matsui et al. [Japanese Patent Application Laid-Open No. 56-55811] requires a lens and a polarizer, and a lens and an analyzer to be arranged in series, and furthermore, because they must be arranged in parallel. There remains a significant problem in that automation is difficult and, therefore, manufacturing costs are difficult to reduce.

[0009]

[Problems to be solved by the invention] Matsumura et al.
5] is a method for solving the problem of the reflection type optical magnetic field sensor head proposed by Matsui et al., Namely, the problem that it is difficult to automate the assembly work and therefore it is difficult to reduce the manufacturing cost. It proposes a configuration in which an analyzer is replaced with one polarizer. Matsumura et al. Use yttrium / iron / garnet (chemical structural formula: Y ₃ Fe ₅ O ₁₂ ) as a Faraday rotator (magneto-optical material). Yttrium / iron / garnate is generally called YIG and can be produced by a known method such as a melt method.
Yttrium / Iron / Garnet (YIG) has a characteristic that its sensitivity is much higher than that of paramagnetic glass, zinc selenide (ZnSe), and the like which have been conventionally used as a Faraday rotator. Therefore, the proposal by Matsumura et al., That is, the use of yttrium / iron / garnet (YIG) as the Faraday rotator of the reflection-type optical magnetic field sensor can be said to be a very interesting proposal in terms of its characteristics. However, when considering the properties and characteristics of light transmission of yttrium / iron / garnet (YIG), a question arises about the practicality of the magneto-optical material of the optical magnetic field sensor as a Faraday rotator. That is, yttrium, iron, and garnet (YIG) already have the characteristic property that they transmit light in the near-infrared wavelength region of 1.1 μm or more well and absorb light in the wavelength region of 0.8 μm well. Because it is known that there is.

At present, generally, as a light source of an optical sensor, a semiconductor laser (LD) or a light emitting diode (LED) having a center wavelength of 0.78 μm to 0.85 μm has been awarded and widely used. Semiconductor lasers (LDs) and light-emitting diodes (LEDs) are widely used as light sources for optical sensors because they are already commercially available at low cost as light source devices and have high photodetector sensitivity. Therefore, it is most preferable to use a commercially available light source device as a light source for the optical magnetic field sensor. In other words, it is a socially necessary to provide a highly sensitive optical magnetic field sensor using a commercially available light source device at low cost. Needless to say, this is the best way to respond to the demands.

[0011] Yttrium, iron and garnet (YIG)
The fact that it absorbs light in the wavelength region of 0.8 μm well means that
If a commercially available light source device is used as the light source, it means that it may be difficult to detect an optical signal. That is, it shows that yttrium, iron, and garnet (YIG) have basic defects and defects in the physical properties and properties required for the magneto-optical material for the optical magnetic field sensor, in other words, the Faraday rotator. .

The inventors of the present application have strong interest and apprehension in Matsumura's proposal. Therefore, the present inventors have conducted various studies on a method of avoiding the drawbacks and fears of yttrium / iron / garnet (YIG), and as a result, have found that bismuth-substituted magnetic garnet, which has been attracting attention as a magneto-optical material, is capable of doing so. I found sex. The bismuth-substituted magnetic garnet proposed here can be manufactured relatively easily by a liquid phase epitaxial (LPE) method, and is excellent in mass productivity. Bismuth-substituted magnetic garnet is represented by the chemical formula (RBi) ₃ (FeA) ₅ O ₁₂ . Where R is
Y means Y or a rare earth element, and A is
It means aluminum Al or gallium Ga.

The Faraday rotation coefficient of the bismuth-substituted magnetic garnet, in other words, the rotation angle of the polarization plane per unit film thickness in the state where the magnetization is saturated, is smaller than the Faraday rotation coefficient of yttrium / iron / garnet (YIG). More than several times, more specifically, for example, about 10 times larger at a wavelength of 0.8 μm. Therefore, when the same effect is expected as the magneto-optical material, it is possible to reduce the film thickness of the magneto-optical material in proportion to the Faraday rotation coefficient. As a result, light absorption loss is reduced, and It suggests that it can be smaller and smaller. That is, by changing the material of the magneto-optical material from yttrium / iron / garnet (YIG) to a bismuth-substituted magnetic garnet, the film thickness of the element becomes thinner, light absorption loss is reduced, and light in the wavelength region of 0.8 μm band is reduced. This suggests that it is possible to develop an optical magnetic field sensor that uses a light source.

The saturation magnetic field [500 to 1200 Oe] of the bismuth-substituted magnetic garnet is about half of the saturation magnetic field [about 1800 Oe] of yttrium / iron / garnet (YIG). Therefore, it is expected that a weak magnetic field can be measured. The fact that a weak magnetic field can be measured means that the distance and interval between the permanent magnet and the optical magnetic field sensor can be made longer. This means improvement in the degree of freedom and flexibility of arrangement and installation of the optical magnetic field sensor, and suggests the possibility of expanding the field of use of the optical magnetic field sensor.

[0015] The inventors of the present application have obtained the conviction that it is possible to develop a reflection type optical magnetic field sensor using a bismuth-substituted magnetic garnet as a magneto-optical material, that is, a Faraday rotator, based on the above-described examination results and the like. In addition, various basic experiments,
And a development experiment was conducted. The inventors of the present application firstly
Japanese Patent Publication No. 3-22595 Yttrium
A reflection-type optical magnetic field sensor (FIG. 1) was manufactured using bismuth-substituted magnetic garnet instead of iron / garnet (YIG). In FIG. 1, reference numeral 1 denotes a light source made of a semiconductor laser or the like, reference numeral 2 denotes a lens, reference numeral 3 denotes a half mirror that reflects part of incident light and transmits part of the light, reference numeral 4 denotes an optical fiber, and reference numeral 5 denotes distributed refraction. Lenses and signs consisting of rate lenses
6 is a polarizer made of rutile single crystal or the like, 7 is a Faraday rotator made of bismuth-substituted rare earth magnetic garnet,
Reference numeral 8 denotes a reflection film made of a metal thin film or the like, and reference numeral 9 denotes a photodetector (power meter). The signal light emitted from the light source 1 is condensed and guided to an optical fiber 4 via a lens 2 and a half mirror 3. The signal light guided to the optical fiber 4 becomes parallel light by the lens 5 and enters the polarizer 6. The signal light is linearly polarized by the polarizer 6. Next, the linearly polarized signal light enters the Faraday rotator 7 and
Part of the light passes through the Faraday rotator and reaches the reflection film 8. The signal light that has reached the reflection film 8 is reflected on the surface of the reflection film 8 and travels backward, and then enters the Faraday rotator 7 and the polarizer 6 again. Signal light transmitted through the polarizing element 6 (reflection return light)
Is coupled to the optical fiber 4 by the lens 5. The signal light (reflected return light) incident on the optical fiber 4 is incident on the half mirror 3. Part of the signal light (reflected return light) that has entered the half mirror 3 is reflected by the half mirror 3 and reaches the photodetector 9, where the light intensity is measured.

Next, the present inventors adopted a bismuth-substituted magnetic garnet as the Faraday rotator, and varied the intensity of the magnetic field applied to the Faraday rotator using the reflection type optical magnetic field sensor shown in FIG. The experiment of optical signal detection was carried out. However, contrary to the expectations of the present inventors, regardless of whether an external magnetic field is applied, the optical signal is
No detection was possible. Therefore, various basic experiments were performed to determine the reason and cause of the inability to detect the optical signal. As a result, in the reflection-type optical magnetic field sensor shown in FIG. 1, the present inventors use a multi-domain structure having a large number of magnetic domains as the Faraday rotation element, regardless of whether an external magnetic field is applied or not. It was concluded that there was no change in strength.

The experimental and examination results obtained by the inventors of the present application show that Matsumura et al. Used the same multi-domain structure yttrium-iron-garnet (YIG) as bismuth-substituted magnetic garnet as a Faraday rotator. Does not agree with the experimental result [Japanese Patent Publication No. 3-22595, Example]. The present inventors still have bismuth-substituted magnetic garnet, which is the same multi-domain structure as yttrium-iron-garnet (YIG),
It does not function effectively as a Faraday rotation element, and the reason why it did not function is unknown.

The present inventors reexamined the above experimental results in detail and conducted more detailed basic experiments. As a result, it was found that the reflective film, the bismuth-substituted magnetic garnet single crystal film, the polarizer, and the optical input / output device In addition, the optical path for optical input / output of the optical input / output device is divided into two, and the angle formed by the two optical paths of the optical input path and the optical output path separated from each other is set to be 5 degrees or more. -Obtained the knowledge that a reflective optical magnetic field sensor can be configured by arranging it,
After diligent research and study, we completed and proposed a reflection type optical magnetic field sensor using a Faraday rotator made of bismuth-substituted magnetic garnet (Japanese Patent Application No. 4-0990976, see FIG. 2).

In FIG. 2, reference numeral 10 denotes a polarizer such as a polar core (trade name) manufactured by Corning, and reference numeral 11 denotes a Faraday rotation made of a bismuth-substituted magnetic garnet single crystal film having an easy axis of magnetization perpendicular to the film surface. And an external magnetic field is applied thereto. Reference numeral 12 denotes a reflection film made of a dielectric multilayer film or the like, reference numeral 13 denotes an optical waveguide formed on glass or a polymer film, or an optical input path made of an optical fiber, and reference numeral 14 denotes glass. Or an optical waveguide formed on a polymer or an optical output path made of an optical fiber. In the reflection type optical magnetic field sensor having the configuration shown in FIG. 2, the signal light emitted from the light source 16 such as a semiconductor laser is guided to the optical input path 13 via the lens 15. Note that the lens 15 installed here can be omitted and the light source 16 and the light input path 13 can be directly coupled, if desired. The signal light incident on the optical input path 13 reaches the sensor head, passes through the polarizer 10 and the Faraday rotator 11, and reaches the reflection film 12. The signal light reaching the reflection film 12 is reflected by the reflection film.
The light is reflected by the surface 12 and returns to the Faraday rotator 11 and then through the polarizer 10 to be incident on the light output path 14 and the photodetector.
Reaches 17. The signal light that has reached the photodetector 17 is detected as an optical signal. In the reflection type optical magnetic field sensor having the configuration shown in FIG. 2, the optical path for optical input / output of the optical input / output device is divided into two and configured as independent optical input paths 13 and optical output paths 14, respectively. Moreover, the arrangement and configuration are such that the angle α between the input path 13 and the light output path 14 is 5 degrees or more.

The reflection type optical magnetic field sensor using the Faraday rotator made of bismuth-substituted magnetic garnet proposed here is
At present, it has sufficient performance required for the optical magnetic field sensor in the market. However, the reflection type optical magnetic field sensor proposed here requires two optical paths, an optical input path and an optical output path, as shown in FIG. 2, and furthermore, two optical paths, an optical input path and an optical output path. The technical difficulty remains that the optical path must be arranged at an angle of about 5 degrees or more.

Accordingly, the inventors of the present application have been keen to develop a more versatile, smaller, and higher-performance reflective optical magnetic field sensor by improving the room for technical improvement left there. An improved study was performed. As a result, a Faraday rotator made of bismuth-substituted magnetic garnet, a polarizer, and,
The knowledge that the optical signal can be detected even if the two optical paths of the optical input path and the optical output path are integrated into one by arranging it so as to be inclined with respect to the normal or the plane of the reflective film. I got Accordingly, the inventors of the present application have further conducted an improvement study based on the knowledge obtained here, and have replaced the (111) bismuth-substituted magnetic garnet single crystal film with the normal of the bismuth-substituted magnetic garnet single crystal film, in other words. In this case, the angle between the magnetization direction and the central axis of the light input / output path, more specifically, the direction in which the light travels, is set so as to be in the range of 10 to 70 degrees.
When they were arranged, they confirmed that the optical paths could be integrated into one, and proposed a new reflection type optical magnetic field sensor (Japanese Patent Application No. 4-116141). However, in the reflection type optical magnetic field sensor proposed here (Japanese Patent Application No. 4-116141), it was stated that the (111) bismuth-substituted magnetic garnet single crystal film must be installed at a predetermined angle. Technical difficulties remain in the assembly work and in the adjustment operation. Next, the present inventors conducted intensive research experiments to solve the technical difficulties in the assembling work and the adjusting operation, and the [111] axis was in the range of 5 to 60 degrees with respect to the film normal. When composed of a bismuth-substituted magnetic garnet single crystal film tilted in
They found that a high-performance reflective optical magnetic field sensor with a single optical path could be obtained very easily, and proposed it as a reflective optical magnetic field sensor that is easy to assemble and adjust [Japanese Patent Application No. 4-42929]. However, the reflection type optical magnetic field sensor proposed here uses a bismuth-substituted magnetic garnet single crystal film in which the expensive [111] axis is tilted within a range of 5 to 60 degrees with respect to the film normal as a Faraday rotator. It has been found that the need to use it leaves a new problem of poor mass productivity and economic disadvantage. The present inventors conducted various experimental studies to solve the remaining problems, and as a result, as a Faraday rotator, a plurality of [111] axes substantially coincide with the film normal. By using a (111) bismuth-substituted magnetic garnet single crystal film, the Faraday rotator is tilted, or a special bismuth-substituted magnetic garnet single crystal film whose [111] axis is tilted with respect to the film normal is used. It has been confirmed that an optical signal can be detected even if the optical input path and the optical output path are combined into one optical path, and a new reflective optical magnetic field sensor was proposed [Japanese Patent Application No. 4-174357]. However, in industrial production, sometimes extremely rarely, when a Faraday rotator composed of two (111) bismuth-substituted magnetic garnet single crystal films is used, a product that does not function sufficiently as a reflection type optical magnetic field sensor It was known that the trouble of generating was generated. That is, in the reflection type optical magnetic field sensor proposed above (Japanese Patent Application No. 4-174357), there is a possibility or possibility that a product that does not function sufficiently as a reflection type optical magnetic field sensor may be generated. In other words, there is a technical defect. It became clear that there was. Therefore, in order to guarantee the performance and reliability of the previously proposed reflection type optical magnetic field sensor (Japanese Patent Application No. 4-174357), functional tests and performance tests were conducted for all products manufactured here. There must be.

[0022]

Means for Solving the Problems The present inventors have improved the technical deficiencies and defects remaining in the reflection type optical magnetic field sensor proposed by the present inventors, and can immediately measure an accurate rotation speed. Highly reliable, more specifically, compact, lightweight, highly accurate, easy to handle, and able to withstand long-term continuous use in harsh environments with high temperatures and vibration. In addition, by providing an inexpensive tachometer / measuring device, we conducted intensive studies and experiments to contribute to international social demands for global environmental protection and energy saving. As a result, first, the reason that a product that does not function sufficiently as a reflection-type optical magnetic field sensor is mixed into the reflection-type optical magnetic field sensor (Japanese Patent Application No. 4-174357) previously proposed is caused by
It has been found that the optical path and the bismuth-substituted magnetic garnet single crystal film constituting the Faraday rotator have a relative optical positional relationship, that is, the optical fine adjustment / alignment operation is omitted.

As a practical matter, it is not easy to carry out an optical fine adjustment / alignment operation in industrial production of a reflection type optical magnetic field sensor. Accordingly, the inventors of the present application have conducted intensive studies to develop a technology that can replace optical adjustment and alignment operations. As a result, as a Faraday rotator, the bismuth-substituted magnetic garnet single crystal film whose [111] axis is inclined within a range of 1 to 60 degrees with respect to the film normal, and the [111] axis is substantially equal to the film normal Using a Faraday rotator composed of multiple (111) bismuth-substituted magnetic garnets and a (111) bismuth-substituted magnetic garnet single crystal film Were found to be able to be substantially avoided, and further intensive studies were made, and experiments for confirming reliability and test production were carried out, thereby completing the present invention. That is, the present invention is an optical magnetic field measuring device arranged in the order of the light input / output path, the polarizer, the Faraday rotator, and the reflection film, wherein the reflection film is
Bismuth is disposed substantially perpendicular to the optical path center of the optical input / output path, and the Faraday rotator has its [111] axis inclined within a range of 1 to 60 degrees with respect to the film normal. It is composed of multiple (111) bismuth-substituted magnetic garnet single-crystal films and a (111) bismuth-substituted magnetic garnet single-crystal film whose [111] axis substantially coincides with the film normal line. A reflection type optical magnetic field sensor head.

The reflection type optical magnetic field sensor head using the Faraday rotator made of bismuth-substituted magnetic garnet according to the present invention has an optical input / output path, a polarizer, and a [111] axis whose angle is 1 to 60 degrees with respect to the film normal. Multiple (111) bismuth-substituted magnetism of bismuth-substituted magnetic garnet single crystal film tilted within the range and (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis is substantially coincident with the film normal It is composed of a garnet single crystal film and a reflective film (see FIGS. 3 and 4).

The reflection type optical magnetic field sensor head of the present invention comprises
From the light source device side, a light input / output path, a polarizer, a Faraday rotator made of a plurality of bismuth-substituted magnetic garnet single crystal films, and a reflection film are arranged in this order (see FIG. 3). That is,
3, reference numeral 18 denotes a polarizer made of a polar core or the like, reference numeral 19 denotes a Faraday rotator made of a plurality of bismuth-substituted magnetic garnet single crystal films, reference numeral 20 denotes a reflection film made of a metal thin film or the like, Reference numeral 21 denotes an optical input / output path composed of an optical fiber, an optical waveguide, or the like. Here, from the viewpoint of miniaturization of the reflection type optical magnetic field sensor head, the light input / output path 21 is an optical path for light input, and at the same time, the signal light reflected by the reflection film 20 is incident on the photodetector. It is needless to say that the function may be provided (see FIG. 9).

In a reflection type optical magnetic field sensor using a bismuth-substituted magnetic garnet single crystal film having a multi-domain structure as a Faraday rotator, an optical signal emitted from an optical input / output path is a lens, a polarizer, and a bismuth-substituted magnetic garnet single crystal. A different magnetic domain, that is, a magnetic domain a, is transmitted through the crystal to the reflective film, reflected by the reflective film, again incident on and transmitted through the bismuth-substituted magnetic garnet single crystal, and reaches the optical input / output path. And magnetic domains
b (see Japanese Patent Application Nos. 4-090976 and 4-
116141, Japanese Patent Application No. 4-174357, and FIGS. 5, 6, and 7].

The reflection type optical magnetic field sensor previously proposed [Japanese Patent Application No. Hei.
4-174357] Sometimes, though very rarely, there are products that do not function sufficiently as a reflection-type optical magnetic field sensor because the optical signal emitted from the optical input / output path depends on the optical positional relationship. , Through the lens, polarizer, and bismuth-substituted magnetic garnet single crystal, to the reflective film, reflected by the reflective film, again entering the bismuth-substituted magnetic garnet single crystal, transmitting, and reaching the optical input / output path Between, different magnetic domains,
That is, the magnetic domain a and the magnetic domain b may not pass through (see FIG. 7).

[111] axis substantially coincides with the film normal
In the Faraday rotator composed of only the (111) bismuth-substituted magnetic garnet single crystal film, the magnetization direction is parallel to the traveling direction of the signal light, as illustrated in FIG. Therefore, for example, in order for the signal light incident on the magnetic domain a of the first layer to pass through a different magnetic domain, that is, the magnetic domain b, the signal light must be placed on the straight line of the optical path as the second layer or the third layer or later. Magnetic domain
b must be present. This means that in the Faraday rotator having the configuration shown in FIG. 7, bismuth replacement is required to ensure that the optical signal emitted from the optical input / output path passes through different magnetic domains, that is, magnetic domain a and magnetic domain b. This shows that there is no method other than increasing the number of stacked magnetic garnet single crystals. In practice, from an economic perspective,
The number of stacked bismuth-substituted magnetic garnet single crystals cannot be increased. Therefore, without increasing the number of stacked bismuth-substituted magnetic garnet single crystals, the optical signal emitted from the optical input / output path is reflected by the reflective film and again reaches the optical input / output path. If it is possible to pass through different magnetic domains, that is, magnetic domain a and magnetic domain b, with higher probability and accuracy, it can be evaluated as an industrial manufacturing technique replacing optical fine adjustment / alignment operation.

In the present invention, the Faraday rotator is represented by [1
11] A bismuth-substituted magnetic garnet single crystal film whose axis is tilted within the range of 1 to 60 degrees with respect to the film normal, and [111]
By using a (111) bismuth-substituted magnetic garnet single crystal film whose axis substantially coincides with the film normal (see FIG. 4), the Faraday rotator can be tilted or complicated fine adjustment operations can be performed. Without this, the effect of making the incidence of defective products occurring in industrial production equal to or less than the allowable limit and substantially zero can be obtained. That is, in the present invention, the optical signal emitted from the optical input / output path is converted into a bismuth-substituted magnetic garnet single crystal film whose [111] axis is inclined within a range of 1 to 60 degrees with respect to the film normal. By passing through a Faraday rotator composed of a (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis is substantially coincident with the film normal,
It is intended to pass through different magnetic domains, that is, magnetic domain a and magnetic domain b, with higher probability and accuracy. This will be described more specifically with reference to FIGS. 3 and 4.
The optical signal emitted from the optical input / output path 21 is converted into a first bismuth-substituted magnetic garnet single crystal 22 constituting the Faraday rotator 19, for example, when the [111] axis substantially coincides with the film normal. Incident on the (111) bismuth-substituted magnetic garnet single crystal film and permeate through the magnetic domain a, and then the second bismuth-substituted magnetic garnet single crystal 23, for example, the [111] axis is 1 degree to 1 degree with respect to the film normal. Through the magnetic domain b of the bismuth-substituted magnetic garnet single crystal film tilted within the range of 60 degrees, the reflection film 20 is formed.
During the reciprocation in the Faraday rotator while being incident on the second bismuth-substituted magnetic garnet single crystal 23 again with higher probability and accuracy, substantially different magnetic domains, that is, magnetic domains. It passes through a and magnetic domain b.

In practicing the present invention, the Faraday rotator is a bismuth-substituted magnetic material in which the same or different types of [111] axes are inclined in the range of 1 to 60 degrees with respect to the film normal. It must be composed of a garnet single crystal film and a (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis is substantially coincident with the film normal. However, the bismuth-substituted magnetic garnet single crystal film in which the [111] axis is tilted within the range of 1 to 60 degrees with respect to the film normal, and the [111] axis substantially coincides with the film normal ( 111) Bismuth-substituted magnetic garnet single-crystal film, except for the configuration, such as which one is arranged on the light source side or combination, and (111) Bismuth-substituted magnetic garnet single-crystal film The number is not particularly limited. Therefore, when practicing the present invention, the type, configuration, and number of the bismuth-substituted magnetic garnet single crystal films constituting the Faraday rotator may be appropriately selected in consideration of the performance and characteristics required for the Faraday rotator. .

In the case of an optical magnetic field sensor head used for general applications, the same, from the viewpoint of practical use, that is, from the viewpoint of the performance and characteristics of the Faraday rotator and the material cost,
[111] a bismuth-substituted magnetic garnet single crystal film whose axis is tilted within the range of 1 to 60 degrees with respect to the film normal,
The object can be sufficiently achieved by using two (111) bismuth-substituted magnetic garnet single crystal films whose axes substantially coincide with the film normal. In the case of having a special purpose, it is preferable to appropriately increase the number of components or to select a bismuth-substituted magnetic garnet single crystal having a three-layer structure grown on both sides of a nonmagnetic garnet substrate.

In practicing the present invention, the composition of the Faraday rotator, that is, the bismuth-substituted magnetic garnet is not particularly limited, but may be represented by the general formula: R _3-X Bi _X Fe _{5- Z} AZO ₁₂ [where , R are Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, at least one selected from the group of Lu, A is at least one selected from the group of Ga, Sc, Al, In, and 0.3 ≦ X ≦ 2.0, 0 ≦ Z ≦
1.0] is suitably selected from magnetic garnet single crystals represented by the formula:

The (111) bismuth-substituted magnetic garnet single crystal film used in the present invention can be produced by a known method. In particular, the liquid phase epitaxial (LPE) method (Shin Solid
Films (Thin Solid Films), Vol.114, p33 (1984)
] Is preferred. When the liquid phase epitaxial method is performed, any known substrate can be used as a substrate for growing a single crystal. However, generally, the lattice constant, which is already commercially available as an SGGG substrate, is 12.490 μm. , Or, 1
2.515 非 non-magnetic garnet [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ]
It is preferable to appropriately select from the above.

[111] axis substantially coincides with the film normal
The (111) bismuth-substituted magnetic garnet single crystal film is a commercially available non-magnetic garnet substrate ([111] axis substantially coincides with the normal line) as a single crystal growing substrate.
It is obtained by growing and growing a bismuth-substituted magnetic garnet single crystal film on a single crystal growth substrate by a liquid phase epitaxial (LPE) method.

The [111] axis of the (111) bismuth-substituted magnetic garnet single crystal film, in other words, the axis of easy magnetization is γ from the film normal.
In order to incline the substrate, a nonmagnetic substrate whose [111] axis is inclined by approximately γ from the normal may be used as a substrate for growing a single crystal. A bismuth-substituted magnetic garnet single crystal film in which the [111] axis is tilted within a range of 1 to 60 degrees with respect to the film normal is used to grow a single crystal nonmagnetic garnet substrate in which the [111] axis is tilted from the normal. It is obtained by growing and growing a bismuth-substituted magnetic garnet single crystal film on a single crystal growth substrate by a liquid phase epitaxial (LPE) method. [111] of the bismuth-substituted magnetic garnet single crystal obtained here
The axis is equal to or greater than the substrate for growing a single crystal.

[111] A non-magnetic substrate whose axis is inclined by γ degrees from the normal is obtained by cutting the ingot by inclining it at a desired inclination angle γ. [111] As the tilt angle γ from the axis normal increases, the number of substrates obtained from the ingot decreases, and the price of the substrates increases. Therefore, it is preferable that the inclination angle γ from the normal line of the [111] axis be selected to a value close to the necessary minimum in consideration of economy from a practical viewpoint. In practicing the present invention, the inclination angle γ of the (111) bismuth-substituted magnetic garnet single crystal film from the normal of the [111] axis is in the range of 1 to 60 degrees, more preferably 3 to 45 degrees. It is better to choose within the range. From a practical point of view, in particular, when economics is important, 3 degrees to 20 degrees
You can choose it at any time. [111] The tilt angle γ from the axis normal is 1
When selected below degrees, the [111] axis is tilted with respect to the membrane normal
No clear effect can be confirmed by using the (111) bismuth-substituted magnetic garnet single crystal film. That is, multiple
It cannot be distinguished from the case of using a (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis substantially coincides with the film normal. On the other hand, if the inclination angle γ from the normal line of the [111] axis is set to 45 degrees or more, particularly 60 degrees or more, it is economically disadvantageous.

In practicing the present invention, the spatial arrangement / combination of the bismuth-substituted magnetic garnet single crystal film is such that the [111] axis is tilted within the range of 1 to 60 degrees with respect to the film normal. Using a garnet single-crystal film and a (111) bismuth-substituted magnetic garnet single-crystal film whose [111] axis substantially coincides with the film normal, a configuration corresponding to the magnetic domain pattern and magnetic domain width of the single-crystal film surface , There is no particular limitation. Also,
Here, the bismuth-substituted magnetic garnet single crystal film in which the [111] axis is inclined within a range of 1 to 60 degrees with respect to the film normal, has a plurality of [111] axes that are 1 to the film normal. Degree to 6
A bismuth-substituted magnetic garnet single crystal film tilted within a range of 0 degrees is laminated, or a [111] axis of a three-layer structure grown on both surfaces of a non-magnetic garnet substrate has one [111] axis with respect to the film normal. Bismuth-substituted magnetic garnet single crystal tilted in the range of from 60 to 60 degrees, or bismuth-substituted magnetic garnet single crystal film in which the [111] axis is tilted in the range of from 1 to 60 degrees with respect to the film normal And a bismuth-substituted magnetic garnet single crystal having a three-layer structure grown on both sides of a nonmagnetic garnet substrate and having a [111] axis inclined within 1 to 60 degrees with respect to the film normal. May be used.

Furthermore, the [111] axis referred to here substantially coincides with the film normal. In the (111) bismuth-substituted magnetic garnet single crystal film, a plurality of [111] axes substantially coincide with the film normal. [111] axis of (111) bismuth-substituted magnetic garnet single crystal films that are consistent with each other, or the three-layer structure grown on both sides of a nonmagnetic garnet substrate has the [111] axis substantially equal to the film normal. Matching bismuth-substituted magnetic garnet single crystals,
Or the [111] axis is substantially coincident with the membrane normal
A (111) bismuth-substituted magnetic garnet single crystal film and a bismuth-substituted magnetic garnet single crystal whose three-layer structure grown on both sides of a nonmagnetic garnet substrate and whose [111] axis substantially coincides with the film normal are appropriately used. May be laminated.

That is, in the case of a bismuth-substituted magnetic garnet film in which the magnetic domain pattern on the surface has a linear shape, the magnetic patterns are closely adhered so that the linear patterns intersect, or are overlapped with a space provided (see FIG. 8). Is good. Further, bismuth-substituted magnetic garnets having different magnetic domain widths may be closely adhered to each other, or may be overlapped with a space. However, in the case of a bismuth-substituted magnetic garnet film having the same magnetic domain width, and the magnetic domain pattern on the surface is a maze pattern, the magnetic domains overlap when they are brought into close contact with each other. More specifically, they need to be placed approximately 400 μm apart. With this configuration, the difference ΔP in the optical signal strength required for detecting the magnetic field by the optical magnetic field sensor is at least 2 dB or more [Japanese Patent Application No. 4-90976].
Can be achieved.

In practicing the present invention, the tilt angle of the bismuth-substituted magnetic garnet single crystal film with respect to the optical path is not particularly limited. When the influence of the reflection on the surface of the bismuth-substituted magnetic garnet single crystal is large, it is preferable to arrange the bismuth-substituted magnetic garnet single crystal at an appropriate inclination in order to prevent the reflected light from returning directly to the light input / output path. . If the antireflection film is applied to the bismuth-substituted magnetic garnet single crystal and the surface reflection is sufficiently suppressed,
From the viewpoint of assembling and adjusting work, it is convenient and preferable to dispose it in a state almost perpendicular to the optical path.

In practicing the present invention, the polarizer does not need to be particularly special, and may be appropriately selected and used from those generally commercially available as desired. However, the point that the thickness is thin and the extinction ratio is high,
In particular, dichroic polarizers are preferred.

In practicing the present invention, the reflective film is not particularly limited. Metal thin film mirrors / mirrors obtained by depositing metal on glass or the like, which are generally commercially available, or bismuth-substituted magnetic garnet thin films, or gold,
Alternatively, it may be appropriately selected from a metal thin film mirror on which aluminum or the like is vapor-deposited, or a dielectric multilayer mirror made of a multilayer film of a metal oxide such as SiO ₂ or TiO _{2 as} desired.

In practicing the present invention, the optical input / output path does not need to be particularly special, and is usually patterned into an optical fiber that is generally commercially available, or glass or a polymer film base material. It may be appropriately selected from the existing optical waveguide, the aerial propagation path, and the like as desired. In general, it is generally preferable to select an optical fiber from the viewpoint of mass productivity and miniaturization.

When forming an optical input / output path with an optical fiber,
There is no particular limitation on the type of optical fiber used, and the like. However, the core diameter of the optical fiber used here is 50 μm
When selected below, the influence of the magnetic domain width of the bismuth-substituted magnetic garnet may appear to make the sensitivity unstable or reduce the light coupling efficiency. Therefore, in general, the purpose can be sufficiently achieved by appropriately selecting from commercially available optical fibers having a core diameter of 50 μm or more.

When carrying out the present invention, the reflection type of the present invention is used.
Coupling the optical magnetic field sensor head with the light source and the photodetector
Is a method using the half mirror shown in FIG. 1, and
Or figure9Optical waveguide and optical coupler as exemplified in
And so on using a signal light splitter.
Figure9At the sign26Is a light source composed of a semiconductor laser, etc.
To the sign27And sign30And sign31Is a fiber optic28
Is an optical waveguide formed on glass or polymer
To the sign29Is a polarizer and multiple bismuth-substituted magnetic
The optical magnetic field sensor head consisting of32
Means a photodetector (power meter). In addition,
Figure if desired9All of the optical fibers shown in
Or, omitting a part of it, in other words, using an optical fiber
Without use, for example, reflective optical magnetic field
The sensor head may be directly connected.

The wavelength of the light source of the optical magnetic field measuring apparatus is selected in consideration of the sensitivity of the Faraday rotator, the light transmittance, the performance and price of the light source, the sensitivity of the detector, and the like.
When practicing the present invention, the wavelength of the light source is as follows: bismuth-substituted magnetic garnet has a region having a relatively small light absorption coefficient called a window; bismuth-substituted rare-earth magnetic garnet has a large Faraday rotation coefficient; bismuth-substituted magnetic garnet Film thickness of 30 to 100μ
・ High-power short-wavelength semiconductor lasers and light-emitting diodes are commercially available at low cost. ・ The sensitivity of the photodetector is high and the wavelength is 780 nm to 850 nm. It is preferred to choose near infrared light. As a next best measure, it is also possible to select light in the wavelength band of 1300 nm and 1550 nm that is practically used in optical fiber communication, or in the wavelength band of 1060 nm where a YAG laser can be used. However, if the wavelength of the light source is
If the ratio is outside the above range, light absorption becomes large, or an obstacle such as a decrease in the Faraday rotation coefficient of the bismuth-substituted magnetic garnet appears, so that it becomes difficult to detect the signal light or the film thickness of the Faraday rotator. Therefore, various problems such as the necessity of increasing the thickness are caused.

Hereinafter, the present invention will be described by way of representative examples.
The embodiments and effects will be described specifically and in detail, but the following examples are for illustrative purposes only and are not intended to limit the embodiments and the scope of the invention. It has not been.

[0048]

【Example】

 Example 1 Manufactured by the Czochralski method according to a conventional method
1 inch (111) garnet single crystal [(GdCa)_Three(GaMgZr)_Five
O₁₂, Ingot] [Lattice constant 12.498 ± 0.002Å]
 [112] Cut at an angle of 5 degrees in the axial direction and make the [111] axis normal.
Single crystal growth of thickness 490-510 μm inclined 5 degrees
Substrate [a₁]. Similarly, the [111] axis is substantially the same as the normal
480-500 μm thick substrate for growing single crystals
[b] was obtained. Platinum oxide [Pb
O, 4N] 843 g, bismuth oxide [Bi_TwoO _Three, 4N] 978 g, oxidation
Ferrous iron [Fe_TwoO_Three, 4N], 128 g, boron oxide [B_TwoO_Three, 5N] 38
g, terbium oxide [Tb_FourO₇, 3N] 4.0g and oxidation
Holmium [Ho_TwoO_Three, 3N] 9.0g. This is precise
Place it in place in a vertical tubular electric furnace and heat to 1000 ° C
Melt, mix well and mix thoroughly, then melt
Bismuth-substituted magnetic garnet cooled to 768 ° C
A melt for growing a single crystal was obtained. Then, according to the usual method,
The substrate for growing a single crystal [a₁],and,
Immerse the substrate [b] and maintain the melt temperature at 768 ° C.
0.5 hours of epitaxial growth to grow a single crystal
[111] axis is tilted 5 degrees to the film normal on both sides of the substrate
Ho_1.1Tb_0.6Bi_1.3Fe_FiveO₁₂Ho with single crystal film_1.1Tb
_0.6Bi_1.3Fe_FiveO ₁₂Single crystal [hereinafter, HoTbBiIG single crystal [A₁Abbreviated
And the [111] axis substantially coincides with the film normal.
Ho_1.1Tb_0.6Bi_1.3Fe_FiveO₁₂Ho with single crystal film_1.1
Tb_0.6Bi_1.3Fe_FiveO₁₂Single crystal [hereinafter, HoTbBiIG single crystal [B₁]When
Abbreviations]. HoTbBiIG single crystal obtained here
[A₁] Is 12μm on one side, 24μm on both sides,
Faraday rotation angle θ in the saturated state_FIs the wavelength 786
It was 22.2 degrees in nm and the saturation field was 1000 Oe. Ma
The HoTbBiIG single crystal obtained here [B₁] Is 13μ on one side
m, thickness of both sides is 26 μm, and magnetization is saturated
Faraday rotation angle θ_FIs 23.1 degrees at a wavelength of 786 nm.
The saturation magnetic field was 1000 Oe.

On one HoTbBiIG single crystal surface of the obtained HoTbBiIG single crystal [A ₁ ], aluminum was deposited by a vapor deposition method to form a reflective film, ie, a mirror, and then the other HoTbBiIG single crystal surface Then, after applying an antireflection film by a usual method, a predetermined size (2.5 mm × 2.5 mm)
To obtain a HoTbBiIG single crystal [A ₁ ] -reflection film block. Next, an anti-reflection film is applied on both sides of the HoTbBiIG single crystal film of the HoTbBiIG single crystal [B ₁ ] by an ordinary method, and then cut into a predetermined size [2.5 mm × 2.5 mm] to cut the HoTbBiIG single crystal [B 1]. ₁ ] obtained a piece.

Subsequently, the HoTbBiIG single crystal [B ₁ ] piece obtained here was used as a HoTbBiIG single crystal [A ₁ ] -reflection film block.
The Faraday rotator-reflection film block was obtained by bringing the film into close contact with the surface of the HoTbBiIG single crystal film, fixing it with a commercially available optical adhesive, and joining it.

From the Faraday rotator-reflection film block obtained here, five were randomly selected, and their H
oTbBiIG A single crystal [B ₁ ] film, on the surface of which is attached a polarizer having an antireflection film [Corning Co., Polar core], fixed with an epoxy adhesive and joined, the polarizer-
A Faraday rotator [A ₁ -B ₁ ] -reflection film block was obtained. A polymer clad optical fiber having a core diameter of 400 μm was attached to the obtained polarizer-Faraday rotator-reflection film block as an optical input / output path to obtain an optical magnetic field sensor head.

The obtained optical magnetic field sensor head was attached to the optical magnetic field sensor head terminal of a reflection type optical magnetic field sensor (see FIG. 1). The tip of the optical magnetic field sensor head was installed at a predetermined position of a magnetic field application device (MAGNET, MAGNET). While variously changing the application state of the magnetic field of the optical magnetic field sensor head, a light source (semiconductor laser, manufactured by Sharp Corporation,
Product name: Semiconductor laser, LT024MD / PD type)
m, and the signal light was made incident on the above-mentioned optical magnetic field sensor head via a lens, a half mirror, and an optical input / output path (an optical fiber having a core diameter of 400 μm). Then, the light is reflected by the optical magnetic field sensor head, and again, a part of the optical signal emitted from the optical fiber is reflected by the half mirror, and the light is detected by a photodetector (manufactured by Ando Electric Co., trade name: power meter, AQ-1111
Mold], and the light intensity of the signal light that reached here was measured. As a result, the magnetic field strength of 1000 F
When the magnetic field was applied, the Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field was applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe was applied to the Faraday rotator was 2.5 dB to 2.6 dB (average value 2.5 dB).

Example 2 Example 1 was repeated except that one side of the single crystal growth substrate [a ₁ ] was brought into contact with the surface of the single crystal growth melt to perform epitaxial growth for 1.0 hour. In the same manner, Ho _1.1 Tb _0.6 Bi _1.3 Fe was applied to one side of the substrate [a ₁ ] for growing a single crystal.
_{5 O 12 Ho 1.1 Tb 0.6 Bi} 1.3 Fe 5 O 12 single crystal having a single crystal film was obtained [hereinafter, HoTbBiIG monocrystalline abbreviated as [A _2]]. The thickness of the HoTbBiIG single crystal [A ₂ ] obtained here was 23 μm. The Faraday rotation angle θ _{F in} a state where the magnetization was saturated was 21.7 degrees at a wavelength of 786 nm. On the surface of the substrate [a ₁ ] of the obtained HoTbBiIG single crystal [A ₂ ], aluminum is deposited by an evaporation method to form a reflection film, ie, a mirror, and then the HoTbBiIG single crystal is formed according to a conventional method.
After applying an anti-reflection film on the surface of [A ₂ ], cut into a predetermined size [2.5 mm × 2.5 mm] and cut HoTbBiIG single crystal [A ₂ ] −
A reflective film block was obtained.

The HoTbBiIG single crystal [A_Two]-Anti
Five randomly selected from the film blocks
HoTbBiIG single crystal obtained in Example 1 [B₁] One piece of HoTbBiIG
Crystal [A _Two]-HoTbBiIG single crystal of reflective film block [A_Two] On the membrane surface
Adhere, fix using commercial optical adhesive and join
I let it. Then, HoTbBiIG single crystal [B₁] Reflection on the surface of the film
Polarizer with anti-reflection coating [Polar, manufactured by Corning Incorporated
Core], fix with epoxy adhesive and join
The polarizer-Faraday rotator [A_Two-B₁]-Reflective film
Got a lock. Polarizer obtained here-Faraday rotator
-400μm core diameter as a light input / output path in the reflective film block
Optical magnetic field sensor with polymer clad optical fiber
Got the head.

The obtained optical magnetic field sensor head was attached to the optical magnetic field sensor head terminal of the test apparatus used in Example 1, and an evaluation test was performed in the same manner as in Example 1. As a result, when a magnetic field strength of 1000 Oe was applied to the Faraday rotator, the Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field is applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe is applied to the Faraday rotator is 2.8 to 3.0 dB (average value).
2.9 dB).

Example 3 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by inclining the ingot 3 degrees in the [112] axis direction
Substrate for single crystal growth with [111] axis inclined at 3 degrees to normal
Except for using [a ₃ ], an optical magnetic field sensor head was manufactured in the same manner as in Example 1, and an evaluation test was performed in the same manner as in Example 1. As a result, when applying a magnetic field of field strength 1000 Oe to Faraday rotator [A ₃ -B _1], Faraday rotator was magnetically saturated. In addition, when no magnetic field is applied to the Faraday rotator, the magnetic field intensity is applied to the Faraday rotator.
The difference in light intensity from the state where a magnetic field of 000 Oe was applied was 2.2 dB to 2.5 dB (average 2.3 dB).

Example 4 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot at an angle of 10 degrees in the [112] axis direction
A magneto-optical sensor head was manufactured in the same manner as in Example 1 except that the substrate [a ₄ ] for growing a single crystal whose [111] axis was inclined by 10 degrees with respect to the normal was used. An evaluation test was performed in the same manner. As a result, when applying a magnetic field of field strength 1000 Oe to the Faraday rotator [A ₄ -B _1], Faraday rotator was magnetically saturated. In addition, when no magnetic field is applied to the Faraday rotator,
The light intensity difference from the state where a magnetic field of 1000 Oe is applied is 2.8 dB
To 3.3 dB (average 3.0 dB).

Example 5 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot at an angle of 20 degrees in the [112] axis direction
An optical magnetic field sensor head was manufactured in the same manner as in Example 1 except that the substrate [a ₅ ] for growing a single crystal whose [111] axis was inclined by 20 degrees with respect to the normal was used. An evaluation test was performed in the same manner. As a result, when applying a magnetic field of field strength 1000 Oe in the Faraday rotator [A ₅ -B _1], Faraday rotator was magnetically saturated. In addition, when no magnetic field is applied to the Faraday rotator,
The light intensity difference from the state where a 1000 Oe magnetic field is applied is 3.0 dB
To 3.4 dB (average value 3.2 dB).

Example 6 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot at an angle of 40 degrees in the [112] axis direction
An optical magnetic field sensor head was manufactured in the same manner as in Example 1 except that the substrate [a ₆ ] for growing a single crystal whose [111] axis was inclined by 40 degrees with respect to the normal was used. An evaluation test was performed in the same manner. As a result, when a magnetic field strength of 1,000 Oe was applied to the Faraday rotator [A ₆ -B ₁ ], the Faraday rotator was magnetically saturated. In addition, when no magnetic field is applied to the Faraday rotator,
3.6dB light intensity difference from 1000 Oe magnetic field applied
From 4.1 to 4.1 dB (average 3.8 dB).

Example 7 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot at an angle of 60 degrees in the [112] axis direction
An optical magnetic field sensor head was manufactured in the same manner as in Example 1 except that the substrate [a ₇ ] for growing a single crystal whose [111] axis was inclined 60 degrees with respect to the normal was used. An evaluation test was performed in the same manner. As a result, when a magnetic field strength of 1000 Oe was applied to the Faraday rotator [A ₇ -B ₁ ], the Faraday rotator was magnetically saturated. In addition, when no magnetic field is applied to the Faraday rotator,
The light intensity difference from the state where a magnetic field of 1000 Oe is applied is 3.3 dB
To 3.5 dB (average value 3.4 dB).

Example 8 Platinum oxide [PbO, 4N] 843 was placed in a platinum crucible having a capacity of 500 ml.
g, bismuth oxide [Bi_TwoO_Three, 4N] 978 g, ferric oxide [Fe_TwoO
_Three , 4N] 120 g, gallium oxide [Ga_TwoO_Three , 4N] 4.5g, oxidation
Boron [B_TwoO_Three, 5N] 38g, gadolinium oxide [Gd_TwoO_Three ,
3N] 6.5 g and yttrium oxide [Y_TwoO_Three, 3N] 4.0g
Was charged. This is placed in the specified position of the precision vertical tubular electric furnace.
Install, heat to 1000 ° C, melt, stir well, uniform
After cooling to 773 ° C,
This was used as a melt for growing a mass-substituted magnetic garnet single crystal. Next
Then, according to a conventional method, the melt obtained here was added to Example 1
The obtained single crystal growth substrate [b] is immersed, and the melt temperature is set to 773 ° C.
0.7 hours of epitaxial growth while maintaining
Y on both sides of single crystal growth substrate [b]_0.9Gd_0.9Bi_1.2Fe_Four
.8Ga_0.2O₁₂Y with single crystal [YGdBiGaIG single crystal] film
_0.9Gd_0.9Bi_1.2Fe_4.8Ga_0.2O ₁₂Single crystal (hereinafter YGdBiGaIG
Single crystal [B_Two]] Film was obtained. YGd obtained here
BiGaIG single crystal [B_Two] Is 16μm on one side and 32μ on both sides
m, the Faraday rotation angle θ in a state where the magnetization is saturated_F
Was 24.4 degrees at a wavelength of 786 nm. The saturation magnetic field is
 It was 600 Oe. Then, according to a conventional method, YGdBiGaIG
Single crystal [B_Two] After applying anti-reflective coating on both sides
And cut to a size of [2.5 mm x 2.5 mm], and the YGdBiGaIG single crystal [B
_Two] I got a piece.

From the YGdBiGaIG single crystal [B ₂ ] pieces obtained here, five pieces were randomly selected, and the H
The oTbBiIG single crystal [A ₁ ] -adhered to the HoTbBiIG single crystal film surface of the reflective film block, and fixed and bonded using a commercially available optical adhesive. Then, on the surface of the YGdBiGaIG single crystal [B ₂ ] film, a polarizer provided with an anti-reflection film (Polycore, manufactured by Corning Corporation) was attached, fixed with an epoxy-based adhesive, and joined to form a polarizer. Faraday rotator [A ₁ -B ₂ ]
-A reflective film block was obtained. A polymer clad optical fiber having a core diameter of 400 μm was attached to the obtained polarizer-Faraday rotator-reflection film block as an optical input / output path to obtain an optical magnetic field sensor head.

The obtained optical magnetic field sensor head was used as a reflection type optical magnetic field sensor composed of an optical splitter [200S-D2 type, manufactured by Mitsubishi Gas Chemical Co., Ltd.]
9 ] (Optical fiber with core diameter of 200 μm)
Attached to. The tip of the optical magnetic field sensor head was installed at a predetermined position of a magnetic field application device (MAGNET, MAGNET). A laser beam with a wavelength of 0.786 μm is made incident from the light source while changing the applied state of the magnetic field of the optical magnetic field sensor head in various ways, and reaches the photodetector (power meter, AQ-1111, manufactured by Ando Electric Co., Ltd.) The light intensity of the obtained signal light was measured. As a result, when a magnetic field strength of 1,000 Oe was applied to the Faraday rotator, the Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field is applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe is applied to the Faraday rotator is 3.5 dB to 3.8 dB (average value).
3.7 dB).

Example 9 In Example 8, the HoTbBiIG single crystal obtained in Example 1 [A
₁ ] -HoTbBiI obtained in Example 3 instead of the reflective film block
An evaluation test was performed in the same manner as in Example 8 except that a G single crystal [A ₃ ] -reflection film block was used. As a result, when applying a magnetic field of field strength 1000 Oe to Faraday rotator [A ₃ -B _2], Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field was applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe was applied to the Faraday rotator was 3.0 dB to 3.5 dB (average 3.3 dB).

Example 10 In Example 8, the HoTbBiIG single crystal obtained in Example 1 [A
₁ ]-HoTbBiI obtained in Example 7 instead of the reflective film block
An evaluation test was performed in the same manner as in Example 8 except that the G single crystal [A ₇ ] -reflection film block was used. As a result, when a magnetic field strength of 1,000 Oe was applied to the Faraday rotator [A ₇ -B ₂ ], the Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field was applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe was applied to the Faraday rotator was 2.7 dB to 3.1 dB (average value 2.8 dB).

Example 11 First, a lead oxide [PbO, 4] was placed in a platinum crucible having a capacity of 500 ml.
N] 843 g, bismuth oxide [Bi ₂ O ₃ , 4N] 978 g, secondary oxide
120 g of iron [Fe ₂ O ₃ , 4N], gallium oxide [Ga ₂ O ₃ , 4N] 4.
5 g, boron oxide [B ₂ O ₃ , 5N] 38 g, gadolinium oxide [Gd ₂ O ₃ , 3N] 6.5 g, and yttrium oxide [Y
₂ O ₃ , 3N] 4.0 g. This is placed at a predetermined position in a precision vertical tubular electric furnace, heated to 1000 ° C and melted, sufficiently stirred and uniformly mixed, and then cooled to a melt temperature of 773 ° C to remove the bismuth-substituted magnet. This was used as a melt for growing a garnet single crystal. Next, the substrate [a ₁ ] for growing a single crystal obtained in Example 1 was immersed in the melt obtained here according to a conventional method, and epitaxial growth was performed for 0.7 hours while maintaining the melt temperature at 773 ° C. On both sides of the substrate for growing a single crystal.
1] The axis is tilted 5 degrees to the membrane normal Y _0.9 Gd _0.9 Bi _1.2 F
e _4.8 Ga _0.2 O ₁₂ Y has a single-crystal film _{0.9 Gd 0.9 Bi 1.2 Fe 4 .8} Ga
_{A 0.2} O ₁₂ single crystal (hereinafter abbreviated as YGdBiGaIG single crystal [A ₈ ]) was obtained. The obtained YGdBiGaIG single crystal [A ₈ ]
One side 15 [mu] m, is in 30 [mu] m thick double-sided, the Faraday rotation angle theta _F in a state saturated with magnetization, at a wavelength 786 nm 23.
7 degrees and the saturation field was 600 Oe.

On one YGdBiGaIG single crystal surface of the obtained YGdBiGaIG single crystal [A ₈ ], aluminum is evaporated by an evaporation method to form a reflection film, ie, a mirror, and then the other YGdBiGaIG single crystal surface Then, after applying an antireflection film by a usual method, a predetermined size (2.5 mm × 2.5 mm)
Then, a YGdBiGaIG single crystal [A ₈ ] -reflection film block was obtained. From the YGdBiGaIG single crystal [A ₈ ] -reflection film blocks obtained here, five were randomly selected, and the YGdBiGaIG single crystal [B ₂ ] pieces obtained in Example 8 were placed on the YGdBiGaIG single crystal film surface. They were brought into close contact with each other and fixed and bonded using a commercially available optical adhesive. Then, on the surface of the YGdBiGaIG single crystal [B ₂ ] film, a polarizer provided with an anti-reflection film (Polycore, manufactured by Corning Corporation) was attached, fixed with an epoxy-based adhesive, and joined to form a polarizer. A Faraday rotator [A ₈ -B ₂ ] -reflection film block was obtained. Hereinafter, an optical magnetic field sensor head was manufactured in the same manner as in Example 8, and an evaluation test was performed in the same manner as in Example 8. As a result, the Faraday rotator was magnetically saturated when a magnetic field of 600 Oe was applied to the Faraday rotator [A ₈ -B ₂ ] . In addition, when no magnetic field is applied to the Faraday rotator, the magnetic field strength
The light intensity difference from the state where the 00 Oe magnetic field is applied is 4.5 dB or less.
It was 4.6 dB (average value 4.6 dB).

Comparative Example 1 One HoT of the HoTbBiIG single crystal [B ₁ ] obtained in Example 1
On the surface of bBiIG single crystal, aluminum is deposited by an evaporation method to form a reflection film, that is, a mirror, and then the other is formed.
HoTbBiIG An antireflection film is applied to the surface of the single crystal according to a conventional method, and cut into a predetermined size (2.5 mm × 2.5 mm).
bBiIG single crystal [B ₁ ] -reflection film block was obtained. From the HoTbBiIG single crystal [B ₁ ] -reflection film block obtained here,
HoTbBiIG obtained in Example 1 by selecting 5 randomly
The single crystal [B ₁ ] piece was brought into close contact with the HoTbBiIG single crystal [B ₁ ] film surface, and fixed and bonded using a commercially available optical adhesive.
Next, on the surface of the HoTbBiIG single crystal [B ₁ ] film, a polarizer with an anti-reflection film [Corning Corporation, Polar Core] was attached, fixed with an epoxy adhesive, and joined.
Polarizer - Faraday rotator [B ₁ - B _1] - was obtained reflective film blocks. A polymer clad optical fiber having a core diameter of 400 μm was attached to the obtained polarizer-Faraday rotator-reflection film block as an optical input / output path to obtain an optical magnetic field sensor head. Next, an evaluation test was performed in the same manner as in Example 1. As a result, a magnetic field strength of 1 is applied to the Faraday rotator [B ₁ - B ₁ ].
When a magnetic field of 000 Oe was applied, the Faraday rotator was magnetically saturated. The light intensity difference between the state where no magnetic field is applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe is applied to the Faraday rotator is 1.7 dB to 2.1 dB.
(Average value 1.8 dB).

Comparative Example 2 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot by tilting it in the [112] axis direction once.
Substrate for single crystal growth with [111] axis tilted by 1 degree with respect to normal
Except for using [a ₁₀ ], an optical magnetic field sensor head was manufactured in the same manner as in Example 1, and an evaluation test was performed in the same manner as in Example 1. As a result, the Faraday rotator was magnetically saturated when a magnetic field of 1,000 Oe was applied to the Faraday rotator [A ₁₀ -B ₁ ]. In addition, when no magnetic field is applied to the Faraday rotator,
1.8dB light intensity difference from 1000 Oe magnetic field applied
To 2.1 dB (average value 2.0 dB).

Comparative Example 3 In Example 1, when cutting the substrate for growing a single crystal,
Obtained by cutting the ingot at an angle of 65 degrees in the [112] axis direction
An optical magnetic field sensor head was manufactured in the same manner as in Example 1 except that the substrate [a ₁₁ ] for growing a single crystal whose [111] axis was tilted 65 degrees with respect to the normal was used. An evaluation test was performed in the same manner. As a result, the Faraday rotator was magnetically saturated when a magnetic field strength of 1000 Oe was applied to the Faraday rotator [A ₁₁ -B ₁ ]. The light intensity difference between the state where no magnetic field is applied to the Faraday rotator and the state where a magnetic field strength of 1000 Oe is applied to the Faraday rotator is 3.2
It was between dB and 3.5 dB (average value 3.3 dB).

Comparative Example 4 In Example 8, the HoTbBiIG single crystal [A ₁₀ ] obtained in Comparative Example 2 was used instead of the HoTbBiIG single crystal [A ₁ ] -reflection film block.
-An optical magnetic field sensor head was manufactured in the same manner as in Example 8 except that the reflective film block was used, and an evaluation test was performed in the same manner as in Example 1. As a result, the Faraday rotator [A
₁₀ -B ₂ ] when a magnetic field strength of 1000 Oe is applied
The Faraday rotator was magnetically saturated. The light intensity difference between a state where no magnetic field was applied to the Faraday rotator and a state where a magnetic field strength of 1000 Oe was applied to the Faraday rotator was 1.8 dB to 2.1 dB (average value 2.0 dB).

[0072]

According to the present invention, a small and lightweight reflective optical magnetic field sensor head can be manufactured and provided industrially very easily using a magneto-optical material having a multi-domain structure.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a configuration of a reflection type optical magnetic field sensor disclosed in Japanese Patent Publication No. 3-22595.

FIG. 2 is a schematic diagram showing a configuration of a reflection type optical magnetic field sensor disclosed in Japanese Patent Application No. 4-90976.

FIG. 3 is a schematic diagram for specifically explaining the basic configuration of the reflection type optical magnetic field sensor head of the present invention.

FIG. 4. The [111] axis of the present invention is tilted with respect to the film normal
A Faraday rotator composed of a (111) bismuth-substituted magnetic garnet single crystal film and a (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis substantially coincides with the film normal,
FIG. 3 is a schematic diagram illustrating a relationship between an optical path, a position of a magnetic domain, and a magnetization direction when the optical path is arranged perpendicular to an optical input / output path (optical path).

FIG. 5. The [111] axis is substantially coincident with the membrane normal.
1) When the Faraday rotator made of a bismuth-substituted magnetic garnet film is arranged at an angle with respect to the optical input / output path (optical path, optical axis), the optical path (optical axis), the normal line, the position of the magnetic domain, the magnetization direction, and the like. It is a schematic diagram which shows the relationship of.

[FIG. 6] A Faraday rotator made of a (111) bismuth-substituted magnetic garnet film whose [111] axis is inclined with respect to the film normal is arranged perpendicular to the optical input / output path (optical path, optical axis). FIG. 4 is a schematic diagram showing a relationship among an optical path (optical axis), a normal, a position of a magnetic domain, and a magnetization direction at the time.

FIG. 7 shows how a Faraday rotator made of a (111) bismuth-substituted magnetic garnet single crystal film whose two [111] axes substantially coincide with the film normal is moved with respect to an optical input / output path [optical path]. It is a schematic diagram which shows the relationship between the optical path at the time of arrange | positioning perpendicularly, the position of a magnetic domain, and a magnetization direction.

FIG. 8 is a schematic diagram showing an example of a Faraday rotator in which bismuth-substituted magnetic garnet films having a linear magnetic domain pattern on the surface are stacked.

FIG. 9 is a schematic diagram showing an example of the entire configuration of a photomagnetic field sensor using the reflection type photomagnetic field sensor head of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Lens 3 ... Half mirror 4 ... Optical fiber 5 ... Lens 6 ... Polarizer 7 ... Faraday rotator 8 ... Reflection film 9 ... Photodetector 10 ... Polarizer 11 ... Faraday rotator 12 ... Reflection film 13 ... Light input path 14 ... Light output path 15 ... Lens 16 ... Light source 17 ... Photodetector 18 Polarizer 19 Faraday rotator 20 Reflective film 21 Optical input / output path 22 Bismuth-substituted magnetic garnet 23 Bismuth-substituted magnetic garnet 24 Bismuth-substituted magnetic garnet 25 Bismuth-substituted magnetic garnet 26 Light source 27 Optical fiber 28 Optical waveguide 29 Optical magnetic field sensor head 30 Optical input / output path 31 Light Fa Iva 32: photodetector

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-146858 (JP, A) JP-A-55-76327 (JP, A) JP-A-5-172917 (JP, A) JP-A-6-127 18639 (JP, A) JP-A-5-333124 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (6)

(57) [Claims] An optical input / output path, a polarizer, a Faraday rotator,
In the optical magnetic field measuring device arranged in the order of the reflection film, the reflection
The film is arranged substantially perpendicular to the optical path center of the light input / output path, and the Faraday rotator is tilted so that its [111] axis is tilted within a range of 1 degree to 60 degrees with respect to the film normal. (111) bismuth-substituted magnetic garnet single crystal film with (111) bismuth-substituted magnetic garnet single crystal film whose [111] axis is substantially coincident with the film normal 1. A reflection type optical magnetic field sensor head comprising: 2. The method according to claim 1, wherein the polarizer, the Faraday rotator, and the reflection film have a (111) garnet single crystal substrate therebetween, or
2. The reflection-type optical magnetic field sensor head according to claim 1, wherein the reflection-type optical magnetic field sensor head is integrally formed without being interposed. 3. A bismuth-substituted magnetic garnet single crystal film whose [111] axis is inclined within a range of 1 to 60 degrees with respect to the film normal, and a [111] axis is a film normal. And (111) bismuth-substituted magnetic garnet single-crystal films substantially corresponding to (111) bismuth-substituted magnetic garnet single-crystal films.
And a reflection type optical magnetic field sensor head according to claim 2. 4. A Faraday rotator comprising: a bismuth-substituted magnetic garnet single crystal film whose [111] axis is inclined within a range of 3 to 45 degrees with respect to the film normal; 4. The reflection-type optical magnetic field sensor head according to claim 1, wherein the magnetic head comprises a (111) bismuth-substituted magnetic garnet single crystal film substantially corresponding to the above. . 5. The method according to claim 5, wherein the [111] axis is from 1 degree to 6 degrees
The (111) bismuth-substituted magnetic garnet single crystal film, which is tilted within the range of 0 degrees or whose [111] axis substantially coincides with the film normal, is formed of the (111) garnet single crystal substrate. 4. The reflection type optical magnetic field sensor head according to claim 1, wherein the reflection type magnetic field sensor head is a (111) bismuth-substituted magnetic garnet single crystal having a three-layer structure grown and formed on both sides. 6. A Faraday rotator having two different chemical compositions.
6. The reflection type optical magnetic field according to claim 1, wherein the reflection type optical magnetic field is formed by laminating at least two types of bismuth-substituted magnetic garnet single crystal films. The sensor head.