JP3114765B2 - Optical magnetic field sensor - 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 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 that detects the strength of a magnetic field that is small and lightweight and that can be easily mass-produced.

[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 or a rotating portion. Due to the progress of science and technology and the increasing social demands for global environmental protection and energy saving, industrial equipment, such as aircraft and ships, consumer equipment,
For example, attempts have been made to implement control of passenger cars and the like with higher altitude and higher precision.
In order to realize more sophisticated and high-precision control of a rotating device / rotating device, its rotation speed [number] must be continuously and accurately measured. To that end, it is necessary to first respond to social demands by developing a simple and lightweight measuring device that can measure the rotation speed more accurately, providing it inexpensively and in large quantities. .

As a method for measuring the rotational speed [number], a method using electromagnetic induction [sensor technology, 1986, 12
Monthly Issue, 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 (1989)) ] Has been proposed.

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 that a transmission line (cable) between the measurement terminal and the device body is susceptible to electromagnetic noise. In addition, since an electric circuit is used, a flammable substance such as an organic solvent, that is, a facility that handles dangerous substances, in other words,
Dangerous goods factories and hazardous materials handling plants have a serious problem that they must implement explosion-proof measures.

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, page 70 (1983), see FIG. 1].

In FIG. 1, reference numeral 1 denotes a light source made of a semiconductor laser or the like, reference numeral 2 denotes a polarizer made of calcite or the like, and reference numeral 3
Is a Faraday rotator made of a magneto-optical material such as zinc selenide, and 4 is an analyzer made of calcite or the like. Light source 1
The light (signal light) emitted from the light enters the polarizer 2.
The signal light transmitted through the polarizer 2 is linearly polarized light having a plane of polarization aligned in one direction. The signal light transmitted through the polarizer 2, that is, the linearly polarized light enters the Faraday rotator 3. The polarization plane of the light transmitted through the Faraday rotator 3 rotates by θ _F according to the external magnetic field Hex due to the Faraday effect. The light transmitted through the Faraday rotator 3 is then
The light enters the analyzer 4 and is transmitted. Now, polarizer 2 and analyzer 4
Is expressed as φ, and the inclination angle of the polarization plane of the light transmitted through the Faraday rotator 3 is expressed as θ _F , the intensity P of the light [signal light] transmitted through the analyzer 4 becomes P = k · cos ² (φ−θ _F ) (1) In the equation (1), k is a proportional constant. Now, suppose that the inclination angle φ between the polarizer 2 and the analyzer 4 is 45 degrees [φ
= 45 °], equation (1) can be rewritten as P = k · (1 + sin2θ _F ) / 2 (2) When the inclination angle θ _F of the polarization plane of the transmitted light is sufficiently small, Equation (2) can be approximated as P = k · (1 + 2θ _F ) / 2 (3). Equation (3) shows that polarizer 2 and analyzer
By setting the inclination angle between 4 to 45 degrees, the inclination angle of the polarization plane of the transmitted light, i.e., the light intensity proportional to the rotation angle theta _F is obtained, in other words, polarization caused by the external magnetic field Hex This means that the wavefront rotation angle θ _F can be detected and measured by the analyzer 4 as light intensity.

Various types and configurations of optical magnetic field sensors have already been proposed, but they can be broadly classified into a transmission type and a reflection type. In the transmissive configuration, due to the nature of the components, the signal light must be arranged and arranged so that the directions of incidence and transmission of the signal light are aligned (see FIG. 1). It is easy to understand that it cannot be installed or adopted depending on the purpose of use and the installation location, without having to explain it again.

[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]. FIG. 2 is a drawing (JP-A-56-55811) showing a configuration of a reflection type optical magnetic field sensor head proposed by Matsui et al. In FIG. 2, signal light is guided from an optical fiber 5a to a polarizer 7 made of rutile single crystal or the like via a lens 6a. The signal light transmitted through the polarizer 7 enters the Faraday rotator 8 and reaches the right-angle prism 9, is reflected by the right-angle prism 9, and enters the Faraday rotator 8 again. The signal light transmitted through the Faraday rotator 8 is
And transmitted through the optical fiber, and the optical fiber on the output side by the lens 6b
It is incident on 5b and reaches the photodetector.

In the reflection type optical magnetic field sensor, as shown in FIG. 2, the input optical fiber and the output optical fiber for the signal light are on the same side with respect to the Faraday rotator 8, in other words, for the output. The optical fiber is in the same direction as the input optical fiber,
In other words, the Faraday rotator 8 is disposed and installed at the tip of the optical magnetic field sensor. 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. However, the reflection type optical magnetic field sensor proposed by Matsui et al., As shown in FIG. 2, has a lens 6a and a polarizer 7, and a lens 6b and an analyzer 10 as shown in FIG.
Must be arranged in series and in parallel, so that it is difficult to automate the assembling work, and therefore, there remains a serious problem that it is difficult to reduce the manufacturing cost.

Matsumura et al. (Japanese Patent Publication No. 3-22595) disclose a method of solving the problem of the reflection type optical magnetic field sensor head proposed by Matsui et al. By replacing the polarizer 7 and the analyzer 10 with one polarizer. A configuration (see FIG. 3) is proposed.

In FIG. 3, reference numeral 11 denotes a light source made of a semiconductor laser or the like, reference numeral 12 denotes a lens, reference numeral 13 denotes a half mirror that reflects part of incident light and transmits part of the light, reference numeral 14 denotes an optical fiber, and reference numeral 15 Is a polarizer made of rutile single crystal, etc.
16 is a Faraday rotator made of a magneto-optical material, 17 is a reflection film made of a metal thin film or the like, and 18 and 19 are photodetectors (power meters). The signal light emitted from the light source 11 is condensed and guided to the optical fiber 14 via the lens 12 and the half mirror 13. A part of the signal light incident on the half mirror 13 is reflected by the half mirror 13 and guided to the optical path 1. By installing the photodetector 18 in the optical path 1,
The fluctuation of the intensity of the signal light emitted from the light source 11 can be measured. The signal light guided to the optical fiber 14 is a polarizer
15 and through the Faraday rotator 16 to reach the reflective film 17. The signal light that has reached the reflection film 17 is reflected by the reflection film 17, travels backward, and enters the Faraday rotator 16 and the polarizer 15 again. The signal light (reflected return light) transmitted through the polarizer 15 enters the optical fiber. The signal light (reflected return light) that has entered the optical fiber 14 enters the half mirror 13. The signal light (reflected return light) incident on the half mirror 13 is reflected by the half mirror 13, guided to the optical path 2, reaches the photodetector 19, and the light intensity is measured.

[0012]

[Problems to be solved by the invention] Matsumura et al.
5] is Yttrium / Iron / Garnet (chemical structural formula: Y ₃ Fe ₅ O ₁₂ ) as a Faraday rotator [magneto-optical material]
Is used. Yttrium / iron / garnet (chemical structural formula: Y ₃ Fe ₅ O ₁₂ ) is generally called YIG and can be easily produced by a known method such as a melt method.
Yttrium / Iron / Garnet (YIG) has traditionally been
Paramagnetic glass and cells that have been used as Faraday rotators
When the Faraday effect is large compared to zinc lenide (ZnSe), etc.
It has such excellent characteristics. Therefore, the proposal by Matsumura et al.
In other words, yttrium, iron, and garnet (YIG)
Proposal for use as Faraday rotator in optical magnetic field sensor
The idea is to make the reflective optical magnetic field sensor head even smaller and higher
It can be said that this is one of the ways to improve performance.

[0013] Yttrium, iron and garnet (YIG)
The proposal for use as a Faraday rotator in a reflection type optical magnetic field sensor can be said to be a very interesting proposal in terms of its characteristics . However, yttrium, iron, garnet (Y
When considering the properties and characteristics of IG) regarding the light transmittance, there arises a question about the practicality of the magneto-optical sensor as a magneto-optical material, that is, 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, semiconductor lasers (LDs) and light emitting diodes (LEDs) having a center wavelength of 0.78 μm to 0.85 μm are generally used as light sources for optical sensors. 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.

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 is shown that yttrium / iron / garnet (YIG) has fundamental defects / defects in physical properties and properties required for a magneto-optical material for an optical magnetic field sensor, that is, a Faraday rotator.

The inventors of the present application had strong interest and apprehension in Matsumura et al.'S proposal. Accordingly, the present inventors have conducted various studies on methods for 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,
I found that possibility. Bismuth-substituted magnetic garnet can be manufactured relatively easily by liquid phase epitaxy (LPE) and is excellent in mass productivity. Bismuth-substituted magnetic garnet has the chemical formula (RBi) ₃ (FeA) ₅ O
Represented by ₁₂ . Here, R means yttrium Y or a rare earth element, and A means aluminum Al, gallium Ga or the like.

The Faraday rotation coefficient of 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.

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. 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. 3) was manufactured using bismuth-substituted magnetic garnet instead of iron / garnet (YIG), and an optical signal detection experiment was performed while changing the magnetic field strength variously. However, regardless of the presence or absence of the application of an external magnetic field, no optical signal could be detected or detected. 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. 3, when the multi-domain structure having a large number of magnetic domains is used as the Faraday rotator, the inventors of the present application can control the light regardless of whether an external magnetic field is applied. It was concluded that there was no change in strength.

The results of the experiments and examinations of the present inventors obtained here show that Matsumura et al. Used the same multi-domain structure of yttrium-iron-garnet (YIG) as bismuth-substituted magnetic garnet as a Faraday rotator. Does not agree with the experimental results of [3-22595, Example]. The inventors of the present application do not yet understand why yttrium / iron / garnet (YIG), a bismuth-substituted magnetic garnet having the same multi-domain structure, does not function effectively as a Faraday rotator or does not function.

The present inventors reexamined the above experimental results in detail and conducted more detailed basic experiments. As a result, the reflection film, the (111) bismuth-substituted magnetic garnet single crystal film, the polarizer, the light input It is composed of an output device, and furthermore, 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 separated optical input path and optical output path becomes 5 degrees or more. That the reflection type optical magnetic field sensor can be configured by setting and arranging it in such a way, and further intensive research and study were conducted, and a reflection type optical magnetic field sensor using a bismuth-substituted magnetic garnet Faraday rotator And proposed [Japanese Patent Application No. 4-90976, FIG. 4].

In FIG. 4, reference numeral 20 denotes a polarizer such as a polar core (trade name) of Corning, and reference numeral 21 denotes a Faraday rotation made of a (111) 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 22 denotes a reflection film made of a dielectric multilayer film or the like, reference numeral 23 denotes an optical waveguide formed on glass or a polymer, or an optical input path made of an optical fiber, and reference numeral 24 denotes a glass or high It means an optical waveguide formed on a molecule or an optical output path composed of an optical fiber.
In the reflection type optical magnetic field sensor having the configuration shown in FIG. 4, signal light emitted from a light source 26 such as a semiconductor laser is guided to an optical input path 23 via a lens 25 (the lens 25 is omitted and the optical input path 23 is omitted). And the light source 26 can be directly coupled). The signal light incident on the optical input path 23 reaches the sensor head, passes through the polarizer 20 and the Faraday rotator 21, and passes through the reflection film.
Reaches 22. The signal light that has reached the reflection film 22 is reflected by the reflection film 22 and returns, passes through the Faraday rotator 21, and then passes through the polarizer 20, enters the light output path 24, reaches the photodetector 27, and Is detected as That is, in the reflection type optical magnetic field sensor having the configuration of FIG. 4, the optical path for optical input / output of the optical input / output device is divided into two, and the independent optical input path 23 and independent optical output path 24 are provided.
The optical input path 23 and the optical output path
24 are arranged and configured such that the angle α formed by them becomes 5 degrees or more.

The reflection type optical magnetic field sensor using the Faraday rotator made of bismuth-substituted magnetic garnet proposed here is
Currently, it has sufficient performance required for optical magnetic field sensors. 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. 4, and furthermore, two optical paths, an optical input path and an optical output path. This leaves technical difficulties and room for improvement, such that the light path must be positioned at an angle of about 5 degrees or more.
That is, in the reflection type optical magnetic field sensor proposed here, it is difficult to reduce the tip portion of the optical magnetic field sensor, that is, the diameter of the probe to 5 mm or less due to the configuration conditions. Therefore, like a cylinder with a diameter of several millimeters drilled at the center of the rotating shaft of a gyro or turbine,
It cannot be used for measuring a magnetic field in a very narrow place.
If the distance between the probe (optical magnetic field sensor head) and the installation location of the photodetector (magnetic field measuring device) is long, the cost of the optical fiber may become a problem.

[0024]

DISCLOSURE OF THE INVENTION The present inventors have developed a bismuth-substituted magnetic material which can be manufactured relatively easily by a liquid phase epitaxy (LPE) method and has excellent various optical characteristics. Develop a more versatile, smaller, and higher-performance reflective optical magnetic field sensor that solves the problems and problems left behind in a reflective optical magnetic field sensor using a garnet Faraday rotator. In order to do so, we conducted intensive improvement research. As a result, a Faraday rotator made of bismuth-substituted magnetic garnet, a polarizer, and the normal of the reflection film,
Alternatively, by arranging the optical path inclining with respect to the plane, the knowledge that an optical signal can be detected even when the two optical paths of the optical input path and the optical output path are combined into one is obtained.
The present inventor has completed the present invention by making improvements.

The reflection type optical magnetic field sensor head using the bismuth-substituted magnetic garnet Faraday rotator of the present invention comprises an optical input / output path, a polarizer, a bismuth-substituted magnetic garnet single crystal film (Faraday rotator), and a reflection film. It is configured. Here, the bismuth-substituted magnetic garnet single crystal film used as the Faraday rotator is (1)
11) Bismuth-substituted magnetic garnet single crystal film.

The reflection type optical magnetic field sensor head of the present invention is
From the light source device side, the light input / output path, the polarizer, the bismuth-substituted magnetic garnet single crystal film (Faraday rotator), the reflection film, in other words, from the tip of the optical magnetic field sensor head,
A reflection film, a bismuth-substituted magnetic garnet single crystal film, a polarizer, and an optical input / output path are arranged in this order (see FIG. 5). Further, the bismuth-substituted magnetic garnet single crystal film as the Faraday rotator is a normal line of the bismuth-substituted magnetic garnet single crystal film, in other words, the magnetization direction and the optical axis of the optical input / output path,
In other words, the angle between the light and the traveling direction is 10 degrees to 7 degrees.
It is set to be within the range of 0 degrees.

That is, in FIG. 5, reference numeral 28 denotes a polarizer made of a polar core or the like, and reference numeral 29 denotes a (111) bismuth-substituted rare earth magnetic element disposed at an angle β from the normal to the optical path (axis). A Faraday rotator (see FIG. 6) made of a garnet single crystal film, reference numeral 30 denotes a reflection film made of a gold thin film or the like, and reference numeral 31 denotes a light input / output path made 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 31 is an optical path for light input, and at the same time, the signal light reflected by the reflection film 30 is incident on the photodetector. Needless to say, a function of branching / separating the data may be provided.

As described above, in the reflection type optical magnetic field sensor using the bismuth-substituted magnetic garnet single crystal film having the multi-domain structure as the Faraday rotator, the optical signal emitted from the optical input / output path 31 is used for the bismuth-substituted magnetic garnet. The light passes through the single crystal 29 to reach the reflection film 30, is reflected by the reflection film 30, and again,
It is necessary to pass through different magnetic domains, that is, magnetic domain a and magnetic domain b, before entering and transmitting the bismuth-substituted magnetic garnet single crystal 29 and reaching the optical input / output path 31. In the present invention, as illustrated in FIG. 6, this purpose is achieved by tilting the Faraday rotator 29, that is, the bismuth-substituted magnetic garnet single crystal 29, so that the light travel direction, that is, a certain angle with respect to the optical axis. Is achieved by having

In the detection of the magnetic field by the optical magnetic field sensor, the reflected light returned from the reflection surface other than the reflection film, more specifically, the surface of the polarizer or the surface of the bismuth-substituted magnetic garnet single crystal, and the light intensity of the light source. optical signal intensity, the optical signal intensity of the consideration of the influence of fluctuation, and when the time for magnetic field sensor head is not applied and the magnetic field is applied bismuth-substituted iron garnet single crystal is magnetically substantially saturated It is known that a difference ΔP of at least 2 dB is required [Japanese Patent Application No. 4-90976].

When practicing the present invention, the difference Δ
P becomes 2 dB or more when the inclination angle β between the normal line of the (111) bismuth-substituted magnetic garnet single crystal film and the optical axis of the light input / output path is selected to be 10 degrees or more. The difference ΔP in optical signal intensity increases as the inclination angle β between the normal to the (111) bismuth-substituted magnetic garnet single crystal film and the optical axis of the optical input / output path increases. However, if the inclination angle β is too large, the signal light is totally reflected on the surface of the bismuth-substituted magnetic garnet single crystal, or the light returning from the reflection film due to the increase in the distance between the light entrance / exit path and the reflection film. Problems such as weakening of the signal occur. Therefore, the inclination angle β between the normal line of the (111) bismuth-substituted magnetic garnet single crystal film and the optical axis of the optical input / output path is in the range of 10 ° to 70 °, more preferably 20 ° to 45 °. It is preferable to choose.

In practicing the present invention, the polarizer does not need to be particularly special, and may be appropriately selected from those generally commercially available as needed. However, dichroic polarizers are particularly preferred in that they are thin and have a high extinction ratio.

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,
D is at least one selected from the group consisting of Dy, Ho, Er, Tm, Yb, and Lu; and A is at least one selected from the group consisting of Ga, Sc, Al, and In, and 0.3 ≦ X <2.0, 0 ≦ Z ≦
1.0] is suitably selected from magnetic garnet single crystals represented by the formula:

The bismuth-substituted magnetic garnet single crystal of the present invention can be produced by a known method. In particular, the liquid phase epitaxial (LPE) method, which is easy to operate and excellent in mass productivity ( Sin Solid Films (Thin Solid Films )
Solid Films) , Vol. 114, p33 (1984)]. When the liquid phase epitaxial method is performed, any known substrate may be used as the substrate, but generally, a lattice constant already commercially available as an SGGG substrate has a lattice constant of 12.490 mm or less. It may be appropriately selected from nonmagnetic garnet [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ] of 12.515%.

In practicing the present invention, the non-magnetic substrate for forming a bismuth-substituted magnetic garnet thin film does not need to be particularly removed. Rather, when the thickness of the bismuth-substituted magnetic garnet single crystal film is very small, several tens of μm, it is preferable to leave the substrate as a support in terms of strength. On the other hand, when the thickness of the bismuth-substituted magnetic garnet is as large as several hundred μm, it is not necessary to use it as a support in terms of strength.

In practicing the present invention, the reflective film is not particularly limited. Metal thin film mirrors / mirrors in which metal is generally deposited on glass or the like, which are generally commercially available, or bismuth-substituted magnetic garnet thin films, or gold, or metal thin film mirrors in which aluminum is deposited on the surface of a nonmagnetic substrate, or It may be appropriately selected as desired from a dielectric multilayer mirror composed of a multilayer film of a metal oxide such as SiO ₂ or TiO ₂ .

In practicing the present invention, the light input / output path does not need to be particularly special, and is usually formed by patterning a commercially available optical fiber or glass or 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, an optical fiber can be preferably used particularly 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. But,
If the core diameter of the optical fiber used here is selected to be 50 μm or less, the influence of the magnetic domain width of the bismuth-substituted magnetic garnet may appear and the sensitivity may become unstable, or the light coupling efficiency may decrease. Therefore, generally, it is generally sufficient to appropriately select from commercially available optical fibers having a core diameter of 50 μm or more.

When the present invention is carried out, the reflection type magnetic field sensor head using the Faraday rotator made of bismuth-substituted magnetic garnet of the present invention, the light source, and the photodetector are connected by the half mirror shown in FIG. The method is performed by using a signal light splitter such as an optical waveguide or an optical coupler as illustrated in FIG. In addition,
If desired, all or a part of the optical fiber shown in FIG. 7 is omitted, in other words, without using an optical fiber, for example, a reflection type optical magnetic field sensor head is directly connected to an optical waveguide. You may.

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.
In practicing the present invention, the wavelength of the light source is such that the bismuth-substituted magnetic garnet has a region having a relatively small light absorption coefficient called a window, and the Faraday rotation coefficient of the bismuth-substituted rare-earth magnetic garnet is large. Is 30 to 100μ
High-output short-wavelength semiconductor lasers and light-emitting diodes are commercially available at low cost.The sensitivity of photodetectors is high, and the near-infrared light with a wavelength of 780 to 850 nm is available. It is preferable to select external light. As a next best measure, it is also possible to select light in the wavelength band of 1300 nm and 1550 nm which 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 deviates from the above range, light absorption increases, or an obstacle such as a decrease in the Faraday rotation coefficient of the bismuth-substituted magnetic garnet appears, which makes it difficult to detect signal light. And / or a problem that the thickness of the Faraday rotator must be increased is not preferred.

Hereinafter, the present invention will be described specifically and in detail with reference to examples, but the following examples are for the purpose of specifically explaining the present invention, and It is not intended to limit aspects or the scope of the invention.

[0041]

Embodiment 1 FIG. 8 shows the overall configuration of this embodiment, which is almost the same as FIG. That is, in FIG. 8, reference numeral 39 denotes a semiconductor laser of 0.786 μm, reference numeral 40 denotes a lens, reference numeral 41 denotes a half mirror, reference numeral 42 denotes a photodetector, reference numeral 43 denotes an optical fiber having a core diameter of 400 μm, reference numeral 44 denotes a lens, and reference numeral 45 denotes Is a glass polarizer (trade name: polar core) manufactured by Corning Incorporated, reference numeral 46 is a Faraday rotator having a tilt angle β of 10 degrees with respect to the optical path of the normal, and reference numeral 47 is a reflection film formed by depositing a metal aluminum thin film on the glass surface. The Faraday rotator 46 was manufactured by the following method. In a platinum crucible with a capacity of 500 ml, 843 g of lead oxide (PbO, 4N)
, Bismuth oxide [Bi ₂ O ₃ , 4N] 978 g, ferric oxide [Fe ₂
O _3, 4N] 128 g, boron oxide [B ₂ O _3, 5N] 38 g, terbium oxide [Tb ₄ O _7, 3N] 4.0 g, oxide ho le Miumu [Ho ₂ O _3,
3N] 9.0 g. This was placed at a predetermined position in a precision vertical tubular electric furnace, heated and melted at 1000 ° C, sufficiently stirred and mixed uniformly, and then cooled to a melt temperature of 770 ° C to obtain a bismuth-substituted magnetic garnet single crystal. A melt for growth was used. On the surface of the melt obtained here, a thickness of 480μ
m and a lattice constant of 12.497 ± 0.002Å
11) One side of a garnet single crystal [(GdCa) ₃ (GaMgZr) ₅ O ₁₂ ) ₃ ] substrate is brought into contact with the substrate while maintaining the melt temperature at 770 ° C.
The epitaxial growth was performed for 2.0 hours. The obtained crystal was a (111) bismuth-substituted magnetic garnet single crystal film having a composition of Ho _1.1 Tb _0.6 Bi _1.3 Fe ₅ O ₁₂ [(HoTbBiIG) single crystal], and its film thickness was 46 μm. . Also,
The Faraday rotation angle θ _{F in} a state where the magnetization was saturated was 42.5 ° at a wavelength of 786 nm. Further, an antireflection film was applied to both end faces of the optical fiber 43, the lens 44, the polarizer 45, and the Faraday rotator 46. The optical signal intensity difference was measured as follows. The light [signal light] emitted from the light source 39 is passed through a lens 40.
To the optical fiber 43, and then the optical fiber 43
The light emitted from the lens was irradiated through a lens 44 onto a sensor head including a polarizer 45, a Faraday rotator 46, and a reflection film 47. Then, a part of the optical signal returned from the sensor head was reflected by the half mirror 41 and received by the photodetector 42 to measure the light intensity. As a result, the difference in light intensity between the state in which no magnetic field was applied to the sensor head and the state in which a magnetic field of 1500 (Oe) sufficient to magnetically saturate the Faraday rotator was 2.5 dB.

Embodiment 2 The same construction as in Embodiment 1 was adopted except that the inclination angle β of the normal line of the Faraday rotator 46 to the optical path in Embodiment 1 was set to 20 degrees. As a result, the difference in light intensity between the state where no magnetic field was applied to the sensor head and the state where a magnetic field 1500 (Oe) sufficient to magnetically saturate the Faraday rotator was applied was 4.9 dB.

Embodiment 3 The same construction as in Embodiment 1 was adopted except that the inclination angle β of the normal line of the Faraday rotator 46 to the optical path in Embodiment 1 was set to 30 degrees. As a result, the difference in light intensity between the state where no magnetic field was applied to the sensor head and the state where a magnetic field 1500 (Oe) sufficient to magnetically saturate the Faraday rotator was applied was 5.9 dB.

COMPARATIVE EXAMPLE 1 The structure of the Faraday rotator 46 was the same as that of the first embodiment except that the inclination angle β of the Faraday rotator 46 with respect to the optical path was 5 degrees. As a result, the difference in light intensity between the state where no magnetic field is applied to the sensor head and the state where a magnetic field 1500 (Oe) sufficient to magnetically saturate the Faraday rotator is applied is as follows:
It was 1.1 dB.

[0045]

According to the present invention, a magneto-optical sensor that uses a magneto-optical material having a multi-domain structure to detect the strength of a magnetic field and that can be mass-produced at a small size, light weight, and low cost is provided. can do.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the operating principle of a photomagnetic field sensor using the Faraday effect.

FIG. 2 is a diagram showing a configuration of a reflection type optical magnetic field sensor disclosed in Japanese Patent Application Laid-Open No. 56-55811.

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

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

FIG. 5 is a configuration diagram of an optical magnetic field sensor head according to the present invention.

FIG. 6 is a diagram showing a positional relationship between an optical path and a magnetic domain when a Faraday rotator made of a (111) bismuth-substituted magnetic garnet film is inclined with respect to an optical input / output path.

FIG. 7 is an example of the entire configuration of a photomagnetic field sensor using a photomagnetic field sensor head according to the present invention.

FIG. 8 is an overall configuration diagram of an optical magnetic field sensor according to the first embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Polarizer 3 ... Faraday rotator 4 ... Analyzer 5a ... Optical fiber 5b ... Optical fiber 6a ... Lens 6b ... Lens 7 ... Polarizer 8: Faraday rotator 9: Right angle prism 10: Analyzer 11: Light source 12: Lens 13: Half mirror 14: Optical fiber 15: Polarizer 16・ ・ ・ Faraday rotator 17 ・ ・ ・ Reflection film 18 ・ ・ ・ Photodetector 19 ・ ・ ・ Photodetector 20 ・ ・ ・ Polarizer 21 ・ ・ ・ Faraday rotator 22 ・ ・ ・ Reflection film 23 ・ ・ ・ Light Input path 24: Optical output path 25: Lens 26: Light source 27: Photodetector 28: Polarizer 29: Faraday rotator 30: Reflective film 31: Light Input / output path 32 ・ ・ ・ Optical input / output path 33 ..Optical magnetic field sensor head 34 ... light source 35 ... photodetector 36 ... optical fiber 37 ... optical fiber 38 ... optical waveguide 39 ... light source 40 ... lens 41 ... Half mirror 42 Photodetector 43 Optical fiber 44 Lens 45 Polarizer 46 Faraday rotator 47 Reflective film

Continuation of the front page (56) References JP-A-52-116121 (JP, A) JP-A-62-188982 (JP, A) JP-A-6-102331 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (1)

(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 film is arranged substantially perpendicular to the optical input path, and the Faraday rotator is a (111) bismuth-substituted magnetic garnet single crystal film, and the (111) 3.) A reflection type optical magnetic field sensor, wherein the angle between the normal line of the bismuth-substituted magnetic garnet single crystal film and the light input / output path is 10 degrees or more and 70 degrees or less.