JP2018080077A - Faraday rotator for magnetic field sensors - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Faraday rotator for magnetic field sensors that has high light detection sensitivity even when using a light source with a wavelength of 750 nm or less, and is suitable for making a magnetic field sensor compact in size.SOLUTION: A Faraday rotator 12 for magnetic field sensors is composed of glass containing DyOof 15% (mol%) or more in terms of oxides. A magnetic field sensor 1 has the Faraday rotator 12, a polarizer 11, a light source 10 and a detector 14. The DyOis a component that has a large absolute value of Verdet constant, and improves Faraday effect, and its content is 15% or more, preferably 20% or more, more preferably 25% or more, further more preferably 30% or more, particularly preferably 50%; and in the point of view of vitrification, 75% or less, preferably 70%, particularly preferably 69% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a Faraday rotator for a magnetic field sensor.

  As a sensor for measuring a magnetic field, there is a sensor for measuring a magnetic field by utilizing a Faraday effect in which a polarization plane of propagating light is rotated by the magnetic field. Since the rotation angle of polarized light changes depending on the strength of the magnetic field, the strength of the magnetic field can be measured by detecting the change in the rotation angle of the light.

  There are two types of magnetic field sensors, a reflective type and a transmissive type. The reflection type is formed by arranging a light source and a detector, a polarizer, a Faraday rotator, and a mirror in this order. On the other hand, the transmission type is formed by arranging a light source, a polarizer, a Faraday rotator, an analyzer, and a photodetector in this order.

  Conventionally, rare earth iron garnet crystals represented by YIG (yttrium iron garnet) have been used as Faraday rotators used in such magnetic field sensors (see, for example, Patent Document 1).

Japanese Patent Publication No. 3-22595

  However, in a magnetic field sensor using a Faraday rotator made of a rare earth iron garnet crystal such as YIG, the light detection sensitivity is low when a light source having a wavelength of 750 nm or less, such as a 633 nm He—Ne laser, which is easily available and inexpensive, is used. There was a problem.

  In view of the above, an object of the present invention is to provide a Faraday rotator for a magnetic field sensor having high light detection sensitivity even when a light source having a wavelength of 750 nm or less is used.

The Faraday rotator for a magnetic field sensor according to the present invention is characterized in that it is made of glass containing 15% or more of Dy ₂ O ₃ in terms of mol% of oxide. Since the rare earth iron garnet crystal is 1100 nm or less and has a large absorption derived from iron ions, it cannot transmit light in the visible light region. On the other hand, glass containing Dy ₂ O ₃ has a high transmittance in the range of 450 to 750 nm, and thus is suitable for a magnetic field sensor using a light source having a wavelength of 750 nm or less as described above.

Further, since the rare earth iron garnet crystal is ferromagnetic, there is a problem that magnetic saturation occurs in a strong magnetic field, and the Faraday rotation angle is not proportional to the strength of the magnetic field. On the other hand, since the glass containing Dy ₂ O ₃ used in the present invention is a paramagnetic substance, magnetic saturation does not occur even in a strong magnetic field, and the Faraday rotation angle is proportional to the strength of the magnetic field.

Furthermore, since the Verde constant indicating the performance of the Faraday rotation angle of the material increases as the Dy ₂ O ₃ content increases, the size of the Faraday rotator can be reduced by using glass containing 15 mol% or more of Dy ₂ O ₃ . As a result, the sensor can be miniaturized.

  A magnetic field sensor of the present invention includes the Faraday rotator, polarizer, light source, and detector described above.

  According to the present invention, it is possible to provide a Faraday rotator for a magnetic field sensor having high light detection sensitivity even when a light source having a wavelength of 750 nm or less is used.

It is typical sectional drawing which shows the basic structure of a reflection type magnetic field sensor. It is typical sectional drawing which shows an example of the manufacturing apparatus for producing glass by the containerless floating method. It is a typical sectional view showing the basic structure of a transmission type magnetic field sensor.

  First, the principle and structure of a reflective magnetic field sensor will be described with reference to FIG.

  FIG. 1 is a schematic cross-sectional view showing the basic structure of a reflective magnetic field sensor.

  The reflection type magnetic field sensor 1 is a sensor that detects a change in magnetic field by an optical signal, and includes a light source 10, a polarizer 11, a Faraday rotator 12, and a mirror 13 arranged in this order. Specifically, input light from the light source 10 passes through the polarizer 11, becomes linearly polarized light, and enters the Faraday rotator 12. The incident light is reflected by the mirror 13 provided on the end face of the Faraday rotator 12 to become detection light, passes through the Faraday rotator 12 and the polarizer 11 again, and is detected by the photodetector 14. Since Faraday rotation does not occur in the absence of a magnetic field, it becomes detection light while maintaining the angle of the polarization plane of the input light, and passes through the polarizer 11 without loss of light. When a magnetic field is applied, the angle of the polarization plane of the detection light passing through the Faraday rotator 12 changes, so that light loss occurs when passing through the polarizer 11. Information on the magnitude of the magnetic field can be obtained from the difference in light intensity between the input light and the detection light at this time. In addition, when light enters the Faraday rotator 12, scattering due to the air interface occurs. Therefore, it is preferable to provide an antireflection film 15 on the incident surface.

    Each element will be described below.

(Faraday rotator 12 for magnetic field sensor)
The Faraday rotator 12 for a magnetic field sensor is generally cylindrical and is made of glass containing 15% or more of Dy ₂ O ₃ in terms of mol% of oxide. The reason for limiting the glass composition in this way will be described below. In the following description regarding the content of each component, “%” means “mol%” unless otherwise specified.

Dy ₂ O ₃ is a component that increases the Faraday effect by increasing the absolute value of the Verde constant. The content of Dy ₂ O ₃ is 15% or more, preferably 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 50% or more, and particularly preferably 51% or more. When the content of dy ₂ O ₃ is too small, the absolute value of the Verdet constant is reduced, a sufficient Faraday effect is difficult to obtain. On the other hand, when the content of _Dy 2 _{O 3} is too large, there is a tendency for vitrification tends to be difficult, 75% or less, it is preferable 70% or less, or less, especially 69%.

  In addition to the above components, the glass used in the present invention may contain various components shown below.

B ₂ O ₃ becomes a glass skeleton and is a component that widens the vitrification range. However, since B ₂ O ₃ does not contribute to the improvement of the Verde constant, if the content is too large, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the content of B ₂ O ₃ is preferably 0 to 85%, 0 to 75%, 0 to 60%, 0 to 50%, 1 to 40%, particularly preferably 1 to 35%.

P ₂ O ₅ becomes a glass skeleton and is a component that widens the vitrification range. However, since P ₂ O ₅ does not contribute to the improvement of the Verde constant, if the content is too large, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the content of P ₂ O ₅ is preferably 0 to 85%, 0 to 75%, 0 to 60%, 0 to 50%, 1 to 40%, particularly preferably 1 to 35%.

The total amount of B ₂ O ₃ and P ₂ O ₅ is preferably 0 to 85%, 0 to 75%, 0 to 60%, 0 to 50%, 1 to 40%, particularly preferably 2 to 35%. .

Al ₂ O ₃ is a component that forms a glass skeleton as an intermediate oxide and widens the vitrification range. However, since Al ₂ O ₃ does not contribute to the improvement of the Verde constant, if the content is too large, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the content of Al ₂ O ₃ is 0 to 85%, 0 to 75%, 0.1 to 60%, 0.2 to 50%, 0.5 to 40%, particularly 1 to 35%. preferable.

SiO ₂ becomes a glass skeleton and is a component that widens the vitrification range. However, since SiO ₂ does not contribute to the improvement of the Verde constant, if the content is too large, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the content of SiO ₂ is preferably 0 to 85%, 0 to 75%, 0 to 60%, 0 to 50%, 1 to 40%, particularly preferably 1 to 35%.

La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , and Y ₂ O ₃ have the effect of improving the stability of vitrification. However, if the content is too large, it becomes difficult to vitrify. Therefore, the contents of La ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ and Y ₂ O ₃ are each preferably 10% or less, particularly preferably 5% or less.

Tb ₂ O ₃ , Eu ₂ O ₃ , Ce ₂ O ₃ , and Pr ₂ O ₃ improve the stability of vitrification and contribute to the improvement of the Verde constant. However, when the content is too large, it becomes difficult to vitrify. Therefore, the contents of Tb ₂ O ₃ , Eu ₂ O ₃ , Ce ₂ O ₃ and Pr ₂ O ₃ are each preferably 15% or less, particularly preferably 10% or less. The contents of Tb ₂ O ₃ , Eu ₂ O ₃ , Ce ₂ O ₃ , and Pr ₂ O ₃ are all expressed by converting each component present in the glass into a trivalent oxide.

  MgO, CaO, SrO, and BaO have the effect of increasing the vitrification stability and chemical durability. However, since it does not contribute to the improvement of the Verde constant, if the content is too large, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the content of these components is preferably 0 to 10%, particularly preferably 0 to 5%.

Ga ₂ O ₃ has the effect of increasing the glass forming ability and expanding the vitrification range. However, when there is too much the content, it will become easy to devitrify. Further, since the Ga ₂ O ₃ it does not contribute to the improvement of the Verdet constant, when the content is too large, a sufficient Faraday effect difficult to obtain. Therefore, the Ga ₂ O ₃ content is preferably 0 to 6%, particularly preferably 0 to 5%.

Fluorine has the effect of increasing the glass forming ability and expanding the vitrification range. However, if its content is too large, it may volatilize during melting, causing a compositional change or affecting the stability of vitrification. Therefore, the content of fluorine _{(F 2} equivalent) 0-10%, 0-7%, particularly preferably 0 to 5%.

Sb ₂ O ₃ can be added as a reducing agent. However, the content of Sb ₂ O ₃ is preferably 0.1% or less in order to avoid coloring or in consideration of environmental load.

  The glass used in the present invention exhibits good light transmission in the wavelength range of 450 to 750 nm. Specifically, the transmittance at an optical path length of 1 mm at a wavelength of 633 nm is preferably 60% or more, 65% or more, 70% or more, 75% or more, and particularly preferably 80% or more. Further, the transmittance at an optical path length of 1 mm at a wavelength of 532 nm is preferably 30% or more, 50% or more, 60% or more, 70% or more, and particularly preferably 80% or more.

  The glass used in the present invention can be produced, for example, by a containerless floating method. FIG. 2 is a schematic cross-sectional view showing an example of a production apparatus for producing glass by a containerless floating method. Hereinafter, the manufacturing method of the glass used for this invention is demonstrated, referring FIG.

  The glass manufacturing apparatus 2 has a mold 20. The mold 20 also serves as a melting container. The molding die 20 has a molding surface 20a and a plurality of gas ejection holes 20b opened in the molding surface 20a. The gas ejection hole 20b is connected to a gas supply mechanism 21 such as a gas cylinder. Gas is supplied from the gas supply mechanism 21 to the molding surface 20a via the gas ejection holes 20b. The type of gas is not particularly limited, and may be, for example, air or oxygen, or a reducing gas containing nitrogen gas, argon gas, helium gas, carbon monoxide gas, carbon dioxide gas, or hydrogen. Good.

  When manufacturing glass using the manufacturing apparatus 2, first, the glass raw material lump 22 is arrange | positioned on the molding surface 20a. As the glass raw material block 22, for example, a raw material powder integrated by press molding or the like, a sintered body obtained by integrating raw material powder by press molding or the like, and a composition equivalent to the target glass composition are used. For example, an aggregate of crystals.

  Next, the glass raw material block 22 is floated on the molding surface 20a by ejecting gas from the gas ejection holes 20b. That is, the glass raw material mass 22 is held in a state where it is not in contact with the molding surface 20a. In this state, the glass material block 22 is irradiated with laser light from the laser light irradiation device 23. Thereby, the glass raw material lump 22 is heated and melted to be vitrified to obtain molten glass. Thereafter, the glass can be obtained by cooling the molten glass. In the step of heating and melting the glass raw material mass 22 and the step of cooling until the temperature of the molten glass and further the glass material becomes at least the softening point or less, at least gas ejection is continued, and the glass raw material mass 22, molten glass, Furthermore, it is preferable to suppress contact between the glass material and the molding surface 20a. The glass raw material mass 22 may be floated on the molding surface 20a using a magnetic force generated by applying a magnetic field, or the glass raw material mass 22 is floated on the molding surface 20a using sound waves. Also good. In addition to the method of irradiating laser light, the method of heating and melting may be radiant heating. In addition, the Faraday rotator 4 for a magnetic field sensor of the present invention can be obtained by subjecting the obtained glass to processing such as cutting and polishing to obtain a desired shape.

(Polarizer 11)
The material of the polarizer 11 may be ceramic, glass, or a polymer material, but a material having a large polarization extinction ratio is preferable. Specifically, a material having an extinction ratio of 20 dB or more, 30 dB or more, 40 dB or more, particularly 50 dB or more is preferable.

(Mirror 13)
The mirror 13 is preferably a thin film in order to reduce the size of the magnetic field sensor. In order to increase the reflectance, a metal film or a dielectric multilayer film (a multilayer film in which high refractive index layers and low refractive index layers are alternately stacked) is more preferable. Examples of the metal film include aluminum, gold, silver, copper, platinum, and chromium. Examples of the material constituting the dielectric multilayer film include niobium oxide, titanium oxide, lanthanum oxide, tantalum oxide, yttrium oxide, gadolinium oxide, tungsten oxide, hafnium oxide, aluminum oxide, etc., magnesium fluoride, calcium fluoride, etc. Fluorides, nitrides such as silicon nitride, silicon, germanium, zinc sulfide and the like. As a method for forming the thin film, a vacuum deposition method, an ion plating method, a sputtering method, or the like can be used.

(Antireflection film 15)
An example of the antireflection film 15 is a dielectric multilayer film. The material constituting the dielectric multilayer film and the method for forming the thin film are the same as described above. In addition to the multilayer film, a single layer film made of silicon oxide or the like can be used as the antireflection film.

(Light source 10)
The light source 10 is preferably a 633 nm He—Ne laser that is easily available and inexpensive.

  Next, the principle and structure of the transmission type magnetic field sensor will be described with reference to FIG.

  FIG. 3 is a schematic cross-sectional view showing the basic structure of the transmission magnetic field sensor.

  The transmission type magnetic field sensor 3 is configured by arranging a light source 10, a polarizer 11, a Faraday rotator 12, an analyzer 16, and a photodetector 14 in this order. Specifically, input light from the light source 10 passes through the polarizer 11, becomes linearly polarized light, and enters the Faraday rotator 12. The incident light passes through the Faraday rotator 12 and the analyzer 16 and becomes detection light. Next, the analyzer 16 is rotated, the intensity of the detection light is measured by the photodetector 14, and the rotation angle when the intensity is maximum is measured. Information on the magnitude of the magnetic field can be obtained from the measured rotation angle. In order to prevent light scattering by the air interface, it is preferable to provide an antireflection film 15 on the incident surface and the exit surface of the Faraday rotator 12.

  It may be a transmission type magnetic field sensor arranged in the order of a light source, a polarizer, a Faraday rotator, an analyzer, and a detector, but considering miniaturization, it is possible to use a light source and a detector, a polarizer, a Faraday rotator, a mirror. The constructed reflective magnetic field sensor is preferred.

  The magnetic field sensor of the present invention can be used not only for detecting the magnitude of the magnetic field but also for various applications. For example, switches (open / close switches for refrigerators, personal computers, etc.), current sensors, encoders (positions and rotation detection of motors in automobiles), electronic compass such as smartphones, and pressure, vibration, temperature, impact, deformation, etc. It can be used as a sensor.

  EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, this invention is not limited to these Examples.

Example 1
_{55Dy 2 O 3 -9P 2 O 5} -30B 2 O 3 -6Al 2 O 3 The formulated raw material so that the glass composition (mol%) was press molded, by 6 hours sintered at 700-1400 ° C. A glass raw material lump was produced.

Next, the glass raw material lump was coarsely pulverized using a mortar to obtain small pieces of 0.05 to 1.5 g. Glass (diameter: about 1 to 10 mm) was produced by a containerless floating method using an apparatus according to FIG. A 100 W CO ₂ laser oscillator was used as the heat source. Moreover, oxygen gas was used as gas for suspending a glass raw material lump, and it supplied with the flow volume of 1-30 L / min.

  A cylindrical Faraday rotator having a diameter of 3 mm and a length of 10 mm was obtained by cutting and polishing the obtained glass. Using the obtained Faraday rotator, a reflection type magnetic field sensor was fabricated as shown in FIG.

  An antireflection film was applied to the surface on which the light of the Faraday rotator was incident in order to prevent light scattering, and a dielectric multilayer film was applied to the other surface to provide a function as a mirror.

  While changing the magnetic field intensity, 633 nm light was incident and the light intensity of the detection light was measured. When the light intensity of the detection light in the absence of a magnetic field was 100%, the light intensity when a magnetic field of 1000 Oe was applied was 65%. In a 2000 Oe magnetic field, the light intensity was 32%. It has been found that the light intensity changes due to the change of the magnetic field intensity, so that it functions as a magnetic field sensor.

(Example 2)
Using the same Faraday rotator as in Example 1, the transmission type magnetic field sensor shown in FIG. 3 was produced. An antireflection film was applied to both ends of the Faraday rotator.

  The analyzer was rotated while changing the intensity of the magnetic field, and the rotation angle (polarization angle) when the intensity of the detection light reached the maximum was measured. In the absence of a magnetic field, the polarization angle of transmitted light was 0 °, but a rotation of 20.2 ° occurred in a magnetic field of 2000 Oe, and a rotation of 50.5 ° in a magnetic field of 5000 Oe. Since the rotation angle changes in proportion to the magnetic field strength, it has been found to function as a magnetic field sensor.

(Comparative example)
A reflective magnetic field sensor was produced in the same manner as in Example 1 except that the Faraday rotator was made of YIG single crystal. As a result, at the wavelength of 633 nm, light did not pass through the Faraday rotator, and light could not be detected.

DESCRIPTION OF SYMBOLS 1 Reflection type magnetic sensor 2 Glass manufacturing apparatus 3 Transmission type magnetic field sensor 10 Light source 11 Polarizer 12 Faraday rotator 13 Mirror 14 Photo detector 15 Antireflection film 16 Analyzer 20: Mold 20a: Molding surface 20b: Gas ejection hole 21: Gas supply mechanism 22: Glass raw material block 23: Laser beam irradiation device

Claims (2)

A Faraday rotator for a magnetic field sensor, comprising a glass containing 15% or more of Dy ₂ O ₃ in terms of mol% oxide. A magnetic field sensor comprising the Faraday rotator, polarizer, light source, and detector according to claim 1.