WO2019239684A1 - ファラデー回転子及び磁気光学素子 - Google Patents

ファラデー回転子及び磁気光学素子 Download PDF

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Publication number
WO2019239684A1
WO2019239684A1 PCT/JP2019/014666 JP2019014666W WO2019239684A1 WO 2019239684 A1 WO2019239684 A1 WO 2019239684A1 JP 2019014666 W JP2019014666 W JP 2019014666W WO 2019239684 A1 WO2019239684 A1 WO 2019239684A1
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Prior art keywords
magnet body
faraday
magnet
optical axis
axis direction
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PCT/JP2019/014666
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English (en)
French (fr)
Japanese (ja)
Inventor
太志 鈴木
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日本電気硝子株式会社
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Priority to JP2020525282A priority Critical patent/JPWO2019239684A1/ja
Publication of WO2019239684A1 publication Critical patent/WO2019239684A1/ja

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • G02F1/093—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect used as non-reciprocal devices, e.g. optical isolators, circulators

Definitions

  • the present invention relates to a Faraday rotator and a magneto-optical element.
  • An optical isolator is a magneto-optical element that propagates light only in one direction and blocks light reflected and returned.
  • Optical isolators are used in laser oscillators used in optical communication systems, laser processing systems, and the like.
  • the wavelength range used in the optical communication system is mainly 1300 nm to 1700 nm, and rare earth iron garnet has been used for the Faraday element of the Faraday rotator in the optical isolator.
  • the wavelength used for laser processing or the like is shorter than the optical communication band and is mainly around 1000 nm.
  • the rare earth iron garnet cannot be used because of its large light absorption. Therefore, a Faraday element made of a paramagnetic crystal is generally used, and terbium gallium garnet (TGG) is widely known.
  • the rotation angle ( ⁇ ) by Faraday rotation needs to be 45 °.
  • This Faraday rotation angle has a relationship of the following formula (1) with the length (L) of the Faraday element, the Verde constant (V), the magnetic flux density parallel to the optical axis (H).
  • the Verde constant is a property that depends on the material. Therefore, in order to adjust the Faraday rotation angle, it is necessary to change the length of the Faraday element and the magnetic flux density parallel to the optical axis applied to the Faraday element. In particular, in recent years, there has been a demand for miniaturization of devices, so that the magnetic flux density applied to the Faraday rotator can be improved by changing the structure of the magnet rather than adjusting the size of the Faraday element or magnet. ing.
  • Patent Document 1 discloses a Faraday rotator including a magnetic circuit constituted by first to third magnets and a Faraday element.
  • the first magnet is magnetized in a direction perpendicular to the optical axis and toward the optical axis.
  • the second magnet is magnetized in a direction perpendicular to the optical axis and away from the optical axis.
  • a third magnet is disposed between them.
  • the third magnet is magnetized in a direction parallel to the optical axis and in a direction from the second magnet toward the first magnet.
  • the region having the highest magnetic flux density is formed in the vicinity of the bonded portion between the first magnet and the third magnet and the bonded portion between the second magnet and the third magnet.
  • a magnetic flux density is large and a stable region is formed in an internal space having a length equivalent to that of the third magnet connecting the two regions.
  • region is used. This is because the length of the Faraday element is also important for obtaining a desired Faraday rotation angle because a paramagnetic crystal such as TGG has a small Verde constant.
  • the magnetic flux density applied to the Faraday element may be biased when the position of the Faraday element is shifted when the Faraday rotator is manufactured. As a result, the Faraday rotation angle varies significantly, and there is a problem that it is difficult to stably obtain a desired Faraday rotation angle.
  • the present invention has been made in view of the above problems, and an object thereof is to provide a Faraday rotator and a magneto-optical element that can stably obtain a Faraday rotation angle of 45 °.
  • the Faraday rotator of the present invention includes a magnetic circuit having first to third magnet bodies each provided with a through-hole through which light passes, and a paramagnetic body that is disposed in the through-hole and transmits light.
  • the magnetic circuit has first to third magnet bodies arranged coaxially in this order in the front-rear direction, and the direction in which light passes through the through-hole of the magnetic circuit is the optical axis direction.
  • the first magnet body is magnetized in a direction perpendicular to the optical axis direction and the through hole side is an N pole, and the second magnet body is a direction parallel to the optical axis direction.
  • the first magnet body side is magnetized so as to have an N pole
  • the third magnet body is magnetized in a direction perpendicular to the optical axis direction and so that the through hole side is an S pole.
  • the length along the optical axis direction of each of the first magnet body, the second magnet body, and the third magnet body is Fara. And 0.56 times the length along the optical axis direction of the chromatography device, the length along the optical axis direction of the Faraday element and less than 15 mm.
  • the length along the optical axis direction of the first to third magnet bodies is set to be equal to or greater than the length along the optical axis direction of the Faraday element, so that the Faraday due to the positional deviation of the Faraday element during assembly. Deviations and fluctuations in the rotation effect can be suppressed. Furthermore, a small Faraday rotator can be formed by making the length along the optical axis direction of the arranged Faraday element shorter than 15 mm.
  • the paramagnetic material is preferably a glass material.
  • the glass material may contain at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. preferable. It is particularly preferable to contain Tb.
  • the glass material contains more than 40% of Tb 2 O 3 in terms of mol% of oxide, and the ratio of Tb 3+ to the total Tb is 55% or more in mol%. preferable. Since such a glass material has a Verde constant of 0.2 min / Oe ⁇ cm or more and is larger than the Verde constant (0.13 min / Oe ⁇ cm) of the conventional TGG, a smaller Faraday element is manufactured. It becomes easy.
  • the cross-sectional area of the through hole in the magnetic circuit is preferably 100 mm 2 or less.
  • the magnetic flux density tends to increase, so that it is easy to reduce the size.
  • the magneto-optical element of the present invention includes the Faraday rotator, a first optical component disposed at one end in the optical axis direction of the magnetic circuit of the Faraday rotator, and a second optical component disposed at the other end.
  • the light passing through the through hole of the magnetic circuit passes through the first optical component and the second optical component.
  • the first optical component and the second optical component may be polarizers.
  • FIG. 1 is a schematic cross-sectional view showing an example of the structure of the Faraday rotator of the present invention.
  • FIG. 2 is a schematic diagram showing a magnetic field strength distribution generated in a through hole of a magnetic circuit having a long second magnet body.
  • FIG. 3 is a schematic diagram showing the magnetic field strength distribution generated in the through hole of the short magnetic circuit in the second magnet body.
  • FIG. 4 is a diagram showing an example of the structure of the first magnet body in the present invention.
  • FIG. 5 is a diagram showing an example of the structure of the second magnet body in the present invention.
  • FIG. 6 is a diagram showing an example of the structure of the third magnet body in the present invention.
  • FIG. 7 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element of the present invention.
  • FIG. 1 is a schematic cross-sectional view showing an example of the structure of the Faraday rotator of the present invention. Note that the letters N and S in FIG. 1 indicate magnetic poles. The same applies to other drawings to be described later.
  • the Faraday rotator 1 is a device used for magneto-optical elements such as optical isolators and optical circulators.
  • the Faraday rotator 1 includes a magnetic circuit 2 provided with a through hole 2a through which light passes, and a Faraday element 14 arranged in the through hole 2a.
  • the Faraday element 14 is made of a paramagnetic material that transmits light.
  • the magnetic circuit 2 includes a first magnet body 11, a second magnet body 12, and a third magnet body 13 each having a through hole.
  • the magnetic circuit 2 includes a first magnet body 11, a second magnet body 12, and a third magnet body 13 that are coaxially arranged in this order in the front-rear direction.
  • positioning coaxially means arrange
  • the through holes 2 a of the magnetic circuit 2 are configured by connecting the through holes of the first magnet body 11, the second magnet body 12, and the third magnet body 13.
  • the first magnet body 11 and the third magnet body 13 are magnetized in the direction perpendicular to the optical axis direction, and the magnetization directions are opposed to each other.
  • the first magnet body 11 is magnetized in a direction perpendicular to the optical axis direction so that the through hole side has an N pole.
  • the third magnet body 13 is magnetized in a direction perpendicular to the optical axis direction so that the through hole side is an S pole.
  • the second magnet body 12 is magnetized in a direction parallel to the optical axis direction so that the first magnet body 11 side has an N pole.
  • the light may be incident on the Faraday rotator 1 from the first magnet body 11 side or may be incident from the third magnet body 13 side.
  • the Faraday rotator 1 of the present invention is characterized by having the following configuration. 1) The length along the optical axis direction of each of the first magnet body 11, the second magnet body 12, and the third magnet body 13 is 0 with respect to the length along the optical axis direction of the Faraday element 14. .56 times or more. 2) The length of the Faraday element 14 along the optical axis direction is less than 15 mm. In the following, the length along the optical axis direction may be simply referred to as the length.
  • each of the first magnet body 11, the second magnet body 12, and the third magnet body 13 is 0.56 times or more, 0.6 times or more the length of the Faraday element 14. It is preferably 0.7 times or more, 0.8 times or more, particularly 0.9 times or more.
  • the magnetic flux density is the highest in the vicinity of the bonding portion between the first magnet body 11 and the second magnet body 12 and the bonding portion between the second magnet body 12 and the third magnet body 13. A large area is easily formed.
  • each length of the first magnet body 11, the second magnet body 12, and the third magnet body 13 is set to be equal to or greater than a length along the optical axis direction of the Faraday element 14.
  • the position of the Faraday element 14 can be made difficult to shift during assembly. Therefore, fluctuations in the Faraday rotation angle can be suppressed. Furthermore, the lengths of the first magnet body 11 and the third magnet body 13 strongly contribute to the magnitude of the magnetic flux density of the magnetic circuit 2. Therefore, if the first magnet body 11 and the third magnet body 13 are too short, a sufficient magnetic flux density cannot be obtained and a 45 ° Faraday rotation angle cannot be obtained. A Faraday rotation angle of 45 ° can be obtained by setting the ratio of the length of each of the first magnet body 11 and the third magnet body 13 to the length of the Faraday element 14 within the above range.
  • the length of each of the first magnet body 11, the second magnet body 12, and the third magnet body 13 is preferably 1.5 times or less that of the Faraday element 14, and 1.3. It is preferable that it is 2 times or less, especially 1.2 times or less. By doing in this way, the Faraday rotator 1 can be reduced in size.
  • the Faraday rotation angle may be referred to as a rotation angle.
  • the Faraday rotator 1 of the present invention by changing the relationship between the lengths of the first magnet body 11 and the third magnet body 13 and the length of the second magnet 12 in particular, the through hole 2a of the magnetic circuit 2 is changed. It is possible to change the shape of the magnetic field strength distribution generated in the above. Specifically, (1) when the length of the first magnet body 11 and the third magnet body 13 is shorter than the length of the second magnet body 12 (when the second magnet body 12 is long), (2) The case where the length of the 1st magnet body 11 and the 3rd magnet body 13 is longer than the length of the 2nd magnet body 12 (when the 2nd magnet body 12 is short) can be mentioned.
  • the through hole of the magnetic circuit 2 is used.
  • the magnetic field intensity distribution generated in 2a becomes asymmetric in the optical axis direction, making it difficult to control the magnetic field distribution. From such a viewpoint, it is preferable that the lengths of the first magnet body 11 and the third magnet body 13 are equal. Therefore, in the magnetic field distribution described below, the lengths of the first magnet body 11 and the third magnet body 13 are assumed to be equal.
  • FIG. 2 is a schematic diagram showing the magnetic field strength distribution which arises in the through-hole of a long magnetic circuit with a 2nd magnet body.
  • the horizontal axis indicates the length along the optical axis direction with the origin 0 as the center of the through hole 2a of the magnetic circuit 2, and the vertical axis indicates the magnetic field strength.
  • the magnetic field distribution has a shape that extends in a concave shape over a wide range around the origin 0 along the optical axis direction. Specifically, a region having the highest magnetic field strength is generated in the vicinity of the bonding portion between the first magnet body 11 and the third magnet body 13 and the bonding portion between the second magnet body 12 and the third magnet body 13.
  • a region S1 having a length equivalent to that of the second magnet body 12 and having a predetermined magnetic field strength a or more is formed.
  • the region S1 having a high magnetic field strength is relatively wide, it is easy to arrange the entire Faraday element 14 in the region S1, and it is easy to suppress fluctuations in the Faraday rotation angle.
  • FIG. 3 is a schematic diagram showing a magnetic field strength distribution generated in a through hole of a magnetic circuit in which the second magnet body is short.
  • the magnetic field distribution has a shape that extends in a convex shape around the origin 0 along the optical axis direction.
  • a region S2 having a predetermined magnetic field strength a or more is formed near the center of the second magnet body 12.
  • the maximum magnetic field strength is (1) a larger value than the magnetic field distribution when the second magnet body 12 is long, so that the magnetic flux density stronger than the Faraday element 14 disposed in the region S2. It is easy to increase the Faraday rotation angle.
  • the magnetic field strength distribution when the first magnet body 11, the second magnet body 12, and the third magnet body 13 have the same length is the characteristic and shape intermediate between the above (1) and (2).
  • the magnetic field is most proximate to the bonding portion between the first magnet body 11 and the third magnet body 13 and the bonding portion between the second magnet body 12 and the third magnet body 13.
  • a region having a high strength is generated, and a region S3 having a length equivalent to that of the second magnet body 12 and having a predetermined magnetic field strength a or more is formed between the two regions.
  • the region S3 is formed to be wider than the region S2 and narrower than the region S1 with the origin 0 as the center.
  • the maximum magnetic field strength is larger than (1) and smaller than (2).
  • the length of the Faraday element 14 is preferably 3 mm to 14 mm, and is preferably 5 mm to 13 mm, 6 mm to 12 mm, particularly 7 mm to 11 mm.
  • the cross-sectional area of the through hole 2a of the magnetic circuit 2 is preferably 100 mm 2 or less. If the cross-sectional area of the through hole 2a is too large, a sufficient magnetic flux density cannot be obtained, and if it is too small, it is difficult to arrange the Faraday element 14 in the through hole 2a.
  • the cross-sectional area of the through hole 2a is preferably 3 mm 2 to 80 mm 2 , 4 mm 2 to 70 mm 2 , 5 mm 2 to 60 mm 2 , particularly preferably 7 mm 2 to 50 mm 2 .
  • the cross-sectional shape of the through hole 2a of the magnetic circuit 2 is not particularly limited, and may be a rectangle or a circle. A rectangle is preferable in terms of facilitating assembly, and a circle is preferable in terms of applying a uniform magnetic field.
  • the cross-sectional shape of the Faraday element 14 and the cross-sectional shape of the through hole 2a of the magnetic circuit 2 do not necessarily match, but are preferably matched from the viewpoint of providing a uniform magnetic field.
  • FIG. 4 is a diagram showing an example of the structure of the first magnet body.
  • FIG. 5 is a diagram illustrating an example of the structure of the second magnet body.
  • FIG. 6 is a diagram illustrating an example of the structure of the third magnet body.
  • the first magnet body 11 shown in FIG. 4 is configured by combining four magnet pieces.
  • the number of magnet pieces constituting the first magnet body 11 is not limited to the above.
  • the first magnet body 11 may be configured by combining six or eight magnet pieces. By configuring the first magnet body 11 by combining a plurality of magnet pieces, the magnetic field can be effectively increased. But the 1st magnet body 11 may consist of a single magnet.
  • the second magnet body 12 shown in FIG. 5 is composed of a single magnet.
  • the second magnet body 12 may be configured by combining two or more magnet pieces.
  • the third magnet body 13 shown in FIG. 6 is configured by combining four magnet pieces in the same manner as the first magnet body 11.
  • the third magnet body 13 may be configured by combining six or eight magnet pieces, or may be a single magnet.
  • the first magnet body 11, the second magnet body 12, and the third magnet body 13 of the present invention are composed of permanent magnets.
  • a rare earth magnet is particularly preferable, and among them, a magnet mainly composed of samarium-cobalt (Sm—Co) and a magnet mainly composed of neodymium-iron-boron (Nd—Fe—B) are preferable. .
  • Paramagnetic material can be used for the Faraday element 14 of the present invention.
  • a glass material it is preferable to use a glass material.
  • Faraday elements made of glass keep a stable Verde constant and a high extinction ratio because there are few fluctuations in the Verde constant due to defects such as single crystal materials and the decrease in extinction ratio and the influence of stress from the adhesive is small be able to.
  • a paramagnetic material other than a glass material can be used.
  • the glass material used for the Faraday element 14 of the present invention contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. Is preferred. It is particularly preferable to contain Tb.
  • the glass material used for the Faraday element 14 of the present invention preferably contains more than 40% of Tb 2 O 3 in terms of mol% of oxide, more than 45%, more than 48%, more than 49%, especially 50%. % Or more is preferable.
  • Tb 2 O 3 a good Faraday effect can be easily obtained.
  • Tb exists in a trivalent or tetravalent state in glass, all of these are expressed as Tb 2 O 3 in this specification.
  • the ratio of Tb 3+ to the total Tb is preferably 55% or more in terms of mol%, and is 60% or more, 70% or more, 80% or more, 90% or more, particularly 95% or more. It is preferable. If the ratio of Tb 3+ to the total Tb is too small, the light transmittance at wavelengths of 300 nm to 1100 nm tends to decrease.
  • the Faraday element 14 of the present invention can contain the following components.
  • “%” means “mol%” unless otherwise specified.
  • SiO 2 becomes a glass skeleton and is a component that widens the vitrification range. 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 SiO 2 is preferably 0% to 50%, particularly 1% to 35%.
  • B 2 O 3 becomes a glass skeleton and is a component that widens the vitrification range.
  • the content of B 2 O 3 is preferably 0% to 50%, particularly 1% to 40%.
  • P 2 O 5 becomes a glass skeleton and is a component that widens the vitrification range.
  • the content of P 2 O 5 is preferably 0% to 50%, particularly 1% to 40%.
  • Al 2 O 3 is a component that enhances glass forming ability. 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 preferably 0% to 50%, particularly preferably 0% to 30%.
  • La 2 O 3 , Gd 2 O 3 , and Y 2 O 3 have an effect of stabilizing vitrification. However, when there is too much the content, it will become difficult to vitrify on the contrary. Therefore, the contents of La 2 O 3 , Gd 2 O 3 and Y 2 O 3 are each preferably 10% or less, particularly preferably 5% or less.
  • Dy 2 O 3 , Eu 2 O 3 and Ce 2 O 3 stabilize vitrification and contribute to the improvement of the Verde constant. However, when there is too much the content, it will become difficult to vitrify on the contrary. Therefore, the contents of Dy 2 O 3 , Eu 2 O 3 and Ce 2 O 3 are each preferably 15% or less, particularly preferably 10% or less. Note that Dy, Eu, and Ce present in the glass exist in a trivalent or tetravalent state, but in the present specification, all of these are expressed as Dy 2 O 3 , Eu 2 O 3 , and Ce 2 O 3 , respectively.
  • the content of these components is preferably 0% to 10%, particularly 0% to 5%.
  • GeO 2 is a component that enhances glass forming ability. However, since GeO 2 does not contribute to the improvement of the Verde constant, it is difficult to obtain a sufficient Faraday effect if its content is too large. Accordingly, the GeO 2 content is preferably 0% to 15%, 0% to 10%, particularly preferably 0% to 9%.
  • Ga 2 O 3 has the effect of increasing the glass forming ability and expanding the vitrification range. However, if the content is too large, devitrification tends to occur. Further, since the Ga 2 O 3 does not contribute to the improvement of the Verdet constant, when the content is too large, a sufficient Faraday effect difficult to obtain. Accordingly, 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 volatilizes during melting and causes compositional changes, which may adversely affect vitrification. Moreover, it is easy to increase striae. Accordingly, the fluorine content (F 2 conversion) is preferably 0% to 10%, 0% to 7%, particularly preferably 0% to 5%.
  • Sb 2 O 3 can be added as a reducing agent.
  • the content is preferably 0.1% or less in order to avoid coloring or in consideration of environmental load.
  • the Faraday element 14 of the present invention exhibits good light transmission in the wavelength range of 300 nm to 1100 nm.
  • the transmittance at an optical path length of 1 mm at a wavelength of 1064 nm is preferably 60% or more, 70% or more, and particularly preferably 80% or more.
  • the transmittance at an optical path length of 1 mm at a wavelength of 633 nm is preferably 30% or more, 50% or more, 70% or more, and particularly preferably 80% or more.
  • the transmittance at an optical path length of 1 mm at a wavelength of 533 nm is preferably 30% or more, 50% or more, 70% or more, and particularly preferably 80% or more.
  • the cross-sectional shape of the Faraday element 14 of the present invention is not particularly limited, but is preferably circular in order to have a uniform Faraday effect.
  • the diameter of the Faraday element 14 is preferably 10 mm or less, preferably 8 mm or less, 5 mm or less, and particularly preferably 3.5 mm or less. If the diameter of the Faraday element 14 is too large, the Faraday element 14 cannot be disposed in the through hole 2 a of the magnetic circuit 2. Alternatively, it is necessary to enlarge the magnetic circuit 2 and it is difficult to reduce the size of the Faraday rotator 1.
  • the lower limit of the diameter of the Faraday element 14 is not particularly limited, but is practically 0.5 mm or more.
  • the Faraday rotator 1 of the present invention is preferably used at a wavelength of 350 nm to 1300 nm, particularly preferably in the range of 450 nm to 1200 nm, 500 nm to 1200 nm, 800 nm to 1100 nm, 900 nm to 1100 nm.
  • FIG. 7 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element of the present invention.
  • the magneto-optical element 20 shown in FIG. 7 is an optical isolator.
  • the optical isolator is a device that blocks reflected return light of laser light.
  • the magneto-optical element 20 includes the Faraday rotator 1 shown in FIG. 1, the first optical component 25 disposed at one end in the optical axis direction of the magnetic circuit 2, and the second optical disposed at the other end. And a component 26.
  • the first optical component 25 and the second optical component 26 are polarizers in this embodiment.
  • the light transmission axis of the second optical component 26 is inclined 45 ° with respect to the light transmission axis of the first optical component 25.
  • the light incident on the magneto-optical element 20 passes through the first optical component 25, becomes linearly polarized light, and enters the Faraday element 14.
  • the incident light is rotated 45 ° by the Faraday element 14 and passes through the second optical component 26.
  • Part of the light that has passed through the second optical component 26 becomes reflected return light, and the polarization plane passes through the second optical component 26 at an angle of 45 °.
  • the reflected return light that has passed through the second optical component 26 is further rotated by 45 ° by the Faraday element 14.
  • the polarization plane of the reflected return light becomes a 90 ° orthogonal polarization plane with respect to the light transmission axis of the first optical component 25. Therefore, the reflected return light cannot be transmitted through the first optical component 25 and is blocked.
  • the magneto-optical element 20 of the present invention has the Faraday rotator 1 of the present invention shown in FIG. 1, a 45 ° Faraday rotation angle can be stably obtained and the size can be reduced.
  • the magneto-optical element 20 shown in FIG. 7 is an optical isolator
  • the magneto-optical element 20 may be an optical circulator.
  • the first optical component 25 and the second optical component 26 may be a wave plate or a beam splitter.
  • the magneto-optical element 20 may be a magneto-optical element other than an optical isolator and an optical circulator.
  • a Faraday rotator at a wavelength of 1064 nm is given as an example, but the present invention is not limited to this wavelength.
  • Example 1 The Faraday element of Example 1 was manufactured as follows. First, the raw material was press-molded and sintered at 700 ° C. to 1400 ° C. for 6 hours to produce a glass raw material lump. The glass raw material lump in this example was prepared so that a glass composition of 55Tb 2 O 3 -10Al 2 O 3 -35B 2 O 3 was obtained.
  • the glass raw material lump was coarsely pulverized into small pieces using a mortar.
  • the glass material was produced by the containerless floating method using the obtained small piece of glass raw material lump.
  • a 100 W CO 2 laser oscillator was used as the heat source.
  • nitrogen gas was used as a gas for suspending the glass raw material lump and supplied at a flow rate of 1 L / min to 30 L / min.
  • the obtained glass material was heat-treated at 800 ° C. for 10 hours in a 4% -H 2 / N 2 atmosphere.
  • the ratio of Tb 3+ to the total Tb was measured using an X-ray photoelectron spectrometer (XPS). Specifically, for the obtained glass material, the ratio of Tb 3+ to the total Tb was calculated from the peak intensity ratio of each Tb ion measured using XPS. As a result, the ratio of Tb 3+ was 99% or more.
  • XPS X-ray photoelectron spectrometer
  • the Verde constant was measured for the obtained glass material.
  • the Verde constant was measured using the rotational analyzer method. Specifically, the obtained glass material was polished to a thickness of 1 mm, the Faraday rotation angle at a wavelength of 1064 nm was measured in a magnetic field of 10 kOe, and the Verde constant was calculated. The measured Verde constant was 0.204 min / Oe ⁇ cm to 0.212 min / Oe ⁇ cm.
  • a cylindrical Faraday element having a diameter of 3 mm and a length of 10 mm was obtained by cutting and polishing the obtained glass.
  • the extinction ratio was 42 dB.
  • the length refers to the length along the optical axis direction in the Faraday rotator.
  • Sm—Co magnets were used as the permanent magnets constituting the first to third magnet bodies.
  • the outer diameter of the first to third magnet bodies was ⁇ 32 mm, and the diameter of the through hole was ⁇ 4 mm.
  • the length of the first magnet body was 10 mm, the length of the second magnet body was 10 mm, and the length of the third magnet body was 10 mm.
  • the Faraday element obtained above was combined with the first to third magnet bodies to form a Faraday rotator.
  • Example 2 Example 1 except that the length of the first magnet body is 12 mm, the length of the second magnet body is 10 mm, the length of the third magnet body is 12 mm, and the length of the Faraday element is 11 mm.
  • a Faraday rotator was produced in the same manner as in Example 1.
  • Example 3 The length of the first magnet body is 8.4 mm, the length of the second magnet body is 9 mm, the length of the third magnet body is 8.4 mm, and the length of the Faraday element is 14.5 mm.
  • a Faraday rotator was produced in the same manner as in Example 1 except that.
  • Example 4 A Faraday rotator was produced in the same manner as in Example 1 except that Nd—Fe—B magnets were used as the permanent magnets constituting the first to third magnet bodies.
  • Example 5 The length of the first magnet body is 12 mm, the length of the second magnet body is 10.4 mm, the length of the third magnet body is 12 mm, and the length of the Faraday element is 8 mm.
  • a Faraday rotator was produced in the same manner as in Example 4.
  • Example 6 Example 1 except that the length of the first magnet body is 10 mm, the length of the second magnet body is 7 mm, the length of the third magnet body is 10 mm, and the length of the Faraday element is 9 mm.
  • a Faraday rotator was produced in the same manner as in Example 4.
  • Example 7 The length of the first magnet body is 9.3 mm, the length of the second magnet body is 9.5 mm, the length of the third magnet body is 9.3 mm, and the length of the Faraday element is 11.
  • a Faraday rotator was produced in the same manner as in Example 1 except that the thickness was 9 mm.
  • Example 8 The length of the first magnet body is 10.6 mm, the length of the second magnet body is 10.4 mm, the length of the third magnet body is 10.6 mm, and the length of the Faraday element is 10.
  • a Faraday rotator was produced in the same manner as in Example 1 except that the thickness was 9 mm.
  • Example 9 The length of the first magnet body is 11.5 mm, the length of the second magnet body is 11 mm, the length of the third magnet body is 11.5 mm, and the length of the Faraday element is 10 mm. Produced a Faraday rotator in the same manner as in Example 1.
  • Example 10 Example 1 except that the length of the first magnet body is 12 mm, the length of the second magnet body is 6 mm, the length of the third magnet body is 12 mm, and the length of the Faraday element is 9 mm.
  • a Faraday rotator was produced in the same manner as in Example 1.
  • the length of the first magnet body is 7.5 mm
  • the length of the second magnet body is 7.5 mm
  • the length of the third magnet body is 7.5 mm
  • the length of the Faraday element is 14.
  • a Faraday rotator was produced in the same manner as in Example 1 except that the thickness was 5 mm.
  • Comparative Example 3 A Faraday rotator was produced in the same manner as in Comparative Example 1 except that a TGG single crystal produced by the Czochralski method was used for the Faraday element. When the Verde constant of the Faraday element was measured, it was 0.125 min / Oe ⁇ cm to 0.134 min / Oe ⁇ cm.
  • Rotational angle variation was determined by preparing 10 Faraday rotators and measuring them. The results of measuring the variation in the rotation angle are shown in Table 1 below.
  • Table 1 the length of the first magnet body is a
  • the length of the second magnet body is b
  • the length of the third magnet body is c
  • the length of the Faraday element is L
  • the wavelength is 1064 nm.
  • Comparative Example 3 and Comparative Example 4 the sizes of the first to third magnet bodies are the same as in Example 1 and Example 4, but the Verde constant is small, so that the rotation angle of 45 ° is not reached. It was. On the other hand, in Example 1 and Example 4, the rotation angle reached 45 °.

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