JP7356631B2 - Magnetic circuits, Faraday rotators and magneto-optical elements - Google Patents
Magnetic circuits, Faraday rotators and magneto-optical elements Download PDFInfo
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本発明は、磁気回路、ファラデー回転子及び磁気光学素子に関する。 The present invention relates to a magnetic circuit, a Faraday rotator, and a magneto-optical element.
ファラデー回転子は、ファラデー素子と、ファラデー素子に磁界を与える磁石とからなる素子である。ファラデー回転子は光を一方向だけに伝搬し、戻り光を阻止する働きがあるため、光アイソレータなどの磁気光学素子として、光通信システムやレーザー加工システムなどのレーザー発振器に用いられてきた。 A Faraday rotator is an element consisting of a Faraday element and a magnet that applies a magnetic field to the Faraday element. Faraday rotators have the ability to propagate light in only one direction and block returning light, so they have been used as magneto-optical elements such as optical isolators and in laser oscillators such as optical communication systems and laser processing systems.
光通信システムで使用される波長域は主に１３００ｎｍ～１７００ｎｍであり、従来のファラデー回転子では、ファラデー素子に希土類鉄ガーネットが用いられてきた。 The wavelength range used in optical communication systems is mainly from 1300 nm to 1700 nm, and in conventional Faraday rotators, rare earth iron garnet has been used for Faraday elements.
一方で、近年レーザー加工などに用いられる波長域は、光通信帯域よりもより短波長側であり、主に１０００ｎｍ付近が利用される。この波長域では、上記希土類鉄ガーネットは光吸収が大きく使用することができないため、ファラデー素子にテルビウム・ガリウム・ガーネット（ＴＧＧ）のような常磁性体結晶が用いられてきた。 On the other hand, the wavelength range used in laser processing and the like in recent years is on the shorter wavelength side than the optical communication band, and is mainly used around 1000 nm. In this wavelength range, the rare earth iron garnet cannot be used because of its large light absorption, so paramagnetic crystals such as terbium gallium garnet (TGG) have been used in Faraday elements.
ところで、このようなファラデー回転子を光アイソレータとして用いるためには、ファラデー回転による回転角度（θ）が４５°である必要がある。この回転角度は、ファラデー素子の長さ（Ｌ）、ベルデ定数（Ｖ）、光軸と平行な磁束密度（Ｂ）と下記の式（１）の関係にあることが知られている。 By the way, in order to use such a Faraday rotator as an optical isolator, the rotation angle (θ) due to Faraday rotation needs to be 45°. It is known that this rotation angle has a relationship with the length (L) of the Faraday element, the Verdet constant (V), and the magnetic flux density (B) parallel to the optical axis as expressed by the following equation (1).
θ＝Ｖ・Ｂ・Ｌ （１） θ=V・B・L (1)
このうち、ベルデ定数はファラデー素子の材料に依存する特性である。一般に、ＴＧＧのような常磁性体は希土類鉄ガーネットに比べてベルデ定数が小さいため、４５°のファラデー回転角を得るためには、ファラデー素子の長さや、ファラデー素子に加わる光軸と平行な磁束密度を大きくする必要があった。特に近年は装置の小型化が望まれているため、ファラデー素子や磁石を大型化するのではなく、磁石の構造を工夫することで、ファラデー素子に加わる磁束密度を向上させる発明が提案されている。 Among these, the Verdet constant is a characteristic that depends on the material of the Faraday element. Generally, a paramagnetic material such as TGG has a smaller Verdet constant than rare earth iron garnet, so in order to obtain a Faraday rotation angle of 45°, the length of the Faraday element and the magnetic flux parallel to the optical axis applied to the Faraday element must be adjusted. It was necessary to increase the density. Particularly in recent years, there has been a desire to miniaturize devices, so inventions have been proposed that improve the magnetic flux density applied to the Faraday element by devising the structure of the magnet, rather than increasing the size of the Faraday element or magnet. .
例えば、特許文献１には、第１～第３の磁石により構成された磁気回路と、ファラデー素子とを備えるファラデー回転子が開示されている。第１の磁石は、光軸と垂直の方向であり、かつ光軸に向かう方向に磁化されている。第２の磁石は、光軸と垂直の方向であり、かつ光軸から離れる方向に磁化されている。これらの間に第３の磁石が配置されている。第３の磁石は、光軸と平行な方向であり、かつ第２の磁石から第１の磁石に向かう方向に磁化されている。この磁気回路では、第１の磁石と第２の磁石の光軸方向に沿う長さをＬ２、第３の光軸方向に沿う長さをＬ３としたとき、Ｌ２／１０≦Ｌ３≦Ｌ２の関係が成立するように構成されている。 For example, Patent Document 1 discloses a Faraday rotator that includes a magnetic circuit made up of 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 placed 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. In this magnetic circuit, when the length of the first magnet and the second magnet along the optical axis direction is L 2 and the length of the third magnet along the optical axis direction is L 3 , L 2 /10≦L 3 The structure is such that the relationship ≦L 2 holds true.
上記の磁気回路では、第３の磁石の貫通孔付近において、第１の磁石と第２の磁石の相互作用で作り出された強い磁界が発生する。この磁界は第３の磁石の磁化方向と逆向きである。このように着磁方向と逆向きの外部磁界が生じる場合、磁石の動作点の移動及びそれに帰属する減磁の影響を考慮する必要がある。説明のため、図７に磁石の減磁曲線（Ｂ－Ｈ曲線及びＪ－Ｈ曲線）の一例を示す。Ｂ－Ｈ曲線３２は、磁束密度Ｂと外部磁界Ｈの関係を表す曲線である。また、Ｊ－Ｈ曲線３３は、磁化Ｊと外部磁界Ｈの関係を表す曲線である。曲線と縦軸、横軸の交点は、それぞれ残留磁束密度Ｂｒ、固有保磁力Ｈｃｊ及び保磁力ＨｃＢを意味する。残留磁束密度Ｂｒは、外部磁界を飽和磁化の状態から０にした時に磁性体に残る磁束密度のことである。保磁力は、磁性体が持つ磁化方向と反対方向の磁界を作用させて、磁化または磁束密度が０になる時の外部磁界の値のことであり、前者が固有保磁力ＨｃＪ、後者が保磁力ＨｃＢと表される。なお、磁性体の磁束密度（Ｂ）、外部磁界の強さ（Ｈ）、磁化の強さ（Ｊ）、真空の透磁率（μ０）は、下記の式（２）の関係にあることが知られている。 In the above magnetic circuit, a strong magnetic field is generated near the through hole of the third magnet due to the interaction between the first magnet and the second magnet. This magnetic field is in the opposite direction to the magnetization direction of the third magnet. When an external magnetic field in the direction opposite to the magnetization direction is generated in this manner, it is necessary to consider the movement of the operating point of the magnet and the effects of demagnetization attributed thereto. For explanation, FIG. 7 shows examples of magnet demagnetization curves (BH curve and JH curve). The BH curve 32 is a curve representing the relationship between the magnetic flux density B and the external magnetic field H. Further, the JH curve 33 is a curve representing the relationship between the magnetization J and the external magnetic field H. The intersections of the curve, the vertical axis, and the horizontal axis mean the residual magnetic flux density Br, the intrinsic coercive force H cj , and the coercive force H cB, respectively. The residual magnetic flux density Br is the magnetic flux density that remains in a magnetic material when the external magnetic field is reduced from a state of saturation magnetization to zero. Coercive force is the value of an external magnetic field when the magnetization or magnetic flux density becomes 0 when a magnetic field is applied in the opposite direction to the magnetization direction of a magnetic material, and the former is the intrinsic coercive force H cJ and the latter is the coercive force. The magnetic force is expressed as H cB . It should be noted that the magnetic flux density (B) of the magnetic material, the strength of the external magnetic field (H), the strength of magnetization (J), and the permeability of vacuum (μ 0 ) have the relationship shown in the following equation (2). Are known.
Ｂ＝μ０Ｈ＋Ｊ （２） B=μ 0 H+J (2)
（外部磁界による不可逆減磁）
図７に示すように、磁石に外部磁界Ｈ１が加えられた場合、磁石の動作点ａ１は、Ｂ－Ｈ曲線３２上を移動し、Ｈ軸へ近い動作点ｂ１へ移動する。また、より大きな外部磁界Ｈ２を与えると、磁石の動作点ａ１は、さらにＨ軸へ近い動作点ｃ１へ移動する。このとき、Ｂ－Ｈ曲線３２上の動作点ｃ１をＪ－Ｈ曲線３３上に投影した動作点ｃ２は、Ｊ－Ｈ曲線３３のクニック点３４（傾きが変化して急激に磁束密度が減少する変化点）を越えてしまう。このように、より大きな外部磁界Ｈ２による減磁の場合、Ｂ－Ｈ曲線３２上の動作点をＪ－Ｈ曲線３３上に投影した動作点ｃ２がＪ－Ｈ曲線３３のクニック点３４を越えることで、外部磁界Ｈ２を取り除いた際に磁石の動作点ａ１が動作点ｄ１へと移動する。ここで、動作点ｄ１は、動作点ｃ１から外部磁界Ｈ２を取り除いたときの動作点であり、動作点ｃ１を通るリコイル透磁率曲線の傾きと平行な直線と、動作点ａ１と原点を通る直線の交点である。このとき、動作点ａ１における磁束密度と、動作点ｄ１における磁束密度の差は外部磁界Ｈ２による不可逆減磁ΔＢであり、再着磁を行わない限り回復しない減磁となる。
(Irreversible demagnetization due to external magnetic field)
As shown in FIG. 7, when an external magnetic field H1 is applied to the magnet, the operating point a1 of the magnet moves on the BH curve 32 to an operating point b1 close to the H axis. Furthermore, when a larger external magnetic field H2 is applied, the operating point a1 of the magnet moves to an operating point c1 closer to the H-axis. At this time, the operating point c2, which is obtained by projecting the operating point c1 on the BH curve 32 onto the JH curve 33, is the knick point 34 of the JH curve 33 (where the slope changes and the magnetic flux density suddenly decreases). (transition point) is exceeded. In this way, in the case of demagnetization due to a larger external magnetic field H2, the operating point c2, which is the operating point on the BH curve 32 projected onto the JH curve 33, exceeds the knick point 34 of the JH curve 33. When the external magnetic field H2 is removed, the operating point a1 of the magnet moves to the operating point d1. Here, the operating point d1 is the operating point when the external magnetic field H2 is removed from the operating point c1, and a straight line that passes through the operating point c1 and is parallel to the slope of the recoil permeability curve, and a straight line that passes through the operating point a1 and the origin. is the intersection of At this time, the difference between the magnetic flux density at the operating point a1 and the magnetic flux density at the operating point d1 is irreversible demagnetization ΔB due to the external magnetic field H2, resulting in demagnetization that does not recover unless re-magnetized.
なお、磁石の動作点とは、図７に示すように、磁石のＢ－Ｈ曲線３２上の点であり、磁気回路内における磁石の磁束密度Ｂ、磁界Ｈの状態を示す点のことである。また、原点からこの点に向かって引いた直線をパーミアンス線３１と呼ぶ。パーミアンス線３１の傾き（Ｂ／Ｈ）は、真空の透磁率（μ０）、パーミアンス係数（Ｐ）と下記の式（３）の関係にあることが知られている。 Note that the operating point of the magnet is a point on the B-H curve 32 of the magnet, as shown in FIG. 7, and is a point that indicates the state of the magnetic flux density B and magnetic field H of the magnet in the magnetic circuit. . Further, a straight line drawn from the origin toward this point is called a permeance line 31. It is known that the slope (B/H) of the permeance line 31 has a relationship with the vacuum permeability (μ 0 ) and the permeance coefficient (P) as expressed by the following equation (3).
Ｂ／Ｈ＝μ０Ｐ （３） B/H=μ 0 P (3)
（高温による不可逆減磁）
図８にネオジム磁石の減磁曲線の温度変化を示す。それぞれ、高温時のＢ－Ｈ曲線３５、低温時のＢ－Ｈ曲線３６、高温時のＪ－Ｈ曲線３７、低温時のＪ－Ｈ曲線３８を示している。ネオジム磁石は温度が上昇すると、残留磁束密度Ｂｒ、固有保磁力Ｈｃｊ及び保磁力ＨｃＢがそれぞれ、Ｂｒ´、Ｈｃｊ´及びＨｃＢ´に移動する。すると、低温時のＢ－Ｈ曲線３６、低温時のＪ－Ｈ曲線３８は、それぞれ高温時のＢ－Ｈ曲線３５、高温時のＪ－Ｈ曲線３７に変化する。このような温度変化において、Ｂ－Ｈ曲線上の動作点がＢ－Ｈ曲線のクニック点３４を越えると、温度条件を元に戻しても磁力が元に戻らない、つまり温度変化による磁石の不可逆減磁が生じる。例えば、動作点ａ１は、低温から高温へ外部温度を変化させると、動作点ｂ１へ移動する。動作点ｂ１は高温時のＢ－Ｈ曲線３５上のクニック点を越えていないため、外部温度を高温から低温へ戻すと、動作点ｂ１から動作点ａ１へ戻ることができる、すなわち可逆減磁となる。一方、よりＨ軸へ近い動作点ａ２は、低温から高温へ外部温度を変化させると、動作点ｂ２へと移動する。この場合は、動作点ｂ２が高温時のＢ－Ｈ曲線３５上のクニック点３４を越えているため、外部温度を高温から低温へ戻しても、動作点ｂ２から動作点ａ２へ戻ることができず、動作点ｃ２へ移る。このとき、動作点ａ２における磁束密度と、動作点ｃ２における磁束密度の差が不可逆減磁ΔＢとなる。特にネオジム磁石は、図８に示すように、温度の上昇によりＢ－Ｈ曲線とＪ－Ｈ曲線がＢ軸（磁束密度）側へ大きく変化することが知られており、高温下において、動作点の移動による不可逆減磁が生じやすい。なお、図８の動作点ｃ２は、図７の動作点ｄ１と同様の方法で求めることができる。
(Irreversible demagnetization due to high temperature)
Figure 8 shows the temperature change of the demagnetization curve of neodymium magnets. A BH curve 35 at high temperature, a BH curve 36 at low temperature, a JH curve 37 at high temperature, and a JH curve 38 at low temperature are shown, respectively. When the temperature of the neodymium magnet increases, the residual magnetic flux density Br, the intrinsic coercive force H cj , and the coercive force H cB move to Br', H cj ', and H cB ', respectively. Then, the BH curve 36 at low temperature and the JH curve 38 at low temperature change to BH curve 35 at high temperature and JH curve 37 at high temperature, respectively. Under such temperature changes, if the operating point on the B-H curve exceeds the knick point 34 of the B-H curve, the magnetic force will not return to its original state even if the temperature conditions are returned to the original state. In other words, the magnet will become irreversible due to temperature changes. Demagnetization occurs. For example, the operating point a1 moves to the operating point b1 when the external temperature is changed from a low temperature to a high temperature. Since the operating point b1 does not exceed the knick point on the BH curve 35 at high temperature, when the external temperature is returned from high to low temperature, the operating point b1 can return to the operating point a1, that is, reversible demagnetization occurs. Become. On the other hand, operating point a2, which is closer to the H-axis, moves to operating point b2 when the external temperature is changed from low to high temperature. In this case, since the operating point b2 exceeds the knick point 34 on the BH curve 35 at high temperature, it is not possible to return from the operating point b2 to the operating point a2 even if the external temperature is returned from a high temperature to a low temperature. First, the process moves to the operating point c2. At this time, the difference between the magnetic flux density at the operating point a2 and the magnetic flux density at the operating point c2 becomes irreversible demagnetization ΔB. In particular, with neodymium magnets, as shown in Figure 8, it is known that the B-H curve and J-H curve greatly change toward the B-axis (magnetic flux density) side as the temperature increases, and the operating point Irreversible demagnetization is likely to occur due to the movement of Note that the operating point c2 in FIG. 8 can be determined in the same manner as the operating point d1 in FIG. 7.
さらに、特許文献１に記載の第３の磁石は、第１、第２の磁石に比べ、磁化方向に短い形状を有している。このような磁化方向に短い形状の磁石では、磁石の形状に依存するパーミアンス係数も考慮する必要がある。通常、パーミアンス係数は磁化方向に短い、すなわち磁極同士が近づく形状の磁石で小さくなる。また、パーミアンス係数は式（３）に示すように、パーミアンス線３１の傾きでもある。例えば、図９に示すように、動作点ａ１を通るパーミアンス線３１は、動作点ｂ１を通るパーミアンス線３１の傾きβよりも大きな傾きα、すなわち、より大きなパーミアンス係数を有していることになる。言い換えれば、値の小さいパーミアンス係数βを有する磁石はＨ軸へ近い位置に動作点があるため、よりＢ－Ｈ曲線３２及びＪ－Ｈ曲線３３上のクニック点３４を越えやすくなり、上述した逆磁界や高温下による不可逆減磁が生じやすくなる。 Furthermore, the third magnet described in Patent Document 1 has a shorter shape in the magnetization direction than the first and second magnets. In such a magnet having a short shape in the magnetization direction, it is also necessary to consider the permeance coefficient which depends on the shape of the magnet. Normally, the permeance coefficient is small in magnets that are short in the magnetization direction, that is, the magnetic poles are close to each other. Further, the permeance coefficient is also the slope of the permeance line 31, as shown in equation (3). For example, as shown in FIG. 9, the permeance line 31 passing through the operating point a1 has a larger slope α, that is, a larger permeance coefficient, than the slope β of the permeance line 31 passing through the operating point b1. . In other words, a magnet with a small permeance coefficient β has an operating point close to the H axis, so it is easier to cross the knick point 34 on the BH curve 32 and JH curve 33, and the above-mentioned reverse Irreversible demagnetization is likely to occur due to magnetic fields or high temperatures.
以上のように、特許文献１に記載の磁気回路の第３の磁石は、磁石として不利な動作点において使用されるため、逆磁界や高温下による不可逆減磁を引き起こしやすい状況にあった。特に、高出力レーザー用光アイソレータなどの磁気光学素子として上記磁気回路を用いる場合、高出力光によるファラデー素子の温度上昇に伴う磁気回路の温度上昇は避けられないため、第３の磁石で高温による不可逆減磁が生じる可能性が高くなっていた。このように第３の磁石で不可逆減磁が生じると、ファラデー素子に十分な磁束密度を安定して与えることができなくなるため、ファラデー回転子が本来の機能を果たせなくなる可能性があった。 As described above, the third magnet of the magnetic circuit described in Patent Document 1 is used at an unfavorable operating point as a magnet, so it is likely to cause irreversible demagnetization due to a reverse magnetic field or high temperature. In particular, when using the above magnetic circuit as a magneto-optical element such as an optical isolator for high-power lasers, it is unavoidable that the temperature of the magnetic circuit increases as the temperature of the Faraday element increases due to high-power light. There was a high possibility that irreversible demagnetization would occur. When irreversible demagnetization occurs in the third magnet in this way, it becomes impossible to stably provide sufficient magnetic flux density to the Faraday element, so there is a possibility that the Faraday rotator will not be able to perform its original function.
本発明は上記課題を鑑みてなされたものであり、外部磁界や温度上昇による不可逆減磁を抑制することができ、かつファラデー素子に十分な磁束密度を安定して与えることができる磁気回路を提供するものである。 The present invention has been made in view of the above problems, and provides a magnetic circuit that can suppress irreversible demagnetization due to external magnetic fields and temperature increases, and can stably provide sufficient magnetic flux density to Faraday elements. It is something to do.
本発明の磁気回路は、光が通過する貫通孔がそれぞれ設けられたサマリウム－コバルト系磁石からなる第１～第３の磁石を有する磁気回路であって、磁気回路は、第１～第３の磁石が前後方向に同軸上にこの順序で配置されてなり、光が磁気回路の貫通孔を通過する方向を光軸方向としたときに、第１の磁石は、光軸方向に垂直な方向に、かつ貫通孔側がＮ極となるように磁化されており、第２の磁石は光軸方向に平行な方向に、かつ第１の磁石側がＮ極となるように磁化されており、第３の磁石は、光軸方向に垂直な方向に、かつ貫通孔側がＳ極となるように磁化されており、第２の磁石が、１、３の磁石以上の保磁力を有することを特徴とする。なお、本発明で単に保磁力と記載する際は、ＨｃＢを指すものとする。 The magnetic circuit of the present invention is a magnetic circuit having first to third magnets made of samarium-cobalt magnets each having a through hole through which light passes, The magnets are arranged coaxially in this order in the front-rear direction, and when the direction in which light passes through the through hole of the magnetic circuit is the optical axis direction, the first magnet is arranged in a direction perpendicular to the optical axis direction. , and is magnetized so that the through-hole side is the north pole, the second magnet is magnetized in a direction parallel to the optical axis direction and so that the first magnet side is the north pole, and the third magnet is magnetized so that the first magnet side is the north pole. The magnet is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side has an S pole, and the second magnet has a coercive force greater than that of the first and third magnets. In addition, when simply describing coercive force in the present invention, it refers to H cB .
上記のような構成において、第２の磁石の貫通孔付近には、第１の磁石と第３の磁石の相互作用で作り出された強い磁界が発生する。しかし、本発明の磁気回路では第２の磁石における保磁力が大きいため、動作点がＢ－Ｈ曲線、Ｊ－Ｈ曲線上のクニック点を越えにくくなり、温度上昇や逆磁界による不可逆減磁発生を抑制することができ、第２の磁石の貫通孔部分における磁束密度を大きく保持しやすくなる。すなわち、ファラデー素子に十分な磁束密度を安定して与えることができる。 In the above configuration, a strong magnetic field created by the interaction between the first magnet and the third magnet is generated near the through hole of the second magnet. However, in the magnetic circuit of the present invention, since the coercive force in the second magnet is large, it becomes difficult for the operating point to exceed the knick point on the BH curve and the JH curve, causing irreversible demagnetization due to temperature rise and reverse magnetic field. This makes it easier to maintain a large magnetic flux density in the through-hole portion of the second magnet. That is, sufficient magnetic flux density can be stably provided to the Faraday element.
さらに、第１～第３の磁石はサマリウム－コバルト系磁石からなる磁石である。サマリウム－コバルト系磁石は、ネオジム磁石と同等の残留磁束密度と保磁力を有するが、温度変化による保磁力の変動が小さく、かつキュリー温度が高いという特徴を有する。そのため、上記磁石からなる磁気回路では、特に高温下において動作点がＢ－Ｈ曲線、Ｊ－Ｈ曲線上のクニック点を越えにくく、不可逆減磁発生を抑制することができ、第２の磁石の貫通孔部分における磁束密度を大きく保持しやすくなる。 Further, the first to third magnets are made of samarium-cobalt magnets. Samarium-cobalt magnets have the same residual magnetic flux density and coercive force as neodymium magnets, but are characterized by small fluctuations in coercive force due to temperature changes and a high Curie temperature. Therefore, in the magnetic circuit made of the above-mentioned magnet, the operating point does not easily exceed the kick point on the B-H curve and the J-H curve, especially under high temperatures, and the occurrence of irreversible demagnetization can be suppressed. It becomes easier to maintain a large magnetic flux density in the through hole portion.
本発明の磁気回路では、第１～第３の磁石が６５０ｋＡ／ｍ以上の保磁力を有することが好ましい。このような保磁力を有することで、第２の磁石における不可逆減磁の発生を抑制することができる。 In the magnetic circuit of the present invention, it is preferable that the first to third magnets have a coercive force of 650 kA/m or more. By having such a coercive force, it is possible to suppress the occurrence of irreversible demagnetization in the second magnet.
本発明の磁気回路では、第２の磁石の光軸方向に沿う長さが、第１、３の磁石の光軸方向に沿う長さ以上であることが好ましい。このようにすれば、第２の磁石における不可逆減磁の発生を抑制することができ、第２の磁石の貫通孔部分における磁束密度を大きく保持しやすくなる。 In the magnetic circuit of the present invention, it is preferable that the length of the second magnet along the optical axis direction is equal to or longer than the length of the first and third magnets along the optical axis direction. In this way, it is possible to suppress the occurrence of irreversible demagnetization in the second magnet, and it becomes easier to maintain a large magnetic flux density in the through-hole portion of the second magnet.
本発明の磁気回路では、第２の磁石の光軸方向に沿う長さが、第１、３の磁石の光軸方向に沿う長さより大きいことが好ましい。 In the magnetic circuit of the present invention, it is preferable that the length of the second magnet along the optical axis direction is longer than the length of the first and third magnets along the optical axis direction.
本発明の磁気回路では、第２の磁石が、第１、３の磁石より大きな保磁力を有することが好ましい。 In the magnetic circuit of the present invention, it is preferable that the second magnet has a larger coercive force than the first and third magnets.
本発明の磁気回路では、貫通孔の断面積が１００ｍｍ２以下であることが好ましい。貫通孔の断面積を１００ｍｍ２以下にすることで、磁束密度が大きくなりやすい。 In the magnetic circuit of the present invention, it is preferable that the cross-sectional area of the through hole is 100 mm 2 or less. By setting the cross-sectional area of the through hole to 100 mm 2 or less, the magnetic flux density tends to increase.
本発明の磁気回路は、光が通過する貫通孔がそれぞれ設けられた第１～第３の磁石を有する磁気回路であって、磁気回路は、第１～第３の磁石が前後方向に同軸上にこの順序で配置されてなり、光が磁気回路の貫通孔を通過する方向を光軸方向としたときに、第１の磁石は、光軸方向に垂直な方向に、かつ貫通孔側がＮ極となるように磁化されており、第２の磁石は光軸方向に平行な方向に、かつ第１の磁石側がＮ極となるように磁化されており、第３の磁石は、光軸方向に垂直な方向に、かつ貫通孔側がＳ極となるように磁化されており、第２の磁石が、第１、３の磁石以上の保磁力を有し、第２の磁石の光軸方向に沿う長さが、第１、３の磁石の光軸方向に沿う長さ以上であることを特徴とする。 The magnetic circuit of the present invention is a magnetic circuit having first to third magnets each having a through hole through which light passes, and the magnetic circuit includes first to third magnets coaxially disposed in the front-back direction. are arranged in this order, and when the direction in which light passes through the through-hole of the magnetic circuit is the optical axis direction, the first magnet is perpendicular to the optical axis direction, and the through-hole side is the N pole. The second magnet is magnetized in a direction parallel to the optical axis direction, with the first magnet side being the north pole, and the third magnet is magnetized in a direction parallel to the optical axis direction. It is magnetized in a vertical direction so that the through-hole side becomes the S pole, and the second magnet has a coercive force greater than that of the first and third magnets, and is along the optical axis direction of the second magnet. It is characterized in that the length is longer than the length along the optical axis direction of the first and third magnets.
上記のような構成において、第２の磁石の貫通孔付近には、第１の磁石と第３の磁石の相互作用で作り出された強い磁界が発生する。しかし、第２の磁石における保磁力が大きいため、動作点がＢ－Ｈ曲線、Ｊ－Ｈ曲線上のクニック点を越えにくくなり、温度上昇や逆磁界による不可逆減磁発生を抑制することができ、第２の磁石の貫通孔部分における磁束密度を大きく保持しやすくなる。また、第２の磁石の光軸方向に沿う長さが、第１、３の磁石の光軸方向に沿う長さ以上であるため、第２の磁石における不可逆減磁の発生を抑制することができ、第２の磁石の貫通孔部分における磁束密度を大きく保持しやすくなる。 In the above configuration, a strong magnetic field created by the interaction between the first magnet and the third magnet is generated near the through hole of the second magnet. However, because the coercive force in the second magnet is large, it becomes difficult for the operating point to exceed the knick point on the BH curve and JH curve, making it possible to suppress the occurrence of irreversible demagnetization due to temperature rise and reverse magnetic field. , it becomes easier to maintain a large magnetic flux density in the through-hole portion of the second magnet. Furthermore, since the length of the second magnet along the optical axis direction is longer than the length of the first and third magnets along the optical axis direction, it is possible to suppress the occurrence of irreversible demagnetization in the second magnet. This makes it easier to maintain a large magnetic flux density in the through-hole portion of the second magnet.
本発明のファラデー回転子は、上記磁気回路と、磁気回路における貫通孔内に配置されており、かつ光が透過する常磁性体からなるファラデー素子とを備えてなることを特徴とする。 The Faraday rotator of the present invention is characterized by comprising the magnetic circuit described above and a Faraday element made of a paramagnetic material that is disposed in a through hole in the magnetic circuit and that transmits light.
本発明のファラデー回転子は、常磁性体がガラス材であることが好ましい。 In the Faraday rotator of the present invention, the paramagnetic material is preferably a glass material.
本発明の磁気光学素子は、上記ファラデー回転子と、ファラデー回転子の磁気回路の光軸方向における一方端に配置されている第１の光学部品及び他方端に配置されている第２の光学部品とを備え、磁気回路の貫通孔を通過する光が、第１の光学部品及び第２の光学部品を通過することを特徴とする。 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 a magnetic circuit of the Faraday rotator, and a second optical component disposed at the other end. It is characterized in that the light passing through the through hole of the magnetic circuit passes through the first optical component and the second optical component.
本発明の磁気光学素子では、第１の光学部品及び第２の光学部品が偏光子であることが好ましい。 In the magneto-optical element of the present invention, it is preferable that the first optical component and the second optical component are polarizers.
本発明によれば、外部磁界や温度上昇による不可逆減磁を抑制することができ、かつファラデー素子に十分な磁束密度を安定して与えることができる磁気回路を提供することができる。 According to the present invention, it is possible to provide a magnetic circuit that can suppress irreversible demagnetization due to an external magnetic field or temperature rise, and can stably provide a sufficient magnetic flux density to a Faraday element.
以下、本発明の実施形態について詳細に説明する。ただし、本発明は以下の実施形態に何ら限定されるものではない。また、各図面において、実質的に同一の機能を有する部材は同一の符号で参照する場合がある。 Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments. Further, in each drawing, members having substantially the same function may be referred to by the same reference numerals.
（磁気回路１）
図１は、本発明の磁気回路の構造を示す模式的断面図である。磁気回路１は、それぞれ貫通孔が設けられた第１の磁石１１、第２の磁石１２及び第３の磁石１３を有する。磁気回路１は、第１の磁石１１、第２の磁石１２及び第３の磁石１３が前後方向に同軸上にこの順序で配置されてなる。なお、同軸上に配置されるとは、光軸方向から見て、各磁石の中央付近が重なるように配置されることをいう。本実施形態では、第１の磁石１１、第２の磁石１２及び第３の磁石１３の貫通孔が連結されることにより、磁気回路の貫通孔２が構成されている。なお、図１中のＮ及びＳの文字は磁極を示し、後述する他の図面においても同様である。
(Magnetic circuit 1)
FIG. 1 is a schematic cross-sectional view showing the structure of the magnetic circuit of the present invention. The magnetic circuit 1 includes a first magnet 11, a second magnet 12, and a third magnet 13, each of which has a through hole. The magnetic circuit 1 includes a first magnet 11, a second magnet 12, and a third magnet 13 arranged coaxially in this order in the front-rear direction. Note that being coaxially arranged means that the magnets are arranged so that the center portions of the magnets overlap when viewed from the optical axis direction. In this embodiment, the through-hole 2 of the magnetic circuit is configured by connecting the through-holes of the first magnet 11, the second magnet 12, and the third magnet 13. Note that the letters N and S in FIG. 1 indicate magnetic poles, and the same applies to other drawings described later.
磁気回路１において、第１の磁石１１と第３の磁石１３は光軸と垂直方向に磁化され、互いに磁化方向が対向している。具体的には、第１の磁石１１は、光軸と垂直な方向に、かつ貫通孔側がＮ極となるように磁化されている。第３の磁石１３は、光軸と垂直な方向に、かつ貫通孔側がＳ極となるように磁化されている。第２の磁石１２は光軸に平行な方向に、かつ第１の磁石１１側がＮ極となるように磁化されている。 In the magnetic circuit 1, the first magnet 11 and the third magnet 13 are magnetized in a direction perpendicular to the optical axis, and their magnetization directions are opposite to each other. Specifically, the first magnet 11 is magnetized in a direction perpendicular to the optical axis so that the through hole side is the north pole. The third magnet 13 is magnetized in a direction perpendicular to the optical axis so that the through-hole side has an S pole. The second magnet 12 is magnetized in a direction parallel to the optical axis so that the first magnet 11 side is the north pole.
磁気回路１を構成する第１～第３の磁石は、サマリウム－コバルト（Ｓｍ－Ｃｏ）を主成分とする磁石から構成されることが好ましい。サマリウム－コバルト系磁石はキュリー温度が６００℃以上であるため、高温下における不可逆減磁を抑制することができる。また、サマリウム－コバルト系磁石の残留磁束密度の温度依存性は、一般に－０．０３％／℃程度であり、ネオジム磁石は－０．１％／℃程度である。また、保磁力の温度依存性は、ネオジム磁石で－０．５％／Ｋ程度、サマリウム－コバルト系磁石で－０．２％／Ｋ程度である。そのため、サマリウム－コバルト系磁石を用いると、磁気回路１の温度上昇による磁石の残留磁束密度及び保磁力の低下を、より効果的に抑制することができる。なお、サマリウム－コバルト（Ｓｍ－Ｃｏ）を主成分とする磁石以外を用いても良い。 Preferably, the first to third magnets constituting the magnetic circuit 1 are composed of magnets containing samarium-cobalt (Sm-Co) as a main component. Since samarium-cobalt magnets have a Curie temperature of 600° C. or higher, irreversible demagnetization at high temperatures can be suppressed. Further, the temperature dependence of the residual magnetic flux density of samarium-cobalt magnets is generally about -0.03%/°C, and that of neodymium magnets is about -0.1%/°C. Further, the temperature dependence of coercive force is about -0.5%/K for neodymium magnets and about -0.2%/K for samarium-cobalt magnets. Therefore, when a samarium-cobalt magnet is used, it is possible to more effectively suppress a decrease in the residual magnetic flux density and coercive force of the magnet due to a rise in the temperature of the magnetic circuit 1. Note that magnets other than those whose main component is samarium-cobalt (Sm-Co) may be used.
磁気回路１を構成する第１～第３の磁石は、保磁力が６５０ｋＡ／ｍ以上であることが好ましく、６６０ｋＡ／ｍ以上がより好ましく、７００ｋＡ／ｍがさらに好ましく、７５０ｋＡ／ｍが特に好ましい。保磁力が低いと、第２の磁石１２が、第１の磁石１１と第３の磁石１３の相互作用で作り出される強い磁界によって動作点がＨ軸へ近づくことにより、磁石が不可逆減磁しやすくなる。また、保磁力が大きいほど高温化で安定した磁気回路１を得ることができるが、サマリウム－コバルト系磁石で得られる保磁力は、現実的には１０００ｋＡ／ｍが上限である。 The first to third magnets constituting the magnetic circuit 1 preferably have a coercive force of 650 kA/m or more, more preferably 660 kA/m or more, even more preferably 700 kA/m, and particularly preferably 750 kA/m. When the coercive force is low, the operating point of the second magnet 12 approaches the H-axis due to the strong magnetic field created by the interaction between the first magnet 11 and the third magnet 13, making it easy for the magnet to be irreversibly demagnetized. Become. Furthermore, the larger the coercive force is, the more stable the magnetic circuit 1 can be obtained at high temperatures; however, in reality, the upper limit of the coercive force that can be obtained with a samarium-cobalt magnet is 1000 kA/m.
また、第１の磁石１１と第３の磁石１３の保磁力は等しいことが好ましい。このようにすれば、第２の磁石１２に均一な磁界を与えることができる。もっとも、第１の磁石１１の保磁力と、第３の磁石１３の保磁力が等しくなくてもよい。 Moreover, it is preferable that the coercive forces of the first magnet 11 and the third magnet 13 are equal. In this way, a uniform magnetic field can be applied to the second magnet 12. However, the coercive force of the first magnet 11 and the coercive force of the third magnet 13 may not be equal.
第２の磁石１２は、第１、第３の磁石以上の保磁力を有する。具体的には、第２の磁石１２の保磁力は、第１、第３の磁石の保磁力の１倍以上であり、１．０５倍以上が好ましく、１．１倍以上が特に好ましい。このようにすれば、第２の磁石１２の貫通孔付近に、第１の磁石１１と第３の磁石１３の相互作用で作り出された強い磁界が発生しても、第２の磁石１２の動作点がＢ－Ｈ曲線、Ｊ－Ｈ曲線上のクニック点を越えにくくなり、温度上昇や逆磁界による不可逆減磁発生を抑制することができ、第２の磁石１２の貫通孔部分における磁束密度を大きく保持しやすくなる。また、サマリウム－コバルト系磁石で得られる保磁力は、現実的には４００～１０００ｋＡ／ｍ程度である。そのため、第２の磁石１２の保磁力は最大で、第１、第３の磁石の保磁力の２．５倍以下が好ましく、２倍以下であることがより好ましく、１．８倍以下であることが特に好ましい。なお、第１の磁石１１の保磁力と、第３の磁石１３の保磁力が等しくない場合は、第１及び第３の磁石のうち、より高い保磁力に対して、上記の値を有するものとする。 The second magnet 12 has a coercive force greater than that of the first and third magnets. Specifically, the coercive force of the second magnet 12 is at least 1 times the coercive force of the first and third magnets, preferably at least 1.05 times, and particularly preferably at least 1.1 times. In this way, even if a strong magnetic field created by the interaction between the first magnet 11 and the third magnet 13 occurs near the through hole of the second magnet 12, the operation of the second magnet 12 will be prevented. This makes it difficult for the point to exceed the knick point on the BH curve and JH curve, making it possible to suppress the occurrence of irreversible demagnetization due to temperature rise and reverse magnetic field, and to reduce the magnetic flux density in the through-hole portion of the second magnet 12. Larger and easier to hold. Further, the coercive force obtained with a samarium-cobalt magnet is actually about 400 to 1000 kA/m. Therefore, the maximum coercive force of the second magnet 12 is preferably 2.5 times or less, more preferably 2 times or less, and 1.8 times or less than the coercive force of the first and third magnets. This is particularly preferred. In addition, if the coercive force of the first magnet 11 and the coercive force of the third magnet 13 are not equal, the one having the above value with respect to the higher coercive force of the first and third magnets. shall be.
また、磁気回路１を構成する第１～第３の磁石の残留磁束密度（Ｂｒ）は、０．７Ｔ以上であることが好ましく、０．８Ｔ以上であることがより好ましく、０．９Ｔ以上であることが特に好ましい。このようにすれば、第２の磁石１２の貫通孔付近に磁束密度の大きい領域を形成することができ、後述するファラデー素子１４に４５°の回転角度を与えることができる。 Further, the residual magnetic flux density (Br) of the first to third magnets constituting the magnetic circuit 1 is preferably 0.7T or more, more preferably 0.8T or more, and 0.9T or more. It is particularly preferable that there be. In this way, a region with high magnetic flux density can be formed near the through hole of the second magnet 12, and a rotation angle of 45 degrees can be given to the Faraday element 14, which will be described later.
また、第１の磁石１１と第３の磁石１３の残留磁束密度は等しいことが好ましい。このようにすれば、第２の磁石１２に均一な磁界を与えることができる。もっとも、第１の磁石１１の保磁力と、第３の磁石１３の残留磁束密度が等しくなくてもよい。 Further, it is preferable that the residual magnetic flux densities of the first magnet 11 and the third magnet 13 are equal. In this way, a uniform magnetic field can be applied to the second magnet 12. However, the coercive force of the first magnet 11 and the residual magnetic flux density of the third magnet 13 may not be equal.
本発明の磁気回路１において、第２の磁石１２の光軸方向に沿う長さが、第１の磁石１１又は第３の磁石１３の光軸方向に沿う長さ以上であることが好ましい。具体的には、第２の磁石１２の長さが、第１の磁石１１及び第３の磁石１３の長さに対して、１倍以上が好ましく、１．０１倍以上であることがより好ましく、１．０５倍以上であることが特に好ましい。このようにすれば、第２の磁石１２の磁化方向の長さが相対的に向上し、第２の磁石１２のパーミアンス係数が大きくなるため、第２の磁石１２の動作点がＢ軸側へ近づき、不可逆減磁の抑制効果が大きくなる。また、第２の磁石１２の光軸方向に沿う長さが大きすぎると、第１の磁石１１と第３の磁石１３の相互作用が弱まるため、第２の磁石１２の貫通孔付近に磁束密度の大きい領域を形成することができなくなる。そのため、第２の磁石１２の光軸方向に沿う長さは、２倍以下が好ましく、１．５倍以下であることがより好ましく、１．４倍以下であることが特に好ましい。なお、第１の磁石１１の光軸方向に沿う長さと、第３の磁石１３の光軸方向に沿う長さが等しくない場合は、第１及び第３の磁石のうち、より長い磁石の光軸方向に沿う長さに対して、上記の値を有するものとする。 In the magnetic circuit 1 of the present invention, it is preferable that the length of the second magnet 12 along the optical axis direction is equal to or longer than the length of the first magnet 11 or the third magnet 13 along the optical axis direction. Specifically, the length of the second magnet 12 is preferably 1 time or more, and more preferably 1.01 times or more, the length of the first magnet 11 and the third magnet 13. , is particularly preferably 1.05 times or more. In this way, the length of the second magnet 12 in the magnetization direction is relatively increased, and the permeance coefficient of the second magnet 12 is increased, so the operating point of the second magnet 12 is shifted to the B-axis side. As the magnet approaches the magnet, the effect of suppressing irreversible demagnetization becomes greater. Furthermore, if the length of the second magnet 12 along the optical axis direction is too large, the interaction between the first magnet 11 and the third magnet 13 will be weakened, resulting in a magnetic flux density near the through hole of the second magnet 12. It becomes impossible to form a large area. Therefore, the length of the second magnet 12 along the optical axis direction is preferably twice or less, more preferably 1.5 times or less, and particularly preferably 1.4 times or less. Note that if the length of the first magnet 11 along the optical axis direction and the length of the third magnet 13 along the optical axis direction are not equal, the light of the longer magnet of the first and third magnets It is assumed that the length along the axial direction has the above value.
本発明の磁気回路１において、第１の磁石１１の光軸方向に沿う長さと、第３の磁石１３の光軸方向に沿う長さが等しいことが好ましい。このようにすれば、第２の磁石１２に均一な磁界を与えることができる。もっとも、第１の磁石１１の光軸方向に沿う長さと、第３の磁石１３の光軸方向に沿う長さが等しくなくともよい。 In the magnetic circuit 1 of the present invention, it is preferable that the length of the first magnet 11 along the optical axis direction is equal to the length of the third magnet 13 along the optical axis direction. In this way, a uniform magnetic field can be applied to the second magnet 12. However, the length of the first magnet 11 along the optical axis direction and the length of the third magnet 13 along the optical axis direction may not be equal.
本発明の磁気回路１において、磁気回路の貫通孔２の断面形状は特に限定されず、矩形や円形であってもよい。組み立てを容易にする点では矩形が好ましく、均一な磁界を付与する点では円形が好ましい。 In the magnetic circuit 1 of the present invention, the cross-sectional shape of the through hole 2 of the magnetic circuit is not particularly limited, and may be rectangular or circular. A rectangular shape is preferred for ease of assembly, and a circular shape is preferred for providing a uniform magnetic field.
磁気回路の貫通孔２の断面積は１００ｍｍ２以下であることが好ましく、３ｍｍ２～８０ｍｍ２がより好ましく、５ｍｍ２～６０ｍｍ２がさらに好ましく、７ｍｍ２～５０ｍｍ２が特に好ましい。断面積が大きくなりすぎると十分な磁束密度が得られず、小さすぎるとファラデー素子１４を磁気回路の貫通孔２内に配置しにくくなる。 The cross-sectional area of the through-hole 2 of the magnetic circuit is preferably 100 mm 2 or less, more preferably 3 mm 2 to 80 mm 2 , even more preferably 5 mm 2 to 60 mm 2 , and particularly preferably 7 mm 2 to 50 mm 2 . If the cross-sectional area is too large, sufficient magnetic flux density cannot be obtained, and if it is too small, it becomes difficult to arrange the Faraday element 14 in the through-hole 2 of the magnetic circuit.
図２は、第１の磁石の構造の一例を示す図である。図２に示す第１の磁石１１は、４個の磁石片を組み合わせて構成されている。なお、第１の磁石１１を構成する磁石片の個数は上記に限定されない。例えば、第１の磁石１１は６個もしくは８個等の磁石片を組み合わせて構成されていてもよい。複数の磁石片を組み合わせて第１の磁石１１を構成することにより、磁界を効果的に大きくすることができる。もっとも、第１の磁石１１は、単体磁石からなっていてもよい。 FIG. 2 is a diagram showing an example of the structure of the first magnet. The first magnet 11 shown in FIG. 2 is constructed by combining four magnet pieces. Note that the number of magnet pieces constituting the first magnet 11 is not limited to the above. For example, the first magnet 11 may be configured by combining six or eight magnet pieces. By configuring the first magnet 11 by combining a plurality of magnet pieces, the magnetic field can be effectively increased. However, the first magnet 11 may be composed of a single magnet.
図３は、第２の磁石の構造の一例を示す図である。図３に示す第２の磁石１２は、１個の単体磁石からなる。なお、第２の磁石１２は、２個以上の磁石片を組み合わせて構成されていてもよい。 FIG. 3 is a diagram showing an example of the structure of the second magnet. The second magnet 12 shown in FIG. 3 consists of one single magnet. Note that the second magnet 12 may be configured by combining two or more magnet pieces.
図４は、第３の磁石の構造の一例を示す図である。図４に示す第３の磁石１３は、第１の磁石１１と同様に、４個の磁石片を組み合わせて構成されている。複数の磁石片を組み合わせて第３の磁石１３を構成することにより、磁界を効果的に大きくすることができる。なお、第３の磁石１３は、６個もしくは８個等の磁石片を組み合わせて構成されていてもよく、単体磁石からなっていてもよい。 FIG. 4 is a diagram showing an example of the structure of the third magnet. The third magnet 13 shown in FIG. 4 is constructed by combining four magnet pieces, similarly to the first magnet 11. By configuring the third magnet 13 by combining a plurality of magnet pieces, the magnetic field can be effectively increased. Note that the third magnet 13 may be constructed by combining six or eight magnet pieces, or may be composed of a single magnet.
（ファラデー回転子１０）
図５は、本発明のファラデー回転子の構造の一例を示す模式的断面図である。ファラデー回転子１０は、光アイソレータや光サーキュレータ等、後述する磁気光学素子２０に用いられる装置である。ファラデー回転子１０は、磁気回路１と、磁気回路の貫通孔２内に配置されたファラデー素子１４とを備える。ファラデー素子１４は、光を透過する常磁性体からなる。
(Faraday rotator 10)
FIG. 5 is a schematic cross-sectional view showing an example of the structure of the Faraday rotator of the present invention. The Faraday rotator 10 is a device used in a magneto-optical element 20, such as an optical isolator or an optical circulator, which will be described later. The Faraday rotator 10 includes a magnetic circuit 1 and a Faraday element 14 arranged in a through hole 2 of the magnetic circuit. The Faraday element 14 is made of a paramagnetic material that transmits light.
ファラデー回転子１０は、図１に示した本発明の磁気回路１を有するため、外部磁界や温度上昇による不可逆減磁が抑制され、かつファラデー素子１４に十分な磁束密度を安定して与えることができるため、安定して使用することが可能である。 Since the Faraday rotator 10 has the magnetic circuit 1 of the present invention shown in FIG. 1, irreversible demagnetization due to an external magnetic field or temperature rise is suppressed, and sufficient magnetic flux density can be stably provided to the Faraday element 14. Therefore, it can be used stably.
また、ファラデー回転子１０には、光を第１の磁石１１側から入射させてもよく、第３の磁石１３側から入射させてもよい。 Furthermore, light may be incident on the Faraday rotator 10 from the first magnet 11 side or from the third magnet 13 side.
また、ファラデー素子１４の断面形状と磁気回路の貫通孔２の断面形状は必ずしも一致させなくともよいが、均一な磁界を与えるという観点では、一致させることが好ましい。 Although the cross-sectional shape of the Faraday element 14 and the cross-sectional shape of the through hole 2 of the magnetic circuit do not necessarily have to match, it is preferable to match them from the viewpoint of providing a uniform magnetic field.
ファラデー素子１４には、常磁性体を用いることができる。中でもガラス材を用いることが好ましい。ガラス材からなるファラデー素子１４は、単結晶材料のような欠陥等によるベルデ定数の変動や消光比の低下が少なく、接着剤からの応力の影響も少ないため、安定したベルデ定数と高い消光比を保つことができる。 A paramagnetic material can be used for the Faraday element 14. Among them, it is preferable to use glass material. The Faraday element 14 made of glass material has a stable Verdet constant and high extinction ratio because it has less variation in Verdet constant and lower extinction ratio due to defects like single crystal materials, and is less affected by stress from adhesives. can be kept.
ファラデー素子１４に用いられるガラス材は、モル％の酸化物換算で、Ｔｂ２Ｏ３の含有量が４０％より多いことが好ましく、４５％以上がより好ましく、４８％以上がさらに好ましく、５１％以上であることが特に好ましい。このようにＴｂ２Ｏ３の含有量を多くすることにより、良好なファラデー効果が得やすくなる。なお、ガラス中においてＴｂは３価や４価の状態で存在するが、本明細書ではこれら全てをＴｂ２Ｏ３に換算した値として表す。 The glass material used for the Faraday element 14 preferably has a Tb 2 O 3 content of more than 40%, more preferably 45% or more, still more preferably 48% or more, and even more preferably 51% in terms of mol% oxide. It is particularly preferable that it is above. By increasing the content of Tb 2 O 3 in this way, it becomes easier to obtain a good Faraday effect. Note that Tb exists in a trivalent or tetravalent state in the glass, but in this specification, all of these are expressed as values converted to Tb 2 O 3 .
ファラデー素子１４に用いられるガラス材において、全Ｔｂに対するＴｂ３＋の割合は、モル％で５５％以上であることが好ましく、６０％以上がより好ましく、８０％以上がさらに好ましく、９０％以上であることが特に好ましい。全Ｔｂに対するＴｂ３＋の割合が少なすぎると、波長３００ｎｍ～１１００ｎｍにおける光透過率が低下しやすくなる。 In the glass material used for the Faraday element 14, the ratio of Tb 3+ to the total Tb is preferably 55% or more in terms of mol%, more preferably 60% or more, even more preferably 80% or more, and even more preferably 90% or more. It is particularly preferable. If the ratio of Tb 3+ to the total Tb is too small, the light transmittance in the wavelength range of 300 nm to 1100 nm tends to decrease.
（磁気光学素子２０）
図６は、本発明の磁気光学素子の構造の一例を示す模式的断面図である。図６に示す磁気光学素子２０は光アイソレータである。磁気光学素子２０は、図５に示したファラデー回転子１０と、磁気回路１の光軸方向における一方端に配置されている第１の光学部品２５及び他方端に配置されている第２の光学部品２６とを備える。第１の光学部品２５及び第２の光学部品２６は、本実施形態では偏光子である。第２の光学部品２６の光透過軸は、第１の光学部品２５の光透過軸に対して４５°傾けられている。
(Magneto-optical element 20)
FIG. 6 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. 6 is an optical isolator. The magneto-optical element 20 includes the Faraday rotator 10 shown in FIG. 5, a first optical component 25 located at one end of the magnetic circuit 1 in the optical axis direction, and a second optical component 25 located at the other end. A component 26 is provided. 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 at 45 degrees with respect to the light transmission axis of the first optical component 25.
磁気光学素子２０に入射する光は、第１の光学部品２５を通過し、直線偏光となって、ファラデー素子１４に入射する。入射した光はファラデー素子１４により４５°回転し、第２の光学部品２６を通過する。第２の光学部品２６を通過した光の一部が反射戻り光となり、偏光面が４５°の角度で第２の光学部品２６を通過する。第２の光学部品２６を通過した反射戻り光は、ファラデー素子１４により、さらに４５°回転され、第１の光学部品２５の光透過軸に対して９０°の直交偏光面となる。そのため、反射戻り光は第１の光学部品２５を透過できず、遮断される。 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 by 45° by the Faraday element 14 and passes through the second optical component 26 . A portion of the light that has passed through the second optical component 26 becomes reflected return light, and passes through the second optical component 26 with the plane of polarization at an angle of 45 degrees. The reflected return light that has passed through the second optical component 26 is further rotated by 45 degrees by the Faraday element 14 to become a polarization plane orthogonal to the light transmission axis of the first optical component 25 at 90 degrees. Therefore, the reflected return light cannot pass through the first optical component 25 and is blocked.
本発明の磁気光学素子２０は、図１に示した本発明の磁気回路１を有するため、外部磁界や温度上昇による不可逆減磁が抑制され、かつファラデー素子１４に十分な磁束密度を安定して与えることができるため、安定して使用することが可能である。 Since the magneto-optical element 20 of the present invention has the magnetic circuit 1 of the present invention shown in FIG. It can be used stably.
なお、図６に示す磁気光学素子２０は光アイソレータであるが、磁気光学素子２０は光サーキュレータであってもよい。この場合には、第１の光学部品２５及び第２の光学部品２６は波長板やビームスプリッタであればよい。もっとも、磁気光学素子２０は、光アイソレータ及び光サーキュレータに限定されない。 Note that although the magneto-optical element 20 shown in FIG. 6 is an optical isolator, the magneto-optical element 20 may be an optical circulator. In this case, the first optical component 25 and the second optical component 26 may be wavelength plates or beam splitters. However, the magneto-optical element 20 is not limited to an optical isolator and an optical circulator.
以下、本発明を実施例に基づいて説明するが、本発明はこれらの実施例に限定されるものではない。 The present invention will be described below based on Examples, but the present invention is not limited to these Examples.
表１は、本発明の実施例１～７及び比較例１を示している。 Table 1 shows Examples 1 to 7 of the present invention and Comparative Example 1.
実施例１～７及び比較例１の磁気回路の磁束密度の平均値は、上記の表１の条件になるように保磁力ＨｃＢ、残留磁束密度Ｂｒ及び長さＬを有する第１～第３の磁石を設定し、第１～第３の磁石で図１のような磁石構造を構成する場合についてシミュレーションを行うことで測定した。なお、上記の磁束密度の平均値は、直径３ｍｍ、長さ１０ｍｍ、ベルデ定数０．２１ｍｉｎ／Ｏｅ・ｃｍのファラデー回転ガラス素子を用いることを想定したものであり、第２の磁石の貫通孔の中央から光軸方向に±５ｍｍの長さにおける磁束密度の平均値のシミュレート値を表すものである。また、上記の「長さ」とは光軸方向に沿う長さのことであり、本実施例では単に長さ又はＬと表記する。 The average value of the magnetic flux density of the magnetic circuits of Examples 1 to 7 and Comparative Example 1 was determined by the first to third magnetic circuits having coercive force H cB , residual magnetic flux density Br, and length L so as to satisfy the conditions shown in Table 1 above. The measurements were made by simulating the case where the first to third magnets constitute a magnet structure as shown in FIG. 1. The average value of the magnetic flux density above is based on the assumption that a Faraday rotating glass element with a diameter of 3 mm, a length of 10 mm, and a Verdet constant of 0.21 min/Oe cm is used. It represents a simulated value of the average value of magnetic flux density in a length of ±5 mm from the center in the optical axis direction. Moreover, the above-mentioned "length" refers to the length along the optical axis direction, and in this embodiment, it is simply written as length or L.
表１から明らかなように、実施例１～７では、第２の磁石の貫通孔の中央から光軸方向に±５ｍｍの長さにおける磁束密度の平均値は１．１３～１．３４Ｔとなり、第１の磁石と第３の磁石の相互作用で作り出された強い磁界の影響を受けても、第２の磁石の貫通孔付近で不可逆減磁が生じにくいため、大きな磁束密度を有する磁気回路が得られた。 As is clear from Table 1, in Examples 1 to 7, the average value of the magnetic flux density at a length of ±5 mm from the center of the through hole of the second magnet in the optical axis direction is 1.13 to 1.34 T, Even if it is affected by the strong magnetic field created by the interaction between the first magnet and the third magnet, irreversible demagnetization is unlikely to occur near the through hole of the second magnet, so a magnetic circuit with a large magnetic flux density is Obtained.
比較例１は、第２の磁石について、ＨｃＢが４１３ｋＡ／ｍ、Ｂｒが０．９５Ｔと小さいこと以外は実施例３と同様に作製された磁気回路であるが、第２の磁石の貫通孔の中央から光軸方向に±５ｍｍ長さにおける磁束密度の平均値は１．０１Ｔと小さくなった。 Comparative Example 1 is a magnetic circuit manufactured in the same manner as Example 3 except that the second magnet has a small H cB of 413 kA/m and a small Br of 0.95 T. The average value of the magnetic flux density in a length of ±5 mm from the center in the optical axis direction was as small as 1.01T.
１ 磁気回路
２ 磁気回路の貫通孔
１０ ファラデー回転子
１１ 第１の磁石
１２ 第２の磁石
１３ 第３の磁石
１４ ファラデー素子
２０ 磁気光学素子
２５ 第１の光学部品
２６ 第２の光学部品
３１ パーミアンス線
３２ Ｂ－Ｈ曲線
３３ Ｊ－Ｈ曲線
３４ クニック点
３５ 高温時のＢ－Ｈ曲線
３６ 低温時のＢ－Ｈ曲線
３７ 高温時のＪ－Ｈ曲線
３８ 低温時のＪ－Ｈ曲線
ａ１、ｂ１、ｃ１、ｄ１、ａ２、ｂ２、ｃ２ 動作点
Ｈ、Ｈ１、Ｈ２ 外部磁界
ΔＢ 不可逆減磁
ＨｃＪ、ＨｃＪ´ 固有保磁力
ＨｃＢ、ＨｃＢ´ 保磁力
Ｂｒ、Ｂｒ´ 残留磁束密度
α、β パーミアンス係数
1 Magnetic circuit 2 Through hole 10 of the magnetic circuit Faraday rotator 11 First magnet 12 Second magnet 13 Third magnet 14 Faraday element 20 Magneto-optical element 25 First optical component 26 Second optical component 31 Permeance line 32 B-H curve 33 J-H curve 34 Knick point 35 B-H curve at high temperature 36 B-H curve at low temperature 37 J-H curve at high temperature 38 J-H curve at low temperature a1, b1, c1 , d1, a2, b2, c2 Operating point H, H1, H2 External magnetic field ΔB Irreversible demagnetization HcJ, HcJ' Intrinsic coercive force HcB, HcB' Coercive force Br, Br' Residual magnetic flux density α, β Permeance coefficient
Claims (11)
前記磁気回路は、前記第１～第３の磁石が前後方向に同軸上にこの順序で配置されてなり、
光が前記磁気回路の前記貫通孔を通過する方向を光軸方向としたときに、前記第１の磁石は、前記光軸方向に垂直な方向に、かつ前記貫通孔側がＮ極となるように磁化されており、
前記第２の磁石は前記光軸方向に平行な方向に、かつ前記第１の磁石側がＮ極となるように磁化されており、
前記第３の磁石は、前記光軸方向に垂直な方向に、かつ前記貫通孔側がＳ極となるように磁化されており、
前記第２の磁石が、前記第１、３の磁石より大きい保磁力を有し、かつ前記第２の磁石の保持力が第１、前記第３の磁石の保持力の１．８倍以下であり、
前記第２の磁石の光軸方向に沿う長さが、前記第１、３の磁石の光軸方向に沿う長さ以上であることを特徴とする、磁気回路。 A magnetic circuit having first to third magnets each provided with a through hole through which light passes,
The magnetic circuit includes the first to third magnets arranged coaxially in this order in the front-rear direction,
When the direction in which light passes through the through-hole of the magnetic circuit is the optical axis direction, the first magnet is oriented in a direction perpendicular to the optical axis direction, with the through-hole side having a north pole. It is magnetized,
The second magnet is magnetized in a direction parallel to the optical axis direction and such that the first magnet side is a north pole,
The third magnet is magnetized in a direction perpendicular to the optical axis direction and with the through hole side having an S pole,
The second magnet has a coercive force larger than that of the first and third magnets, and the coercive force of the second magnet is 1.8 times or less than the coercive force of the first and third magnets. can be,
A magnetic circuit characterized in that the length of the second magnet along the optical axis direction is greater than or equal to the length of the first and third magnets along the optical axis direction.
前記磁気回路は、前記第１～第３の磁石が前後方向に同軸上にこの順序で配置されてなり、
光が前記磁気回路の前記貫通孔を通過する方向を光軸方向としたときに、前記第１の磁石は、前記光軸方向に垂直な方向に、かつ前記貫通孔側がＮ極となるように磁化されており、
前記第２の磁石は前記光軸方向に平行な方向に、かつ前記第１の磁石側がＮ極となるように磁化されており、
前記第３の磁石は、前記光軸方向に垂直な方向に、かつ前記貫通孔側がＳ極となるように磁化されており、
前記第２の磁石の光軸方向に沿う長さが、前記第１、３の磁石の光軸方向に沿う長さ以上であり、
前記第２の磁石が、前記第１、３の磁石より大きい保磁力を有し、かつ前記第２の磁石の保持力が第１、前記第３の磁石の保持力の１．８倍以下であることを特徴とする、磁気回路。 A magnetic circuit having first to third magnets made of samarium-cobalt magnets each having a through hole through which light passes,
The magnetic circuit includes the first to third magnets arranged coaxially in this order in the front-rear direction,
When the direction in which light passes through the through-hole of the magnetic circuit is the optical axis direction, the first magnet is oriented in a direction perpendicular to the optical axis direction, with the through-hole side having a north pole. It is magnetized,
The second magnet is magnetized in a direction parallel to the optical axis direction and such that the first magnet side is a north pole,
The third magnet is magnetized in a direction perpendicular to the optical axis direction and with the through hole side having an S pole,
The length of the second magnet along the optical axis direction is greater than or equal to the length of the first and third magnets along the optical axis direction,
The second magnet has a coercive force larger than that of the first and third magnets, and the coercive force of the second magnet is 1.8 times or less than the coercive force of the first and third magnets. A magnetic circuit characterized by :
前記ファラデー回転子の前記磁気回路の前記光軸方向における一方端に配置されている第１の光学部品及び他方端に配置されている第２の光学部品とを備え、
前記磁気回路の前記貫通孔を通過する光が、前記第１の光学部品及び前記第２の光学部品を通過する、磁気光学素子。 A Faraday rotator according to claim 8 or 9 ;
comprising a first optical component disposed at one end of the magnetic circuit of the Faraday rotator in the optical axis direction and a second optical component disposed at the other end;
A magneto-optical element, wherein light passing through the through hole of the magnetic circuit passes through the first optical component and the second optical component.
The magneto-optical element according to claim 10 , wherein the first optical component and the second optical component are polarizers.
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| JP2000241765A (en) | 1999-02-23 | 2000-09-08 | Tokin Corp | Faraday rotator and optical isolator |
| WO2011078381A1 (en) | 2009-12-25 | 2011-06-30 | 日立金属株式会社 | Magnetic circuit for a faraday rotator and method for manufacturing a magnetic circuit for a faraday rotator |
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| JP2016180858A (en) | 2015-03-24 | 2016-10-13 | 住友金属鉱山株式会社 | Faraday rotator |
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| US5715080A (en) * | 1992-09-11 | 1998-02-03 | Scerbak; David G. | Compact uniform field Faraday isolator |
| JPH11101955A (en) * | 1997-09-26 | 1999-04-13 | Tokin Corp | Isolator for optical use |
| US8547636B1 (en) * | 2010-11-03 | 2013-10-01 | Electro-Optics Technology, Inc. | Tunable magnet structure |
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| JP2000241765A (en) | 1999-02-23 | 2000-09-08 | Tokin Corp | Faraday rotator and optical isolator |
| WO2011078381A1 (en) | 2009-12-25 | 2011-06-30 | 日立金属株式会社 | Magnetic circuit for a faraday rotator and method for manufacturing a magnetic circuit for a faraday rotator |
| US20150198823A1 (en) | 2014-01-13 | 2015-07-16 | Coherent Lasersystems Gmbh & Co. Kg | Faraday rotator for an optical isolator |
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