CN210155454U - Magnetic circuit, Faraday rotator, and magneto-optical element - Google Patents
Magnetic circuit, Faraday rotator, and magneto-optical element Download PDFInfo
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- CN210155454U CN210155454U CN201920798390.XU CN201920798390U CN210155454U CN 210155454 U CN210155454 U CN 210155454U CN 201920798390 U CN201920798390 U CN 201920798390U CN 210155454 U CN210155454 U CN 210155454U
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Abstract
The utility model provides a magnetic circuit and possess Faraday optical rotator and magneto-optical element of this magnetic circuit. The magnetic circuit (1) has first to third magnets each including a samarium-cobalt magnet and provided with a through hole through which light passes, the first to third magnets being coaxially arranged in the front-rear direction, the first magnet (11) being magnetized in a direction perpendicular to the optical axis direction so that the through hole side becomes an N pole, the second magnet (12) being magnetized in a direction parallel to the optical axis direction so that the first magnet (11) side becomes an N pole, the third magnet (13) being magnetized in a direction perpendicular to the optical axis direction so that the through hole side becomes an S pole, the second magnet having a coercive force equal to or larger than that of the first and third magnets. This makes it possible to stably provide a sufficient magnetic flux density to the faraday element while suppressing irreversible demagnetization caused by an external magnetic field and a temperature rise.
Description
Technical Field
The utility model relates to a magnetic circuit, Faraday optical rotator and magneto-optical element.
Background
The faraday rotator is an element composed of a faraday element and a magnet for applying a magnetic field to the faraday element. Faraday rotators have a function of propagating light only in one direction and blocking return light, and therefore are used as magneto-optical elements such as optical isolators and the like in laser oscillators such as optical communication systems and laser processing systems.
The wavelength band used in optical communication systems is mainly 1300nm to 1700nm, and in current faraday rotators, rare-earth iron garnet is used for faraday elements.
On the other hand, in recent years, a wavelength band used for laser processing or the like is on a shorter wavelength side than an optical communication band, and about 1000nm is mainly used. In this wavelength band, the rare earth iron garnet cannot be used because of its large light absorption, and thus a paramagnetic crystal such as Terbium Gallium Garnet (TGG) is used for the faraday element.
However, in order to use such a faraday rotator as an optical isolator, the rotation angle (θ) of faraday rotation needs to be 45 °. It is known that the rotation angle has a relationship expressed by the following formula (1) with the length (L) of the faraday element, the verdet constant (V), and the magnetic flux density (B) parallel to the optical axis.
θ＝V·B·L (1)
The verdet constant depends on the characteristics of the material of the faraday element. Generally, since a paramagnetic material such as TGG has a smaller verdet constant than a rare-earth iron garnet, it is necessary to increase the length of the faraday element and the magnetic flux density parallel to the optical axis applied to the faraday element in order to obtain a faraday rotation angle of 45 °. In particular, in recent years, miniaturization of the apparatus has been desired, and therefore, there has been proposed a technique for improving the magnetic flux density applied to the faraday element by designing the structure of the magnet without increasing the size of the faraday element or the magnet.
For example, patent document 1 discloses a faraday rotator having a magnetic circuit including 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 therebetween. 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 the magnetic circuit, the length of the first magnet and the second magnet along the optical axis direction is L2And L is the length along the third optical axis3When L is2/10≤L3≤L2The relationship of (1) holds.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open No. 2009 and 229802.
SUMMERY OF THE UTILITY MODEL
Technical problem to be solved by the utility model
In the magnetic circuit, a strong magnetic field generated by the interaction between the first magnet and the second magnet occurs in the vicinity of the through hole of the third magnet. The magnetic field is in a direction opposite to the magnetization direction of the third magnet. In this way, when an external magnetic field in the direction opposite to the magnetization direction is generated, it is necessary to consider the influence of the movement of the operating point of the magnet and demagnetization attributed thereto. For explanation, fig. 7 shows an example of demagnetization curves (B-H curve and J-H curve) of the magnet. The B-H curve 32 is a curve showing the relationship between the magnetic flux density B and the external magnetic field H. The J-H curve 33 is a curve showing the relationship between the magnetization J and the external magnetic field H. The intersection points of the curve and the vertical and horizontal axes indicate the remanence Br and intrinsic coercivity H, respectivelycJAnd coercive force HcB. The residual magnetic flux density Br is the magnetic flux density remaining in the magnetic body when the external magnetic field is changed from the state of saturation magnetization to 0. The coercive force is a value of an external magnetic field when a magnetic field in a direction opposite to the magnetization direction held by the magnetic body acts and the magnetization or magnetic flux density becomes 0, the former being expressed as an inherent coercive force HcJThe latter, theExpressed as coercive force HcB. The magnetic flux density (B) of the magnetic material, the external magnetic field strength (H), the magnetization (J), and the magnetic permeability (μ) in vacuum are known0) Has the following relation of formula (2).
B＝μ0H+J (2)
(irreversible demagnetization by 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 B-H curve 32 and moves to the operating point B1 close to the H axis. In addition, when a larger external magnetic field H2 is supplied, the operating point a1 of the magnet moves to the operating point c1 closer to the H axis. At this time, the operating point c1 on the B-H curve 32 is projected to the operating point c2 on the J-H curve 33 beyond the inflection point 34 (the changing point where the magnetic flux density sharply decreases while changing in a gradient) of the J-H curve 33. In this way, when demagnetization occurs due to a larger external magnetic field H2, the operating point a1 of the magnet moves to the operating point d1 when the external magnetic field H2 is removed by projecting the operating point on the B-H curve 32 to the operating point c2 on the J-H curve 33 beyond the inflection point 34 of the J-H curve 33. Here, the operating point d1 is an operating point when the external magnetic field H2 is removed from the operating point c1, and is an intersection point of a straight line parallel to the inclination of the recoil permeability curve passing through the operating point c1 and a straight line passing through the operating point a1 and the origin. 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 Δ B by the external magnetic field H2, and demagnetization is performed in which recovery is not performed unless demagnetization is performed.
As shown in fig. 7, the operating point of the magnet is a point on a B-H curve 32 of the magnet, and is a point indicating the state of the magnetic flux density B and the magnetic field H of the magnet in the magnetic path. A straight line drawn from the origin toward the point is referred to as a magnet wire 31. The magnetic permeability (μ) of the magnet wire 31 is known to be inclined (B/H) in vacuum0) The permeability (P) and the following formula (3).
B/H＝μ0P (3)
(irreversible demagnetization by high temperature)
Fig. 8 shows the temperature change of the demagnetization curve of the neodymium magnet. Respectively show a B-H curve 35 at a high temperature and a B-H curve at a low temperatureB-H curve 36, J-H curve 37 at high temperature, and J-H curve 38 at low temperature. When the temperature of the neodymium magnet is increased, the residual magnetic flux density Br and the inherent coercive force HcJAnd coercive force HcBTo Br' and H, respectivelycJ' and HcB' move. Then, the B-H curve 36 at low temperature and the J-H curve 38 at low temperature are changed to a B-H curve 35 at high temperature and a J-H curve 37 at high temperature, respectively. In such a temperature change, when the operating point on the B-H curve exceeds the turning point 34 of the B-H curve, the magnetic force does not recover, that is, irreversible demagnetization of the magnet due to the temperature change occurs even if the temperature condition recovers. For example, when the external temperature changes from a low temperature to a high temperature, the action point a1 moves to the action point b 1. Since the operating point B1 does not exceed the inflection point on the B-H curve 35 at high temperature, when the external temperature returns from high temperature to low temperature, the external temperature can return from the operating point B1 to the operating point a1, that is, reversible demagnetization can be achieved. On the other hand, when the external temperature changes from low to high, the operating point a2 closer to the H axis moves to the operating point b 2. In this case, since the operating point B2 does not exceed the inflection point 34 on the B-H curve 35 at the high temperature, even if the external temperature returns from the high temperature to the low temperature, the external temperature cannot return from the operating point B2 to the operating point a2 and move to the operating point c 2. 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 Δ B. In particular, as shown in fig. 8, it is known that the B-H curve and the J-H curve of a neodymium magnet greatly change toward the B axis (magnetic flux density) due to a temperature rise, and irreversible demagnetization is likely to occur due to movement of the operating point at high temperature. The operating point c2 in fig. 8 can be obtained by the same method as the operating point d1 in fig. 7.
Further, the third magnet described in patent document 1 has a shape shorter than the first and second magnets in the magnetization direction, and in this magnet having a shape shorter in the magnetization direction, the magnetic permeability depending on the shape of the magnet is also considered, and in general, the magnetic permeability is smaller in a magnet having a shape shorter in the magnetization direction, that is, having magnetic poles close to each other, and the magnetic permeability is also the slope of the magnet wire 31 as shown in formula (3). for example, as shown in fig. 9, the magnet wire 31 passing through the operating point a1 has a slope α larger than the slope β of the magnet wire 31 passing through the operating point B1, that is, a larger magnetic permeability, and in other words, the magnet having a small magnetic permeability β has an operating point at a position close to the H axis, and therefore, the magnet more easily exceeds the inflection point 34 on the B-H curve 32 and the J-H curve 33, and the above-described reverse magnetic field and irreversible demagnetization caused by high temperature are easily generated.
As described above, the third magnet of the magnetic circuit described in patent document 1 is used as a magnet at an unfavorable operating point, and therefore, irreversible demagnetization is likely to occur in a reverse magnetic field and at a high temperature. In particular, when the magnetic circuit is used as the magneto-optical element of the high-output laser isolator lamp, the temperature rise of the magnetic circuit accompanying the temperature rise of the faraday element due to the high-output light cannot be avoided, and therefore, the third magnet is likely to undergo irreversible demagnetization due to a high temperature. When irreversible demagnetization occurs in the third magnet, a sufficient magnetic flux density cannot be stably supplied to the faraday rotator, and thus the faraday rotator may not be able to achieve its original function.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a magnetic circuit capable of suppressing irreversible demagnetization caused by an external magnetic field and a temperature rise and stably providing sufficient magnetic flux density to a faraday element.
Means for solving the problems
The utility model discloses a magnetic circuit has the first ~ third magnet that has the perforating hole that supplies light to pass through respectively of compriseing samarium-cobalt system magnet, its characterized in that: the magnetic path is composed of first to third magnets coaxially arranged in the front-rear direction in this order, and when the direction of light passing through the through hole of the magnetic path is set to the optical axis direction, the first magnet is magnetized in the direction perpendicular to the optical axis direction so that the through hole side is provided with the N pole, the second magnet is magnetized in the direction parallel to the optical axis direction so that the first magnet side is provided with the N pole, the third magnet is magnetized in the direction perpendicular to the optical axis direction so that the through hole side is provided with the S pole, and the second magnet has the first magnet and the correctionForce. Furthermore, the coercivity is described as H in the present inventioncB。
In the above configuration, a strong magnetic field is generated in the vicinity of the through hole of the second magnet by the interaction between the first magnet and the third magnet. However, in the magnetic circuit of the present invention, since the coercive force of the second magnet is large, the operating point hardly exceeds the turning point on the B-H curve or the J-H curve, and occurrence of irreversible demagnetization due to temperature rise and a reverse magnetic field can be suppressed, and the magnetic flux density in the through hole portion of the second magnet can be easily maintained largely. That is, a sufficient magnetic flux density can be stably supplied to the faraday element.
The first to third magnets are magnets made of samarium-cobalt magnets. The samarium-cobalt magnet has a residual magnetic flux density and a coercive force equivalent to those of a neodymium magnet, but has characteristics that a change in coercive force due to a temperature change is small and a curie temperature is high. Therefore, in the magnetic circuit including the magnet, the operating point is hard to exceed the turning point on the B-H curve or the J-H curve particularly at high temperature, and the occurrence of irreversible demagnetization can be suppressed, and the magnetic flux density in the through hole portion of the second magnet can be easily maintained to a large extent.
In the magnetic circuit of the present invention, it is preferable that the first to third magnets have a coercive force of 650kA/m or more. By having such a coercive force, the occurrence of irreversible demagnetization in the second magnet can be suppressed.
In the magnetic circuit of the present invention, it is preferable that the length of the second magnet in the optical axis direction is equal to or longer than the length of the first and third magnets in the optical axis direction. Accordingly, it is possible to suppress the occurrence of irreversible demagnetization in the second magnet and easily maintain the magnetic flux density in the through hole portion of the second magnet to a large extent.
In the magnetic circuit of the present invention, it is preferable that the length of the second magnet in the optical axis direction is larger than the lengths of the first and third magnets in the optical axis direction.
In the magnetic circuit of the present invention, it is preferable that the second magnet has a coercive force larger than those of the first and third magnets.
The magnetic circuit of the utility modelIn the above-described aspect, the cross-sectional area of the through-hole is preferably 100mm2The following. The cross-sectional area of the through-hole is set to 100mm2Hereinafter, the magnetic flux density tends to increase.
The utility model discloses a magnetic circuit has the first ~ third magnet that is provided with the perforating hole that supplies light to pass through respectively, a serial communication port, the magnetic circuit is disposed in proper order on the same axle by first ~ third magnet in the front rear direction and constitutes, when establishing the direction of the perforating hole that passes through the magnetic circuit as the optical axis direction with light, first magnet is magnetized in the direction perpendicular with the optical axis direction with the mode that makes the perforating hole side become the N utmost point, second magnet is magnetized in the direction parallel with the optical axis direction with the mode that makes the first magnet side become the N utmost point, third magnet is magnetized in the direction perpendicular with the optical axis direction with the mode that makes the perforating hole side become the S utmost point, the second magnet has the coercive force more than first magnet and third magnet, the length of second magnet along the optical axis direction is more than the length of first magnet and third magnet along the optical axis direction.
In the above configuration, a strong magnetic field is generated in the vicinity of the through hole of the second magnet by the interaction between the first magnet and the third magnet. However, since the coercive force of the second magnet is large, the operating point hardly exceeds the turning point on the B-H curve or the J-H curve, the occurrence of irreversible demagnetization due to temperature rise and the reverse magnetic field can be suppressed, and the magnetic flux density in the through-hole portion of the second magnet can be easily maintained largely. Further, since the length of the second magnet in the optical axis direction is equal to or greater than the length of the first and third magnets in the optical axis direction, it is possible to suppress the occurrence of irreversible demagnetization in the second magnet and easily maintain the magnetic flux density in the through hole portion of the second magnet to a large extent.
The Faraday rotator of the present invention comprises the magnetic circuit and a Faraday element which is disposed in the through hole of the magnetic circuit and is composed of a paramagnetic material capable of transmitting light.
The paramagnetic material of the faraday optical rotator of the present invention is preferably a glass material.
The magneto-optical element of the present invention includes the above faraday rotator, a first optical member disposed at one end of the magnetic circuit of the faraday rotator in the optical axis direction, and a second optical member disposed at the other end, and light passing through the through hole of the magnetic circuit passes through the first optical member and the second optical member.
In the magneto-optical element of the present invention, it is preferable that the first optical member and the second optical member are polarizers.
Effect of the utility model
According to the present invention, a magnetic circuit can be provided which can suppress irreversible demagnetization caused by an external magnetic field and a temperature rise and can stably provide sufficient magnetic flux density to a faraday element.
Drawings
Fig. 1 is a schematic cross-sectional view showing an example of the structure of a magnetic circuit according to the present invention.
Fig. 2 is a diagram showing an example of the structure of the first magnet according to the present invention.
Fig. 3 is a diagram showing an example of the structure of the second magnet according to the present invention.
Fig. 4 is a diagram showing an example of the structure of the third magnet according to the present invention.
Fig. 5 is a schematic cross-sectional view showing an example of the structure of the faraday rotator according to the present invention.
Fig. 6 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element according to the present invention.
Fig. 7 is a diagram showing an example of demagnetization curves (B-H curve and J-H curve) of the magnet.
Fig. 8 is a diagram showing an example of temperature changes (B-H curve and J-H curve) of the demagnetization curve of a neodymium magnet.
Fig. 9 is a diagram showing an example of demagnetization curves (B-H curve and J-H curve) of the magnet.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the drawings, components having substantially the same function are sometimes referred to by the same reference numerals.
(magnetic circuit 1)
Fig. 1 is a schematic cross-sectional view showing the structure of a magnetic circuit according to the present invention. The magnetic circuit 1 includes a first magnet 11, a second magnet 12, and a third magnet 13 each having a through hole. The magnetic circuit 1 is configured by arranging a first magnet 11, a second magnet 12, and a third magnet 13 coaxially in the front-rear direction in this order. The coaxial arrangement means that the magnets are arranged so as to overlap each other near the center of each magnet when viewed from the optical axis direction. In the present embodiment, the through-holes connecting the first magnet 11, the second magnet 12, and the third magnet 13 constitute the through-hole 2 of the magnetic circuit. Note that the characters N and S in fig. 1 denote magnetic poles, and the same applies to other drawings described later.
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 the 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 becomes the N-pole. The third magnet 13 is magnetized in a direction perpendicular to the optical axis so that the through-hole side becomes the S-pole. The second magnet 12 is magnetized in a direction parallel to the optical axis so that the first magnet 11 side becomes an N pole.
The first to third magnets constituting the magnetic circuit 1 are preferably made of a magnet having samarium-cobalt (Sm-Co) as a main component. The samarium-cobalt magnet has a Curie temperature of 600 ℃ or higher, and therefore, irreversible demagnetization at high temperatures can be suppressed. Further, the temperature dependency of the residual magnetic flux density of the samarium-cobalt magnet is generally about-0.03%/deg.C, and the temperature dependency of the neodymium magnet is about-0.1%/deg.C. In addition, the temperature dependence of coercive force is about-0.5%/K in a neodymium magnet and about-0.2%/K in a samarium-cobalt magnet. Therefore, when the samarium-cobalt-based magnet is used, the decrease in the residual magnetic flux density and coercive force of the magnet due to the temperature increase of the magnetic circuit 1 can be more effectively suppressed. In addition, a magnet having samarium-cobalt (Sm-Co) as a main component may be used.
The coercive force of the first to third magnets constituting the magnetic circuit 1 is preferably 650kA/m or more, more preferably 660kA/m or more, still more preferably 700kA/m, and particularly preferably 750 kA/m. When the coercive force is low, the second magnet 12 is likely to irreversibly demagnetize because the operating point is brought close to the H axis by a strong magnetic field generated by the interaction between the first magnet 11 and the third magnet 13. Further, as the coercive force is larger, the magnetic circuit 1 stabilized at a high temperature can be obtained, but the coercive force obtained by the samarium-cobalt magnet is actually 1000kA/m as an upper limit.
The coercive force of the first magnet 11 and the coercive force of the third magnet 13 are preferably equal to each other. This makes it possible to provide a uniform magnetic field 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.
The second magnet 12 has a coercive force equal to or higher than that of the first and third magnets. Specifically, the coercive force of the second magnet 12 is 1 time or more, preferably 1.05 times or more, and particularly preferably 1.1 times or more of the coercive force of the first and third magnets. Accordingly, even if a strong magnetic field is generated in the vicinity of the through-hole of the second magnet 12 due to the interaction between the first magnet 11 and the third magnet 13, the operating point of the second magnet 12 is less likely to exceed the turning point on the B-H curve or the J-H curve, and the occurrence of irreversible demagnetization due to temperature rise and the inverse magnetic field can be suppressed, and the magnetic flux density in the through-hole portion of the second magnet 12 can be easily maintained to a large extent. In addition, the coercive force obtained from the samarium-cobalt magnet is actually about 400 to 1000 kA/m. Therefore, the coercive force of the second magnet 12 is preferably 2.5 times or less, more preferably 2 times or less, and particularly preferably 1.8 times or less the coercive force of the maximum first and third magnets. When the coercive force of the first magnet 11 and the coercive force of the third magnet 13 are not equal to each other, the magnet having the higher coercive force of the first and third magnets is set to the value described above.
The remanence (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 particularly preferably 0.9T or more. Accordingly, a region having a large magnetic flux density can be formed in the vicinity of the through hole of the second magnet 12, and a rotation angle of 45 ° can be provided to the faraday element 14 described later.
The first magnet 11 and the third magnet 13 preferably have the same residual magnetic flux density. This makes it possible to provide a uniform magnetic field 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 to each other.
In the magnetic circuit 1 of the present invention, the length of the second magnet 12 in the optical axis direction is preferably equal to or greater than the length of the first magnet 11 or the third magnet 13 in the optical axis direction. Specifically, the length of the second magnet 12 is preferably 1 time or more, more preferably 1.01 times or more, and particularly preferably 1.05 times or more, the length of the first magnet 11 and the third magnet 13. Accordingly, the length of the magnetization direction of the second magnet 12 is relatively increased, and the magnetic permeability of the second magnet 12 is increased, so that the operating point of the second magnet 12 approaches the B axis side, and the effect of suppressing irreversible demagnetization is increased. Further, when the length of the second magnet 12 in the optical axis direction is too large, the interaction between the first magnet 11 and the third magnet 13 is weakened, and therefore, a region having a large magnetic flux density cannot be formed in the vicinity of the through hole of the second magnet 12. Therefore, the length of the second magnet 12 in the optical axis direction is preferably 2 times or less, more preferably 1.5 times or less, and particularly preferably 1.4 times or less. In addition, in the case where the length of the first magnet 11 in the optical axis direction and the length of the third magnet 13 in the optical axis direction are not equal, the magnet having the longer length in the optical axis direction out of the first and third magnets is made to have the above-described value.
In the magnetic circuit 1 of the present invention, the length of the first magnet 11 in the optical axis direction and the length of the third magnet 13 in the optical axis direction are preferably equal to each other. This makes it possible to provide a uniform magnetic field to the second magnet 12. However, the length of the first magnet 11 in the optical axis direction and the length of the third magnet 13 in the optical axis direction may not be equal to each other.
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 preferable at a point where assembly is easy, and a circular shape is preferable at a point where a uniform magnetic field is applied.
The cross-sectional area of the through-hole 2 of the magnetic circuit is preferably 100mm2Hereinafter, more preferably 3mm2～80mm2More preferably 5mm2～60mm2Particularly preferably 7mm2～50mm2. When the sectional area is too large, the fluid cannot be filledIf the fractional magnetic flux density is too small, it is difficult to dispose the faraday element 14 in the through hole 2 of the magnetic circuit.
Fig. 2 is a diagram showing an example of the structure of the first magnet. The first magnet 11 shown in fig. 2 is configured by combining 4 magnet pieces. 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 6 or 8 magnet pieces or the like. By combining a plurality of magnet pieces to form the first magnet 11, the magnetic field can be effectively increased. However, the first magnet 11 may be formed of a single magnet.
Fig. 3 is a diagram showing an example of the structure of the second magnet. The second magnet 12 shown in fig. 3 is constituted by 1 single magnet. The second magnet 12 may be configured by combining 2 or more magnet pieces.
Fig. 4 is a diagram showing an example of the structure of the third magnet. The third magnet 13 shown in fig. 4 is configured by combining 4 magnet pieces, similarly to the first magnet 11. By combining a plurality of magnet pieces to form the third magnet 13, the magnetic field can be effectively increased. The third magnet 13 may be formed by combining 6 or 8 magnet pieces or the like, or may be formed by a single magnet.
(Faraday rotator 10)
Fig. 5 is a schematic cross-sectional view showing an example of the structure of the faraday rotator according to the present invention. The faraday rotator 10 is used for a magneto-optical element 20 described later, such as an optical isolator or an optical circulator. The faraday rotator 10 includes a magnetic circuit 1 and a faraday element 14 disposed in a through hole 2 of the magnetic circuit. The faraday element 14 is made of a paramagnetic material that can transmit light.
Since the faraday rotator 10 has the magnetic circuit 1 of the present invention shown in fig. 1, irreversible demagnetization caused by an external magnetic field and a temperature rise can be suppressed, and sufficient magnetic flux density can be stably supplied to the faraday element 14, and thus, the faraday rotator can be stably used.
Further, light may be made incident on the faraday rotator 10 from the first magnet 11 side or may be made incident from the third magnet 13 side.
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 have to be uniform, but are preferably uniform from the viewpoint of providing a uniform magnetic field.
A paramagnetic material can be used for the faraday element 14. Among them, a glass material is preferably used. The faraday element 14 made of a glass material is less likely to have a fluctuation in the verdet constant and a decrease in the extinction ratio due to defects in a single crystal material, etc., and is less likely to be affected by stress from a binder, so that a stable verdet constant and a high extinction ratio can be maintained.
Glass material for Faraday element 14 has Tb converted to oxide in mol%2O3The content of (b) is preferably more than 40%, more preferably 45% or more, further preferably 48% or more, particularly preferably 51% or more. Thus, by increasing Tb2O3The content of (3) makes it easy to obtain a good Faraday effect. Note that Tb is present in the glass in a state of 3-valent or 4-valent, but in the present specification, all of them are converted to Tb2O3The values of (b) indicate (a).
Of the glass materials used for the Faraday element 14, Tb3+The proportion of the total Tb is preferably 55% or more, more preferably 60% or more, still more preferably 80% or more, and particularly preferably 90% or more in mol%. Tb3+When the ratio to total Tb is too small, the light transmittance at a wavelength of 300nm to 1100nm tends to decrease.
(magneto-optical element 20)
Fig. 6 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element according to 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 member 25 disposed at one end in the optical axis direction of the magnetic circuit 1, and a second optical member 26 disposed at the other end. The first optical member 25 and the second optical member 26 are polarizers in the present embodiment. The light transmission axis of the second optical member 26 is inclined at 45 ° with respect to the light transmission axis of the first optical member 25.
The light incident on the magnetic optical element 20 is linearly polarized by the first optical member 25 and is incident on the faraday element 14. The incident light is rotated by 45 ° by the faraday element 14 and passes through the second optical member 26. A part of the light passing through the second optical member 26 becomes reflected return light, and passes through the second optical member 26 at an angle of 45 ° to the plane of polarization. The reflected return light having passed through the second optical member 26 is further rotated by 45 ° by the faraday element 14, and becomes a cross polarization plane of 90 ° with respect to the light transmission axis of the first optical member 25. Therefore, the reflected return light is not transmitted through the first optical member 25 and is blocked.
The magneto-optical element 20 of the present invention has the magnetic circuit 1 of the present invention shown in fig. 1, and therefore, irreversible demagnetization caused by an external magnetic field and a temperature rise can be suppressed, and sufficient magnetic flux density can be stably provided to the faraday element 14, and therefore, the magneto-optical element can be stably used.
The magneto-optical element 20 shown in fig. 6 is an optical isolator, but the magneto-optical element 20 may be an optical circulator. In this case, the first optical member 25 and the second optical member 26 may be wavelength plates or beam splitters. However, the magneto-optical element 20 is not limited to the optical isolator and the optical circulator.
Examples
The present invention will be described below with reference to examples, but the present invention is not limited to these examples.
Table 1 below shows examples 1 to 7 of the present invention and comparative example 1.
[ TABLE 1 ]
The coercive force H was set so as to satisfy the conditions of Table 1cBAnd first to third magnets having a residual magnetic flux density Br and a length L, and in the case where the magnet structure as shown in fig. 1 is configured by the first to third magnets, the average value of the magnetic flux densities of the magnetic circuits of examples 1 to 7 and comparative example 1 was measured by simulation. The average value of the magnetic flux densities is a value assuming that a Faraday rotation glass element having a diameter of 3mm, a length of 10mm and a Vid constant of 0.21min/Oe · cm is used, and represents a magnetic flux density of a length of + -5 mm from the center of the through hole of the second magnet in the optical axis directionAnalog value of the mean value of (a). In addition, the above-mentioned "length" is a length along the optical axis direction, and is expressed as a length or L alone in the present embodiment.
As seen from table 1, in examples 1 to 7, the average value of the magnetic flux density of the length of ± 5mm from the center of the through hole of the second magnet in the optical axis direction was 1.13 to 1.34T, and even when the magnetic field generated by the interaction between the first magnet and the third magnet was affected, irreversible demagnetization was less likely to occur in the vicinity of the through hole of the second magnet, and therefore, a magnetic circuit having a large magnetic flux density could be obtained.
Comparative example 1, H of second magnetcBA magnetic circuit was fabricated in the same manner as in example 3, except that 413kA/m and Br were as small as 0.95T, but the average value of the magnetic flux density of ± 5mm in length along the optical axis direction from the center of the through hole of the second magnet was as small as 1.01T.
Description of the symbols
1 magnetic circuit
2 through hole of magnetic circuit
10 st optical rotator
11 a magnet
12 two magnets
13 three magnets
14 st element
20 optical element
25 an optical component
26 two optical components
31 wire
32-H curve
Curve 33-H
34 break point
B-H curve at 35 deg.C
B-H curve at 36 deg.C
37J-H curve at high temperature
38J-H curve at low temperature
a1, b1, c1, d1, a2, b2 and c2 action points
H. H1, H2 external magnetic field
Reversible demagnetization of delta B
HcJ, HcJ' have coercive force
Hard strength of HcB and HcB
Residual flux density of Br, Br
α, β.
Claims (11)
1. A magnetic circuit comprising first to third magnets each of which is composed of a samarium-cobalt magnet and is provided with through holes through which light passes, characterized in that:
the magnetic path is formed by arranging the first to third magnets coaxially in the front-rear direction in order,
the first magnet is magnetized in a direction perpendicular to the optical axis direction so that the through hole side becomes an N-pole when a direction in which light passes through the through hole of the magnetic circuit is defined as the optical axis direction,
the second magnet is magnetized in a direction parallel to the optical axis direction so that the first magnet side becomes an N pole,
the third magnet is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side becomes an S-pole,
the second magnet has a coercive force equal to or higher than that of the first magnet and that of the third magnet.
2. The magnetic circuit of claim 1, wherein:
the first to third magnets have a coercive force of 650kA/m or more.
3. A magnetic circuit according to claim 1 or 2, characterized in that:
the length of the second magnet in the optical axis direction is equal to or greater than the length of the first magnet and the third magnet in the optical axis direction.
4. A magnetic circuit according to claim 1 or 2, characterized in that:
the second magnet has a length in the optical axis direction that is greater than lengths in the optical axis direction of the first magnet and the third magnet.
5. A magnetic circuit according to claim 1 or 2, characterized in that:
the second magnet has a larger coercive force than the first magnet and the third magnet.
6. A magnetic circuit according to claim 1 or 2, characterized in that:
the cross section of the through hole is 100mm2The following.
7. A magnetic circuit comprising first to third magnets each provided with a through hole through which light passes, characterized in that:
the magnetic path is formed by arranging the first to third magnets coaxially in the front-rear direction in order,
the first magnet is magnetized in a direction perpendicular to the optical axis direction so that the through hole side becomes an N-pole when a direction in which light passes through the through hole of the magnetic circuit is defined as the optical axis direction,
the second magnet is magnetized in a direction parallel to the optical axis direction so that the first magnet side becomes an N pole,
the third magnet is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side becomes an S-pole,
the second magnet has a coercive force equal to or higher than that of the first magnet and that of the third magnet,
the length of the second magnet in the optical axis direction is equal to or greater than the length of the first magnet and the third magnet in the optical axis direction.
8. A faraday rotator, comprising:
the magnetic circuit of any of claims 1-7; and
and a faraday element which is disposed in the through hole of the magnetic circuit and is composed of a paramagnetic material that transmits light.
9. A Faraday rotator according to claim 8, characterized in that:
the paramagnetic substance is made of glass material.
10. A magneto-optical element, comprising:
a faraday rotator according to claim 8 or 9; and
a first optical member disposed at one end of the magnetic circuit of the Faraday rotator in the optical axis direction and a second optical member disposed at the other end,
the light passing through the through hole of the magnetic circuit passes through the first optical member and the second optical member.
11. The magneto-optical element of claim 10, wherein:
the first optical component and the second optical component are polarizers.
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| JP2018-104884 | 2018-05-31 | ||
| JP2018104884 | 2018-05-31 | ||
| JP2019038635A JP7356631B2 (en) | 2018-05-31 | 2019-03-04 | Magnetic circuits, Faraday rotators and magneto-optical elements |
| JP2019-038635 | 2019-03-04 |
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| CN210155454U true CN210155454U (en) | 2020-03-17 |
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| JP7484470B2 (en) | 2020-06-15 | 2024-05-16 | 日本電気硝子株式会社 | Magnetic circuit, Faraday rotator, and magneto-optical device |
| JP7476686B2 (en) * | 2020-06-15 | 2024-05-01 | 日本電気硝子株式会社 | Magnetic circuit, Faraday rotator, and magneto-optical device |
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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 |
| JP2000241765A (en) | 1999-02-23 | 2000-09-08 | Tokin Corp | Faraday rotator and optical isolator |
| EP2518552A4 (en) | 2009-12-25 | 2017-06-07 | Hitachi Metals, Ltd. | Magnetic circuit for a faraday rotator and method for manufacturing a magnetic circuit for a faraday rotator |
| US8547636B1 (en) * | 2010-11-03 | 2013-10-01 | Electro-Optics Technology, Inc. | Tunable magnet structure |
| US9304337B2 (en) | 2014-01-13 | 2016-04-05 | Coherent Lasersystems Gmbh | Faraday rotator for an optical isolator |
| JP2016180858A (en) | 2015-03-24 | 2016-10-13 | 住友金属鉱山株式会社 | Faraday rotator |
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| JP7356631B2 (en) | 2023-10-05 |
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