Faraday rotor, magnetic circuit, and magneto-optical element

Abstract

The present invention provides a Faraday rotor that can increase the magnetic flux density in the region where the Faraday element is located. [Solution] The Faraday rotor 1 of the present invention comprises a magnetic circuit 2 having a first magnet body 3 having a through hole 3c and a second magnet body 4 having at least a part of it disposed within the through hole 3c, a reflective film 6 disposed on the second magnet body 4, and a Faraday element 5 disposed on the reflective film 6, wherein when the direction through the through hole 3c of the first magnet body 3 is defined as the axial direction A, the first magnet body 3 is magnetized in a direction perpendicular to the axial direction A, the second magnet body 4 is magnetized in the axial direction A, the second magnet body 4 has a first main surface 4a and a second main surface 4b facing each other, the first main surface 4a is located within the through hole 3c of the first magnet body 3, and the Faraday element 5 is disposed on the reflective film 6 provided on the first main surface 4a of the second magnet body 4.

Description

【Technical Field】 【0001】 The present invention relates to a Faraday rotor, a magnetic circuit, and a magneto-optical element. 【Background Art】 【0002】 As a magneto-optical element including a Faraday rotor, an optical isolator is widely known. An optical isolator is a magneto-optical element that propagates light in only one direction and blocks the light reflected back. The optical isolator is used in a laser oscillator used in an optical communication system, a laser processing system, or the like. 【0003】 In a conventional optical isolator, a Faraday element is disposed in a cylindrical magnetic circuit constituted by a magnet. Light enters from one end face of the Faraday element and exits from the other end face. Along with this, the polarization plane of the light rotates. In the Faraday element, when the surface where light enters is defined as the incident surface and the surface where light exits is defined as the exit surface, in the conventional optical isolator, the incident surface and the exit surface are different surfaces from each other. 【0004】 In recent years, an optical isolator has been proposed in which the incident surface and the exit surface are the same surface by reflecting the light incident on the Faraday element. In Patent Document 1 below, an example of such an optical isolator is disclosed. 【0005】 In the optical isolator described in Patent Document 1, a heat sink is provided on the magnet. A disk-shaped Faraday element is provided on the heat sink. The light incident on the Faraday element is reflected by the heat sink. Then, the light exits from the same surface as the surface where the light enters in the Faraday element. 【Prior Art Documents】 【Patent Documents】 【0006】 【Patent Document 1】 German Patent Application Publication No. 102010028213 [Overview of the project] [Problems that the invention aims to solve] 【0007】 However, in the optical isolator described in Patent Document 1, the magnetic flux density cannot be sufficiently high in the region where the Faraday element is located. 【0008】 The present invention has been made in view of the above problems, and aims to provide a Faraday rotor, a magnetic circuit, and a magneto-optical element that can increase the magnetic flux density in the region where the Faraday element is located. [Means for solving the problem] 【0009】 A Faraday rotor according to embodiment 1 of the present invention comprises a magnetic circuit having a first magnet body having a through hole and a second magnet body having at least a portion of it disposed within the through hole, a reflective film disposed on the second magnet body, and a Faraday element disposed on the reflective film, wherein when the direction in which the first magnet body passes through the through hole is defined as the axial direction, the first magnet body is magnetized in a direction perpendicular to the axial direction, the second magnet body is magnetized in the axial direction, the second magnet body has a first main surface and a second main surface facing each other, the first main surface is located within the through hole of the first magnet body, and the Faraday element is disposed on the reflective film provided on the first main surface of the second magnet body. 【0010】 In the Faraday rotor of embodiment 2, it is preferable that, in embodiment 1, the first magnet body is magnetized in a direction perpendicular to the axial direction and with the through-hole side being the north pole. 【0011】 In the Faraday rotor of embodiment 3, it is preferable that, in embodiment 1, the first magnet body is magnetized in a direction perpendicular to the axial direction and with the through-hole side being the south pole. 【0012】 In the Faraday rotor of embodiment 4, it is preferable that the first magnet body includes four magnet pieces in any one embodiment from embodiment 1 to embodiment 3. 【0013】 In the Faraday rotor of embodiment 5, it is preferable that the Faraday elements are fixed in any one embodiment from embodiment 1 to embodiment 4, and that the rotor further includes a chiller for cooling the Faraday elements. 【0014】 In the Faraday rotor of embodiment 6, it is preferable that, in any one embodiment from embodiment 1 to embodiment 5, the Faraday element is located both inside and outside the through-hole of the first magnet body. 【0015】 In the Faraday rotor of Embodiment 7, in any one embodiment from Embodiments 1 to 6, when the dimension of the first magnet body along the direction perpendicular to the axial direction is the width w1 of the first magnet body, and the dimension of the second magnet body along the direction perpendicular to the axial direction is the width w2 of the second magnet body, it is preferable that the ratio of the width w1 to the width w2, w1 / w2, is 1.2 or more and 5.0 or less. 【0016】 In the Faraday rotor of embodiment 8, in any one embodiment from embodiment 1 to embodiment 7, it is preferable that the shape of the first magnet body is cylindrical and the outer shape of the first magnet body when viewed from the axial direction is square. 【0017】 In the Faraday rotor of embodiment 9, it is preferable that the shape of the first magnet body is cylindrical in any one embodiment from embodiment 1 to embodiment 7. 【0018】 In the Faraday rotor of Embodiment 10, in any one of Embodiments 1 to 9, the reflection film is provided on both the first main surface and the second main surface of the second magnetic body, the Faraday element is a first Faraday element, and a second Faraday element disposed on the reflection film provided on the second main surface of the second magnetic body is further provided, and it is preferable that the second main surface of the second magnetic body is located in the through hole of the first magnetic body. 【0019】 The magnetic circuit according to Embodiment 11 of the present invention includes a first magnetic body having a through hole and a second magnetic body at least partially disposed in the through hole of the first magnetic body. When the direction passing through the through hole of the first magnetic body is taken as the axial direction, the first magnetic body is magnetized in a direction perpendicular to the axial direction, the second magnetic body is magnetized in the axial direction, the second magnetic body has a first main surface and a second main surface facing each other, and the first main surface is located in the through hole of the first magnetic body. 【0020】 In the magnetic circuit of Embodiment 12, in Embodiment 11, it is preferable that the first magnetic body is magnetized in a direction perpendicular to the axial direction and such that the through hole side becomes the N pole. 【0021】 In the magnetic circuit of Embodiment 13, in Embodiment 11, it is preferable that the first magnetic body is magnetized in a direction perpendicular to the axial direction and such that the through hole side becomes the S pole. 【0022】 The magneto-optical element according to Embodiment 14 of the present invention includes a Faraday rotor according to any one of Embodiments 1 to 10 and an optical component disposed on the optical path of light passing through the Faraday element. 【0023】 In the magneto-optical element of Embodiment 15, in Embodiment 14, it is preferable that the optical component is a polarizer or a mirror. 【Advantages of the Invention】 【0024】 According to the present invention, it is possible to provide a Faraday rotor, a magnetic circuit, and a magneto-optical element that can increase the magnetic flux density in a portion where the Faraday element is located. 【Brief Description of the Drawings】 【0025】 [Figure 1] FIG. 1 is a schematic cross-sectional view showing a Faraday rotor according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a schematic plan view showing a Faraday rotor according to a first embodiment of the present invention. [Figure 3] FIG. 3 is a schematic cross-sectional view showing an example of an optical path when the Faraday rotor according to a first embodiment of the present invention is used. [Figure 4] FIG. 4 is a schematic cross-sectional view showing a Faraday rotor of a comparative example. [Figure 5] FIG. 5 is a diagram showing the relationship between the position in the axial direction and the position in the width direction of the Faraday rotor according to a first embodiment of the present invention and the magnetic flux density. [Figure 6] FIG. 6 is a schematic cross-sectional view showing an example of a conventional Faraday rotor. [Figure 7] FIG. 7 is a schematic cross-sectional view showing a Faraday rotor according to a second embodiment of the present invention. [Figure 8] FIG. 8 is a schematic plan view showing a Faraday rotor according to a third embodiment of the present invention. [Figure 9] FIG. 9 is a schematic cross-sectional view showing a Faraday rotor according to a fourth embodiment of the present invention. [Figure 10] FIG. 10 is a schematic cross-sectional view showing a magneto-optical element according to a fifth embodiment of the present invention. [Figure 11] FIG. 11 is a schematic cross-sectional view showing a magneto-optical element according to a sixth embodiment of the present invention. 【Embodiments for Carrying Out the Invention】 【0026】 Preferred embodiments of the present invention will be described below. However, the following embodiments are merely illustrative, and the present invention is not limited to these embodiments. In addition, in each drawing, components having substantially the same function may be referred to by the same reference numerals. 【0027】 (Faraday rotor) (First Embodiment) Figure 1 is a schematic cross-sectional view showing a Faraday rotor according to the first embodiment of the present invention. In Figure 1, the letters N and S indicate magnetic poles, and the arrows indicate the direction of magnetization. The same applies to other drawings described later. 【0028】 The Faraday rotor 1 is a device used in magneto-optical elements such as optical isolators and optical circulators. The Faraday rotor 1 comprises a magnetic circuit 2, a Faraday element 5, and a reflective film 6. The Faraday element 5 has a plate-like shape. The Faraday element 5 is made of a paramagnetic material that transmits light. 【0029】 Magnetic circuit 2 is a magnetic circuit according to one embodiment of the present invention. Specifically, magnetic circuit 2 has a first magnet body 3 and a second magnet body 4. Magnetic circuit 2 is formed by combining the first magnet body 3 and the second magnet body 4. 【0030】 More specifically, the first magnet body 3 is cylindrical in shape. Therefore, the first magnet body 3 has a first open end face 3a and a second open end face 3b, and a through hole 3c. The through hole 3c is provided from the first open end face 3a to the second open end face 3b. When the direction through which the through hole 3c passes is defined as the axial direction A, the first open end face 3a and the second open end face 3b face each other in the axial direction A. On the other hand, the second magnet body 4 has a columnar shape. At least a portion of the second magnet body 4 is placed inside the through hole 3c of the first magnet body 3. 【0031】 Figure 2 is a schematic plan view of a Faraday rotor according to the first embodiment. Figure 2 can also be described as a view of the Faraday rotor from the axial direction. Note that Figure 1 above is a schematic cross-sectional view along line II in Figure 2. 【0032】 When viewed from axial direction A, in this embodiment, the outer shape of the first magnet body 3 is square, and the shape of the through hole 3c is also square. Similarly, when viewed from axial direction A, in this embodiment, the outer shape of the second magnet body 4 is square. However, the outer shape of the first magnet body 3, the shape of the through hole 3c, and the outer shape of the second magnet body 4 are not limited to those described above. 【0033】 Returning to Figure 1, the second magnet body 4 has a first main surface 4a and a second main surface 4b. The first main surface 4a and the second main surface 4b face each other in the axial direction A. The first main surface 4a of the second magnet body 4 is located within the through hole 3c of the first magnet body 3. On the other hand, the second main surface 4b of the second magnet body 4 is flush with the second open end surface 3b of the first magnet body 3. In this way, the entirety of the second magnet body 4 is located within the through hole 3c of the first magnet body 3. Note that the second main surface 4b of the second magnet body 4 may be substantially flush with the second open end surface 3b of the first magnet body 3, may be located within the through hole 3c of the first magnet body 3, or may be located outside the through hole 3c. It is sufficient that at least a portion of the second magnet body 4, including the first main surface 4a, i.e., all or part of the first main surface 4a, is located within the through hole 3c. 【0034】 The first magnet body 3 is magnetized in a direction perpendicular to the axial direction A. Specifically, the first magnet body 3 is magnetized in a direction perpendicular to the axial direction, and with the through-hole 3c side being the north pole. However, the first magnet body 3 may also be magnetized in a direction perpendicular to the axial direction A, and with the through-hole 3c side being the south pole. 【0035】 The second magnet body 4 is magnetized in the axial direction A. Specifically, the second magnet body 4 is magnetized such that the side facing the first main surface 4a is the north pole. However, the second magnet body 4 may also be magnetized such that the side facing the first main surface 4a is the south pole. 【0036】 A reflective film 6 is provided on the first main surface 4a of the second magnet body 4. A Faraday element 5 is provided on the reflective film 6. When viewed from the axial direction A, the outer shape of the Faraday element 5 in this embodiment is square. However, the outer shape of the Faraday element 5 is not limited to the above. 【0037】 Figure 3 is a schematic cross-sectional view showing an example of an optical path when the Faraday rotor according to the first embodiment is used. 【0038】 Light B enters the Faraday element 5 in the Faraday rotator 1. The light B that enters the Faraday element 5 is reflected by the reflective film 6. The light reflected by the reflective film 6 is emitted from the Faraday element 5. In this way, light B is transmitted through the Faraday element 5 accompanied by reflection. 【0039】 The Faraday rotor 1 can be used in magneto-optical elements such as optical isolators and optical circulators, along with optical components such as mirrors and polarizers. For example, the optical path can be adjusted using a mirror. On the other hand, the light that has passed through the polarizer can be made linearly polarized. Therefore, this linearly polarized light can be incident on the Faraday element 5. 【0040】 In the Faraday rotator 1 of this embodiment, light B transmitted through the Faraday element 5 rotates due to the Faraday effect. The angle at which the polarization plane of light B rotates in this way is the rotation angle. Specifically, in this embodiment, the rotation angle is 45°. However, the rotation angle may be, for example, 22.5°. When this Faraday rotator 1 is used as an optical isolator, the polarization plane of light B may be rotated by 45° in the following way. For example, by using a reflector, light B may be transmitted twice through the Faraday element 5 in one Faraday rotator 1. Alternatively, for example, two Faraday rotators 1 may be used in an optical isolator. Then, light B may be transmitted once through each Faraday element 5 in the two Faraday rotators 1. 【0041】 The features of this embodiment are as follows: 1) The first magnet body 3 is magnetized in a direction perpendicular to the axial direction A, and the second magnet body 4 is magnetized in the axial direction A. 2) The first main surface 4a of the second magnet body 4 is located within the through hole 3c of the first magnet body 3, and the Faraday element 5 is arranged on a reflective film 6 provided on the first main surface 4a of the second magnet body 4. This makes it possible to increase the magnetic flux density in the portion of the Faraday rotor 1 where the Faraday element 5 is located. The details of this will be explained below. 【0042】 The comparative example shown in Figure 4 differs from the first embodiment in that the first magnet body 3 is not provided. Specifically, in the Faraday rotor 101 of the comparative example, a reflective film 6 is provided on the main surface 104a of the prismatic magnet body 104. The Faraday element 5 is arranged on the reflective film 6. The magnet body 104 is configured in the same way as the second magnet body 4 in the first embodiment. 【0043】 In the Faraday rotor of the first embodiment and the comparative example, the magnetic flux density of the portion where the Faraday elements are located was compared. In this comparison, the dimensions of each part of the Faraday rotor were as follows: Here, the dimension along the axial direction of the magnet body is defined as the height of the magnet body. When the direction perpendicular to the axial direction is defined as the width direction, the dimension along the width direction of the magnet body is defined as the width of the magnet body. The dimension along the width direction of the through hole provided in the magnet body is defined as the width of the through hole. 【0044】 In the first embodiment, the external shapes of the first magnet body 3 and the second magnet body 4 when viewed from the axial direction A, and the shape of the through hole 3c in the first magnet body 3 when viewed from the axial direction A, are square. The widths of the first magnet body 3 and the second magnet body 4, and the width of the through hole in the first magnet body 3, each correspond to the length of one side of the square shape when viewed from the axial direction A. 【0045】 In the first embodiment, the height of the first magnet body 3 was 65 mm, the width was 120 mm, and the width of the through hole 3c in the first magnet body 3 was 60 mm. The height of the second magnet body 4 was 60 mm, and the width was 60 mm. On the other hand, in the comparative example, the height of the magnet body 104 was 60 mm, and the width was 60 mm. 【0046】 In the comparative example, the magnetic flux density in the area where the Faraday element 5 was located was approximately 0.3T. In contrast, in the first embodiment, the magnetic flux density in the area where the Faraday element 5 was located could be increased to approximately 0.8T. The distribution of the magnetic flux density in the first embodiment is shown in more detail below. 【0047】 Figure 5 shows the relationship between the axial position and the widthwise position of the Faraday rotor according to the first embodiment and the magnetic flux density. The horizontal axis in Figure 5 shows the position in the axial direction A, with the second main surface 4b of the second magnet body 4 shown in Figure 1 set to 0 mm. The position at 60 mm on the horizontal axis is the position of the first main surface 4a of the second magnet body 4. The position at 65 mm on the horizontal axis is the position of the first open end surface 3a of the first magnet body 3. The solid line in Figure 5 shows the results at the center in the widthwise direction. The dashed line in Figure 5 shows the results at a position 10 mm away from the center in the widthwise direction. The dashed line in Figure 5 shows the results at a position 20 mm away from the center in the widthwise direction. 【0048】 As shown by the solid line in Figure 5, at the center in the width direction, the magnetic flux density is highest at a position of 60 mm on the horizontal axis, and the magnetic flux density decreases as the value on the horizontal axis increases. In other words, the magnetic flux density is highest at the position of the first main surface 4a of the second magnet body 4, and the magnetic flux density decreases as the distance from the second magnet body 4 in the axial direction A increases. This is also true at positions 10 mm and 20 mm away from the center in the width direction, as shown by the dashed and dotted lines in Figure 5. 【0049】 However, it can be seen that the magnetic flux density is approximately 0.8T to 1T at all positions from 60mm to at least 70mm along the horizontal axis, regardless of the position in the width direction. Therefore, in the Faraday rotor 1 of the first embodiment, if the thickness of the Faraday element 5 arranged on the first main surface 4a of the second magnet body 4 is at least 10mm or less, the magnetic flux density of the entire portion where the Faraday element 5 is located can be approximately 0.8T to 1T. 【0050】 In Figure 5, the position at 65 mm on the horizontal axis corresponds to the position of the first open end face 3a of the first magnet body 3 shown in Figure 1. On the other hand, positions beyond 65 mm on the horizontal axis correspond to positions outside the through hole 3c of the first magnet body 3. In the Faraday rotor 1, the magnetic flux density can be increased from inside the through hole 3c to outside the through hole 3c. 【0051】 In addition, as shown in Figure 5, in the first embodiment, it can be seen that the difference in magnetic flux density is small even if the positions in the width direction are different. Therefore, in the Faraday rotor 1, the magnetic flux density in the part where the Faraday element 5 is located can be increased, and the variation in magnetic flux density in the width direction can be reduced. 【0052】 Incidentally, in the conventional Faraday rotor 111 schematically shown in Figure 6, light enters from one end face of the columnar Faraday element 115 placed in the through hole 112a of the magnetic circuit 112, and exits from the other end face. As a result, the plane of polarization of the light rotates due to the Faraday effect. When the rotation angle of the plane of polarization of the light due to Faraday rotation is θ, the length of the Faraday element 115 is L, the Verde constant of the Faraday element 115 is V, and the magnetic flux density in the direction in which light passes through the Faraday element 115 is H, the rotation angle θ can be expressed as θ = V × H × L. For example, when the magnetic flux density H is 0.8T and the Verde constant V of the Faraday element 115 is 0.1min / Oe·cm, if the length L of the Faraday element 115 is 33.75 mm, the rotation angle θ will be 45°. 【0053】 In the Faraday rotor 1 of the first embodiment shown in Figure 1, when the angle of incidence of light on the Faraday element 5 is 0°, the above equation holds true by setting L in the above equation to twice the thickness of the Faraday element 5. When the angle of incidence of light on the Faraday element 5 is 0°, the magnetic flux density H is 0.8T, and the Verde constant V of the Faraday element 5 is 0.1min / Oe·cm, the rotation angle θ becomes 22.5° because the thickness of the Faraday element 5 is 8.44 mm. Then, when light passes through the Faraday element 5 twice, the rotation angle θ becomes 45°. 【0054】 However, if the angle of incidence of light on the Faraday element 5 is not 0°, the relationship between the thickness of the Faraday element 5 and the rotation angle θ changes. Therefore, the thickness of the Faraday element 5 should be adjusted appropriately according to the angle of incidence of light on the Faraday element 5. The angle of incidence of light on the Faraday element 5 is preferably 45° or less, more preferably 30° or less, and particularly preferably 15° or less. If the angle of incidence of light on the Faraday element 5 is too large, the Faraday element 5 needs to be made larger, which tends to increase the size of the Faraday rotor 1. 【0055】 As described above, in the Faraday rotor 1 of the first embodiment related to the above comparison, when the thickness of the Faraday element 5 is at least 10 mm or less, the magnetic flux density of the entire portion where the Faraday element 5 is located is about 0.8 T to 1 T. Therefore, by appropriately adjusting the thickness of the Faraday element 5, the rotation angle θ of the polarization plane of light that has passed through the Faraday element 5 once can be preferably set to 22.5°. 【0056】 The configuration of the first embodiment will be described in more detail below. 【0057】 The second magnetic body 4 shown in Figure 2 consists of one magnet. On the other hand, the first magnetic body 3 contains four magnetic pieces. Specifically, the four magnetic pieces are the first magnetic piece 3A, the second magnetic piece 3B, the third magnetic piece 3C, and the fourth magnetic piece 3D. The first magnetic body 3 is formed by combining these magnetic pieces. The number of magnetic pieces that make up the first magnetic body 3 is not limited to the above. For example, the first magnetic body 3 may be formed by combining six or eight magnetic pieces. By forming the first magnetic body 3 by combining multiple magnetic pieces, the magnetic field can be effectively increased. However, the first magnetic body 3 may consist of one magnet. 【0058】 For example, permanent magnets can be used for each magnetic piece of the first magnetic body 3 and the second magnetic body 4. Examples of permanent magnets used in the first magnetic body 3 and the second magnetic body 4 include rare earth magnets. Examples of rare earth magnets include magnets mainly composed of samarium-cobalt (Sm-Co) and magnets mainly composed of neodymium-iron-boron (Nd-Fe-B). 【0059】 For example, a metal film can be used as the reflective film 6. In this case, for example, Ag can be used as the material for the reflective film 6. Alternatively, a dielectric multilayer film may be used as the reflective film 6. Specifically, a dielectric multilayer film is a laminated film in which a low refractive index film with a relatively low refractive index and a high refractive index film with a relatively high refractive index are alternately stacked. 【0060】 The reflective film 6 can be formed, for example, by sputtering or vacuum deposition. The reflective film 6 may be formed on the main surface of the Faraday element 5 by the method described above, or on the first main surface 4a of the second magnet body 4. The reflective film 6 may be positioned between the first main surface 4a of the second magnet body 4 and the Faraday element 5. 【0061】 In the first embodiment, a laminate of the Faraday element 5 and the reflective film 6 is formed, and then the laminate is placed on the first main surface 4a of the second magnet body 4. Therefore, when viewed from the axial direction A, all parts of the reflective film 6 overlap with the Faraday element 5. The shape of the reflective film 6 when viewed from the axial direction A is square. However, the shape of the reflective film 6 is not limited to the above. 【0062】 Alternatively, the reflective film 6 may be formed on the first main surface 4a of the second magnet body 4, and then the Faraday element 5 may be provided on the reflective film 6. In this case, when viewed from the axial direction A, the outer edge of the reflective film 6 may be located outside the outer edge of the Faraday element 5. 【0063】 For example, a paramagnetic material can be used for the Faraday element 5. It is preferable to use a paramagnetic glass material as the material for the Faraday element 5. When a glass material is used for the Faraday element 5, unlike when a single crystal material is used, the influence of defects in the material is small. As a result, the Verde constant fluctuates less in the glass material, and the extinction ratio does not decrease easily. Therefore, the Verde constant can be stabilized in the Faraday element 5, and a high extinction ratio can be maintained. Note that paramagnetic materials other than glass can also be used for the Faraday element 5. 【0064】 It is preferable that the glass material used in the Faraday element 5 contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. It is particularly preferable that the glass material contains Tb. 【0065】 The Tb2O3 content in the glass material used for the Faraday element 5 is preferably more than 20% in terms of mol% oxide, more preferably 25% or more, even more preferably 28% or more, even more preferably 29% or more, 30% or more, 31% or more, 32% or more, 34% or more, 36% or more, 38% or more, 40% or more, 41% or more, and particularly preferably 49% or more. Increasing the Tb2O3 content in this way makes it easier to obtain a good Faraday effect. Note that Tb exists in the glass in trivalent and tetravalent states, but in this specification, all of these are represented as Tb2O3. 【0066】 In the glass material used in the Faraday element 5, Tb relative to total Tb 3+ The proportion of is preferably 55% or more in mole percent, more preferably 60% or more, even more preferably 70% or more, even more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more. Tb relative to total Tb 3+ If the proportion is too low, the light transmittance in the wavelength range of 300nm to 1100nm tends to decrease. 【0067】 Furthermore, the Faraday element 5 can contain the following components. In the following descriptions of the component content, unless otherwise specified, "%" means "molar percent". 【0068】 SiO2 forms the glass skeleton and is a component that broadens the vitrification range. The vitrification range is the range of compositions in which glass can be obtained. Since SiO2 does not contribute to improving the Verde constant, if the SiO2 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the SiO2 content is preferably 0% to 50%, and particularly preferably 1% to 35%. 【0069】 B2O3 forms the glassy framework and is a component that broadens the vitrification range. However, since B2O3 does not contribute to improving the Verde constant, if the B2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the B2O3 content is preferably 0% to 50%, and particularly preferably 1% to 40%. 【0070】 P2O5 forms the glass skeleton and is a component that broadens the vitrification range. However, since P2O5 does not contribute to improving the Verde constant, if the P2O5 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the P2O5 content is preferably 0% to 50%, and particularly preferably 1% to 40%. 【0071】 Al2O3 is a component that enhances glass-forming ability. Glass-forming ability is an indicator of how easily glass is formed in a material. The higher the glass-forming ability of a material, the easier it is to form glass. Since Al2O3 does not contribute to improving the Verde constant, if the Al2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the Al2O3 content is preferably 0% to 50%, and particularly preferably 0% to 30%. 【0072】 La2O3, Gd2O3, and Y2O3 are components that stabilize vitrification. However, if the content of La2O3, Gd2O3, or Y2O3 is too high, vitrification will be suppressed. Therefore, it is preferable that the content of La2O3, Gd2O3, and Y2O3 is 10% or less each, and particularly preferable that it be 5% or less. 【0073】 Dy2O3, Eu2O3, and Ce2O3 are components that stabilize vitrification and contribute to improving the Verde constant. However, if the content of Dy2O3, Eu2O3, or Ce2O3 is too high, vitrification will be suppressed. Therefore, it is preferable that the content of Dy2O3, Eu2O3, and Ce2O3 is 15% or less each, and particularly preferable that it is 10% or less. Note that Dy, Eu, and Ce present in the glass exist in trivalent and tetravalent states, but in this specification, all of these are represented as Dy2O3, Eu2O3, and Ce2O3, respectively. 【0074】 MgO, CaO, SrO, and BaO are components that stabilize vitrification and increase the chemical durability of the glass material. However, since MgO, CaO, SrO, and BaO do not contribute to improving the Verde constant, if the content of MgO, CaO, SrO, or BaO is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, it is preferable that the content of MgO, CaO, SrO, and BaO is 0% to 10%, and particularly preferable that it is 0% to 5%. 【0075】 GeO2 is a component that enhances glass-forming ability. However, since GeO2 does not contribute to improving the Verde constant, if the GeO2 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, the GeO2 content is preferably 0% to 15%, more preferably 0% to 10%, and particularly preferably 0% to 9%. 【0076】 Ga2O3 is a component that enhances glass-forming ability and broadens the vitrification range. However, if the Ga2O3 content is too high, the glass material becomes prone to devitrification. In addition, since Ga2O3 does not contribute to improving the Verde constant, if the Ga2O3 content is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, a Ga2O3 content of 0% to 6% is preferable, and 0% to 5% is particularly preferable. 【0077】 Fluorine is a component that enhances glass-forming ability and broadens the vitrification range. However, if the fluorine content is too high, fluorine may volatilize during the melting of the raw material, causing changes in composition and potentially adversely affecting vitrification. In addition, it tends to increase the striations in the glass material. Therefore, the fluorine content (F2 equivalent) is preferably 0% to 10%, more preferably 0% to 7%, and particularly preferably 0% to 5%. 【0078】 Sb2O3 can be added as a reducing agent. However, to avoid discoloration or to consider the environmental impact, it is preferable that the Sb2O3 content be 0.1% or less. 【0079】 The following describes a preferred configuration for the Faraday rotor of the present invention. When the width of the first magnet body 3 shown in Figure 1 is w1 and the width of the second magnet body 4 is w2, the ratio w1 / w2 of width w1 to width w2 is preferably 1.2 or more, more preferably 1.3 or more, even more preferably 1.5 or more, even more preferably 1.7 or more, even more preferably 1.9 or more, particularly preferably 2.0 or more, and most preferably 2.1 or more. This makes it possible to more reliably increase the magnetic flux density in the portion of the Faraday rotor 1 where the Faraday element 5 is located. 【0080】 On the other hand, the ratio w1 / w2 is preferably 5.0 or less, more preferably 4.5 or less, even more preferably 4.0 or less, and even more preferably 3.8 or less. This makes it possible to further miniaturize the Faraday rotor 1. 【0081】 When the height of the first magnet body 3 is h1 and the height of the second magnet body 4 is h2, the ratio h1 / h2 of height h1 to height h2 is preferably 1.01 or higher, and more preferably 1.02 or higher, 1.04 or higher, 1.05 or higher, 1.07 or higher, or 1.08 or higher. This makes it possible to more reliably increase the magnetic flux density in the portion of the Faraday rotor 1 where the Faraday element 5 is located. In addition, it is possible to reduce the variation in magnetic flux density in the width direction. As a result, when the Faraday rotor 1 is used in a magneto-optical element, even if a misalignment of the reflector or the like occurs and a shift occurs in the position where the magnetic flux incident on the Faraday element 5, the deviation in the rotation angle can be suppressed. Therefore, the variation in the rotation angle can be suppressed. 【0082】 On the other hand, the ratio h1 / h2 is preferably 1.5 or less, and more preferably 1.45 or less. This prevents the height of the first magnet body 3 from becoming too high, and allows for miniaturization of the Faraday rotor 1. In addition, even when the angle of incidence of light on the Faraday element 5 is large, light can be incident on the Faraday element 5 and reflected by the reflective film 6. Therefore, the degree of freedom of the angle of incidence of light can be increased. 【0083】 Furthermore, when the angle of incidence of light on the Faraday element 5 is large, the light passes through a wide area in the width direction of the Faraday element 5. However, in the Faraday rotor 1, the uniformity of the magnetic flux density in the width direction of the portion where the Faraday element 5 is located is high. Therefore, the degree of freedom of the angle of incidence of light can be increased, and variations in the rotation angle can be suppressed. 【0084】 It is preferable that the Faraday element 5 is located both inside and outside the through-hole 3c of the first magnet body 3. In this case, the thickness of the Faraday element 5 is increased. More specifically, in the Faraday rotor 1, the magnetic flux density can be increased from inside the through-hole 3c to outside the through-hole 3c. Therefore, the thickness of the Faraday element 5 can be increased in the portion of the Faraday rotor 1 where the magnetic flux density is high. In the portion of high magnetic flux density, the optical path length of light passing through the Faraday element 5 can be increased. Consequently, the rotation angle can be increased more reliably. 【0085】 In the magnetic circuit 2 according to one embodiment of the present invention, the first magnet body 3 is magnetized in a direction perpendicular to the axial direction A. The second magnet body 4 is magnetized in the axial direction A. The first main surface 4a of the second magnet body 4 is located within the through hole 3c of the first magnet body 3. With these configurations, the magnetic flux density can be increased from inside to outside the through hole 3c. As in the first embodiment, by having the Faraday element 5 located both inside and outside the through hole 3c of the first magnet body 3, the rotation angle can be increased more reliably without increasing the size of the magnetic circuit 2 in order to increase the magnetic flux density. However, the Faraday element 5 may be located only inside the through hole 3c of the first magnet body 3. 【0086】 In the magnetic circuit 2 of the present invention, the first magnet body 3 may be magnetized in a direction perpendicular to the axial direction A and with the through-hole 3c side being the north pole, or it may be magnetized in a direction perpendicular to the axial direction A and with the through-hole 3c side being the south pole. The second magnet body 4 may be magnetized with the first main surface 4a side being the north pole, or it may be magnetized with the first main surface 4a side being the south pole. 【0087】 As shown in Figure 1, in the first embodiment, the inner wall of the first magnet body 3 facing the through hole 3c is not in contact with the Faraday element 5. However, the inner wall of the first magnet body 3 and the Faraday element 5 may be in contact. 【0088】 The second to fourth embodiments are shown below. In the second to fourth embodiments, as in the first embodiment, the Faraday rotor has the following configuration: 1) The first magnet body is magnetized in a direction perpendicular to the axial direction, and the second magnet body is magnetized in the axial direction. 2) The first main surface of the second magnet body is located within the through hole of the first magnet body, and the Faraday element is arranged on a reflective film 6 provided on the first main surface of the second magnet body. As a result, in the second to fourth embodiments as well, the magnetic flux density in the portion where the Faraday element is located can be increased. 【0089】 (Second embodiment) Figure 7 is a schematic cross-sectional view showing a Faraday rotor according to the second embodiment. 【0090】 This embodiment differs from the first embodiment in that a chiller 24 is provided so as to be in contact with the Faraday element 5. The chiller 24 is a component that cools the Faraday element 5. Specifically, the chiller 24 in this embodiment lowers the temperature of the chiller 24 itself by circulating water, liquid nitrogen, or the like inside. Note that in Figure 7, the configuration of the liquid flow path and other components in the chiller 24 is omitted. The chiller 24 cools the Faraday element 5 by being in contact with it. However, the configuration of the chiller 24 is not limited to the above. 【0091】 A portion of the chiller 24 is provided between the inner wall of the first magnet body 3 facing the through hole 3c and the Faraday element 5. The chiller 24 is in contact with both the inner wall of the first magnet body 3 and the Faraday element 5. As a result, the chiller 24 fixes the Faraday element 5 and cools the Faraday element 5. 【0092】 For the chiller 24, non-magnetic materials such as aluminum, copper, or brass can be used as the material. 【0093】 In this embodiment, similar to the first embodiment, the laminate of the Faraday element 5 and the reflective film 6 is provided on the first main surface 4a of the second magnet body 4. Furthermore, in this embodiment, no adhesive is required to fix the laminate of the Faraday element 5 and the reflective film 6. Therefore, there is no stress effect on the Faraday element 5 due to the adhesive. Thus, it is easier to stabilize the Verde constant and maintain a high extinction ratio in the Faraday element 5. 【0094】 The rotation angle of the plane of polarization of light due to Faraday rotation depends on temperature. In this embodiment, the chiller 24 can suppress the rise in temperature of the Faraday element 5. For example, the Faraday element 5 may be cooled by the chiller 24 so that its temperature is kept at room temperature. In this case, the rotation angle of the plane of polarization of light that has passed through the Faraday element 5 once can be stably set to, for example, 22.5°. Alternatively, for example, the Faraday element 5 may be cooled by the chiller 24 so that its temperature is kept at around 200K. In this case, the rotation angle of the plane of polarization of light that has passed through the Faraday element 5 once can be stably set to, for example, 45°. 【0095】 As shown in Figure 7, the chiller 24 is in contact with the entire side surface of the Faraday element 5. This allows the chiller 24 to effectively cool the Faraday element 5. However, the chiller 24 does not necessarily have to be in contact with the entire side surface of the Faraday element 5; it may be in contact with only a part of the side surface. 【0096】 In this embodiment, the Faraday element 5 is located both inside and outside the through-hole 3c of the first magnet body 3. However, the Faraday element 5 may also be located only inside the through-hole 3c of the first magnet body 3. In this case, the thickness of the Faraday element 5 is thin. This allows for higher cooling efficiency of the Faraday element 5. 【0097】 (Third embodiment) Figure 8 is a schematic plan view showing a Faraday rotor according to the third embodiment. 【0098】 This embodiment differs from the first embodiment in the shapes of the first magnet body 33, the second magnet body 34, the Faraday element 35, and the reflective film 36. Specifically, the first magnet body 33 is cylindrical. The second magnet body 34 is cylindrical. The Faraday element 35 is disc-shaped. In this case, it is easy to apply a uniform magnetic field to the Faraday element 35. In this embodiment, similar to the Faraday element 35, the reflective film 36 is also circular when viewed from the axial direction. 【0099】 The first magnetic body 33 is composed of four magnetic pieces combined together. However, the number of magnetic pieces constituting the first magnetic body 33 is not limited to the above. Alternatively, the first magnetic body 33 may consist of a single magnet. 【0100】 In this embodiment, the widths of the first magnet body 33 and the second magnet body 34, as well as the width of the through hole in the first magnet body 33, each correspond to the diameter of a circle when viewed from the axial direction. 【0101】 In the first to third embodiments, the Faraday rotor has only one Faraday element. However, the Faraday rotor according to the present invention may have two Faraday elements. This example is shown in the fourth embodiment. In the fourth embodiment, the Faraday element corresponding to the Faraday element in the first to third embodiments is described as the first Faraday element. 【0102】 (Fourth embodiment) Figure 9 is a schematic cross-sectional view showing a Faraday rotor according to the fourth embodiment. 【0103】 This embodiment differs from the first embodiment in that it has two Faraday elements and in the position of the second main surface 4b of the second magnet body 4. This embodiment also differs from the first embodiment in that it has a reflective film 6 on both the first main surface 4a and the second main surface 4b of the second magnet body 4. 【0104】 Specifically, the Faraday rotor 41 has a first Faraday element 45A and a second Faraday element 45B. The first Faraday element 45A is positioned on a reflective film 6 provided on the first main surface 4a of the second magnet body 4. The second Faraday element 45B is positioned on a reflective film 6 provided on the second main surface 4b of the second magnet body 4. Both the first main surface 4a and the second main surface 4b of the second magnet body 4 are located within the through hole 3c of the first magnet body 3. 【0105】 In this embodiment as well, the first magnet body 3 and the second magnet body 4 are magnetized, similar to the first embodiment, and the first main surface 4a of the second magnet body 4 is positioned within the through hole 3c of the first magnet body 3. The first Faraday element 45A is positioned on the reflective film 6 provided on the first main surface 4a. This makes it possible to increase the magnetic flux density in the portion of the Faraday rotor 41 where the first Faraday element 45A is located. 【0106】 In addition, the second main surface 4b of the second magnet body 4 is positioned within the through hole 3c of the first magnet body 3, and the second Faraday element 45B is positioned on the reflective film 6 provided on the second main surface 4b. This makes it possible to increase the magnetic flux density in the portion of the Faraday rotor 41 where the second Faraday element 45B is located. 【0107】 When the Faraday rotor 41 has a first Faraday element 45A and a second Faraday element 45B, the ratio h1 / h2 of the height h1 in the first magnet body 3 to the height h2 in the second magnet body 4 is preferably 1.005 or more, and more preferably 1.01 or more. This makes it possible to more reliably increase the magnetic flux density in the portion of the Faraday rotor 41 where the first Faraday element 45A is located and where the second Faraday element 45B is located. In addition, it is possible to reduce the variation in magnetic flux density in the width direction. 【0108】 On the other hand, the ratio h1 / h2 is preferably 1.5 or less, and more preferably 1.4 or less. This prevents the height of the first magnet body 3 from becoming too high, and allows for miniaturization of the Faraday rotor 41. In addition, even when the angle of incidence of light to the first Faraday element 45A or the second Faraday element 45B is large, light can be incident on the first Faraday element 45A or the second Faraday element 45B, and the light can be reflected by the reflective film 6. Therefore, the degree of freedom of the angle of incidence of light can be increased. 【0109】 As in the fourth embodiment, when two Faraday elements are provided, it is sufficient that at least the first main surface 4a of the second magnet body 4 is located within the through hole 3c of the first magnet body 3. The first Faraday element 45A is then positioned on the reflective film 6 provided on this first main surface 4a. This makes it possible to increase the magnetic flux density in the area where the first Faraday element 45A is located. 【0110】 On the other hand, for example, the second main surface 4b of the second magnet body 4 may be located outside the through hole 3c of the first magnet body 3. The second Faraday element 45B may be placed on the reflective film 6 provided on this second main surface 4b. In this case, variations in magnetic flux density can be suppressed in the area where the second Faraday element 45B is located. 【0111】 The magnetic circuit is composed of a combination of the first magnet 3 and the second magnet 4. Therefore, in this example, no other magnets are placed around the portion of the second magnet 4 that is located outside the through-hole 3c of the first magnet 3. In other words, the portion of the second magnet 4 that is located outside the through-hole 3c of the first magnet 3 is exposed to magnets other than the second magnet 4. 【0112】 (Magneto-optical element) (Fifth embodiment) Figure 10 is a schematic cross-sectional view showing a magneto-optical element according to a fifth embodiment of the present invention. 【0113】 The magneto-optical element 50 is an optical isolator. The magneto-optical element 50 comprises a Faraday rotor 21 and a Faraday rotor 51, and a pair of polarizers and a plurality of reflectors as optical components. The pair of polarizers are specifically a first polarizer 56A and a second polarizer 56B. The plurality of reflectors are specifically a first reflector 57A and a second reflector 57B. 【0114】 One of the Faraday rotors 21 of the magneto-optical element 50 is the Faraday rotor 21 of the second embodiment shown in Figure 7. However, instead of the Faraday rotor 21, a Faraday rotor according to the present invention other than that of the second embodiment may be used. 【0115】 The other Faraday rotor 51 of the magneto-optical element 50 is also a Faraday rotor according to one embodiment of the present invention. The Faraday rotor 51 differs from the Faraday rotor 21 in the direction of magnetization of the magnetic circuit 52. Specifically, the magnetic circuit 52 has a first magnet body 53 and a second magnet body 54. The shapes of the first magnet body 53 and the second magnet body 54 in the Faraday rotor 51 are the same as the shapes of the first magnet body 3 and the second magnet body 4 in the Faraday rotor 21. In the magnetic circuit 52 of the Faraday rotor 51, similar to the magnetic circuit 2 of the Faraday rotor 21, the entirety of the second magnet body 54 is arranged within the through hole of the first magnet body 53. 【0116】 The second magnet body 54 has a first main surface 54a and a second main surface 54b. The first main surface 54a and the second main surface 54b face each other in the axial direction. The first main surface 54a of the second magnet body 54 is located within the through hole of the first magnet body 53. 【0117】 The first magnet body 53 is magnetized in a direction perpendicular to the axial direction, and with the through-hole side being the south pole. The second magnet body 54 is magnetized in the axial direction. More specifically, in this embodiment, the second magnet body 54 is magnetized with the first main surface 54a side being the south pole. That is, the first magnet body 53 in the Faraday rotor 51 is magnetized in the opposite direction to the first magnet body 3 in the Faraday rotor 21. The second magnet body 54 in the Faraday rotor 51 is also magnetized in the opposite direction to the second magnet body 4 in the Faraday rotor 21. 【0118】 A reflective film 6 is provided on the first main surface 54a of the second magnet body 54. A Faraday element 5 is provided on the reflective film 6. 【0119】 In the magneto-optical element 50, the first main surface 4a of the second magnet body 4 in the Faraday rotor 21 is located on the Faraday rotor 51 side. The first main surface 54a of the second magnet body 54 in the Faraday rotor 51 is located on the Faraday rotor 21 side. Therefore, the Faraday elements 5 of the Faraday rotor 21 and the Faraday rotor 51 face each other. In the magneto-optical element 50, the Faraday rotors 21 and 51 are arranged so that their axial directions are parallel to each other. 【0120】 All optical components of the magneto-optical element 50 are positioned on the optical path of light B passing through the Faraday elements 5 of the Faraday rotor 21 and the Faraday rotor 51. Specifically, a first polarizer 56A is positioned where light B is incident on the magneto-optical element 50. A second polarizer 56B is positioned where light B is emitted from the magneto-optical element 50. 【0121】 The first reflector 57A is positioned between the Faraday element 5 of the Faraday rotor 21 and the first polarizer 56A. More specifically, the first reflector 57A is positioned to change the direction of light B that has passed through the first polarizer 56A, causing the light B to be incident on the Faraday element 5 of the Faraday rotor 21. The second reflector 57B is positioned between the Faraday element 5 of the Faraday rotor 51 and the second polarizer 56B. More specifically, the second reflector 57B is positioned to change the direction of light B that has passed through the Faraday element 5 of the Faraday rotor 51, causing the light B to be incident on the second polarizer 56B. 【0122】 Light B incident on the magneto-optical element 50 becomes linearly polarized upon passing through the first polarizer 56A. The linearly polarized light B is reflected by the first reflector 57A and incident on the Faraday element 5 in the Faraday rotator 21. As light B passes through the Faraday element 5, the polarization plane of light B rotates by 22.5°. Light B emitted from the Faraday element 5 is incident on the Faraday element 5 in the Faraday rotator 51. As light B passes through the Faraday element 5, the polarization plane of light B rotates by another 22.5°. Light B emitted from the Faraday element 5 is reflected by the second reflector 57B and passes through the second polarizer 56B. 【0123】 In other words, when light B is incident on the magneto-optical element 50, it becomes linearly polarized, and then the polarization plane of light B rotates by a total of 45°. In this state, light B is emitted from the magneto-optical element 50. 【0124】 In the magneto-optical element 50, the magnetization directions in the magnetic circuits of the multiple Faraday rotors, where the Faraday elements 5 face each other, are different. Specifically, in this embodiment, the magnetization direction in the magnetic circuit 2 of the Faraday rotor 21 and the magnetization direction in the magnetic circuit 52 of the Faraday rotor 51 are opposite to each other. As a result, the polarization plane of light B can be rotated in the same direction by the Faraday rotors 21 and 51. 【0125】 More specifically, the second magnet body 4 of the Faraday rotor 21 is magnetized such that the second main surface 4b side is the south pole and the first main surface 4a side is the north pole. The second magnet body 54 of the Faraday rotor 51 is magnetized such that the first main surface 54a side is the south pole and the second main surface 54b side is the north pole. In the magneto-optical element 50, the Faraday elements 5 of the Faraday rotor 21 and the Faraday rotor 51 face each other. 【0126】 As a result, in Figure 10, the main surfaces are arranged in the following order from left to right: the second main surface 4b of the second magnet body 4, the first main surface 4a of the second magnet body 4, the first main surface 54a of the second magnet body 54, and the second main surface 54b of the second magnet body 54. In other words, the Faraday rotor 21 and the Faraday rotor 51 are positioned such that, when viewed from outside the magneto-optical element 50, the direction of magnetization of the second magnet body 4 and the direction of magnetization of the second magnet body 54 are the same. 【0127】 Furthermore, in the magneto-optical element 50, the relationship between the direction of magnetization in the second magnet body 4 and the direction of propagation of light B, and the relationship between the direction of magnetization in the second magnet body 54 and the direction of propagation of light B, are equivalent. As a result, the polarization plane of light B can be rotated in the same direction by the Faraday rotor 21 and the Faraday rotor 51. 【0128】 Furthermore, some of the light B whose plane of polarization has been rotated by 45° by the magneto-optical element 50 may be reflected and return to the magneto-optical element 50. Such light is called reflected light. After passing through the second polarizer 56B, the reflected light passes through the Faraday elements 5 in the Faraday rotator 51 and Faraday rotator 21. As a result, the plane of polarization of the reflected light is rotated by another 45° from its already rotated state. Consequently, the angle of the plane of polarization of the reflected light becomes 90° with respect to the light transmission axis of the first polarizer 56A. Therefore, the reflected light cannot pass through the first polarizer 56A and is blocked. 【0129】 As described above, in the magneto-optical element 50, some of the multiple reflectors are arranged to change the direction of light that has passed through the polarizer and to cause it to enter the Faraday element 5. Other reflectors are arranged to change the direction of light that has passed through the Faraday element 5 and to cause it to enter the polarizer. The arrangement of the reflectors is not limited to the above. For example, at least one reflector may be arranged so that light passes through the same Faraday element 5 multiple times. Alternatively, at least one reflector may be arranged so that light that has passed through the Faraday element 5 in one Faraday rotor 21 enters the Faraday element 5 in another Faraday rotor 51. 【0130】 Since the magneto-optical element 50 has the Faraday rotor 21 and Faraday rotor 51 of the present invention, the magnetic flux density in the portion where each Faraday element 5 is located can be increased. 【0131】 (Sixth embodiment) Figure 11 is a schematic cross-sectional view showing a magneto-optical element according to the sixth embodiment. 【0132】 This embodiment differs from the fifth embodiment in that it does not have a reflector. That is, the optical component in this embodiment is a pair of polarizers. This embodiment also differs from the fifth embodiment in the arrangement of the pair of polarizers. 【0133】 The pair of polarizers are specifically a first polarizer 56A and a second polarizer 56B. The first polarizer 56A is positioned where light B is incident on the magneto-optical element 60. More specifically, the first polarizer 56A is positioned so that light B that has passed through the first polarizer 56A is incident on the Faraday element 5 of the Faraday rotator 21 without changing its direction of travel. The second polarizer 56B is positioned where light B is emitted from the magneto-optical element 60. More specifically, the second polarizer 56B is positioned so that light B that has passed through the Faraday element 5 of the Faraday rotator 51 is incident on the second polarizer 56B without changing its direction of travel. 【0134】 Light B incident on the magneto-optical element 60 becomes linearly polarized by passing through the first polarizer 56A. The linearly polarized light B is incident on the Faraday element 5 in the Faraday rotator 21. As light B passes through the Faraday element 5, the polarization plane of light B rotates by 22.5°. Light B emitted from the Faraday element 5 is incident on the Faraday element 5 in the Faraday rotator 51. As light B passes through the Faraday element 5, the polarization plane of light B rotates by another 22.5°. Light B emitted from the Faraday element 5 passes through the second polarizer 56B. 【0135】 In other words, when light B is incident on the magneto-optical element 60, it becomes linearly polarized, and then the polarization plane of light B rotates by a total of 45°. In this state, light B is emitted from the magneto-optical element 60. 【0136】 Since the magneto-optical element 60 has the Faraday rotor 21 and Faraday rotor 51 of the present invention, the magnetic flux density in the portion where each Faraday element 5 is located can be increased. 【0137】 The magneto-optical element 50 of the fifth embodiment and the magneto-optical element 60 of the sixth embodiment are optical isolators. However, the magneto-optical element of the present invention may also be an optical circulator. In this case, the optical component of the magneto-optical element may be a waveplate or a beam splitter. Furthermore, the magneto-optical element of the present invention may be a magneto-optical element other than an optical isolator or optical circulator. [Explanation of Symbols] 【0138】 1…Faraday rotor 2…Magnetic circuit 3…First magnetic body 3A~3D...1st to 4th magnetic pieces 3a, 3b…First and second open end faces 3c...Through hole 4…Second magnetic body 4a, 4b…First and second principal surfaces 5…Faraday phenomenon 6…Reflection film 21... Faraday rotor 24... Chiller 33, 34… First and second magnetic bodies 35…Faraday Phenomenon 36...Reflection film 41... Faraday rotor 45A, 45B… First and second Faraday elements 50…Magneto-optical elements 51... Faraday rotor 52…Magnetic circuits 53, 54… First and second magnetic bodies 54a, 54b… First and second main surfaces 56A, 56B… First and second polarizers 57A, 57B…First and second reflecting mirrors 60…Magneto-optical element 101... Faraday rotor 104...Magnetic body 104a…main surface 111... Faraday rotor 112…Magnetic circuit 112a...Through hole 115... Faraday effect

Claims

[Claim 1] A magnetic circuit comprising a first magnet body having a through hole, and a second magnet body having at least a portion of it disposed within the through hole, A reflective film disposed on the second magnet body, A Faraday element disposed on the reflective film, Equipped with, When the direction in which the first magnet body passes through the through hole is defined as the axial direction, the first magnet body is magnetized in a direction perpendicular to the axial direction, and the second magnet body is magnetized in the axial direction. The second magnet body has a first main surface and a second main surface facing each other, and the first main surface is located within the through hole of the first magnet body. A Faraday rotor in which the Faraday element is arranged on the reflective film provided on the first main surface of the second magnet body. [Claim 2] The Faraday rotor according to claim 1, wherein the first magnet body is magnetized in a direction perpendicular to the axial direction and such that the through-hole side is the north pole. [Claim 3] The Faraday rotor according to claim 1, wherein the first magnet body is magnetized in a direction perpendicular to the axial direction and such that the through-hole side is the south pole. [Claim 4] The Faraday rotor according to claim 1, wherein the first magnetic body includes four magnetic pieces. [Claim 5] The Faraday rotor according to claim 1, further comprising a chiller for fixing the Faraday elements and for cooling the Faraday elements. [Claim 6] The Faraday rotor according to claim 1, wherein the Faraday element is positioned both inside and outside the through-hole of the first magnet body. [Claim 7] The Faraday rotor according to claim 1, wherein when the dimension of the first magnet body along the direction perpendicular to the axial direction is the width w1 of the first magnet body, and the dimension of the second magnet body along the direction perpendicular to the axial direction is the width w2 of the second magnet body, the ratio w1 / w2 of the width w1 to the width w2 is 1.2 or more and 5.0 or less. [Claim 8] The Faraday rotor according to claim 1, wherein the shape of the first magnet body is cylindrical, and the outer shape of the first magnet body when viewed from the axial direction is square. [Claim 9] The Faraday rotor according to claim 1, wherein the shape of the first magnet body is cylindrical. [Claim 10] The reflective film is provided on both the first main surface and the second main surface of the second magnet body. The Faraday element is the first Faraday element, The present invention further comprises a second Faraday element disposed on the reflective film provided on the second main surface of the second magnet body, The Faraday rotor according to claim 1, wherein the second main surface of the second magnet body is located within the through hole of the first magnet body. [Claim 11] A first magnet body having a through hole, A second magnet body, in which at least a portion is disposed within the through hole of the first magnet body, Equipped with, When the direction in which the first magnet body passes through the through hole is defined as the axial direction, the first magnet body is magnetized in a direction perpendicular to the axial direction, and the second magnet body is magnetized in the axial direction. A magnetic circuit in which the second magnet body has a first main surface and a second main surface facing each other, and the first main surface is located within the through hole of the first magnet body. [Claim 12] The magnetic circuit according to claim 11, wherein the first magnet body is magnetized in a direction perpendicular to the axial direction and such that the through-hole side is the north pole. [Claim 13] The magnetic circuit according to claim 11, wherein the first magnet body is magnetized in a direction perpendicular to the axial direction and such that the through-hole side is the south pole. [Claim 14] A Faraday rotor according to any one of claims 1 to 10, An optical component arranged on the optical path of light passing through the Faraday element, A magneto-optical element equipped with the following features. [Claim 15] The magneto-optical element according to claim 14, wherein the optical component is a polarizer or a mirror.

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