阅读说明：本技术 法拉第旋光器及磁光学元件 (Faraday rotator and magneto-optical element ) 是由 铃木太志 于 2019-06-11 设计创作，主要内容包括：本发明提供一种法拉第旋光器及磁光学元件,其包括：具有分别设置有供光通过的贯通孔的第一～第三磁体的磁路(2)；配置于贯通孔(2a)内且由可透射光的顺磁性体构成的法拉第元件(14),第一磁体(11)以使贯通孔侧为N极的方式在与光轴方向垂直的方向上被磁化,第二磁体(12)以使第一磁体侧为N极的方式在与光轴方向平行的方向上被磁化,第三磁体(13)以使贯通孔侧为S极的方式在与光轴方向垂直的方向上被磁化,第一～第三磁体沿光轴方向的长度为法拉第元件(14)沿光轴方向的长度的0.56倍以上,法拉第元件(14)的上述长度低于15mm。由此,能够稳定地得到45°的旋转角且更小型的法拉第旋光器及磁光学元件。(The invention provides a Faraday rotator and a magneto-optical element, comprising: a magnetic circuit (2) having first to third magnets each provided with a through hole through which light passes; and a Faraday element (14) which is disposed in the through-hole (2a) and is composed of a paramagnetic material that can transmit light, wherein the first magnet (11) is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side is N-pole, the second magnet (12) is magnetized in a direction parallel to the optical axis direction so that the first magnet side is N-pole, the third magnet (13) is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side is S-pole, the length of the first to third magnets in the optical axis direction is 0.56 times or more the length of the Faraday element (14) in the optical axis direction, and the length of the Faraday element (14) is less than 15 mm. Thus, a Faraday rotator and a magneto-optical element with a 45 DEG rotation angle and a smaller size can be stably obtained.)

1. A faraday rotator, comprising:

a magnetic circuit having first to third magnets each provided with a through hole through which light passes; and

a Faraday element which is disposed in the through hole and is composed of a paramagnetic substance that transmits light,

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 set 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 length of each of the first, second, and third magnetic bodies in the optical axis direction is 0.56 times or more the length of the Faraday element in the optical axis direction,

the length of the Faraday element in the optical axis direction is less than 15 mm.

2. A faraday rotator according to claim 1, characterized in that:

the paramagnetic substance is made of glass material.

3. A faraday rotator according to claim 2, characterized in that:

the glass material contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm.

4. A faraday rotator according to claim 3, characterized in that:

the glass material contains Tb.

5. A faraday rotator according to claim 2, characterized in that:

the glass material contains more than 40% of Tb calculated by mol% of oxide conversion₂O₃And Tb³⁺The ratio of the total Tb is 55% or more in terms of mol%.

6. A Faraday rotator according to any of claims 1-5, characterized in that:

in the magnetic circuitThe cross-sectional area of the through-hole is 100mm²The following.

7. A magneto-optical element, comprising:

a Faraday rotator according to any one of claims 1-6; 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.

8. The magneto-optical element of claim 7, wherein:

the first optical component and the second optical component are polarizers.

Technical Field

The present invention relates to a faraday rotator and a magneto-optical element.

Background

An optical isolator is a magneto-optical element that propagates light in only one direction and prevents the return light from being reflected. Optical isolators are used in laser oscillators used in optical communication systems, laser processing systems, and the like.

Currently, the wavelength band used in optical communication systems is mainly 1300nm to 1700nm, and rare-earth iron garnet is used for the faraday element of the faraday rotator in the optical isolator.

On the other hand, the wavelength used for laser processing and the like is shorter than the optical communication band, and is mainly around 1000 nm. In this wavelength band, the rare earth iron garnet cannot be used because it has a large light absorption. Therefore, a faraday element composed of a paramagnetic substance crystal, in particular, well-known Terbium Gallium Garnet (TGG), is generally used.

In order to function as an optical isolator, the rotation angle (θ) of faraday rotation needs to be 45 °. The relationship between the faraday rotation angle, the length (L) of the faraday element, the verdet constant (V), and the magnetic flux density (H) parallel to the optical axis satisfies the following expression (1).

Theta is V.H.L formula (1)

The verdet constant depends on the material properties. Therefore, in order to adjust the faraday rotation angle, it is necessary to change the length of the faraday element or the magnetic flux density parallel to the optical axis applied to the faraday element. In particular, in recent years, miniaturization of devices has been demanded, and therefore, the magnetic flux density applied to the faraday rotator is increased by changing the structure of the magnet without adjusting the size of the faraday element or the magnet.

For example, patent document 1 below discloses a faraday rotator including 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 between the first and second magnets. The third magnet is magnetized in a direction parallel to the optical axis and from the second magnet toward the first magnet. The magnetic circuit is configured such that the relationship of L2/10L 3L 2 is satisfied when the length of the first magnet and the second magnet in the optical axis direction is L2 and the length of the first magnet and the second magnet in the third optical axis direction is L3.

Disclosure of Invention

Technical problem to be solved by the invention

When the magnetic circuit is formed by the structure described in patent document 1, a region having the highest magnetic flux density is formed in the vicinity of the joint portion between the first magnet and the third magnet and the joint portion between the second magnet and the third magnet. Further, a stable region having a large magnetic flux density is formed in the inner space having the same length as the third magnet connecting the two regions.

However, in patent document 1, a faraday element having a size exceeding the above-described region is used. This is because the verdet constant of a paramagnetic substance crystal such as TGG is small, and therefore, the length of the faraday element is also important in order to obtain a desired faraday rotation angle. However, if an element that exceeds the region where stable magnetic flux density is exhibited is used as described above, when the position of the faraday element is shifted in the manufacturing process of the faraday rotator, the magnetic flux density applied to the faraday element varies. As a result, the faraday rotation angle varies significantly, and it is difficult to stably obtain a desired faraday rotation angle.

The present invention has been made in view of the above-described problems, and an object thereof is to provide a faraday rotator and a magneto-optical element capable of stably obtaining a faraday rotation angle of 45 °.

Means for solving the problems

The Faraday rotator of the present invention is characterized by comprising: a magnetic circuit having first to third magnets each provided with a through hole through which light passes; and a faraday element disposed in the through hole and composed of a paramagnetic material that transmits light, wherein the magnetic circuit is composed of first to third magnets disposed coaxially in the front-rear direction, the first magnet is magnetized in a direction perpendicular to the optical axis direction such that the through hole side becomes an N pole, the second magnet is magnetized in a direction parallel to the optical axis direction such that the first magnet side becomes an N pole, the third magnet is magnetized in a direction perpendicular to the optical axis direction such that the through hole side becomes an S pole, the length of each of the first, second, and third magnets in the optical axis direction is 0.56 times or more the length of the faraday element in the optical axis direction, and the length of the faraday element in the optical axis direction is less than 15 mm. According to the above configuration, the region having the highest magnetic flux density is easily formed in the vicinity of the joint portion between the first magnet and the second magnet and the joint portion between the second magnet and the third magnet. Here, by setting the lengths of the first to third magnets in the optical axis direction to be equal to or greater than the length of the faraday element in the optical axis direction, it is possible to suppress variation or variation in the faraday rotation effect due to misalignment of the faraday element during assembly. Further, by setting the length of the arranged faraday element in the optical axis direction to be shorter than 15mm, a small faraday rotator can be formed.

In the faraday rotator of the present invention, the paramagnetic substance is preferably a glass material.

In the Faraday rotator of the present invention, the glass material preferably contains at least one rare earth element selected from the group consisting of Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. In particular, Tb is preferably contained.

In the Faraday rotator of the present invention, it is preferable that the glass material contains more than 40% of Tb in terms of oxide conversion in mol%₂O₃And Tb³⁺The ratio of the total Tb is 55% or more in terms of mol%. The glass material has a Vickers constant of 0.2 min/Oe-cm or more, and is larger than the Vickers constant (0.13 min/Oe-cm) of the conventional TGG, so that a Faraday element having a smaller size can be easily produced.

In the Faraday rotator of the present invention, the cross-sectional area of the through-hole in the magnetic path is preferably 100mm²The following. The cross-sectional area of the through-hole is set to 100mm²Hereinafter, the magnetic flux density is likely to increase, and thus, the size reduction is likely to be performed.

The magneto-optical element of the present invention is characterized by comprising: the above Faraday rotator; 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, wherein 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, the first optical member and the second optical member may be polarizers.

Effects of the invention

According to the present invention, it is possible to provide a faraday rotator and a magneto-optical element capable of stably obtaining a faraday rotation angle of 45 °.

Drawings

Fig. 1 is a schematic cross-sectional view showing an example of the structure of a faraday rotator according to the present invention.

Fig. 2 is a schematic diagram showing the magnetic field intensity distribution generated in the through hole of the long magnetic circuit by the second magnet.

Fig. 3 is a schematic diagram showing the magnetic field intensity distribution generated in the through hole of the short magnetic circuit by the second magnet.

Fig. 4 is a diagram showing an example of the configuration of the first magnet according to the present invention.

Fig. 5 is a diagram showing an example of the structure of the second magnet according to the present invention.

Fig. 6 is a diagram showing an example of the structure of the third magnet according to the present invention.

Fig. 7 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element of the present invention.

Detailed Description

Preferred embodiments of the present invention will be described below. However, the following embodiments are simply illustrative, and the present invention is not limited to the following embodiments. In the drawings, components having substantially the same function are sometimes denoted by the same reference numerals.

(Faraday rotator)

Fig. 1 is a schematic cross-sectional view showing an example of the structure of a faraday rotator according to the present invention. In fig. 1, characters N and S denote magnetic poles. The same applies to other drawings described later.

The faraday rotator 1 is a device used for magneto-optical elements such as an optical isolator and an optical circulator. The faraday rotator 1 includes: a magnetic circuit 2 provided with a through hole 2a through which light passes; and a faraday element 14 disposed in the through hole 2 a. The faraday element 14 is made of a paramagnetic material that can transmit light.

The magnetic circuit 2 includes a first magnet 11, a second magnet 12, and a third magnet 13 each provided with a through hole. In the magnetic circuit 2, the first magnet 11, the second magnet 12, and the third magnet 13 are coaxially arranged in this order in the front-rear direction. The coaxial arrangement means an arrangement in which the magnets overlap each other near the center when viewed from the optical axis direction. In the present embodiment, the through-holes of the first magnet 11, the second magnet 12, and the third magnet 13 are connected to each other to form the through-hole 2a of the magnetic circuit 2.

In the magnetic circuit 2, the first magnet 11 and the third magnet 13 are magnetized in a direction perpendicular to the optical axis direction, and the magnetization directions are opposite to each other. Specifically, the first magnet 11 is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side becomes the N-pole. The third magnet 13 is magnetized in a direction perpendicular to the optical axis direction so that the through-hole side becomes the S pole. The second magnet 12 is magnetized in a direction parallel to the optical axis direction so that the first magnet 11 side becomes the N-pole.

In the faraday rotator 1, light may be made incident from the first magnet 11 side or may be made incident from the third magnet 13 side.

The faraday rotator 1 of the present invention has the following structure. 1) The length of each of the first magnet 11, the second magnet 12, and the third magnet 13 in the optical axis direction is 0.56 times or more the length of the faraday element 14 in the optical axis direction. 2) The length of the faraday element 14 in the optical axis direction is less than 15 mm. Hereinafter, the length along the optical axis direction may be simply referred to as a length.

The length of each of the first magnet 11, the second magnet 12, and the third magnet 13 is 0.56 times or more, preferably 0.6 times or more, 0.7 times or more, 0.8 times or more, and particularly preferably 0.9 times or more the length of the faraday element 14. When the magnetic circuit 2 as shown in fig. 1 is formed, a region having the highest magnetic flux density is easily formed in the vicinity of the joint portion between the first magnet 11 and the second magnet 12 and the joint portion between the second magnet 12 and the third magnet 13. Here, by setting the respective lengths of the first magnet 11, the second magnet 12, and the third magnet 13 to be equal to or greater than the length of the faraday element 14 in the optical axis direction, the position of the faraday element 14 can be made less likely to shift during assembly. Therefore, the fluctuation of the faraday rotation angle can be suppressed. Further, the lengths of the first magnet 11 and the third magnet 13 greatly contribute to the magnitude of the magnetic flux density of the magnetic circuit 2. Therefore, if the first magnet 11 and the third magnet 13 are too short, a sufficient magnetic flux density cannot be obtained, and a faraday rotation angle of 45 ° cannot be obtained. By setting the ratio of the length of each of the first magnet 11 and the third magnet 13 to the length of the faraday element 14 within the above range, a faraday rotation angle of 45 ° can be obtained. Further, when the first magnet 11 and the third magnet 13 are excessively long, the magnetic circuit 2 becomes larger than necessary, and it is difficult to miniaturize the faraday rotator 1. Therefore, the length of each of the first magnet 11, the second magnet 12, and the third magnet 13 is preferably 1.5 times or less, more preferably 1.3 times or less, and particularly preferably 1.2 times or less of that of the faraday element 14. This makes it possible to reduce the size of the faraday rotator 1. Hereinafter, the faraday rotation angle may be referred to as a rotation angle.

In the faraday rotator 1 of the present invention, the shape of the magnetic field intensity distribution generated in the through-hole 2a of the magnetic circuit 2 can be changed by changing the relationship between the lengths of the first magnet 11 and the third magnet 13, and the length of the second magnet 12 in particular. Specifically, there can be mentioned: (1) the case where the lengths of the first magnet 11 and the third magnet 13 are shorter than the length of the second magnet 12 (the case where the second magnet 12 is longer), and (2) the case where the lengths of the first magnet 11 and the third magnet 13 are longer than the length of the second magnet 12 (the case where the second magnet 12 is shorter). Further, when one of the first magnet 11 and the third magnet 13 is longer than the second magnet 12 and the other has a shape shorter than the second magnet 12, the magnetic field intensity distribution generated in the through-hole 2a of the magnetic circuit 2 becomes asymmetric in the optical axis direction and the magnetic field distribution is difficult to control. From this viewpoint, the lengths of the first magnet 11 and the third magnet 13 are preferably equal. Therefore, in the magnetic field distribution described below, the lengths of the first magnet 11 and the third magnet 13 are set to be equal.

(1) Case where the second magnet 12 is long

Fig. 2 is a schematic diagram showing the magnetic field intensity distribution generated in the through hole of the long magnetic circuit by the second magnet. The horizontal axis represents the length in the optical axis direction with the center of the through hole 2a of the magnetic circuit 2 as the origin 0, and the vertical axis represents the magnetic field strength. In the present embodiment, the magnetic field distribution has a shape that widely expands in a concave shape around the origin 0 in the optical axis direction. Specifically, a region having the highest generated magnetic field strength is formed in the vicinity of the joint between the first magnet 11 and the third magnet 13 and the joint between the second magnet 12 and the third magnet 13, and a region S1 having a length equal to that of the second magnet 12 and having a predetermined magnetic field strength a or higher is formed between the two regions. Since the region S1 in which the magnetic field strength is high is relatively large, the entire faraday element 14 can be easily arranged in the region S1, and the fluctuation of the faraday rotation angle can be easily suppressed.

(2) The case where the second magnet 12 is short

Fig. 3 is a schematic diagram showing the magnetic field intensity distribution generated in the through hole of the short magnetic circuit by the second magnet. In the present embodiment, the magnetic field distribution has a shape that expands convexly around the origin 0 in the optical axis direction. Specifically, a region S2 equal to or higher than a predetermined magnetic field strength "a" is formed near the center of the second magnet 12. At this time, in the region S2, since the maximum magnetic field strength has a value larger than the magnetic field distribution in the case where (1) the second magnet 12 is long, a stronger magnetic flux density can be applied to the faraday element 14 disposed in the region S2, and the faraday rotation angle can be easily increased.

The magnetic field intensity distribution when the first magnet 11, the second magnet 12, and the third magnet 13 have the same length has the characteristics and the shape intermediate between (1) and (2) described above. Specifically, as in (1), regions where the magnetic field strength is highest are formed in the vicinity of the joint between the first magnet 11 and the third magnet 13 and the joint between the second magnet 12 and the third magnet 13, and a region S3 having a length equal to that of the second magnet 12 and having a predetermined magnetic field strength a or higher is formed between the two regions. At this time, the region S3 is formed to be wider than the region S2 with the origin 0 as the center and narrower than the region S1. On the other hand, the maximum magnetic field strength is larger than (1) and smaller than (2).

However, a magnetic field in a direction parallel to the optical axis direction is applied to the faraday rotation. Therefore, when the faraday element 14 is lengthened, the magnetic circuit 2 needs to be lengthened in order to form the magnetic field in the above-described direction in the through hole 2a of the magnetic circuit 2. As a result, it is difficult to miniaturize the faraday rotator 1. On the other hand, when the faraday element 14 is too short, a rotation angle of 45 ° cannot be obtained. Therefore, the length of the Faraday element 14 is preferably 3 to 14mm, more preferably 5 to 13mm, 6 to 12mm, and particularly preferably 7 to 11 mm. By setting the length of the faraday element 14 within the above range, a rotation angle of 45 ° can be obtained, and miniaturization of the faraday rotator 1 and the magneto-optical element using the same becomes possible.

The cross-sectional area of the through-hole 2a of the magnetic circuit 2 is preferably 100mm²The following. When the cross-sectional area of the through-hole 2a is too large, a sufficient magnetic flux density cannot be obtained, and when it is too small, it is difficult to dispose the faraday element 14 in the through-hole 2 a. The cross-sectional area of the through-hole 2a is preferably 3mm²～80mm²、4mm²～70mm²、5mm²～60mm²Particularly preferably 7mm²～50mm²。

The cross-sectional shape of the through-hole 2a of the magnetic circuit 2 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 shape of the faraday element 14 and the cross-sectional shape of the through hole 2a of the magnetic circuit 2 do not necessarily have to be uniform, but are preferably uniform from the viewpoint of applying a uniform magnetic field.

Fig. 4 is a diagram showing an example of the configuration of the first magnet. Fig. 5 is a diagram showing an example of the structure of the second magnet. Fig. 6 is a diagram showing an example of the structure of the third magnet.

The first magnet 11 shown in fig. 4 is formed by combining four magnet pieces. The number of magnet pieces constituting the first magnet 11 is not limited to the above. For example, six or eight pieces of equal magnet may be combined to form the first magnet 11. 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.

The second magnet 12 shown in fig. 5 is formed of a single magnet. In addition, two or more magnet pieces may be combined to form the second magnet 12.

The third magnet 13 shown in fig. 6 is formed by combining four magnet pieces similarly to the first magnet 11. The third magnet 13 may be formed by combining six or eight pieces of equal magnet, or may be formed by a single magnet.

The first magnet 11, the second magnet 12, and the third magnet 13 of the present invention are formed of permanent magnets. As the permanent magnet, a rare earth magnet is particularly preferable, and among them, a magnet containing samarium-cobalt magnet (Sm — Co) as a main component or a magnet containing neodymium-iron-boron magnet (Nd — Fe — B) as a main component is preferable.

In the faraday element 14 of the present invention, a paramagnetic material can be used. Among them, a glass material is preferably used. Since fluctuation in the verdet constant and decrease in the extinction ratio due to defects such as single crystal materials are small and influence of stress from the adhesive is small, the faraday element made of a glass material can maintain a stable verdet constant and a high extinction ratio. In addition, a paramagnetic material other than a glass material may be used for the faraday element 14.

The glass material used for the faraday element 14 of the present invention preferably contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. Tb is particularly preferably contained.

It is preferable that the glass material used for the Faraday element 14 of the present invention contains Tb in an amount exceeding 40% in terms of mole% of oxide₂O₃Preferably 45% or more, 48% or more, 49% or more, particularly 50% or more. Thus, by increasing Tb₂O₃Becomes easy to obtain a good faraday effect. In addition, Tb is present in a trivalent or tetravalent state in the glass, but in the present specification, these are all represented as Tb₂O₃。

Among the glass materials of the present invention, Tb is preferred³⁺The proportion of the total Tb is 55% or more, preferably 60% or more, 70% or more, 80% or more, 90% or more, and particularly 95% or more in mol%. If Tb³⁺When the ratio of Tb to total Tb is too low, the light transmittance at a wavelength of 300nm to 1100nm is likely to decrease.

The faraday element 14 of the present invention can further contain the following components. In the following description of the content of each component, "%" means "% by mole" unless otherwise specified.

SiO₂The glass skeleton is a component for widening the vitrification range. However, since the Verdet constant is not increased, it is difficult to obtain a sufficient Faraday effect if the content is too high. Therefore, SiO is preferable₂The content of (A) is 0% to 50%, particularly 1% to 35%.

B₂O₃The glass skeleton is a component for widening the vitrification range. However, B₂O₃There is no benefit in increasing the Verdet constant, so that if the content thereof is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, B is preferred₂O₃The content of (A) is 0% to 50%, particularly 1% to 40%.

P₂O₅The glass skeleton is a component for widening the vitrification range. However, P₂O₅There is no benefit in increasing the Verdet constant, so that if the content thereof is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, P is preferred₂O₅The content of (A) is 0% to 50%, particularly 1% to 40%.

Al₂O₃Is a component for improving glass forming ability. However, Al₂O₃There is no benefit in increasing the Verdet constant, so that if the content thereof is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, Al is preferable₂O₃The content of (A) is 0% to 50%, particularly 0% to 30%.

La₂O₃、Gd₂O₃、Y₂O₃Has the effect of stabilizing vitrification. However, if the content is too high, vitrification becomes difficult. Therefore, La is preferable₂O₃、Gd₂O₃、Y₂O₃The content of (A) is respectively 10%The content is particularly 5% or less.

Dy₂O₃、Eu₂O₃、Ce₂O₃Stabilize vitrification and also contribute to an increase in the Verdet constant. However, if the content is too high, vitrification becomes difficult. Thus, Dy is preferred₂O₃、Eu₂O₃、Ce₂O₃The content of (A) is 15% or less, particularly 10% or less. In addition, Dy, Eu, and Ce present in the glass exist in a trivalent or tetravalent state, but in the present specification, these are all represented as Dy₂O₃、Eu₂O₃、Ce₂O₃。

MgO, CaO, SrO and BaO have the effect of stabilizing vitrification and also have the effect of improving chemical durability. However, since the Verdet constant is not increased, it is difficult to obtain a sufficient Faraday effect if the content is too high. Therefore, the content of each of these components is preferably 0% to 10%, particularly 0% to 5%.

GeO₂Is a component for improving glass forming ability. However, GeO₂There is no benefit in increasing the Verdet constant, so that if the content thereof is too high, it becomes difficult to obtain a sufficient Faraday effect. Accordingly, GeO is preferred₂The content of (A) is 0% -15%, 0% -10%, especially 0% -9%.

Ga₂O₃Has the effects of improving glass forming ability and enlarging vitrification range. However, if the content thereof is too high, devitrification becomes easy. In addition, Ga₂O₃There is no benefit in increasing the Verdet constant, so that if the content thereof is too high, it becomes difficult to obtain a sufficient Faraday effect. Therefore, Ga is preferred₂O₃The content of (A) is 0% to 6%, particularly 0% to 5%.

Fluorine has the effect of improving the glass forming ability and enlarging the vitrification range. However, if the content thereof is too high, it may volatilize during melting to cause a change in composition, and there is a risk of adversely affecting vitrification. In addition, the beads are easily added. Therefore, it is preferableContent of fluorine (F)₂Converted) to 0% to 10%, 0% to 7%, particularly 0% to 5%.

Can add Sb₂O₃As a reducing agent. However, in order to avoid coloring or to take the burden on the environment into consideration, the content is preferably 0.1% or less.

The Faraday element 14 of the present invention exhibits excellent light transmittance in the wavelength range of 300nm to 1100 nm. Specifically, the transmittance of the optical path length of 1mm at a wavelength of 1064nm is preferably 60% or more, 70% or more, particularly 80% or more. The transmittance at an optical path length of 1mm at a wavelength of 633nm is preferably 30% or more, 50% or more, 70% or more, particularly 80% or more. Further, the transmittance at an optical path length of 1mm at a wavelength of 533nm is preferably 30% or more, 50% or more, 70% or more, particularly 80% or more.

The cross-sectional shape of the faraday element 14 of the present invention is not particularly limited, and is preferably circular in order to have a uniform faraday effect. The diameter of the Faraday element 14 is preferably 10mm or less, more preferably 8mm or less, 5mm or less, particularly 3.5mm or less. If the diameter of the faraday element 14 is too large, the faraday element 14 cannot be disposed in the through hole 2a of the magnetic circuit 2. Alternatively, the magnetic circuit 2 needs to be enlarged, and miniaturization of the faraday rotator 1 becomes difficult. The lower limit of the diameter of the faraday element 14 is not particularly limited, but is actually 0.5mm or more.

The Faraday rotator 1 of the present invention is preferably used at a wavelength of 350nm to 1300nm, and particularly preferably used in the range of 450nm to 1200nm, 500nm to 1200nm, 800nm to 1100nm, 900nm to 1100 nm.

(magneto-optical element)

Fig. 7 is a schematic cross-sectional view showing an example of the structure of the magneto-optical element of the present invention.

The magneto-optical element 20 shown in fig. 7 is an optical isolator. An optical isolator is a device that blocks the reflected return light of laser light. The magneto-optical element 20 includes the faraday rotator 1 shown in fig. 1, a first optical member 25 disposed at one end in the optical axis direction of the magnetic circuit 2, 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.

Since the magneto-optical element 20 of the present invention includes the faraday rotator 1 of the present invention shown in fig. 1, a 45 ° faraday rotation angle can be stably obtained and the size can be reduced.

While the magneto-optical element 20 shown in fig. 7 is an optical isolator, 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. The magneto-optical element 20 may be a magneto-optical element other than an optical isolator and an optical circulator.

< example >

The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

In this embodiment, a faraday rotator having a wavelength of 1064nm is exemplified as an example, but the present invention is not limited to this wavelength.

(example 1)