Optical isolator

Abstract

To provide an optical isolator with which optical path displacement hardly occurs, and which can be located efficiently in a limited space.SOLUTION: Provided is an optical isolator 1 comprising: a magnet 2 having a through-hole 2a which light enters in a forward direction X and passes through the inside; a Faraday element 3 that passes light through and is located in the inside of the through-hole 2a of the magnet 2; a first polarizer 4 located on the incidence side of the magnet 2; and a second polarizer 5 located on the emission side of the magnet 2. The magnet 2 includes a first magnet body 6, a second magnet body 7, and a third magnet body 8 each having a through-hole. The distance between an incidence plane 4a of the first polarizer 4 and an emission plane 5b of the second polarizer 5 in the forward direction X is shorter than the longest distance among distances between two outer circumferential edge points in a cross section of the magnet 2.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an optical isolator. [Background technology]

[0002] An optical isolator is a magneto-optical element that allows light to propagate in only one direction and blocks reflected light from returning. Optical isolators are used, for example, in laser oscillators used in optical communication systems and laser processing systems.

[0003] Patent Document 1 listed below discloses an example of an optical isolator. In this optical isolator, a Faraday rotator is disposed inside a magnetic structure. A pair of polarizers are provided on either side of the Faraday rotator in the direction of the optical axis of light passing through the Faraday rotator. In the optical isolator of Patent Document 1, the distance between the polarizers in the optical axis direction is larger than the outer diameter of the magnetic structure in a direction perpendicular to the optical axis direction (see FIG. 1 of Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-051105 Summary of the Invention [Problem to be solved by the invention]

[0005] However, optical isolators such as those described in Patent Document 1 are designed with a long optical path length as described above, which makes them prone to optical path misalignment. Also, depending on the design of the device in which the optical isolator is used, it may not be possible to place the optical isolator in a limited space.

[0006] An object of the present invention is to provide an optical isolator that can reduce the occurrence of optical path deviation and can be efficiently arranged in a limited space. [Means for solving the problem]

[0007] The optical isolator according to aspect 1 of the present invention comprises a magnet having a through hole through which light enters in the forward direction and passes through the interior thereof, a Faraday element that transmits the light and is provided inside the through hole of the magnet, a first polarizer arranged on the entrance side of the magnet and a second polarizer arranged on the exit side of the magnet, when the side into which the light enters in the forward direction is defined as the entrance side and the side from which the light exits is defined as the exit side, the magnet has a first magnetic body, a second magnetic body, and a third magnetic body, each having a through hole, the first magnetic body, the second magnetic body, and the third magnetic body being stacked in this order, and the through hole of the first magnetic body, the through hole of the second magnetic body, and the through hole of the third magnetic body the holes are connected, the first magnet body is magnetized in a direction perpendicular to the forward direction so that the through-hole side is the north pole, the second magnet body is magnetized in a direction parallel to the forward direction so that the first magnet body side is the north pole, and the third magnet body is magnetized in a direction perpendicular to the forward direction so that the through-hole side is the south pole, and when the incident side surface in the forward direction is the incident surface, the exit side surface in the forward direction is the exit surface, and a cross section along the direction perpendicular to the forward direction is a transverse cross section, the distance between the incident surface of the first polarizer and the exit surface of the second polarizer in the forward direction is shorter than the longest distance between two points on the outer periphery of the magnet in the transverse cross section.

[0008] In the optical isolator of aspect 2, in aspect 1, it is preferable that the optical isolator further includes a first polarizer holder that houses the first polarizer and a second polarizer holder that houses the second polarizer, and that the distance between the incident surface of the first polarizer holder and the exit surface of the second polarizer holder in the forward direction is shorter than the longest distance between two points on the outer edge of the magnet in the cross section.

[0009] The optical isolator of aspect 3 is the same as that of aspect 1 or aspect 2, and further includes a housing that houses the magnet and the Faraday element therein and has a first opening located on the incident side and a second opening located on the output side; a first lid that has a first opening through which the light passes and closes the first opening of the housing; and a second lid that has a second opening through which the light passes and closes the second opening of the housing, and it is preferable that the first lid is disposed between the magnet and the first polarizer, and the second lid is disposed between the magnet and the second polarizer.

[0010] The optical isolator of aspect 4 is the same as that of aspect 2, and further includes a housing that houses the magnet and the Faraday element therein and has a first opening located on the incident side and a second opening located on the exit side; a first lid that has a first opening through which the light passes and closes the first opening of the housing; and a second lid that has a second opening through which the light passes and closes the second opening of the housing, and it is preferable that the first lid is positioned between the magnet and the first polarizer holder, and the second lid is positioned between the magnet and the second polarizer holder.

[0011] In the optical isolator of aspect 5, in aspect 4, it is preferable that at least a portion of the first polarizer holder is located inside the first lid body, the first lid body has a first mating portion that mated with the first polarizer holder, and at least a portion of the second polarizer holder is located inside the second lid body, and the second lid body has a second mating portion that mated with the second polarizer holder.

[0012] In the optical isolator of aspect 6, in any one of aspects 1 to 5, it is preferable that the longest distance between two points on the outer edge of the cross-section of the magnet is the diameter of the circle when the outer shape of the cross-section of the magnet is a circle, or the length of the longest diagonal of the regular polygon when the outer shape of the cross-section of the magnet is a regular polygon.

[0013] In the optical isolator of aspect 7, in any one of aspects 1 to 5, it is preferable that the longest distance between two points on the outer edge of the cross-section of the magnet is the diameter of the circle when the outer shape of the cross-section of the magnet is a circle, or is the diameter of the inscribed circle of the regular polygon when the outer shape of the cross-section of the magnet is a regular polygon.

[0014] In the optical isolator of aspect 8, in any one of aspects 1 to 7, it is preferable that the ratio of the length of the Faraday element in the forward direction to the length of the magnet (length of Faraday element / length of magnet) is 0.25 or more and 1.0 or less.

[0015] In the optical isolator of aspect 9, in any one of aspects 1 to 8, it is preferable that the length of the Faraday element is 3 mm to 30 mm, the Verdet constant of the Faraday element is 0.01 min / Oe·cm to 1 min / Oe·cm, and the magnetic flux density of the Faraday element is 0.3 T to 3.0 T.

[0016] In the optical isolator of Aspect 10, in any one of Aspects 1 to 9, it is preferable that the magnet has a rectangular outer shape in the cross section. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide an optical isolator that can reduce the occurrence of optical path deviation and can be efficiently arranged in a limited space. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic perspective view showing an optical isolator according to one embodiment of the present invention. [Figure 2] FIG. 2 is a simplified schematic diagram showing a cross section of the optical isolator shown in FIG. 1 taken along the forward direction. [Figure 3]FIG. 3 is a diagram showing an example of the structure of the first magnetic body. [Figure 4] FIG. 4 is a diagram showing an example of the structure of the second magnetic body. [Figure 5] FIG. 5 is a diagram showing an example of the structure of the third magnetic body. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a cross section in the forward direction of an optical isolator according to one embodiment of the present invention. [Figure 7] FIG. 7 is a schematic perspective view showing an optical isolator of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0019] Preferred embodiments will be described below. However, the following embodiments are merely examples, and the present invention is not limited to the following embodiments. In addition, in each drawing, components having substantially the same functions may be referred to by the same reference numerals.

[0020] [Optical isolator] Fig. 1 is a schematic perspective view showing an optical isolator according to one embodiment of the present invention. Fig. 2 is a schematic simplified view showing a cross section along the forward direction of the optical isolator shown in Fig. 1. Note that Fig. 2 shows a magnet, a Faraday element, a first polarizer, and a second polarizer, and does not show other components.

[0021] In this specification, the forward direction is defined as the direction parallel to the direction in which light passes through the optical isolator, from the incident side to the outgoing side when light passes through the optical isolator. The side in which light enters in the forward direction is defined as the incident side, and the side in which light exits in the forward direction is defined as the outgoing side. In addition, the cross section of each component constituting the optical isolator, taken along a direction perpendicular to the forward direction, is defined as a transverse cross section.

[0022] As shown in FIG. 2, the optical isolator 1 includes a magnet 2, a Faraday element 3, a first polarizer 4, and a second polarizer 5.

[0023] The magnet 2 has a rectangular cylindrical shape. The magnet 2 has a first end face 2b, a second end face 2c, and a side face 2d. The first end face 2b and the second end face 2c face each other. The side face 2d connects the first end face 2b and the second end face 2c. The magnet 2 has a through-hole 2a that penetrates the magnet 2 from the first end face 2b to the second end face 2c. Light passes through the through-hole 2a in the magnet 2 in the forward direction X.

[0024] The magnet 2 has a first magnet body 6, a second magnet body 7, and a third magnet body 8. The first magnet body 6, the second magnet body 7, and the third magnet body 8 are stacked in the forward direction X. More specifically, from the incident side, the first magnet body 6, the second magnet body 7, and the third magnet body 8 are stacked in this order. However, unlike FIG. 2 , the first magnet body 6, the second magnet body 7, and the third magnet body 8 may be stacked in this order from the output side. The first magnet body 6, the second magnet body 7, and the third magnet body 8 each have a through hole. The through holes of the first magnet body 6, the second magnet body 7, and the third magnet body 8 are connected to each other, thereby forming the through hole 2a of the magnet 2.

[0025] 2, the first magnet body 6 is magnetized in a direction perpendicular to the forward direction X so that the side facing the through hole 2a has an N pole. The second magnet body 7 is magnetized in a direction parallel to the forward direction X so that the side facing the first magnet body 6 has an N pole. The third magnet body 8 is magnetized in a direction perpendicular to the forward direction X so that the side facing the through hole 2a has an S pole.

[0026] FIG. 3 is a diagram showing an example of the structure of the first magnet body (a simplified cross-sectional view of the first magnet body). The first magnet body 6 shown in FIG. 3 is formed by combining four magnet pieces and has a rectangular (square) cross-sectional shape as a whole. The first magnet body 6 may also have a circular cross-sectional shape as a whole. The number of magnet pieces that make up the first magnet body 6 is not limited to the above. For example, the first magnet body 6 may be formed by combining six or eight magnet pieces. By combining multiple magnet pieces to form the first magnet body 6, the magnetic field can be effectively increased. However, the first magnet body 6 may also be formed from a single magnet.

[0027] FIG. 4 is a diagram showing an example of the structure of the second magnet body (a simplified cross-sectional view of the second magnet body). The second magnet body 7 shown in FIG. 4 is made up of a single magnet. The second magnet body 7 has a rectangular (square) cross-sectional shape. The second magnet body 7 may also have a circular cross-sectional shape. The second magnet body 7 may also be made up of a combination of two or more magnet pieces.

[0028] FIG. 5 is a diagram showing an example of the structure of the third magnet body (a simplified cross-sectional view of the third magnet body). Similar to the first magnet body 6, the third magnet body 8 shown in FIG. 5 is constructed by combining four magnet pieces and has a rectangular (square) cross-sectional shape overall. The third magnet body 8 may also have a circular cross-sectional shape overall. By combining multiple magnet pieces to form the third magnet body 8, the magnetic field can be effectively increased. The third magnet body 8 may be constructed by combining six or eight magnet pieces, or may consist of a single magnet.

[0029] As shown in Figures 3 to 5, the outer shape of the cross section of the magnet 2 is square. However, the outer shape of the cross section of the magnet 2 is not limited to the above and may be, for example, a quadrangle other than a square, or may be circular, etc. Therefore, the shape of the magnet 2 is not limited to a rectangular tube and may be, for example, a cylindrical shape, etc. Furthermore, the cross section of the through hole 2a in the magnet 2 is square. However, the cross section of the through hole 2a is not limited to the above and may be, for example, a circular shape, etc.

[0030] Returning to FIG. 2, a Faraday element 3 is provided within the through-hole 2a of the magnet 2. The Faraday element 3 is made of a paramagnetic material that transmits light. The Faraday element 3 is provided so as to extend in the forward direction X. More specifically, the Faraday element 3 is arranged so as to extend from the through-hole of the first magnet body 6, through the through-hole of the second magnet body 7, and to the through-hole of the third magnet body 8. However, the Faraday element 3 is provided in a portion of the through-hole of the first magnet body 6 and does not reach the first end face 2b of the magnet 2. The Faraday element 3 is also provided in a portion of the through-hole of the third magnet body 8 and does not reach the second end face 2c of the magnet 2.

[0031] A first polarizer 4 is disposed on the incident side of the magnet 2. On the other hand, a second polarizer 5 is disposed on the exit side of the magnet 2. The first polarizer 4 and the second polarizer 5 face each other with the Faraday element 3 sandwiched between them in the forward direction X. In this embodiment, light enters from the first polarizer 4 side, passes through the Faraday element 3, and exits from the second polarizer 5 side.

[0032] The first polarizer 4 and the second polarizer 5 each have a light transmission axis. Light that passes through the first polarizer 4 becomes linearly polarized light according to the light transmission axis. The Faraday element 3 rotates the polarization plane of the linearly polarized light. The angle by which the Faraday element 3 rotates the polarization plane is the rotation angle. The angle between the light transmission axis of the second polarizer 5 and the light transmission axis of the first polarizer 4 is set to be equal to the rotation angle.

[0033] The optical isolator 1 of this embodiment is characterized in that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X is shorter than the longest distance L2 between two points on the outer periphery of the magnet 2 in a cross section. More specifically, as shown in FIGS. 1 and 2 , the optical isolator 1 is designed so that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 is short. Therefore, the optical isolator 1 is thinner than a conventional optical isolator 101 as shown in FIG. 7 . In this way, the optical isolator 1 is designed so that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 is short, which shortens the optical path length and thus reduces the likelihood of optical path deviation. Furthermore, the optical isolator 1 is designed to shorten the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5, allowing for efficient placement in a limited space, thereby broadening the design options for devices that use the optical isolator 1.

[0034] When the outer shape of the cross section of magnet 2 is square (including when it is approximately square), as in this embodiment, the longest distance L2 between two points on the outer periphery of the cross section of magnet 2 can be calculated from the diameter of the circumscribing circle of the square. Alternatively, when the outer shape of the cross section of magnet 2 is square, the longest distance L2 between two points on the outer periphery of the cross section of magnet 2 can be calculated from the length of the diagonal of the square (for example, L2 in FIG. 4).

[0035] If the outer shape of the cross section of magnet 2 is circular (including approximately circular), the longest distance L2 between two points on the outer periphery of the cross section of magnet 2 can be calculated from the diameter of the circle. Alternatively, if the outer shape of magnet 2 is elliptical (including approximately elliptical), the longest distance L2 between two points on the outer periphery of the cross section of magnet 2 can be calculated from the major axis of the ellipse.

[0036] If the outer shape of the cross section of the magnet 2 is a regular polygon (including cases where it is an approximately regular polygon, and if a regular polygon is expressed as a regular n-gon, including cases where n = even), the longest distance L2 between two points on the outer periphery in the cross section of the magnet 2 can be calculated from the diameter of the circumscribing circle of the regular polygon. Alternatively, if the outer shape of the cross section of the magnet 2 is a regular polygon (including cases where it is an approximately regular polygon, and if a regular polygon is expressed as a regular n-gon, including cases where n = odd or even), the longest distance L2 between two points on the outer periphery in the cross section of the magnet 2 can be calculated from the length of the longest diagonal of the regular polygon.

[0037] Alternatively, if the outer shape of the cross section of magnet 2 is rectangular (including the case where it is approximately rectangular), the longest distance L2 between two points on the outer edge of the cross section of magnet 2 can be determined from the length of the diagonal of the rectangle.

[0038] Note that, even if the outer shape of the cross section of magnet 2 is other than the above-mentioned outer shapes, it is sufficient to determine the longest distance L2 between two points on the outer periphery of the cross section of magnet 2 from the same perspective. For example, even if the outer shape of the cross section of magnet 2 is a convex polygon that is not a regular polygon, the longest distance L2 between two points on the outer periphery of the cross section can be determined from the length of the longest diagonal line.

[0039] In this embodiment, the ratio (L1 / L2) of the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X to the longest distance L2 between two points on the outer periphery of the cross section of the magnet 2 is preferably 0.3 or more, more preferably 0.4 or more, and preferably 0.95 or less, more preferably 0.9 or less. When the ratio (L1 / L2) is within the above range, optical path deviation in the optical isolator 1 can be made even less likely to occur, and the optical isolator 1 can be arranged more efficiently in a limited space.

[0040] In this embodiment, it is preferable that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X is shorter than the diameter D (e.g., D in FIGS. 2 and 5) of the inscribed circle at the outer periphery of the magnet 2. In this case, it is possible to further reduce the likelihood of optical path deviation in the optical isolator 1, and the optical isolator 1 can be arranged more efficiently in a limited space. Note that, when the outer shape of the cross section of the magnet 2 is square as in this embodiment, the diameter D of the inscribed circle coincides with the dimension of the magnet 2 in the height direction. From the same viewpoint, even when the outer diameter of the cross section of the magnet 2 is not square, it is also preferable that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X is shorter than the dimension of the magnet 2 in the height direction.

[0041] In this embodiment, the ratio (L1 / D) of the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X to the diameter D of the inscribed circle at the outer periphery of the magnet 2 is preferably 0.5 or more, more preferably 0.6 or more, and preferably 1.4 or less, more preferably 0.95 or less. When the ratio (L1 / D) is within the above range, optical path deviation in the optical isolator 1 can be made even less likely to occur, and the optical isolator 1 can be arranged more efficiently in a limited space.

[0042] In this embodiment, the ratio (L3 / La) of the length L3 of the Faraday element 3 in the forward direction X to the length La of the magnet 2 is preferably 0.25 or more, more preferably 0.3 or more, and preferably 1.0 or less, more preferably 0.8 or less. When the ratio (L3 / La) is within the above range, the magnetic field can be effectively utilized even when the distance L1 between the entrance surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 is shortened, and the optical characteristics of the optical isolator 1 can be further improved.

[0043] Other details of each member constituting the optical isolator 1 will be described below.

[0044] (Magnet and Faraday element) Magnet 2 is made of a permanent magnet. The permanent magnet is preferably a rare earth magnet, and more preferably a magnet mainly composed of samarium-cobalt (Sm-Co) or neodymium-iron-boron (Nd-Fe-B).

[0045] The length La of the magnet 2 is preferably 6 mm or more, more preferably 15 mm or more, and is preferably 90 mm or less, more preferably 80 mm or less.

[0046] A paramagnetic material can be used for the Faraday element 3. Preferably, a glass material is used as the paramagnetic material. A Faraday element 3 made of a glass material is less susceptible to fluctuations in the Verdet constant and decreases in the extinction ratio due to defects, etc., as in single-crystal materials, and is also less susceptible to stress from adhesives, so it can maintain a stable Verdet constant and a high extinction ratio. Note that a paramagnetic material other than a glass material can also be used for the Faraday element 3.

[0047] The length L3 of the Faraday element 3 is preferably 3 mm or more, more preferably 8 mm or more, and even more preferably 12 mm or more, and is preferably 30 mm or less, more preferably 25 mm or less, and even more preferably 22 mm or less. When the length L3 of the Faraday element 3 is within the above range, the Faraday rotation angle can be more reliably adjusted to the desired range.

[0048] Although there are no particular limitations on the cross-sectional shape of the Faraday element 3, a circular shape is preferable in order to obtain a uniform Faraday effect. The diameter of the Faraday element 3 can be, for example, 1 mm or more and 10 mm or less.

[0049] The Verdet constant of the Faraday element 3 is preferably 0.01 min / Oe·cm or more, more preferably 0.04 min / Oe·cm or more, even more preferably 0.06 min / Oe·cm or more, and is preferably 1 min / Oe·cm or less, more preferably 0.8 min / Oe·cm or less, even more preferably 0.7 min / Oe·cm or less.

[0050] The magnetic flux density of the Faraday element 3 is preferably 0.3 T or more, more preferably 0.5 T or more, and even more preferably 0.6 T or more, and is preferably 3.0 T or less, more preferably 2.5 T or less, and even more preferably 2.0 T or less.

[0051] When the Faraday element 3 is a glass material, the glass material preferably contains at least one rare earth element selected from Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm. The glass material preferably contains Tb. Note that Tb exists in the glass material in a trivalent or tetravalent state, but in this specification, all of these are expressed as values ​​converted to Tb2O3.

[0052] In glass materials, Tb relative to total Tb 3+ The ratio of Tb to total Tb is preferably 55% or more, more preferably 60% or more, even more preferably 80% or more, and even more preferably 90% or more, in mole percent. 3+ If the proportion is too small, the light transmittance in the wavelength range of 300 nm to 1100 nm tends to decrease.

[0053] The glass material may contain, for example, in mole percent, 20% to 80% of Tb2O3, 20% to 70% of B2O3+P2O5, and 0% to 45% of SiO2.

[0054] The content of Tb2O3 is, in mole percent, preferably 20% to 80%, more preferably 30% to 80%, still more preferably 40% to 80%, and particularly preferably 51% to 80%. When the content of Tb2O3 is within the above range, a good Faraday effect can be obtained even more effectively.

[0055] B2O3+P2O5 (the sum of the contents of B2O3 and P2O5) is preferably 20% to 70%, more preferably 25% to 60%, even more preferably 30% to 55%, and particularly preferably 30% to 45%, in mole percent. When the sum of the contents of B2O3 and P2O5 is within the above range, the vitrification range can be particularly easily expanded. The preferred contents of B2O3 and P2O5 are as follows:

[0056] The B2O3 content is, in mole percent, preferably 0% to 70%, more preferably 0% to 60%, even more preferably 0% to 55%, and particularly preferably 1% to 45%. When the B2O3 content is within the above range, the vitrification range can be further expanded while obtaining the Faraday effect.

[0057] The content of P2O5 is, in mole percent, preferably 0% to 70%, more preferably 0% to 60%, even more preferably 0% to 55%, and particularly preferably 1% to 45%. When the content of P2O5 is within the above range, the vitrification range can be further expanded while obtaining the Faraday effect.

[0058] The SiO2 content is, in mole percent, preferably 0% to 45%, more preferably 0% to 40%, even more preferably 0% to 35%, and particularly preferably 1% to 30%. When the SiO2 content is within the above range, the vitrification range can be further expanded while obtaining the Faraday effect.

[0059] A pipe member may be provided inside the through hole 2a of the magnet 2. More specifically, as shown in FIGS. 3 to 5 and FIG. 6 described later, a pipe member 9 may be provided in the through hole 2a of the magnet 2. In this embodiment, the pipe member 9 is a metal pipe. The pipe member 9 has a cylindrical shape. Specifically, the pipe member 9 has a through hole 9a, through which light passes. Therefore, a Faraday element 3 is provided inside the pipe member 9.

[0060] The cross section of the through hole 9a in the pipe member 9 is circular. In this embodiment, the pipe member 9 is made of SUS304.

[0061] The wall thickness of the pipe member 9 is preferably 0.1 mm or less, more preferably 0.08 mm or less, even more preferably 0.05 mm or less, and particularly preferably 0.045 mm or less, which allows the optically effective diameter of the optical isolator 1 to be increased without increasing the size of the optical isolator 1.

[0062] On the other hand, the wall thickness of the pipe member 9 is preferably 0.03 mm or more, and more preferably 0.035 mm or more. In this case, the strength of the pipe member 9 can be further increased. Note that the pipe member 9 does not necessarily have to be provided. In this case, it is sufficient that the Faraday element 3 is provided inside the through hole 2a of the magnet 2.

[0063] (First and second polarizers) For example, a polarizing beam splitter (PBS) can be used as the first polarizer 4 and the second polarizer 5. For example, a polarizing beam splitter formed by joining two triangular prisms via a polarization separation film can be used. For example, glass can be used as the material of the prisms.

[0064] When the first polarizer 4 and the second polarizer 5 are PBSs, P-polarized light or S-polarized light passes through the first polarizer 4 and enters the Faraday element 3. The second polarizer 5 is arranged to pass either the P-polarized light or the S-polarized light that enters the Faraday element 3 in the forward direction X. However, the first polarizer 4 and the second polarizer 5 are not limited to PBSs.

[0065] (Polarizer holder, housing, and lid) FIG. 6 is a schematic cross-sectional view showing a cross section in the forward direction of an optical isolator according to one embodiment of the present invention.

[0066] As shown in Figure 6, the first polarizer 4 is housed in a first polarizer holder 10. The first polarizer holder 10 has a pair of end faces and a side face 10c. The side face 10c extends in the forward direction X. The side face 10c connects the pair of end faces. One of the pair of end faces is an incident face 10a, and the other is an exit face 10b.

[0067] The second polarizer 5 is housed in a second polarizer holder 11. The second polarizer holder 11 has a pair of end faces and a side face 11c. The side face 11c extends in the forward direction X. The side face 11c connects the pair of end faces. One of the pair of end faces is an incident face 11a, and the other is an exit face 11b.

[0068] The outer shape of the cross section of the first polarizer holder 10 is circular. Similarly, the outer shape of the cross section of the second polarizer holder 11 is circular. However, the outer shapes of the cross sections of the first polarizer holder 10 and the second polarizer holder 11 are not limited to these.

[0069] An aluminum alloy is used as the material for the first polarizer holder 10 and the second polarizer holder 11. However, the material for the first polarizer holder 10 and the second polarizer holder 11 is not limited to this.

[0070] In this embodiment, it is preferable that the distance L4 between the incident surface 10a of the first polarizer holder 10 and the exit surface 11b of the second polarizer holder 11 is shorter than the longest distance L2 between two points on the outer periphery of the cross section of the magnet 2. In this case, it is possible to make it even less likely that an optical path deviation will occur in the optical isolator 1, and the optical isolator 1 can be arranged more efficiently in a limited space.

[0071] In this embodiment, the ratio (L4 / L2) of the distance L4 between the incident surface 10a of the first polarizer holder 10 and the exit surface 11b of the second polarizer holder 11 to the longest distance L2 between two points on the outer periphery in the cross section of the magnet 2 is preferably 0.3 or more, more preferably 0.4 or more, even more preferably 0.5 or more, and is preferably 1.3 or less, more preferably 1.2 or less, even more preferably 0.9 or less, and most preferably 0.8 or less. When the ratio (L4 / L2) is within the above range, optical path deviation in the optical isolator 1 can be made even less likely to occur, and the optical isolator 1 can be arranged more efficiently in a limited space.

[0072] In this embodiment, the ratio (L4 / D) of the distance L4 between the incident surface 10a of the first polarizer holder 10 and the exit surface 11b of the second polarizer holder 11 to the diameter D of the inscribed circle at the outer periphery of the magnet 2 is preferably 0.5 or more, more preferably 0.6 or more, and preferably 1.5 or less, more preferably 1.2 or less. When the ratio (L4 / D) is within the above range, optical path deviation in the optical isolator 1 can be made even less likely to occur, and the optical isolator 1 can be arranged more efficiently in a limited space.

[0073] As shown in FIG. 6, the magnet 2 is housed in a housing 12, a first cover 13, and a second cover 14. The housing 12 is cylindrical in shape. The housing 12 has a pair of end faces, a side face, and an inner wall. The side face and the inner wall face each other. The side face and the inner wall extend in the forward direction X. The side face and the inner wall connect the pair of end faces. One of the pair of end faces is an end face on the incident side, and the other is an end face on the exit side.

[0074] The housing 12 has a first open portion 12a and a second open portion 12b. The first open portion 12a is located on the incident side. The second open portion 12b is located on the output side. When viewed from the forward direction X, the magnet 2 is not covered by the housing 12. More specifically, when viewed from either the incident side or the output side, the magnet 2 is not covered by the housing 12.

[0075] The first cover 13 is disposed between the magnet 2 and the first polarizer 4 (first polarizer holder 10). The first cover 13 closes the first opening 12a of the housing 12. On the other hand, the second cover 14 is disposed between the magnet 2 and the second polarizer 5 (second polarizer holder 11). The second cover 14 closes the second opening 12b of the housing 12. However, the first cover 13 and the second cover 14 do not completely close the housing 12. More specifically, the first cover 13 has a first opening 13a. Similarly, the second cover 14 has a second opening 14a. Light passes through the first opening 13a and the second opening 14a.

[0076] An aluminum alloy is used as the material for the housing 12, the first cover 13, and the second cover 14. However, the materials for the housing 12, the first cover 13, and the second cover 14 are not limited to this.

[0077] In this embodiment, the housing 12 has a first opening 12a and a second opening 12b, which are closed by a first cover 13 and a second cover 14. In this case, the housing 12, the first cover 13, and the second cover 14 are all independent members, which facilitates processing of these members. For example, multiple housings 12 can be easily obtained by dividing a single pipe-shaped member. Alternatively, for example, the first cover 13 and the second cover 14 can be obtained in the same process. This reduces the cost of manufacturing the optical isolator 1. In addition, assembly is facilitated during the manufacturing of the optical isolator 1. This effectively increases the productivity of the optical isolator 1.

[0078] Incidentally, when manufacturing the optical isolator 1, the angle of the first polarizer 4 is adjusted by rotating the first polarizer holder 10. Similarly, the angle of the second polarizer 5 is adjusted by rotating the second polarizer holder 11. In this embodiment, a portion of the first polarizer holder 10 is located inside the first cover 13. Similarly, a portion of the second polarizer holder 11 is located inside the second cover 14. Specifically, a portion of the first polarizer holder 10 is located inside the recess of the first cover 13. The remaining portion of the first polarizer holder 10 is located outside the recess. A portion of the second polarizer holder 11 is located inside the recess of the second cover 14. The remaining portion of the second polarizer holder 11 is located outside the recess. This makes it easier to adjust the angles of the first polarizer 4 and the second polarizer 5, and by shortening the distance L4 between the incident surface 10a of the first polarizer holder 10 and the exit surface 11b of the second polarizer holder 11, the optical isolator 1 can be made smaller.

[0079] The first cover 13 is fitted to the first polarizer holder 10. More specifically, the first fitting portion 13b of the first cover 13 is fitted to the side surface 10c and the exit surface 10b of the first polarizer holder 10. This makes it easier to fix the position of the first polarizer holder 10. This makes it possible to suppress deviation of the light transmission axis of the first polarizer 4. In addition, the accuracy of the optical axis in the optical isolator 1 can be improved.

[0080] The second cover 14 is fitted to the second polarizer holder 11. More specifically, the second fitting portion 14b of the second cover 14 is fitted to the side surface 11c and the incident surface 11a of the second polarizer holder 11. This makes it easier to fix the position of the second polarizer holder 11. This makes it possible to suppress deviation of the light transmission axis of the second polarizer 5. In addition, the accuracy of the optical axis in the optical isolator 1 can be improved.

[0081] In this embodiment, the first polarizer holder 10 and the first lid 13 are fixed with an adhesive. The second polarizer holder 11 and the second lid 14 are fixed with an adhesive. However, the means for fixing the first polarizer holder 10 and the second polarizer holder 11 are not limited to these.

[0082] For example, the first polarizer holder 10 and the second polarizer holder 11 may be fixed by magnetic force. Specifically, for example, a magnetic material may be embedded in the first polarizer holder 10 and the second polarizer holder 11. The first polarizer holder 10 may be indirectly fixed to the magnet 2 by magnetic force via the first cover 13. The second polarizer holder 11 may be indirectly fixed to the magnet 2 by magnetic force via the second cover 14.

[0083] As described above, when manufacturing the optical isolator 1, the angle of the first polarizer 4 is adjusted by rotating the first polarizer holder 10. The shape of the portion where the first cover 13 and the first polarizer holder 10 are fitted together is circular when viewed from the forward direction X. Therefore, before the first cover 13 and the first polarizer holder 10 are fixed together with an adhesive or the like, the side surface 10c of the first polarizer holder 10 can be slid along the inner wall of the first cover 13. This makes it difficult for the first polarizer holder 10 to become misaligned when it is rotated.

[0084] Similarly, before the second lid 14 and the second polarizer holder 11 are fixed together with an adhesive or the like, the side surface 11c of the second polarizer holder 11 can be slid along the inner wall of the second lid 14. This makes it difficult for the second polarizer holder 11 to become misaligned when the second polarizer holder 11 is rotated. However, the first lid 13 and the first polarizer holder 10, and the second lid 14 and the second polarizer holder 11 do not necessarily need to be fitted together.

[0085] In this embodiment, the first cover 13 and the second cover 14 are fitted to the housing 12. This improves the vibration resistance and impact resistance of the optical isolator 1. However, the housing 12, the first cover 13, and the second cover 14 do not necessarily have to be fitted to each other.

[0086] In this embodiment, the first cover 13 and the second cover 14 are fixed to the housing 12 by screwing. Note that the means for fixing the first cover 13 and the second cover 14 to the housing 12 is not limited to screwing. For example, the first cover 13 and the second cover 14 may be fixed to the housing 12 by adhesive or the like.

[0087] In this embodiment, the outer shape of the first polarizer holder 10 and the outer shape of the second polarizer holder 11 in their transverse cross sections are circular, and the outer shape of the magnet 2 in their transverse cross sections is quadrangular (more preferably square). By making the outer shapes of the first polarizer holder 10 and the second polarizer holder 11 circular in this way, it is possible to easily adjust the angles of the first polarizer 4 and the second polarizer 5. For example, as described above, the side surface 10c of the first polarizer holder 10 can be slid along the inner wall of the first lid 13. The side surface 11c of the second polarizer holder 11 can be slid along the inner wall of the second lid 14.

[0088] On the other hand, by making the outer shape of the magnet 2 rectangular, it is possible to increase the magnetic flux density in the magnet 2. Specifically, for example, for a magnet 2 of the same volume, it is possible to increase the magnetic flux density in the magnet 2 by making the outer shape of the cross section rectangular rather than by making the outer shape of the cross section circular or the like. Therefore, in this embodiment, it is possible to increase the magnetic flux density of the magnet 2 even when the optical isolator 1 is made small.

[0089] In the present invention, the first polarizer holder 10, the second polarizer holder 11, the housing 12, the first lid 13, and the second lid 14 are not necessarily provided. In the present invention, it is sufficient that the distance L1 between the incident surface 4a of the first polarizer 4 and the exit surface 5b of the second polarizer 5 in the forward direction X is shorter than the longest distance L2 between two points on the outer periphery of the magnet 2 in its cross section. This makes it difficult for optical path deviation to occur in the optical isolator 1, and the optical isolator 1 can be efficiently arranged in a limited space. [Explanation of symbols]

[0090] 1...Optical isolator 2...Magnet 2a,9a…Through hole 2b, 2c...First and second end faces 2d,10c,11c…side 3...Faraday element 4, 5...First and second polarizers 4a,10a,11a...Incidence surface 5b,10b,11b...Emission surface 6, 7, 8...1st, 2nd, 3rd magnet bodies 9...Pipe member 10, 11...First and second polarizer holders 12...Housing 12a, 12b...First and second openings 13, 14...First and second lids 13a, 14a...first and second openings 13b, 14b...first and second fitting portions

Claims

1. a magnet having a through hole through which light enters in the forward direction and passes; a Faraday element that transmits the light and is provided inside the through hole of the magnet; When the side where the light in the forward direction is incident is defined as an incident side and the side where the light is emitted is defined as an emission side, a first polarizer disposed on the incident side of the magnet; a second polarizer disposed on the output side of the magnet; Equipped with the magnet includes a first magnet body, a second magnet body, and a third magnet body, each having a through hole; the first magnet body, the second magnet body, and the third magnet body are stacked in this order, and the through hole of the first magnet body, the through hole of the second magnet body, and the through hole of the third magnet body are in communication with each other; the first magnet body is magnetized in a direction perpendicular to the forward direction and with the through hole side as the north pole, the second magnet body is magnetized in a direction parallel to the forward direction and with the first magnet body side as the north pole, the third magnet body is magnetized in a direction perpendicular to the forward direction and such that the through hole side is the south pole, When the incident side surface in the forward direction is an incident surface, the exit side surface in the forward direction is an exit surface, and a cross section along a direction perpendicular to the forward direction is a transverse cross section, An optical isolator characterized in that the distance between the incident surface of the first polarizer and the exit surface of the second polarizer in the forward direction is shorter than the longest distance between two points on the outer periphery of the magnet in the cross section.

2. a first polarizer holder that houses the first polarizer; a second polarizer holder that houses the second polarizer; Furthermore, 2. The optical isolator of claim 1, wherein the distance between the incident surface of the first polarizer holder and the exit surface of the second polarizer holder in the forward direction is shorter than the longest distance between two points on the outer periphery of the magnet in the cross section.

3. a housing that houses the magnet and the Faraday element therein and has a first opening located on the incident side and a second opening located on the exit side; a first cover having a first opening through which the light passes and closing the first open portion of the housing; a second cover having a second opening through which the light passes and closing the second open portion of the housing; Furthermore, the first lid is disposed between the magnet and the first polarizer, 2. The optical isolator according to claim 1, wherein the second lid is disposed between the magnet and the second polarizer.

4. a housing that houses the magnet and the Faraday element therein and has a first opening located on the incident side and a second opening located on the exit side; a first cover having a first opening through which the light passes and closing the first open portion of the housing; a second cover having a second opening through which the light passes and closing the second open portion of the housing; Furthermore, the first lid is disposed between the magnet and the first polarizer holder, 3. The optical isolator according to claim 2, wherein the second lid is disposed between the magnet and the second polarizer holder.

5. At least a part of the first polarizer holder is located inside the first lid, and the first lid has a first fitting portion that fits with the first polarizer holder, 5. The optical isolator according to claim 4, wherein at least a portion of the second polarizer holder is located inside the second lid, and the second lid has a second engaging portion that engages with the second polarizer holder.

6. An optical isolator according to any one of claims 1 to 5, characterized in that the longest distance between two points on the outer periphery of the magnet in the cross section is the diameter of the circle when the outer shape of the cross section of the magnet is a circle, or the length of the longest diagonal of the regular polygon when the outer shape of the cross section of the magnet is a regular polygon.

7. An optical isolator according to any one of claims 1 to 5, characterized in that the longest distance between two points on the outer periphery of the magnet in the cross section is the diameter of the circle when the outer shape of the cross section of the magnet is a circle, or is the diameter of the inscribed circle of the regular polygon when the outer shape of the cross section of the magnet is a regular polygon.

8. 6. The optical isolator according to claim 1, wherein the ratio of the length of the Faraday element to the length of the magnet in the forward direction (length of Faraday element / length of magnet) is 0.25 or more and 1.0 or less.

9. 6. The optical isolator according to claim 1, wherein the length of the Faraday element is 3 mm to 30 mm, the Verdet constant of the Faraday element is 0.01 min / Oe cm to 1 min / Oe cm, and the magnetic flux density of the Faraday element is 0.3 T to 3.0 T.

10. 6. The optical isolator according to claim 1, wherein the magnet has a rectangular outer shape in the cross section.

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