Optical isolator

Abstract

The present invention provides a more compact optical isolator.　An optical isolator 1 is characterized by comprising: a magnet 7 having a through-hole 7a through which light is incident and passes in the forward direction; a Faraday element 2 that transmits light and is disposed inside the through-hole 7a of the magnet 7; a first polarizer 3 that is disposed on the incident side of the magnet 7, the incident side being a side on which light is incident in the forward direction; a second polarizer 4 that is disposed on the emission side of the magnet 7, the emission side being a side to which light is emitted in the forward direction; a first polarizer holder 5 storing the first polarizer 3; and a second polarizer holder 6 storing the second polarizer 4, the area of the first polarizer holder 5 being smaller than the area of the magnet 7 when viewed from the forward direction, the area of the second polarizer holder 6 being smaller than the area of the magnet 7 when viewed from the forward direction.

Description

Optical isolator

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

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

[0003] In Patent Document 1, the magnet structure is housed in an inner case, which is housed in an outer case, and a pair of polarizers are arranged inside the outer case so as to face each other with a Faraday rotator sandwiched therebetween.

[0004] JP 2016-051105 A

[0005] In an optical isolator, a structure for holding a polarizer can prevent damage to the polarizer, misalignment of the optical axis, etc. Meanwhile, in recent years, there has been a demand for further miniaturization of optical isolators. However, the optical isolator disclosed in Patent Document 1 has difficulty in miniaturization due to the structure for holding the polarizer.

[0006] An object of the present invention is to provide an optical isolator that can be made smaller.

[0007] The optical isolator of 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, a Faraday element that transmits the light and is arranged inside the through hole of the magnet, a first polarizer arranged on the incident side of the magnet, a second polarizer arranged on the exit side of the magnet, a first polarizer holder that houses the first polarizer, and a second polarizer holder that houses the second polarizer, when the side into which the light enters in the forward direction is defined as the incident side and the side from which the light exits is defined as the exit side, and is characterized in that when viewed from the forward direction, the area of ​​the first polarizer holder is smaller than the area of ​​the magnet, and when viewed from the forward direction, the area of ​​the second polarizer holder is smaller than the area of ​​the magnet.

[0008] In the optical isolator of aspect 2, in aspect 1, it is preferable that the optical isolator further comprises a housing having an inner wall and housing the magnet and the Faraday element therein, a first lid that houses the first polarizer holder together with the housing, and a second lid that houses the second polarizer holder together with the housing, wherein the first polarizer holder and the second polarizer holder each have a side that extends in the forward direction and faces the inner wall of the housing, the first lid has a portion that is in contact with both the side of the first polarizer holder and the inner wall of the housing, and the second lid has a portion that is in contact with both the side of the second polarizer holder and the inner wall of the housing.

[0009] The optical isolator of aspect 3 is preferably the same as that of aspect 2, further comprising a first fiber collimator connected to the first lid body and a second fiber collimator connected to the second lid body.

[0010] In the optical isolator of Aspect 4, in Aspect 1 or Aspect 2, it is preferable that the first polarizer holder has a first base and a first extension extending from the first base in the forward direction and positioned inside the outer peripheral edge of the first base when viewed from the forward direction, and the second polarizer holder has a second base and a second extension extending from the second base in the forward direction and positioned inside the outer peripheral edge of the second base when viewed from the forward direction, and the first base and the second base are in contact with the magnet.

[0011] The optical isolator of aspect 5 is the same as that of aspect 4, and further includes a housing having an inner wall and housing the magnet and the Faraday element therein, a first lid that houses the first polarizer holder together with the housing, and a second lid that houses the second polarizer holder together with the housing, wherein the first base of the first polarizer holder and the second base of the second polarizer holder each have a side that extends in the forward direction and faces the inner wall of the housing, the first lid has a portion in contact with both the side of the first base and the inner wall of the housing, and the second lid has a portion in contact with both the side of the second base and the inner wall of the housing.

[0012] The optical isolator of aspect 6 is preferably the same as in aspect 5, further comprising a first fiber collimator connected to the first lid body and a second fiber collimator connected to the second lid body.

[0013] In the optical isolator of Aspect 7, in any one of Aspects 1 to 6, it is preferable that the optical isolator further includes a pipe member arranged inside the through hole of the magnet, the Faraday element is arranged inside the pipe member, the pipe member has a first protrusion protruding from the magnet toward the incident side and a second protrusion protruding from the magnet toward the output side, the first polarizer holder has a through hole through which the light passes, the second polarizer holder has a through hole through which the light passes, the first protrusion is in contact with the inner wall of the first polarizer holder facing the through hole, and the second protrusion is in contact with the inner wall of the second polarizer holder facing the through hole.

[0014] In the optical isolator of aspect 8, in aspect 7, it is preferable that the first polarizer holder holds the first polarizer so that the first protrusion of the pipe member does not come into contact with the first polarizer, and the second polarizer holder holds the second polarizer so that the second protrusion of the pipe member does not come into contact with the second polarizer.

[0015] In the optical isolator of Aspect 9, in any one of Aspects 1 to 8, it is preferable that the magnet has a first magnetic body, a second magnetic body, and a third magnetic body, each having a through hole, and that the first magnetic body, the second magnetic body, and the third magnetic body are stacked in this order from the incident side, 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 are connected, the first magnetic body is magnetized in a direction perpendicular to the forward direction so that the through hole side is the north pole, the second magnetic 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 magnetic body is magnetized in a direction perpendicular to the forward direction so that the through hole side is the south pole.

[0016] The optical isolator of aspect 10 of the present invention is characterized in that, in any one of aspects 1 to 9, when a cross section along a direction perpendicular to the forward direction is taken as a transverse cross section, the outer shape of the magnet in the transverse cross section is rectangular, and the outer shape of the first polarizer holder in the transverse cross section and the outer shape of the second polarizer holder in the transverse cross section are circular.

[0017] According to the present invention, it is possible to provide an optical isolator that can be made smaller.

[0018] FIG. 1 is a schematic perspective view of an optical isolator according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view showing a cross section of the optical isolator according to the first embodiment of the present invention along the light transmission direction. FIG. 3 is a schematic cross-sectional view of a portion of the optical isolator according to the first embodiment of the present invention where a magnet is located. FIG. 4 is a schematic view showing the positional relationship between a first polarizer holder and a magnet when the optical isolator according to the first embodiment of the present invention is viewed from the forward direction. FIG. 5 is a schematic perspective view of a first polarizer holder and a first polarizer according to the first embodiment of the present invention. FIG. 6 is a schematic perspective view showing an enlarged cross section of a portion near the first polarizer holder according to the first embodiment of the present invention along the light transmission direction. FIG. 7 is a schematic perspective view showing an enlarged cross section of a portion near the second polarizer holder according to the first embodiment of the present invention along the light transmission direction. FIG. 8 is a schematic perspective view of an optical isolator according to a modified example of the first embodiment of the present invention. FIG. 9 is a schematic perspective view showing a cross section of a portion near the second polarizer holder according to the second embodiment of the present invention along the light transmission direction. FIG. 10 is a schematic diagram of a magnet according to the second embodiment of the present 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] (First Embodiment) Fig. 1 is a schematic perspective view of an optical isolator according to a first embodiment of the present invention, and Fig. 2 is a schematic perspective view showing a cross section of the optical isolator according to the first embodiment along the direction in which light passes.

[0021] The optical isolator 1 shown in Fig. 1 is capable of inputting and outputting light via an optical fiber. As shown in Fig. 2, the optical isolator 1 includes a Faraday element 2, a first polarizer 3, a second polarizer 4, a first polarizer holder 5, a second polarizer holder 6, a magnet 7, and a pipe member 8. The optical isolator 1 further includes a housing 12, a first cover 13, a second cover 14, a first fiber collimator 15, and a second fiber collimator 16.

[0022] The magnet 7 has a rectangular cylindrical shape. Specifically, the magnet 7 has a through-hole 7a. More specifically, the magnet 7 has a pair of end faces and a side face 7d. The side face 7d connects the pair of end faces. The through-hole 7a is provided from one end face to the other end face. Light passes through the through-hole 7a in the forward direction.

[0023] That is, in this specification, the forward direction is the direction parallel to the direction in which light passes through the optical isolator, and is the direction in which light passes from the incident side to the outgoing side when passing through the optical isolator. Hereinafter, the side in which light in the forward direction enters will be referred to as the incident side, and the side in which light in the forward direction exits will be referred to as the outgoing side. In each component, the cross section along the direction perpendicular to the forward direction will be referred to as the transverse cross section.

[0024] FIG. 3 is a schematic cross-sectional view of a portion where a magnet is located in the optical isolator according to the first embodiment.

[0025] The outer shape of the cross section of the magnet 7 is a square. However, the outer shape of the cross section of the magnet 7 is not limited to the above and may be, for example, a quadrangle other than a square, or may be a circle, etc. Therefore, the shape of the magnet 7 is not limited to a rectangular tube and may be, for example, a cylindrical shape.

[0026] The cross-sectional shape of the through-hole 7a in the magnet 7 is square. However, the cross-sectional shape of the through-hole 7a is not limited to the above, and may be, for example, circular.

[0027] A pipe member 8 is provided inside the through hole 7a of the magnet 7. In this embodiment, the pipe member 8 is a metal pipe. The pipe member 8 has a cylindrical shape. Specifically, the pipe member 8 has a through hole 8a. Light passes through the through hole 8a. The cross-sectional shape of the through hole 8a in the pipe member 8 is circular. In this embodiment, SUS304 is used as the material for the pipe member 8. However, the material for the pipe member 8 is not limited to the above.

[0028] Returning to Fig. 2, the Faraday element 2 is provided inside the pipe member 8. More specifically, the Faraday element 2 is disposed in the through hole 8a of the pipe member 8 at a portion that is located inside the through hole 7a of the magnet 7. Note that the pipe member 8 does not necessarily have to be provided. In this case, it is sufficient that the Faraday element 2 is provided inside the through hole 7a of the magnet 7.

[0029] The first polarizer 3 is housed in a first polarizer holder 5. The first polarizer holder 5 abuts against the end face of a magnet 7 on the incident side. On the other hand, the second polarizer 4 is housed in a second polarizer holder 6. The second polarizer holder 6 abuts against the end face of the magnet 7 on the exit side.

[0030] A through-hole 5a is formed in the first polarizer holder 5. The first polarizer 3 is disposed so as to cover the through-hole 5a. Similarly, a through-hole 6a is formed in the second polarizer holder 6. The second polarizer 4 is disposed so as to cover the through-hole 6a.

[0031] The through-hole 5 a of the first polarizer holder 5 and the through-hole 6 a of the second polarizer holder 6 are connected to the through-hole 7 a of the magnet 7. Light passes through the through-hole 5 a of the first polarizer holder 5, the through-hole 7 a of the magnet 7, and the through-hole 6 a of the second polarizer holder 6.

[0032] An aluminum alloy is used as the material of the first polarizer holder 5 and the second polarizer holder 6. However, the material of the first polarizer holder 5 and the second polarizer holder 6 is not limited to the above.

[0033] 2, the magnet 7 and the Faraday element 2 are housed in a housing 12. The first polarizer holder 5, together with the housing 12, is housed by a first cover 13. The second polarizer holder 6, together with the housing 12, is housed by a second cover 14.

[0034] Specifically, the housing 12 is cylindrical in shape. 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, the magnet 7 is not covered by the housing 12. More specifically, when viewed from either the incident side or the output side, the magnet 7 is not covered by the housing 12.

[0035] More specifically, the housing 12 has a pair of end faces, a side face, and an inner wall 12c. The side face and the inner wall 12c face each other. The side face and the inner wall 12c extend in the forward direction. The side face and the inner wall 12c connect the pair of end faces. One of the pair of end faces is an incident-side end face 12e, and the other is an exit-side end face 12f.

[0036] The first cover 13 closes the first opening 12a of the housing 12. On the other hand, 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.

[0037] 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 those mentioned above. The first cover 13 and the second cover 14 do not necessarily have to be provided.

[0038] A first fiber collimator 15 is provided on the first polarizer holder 5 side. Specifically, the first fiber collimator 15 is fixed to the first cover 13 by screwing. A second fiber collimator 16 is provided on the second polarizer holder 6 side. Specifically, the second fiber collimator 16 is fixed to the second cover 14 by screwing. However, the means for fixing the first fiber collimator 15 and the second fiber collimator 16 is not limited to screwing.

[0039] The first polarizer 3 and the second polarizer 4 face each other with the Faraday element 2 sandwiched between them in the forward direction. The first polarizer 3 and the second polarizer 4 each have a light transmission axis. Light that passes through the first polarizer 3 becomes linearly polarized light according to the light transmission axis. The Faraday element 2 rotates the polarization plane of the linearly polarized light. The angle by which the Faraday element 2 rotates the polarization plane is the rotation angle. The angle of the light transmission axis of the second polarizer 4 relative to the light transmission axis of the first polarizer 3 is set to be equal to the rotation angle.

[0040] In this embodiment, both the first polarizer 3 and the second polarizer 4 are polarizing beam splitters (PBS). Therefore, P-polarized light or S-polarized light passes through the first polarizer 3 and enters the Faraday element 2. The second polarizer 4 is arranged to pass either the P-polarized light or the S-polarized light that enters the Faraday element 2 in the forward direction. However, the first polarizer 3 and the second polarizer 4 are not limited to PBSs.

[0041] In this embodiment, light passes through the first fiber collimator 15 and enters the first polarizer 3. The light passes through the first polarizer 3, becomes linearly polarized light, and enters the Faraday element 2. The polarization plane of the light that has passed through the Faraday element 2 is then rotated. The light emitted from the Faraday element 2 enters the second polarizer 4. The light that has passed through the second polarizer 4 passes through the second fiber collimator 16 and is guided from the optical isolator 1 to the optical fiber. Note that the first fiber collimator 15 and the second fiber collimator 16 are not necessarily provided.

[0042] Figure 4 is a schematic diagram showing the positional relationship between the first polarizer holder and the magnet when the optical isolator according to the first embodiment is viewed from the forward direction. The first cover 12 shown in Figure 2 is omitted from Figure 4. The magnet 7 and the housing 12 are hatched in Figure 4. Hereinafter, the area of ​​a component when viewed from the forward direction is the area of ​​the shape defined by the outer shape of the component, unless otherwise specified. For example, the area of ​​the first polarizer holder 5 when viewed from the forward direction does not exclude the area of ​​the through-hole 5a, unless otherwise specified.

[0043] A feature of this embodiment is that, as shown in FIG. 4 , when viewed from the forward direction, the area of ​​the first polarizer holder 5 is smaller than the area of ​​the magnet 7, and the area of ​​the second polarizer holder 6 is smaller than the area of ​​the magnet 7. This makes it possible to prevent the optical isolator 1 from becoming larger, which would be caused by the configuration for holding the first polarizer 3 and the second polarizer 4. In addition, even when the first cover 13 and the second cover 14 are provided, the first polarizer holder 5 and the second polarizer holder 6 housed therein are small. This makes it possible to prevent the first cover 13 and the second cover 14 from becoming larger. This allows for the optical isolator 1 to be made smaller.

[0044] The configuration of this embodiment will be described in more detail below.

[0045] Fig. 5 is a schematic perspective view of a first polarizer holder and a first polarizer in the first embodiment. Fig. 6 is a schematic perspective view showing an enlarged cross section along the light transmission direction near the first polarizer holder in the first embodiment. Fig. 7 is a schematic perspective view showing an enlarged cross section along the light transmission direction near the second polarizer holder in the first embodiment.

[0046] As shown in Fig. 5, the first polarizer holder 5 has a first base 5A and a pair of first extensions 5B. Each first extension 5B extends in the forward direction from the first base 5A and is located inside the outer periphery of the first base 5A when viewed in the forward direction. The pair of first extensions 5B face each other in a direction perpendicular to the forward direction. The pair of first extensions 5B sandwich the first polarizer 3.

[0047] In this embodiment, the first base 5A has a cylindrical shape. As shown in FIG. 6 , the first base 5A has the through-hole 5a. The first polarizer 3 is arranged to cover the through-hole 5a of the first base 5A. As shown in FIG. 5 , the first base 5A has a side surface 5d extending in the forward direction. Furthermore, the surface of the first base 5A on which the first extension 5B is provided includes an outer circumferential portion 5e. Specifically, the outer circumferential portion 5e is a portion of the surface that is located outside the first extension 5B when viewed from the forward direction.

[0048] On the other hand, each first extension portion 5B has a substantially semi-cylindrical shape. Each first extension portion 5B has a side surface extending in the forward direction. The side surface of each first extension portion 5B includes a curved first side surface 5f and a flat second side surface 5g. Each first extension portion 5B holds the first polarizer 3 by means of the second side surface 5g.

[0049] 7 is configured similarly to the first polarizer holder 5. The second polarizer holder 6 has a second base 6A and a pair of second extensions 6B. Each second extension 6B extends in the forward direction from the second base 6A and is located inside the outer periphery of the second base 6A when viewed in the forward direction.

[0050] The through-hole 6a is provided in the second base 6A. The second polarizer 4 is arranged to cover the through-hole 6a in the second base 6A. The second base 6A has a side surface 6d extending in the forward direction. Furthermore, the surface of the second base 6A on which the second extension 6B is provided includes an outer periphery 6e. Specifically, the outer periphery 6e is a portion of the surface that is located outside the second extension 6B when viewed from the forward direction.

[0051] Each second extension 6B has a substantially semi-cylindrical shape. Each second extension 6B has a side surface extending in the forward direction. The side surface of each second extension 6B includes a curved third side surface 6f and a flat fourth side surface 6g. Each second extension 6B supports the second polarizer 4 by the fourth side surface 6g.

[0052] Returning to FIG. 5 , in the first polarizer holder 5, the shape of the first base 5A and the number and shape of the first extensions 5B are not limited to those described above. For example, the first polarizer holder 5 may have one first extension 5B, and the first extension 5B may have a through-hole. In this case, it is sufficient that the first polarizer 3 is held within the through-hole. Alternatively, the first polarizer holder 5 may have three or more first extensions 5B. In this case, the first polarizer 3 may be held by the multiple first extensions 5B. The same applies to the second polarizer holder 6.

[0053] In the first polarizer holder 5, the first base 5A and the pair of first extensions 5B are integrally configured. Alternatively, the first base 5A and the pair of first extensions 5B may be configured separately, and the first base 5A and the pair of first extensions 5B may be joined together. Alternatively, the first polarizer holder 5 may be configured only with the first base 5A. In this case, for example, the first polarizer 3 may be held in the through hole 5a of the first base 5A. The same applies to the second polarizer holder 6.

[0054] The first polarizer holder 5 and the second polarizer holder 6 shown in Fig. 2 are fixed to the magnet 7 with an adhesive. In this specification, a case where members are joined together with an adhesive or the like and the adhesive or the like is located between the members is also considered to be a case where the members are in contact with each other. The first polarizer holder 5 and the second polarizer holder 6 are in contact with the magnet 7.

[0055] As in this embodiment, it is preferable that the first base 5A of the first polarizer holder 5 and the second base 6A of the second polarizer holder 6 are in contact with the magnet 7. In this case, the contact area between the first polarizer holder 5 and the second polarizer holder 6 and the magnet 7 is large. This increases the bonding strength between the first polarizer holder 5 and the second polarizer holder 6 and the magnet 7. This increases the vibration resistance and impact resistance of the optical isolator 1.

[0056] The configuration of the first polarizer holder 5 and the second polarizer holder 6 and the magnet 7 is not limited to a configuration in which they are fixed by an adhesive. For example, the first polarizer holder 5 and the second polarizer holder 6 and the magnet 7 may not be fixed by an adhesive, and the first polarizer holder 5 and the second polarizer holder 6 and the magnet 7 may be attracted to each other by magnetic force. In this case, for example, a magnetic material may be embedded in the first polarizer holder 5 and the second polarizer holder 6. Alternatively, in the present invention, the object to which the first polarizer holder 5 and the second polarizer holder 6 are fixed by an adhesive may be something other than the magnet 7.

[0057] As in this embodiment, it is preferable that the outer shape of the first polarizer holder 5 and the outer shape of the second polarizer holder 6 are circular in cross section, and that the outer shape of the magnet 7 is rectangular in cross section. By making the outer shapes of the first polarizer holder 5 and the second polarizer holder 6 circular, it is easy to adjust the angles of the first polarizer 3 and the second polarizer 4.

[0058] On the other hand, by making the outer shape of the magnet 7 rectangular, it is possible to increase the magnetic flux density in the magnet 7. Specifically, for example, for a magnet of the same volume, the magnetic flux density in the magnet can be increased 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, the magnetic flux density of the magnet 7 can be increased even when the optical isolator 1 is made small.

[0059] A portion of the first polarizer holder 5 is located inside the housing 12. The remaining portion of the first polarizer holder 5 is located outside the housing 12. Similarly, a portion of the second polarizer holder 6 is located inside the housing 12. The remaining portion of the second polarizer holder 6 is located outside the housing 12. This allows the optical isolator 1 to be made more compact.

[0060] 6 , in this embodiment, the first base 5A of the first polarizer holder 5 and a portion of each first extension 5B are located inside the housing 12. Therefore, the entire side surface 5d of the first base 5A and a portion of the first side surface 5f of each first extension 5B face each other with the inner wall 12c of the housing 12. More specifically, at least a portion of the portion of each first extension 5B of the first polarizer holder 5 that holds the first polarizer 3 is located outside the housing 12.

[0061] 7 , the entire side surface 6d of the second base 6A of the second polarizer holder 6 and a part of the third side surface 6f of each second extension 6B face each other and the inner wall 12c of the housing 12. At least a part of the portion of each second extension 6B of the second polarizer holder 6 that holds the second polarizer 4 is located outside the housing 12.

[0062] As described above, by arranging the first polarizer holder 5 and the second polarizer holder 6, it is possible to prevent the light reflected by the first polarizer 3 and the second polarizer 4 from being irradiated onto the housing 12. This makes it possible to prevent heat generation in the housing 12. In addition, it is possible to prevent the light from returning to the incident side.

[0063] As shown in Fig. 6, the first cover 13 has a first opening 13a. More specifically, the first cover 13 has an inner wall 13b and a side surface 13d. The inner wall 13b faces the first opening 13a. The side surface 13d and the inner wall 13b face each other. The side surface 13d and the inner wall 13b extend in the forward direction.

[0064] In the following description, unless otherwise specified, the cross-sectional area of ​​a member is the area of ​​the shape defined by the outer shape of the cross-section of the member. For example, unless otherwise specified, the cross-sectional area of ​​the first lid 13 does not exclude the area of ​​the first opening 13a.

[0065] The cross-sectional area of ​​the first lid 13 is not constant. Specifically, the first lid 13 has a first step portion 13e. Portions of the first lid 13 having a constant cross-sectional area are connected by the first step portion 13e. More specifically, the cross-sectional area of ​​the portion of the first lid 13 located on the incident side of the first step portion 13e is larger than the cross-sectional area of ​​the portion of the first lid 13 located on the exit side of the first step portion 13e.

[0066] The cross-sectional area of ​​the first opening 13a in the first lid 13 is also not constant. Specifically, the first lid 13 has a second step 13f. Portions of the first opening 13a with constant cross-sectional areas are connected by the second step 13f. More specifically, the cross-sectional area of ​​the portion of the first opening 13a located on the incident side of the second step 13f is smaller than the cross-sectional area of ​​the portion of the first opening 13a located on the exit side of the first step 13e.

[0067] The first cover 13 has a portion that is located between the first polarizer holder 5 and the housing 12 in a direction perpendicular to the forward direction. Specifically, the first cover 13 has a portion that is in contact with both the side surface 5 d of the first base 5A and the first side surface 5 f of the first extension 5B of the first polarizer holder 5, and the inner wall 12 c of the housing 12. This makes it difficult for the optical axis of the optical isolator 1 to become misaligned.

[0068] In particular, it is preferable that a portion of the first cover 13 contacts both the side surface 5d of the first base 5A of the first polarizer holder 5 and the inner wall 12c of the housing 12. In this case, the housing 12, the first cover 13, and the first polarizer holder 5 can be suitably fixed by screw fastening. Note that the means for fixing the housing 12, the first cover 13, and the first polarizer holder 5 is not limited to screw fastening. For example, the housing 12, the first cover 13, and the first polarizer holder 5 may be fixed by an adhesive or the like.

[0069] The first cover 13 and the first polarizer holder 5 are fitted together. More specifically, the inner wall 13b and the second step 13f of the first cover 13 are fitted together with the side surface 5d and the outer peripheral portion 5e of the first base 5A of the first polarizer holder 5 and the first side surface 5f of the first extension 5B. This effectively stabilizes the positioning of the first polarizer holder 5. This prevents misalignment of the light transmission axis of the first polarizer 3. In addition, the accuracy of the optical axis of the optical isolator 1 can be improved.

[0070] The first cover 13 and the housing 12 are fitted together. More specifically, the side surface 13d and the first step portion 13e of the first cover 13 are fitted together with the inner wall 12c and the incident-side end surface 12e of the housing 12. This improves the vibration resistance and impact resistance of the optical isolator 1.

[0071] As shown in Fig. 7, the second cover 14 is configured similarly to the first cover 13. Specifically, the second cover 14 has a second opening 14a. More specifically, the second cover 14 has an inner wall 14b and a side surface 14d. The inner wall 14b faces the second opening 14a. The side surface 14d and the inner wall 14b face each other. The side surface 14d and the inner wall 14b extend in the forward direction.

[0072] The cross-sectional area of ​​the second lid 14 is not constant. Specifically, the second lid 14 has a third step portion 14e. Portions of the second lid 14 with constant cross-sectional areas are connected by the third step portion 14e. More specifically, the cross-sectional area of ​​the portion of the second lid 14 located on the emission side of the third step portion 14e is larger than the cross-sectional area of ​​the portion of the second lid 14 located on the incidence side of the third step portion 14e.

[0073] The cross-sectional area of ​​the second opening 14a in the second lid 14 is also not constant. Specifically, the second lid 14 has a fourth step 14f. Portions of the second opening 14a with constant cross-sectional areas are connected by the fourth step 14f. More specifically, the cross-sectional area of ​​the portion of the second opening 14a located closer to the exit side than the fourth step 14f is smaller than the cross-sectional area of ​​the portion of the second opening 14a located closer to the entrance side than the fourth step 14f.

[0074] The second cover 14 has a portion that is located between the second polarizer holder 6 and the housing 12 in a direction perpendicular to the forward direction. Specifically, the second cover 14 has a portion that is in contact with both the side surface 6d of the second base 6A and the third side surface 6f of the second extension 6B of the second polarizer holder 6, and the inner wall 12c of the housing 12. This makes it difficult for the optical axis of the optical isolator 1 to become misaligned.

[0075] In particular, it is preferable that a portion of the second cover 14 contacts both the side surface 6d of the second base 6A of the second polarizer holder 6 and the inner wall 12c of the housing 12. In this case, the housing 12, the second cover 14, and the second polarizer holder 6 can be suitably fixed by screw fastening. Note that the means for fixing the housing 12, the second cover 14, and the second polarizer holder 6 is not limited to screw fastening. For example, the housing 12, the second cover 14, and the second polarizer holder 6 may be fixed by an adhesive or the like.

[0076] The second cover 14 and the second polarizer holder 6 are fitted together. More specifically, the inner wall 14b and the fourth step 14f of the second cover 14 are fitted together with the side surface 6d and the outer peripheral portion 6e of the second base 6A of the second polarizer holder 6 and the third side surface 6f of the second extension 6B. This effectively stabilizes the positioning of the second polarizer holder 6. This prevents the optical transmission axis of the second polarizer 4 from shifting. In addition, the accuracy of the optical axis of the optical isolator 1 can be improved.

[0077] The second cover 14 and the housing 12 are fitted together. More specifically, the side surface 14d and the third step portion 14e of the second cover 14 are fitted together with the inner wall 12c and the end surface 12f on the output side of the housing 12. This improves the vibration resistance and impact resistance of the optical isolator 1.

[0078] 2 , the portion where the first cover 13 and the first polarizer holder 5 are fitted to each other and the portion where the second cover 14 and the second polarizer holder 6 are fitted to each other preferably have a circular shape when viewed from the forward direction. This makes it possible to easily adjust the angle of the linearly polarized light emitted to the outside even after the magnet 7, the first polarizer holder 5, and the second polarizer holder 6 are stored in the housing 12, the first cover 13, and the second cover 14. In addition, the magnet 7, the first polarizer holder 5, and the second polarizer holder 6 can be stored in a suitable manner.

[0079] The first cover 13, the housing 12, and the first polarizer holder 5 do not necessarily have to be fitted together. The second cover 14, the housing 12, and the second polarizer holder 6 do not necessarily have to be fitted together.

[0080] 3, a gap A is provided between the inner wall 12c of the housing 12 and the side surface 7d of the magnet 7. The distance between the inner wall 12c of the housing 12 and the side surface 7d of the magnet 7 is, for example, about 1 mm.

[0081] As in this embodiment, it is preferable to provide a gap A between the inner wall 12c of the housing 12 and the side surface 7d of the magnet 7. This makes it possible to adjust the angle of the linearly polarized light emitted to the outside even after the magnet 7, the first polarizer holder 5, and the second polarizer holder 6 are housed in the housing 12, the first cover 13, and the second cover 14 shown in Fig. 2. This makes it possible to increase the accuracy of the angle of the linearly polarized light emitted to the outside in the optical isolator 1.

[0082] It is preferable that the housing 12 be made of A5052, an Al-Mg alloy, or A6063, an Al-Mg-Si alloy. This allows the strength of the housing 12 to be suitably increased. It is even more preferable that the housing 12 be made of A6063. In this case, a rectangular tubular member can be easily obtained by extrusion molding. This makes it particularly easy to obtain the housing 12, and increases productivity. Furthermore, the strength of the housing 12 can be increased while the wall thickness can be reduced.

[0083] When A5052 is used as the material for the housing 12, the housing 12 may be formed by, for example, cutting. However, the material for the housing 12 is not limited to the above. For example, A6061, which is an Al-Mg-Si alloy, may also be suitably used as the material for the housing 12.

[0084] It is preferable that the thickness of the housing 12 is 1 mm or more and 3.5 mm or less. In this case, the optical isolator 1 can be made more compact. When A6063 is used as the material of the housing 12, the strength of the housing 12 can be increased even when the thickness of the housing 12 is within the above range. In particular, it is preferable that A6063 is used as the material of the housing 12 and that the thickness of the housing 12 is 1 mm or more and 3.5 mm or less. This makes it possible to more reliably make the optical isolator 1 more compact and more reliably make the optical isolator 1 less susceptible to breakage.

[0085] As shown in Figure 2, the pipe member 8 is provided inside the through-hole 7a of the magnet 7. The pipe member 8 has a first protrusion 8b and a second protrusion 8c. The first protrusion 8b is a portion that protrudes from the magnet 7 toward the incident side. The second protrusion 8c is a portion that protrudes from the magnet 7 toward the exit side.

[0086] In this embodiment, the first protrusion 8b of the pipe member 8 protrudes into the through-hole 5a in the first polarizer holder 5. The first protrusion 8b is in contact with the inner wall of the first polarizer holder 5 that faces the through-hole 5a. The first protrusion 8b is fixed to the inner wall with an adhesive.

[0087] On the other hand, the second protrusion 8c of the pipe member 8 protrudes into the through-hole 6a in the second polarizer holder 6. The second protrusion 8c is in contact with the inner wall of the second polarizer holder 6 that faces the through-hole 6a. The second protrusion 8c is fixed to the inner wall with an adhesive.

[0088] The arrangement of the pipe member 8 can be stabilized by the pipe member 8 being in contact with the inner wall of the first polarizer holder 5 facing the through hole 5a and the inner wall of the second polarizer holder 6 facing the through hole 6a. The Faraday element 2 is disposed inside the through hole 8a of the pipe member 8. Therefore, with the above configuration, the arrangement of the Faraday element 2 can also be stabilized. This can improve the accuracy of the optical axis in the optical isolator 1.

[0089] As in this embodiment, it is preferable that the first protrusion 8b of the pipe member 8 is fixed to the inner wall facing the through-hole 5a of the first polarizer holder 5. It is preferable that the second protrusion 8c is fixed to the inner wall facing the through-hole 6a of the second polarizer holder 6. This makes it possible to effectively stabilize the arrangement of the pipe member 8 and the Faraday element 2.

[0090] Alternatively, the pipe member 8 may be fixed with an adhesive to the inner wall of the magnet 7 facing the through-hole 7a. In this case as well, the arrangement of the pipe member 8 and the Faraday element 2 can be effectively stabilized.

[0091] In manufacturing the optical isolator 1, the directions of the light transmission axes of the first polarizer 3 and the second polarizer 4 can be adjusted before the pipe member 8 is fixed with an adhesive or the like. For example, before the first lid 13 and the second lid 14 are provided, the direction of the light transmission axis of the first polarizer 3 can be adjusted by rotating the first polarizer holder 5 around the pipe member 8 as a central axis. This makes it difficult for the first polarizer holder 5 to become misaligned during this adjustment. Similarly, when adjusting the direction of the light transmission axis of the second polarizer 4, the second polarizer holder 6 is also unlikely to become misaligned.

[0092] In this embodiment, the first polarizer holder 5 holds the first polarizer 3 with a space provided between them so that the first protrusion 8b of the pipe member 8 does not come into contact with the first polarizer 3. This makes it difficult for the first polarizer 3 to be scratched. Similarly, the second polarizer holder 6 holds the second polarizer 4 with a space provided between them so that the second protrusion 8c of the pipe member 8 does not come into contact with the second polarizer 4. This makes it difficult for the second polarizer 4 to be scratched.

[0093] The thickness of the pipe member 8 is preferably 0.1 mm or less, more preferably 0.08 mm or less, even more preferably 0.05 mm or less, and even more 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.

[0094] On the other hand, the thickness of the pipe member 8 is preferably 0.02 mm or more, and more preferably 0.03 mm or more, so that the pipe member 8 has sufficient strength.

[0095] However, the first fiber collimator 15 and the second fiber collimator 16 do not necessarily have to be provided, and this example will be shown as a modified example of the first embodiment.

[0096] (Modification) FIG. 8 is a schematic perspective view of an optical isolator according to a modification of the first embodiment.

[0097] This modification differs from the first embodiment in that the first fiber collimator and the second fiber collimator are not provided. Except for the above, the optical isolator 1A of this modification has the same configuration as the optical isolator 1 of the first embodiment. The optical isolator 1A can be used as a free-space optical isolator.

[0098] In this modification, as in the first embodiment, the area of ​​the first polarizer holder 5 is smaller than the area of ​​the magnet when viewed from the forward direction, and the area of ​​the second polarizer holder 6 is smaller than the area of ​​the magnet when viewed from the forward direction, which allows for further miniaturization of the optical isolator 1A.

[0099] Second Embodiment Fig. 9 is a schematic perspective view showing a cross section of an optical isolator according to a second embodiment, taken along the direction in which light passes. Fig. 10 is a schematic view of a magnet in the second embodiment.

[0100] 9, this embodiment differs from the first embodiment in that the magnet 27 has multiple magnet bodies. Specifically, the magnet 27 has a first magnet body 27A, a second magnet body 27B, and a third magnet body 27C. Except for the above, the optical isolator of the second embodiment has the same configuration as the optical isolator 1 of the first embodiment.

[0101] The first magnet body 27A, the second magnet body 27B, and the third magnet body 27C are stacked in the forward direction. More specifically, from the incident side, the first magnet body 27A, the second magnet body 27B, and the third magnet body 27C are stacked in this order. The first magnet body 27A, the second magnet body 27B, and the third magnet body 27C each have a through hole. The through holes of the first magnet body 27A, the second magnet body 27B, and the third magnet body 27C are connected to each other, thereby forming a through hole 27a of the magnet 27. A pipe member 8 is provided inside the through hole 27a. A Faraday element 2 is provided inside the pipe member 8.

[0102] 10, the first magnet body 27A is magnetized in a direction perpendicular to the forward direction so that the through-hole side is the north pole. The second magnet body 27B is magnetized in a direction parallel to the forward direction so that the first magnet body 27A side is the north pole. The third magnet body 27C is magnetized in a direction perpendicular to the forward direction so that the through-hole side is the south pole.

[0103] 9 , in this embodiment, as in the first embodiment, the area of ​​the first polarizer holder 5 is smaller than the area of ​​the magnet 27 when viewed from the forward direction, and the area of ​​the second polarizer holder 6 is smaller than the area of ​​the magnet 27 when viewed from the forward direction. This allows for further miniaturization of the optical isolator.

[0104] DESCRIPTION OF SYMBOLS 1, 1A... Optical isolator 2... Faraday element 3, 4... First and second polarizers 5, 6... First and second polarizer holders 5A, 6A... First and second bases 5B, 6B... First and second extensions 5a, 6a... Through hole 5d, 6d... Side surface 5e, 6e... Outer periphery 5f, 6f... First and third side surfaces 5g, 6g... Second and fourth side surfaces 7... Magnet 7a... Through hole 7d... Side surface 8... Pipe member 8a... Through hole 8b, 8c... First and second protrusions 12... Housing 12a, 12b... First and second openings 12c... Inner wall 12e, 12f... End surface 13, 14... First and second lids 13a, 14a... First and second openings 13b, 14b... inner wall 13d, 14d... side surface 13e, 14e... first and third step portions 13f, 14f... second and fourth step portions 15, 16... first and second fiber collimators 27... magnet 27a... through hole 27A to 27C... first to third magnet bodies

Claims

1. An optical isolator comprising: a magnet having a through hole through which light enters in the forward direction and passes inside; a Faraday element that transmits the light and is located inside the through hole of the magnet; a first polarizer arranged on the incident side of the magnet, where the side into which the light enters in the forward direction is the incident side and the side from which the light exits is the exit side; a second polarizer arranged on the exit side of the magnet; a first polarizer holder that houses the first polarizer; and a second polarizer holder that houses the second polarizer, wherein when viewed from the forward direction, the area of ​​the first polarizer holder is smaller than the area of ​​the magnet, and when viewed from the forward direction, the area of ​​the second polarizer holder is smaller than the area of ​​the magnet.

2. The optical isolator of claim 1, further comprising: a housing having an inner wall and housing the magnet and the Faraday element therein; a first lid that, together with the housing, houses the first polarizer holder; and a second lid that, together with the housing, houses the second polarizer holder, wherein the first polarizer holder and the second polarizer holder each have a side that extends in the forward direction and faces the inner wall of the housing; the first lid has a portion that contacts both the side of the first polarizer holder and the inner wall of the housing; and the second lid has a portion that contacts both the side of the second polarizer holder and the inner wall of the housing.

3. The optical isolator according to claim 2, further comprising: a first fiber collimator connected to the first lid; and a second fiber collimator connected to the second lid.

4. An optical isolator as described in claim 1, characterized in that the first polarizer holder has a first base and a first extension extending from the first base in the forward direction and positioned inside the outer periphery of the first base when viewed from the forward direction, the second polarizer holder has a second base and a second extension extending from the second base in the forward direction and positioned inside the outer periphery of the second base when viewed from the forward direction, and the first base and the second base are in contact with the magnet.

5. The optical isolator of claim 4, further comprising: a housing having an inner wall and housing the magnet and the Faraday element therein; a first lid that, together with the housing, houses the first polarizer holder; and a second lid that, together with the housing, houses the second polarizer holder; wherein the first base of the first polarizer holder and the second base of the second polarizer holder each have a side that extends in the forward direction and faces the inner wall of the housing; the first lid has a portion in contact with both the side of the first base and the inner wall of the housing; and the second lid has a portion in contact with both the side of the second base and the inner wall of the housing.

6. The optical isolator according to claim 5, further comprising: a first fiber collimator connected to said first lid; and a second fiber collimator connected to said second lid.

7. The optical isolator of claim 1, further comprising a pipe member disposed inside the through hole of the magnet, the Faraday element being disposed inside the pipe member, the pipe member having a first protrusion protruding from the magnet toward the incident side and a second protrusion protruding from the magnet toward the output side, the first polarizer holder having a through hole through which the light passes, the second polarizer holder having a through hole through which the light passes, the first protrusion being in contact with the inner wall of the first polarizer holder facing the through hole, and the second protrusion being in contact with the inner wall of the second polarizer holder facing the through hole.

8. The optical isolator described in claim 7, characterized in that the first polarizer holder holds the first polarizer so that the first protrusion of the pipe member does not come into contact with the first polarizer, and the second polarizer holder holds the second polarizer so that the second protrusion of the pipe member does not come into contact with the second polarizer.

9. The optical isolator described in claim 1, characterized in that the magnet has 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 from the incident side, 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 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.

10. The optical isolator of claim 1, characterized in that, when a cross section taken along a direction perpendicular to the forward direction is taken as a transverse cross section, the magnet has a rectangular outer shape in the transverse cross section, and the first polarizer holder and the second polarizer holder have circular outer shapes in the transverse cross sections.

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