Optical coupling section and optical switch

Abstract

The purpose of the present disclosure is to provide an optical coupling unit and an optical switch with which it is possible to achieve stable optical characteristics with respect to external factors, with low power consumption and in a more economical manner. In order to achieve the above purpose, the present disclosure provides an optical coupling unit that couples single-core optical fibers disposed in two ferrules using a sleeve, wherein a first ferrule out of the two ferrules comprises a plurality of optical fibers which are disposed in a bundle on the same circumference about a ferrule central axis in the fiber hole, at least one of the two ferrules is rotatable about the ferrule central axis, and the end parts of the ferrules abutting against each other have a convex spherical shape having a center point on the ferrule central axis.

Description

[Technical Field]

[0001] The present invention relates to an optical coupling unit used mainly for switching the path of an optical line using a single-mode optical fiber in an optical fiber network, and an optical switch using the same. [Background technology]

[0002] Various methods have been proposed for all-optical switches that switch the path of light while keeping it as it is, as shown in Non-Patent Document 1. Among these, optical fiber mechanical optical switches, which use a robot arm or motor to control the butting of optical fibers or optical connectors, are inferior to other methods in that they have slow switching speeds, but they have many advantages over other methods, such as low loss, low wavelength dependency, multi-port capability, and a self-holding function that maintains the switched state even when power is lost. Typical structures include a method that translates a stage using an optical fiber V-groove, a method that translates or changes the angle of a mirror or prism to selectively couple multiple optical fibers output from an input optical fiber, and a method that uses a robot arm to connect a jumper cable with an optical connector.

[0003] Also, a method has been proposed in which a multicore fiber is used as the optical path to be switched. For example, by combining a multicore fiber with a three-dimensional MEMS optical switch (see, for example, Non-Patent Document 2), it becomes possible to switch multiple paths simultaneously. Also, by performing switching by rotating a cylindrical ferrule into which a multicore fiber is inserted (see, for example, Patent Document 1), optical components such as lenses and prisms are not required, and the configuration can be simplified. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2-82212 [Non-patent literature]

[0005] [Non-Patent Document 1] M. Stepanovsky, “A Comparative Review of MEMS-Based Optical Cross-Connects for All-Optical Networks From the Past to the Present Day,” IEEE Communications Surveys & Tutorials,vоl.21,nо.3,pp.2928-2946,2019. [Non-patent document 2] K. Hiruma, T. Sugawara, K. Tanaka, E. Nomoto, and Y. Lee, “Proposal of High-capacity and High-reliability Optical Switch Equipmet with Multi-core Fibers,” 18th OptoElectronics and Communications Conference held jointly with 2013 International Conference on Photonics in Switching(OECC / PS), ThT1-2, 2013. [Non-patent document 3] B. Jian, “The Non-Contact Connector:A New Category of Optical Fiber Connector,” 2015 Optical Fiber Communications Conference and Exhibition (OFC), W2A.1, 2015. [Non-patent document 4] Hajime Arao, Sho Yagabe, Fumiya Uehara, Dai Sasaki, and Takayuki Shimazu, "FlexAirConnecT: A Dust-Resistant Optical Multi-Fiber Connector Featuring Low Loss and Low Mating Force," SEI Technical Review, No. 193, pp. 26-31, July 2018. [Non-Patent Document 5] Chisato Fukai, Yoshiteru Abe, and Kazunori Katayama, “Multi-Fiber Cylindrical Ferrule for Remote Rotary Optical Fiber Switching,” 2022 Optical Fiber Communications Conference and Exhibition(OFC),Th2A.11,2022. Summary of the Invention [Problem to be solved by the invention]

[0006] However, the prior art described in the aforementioned Non-Patent Document 1 has problems in that it is difficult to further reduce power consumption, miniaturize, and improve cost efficiency. Specifically, the method of translating the aforementioned optical fiber V-groove stage or prism generally uses a motor as a drive source. However, because the mechanism linearly moves a heavy object such as a stage, the motor requires a certain amount of torque, and power consumption is required to obtain an appropriate output to maintain the required torque. Furthermore, optical axis alignment using a single-mode optical fiber requires an accuracy of approximately 1 μm or less, so a mechanism (typically a ball screw) that converts the motor's rotational motion into linear motion must convert it into linear motion in sub-μm steps. Considering that the optical fiber pitch of a typical output optical fiber array is approximately 125 μm in cladding outer diameter or 250 μm in coating outer diameter, the larger the output optical fiber array, the longer the actual motor drive time must be, resulting in increased power consumption. For this reason, such optical fiber-based mechanical optical switches generally require a power of several hundred mW or more. Furthermore, the robot arm method using an optical connector has the problem that the robot arm itself, which controls the insertion and removal of the optical connector or ferrule, requires a large amount of power of several tens of watts or more.

[0007] Furthermore, in the optical path switching using a multicore fiber described in Non-Patent Document 2, the process of manufacturing the optical switch requires a collimating mechanism for coupling to the optical fiber array on the output side and a vibration isolation mechanism for obtaining stable optical characteristics against external factors such as vibration, which makes the assembly process complicated.

[0008] In the optical path switching using a cylindrical ferrule into which a multicore fiber is inserted, as described in Patent Document 1, the ferrule is tightly inserted into a sleeve to align the central axis, and there is a problem that a large amount of energy and power is required to drive the rotation due to the friction between the ferrule and the sleeve. Furthermore, to prevent the opposing fiber end faces from being scratched as the ferrule rotates, which would deteriorate optical characteristics such as connection loss, a mechanism is required to separate the ferrule end faces every time the ferrule rotates, which poses a problem of requiring extra energy to drive the rotation.

[0009] On the other hand, there is also a method to prevent scratches on the fiber end face due to contact by providing a gap in advance in the cylindrical ferrule into which the optical fiber is inserted so that the fibers do not come into contact (for example, Non-Patent Document 3). However, in order to suppress signal degradation due to reflection caused by the air layer that is created between the fiber end faces due to the gap, a special coating to prevent reflection is required, which poses the problem of increased costs.

[0010] Another method for preventing reflection is to polish the ferrule end face at an angle (see, for example, Non-Patent Document 4). However, with a ferrule polished at an angle, there are problems such as interference between the ferrule end faces when switching by rotation, or the need for a large gap resulting in high connection loss.

[0011] In addition, in the optical path switching using a cylindrical ferrule into which multiple fibers are inserted, as described in Non-Patent Document 5, the ferrule is polished to a spherical surface, the fiber end faces are polished at an angle, and the center of the ferrule is polished flat, minimizing gaps on the fiber end faces. This makes it possible to prevent scratches on the fiber end faces due to contact, while also preventing reflection and minimizing connection loss due to gaps. However, there is a problem in the manufacturing process of the ferrule mold, where it is difficult to control the fiber hole position with high precision, resulting in excessive axial misalignment loss due to misalignment of the fiber hole. Furthermore, there is a problem in that it is difficult to bring the fiber hole close to the center of the ferrule end face, and the fiber hole is far from the center of the ferrule end face, resulting in large rotational angle misalignment loss during switching.

[0012] In order to solve the above problems, an object of the present invention is to provide an optical coupling section and an optical switch that can realize stable optical characteristics against external factors with low power consumption and more economically. [Means for solving the problem]

[0013] The optical coupling unit according to the present disclosure includes: An optical coupling unit that couples single-core optical fibers arranged in two ferrules using a sleeve, a first ferrule of the two ferrules has a plurality of optical fibers arranged in a bundle shape in a fiber hole on the same circumference centered on the central axis of the ferrule; At least one of the two ferrules is rotatable around the ferrule central axis, The ends of the two ferrules that are butted together have a convex spherical shape with a center point on the central axis of the ferrules.

[0014] The optical coupling unit and optical switch of the present disclosure may include two ferrules in which single-core single-mode optical fibers are arranged parallel to and at the same distance from the central axis of the ferrules. In this case, the butted ends of the two ferrules have convex spherical shapes, and the tips of the ends of the two ferrules are butted together so that their central axes coincide, and one of the ferrules is rotated.

[0015] More specifically, the optical coupling unit according to the present disclosure includes: a first ferrule having a convex spherical end face, in which a plurality of single-core single-mode optical fibers are arranged in a bundle shape so that the core centers of the single-core single-mode optical fibers are aligned on the same circumference in the center of the ferrule cross section; a second ferrule having a convex spherical end face, in which the core centers of one or more single-core single-mode optical fibers are arranged on a circumference having the same diameter as the circumference on which the core centers of the single-mode optical fibers in the first ferrule are arranged, from the center in a cross section of the ferrule; and a cylindrical sleeve having a hollow portion into which the first ferrule and the second ferrule are inserted so that the central axes of the first ferrule and the second ferrule are aligned, and a predetermined gap is provided between the outer diameter of each of the first ferrule and the second ferrule and the inner diameter of the hollow portion so that the first ferrule and the second ferrule can rotate.

[0016] In this invention, the ends of two ferrules, each with a single-mode optical fiber arranged parallel to the ferrule central axis and at the same distance from the ferrule central axis, have a convex spherical shape, and by butting the tips of the two ferrule ends together so that their central axes coincide and rotating them around the central axis of one of the ferrules, the end faces of the opposing optical fibers do not come into contact with each other, preventing deterioration of optical characteristics such as connection loss due to scratches on the end faces of the optical fibers caused by contact.In addition, because the end faces of the opposing optical fibers are non-parallel to each other, the amount of light reflection can be reduced, eliminating the need for a reflective coating and making it possible to provide a more economical optical coupling unit and optical switch.

[0017] Furthermore, the present invention uses an axially rotatable mechanism on either the input or output side of the optical coupling section that performs optical switching, thereby minimizing the energy required by the actuator, i.e., torque output, and enabling low power consumption. Furthermore, the amount of optical axis misalignment in directions other than the axial rotation of the input ferrule is compensated for by the sleeve in the optical coupling section, enabling low loss. In addition, the present invention does not require a collimator or special vibration isolation mechanism, and instead is composed of commonly used optical connection components such as ferrules and sleeves, making it compact and economical.

[0018] Here, a dummy fiber may be arranged inside the plurality of optical fibers arranged in a bundle on the same circumference centered on the central axis of the ferrule, and the end face of the dummy fiber may form part of the convex spherical shape.

[0019] Furthermore, the return loss of the convex spherical shape may be equal to or greater than a predetermined value. For example, in the optical coupling unit according to the present disclosure, the angle between a cross section perpendicular to the central axis of the ferrule and the end face of the single-mode optical fiber may be equal to or greater than 4.5 degrees in each of the first and second ferrules. This allows the return loss of the convex spherical shape to be equal to or greater than 40 dB.

[0020] In addition, the excess loss T due to the gap between the end faces of the two ferrules is G For example, in the optical coupling unit according to the present disclosure, the gap between the end face of the single-mode optical fiber of the first ferrule and the end face of the single-mode optical fiber of the second ferrule, the optical axis of which is aligned with that of the single-mode optical fiber, may be 22 μm or less. This reduces excess loss T due to the gap. G can be suppressed to 0.1 dB or less.

[0021] In addition, the excess loss T due to the rotation angle misalignment of the two ferrules RFor example, in the optical coupling unit according to the present disclosure, the distance from the central axis of the ferrule to the core center of each of the single-mode optical fibers in the first ferrule and the second ferrule may be 250 μm or less. This reduces the excess loss T due to rotation angle misalignment. R can be reduced to 0.1 dB or less.

[0022] The return loss in the convex spherical shape and the excess loss T due to the gap between the butted end faces of the two ferrules G For example, in the optical coupling unit according to the present disclosure, the plurality of optical fibers may be single-mode optical fibers, and the radius of curvature of the convex spherical shape in each of the first ferrule and the second ferrule may be 0.7 mm or more and 3.2 mm or less.

[0023] Specifically, the optical switch according to the present disclosure has: the optical coupling portion; and a rotation mechanism that rotates one of the two ferrules of the optical coupling portion around the central axis of the ferrule.

[0024] For example, the optical switch according to the present disclosure may include: an actuator that rotates the rotation mechanism at a constant angular step and stops the rotation mechanism at an arbitrary angular step; a bearing constituting the rotation mechanism; may further comprise:

[0025] The above inventions can be combined as much as possible. [Effects of the Invention]

[0026] According to the present disclosure, it is possible to provide an optical coupling section and an optical switch that can achieve stable optical characteristics against external factors with low power consumption and more economically. [Brief explanation of the drawings]

[0027] [Figure 1]An example of how the present invention is used will be described below. [Figure 2] 1 shows an example of a schematic configuration of the present invention. [Figure 3] FIG. 2 is a front view of the end of the output ferrule. [Figure 4] FIG. 2 is a front view of the end of the input ferrule. [Figure 5] FIG. 2 is a view showing the optical coupling portion in a plane along the longitudinal direction. [Figure 6] An example of the relationship between the excess loss and the clearance between the outer diameter of the ferrule and the inner diameter of the sleeve is shown. [Figure 7] 1 shows the vicinity of the end of the ferrule of the optical coupling portion of the present invention. [Figure 8] 1 shows an example of the relationship between the angle formed by the cross section perpendicular to the central axis of the ferrule and the end face of the single-mode optical fiber and the return loss. [Figure 9] 1 shows an example of the relationship between excess loss and the gap in an optical fiber. [Figure 10] 1 shows an example of the relationship between the radius of curvature of a convex spherical ferrule end face and the angle formed between a cross section perpendicular to the central axis and the end face of a single-mode optical fiber. [Figure 11] 1 shows an example of the relationship between the radius of curvature of the convex spherical ferrule end face and the distance from the tip of the ferrule to the end face of a single-mode optical fiber. [Figure 12] An example of the relationship between the core arrangement radius and excess loss due to rotation angle deviation is shown below. [Figure 13] 1 shows the coupling form of the optical coupling portion of the present invention according to the first embodiment. [Figure 14] 10 shows the coupling form of the optical coupling portion of the present invention according to the second embodiment. [Figure 15] 10 shows a cross section of an input-side ferrule of an optical coupling unit according to a second embodiment of the present invention. [Figure 16] 10 shows a cross section of an input-side ferrule of an optical coupling unit according to a second embodiment of the present invention. [Figure 17] 3 shows a side view of the output flange of the present invention according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings indicate the same components.

[0029] (Embodiment 1) FIG. 1 is a diagram illustrating an example of an embodiment of the present invention. This embodiment describes a configuration in which light is input through an input-side optical fiber S01 and output through an output-side optical fiber S04, but the direction of light may be reversed. The present invention enables the input-side optical fiber S01 connected to a front-stage optical switch component S00 to be switched to a specific port of an inter-optical switch optical fiber S02 in the front-stage optical switch component S00, and the port of the inter-optical switch optical fiber S02 to a desired output-side optical fiber S04 in the rear-stage optical switch component S03. The present invention relates to optical switches corresponding to the front-stage optical switch component S00 and the rear-stage optical switch component S03. Hereinafter, the front-stage optical switch component S00 will be abbreviated as the optical switch S00, and the rear-stage optical switch component S03 will be abbreviated as the optical switch S03. The optical switch S00 and the optical switch S03 are in a left-right mirror image relationship and have the same configuration, so the detailed configuration will be described below using the optical switch S00.

[0030] FIG. 2 is a block diagram showing the configuration according to the embodiment of the present invention. The optical coupling unit S8 of the optical switch S00 according to this embodiment has: a first ferrule in which the core centers of a plurality of single-mode optical fibers are arranged on the same circumference from the center in a cross section of the ferrule; a second ferrule in which the core centers of one or more single-mode optical fibers are arranged on a circumference having the same diameter from the center in a cross section of the ferrule as the circumference on which the core centers of the single-mode optical fibers in the first ferrule are arranged; and a cylindrical sleeve S17 having a hollow portion into which the first ferrule and the second ferrule are inserted so that the central axes of the first ferrule and the second ferrule coincide, with a predetermined gap provided between the outer diameter of each of the first ferrule and the second ferrule and the inner diameter of the hollow portion so that the first ferrule and the second ferrule can rotate.

[0031] 2, the input optical fiber S1 is configured to consist of one single-core single-mode optical fiber, and the input ferrule S6 is configured to be the second ferrule. The output optical fiber S9 is configured to consist of multiple single-core single-mode optical fibers, and the output ferrule S7 is configured to be the first ferrule. The input optical fiber S1 corresponds to the input optical fiber S01 in FIG. 1, and the output optical fiber S9 corresponds to the inter-optical-switch optical fiber S02 in FIG. 1.

[0032] The optical switch S00 shown in Fig. 2 has an optical coupling unit S8 composed of an input ferrule S6 into which an input optical fiber S1 is inserted, and an output ferrule S7 into which an output optical fiber S9 is inserted. The input optical fiber S1 is fixed using an adhesive or the like at a predetermined position in a fiber hole provided in the input ferrule S6. The output optical fiber S9 is fixed using an adhesive or the like at a predetermined position in a fiber hole provided in the output ferrule S7.

[0033] When light is incident from the input optical fiber S1, the optical switch S00 can connect the input optical fiber S1 to any one of the output optical fibers S9 by fixing the output ferrule S7 and rotating the input ferrule S6, and output the incident light from one of the output optical fibers S9. This optical switch S00 can be used as a 1xN relay-type optical switch. Conversely, light can also be incident from the output optical fiber S9. For example, light can be incident on multiple single-mode optical fibers among the output optical fibers S9, and then, by fixing the output ferrule S7 and rotating the input ferrule S6, any one of the output optical fibers S9 can be connected to the input optical fiber S1, and only one light selected from the multiple incident light beams can be output from the input optical fiber S1. Furthermore, as shown in Figure 1, an NxN optical switch can be constructed by combining multiple optical switches. Here, the output-side ferrule S7 is fixed and the input-side ferrule S6 is rotated, but any configuration is possible as long as either the input-side ferrule S6 or the output-side ferrule S7 is fixed and the opposing fiber can be switched by rotating the opposing side, so the input-side ferrule S6 may be fixed and the output-side ferrule S7 may be rotated. Also, although one input-side ferrule S6 is used, it is also possible to arrange multiple optical fibers.

[0034] The following describes an optical switch S00 in which the output ferrule S7 is fixed and the input ferrule S6 is rotated. The output ferrule S7 is fixed by a rotation stop mechanism (not shown) to prevent axial rotation. The actuator S3 rotates the input ferrule S6 by any angle in response to a signal from a control circuit S4. The input ferrule S6 rotates when the output of the actuator S3 is transmitted via a rotation mechanism S5. The input ferrule S6 also has a certain excess length S2 to allow for twisting of the input optical fiber S1. The optical coupling section S8 is configured to suppress axial misalignment of the ferrule central axis using an axial misalignment adjustment mechanism (not shown) to avoid excessive loss due to axial misalignment.

[0035] The optical coupling unit S8 of the optical switch S00 according to this embodiment has: The input side ferrule S6 and the output side ferrule S7 are respectively A convex spherical end portion is provided in the direction of the central axis, The tip of the input ferrule S6 and the tip of the output ferrule S7 are butted against each other.

[0036] FIG. 3 is a schematic diagram showing the front end of an output ferrule S7 according to an embodiment of the present invention. As shown in the figure, multiple optical fibers are bundled together and arranged inside a fiber hole S11 with a diameter S21 provided in the center of the output ferrule S7. The core centers of the output optical fibers S9 are arranged on the circumference of a circle with a core arrangement radius Rcore relative to the center of the output ferrule S7. While FIG. 3 illustrates an example in which a dummy fiber S10 is arranged at the center and a total of six output optical fibers S9 are arranged, this is not limiting, as long as the core centers of the multiple output optical fibers S9 are arranged on the circumference of a circle with a core arrangement radius Rcore. The dummy fiber S10 may be any optical fiber having the same strength and outer diameter as the output optical fiber S9, and may be a fiber without a core, i.e., a fiber that does not transmit light.

[0037] FIG. 4 is a schematic diagram showing the front end of an input ferrule S6 according to an embodiment of the present invention. As shown in FIG. 4, a plurality of optical fibers are bundled and arranged inside a fiber hole S11 provided in the center of the input ferrule S6, and the core center of the input optical fiber S1 is arranged on the circumference of a circle with a core arrangement radius Rcore relative to the center of the input ferrule S6. While FIG. 4 illustrates an example in which one input optical fiber S1 is arranged on the y-axis (x=0) and arranged at the center of the input ferrule S6 together with six other dummy fibers S10, the arrangement is not limited thereto as long as the core center of the input optical fiber S1 is arranged on the circumference of a circle with a core arrangement radius Rcore. For example, one or more fiber holes capable of accommodating one optical fiber may be provided on the circumference of a circle with a core arrangement radius Rcore relative to the central axis of the input ferrule S6, and the input optical fiber S1 may be arranged in one of the fiber holes. The dummy fiber S10 may be any optical fiber having the same strength and outer diameter as the input-side optical fiber S1, and may be a fiber without a core, that is, a fiber that does not transmit light.

[0038] The outer diameter of the dummy fiber S10 arranged at the center of the output ferrule S7 and the input ferrule S6 may be different from the outer diameter of the output optical fiber S9 and the input optical fiber S1. For example, by making the outer diameter of the dummy fiber S10 arranged at the center larger than 125 μm, it becomes possible to arrange six or more output optical fibers S9 on the circumference of a circle with a core arrangement radius Rcore.

[0039] However, it is important to minimize the transmission loss of the optical coupling portion S8, and it is desirable that each core of the output optical fiber S9 has the same optical characteristics as the core of the input optical fiber S1 in that it has a mode field diameter that is approximately the same as that of the core of the input optical fiber S1. It is also important to minimize excess loss due to axial misalignment, and it is desirable that the ferrule outer diameter S15 of the output ferrule S7 is approximately the same as the ferrule outer diameter S15 of the input ferrule S6.

[0040] In this embodiment, the input side ferrule S6 and the output side ferrule S7 are made of zirconia, and the input side optical fiber S1 and the output side optical fiber S9 are made of quartz glass, but this is not limited to this and any optical fiber capable of communicating signal light in the communication wavelength band may be used.

[0041] 5 is a schematic diagram of an optical coupling unit S8 according to an embodiment of the present invention, shown on a longitudinal surface. An input ferrule S6, into which an input optical fiber S1 is inserted, and an output ferrule S7, into which an output optical fiber S9 is inserted, are aligned in a cylindrical sleeve S17 having a hollow portion with an inner diameter S16 that is slightly larger than the outer diameter S15 of the ferrules, by about a sub-micron. A slight clearance C, on the order of sub-micron, is provided between the input ferrule S6 and the output ferrule S7 to control axial misalignment within a certain tolerance range and to prevent interference with the axial rotation of the input ferrule S6.

[0042] Figure 6 shows the excess loss T for the clearance C between the ferrule outer diameter S15 and the sleeve inner diameter S16 of the input ferrule S6 and the output ferrule S7. C In optical coupling between optical fibers, the misalignment of the fiber cores is a factor in excess loss. Since an increase in excess loss limits the overall length of the optical path, it is necessary to reduce the misalignment of the fiber cores. Here, the clearance C between the ferrule outer diameter S15 and the sleeve inner diameter S16 corresponds to the misalignment of the fiber cores, so the clearance C (unit: μm) between the ferrule outer diameter S15 and the sleeve inner diameter S16 and the excess loss T C The relationship (unit: dB) can be expressed by Equation 1.

number

[0043] 7 is a schematic diagram showing in more detail the vicinity of the end of the ferrule of the optical coupling unit S8 according to the embodiment of the present invention. The end of the input side ferrule S6 and the output side ferrule S7 are aligned along the ferrule central axis A. C The output ferrule S7 of this embodiment has a convex spherical shape with a center point on the top. Specifically, as shown in FIG. 3, the output ferrule S7 has a dummy fiber S10 arranged at the center of the fiber hole S11, and the output optical fiber S9 arranged around the dummy fiber S10. The end faces of the output optical fiber S9 and dummy fiber S10 arranged in the output ferrule S7 form the convex spherical shape of the end of the output ferrule S7. As shown in FIG. 4, the output ferrule S6 of this embodiment has a dummy fiber S10 arranged at the center of the fiber hole S11, and the input optical fiber S1 and dummy fiber S10 arranged around the dummy fiber S10. The end faces of the input optical fiber S1 and dummy fiber S10 arranged in the output ferrule S6 form the convex spherical shape of the end of the input ferrule S6.

[0044] The dummy fibers S10 disposed in the input ferrule S6 and the output ferrule S7 are butted against each other at their respective ends. As described above, the input fiber S1 and the output fiber S9 are aligned along the ferrule central axis A in the cross section of the ferrules. CThe input fiber S1 and output fiber S9 are arranged at a position of the core arrangement radius Rcore from the center axis A of the ferrule to prevent the end faces of the input fiber S1 and output fiber S9 from coming into contact and being damaged when switching by rotation. C The angle θ between the cross section perpendicular to the ferrule and the end face of the single-core optical fiber is controlled. For example, a convex spherical shape can be fabricated by using polishing techniques used in the fabrication of general optical connectors. In FIG. 7, the end faces of the dummy fibers S10 arranged along the central axes of the ferrules are butted together. However, this is not limiting as long as the end faces of the input fiber S1 and the output fiber S9 do not come into contact with each other. For example, when polishing the ferrule end faces, the amount of fiber retraction may be increased to prevent the end faces of the input fiber S1 and the output fiber S9 from coming into contact with each other when the input ferrule S6 and the output ferrule S7 are butted together.

[0045] Fig. 8 is a diagram showing an example of the relationship between the angle θ formed between a cross section perpendicular to the ferrule central axis and the end face of a single-mode optical fiber, and the return loss R. In the optical coupling section S8, if there is an area with a different refractive index between the end face of the input optical fiber S1 and the end face of the output optical fiber S9, reflection will cause deterioration of the signal characteristics. In the configuration of the present invention shown in Fig. 7, there is a gap G between the end face of the input optical fiber S1 and the end face of the output optical fiber S9, and since silica glass and air have different refractive indices, some measure must be taken to reduce reflection. In the present invention, reflection is reduced by controlling the angle θ. Ferrule central axis A C The relationship between the angle θ (unit: degrees) formed by the cross section perpendicular to the surface and the end face of the single-mode optical fiber and the return loss R (unit: dB) can be expressed by Equation 2.

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[0046] Figure 9 shows the excess loss T G In the optical coupling between the input optical fiber S1 and the output optical fiber S9, if a gap G exists between the end face of the input optical fiber S1 and the end face of the output optical fiber S9, the distribution of the output light from the input optical fiber S1 will be broadened, and the coupling efficiency with the core of the output optical fiber S9 will decrease, which will cause excess loss. The relationship between the gap G (unit: μm) and excess loss T G The relationship (unit: dB) can be expressed by Equation 4.

number

[0047] Figure 10 shows the relationship between the radius of curvature Rcur of the convex spherical ferrule end face and the ferrule central axis A C 1 is a diagram showing an example of the relationship between the radius of curvature Rcur (unit: mm) of the convex spherical ferrule end face and the angle θ formed by the cross section perpendicular to the ferrule end face and the central axis A of the ferrule. C The relationship between the angle θ (unit: degrees) formed by the cross section perpendicular to the surface and the end face of the single mode optical fiber can be expressed by Equation 5 using the core arrangement radius Rcore (unit: μm).

number

[0048] 11 is a diagram showing an example of the relationship between the radius of curvature Rcur of the convex spherical ferrule end face and the distance D from the ferrule tip to the end face of the single-mode optical fiber. The distance D from the ferrule tip to the end face of the single-mode optical fiber corresponds to half of the gap G between the end face of the input optical fiber S1 and the end face of the output optical fiber S9, and the radius of curvature Rcur (unit: mm) of the convex spherical ferrule end face and the ferrule central axis A C This can be expressed by Equation 6 using the angle θ (unit: degrees) formed by the cross section perpendicular to the plane and the end face of the single mode optical fiber.

number

[0049] Figure 11 shows the relationship between the radius of curvature Rcur and the distance D from the ferrule tip to the fiber end face when the core arrangement radius Rcore is 125, 150, 200, and 250 μm. For example, when the core arrangement radius Rcore is 125 μm, 150 μm, 200 μm, and 250 μm, by adjusting the radius of curvature Rcur to 0.7 mm or more, 1.0 mm or more, 1.8 mm or more, and 2.8 mm or more, respectively, the distance D from the ferrule tip to the fiber end face becomes 11 μm or less, that is, the gap G becomes 22 μm or less, and the excess loss T due to the gap as shown in Figure 9 is G The outer diameter of a typical single-mode optical fiber is 125 μm, and when the single-mode optical fiber is arranged in a bundle as shown in FIG. 3, by polishing the ferrule end face so that the radius of curvature Rcur is 0.7 mm to 1.5 mm, the return loss R of 40 dB or more and the excess loss T of 0.1 dB or less can be suppressed. G This can be achieved.

[0050] The optical coupling portion S8 of the optical switch S00 according to this embodiment has the following characteristics: In each of the input side ferrule S6 and the output side ferrule S7, The radius of curvature of the convex spherical shape may be 0.7 mm or more and 3.2 mm or less.

[0051] Next, the requirements for the actuator S3 in FIG. 2, the output-side ferrule S7 described in FIG. 3, and the input-side ferrule S6 described in FIG. 4 will be described. The actuator S3 is a drive mechanism that rotates at any angle step in response to a pulse signal from the control circuit S4 and has a constant static torque for each angle step, and a stepping motor, for example, is used. Note that other methods may also be used for the actuator S3 as long as the drive mechanism rotates at any angle step in response to a pulse signal from the control circuit S4 and has a constant static torque for each angle step. The rotation speed and rotation angle are determined by the period and number of pulses of the pulse signal from the control circuit S4, and the angle step and static torque may be adjusted via a reduction gear. Note that, as mentioned above, the input-side ferrule S6 in the optical coupling unit S8 has a ferrule central axis A. C Since the input ferrule S6 is designed to rotate around the center of gravity, the static torque required to maintain the rotation angle of the input ferrule S6 is applied by the actuator S3.

[0052] This provides a self-holding function that does not require power when stationary after switching, and it is possible to minimize the driving energy required when switching optical paths, making it possible to provide a low-power optical switch.

[0053] Here, in a stepping motor, if the number of angle steps at which the angle position is maintained when power supply is stopped is defined as the number of static angle steps, the number of static angle steps is a natural number multiple of the number of cores having the same core arrangement radius Rcore in the output-side optical fiber S9.

[0054] In addition, the excess loss due to the rotation angle deviation at the optical coupling section S8 is calculated as T R (unit: dB), the rotation angle deviation related to the static angle accuracy of the stepping motor is Φ (unit: °), and the core arrangement radius Rcore (unit: μm), the relationship between these can be expressed by Equation 7.

number

[0055] 13 is a schematic diagram showing an example of the coupling configuration of the optical coupling unit S8 according to the first embodiment of the present invention. The output ferrule S7 is attached to a notched output flange S19, which is attached to a fixture S27 with fixing screws S25, thereby fixing the axial direction and the axial rotation direction. The input ferrule S6 is attached to a rotating flange S29, which is provided with a bearing S26, which is also attached to the fixture S27 with fixing screws S25, thereby fixing the axial direction. A sleeve S17 is built into the fixture S27, and the input ferrule S6 and the output ferrule S7 are inserted into the sleeve S17 to align the ferrule central axes. The output ferrule S7 is fixed, and the input ferrule S6 rotates within the sleeve S17 by the rotation mechanism S5 of the bearing S26, around the center of the ferrule cylinder. As a result, the core of the input optical fiber S1 inserted into the input ferrule S6 rotates, switching the core of the output optical fiber S9 facing the input optical fiber S1. While zirconia, for example, is used for the bearing S26, other materials may also be used as long as they can be manufactured with high dimensional accuracy. Furthermore, by using a low-rigidity hollow metal frame for the fixing jig S27, for example, it is possible to reduce axial misalignment of the input ferrule S6 due to axial wobble during rotation of the actuator S3.

[0056] A side view of the notched output flange S19 attached to the output ferrule S7 is shown in Fig. 17. As shown in Fig. 17, the capillary S23 is aligned with the fiber hole S30 of the output ferrule S7 attached to the output flange S19 and the ferrule central axis A. CBy arranging the capillary S23 at a position where the diameters of the capillary S23 and the fiber hole S30 of the output ferrule S7 are aligned, tapering the capillary S23 in the longitudinal direction and approximating the diameter of its tip to the diameter of the fiber hole S30 of the output ferrule S7, it is possible to prevent the output optical fiber S9 from getting caught on a step when inserting it into the output ferrule S7, and further to prevent the optical fiber from breaking. The same applies to the rotating flange S29 attached to the input ferrule S6. In this embodiment, an example is shown in which a capillary tapered in the longitudinal direction is inserted inside the flange, but the shape of the inside of the flange is not limited to this as long as it allows the optical fiber to be inserted into the fiber hole and protects the optical fiber when the optical coupling unit is fabricated.

[0057] In this invention, the ends of two ferrules, each with a single-mode optical fiber arranged parallel to and at the same distance from the central axis, are convex, and by butting the tips of the two ferrule ends together so that their central axes coincide, and rotating one of the ferrules around its central axis, the end faces of the opposing optical fibers do not come into contact with each other, preventing deterioration of optical properties such as connection loss due to scratches on the end faces of the optical fibers caused by contact. Furthermore, by making the end faces of the opposing optical fibers non-parallel to each other, the amount of light reflection can be reduced, eliminating the need for a reflective coating, and providing a more economical optical coupling unit and optical switch.

[0058] Furthermore, in the present invention, one of the input and output sides of the optical coupling unit S8 that performs optical switching is configured as an axially rotatable mechanism, which minimizes the energy required by the actuator S3, i.e., the torque output, and enables low power consumption. Furthermore, the amount of optical axis misalignment in directions other than the axial rotation of the input ferrule S6 is compensated for by the sleeve S17 in the optical coupling unit S8, enabling low loss. In addition, the present invention does not include a collimator or special vibration isolation mechanism, and instead is composed of commonly used optical connection components such as ferrules and sleeves, making it compact and economical.

[0059] Therefore, the present invention makes it possible to provide an optical coupling unit and an optical switch that can achieve stable optical characteristics against external factors such as temperature and vibration with low power consumption and more economically. As a result, the optical coupling unit and the optical switch can be used as an optical switch that switches paths in optical lines using single-mode optical fibers in optical fiber networks, regardless of location, in any facility.

[0060] (Embodiment 2) The configuration and operation of the optical switch S00 according to this embodiment will be specifically described below with reference to Figures 14 and 15. In the optical switch S00 of this embodiment, the input ferrule S6 of the optical coupling section S8 is attached to the input flange S18 instead of the rotating flange S29, and the position at which the bearing S26 is provided differs from that of the optical switch S00 of embodiment 1. The rotation mechanism of the input ferrule S6 will be described below. Note that the contents other than those described below are the same as those of embodiment 1.

[0061] 14 is a schematic diagram showing the coupling form of the optical coupling unit S8 according to this embodiment. As in the first embodiment, the output ferrule S7 is attached to the notched output flange S19, and the output flange S19 is attached to the fixing jig S27 with fixing screws S25, so that the axial direction and the axial rotation direction are fixed.

[0062] The input ferrule S6 is attached to a notched input flange S18. The input flange S18 is attached to a fixture S27 with removable fixing screws S25, fixing the axial direction and axial rotation direction. Loosening the fixing screws S25 allows the input flange S18 to rotate, which in turn allows the input ferrule S6 attached to the input flange S18 to rotate. The input flange S18 may also have a structure as shown in FIG. 15, as described below. A separate fixing screw (not shown) may be provided to fix the axial direction. The input ferrule S6 has a smaller ferrule outer diameter S15 than the output ferrule S7, is attached to a bearing S26, and is rotated by a rotation mechanism S5 of the bearing S26. In other words, with the output ferrule S7 fixed and the input flange S18 rotatable, the input ferrule S6 rotates within the sleeve S17 around the center of the ferrule cylinder by the rotation mechanism S5 of the bearing S26. As a result, the core of the input-side optical fiber S1 inserted into the input-side ferrule S6 rotates, and the core of the output-side optical fiber S9 opposite to the input-side optical fiber S1 is switched.

[0063] Fig. 15 is a schematic diagram showing a cross section of the input ferrule S6 of the optical coupling section S8 according to this embodiment. A bearing S26 is attached around the input ferrule S6, allowing the input ferrule S6 to rotate freely within the sleeve S17. Fig. 15 also shows an example in which a fixing spring S28 is used as a method for fixing the input flange S18. A groove as shown in Fig. 15 is provided in advance in the input flange S18, and the tip of the fixing spring S28 is clamped in the groove to fix the input flange S18 and the input ferrule S6 fixed thereto. The fixing spring S28 is urged in the direction of the arrow D SBy applying a force to the input ferrule S6, the input ferrule S6 is released from the fixed state and becomes rotatable. For example, by linking the fixing and releasing of this fixing spring S28 with a control circuit S4 (not shown) that controls the actuator S3, it is possible to control the optical fiber switching all at once. Also, as shown in FIG. 16, by forming the outer periphery of the input flange S18 into a shape in which multiple gears are arranged so that the grooves are offset along the longitudinal direction of the input ferrule S6, it is possible to perform more precise control of the rotation angle. Furthermore, instead of using the fixing spring S28, a magnet or solenoid may be used as a method for fixing and releasing the input flange S18.

[0064] As described above, according to the present invention, it is possible to provide an optical coupling section and an optical switch that can realize stable optical characteristics against external factors with low power consumption and more economically.

[0065] The above inventions can be combined as much as possible. [Industrial Applicability]

[0066] The optical couplers and optical switches according to the present disclosure can be applied to the optical communication industry. [Explanation of symbols]

[0067] S00: Front-stage optical switch component S00: Optical switch S01: Input optical fiber S02: Optical fiber between optical switches S03: Post-stage optical switch component S03: Optical switch S04: Output optical fiber S1: Input optical fiber S2: Extra length S3: Actuator S4: Control circuit S5: Rotation mechanism S6: Input ferrule S7: Output ferrule S8: Optical coupling part S9: Output optical fiber S10: Dummy fiber S11: Fiber hole S15: Ferrule outer diameter S16: Sleeve inner diameter S17: Sleeve S18: Input flange S19: Output flange S21: Fiber hole diameter S23: Capillary S25: Fixing screw S26: Bearing S27: Fixture S28: Fixed spring S29: Rotating flange S30: Fiber hole

Claims

1. An optical coupling unit that couples single-core optical fibers arranged in two ferrules using a sleeve, a first ferrule of the two ferrules has a plurality of optical fibers arranged in a bundle shape in a fiber hole on the same circumference centered on the central axis of the ferrule; At least one of the two ferrules is rotatable around the ferrule central axis, the butted ends of the two ferrules have a convex spherical shape with a center point on the central axis of the ferrules, The radius of curvature Rcur [mm] of the convex spherical shape satisfies formula (5a), and The distance D from the tip of the ferrule to the end face of the optical fiber is 11 μm or less. An optical coupling unit characterized by: [Number 5a] Here, Rcore is the core arrangement radius [mm].

2. the first ferrule includes a dummy fiber inside the plurality of optical fibers arranged in a bundle on the same circumference centered on the central axis of the ferrule; the end surface of the dummy fiber constitutes a part of the convex spherical shape; The optical coupling section according to claim 1 .

3. The optical coupling unit according to claim 1 or 2; a rotation mechanism that rotates one of the two ferrules of the optical coupling unit around a central axis of the ferrule; An optical switch comprising:

4. an actuator that rotates the rotation mechanism at a constant angular step and stops the rotation mechanism at an arbitrary angular step; a bearing constituting the rotation mechanism; 4. The optical switch according to claim 3, further comprising:

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