JP2010286718A - Multi-core fiber terminal and connection structure thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terminal structure for effectively suppressing an increase in connection loss of a multi-core fiber. <P>SOLUTION: A multi-core fiber terminal 100 includes: an SM (Single Mode) type multi-core fiber 10 having a plurality of SM type cores 11; and a graded-index lens array 20 melt-secured to the end surface 10a of the multi-core fiber. In the graded-index lens array 20, a refractive-index changing area 21 is set so as to align with the core arrangement at the end surface 10a of the SM type multi-core fiber 10. For examples, when the graded-index lens array is constituted of a GI (Graded Index) type multi-core fiber, each of the GI type cores is fit for the refractive-index changing area 21, then, the beam diameter of the light emitted from the end surface 10a of the SM type multi-core fiber 10 is made larger. Besides, by adjusting the thickness D of the graded-index lens array 20, the light having a suppressed divergence angle also is obtained. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a multi-core fiber terminal including a multi-core fiber having a plurality of cores each individually functioning as an optical waveguide as a part of an optical fiber network, and in particular, a low-loss connection to a network resource having the same core arrangement. It relates to a structure for realizing.

  Conventionally, in order to provide an FTTH (Fiber To The Home) service that enables optical communication between a single transmission station and a plurality of subscribers, for example, as shown in FIG. Thus, a so-called PON (Passive Optical Network) system is realized in which each subscriber shares one optical fiber.

  That is, the PON system shown in FIG. 6 is between the terminal station 1 (transmitting station), which is the final relay station of an existing communication system such as the Internet, and between the terminal station 1 and the subscriber home 2 (subscriber). And an installed optical fiber network. This optical fiber network includes a closure (including an optical splitter 30) provided as a branch point, an optical communication line 12 from the terminal station 1 to the closure, and an optical communication line 31 from the closure to each subscriber home 2. Has been.

  The terminal station 1 includes a station-side terminal device 10 (OLT: Optical Line Terminal) and an optical splitter 11 that branches a multiplexed signal from the OLT 10. On the other hand, the subscriber's home 2 is provided with a subscriber-side terminal device 20 (ONU: Optical Network Unit). In addition, the closure as a branching point of the optical fiber network laid between the terminal station 1 and the subscriber's home 2 includes at least an optical splitter 30 for further branching the multiplexed signal that has arrived, and service contents A wavelength selection filter or the like for limiting the frequency is arranged.

  As described above, in the PON system shown in FIG. 6, the optical splitter 11 is provided in the terminal station 1 and the optical splitter 30 is also provided in the closure arranged on the optical fiber network. One station-side terminal device 10 can provide FTTH service to a plurality of subscribers.

  However, in a PON system in which a plurality of subscribers share a single optical fiber through multistage optical splitters as described above, future transmission capacity such as congestion control (Congestion Control) and securing of a receiving dynamic range, etc. It is true that there is a technical challenge against this increase. As a means for solving this technical problem (congestion control, ensuring a dynamic range, etc.), a transition to an SS (SingleStar) system can be considered. When migrating to the SS system, the number of fiber cores on the inner side of the station increases with respect to the PON system. Therefore, it is essential to make the diameter and the ultra-high density of the optical cable inside the station. A multi-core fiber is suitable as the optical fiber for ultra-fine diameter and ultra-high density.

  For example, as a multi-core fiber, the optical fiber disclosed in Patent Document 1 has seven or more cores arranged two-dimensionally in its cross section. Patent Document 2 discloses an optical fiber in which a plurality of cores are aligned in a straight line, and it is described that connection with an optical waveguide / semiconductor optical integrated device is facilitated.

JP 05-341147 A JP-A-10-104443

  The inventors have found the following problems as a result of examining the above-described conventional technology.

  That is, the multicore fiber described in Patent Document 1 is difficult to connect to an optical device or the like at the transmission end or the reception end. As described in Patent Document 2, an optical device such as an optical waveguide or a semiconductor optical integrated device that is normally manufactured has a plurality of optical transmission / reception elements (light emitting area or light receiving area) arranged in one dimension. In general, such an optical device is optically coupled to a multi-core fiber in which a plurality of cores are two-dimensionally arranged in the cross section (hereinafter, this arrangement state is referred to as a two-dimensional core array). It was difficult.

  In addition, since the multi-core fiber described in Patent Document 2 is intended for optical connection with a one-dimensionally arranged optical transmission / reception element, the cores are arranged one-dimensionally. In this case, since it is difficult to significantly increase the number of cores per multi-core fiber, it cannot be used as an optical transmission line.

  On the other hand, in FTTH, the number of fiber cores increases as the number of subscribers increases, so it is also true that the fiber storage space in the station is being pressed, and a multi-core fiber having a one-dimensional core arrangement and a multi-core having a two-dimensional core arrangement. It can be easily imagined that the demand for using any of the fibers will increase. However, considering the connection between the multicore fiber and other network resources, it is necessary to correct the rotation of the core arrangement around the longitudinal direction of the multicore fiber, unlike the connection of the single core fiber. Is easily expected to become extremely complicated. Also, in practice, all core alignments occur due to variations in the core position within the multi-core fiber (manufacturing variation of the multi-core fiber) and misalignment between the multi-core fibers in the connector section (connector eccentricity and fitting tolerance). It was difficult to achieve low connection loss.

  The present invention has been made in order to solve the above-described problems, and includes various multi-core fibers including a multi-core fiber that can be applied as a part of an optical waveguide in an optical communication system and having the same core arrangement. It is an object of the present invention to provide a multi-core fiber terminal having a structure for effectively suppressing an increase in connection loss between network resources (connection objects) and a connection structure thereof.

  In order to solve the above-described problem, a multi-core fiber terminal according to the present invention has a connection accuracy of a multi-core fiber having a plurality of cores and other network resources (including multi-core fibers having the same core arrangement). A structure for relaxing tolerance is provided. Specifically, the multi-core fiber terminal includes a single-mode (hereinafter referred to as SM) type multi-core fiber that can be applied as a part of an optical fiber network regardless of inside or outside a station, and a refraction fixed to an end face of the SM-type multi-core fiber. A rate distribution type lens array is provided.

  The SM type multi-core fiber has a plurality of SM type cores each functioning as an optically independent single mode optical waveguide, and a clad that integrally covers the plurality of SM type cores and maintains the core arrangement in the cross section. . The gradient index lens array has a first end face facing the end face of the SM type multi-core fiber, and a second end face facing the first end face. In the gradient index lens array, the refractive index change region is set so as to coincide with the core arrangement on the end face of the SM type multi-core fiber.

  In particular, in order to realize a low-loss connection with other network resources, the gradient index lens array inputs light propagating through one SM core in an SM type multi-core fiber, Light having a beam diameter larger than the mode field diameter (hereinafter referred to as MFD) and a divergence angle smaller than the divergence angle of the light propagated through the one SM type core is output. Normally, the beam diameter of the light output from the second end face of the gradient index lens array is optimal in consideration of the core spacing and core position error at the end face of the SM type multi-core fiber, the eccentricity of the connecting connector, the fitting tolerance, etc. The value is determined. However, considering the application of the multi-core fiber terminal to the optical transmission line in the wavelength band of 1.3 μm to 1.55 μm for performing single mode optical communication, the beam diameter of the light output from the gradient index lens array Is preferably 15 μm or more.

  When manufacturing a gradient index lens array at a lower cost, it is practical to use a part of a GI type multi-core fiber having a plurality of graded index (hereinafter referred to as GI) type cores. This GI type multi-core fiber has a plurality of GI type cores each functioning as an optical waveguide having an optically independent GI type refractive index profile, and a clad that integrally covers the plurality of GI type cores. In particular, the GI type multi-core fiber has a plurality of GI type cores arranged on the end face thereof so as to coincide with the core arrangement on the end face of the SM type multi-core fiber. Therefore, in the multicore fiber terminal, the center position of each SM core on the end face of the SM type multicore fiber and the refractive index peak position on the first end face of the gradient index lens array substantially coincide.

  The multi-core fiber terminal connection structure according to the present invention includes first and second multi-core fibers each having the same structure as a multi-core fiber (multi-core fiber according to the present invention) having the above-described structure. In the connection structure, the second end face in the gradient index lens array of the first multicore fiber terminal and the second end face in the gradient index lens array of the second multicore fiber terminal face each other, These first and second multi-core fiber terminals are connected and fixed.

  According to the multi-core fiber terminal according to the present invention, the position variation of each SM-type core in the SM-type multi-core fiber (manufacturing variation of the SM-type multi-core fiber) and the position shift between the SM-type multi-core fibers in the connector section (connector) Even in the presence of eccentricity and fitting tolerance, low-loss connections are realized for all SM cores.

It is a figure which shows the structure of one Embodiment of the multi-core fiber terminal which concerns on this invention. It is a figure for demonstrating the function of the multi-core fiber terminal which concerns on this embodiment. It is a figure for demonstrating the manufacturing process of the multi-core fiber terminal which concerns on this embodiment. It is a figure for demonstrating the thickness determination process of the gradient index lens array while showing the propagation state of the light in a GI type | mold core. It is a figure for demonstrating one Embodiment of the connection structure of the multi-core fiber terminal which concerns on this invention. It is a figure which shows the structure of the conventional optical communication system (PON system).

  Hereinafter, each embodiment of the multi-core fiber according to the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram showing a configuration of an embodiment of a multi-core fiber terminal according to the present invention. The multi-core fiber terminal 100 shown in FIG. 1 relaxes the tolerance of connection accuracy when connecting a multi-core fiber having a plurality of cores and other network resources (including multi-core fibers having the same core arrangement). It has a structure to make it. FIG. 2 is a diagram for explaining the function of the multi-core fiber terminal 100 shown in FIG.

  Specifically, the multi-core fiber terminal 100 is fixed to an SM type multi-core fiber 10 that can be applied as a part of an optical fiber network regardless of inside or outside a station, and an end face 10a (light input / output end face) of the SM type multi-core fiber 10. The gradient index lens array 20 is provided.

  As shown in FIG. 1, the SM type multi-core fiber 10 integrally covers a plurality of SM type cores 11 each functioning as an optically independent single mode optical waveguide, and the plurality of SM type cores 11. In addition, it has a cladding 12 that holds the core array in its cross section. The gradient index lens array 20 has a first end face 20a facing the end face 10a of the SM type multi-core fiber 10, and a second end face 20b facing the first end face 20a, and the second end face 20b is the end face 10a. As a result, the gradient index lens array 20 is fixed to the end surface 10a of the multi-core fiber terminal 10. In the gradient index lens array 20, a refractive index change region 21 is set so as to coincide with the core arrangement on the end face 10 a of the SM type multi-core fiber 10.

  In addition, the thickness D of the gradient index lens array 20 includes the divergence angle and beam of light output from the second end surface 20b of the gradient index lens array 20 together with the maximum refractive index variation in the refractive index variation region 21. Fine-tuned to control the diameter. Further, by adjusting the thickness D, it is possible to output light close to parallel light with a divergence angle suppressed from the second end face 20b of the gradient index lens array 20.

  In the present embodiment, the gradient index lens array 20 having the above-described structure is provided with an SM type multi-core fiber in order to realize a low-loss connection with other network resources as shown in FIG. 10, the light propagated through one SM core 11 is input, the beam diameter is larger than the MFD of the one SM core 11, and the divergence angle of the light propagated through the one SM core 11 Outputs light with a small divergence angle. In particular, considering the application of the multi-core fiber terminal to an optical transmission line in the wavelength band of 1.3 μm to 1.55 μm for performing single mode optical communication, output from the second end face 20b of the gradient index lens array 20 The beam diameter of the emitted light is preferably 15 μm or more. Furthermore, it is preferable that the divergence angle of the output light is within a half angle of 5 degrees.

  Subsequently, a manufacturing process of the multi-core fiber terminal according to the present embodiment will be described with reference to FIG.

  First, in the manufacture of the multicore fiber terminal 100, as shown in FIG. 3A, in order to obtain the SM type multicore fiber 10 and the gradient index lens array 20 applied to a part of the optical transmission line. GI type multi-core fiber 200 is prepared.

  The prepared SM type multi-core fiber 10 has a fiber diameter (cladding diameter) of 125 μm and a seven-core SM type core 11. The diameter of each SM type core is 9 μm, and the minimum interval between the SM cores 11 is 40 μm at the end face 10a. On the other hand, the above-described GI type multi-core fiber 200 integrally covers a plurality of GI type cores 210 each functioning as an optical waveguide having an optically independent GI type refractive index profile, and the plurality of GI type cores 210. The clad 220 is provided. In particular, the GI type multi-core fiber 200 has a plurality of GI type cores 210 arranged on the end face 200a so as to coincide with the core arrangement on the end face 10a of the SM type multi-core fiber 10.

  Subsequently, the SM core 11 and the GI core 210 are aligned with the end face 10a of the prepared SM type multicore fiber 10 and the end face 200a of the GI type multicore fiber 200 attached to each other. This alignment work is performed while measuring the power of light passing through at least two propagation paths among the propagation paths composed of the SM-type core 11 and the GI-type core 210 each corresponding to the position. This is done by adjusting the positional relationship between the SM type multi-core fiber 10 and the GI type multi-core fiber 200. At the end of the alignment operation, the center position of each SM core 11 on the end face 10a of the SM type multi-core fiber 10 and the refractive index peak position of the end face 200a of the GI multi-core fiber 200 (center position of the GI type core 210) are It is almost coincident.

  When the above alignment process is completed, the end face 10a of the SM type multi-core fiber 10 and the end face 200a of the GI type multi-core fiber 200 are fusion-connected. Thereafter, as shown in FIG. 3B, the GI type multi-core fiber 200 is cut at a position away from the end face 200a constituting the fusion part by a distance D, whereby the multi-core fiber terminal 100 is obtained. That is, the tip portion of the GI type multi-core fiber 200 fixed to the end face 10 a of the SM type multi-core fiber 10 becomes the gradient index lens array 20.

  In addition, each GI type | mold core 210 of the above-mentioned GI type | mold multi-core fiber 200 takes the peak in the center, and the refractive index distribution 250 from which a refractive index falls with the square of distance as it leaves | separates from this center is shown. Have The light propagating through the GI type core 210 propagates while converging at a constant period. Accordingly, by appropriately selecting the cutting position of the GI type multi-core fiber 200, that is, the distance D from the end surface 200a (corresponding to the thickness of the gradient index lens array 20), light having a desired beam diameter, and further diverging. Light close to parallel light with a suppressed angle can be obtained. In the gradient index lens array 20 obtained at this time, the outer diameter is 125 μm and the number of lenses (the number of GI cores 210 corresponding to the refractive index changing region 21) is the same as the cladding diameter of the SM multicore fiber 10 described above. ) Is 7, and the lens diameter (outer diameter of the GI core 210) is 20 μm. The distance between adjacent lenses (the distance between the lens centers) is 40 μm.

  In the multi-core fiber terminal 100 manufactured as described above, the allowable deviation amount between the SM-type core 11 and the GI-type core 210 (corresponding to the lens portion that is the refractive index changing region 21) connects the SM-type multi-core fibers to each other. This is 2.2 times (= 20 μm / 9 μm). In addition, when a connector is connected with a rotation error of 1 degree around the longitudinal direction of the multi-core fiber terminal 100, the SM-type core 11 in the SM-type multi-core fiber 10 having the above-described structure (the outer diameter is 9 μm), An axial misalignment of about 0.7 μm occurs. However, by providing the above-described gradient index lens array 20 on the end face 10a of the SM type multi-core fiber 10, the multi-core fiber terminal 100 is light that is substantially unaffected by this 0.7 μm axis deviation. Connection characteristics are obtained. In addition, since the lens interval is about the same as the beam diameter of the light output from the second end face 20b of the gradient index lens array 20, crosstalk to the adjacent channel (adjacent core) is sufficiently suppressed. Is done.

  The multi-core fiber terminal 100 having the above-described characteristics is inserted into the through hole 310 of the connector ferrule 300 from the gradient index lens array 20 side, as shown in FIG. Thereafter, the tip portion of the multi-core fiber terminal 100 including the gradient index lens array 20 and the connector ferrule 300 are bonded and fixed. The connector ferrule 300 includes end faces 300a and 300b facing each other and a through hole 310 that connects the end faces 300a and 300b.

  When the connector ferrule 300 is bonded and fixed to the tip portion of the multi-core fiber terminal 100 including the gradient index lens array 20, the end face 300b of the connector ferrule 300 is polished together with the second end face 20b of the gradient index lens array 20. The At this time, the polishing amount is adjusted as necessary so that the divergence angle of the output light from the second end face 20b becomes small.

  In the manufacturing method shown in FIG. 3, only the required length (thickness of the gradient index lens array 20) is obtained after the aligned GI type multicore fiber 200 and SM type multicore fiber 10 are fused and fixed. The GI type multi-core fiber 200 was cut. However, the multi-core fiber terminal 100 according to the present embodiment is previously cut out from the prepared GI-type multi-core fiber 200 with a desired thickness D, and this cut-out portion (corresponding to the gradient index lens array 20) is SM type. After aligning with respect to each SM type core 11 of the multi-core fiber 10, the SM type multi-core fiber 10 may be fused and fixed. The alignment operation in this case is performed, for example, by placing an observation device on the second end face 20b of the gradient index lens array 20 and observing an image captured from the observation device.

  Next, an embodiment of a multi-core fiber terminal connection structure according to the present invention will be described with reference to FIG. In addition, the connection structure of the multi-core fiber terminal according to the present embodiment includes the first and second multi-core fiber terminals 100A and 100B obtained through the manufacturing process shown in FIG. Moreover, the core arrangements in the prepared first and second multi-core fiber terminals 100A and 100B coincide with each other.

  The first multi-core fiber terminal 100A includes a plurality of SM-type cores, an SM-type multi-core fiber 10A having a clad that integrally covers the plurality of SM-type cores, and a refractive index distribution type corresponding to the tip portion of the GI-type multi-core fiber. A lens array 20A is provided. A connector ferrule 300A is bonded and fixed to the tip portion of the first multi-core fiber terminal 100A including the gradient index lens array 20A.

  On the other hand, the second multi-core fiber terminal 100B includes a plurality of SM-type cores, an SM-type multi-core fiber 10B having a clad that integrally covers the plurality of SM-type cores, and a refractive index corresponding to the tip portion of the GI-type multi-core fiber. A distributed lens array 20B is provided. Similarly to the first multicore fiber terminal 100A described above, the connector ferrule 300B is bonded and fixed to the tip portion of the second multicore fiber terminal 100B including the gradient index lens array 20B.

  In the multi-core fiber terminal connection structure according to the present embodiment, the end face of the first multi-core fiber terminal 100A prepared as described above (corresponding to the second end face of the gradient index lens array 20A) and the second multi-core fiber terminal. In the state where the end face of 100B (corresponding to the second end face of the gradient index lens array 20B) is abutted, the alignment of the core array on each end face is performed. As shown in the manufacturing process of FIG. 3A, the alignment operation is configured by the core path in the SM type multi-core fiber terminal 100A and the core path in the second multi-core fiber terminal 100B, each of which corresponds to the position. This is performed by adjusting the positional relationship between the first multicore fiber terminal 100A and the second multicore fiber terminal 100B while measuring the power of light passing through at least two of the propagation paths.

  When the alignment operation between the first and second multi-core fiber terminals 100A and 100B is completed as described above, the adhesive applied between the end face of the first multi-core fiber terminal 100A and the end face of the second multi-core fiber terminal 100B. By curing the agent, the connection structure of the multi-core fiber terminal can be obtained.

  In the above-described embodiment, a multicore fiber terminal including a multicore fiber in which a plurality of cores are two-dimensionally arranged on the end face has been described. However, the core arrangement on the end face of the multicore fiber may be one-dimensional.

  The multi-core fiber terminal according to the present invention can be applied to an optical communication system as a part of an optical transmission line.

  10, 10A, 10B ... SM type multi-core fiber, 11 ... SM type core, 20, 20A, 20B ... Gradient index lens array, 100, 100A, 100B ... Multi-core fiber terminal, 200 ... GI type multi-core fiber, 210 ... GI Type core.

Claims (5)

A plurality of SM cores each functioning as an optically independent single-mode optical waveguide; an SM type multi-core fiber having a clad that integrally covers the plurality of SM cores and holds the core arrangement in its cross section; ,
A gradient index lens array fixed to an end face of the SM type multi-core fiber, having a first end face facing the end face of the SM type multi-core fiber and a second end face facing the first end face, and A multicore fiber terminal comprising: a gradient index lens array in which a refractive index change region is set so as to coincide with a core arrangement on an end face of an SM type multicore fiber. The gradient index lens array receives light propagating through one SM core in the SM multicore fiber, has a beam diameter larger than the mode field diameter of the one SM core, and the one 2. The multi-core fiber terminal according to claim 1, wherein light having a divergence angle smaller than the divergence angle of the light propagated through the SM core is output. The multi-core fiber terminal according to claim 2, wherein a beam diameter of light output from the gradient index lens array is 15 µm or more. The gradient index lens array has a plurality of GI cores each functioning as an optical waveguide having an optically independent GI refractive index distribution, and a clad integrally covering the plurality of GI cores. 2. A GI type multi-core fiber, comprising a GI type multi-core fiber in which the plurality of GI type cores are arranged so as to coincide with a core arrangement at an end face of the SM type multi-core fiber. The described multi-core fiber terminal. A first multicore fiber terminal having the same structure as the multicore fiber terminal according to any one of claims 1 to 4,
A second multi-core fiber terminal having the same structure as the multi-core fiber terminal according to any one of claims 1 to 4,
In a state where the second end face in the gradient index lens array of the first multicore fiber terminal and the second end face in the gradient index lens array of the second multicore fiber terminal face each other, the first and first 2 Multi-core fiber terminal connection structure in which multi-core fiber terminals are connected and fixed.

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