CN113325516A - Optical fiber coupler and optical fiber coupling method - Google Patents
Optical fiber coupler and optical fiber coupling method Download PDFInfo
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- CN113325516A CN113325516A CN202110659170.0A CN202110659170A CN113325516A CN 113325516 A CN113325516 A CN 113325516A CN 202110659170 A CN202110659170 A CN 202110659170A CN 113325516 A CN113325516 A CN 113325516A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/25—Preparing the ends of light guides for coupling, e.g. cutting
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/02—Optical fibres with cladding with or without a coating
- G02B6/036—Optical fibres with cladding with or without a coating core or cladding comprising multiple layers
- G02B6/03616—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference
- G02B6/03688—Optical fibres characterised both by the number of different refractive index layers around the central core segment, i.e. around the innermost high index core layer, and their relative refractive index difference having 5 or more layers
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/255—Splicing of light guides, e.g. by fusion or bonding
- G02B6/2551—Splicing of light guides, e.g. by fusion or bonding using thermal methods, e.g. fusion welding by arc discharge, laser beam, plasma torch
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
Abstract
The present invention relates to the field of optical fiber technologies, and in particular, to an optical fiber coupler and an optical fiber coupling method. The optical fiber coupler comprises a multi-core multi-cladding optical fiber and a sleeve; the first end of the multi-core multi-cladding optical fiber is coupled with the sleeve; the multicore multi-clad fiber contains at least two cores, and the outer cladding of each core includes from inside to outside in proper order: an inner cladding, a depressed inner cladding, an annular cladding, an outer cladding, a depressed outer cladding, and a mechanical cladding; the outer surface radius of the multi-core multi-cladding optical fiber is larger than the preset minimum radius, and the core distance between any two fiber cores is larger than the preset minimum core distance. The multi-core optical fiber coupler provided by the invention has the advantages that the multi-core multi-cladding optical fiber is tapered and then can be welded with the multi-core optical fiber in a low-loss manner; and can realize low-loss fusion welding with standard single mode fiber, and has lower macrobend loss. In another aspect, the invention also provides a method for coupling optical fibers using the optical fiber coupler.
Description
[ technical field ] A method for producing a semiconductor device
The present invention relates to the field of optical fiber technologies, and in particular, to an optical fiber coupler and an optical fiber coupling method.
[ background of the invention ]
Because the multi-core fiber can provide a new multiplexing dimension of space, the capacity of a communication system can be greatly increased, and the use of the multi-core fiber in the communication system is increasingly emphasized to meet the requirements of the future communication system. The multi-core optical fiber communication system needs to be compatible with the existing single-mode optical fiber communication system, and the multi-core optical fiber and the single-mode optical fiber need to realize low-loss connection. In order to connect a single-mode optical fiber and a multi-core optical fiber, a fiber coupler is generally used as a bridge. Therefore, the optical fiber coupler and the bridging optical fiber in the optical fiber coupler become one of the key technologies for popularizing the practical application of the multi-core optical fiber and reducing the use cost of the multi-core optical fiber.
At present, the preparation of the multi-core optical fiber coupler is generally prepared by a fusion tapering method of a multi-clad optical fiber, such as the following applications: 201811089100.0 and 201811393656.9, the bridging fibers used are single core multi-clad fibers. When the single-core multi-cladding optical fiber is used as a bridging optical fiber, a fusion tapering method is used for fusing a plurality of standard single-mode optical fibers and a plurality of multi-single-core cladding optical fibers, the standard single-mode optical fibers and the multi-single-core cladding optical fibers penetrate into the sleeve to be tapered, and the standard single-mode optical fibers and the multi-single-core cladding optical fibers are fused after being cut. The method has large insertion loss ratio because the tapering and cutting precision of the optical fiber bundle consisting of a plurality of single-core multi-cladding optical fibers are difficult to control.
In summary, the preparation process of various multi-core fiber couplers is affected by the type of the used bridging fiber, so that problems exist in the aspects of processing precision, processing difficulty, cost, loss and the like.
[ summary of the invention ]
Aiming at the defects of the prior art, the invention aims to solve the technical problems of the prior optical fiber coupler in the aspects of processing precision, processing difficulty, cost, loss and the like.
To achieve the above object, in a first aspect, the present invention provides an optical fiber coupler comprising a multi-core multi-clad optical fiber 10 and a ferrule 20; a first end of the multi-core, multi-clad optical fiber 10 is coupled to the ferrule 20; the multicore multi-clad fiber 10 includes at least two cores 11, and the cladding outside each core 11 sequentially includes from inside to outside: inner cladding 12, depressed inner cladding 13, annular cladding 14, outer cladding 15, depressed outer cladding 16, and mechanical cladding 17; the outer surface radius of the multi-core multi-clad fiber 10 is larger than the preset minimum radius, and the core interval between any two fiber cores 11 is larger than the preset minimum core interval.
Preferably, the depressed inner cladding 13 has a refractive index less than that of the core 11, the depressed inner cladding 13 has a refractive index less than that of the inner cladding 12, and the depressed outer cladding 16 has a refractive index less than that of the outer cladding 15.
Preferably, the cladding outside each core 11 of the multicore multi-clad fiber 10 is of a step-index profile.
Preferably, the radius of each cladding is within a predetermined radius of the cladding, and the relative refractive index difference of each cladding is within a predetermined relative refractive index difference of the cladding.
Preferably, each core 11 of the multicore, multi-clad fiber 10 has the same properties.
In a second aspect, the present invention also provides a method for coupling optical fibers, comprising the steps of: obtaining a fiber coupler 1 provided in a first aspect; tapering a second end of the multi-core multi-clad fiber 10 of the optical fiber coupler 1 to enable the core spacing of the second end of the multi-core multi-clad fiber 10 to reach a preset core spacing threshold value, and fixing the second end of the multi-core multi-clad fiber 10 and the multi-core fiber 2; single-mode optical fibers 3 are inserted into the ferrules 20 of the optical fiber couplers 1, and each single-mode optical fiber 3 is aligned with and fixed to one core 11 of the multi-core multi-clad optical fiber 10.
Preferably, the tapering process is performed on the second end of the multi-core multi-clad fiber 10 of the fiber coupler 1, and specifically includes: the fiber core 11, the inner cladding 12, the sunken inner cladding 13 and the annular cladding 14 of the multi-core multi-clad fiber (10) before the second end is tapered form a tapered fiber core, and the outer cladding 15, the sunken outer cladding 16 and the mechanical cladding 17 of the multi-core multi-clad fiber 10 before the second end is tapered form a tapered cladding.
Preferably, the fixing the second end of the multi-core multi-clad fiber 10 to the multi-core fiber 2 specifically includes: the second end of the multi-core multi-clad fiber 10 is cut, and the cut end surface is fusion-spliced with the multi-core fiber 2.
Preferably, before each single-mode optical fiber 3 is aligned and fixed with one core 11 of the multi-core multi-clad optical fiber 10, the method further includes: the coating layer of each single mode optical fiber 3 is stripped off, and the single mode optical fiber 3 is cut.
Preferably, each single-mode fiber 3 is aligned with and fixed to one core 11 of the multi-core multi-clad fiber 10, and specifically includes: a single mode optical fiber 3 is inserted into the ferrule 20; aligning the single-mode fiber 3 with one fiber core 11 of the multi-core multi-clad fiber 10, and fixing after aligning; the alignment and fixation of all the single-mode optical fibers 3 to each core 11 of the multi-core multi-clad optical fiber 10 are sequentially completed.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects: the invention provides a bridging fiber of a fiber coupler, which comprises a plurality of multi-clad fiber cores, wherein the multi-core multi-clad fiber comprises: the fiber core, the inner cladding, the sunken inner cladding, the annular cladding, the outer cladding, the sunken outer cladding and the mechanical cladding have the advantages of simple preparation process, no need of treatment such as corrosion and the like, good expandability and high yield.
The optical fiber coupler provided by the invention has the advantages that one optical fiber comprises a plurality of fiber cores with multiple claddings, the sunken inner claddings are used as channels, the refractive index of the sunken inner claddings is smaller than that of the fiber cores and the inner claddings, the coverage range of a field can be limited when the optical fiber is bent, and the field is prevented from leaking to the annular claddings, so that the multi-core and multi-cladding optical fiber has small macrobend loss.
The multi-core optical fiber coupler provided by the invention has the advantages that after the multi-core multi-cladding optical fiber is subjected to tapering, the fiber core, the inner cladding, the sunken inner cladding and the annular cladding form a new fiber core, and the outer cladding, the sunken outer cladding and the mechanical cladding form a new cladding, so that the multi-core optical fiber coupler has lower welding loss when being welded with the multi-core optical fiber. By matching the mode fields of the multi-core multi-cladding optical fiber and the standard single-mode optical fiber, the multi-core multi-cladding optical fiber and the standard single-mode optical fiber have low fusion loss during fusion.
The optical fiber coupler provided by the invention has the advantages that the refractive index of the sunken outer cladding of the multi-core multi-cladding optical fiber is smaller than that of the outer cladding, the field coverage range can be limited, the field is prevented from leaking outwards, and therefore, the optical fiber coupler has small crosstalk between cores after being welded with the multi-core optical fiber.
The preparation method of the optical fiber coupler and the optical fiber coupling method provided by the invention have the advantages that the steps of the process flow are fewer, the problem of high difficulty in cutting the optical fiber bundle is avoided, the repeatability is high, and the realization is easy.
[ description of the drawings ]
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly described below. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
FIG. 1 is a schematic structural diagram of an optical fiber coupler according to the present invention;
FIG. 2 is a schematic diagram of a conventional fiber coupler structure and coupling method;
FIG. 3 is a schematic diagram of a coupling method of an optical fiber coupler according to the present invention;
FIG. 4 is a schematic diagram of a cladding structure outside each core in a fiber optic coupler according to the present invention;
FIG. 5 is a schematic illustration of the refractive index of the cladding outside each core in a fiber coupler according to the present invention;
FIG. 6 is a flow chart of a method for coupling optical fibers according to the present invention;
FIG. 7 is a schematic view of a coupling structure after coupling by using the optical fiber coupling method provided by the present invention;
FIG. 8 is a flow chart of a method for coupling optical fibers according to the present invention;
FIG. 9 is a schematic view of a coupling structure after coupling by using the optical fiber coupling method provided by the present invention;
wherein the reference numbers are as follows:
10: multi-core multi-clad fiber, 11: core, 12: inner cladding, 13: depressed inner cladding, 14: annular cladding, 15: outer cladding, 16: depressed outer cladding, 17: mechanical cladding, 20: the casing pipe is provided with a plurality of casing pipes,
1: fiber coupler, 2: multi-core fiber, 3: single-mode optical fiber, 4: fusion-spliced cross section of the multi-core multi-clad fiber 10 and the multi-core fiber 2, 5: the single mode fiber 3 and the multi-core multi-clad fiber 10 are fusion-spliced in cross section.
[ detailed description ] A method for producing a semiconductor device
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
First, the definitions of some terms involved in the present invention are explained as follows:
(1) relative refractive index difference Δ i:
where Δ i is the relative refractive index difference of the cladding layers of the core, niIs the refractive index of the i-th layer of fiber material, n0The refractive index of the outermost mechanical cladding. The refractive index profile of each cladding is the value of the refractive index of that cladding at each radial point, and unless otherwise specified, Δ i in the present invention is the relative refractive index difference with the largest absolute value in each core cladding.
(2) Radius: ri denotes the radius of each cladding, the index i is {1, 2, 3, 4, 5, 6, 7}, which sequentially denotes each cladding from inside to outside, and Ri denotes the distance from the centerline of the fiber to the point at which the cladding is farthest from the centerline.
Example 1:
in order to solve the problem of large insertion loss when the existing single-core multi-clad optical fiber is used as a bridging optical fiber of an optical fiber coupler, a multi-core multi-clad optical fiber can be used as the bridging optical fiber, but the diameter of the outermost layer of the common multi-core multi-clad optical fiber is close to the diameter of the outermost layer of a single-mode optical fiber, and the common multi-core multi-clad optical fiber cannot be directly coupled with a plurality of single-mode optical fibers. The embodiment of the invention provides an optical fiber coupler, which uses a multi-core multi-cladding optical fiber as a bridging optical fiber, each cladding has specific optical performance parameters, and the radius of the cladding meets a certain specification, so that low-loss fusion can be realized with a standard single-mode optical fiber simply and conveniently, and the low-loss fusion can be realized with the multi-core optical fiber after being prepared by a micro-tapering method.
As shown in the longitudinal cross-sectional view of fig. 1, the present embodiment provides a fiber coupler comprising a multi-core multi-clad fiber 10 and a ferrule 20. In each of the structural diagrams used in the present embodiment, the broken line indicates the core, the thin solid line indicates the cladding outside the core, and the thick solid line indicates the outer surfaces of the optical fiber and the jacket. In order to simplify the illustration lines, the number of cores 11 shown in the cross section of the multicore multi-clad fiber 10 in fig. 1 is 2, and in actual use, the number of cores 11 may be selected according to the number of cores of the multicore fiber to be coupled.
In the existing optical fiber coupling technical solution, as shown in a longitudinal cross-sectional view of fig. 2, a plurality of single-core multi-clad optical fibers are generally used as bridging optical fibers, a second end of each bridging optical fiber is connected with one single-mode optical fiber, after first ends of the plurality of bridging optical fibers are inserted into a sleeve, the plurality of bridging optical fibers and the sleeve are tapered and cut together, and the tapered and cut first ends are welded with the multi-core optical fibers. In the scheme, the optical fiber bundle consisting of a plurality of bridging optical fibers needs to be tapered and cut, a large error exists in the cutting process, the end face of the optical fiber bundle is not flat, and the insertion loss after coupling is large.
In the technical solution provided in this embodiment, as shown in a longitudinal cross-sectional view in fig. 3, a multi-core multi-clad fiber 10 is used as a bridge fiber, the multi-core multi-clad fiber 10 includes at least two cores 11, when the multi-core multi-clad fiber 10 is used as the bridge fiber, a single-mode fiber is inserted into a sleeve 20 coupled to a first end of the multi-core multi-clad fiber 10, each single-mode fiber is aligned with one core 11 and fixedly connected, and a second end of the multi-core multi-clad fiber 10 is tapered and cut and then connected to the multi-core fiber. In the optical fiber coupler provided by the embodiment, the first end is assisted by the sleeve, and each fiber core 11 is respectively connected and fixed with one single-mode optical fiber, so that the processing is simple and convenient; on the other hand, when the second end is connected with the multi-core fiber, the multi-core multi-clad fiber 10 is directly tapered and cut, and the optical fiber bundle consisting of a plurality of fibers does not need to be tapered and cut, so that the process difficulty is low, the error caused by the process is small, and the insertion loss after coupling can be reduced.
The optical fiber coupler is used for guiding an optical signal in each fiber core of the multi-core optical fiber into a corresponding single-mode optical fiber, so that the multi-core optical fiber needs to be connected with a plurality of single-mode optical fibers. Because the diameter of the outermost layer of the common multi-core optical fiber is closer to that of the common single-mode optical fiber, one multi-core optical fiber cannot be directly used as a bridging optical fiber to be connected with a plurality of single-mode optical fibers. For example, the most common 7-core fiber typically has an outer diameter of 150 μm and a core pitch of 42 μm, while the g.652 standard single-mode fiber typically has a cladding diameter of 125 μm and a core diameter of 8.8 μm. It can be seen from the above data that the outer diameter of a common 7-core fiber is close to that of a standard single-mode fiber, and cannot be directly used as a coupler to be connected with a plurality of single-mode fibers simultaneously. In the optical fiber coupler provided in this embodiment, the outer surface radius of the multi-core multi-clad optical fiber 10 needs to reach the preset minimum radius, and the core distance between any two fiber cores 11 also needs to reach the minimum preset core distance, so as to provide sufficient space to fix a plurality of single-mode optical fibers, and meet the requirement for connection with a plurality of single-mode optical fibers. In the specific use of the embodiment of the invention, the preset minimum radius and the preset minimum core spacing are determined according to the radius, the fiber core diameter and the number of the single mode fibers which are actually connected.
In this embodiment, in order to connect to a plurality of single-mode fibers, the multicore multi-clad fiber 10 with a larger radius is used as a bridging fiber, and the radius of the second end of the multicore multi-clad fiber 10 is larger than that of the ordinary multicore fiber, so when the optical fiber coupler provided in this embodiment is used to connect to a multicore fiber, the second end needs to be tapered to match the diameter and the core pitch of the ordinary multicore fiber.
Further, in order to reduce the insertion loss after coupling connection, the mode field of each core 11 in the multi-core multi-clad fiber 10 needs to be matched with the mode field of the fiber connected with the multi-core multi-clad fiber. In order to ensure that the first end which does not need to be tapered matches with the mode field of each single-core single-mode fiber and the second end which needs to be tapered matches with the mode field of each fiber core of the multi-core fiber, a plurality of claddings with specific optical parameters and structures need to be wrapped outside each fiber core 11. As shown in fig. 4, which is an enlarged schematic cross-sectional view of each core 11 and its outer cladding in fig. 1, the outer cladding of each core 11 sequentially includes, from inside to outside: inner cladding 12, depressed inner cladding 13, annular cladding 14, outer cladding 15, depressed outer cladding 16, and mechanical cladding 17. After the second end of the multi-core multi-clad fiber 10 is tapered, the fiber core 11, the inner cladding 12, the sunken inner cladding 13 and the annular cladding 14 form a tapered fiber core, the outer cladding 15, the sunken outer cladding 16 and the mechanical cladding 17 form a tapered cladding, and the second end of the multi-core multi-clad fiber 10 is fused with the multi-core fiber after being tapered.
In order to ensure the optical performance of each cladding before and after tapering, the cladding outside each fiber core 11 of the multi-core multi-clad fiber 10 has a step-index profile structure, the refractive indexes inside the fiber core 11 and each cladding are uniformly distributed, and the refractive indexes are suddenly changed at the interfaces between the fiber core 11 and the inner cladding 12, and between each cladding and the adjacent cladding. The refractive index profile of each cladding layer is shown in fig. 5, and it can be seen that the refractive index inside each cladding layer remains uniform, but the refractive index changes abruptly at the interface of the respective layers. In fig. 5, the abscissa represents the radius interval of each structure in fig. 4, and the ordinate is a reference of relative value magnitude only and does not include specific numerical value meanings.
Further, as shown in FIG. 5, the depressed inner cladding 13 has a refractive index smaller than that of the core 11 and smaller than that of the inner cladding 12. Therefore, the depressed inner cladding 13 can be used as a channel to limit the field coverage when the fiber is bent, and prevent the field from leaking to the annular cladding 14, so that the multi-core multi-clad fiber 10 has small macrobending loss. The depressed outer cladding 16 has a refractive index smaller than that of the outer cladding 15, and can limit the field coverage and prevent the field from leaking to the outer cladding 15, so that the multi-core multi-clad fiber 10 and the multi-core fiber have small inter-core crosstalk after fusion splicing.
In order to provide optimal optical performance of the fiber coupler, the radius of each cladding of each core 11 is within a predetermined radius of the cladding, and the relative refractive index difference of each cladding of each core 11 is within a predetermined relative refractive index difference of the cladding. In the practical use of the embodiment of the present invention, the preset radius range and the preset relative refractive index difference range are determined according to the actual optical test result by referring to the factors of different coating materials, different preset minimum radii and different preset minimum core pitches of the multi-core multi-cladding optical, different processing accuracy, and the like, and the standard is that the best optical performance can be obtained after coupling.
A set of preset radius ranges and preset relative refractive index difference ranges are provided below. The range value is only an implementation example in a specific scenario, and any combination of materials, predetermined radius ranges and predetermined relative refractive index ranges that can achieve the best optical performance after coupling in different implementation scenarios is included in the protection scope of the embodiment of the present invention, and is not limited to the specific data provided in the embodiment. Although the embodiments of the present invention are not specifically illustrated, it is understood by those skilled in the art that the above parameter ranges can all make the prepared multi-core fiber coupler have an improvement over the prior art.
The fiber core 11 is a germanium-doped quartz glass layer, the radius R1 of the fiber core is 4.7-4.9 μm, and the relative refractive index difference delta 1 is 0.54-0.81%.
The inner cladding 12 is mainly doped with germanium, the radius R2 of the inner cladding is 10.2-10.6 μm, and the relative refractive index difference delta 2 is 0.21-0.48%.
The radius R3 of the depressed inner cladding 13 is 14.8-16.8 μm, and the relative refractive index difference delta 3 is-0.14%.
The annular cladding 14 is doped with germanium, has a radius R4 of 19.7-21.7 μm, and a relative refractive index difference Δ 4 of 0.23-0.50%.
The outer cladding 15 has a radius R5 of 30.0-35 μm and a relative refractive index difference Δ 5 of 0.0%.
The depressed outer cladding layer 16 is doped primarily with fluorine and has a radius R6 of 40.0 μm to 44.6 μm and a relative refractive index difference Δ 6 of-0.62% to-0.34%.
The mechanical cladding 17 has a radius R7 of 60.0 to 65.0 μm and a relative refractive index difference Δ 7 of 0.0%.
In this particular implementation scenario, the optimum predetermined radius range and the predetermined relative refractive index difference range determined experimentally are shown in table 1.
| Radius (mum) | Relative refractive index difference (%) | |
| |
4.8 | 0.68 |
| |
10.4 | 0.34 |
| Depressed |
15.8 | 0 |
| |
20.7 | 0.37 |
| |
32.5 | 0 |
| Depressed |
42.3 | -0.48 |
| |
62.1 | 0 |
TABLE 1
Furthermore, in order to ensure the optical performance after coupling and avoid the instability of optical signals caused by different light guide performance of fiber cores, the identity of each fiber core needs to be ensured in the preparation process of the multi-core multi-cladding optical fiber, so that the light guide performance of each fiber core is consistent.
On the other hand, the sleeve 20 only plays a role of auxiliary fixation, and does not relate to the optical characteristics after coupling, and the sleeve 20 may be overlapped with the part needing tapering, so that the sleeve is made of the material capable of tapering. In order to look over the position and the physique of the single mode fiber penetrating into the sleeve 20 during coupling, facilitate processing and reduce cost, the sleeve made of glass is preferably used in the scheme.
The optical fiber coupler provided by the embodiment uses the multi-core multi-clad optical fiber as the bridging optical fiber, so that the problem of high difficulty in cutting the optical fiber bundle of the conventional optical fiber coupler is solved, and the optical fiber coupler has high repeatability of the coupling process and is easy to realize. The refractive index of the sunken outer cladding of the multi-core multi-cladding optical fiber is smaller than that of the outer cladding, so that the coverage range of a field can be limited, the field is prevented from being leaked outwards, and the multi-core multi-cladding optical fiber has small crosstalk between cores after being welded. By matching the mode fields of the multi-core multi-cladding optical fiber and the standard single-mode optical fiber, the multi-core multi-cladding optical fiber and the standard single-mode optical fiber have low fusion loss during fusion.
Example 2:
on the basis of the optical fiber coupler provided in embodiment 1, this embodiment also provides an optical fiber coupling method, in which the optical fiber coupler provided in embodiment 1 is used to couple a single-mode optical fiber and a multi-core optical fiber.
As shown in fig. 6, the specific steps of the method for coupling optical fibers provided in this embodiment are as follows. After the following steps 101 to 103, the connection structure of the optical fiber coupler 1, the multi-core fiber 2 and the plurality of single-mode fibers 3 is shown in fig. 7, wherein the inside of the dashed frame is the whole structure of the optical fiber coupler 1.
Step 101: the optical fiber coupler 1 provided in one embodiment 1 was obtained.
In the optical fiber coupling method provided in this embodiment, the optical fiber coupler 1 provided in embodiment 1 is used to couple a single multi-core optical fiber 2 and a plurality of single-mode optical fibers 3. The length of the multi-core multi-clad fiber 10 used in the fiber coupler 1 is determined according to actual connection requirements, and after comprehensively considering the processing difficulty during coupling and the signal quality after coupling, the optimal length measured by experiments is 15cm-20 cm.
Step 102: tapering the second end of the multi-core multi-clad fiber 10 of the optical fiber coupler 1 to make the core interval of the second end of the multi-core multi-clad fiber 10 reach a preset core interval threshold, and fixing the second end of the multi-core multi-clad fiber 10 and the multi-core fiber 2.
In order to match the diameters of the plurality of single-mode fibers 3, the diameter and core pitch of the multi-core multi-clad fiber 10 in the fiber coupler 1 are larger than those of the multi-core fiber 2. Therefore, when the optical fiber coupler 1 is coupled with the multi-core optical fiber 2, one end of the multi-core multi-clad optical fiber 10 needs to be tapered, and in the tapering process, the diameter and the core pitch of the multi-core multi-clad optical fiber 10 are matched with those of the multi-core optical fiber 2 by controlling the tapering parameters, and the core mode field and the positions of the cores 11 of the multi-core multi-clad optical fiber 10 are also matched with those of the multi-core optical fiber 2. In actual use, a commercial large cladding diameter fiber tapering machine may be used, as it relates to the tapering of multi-core, multi-clad fibers. Furthermore, in order to obtain the best optical performance after coupling, the length of the tapered cone is not too long, and the too long tapered cone length can influence the protection packaging of the subsequent multi-core coupler, so that the volume of the multi-core coupler is increased; meanwhile, the length of the taper is not too short, and the mechanical properties of the cladding of the multi-core multi-cladding optical fiber 10 can be changed due to the too short length of the taper, so that light conducted in the optical fiber cannot be effectively constrained, and the loss of the device is increased. In a specific implementation, the length of the taper with the best optical performance can be selected according to actual test values. For example, in a specific implementation scenario, a seven-core fiber is coupled, the seven-core fiber has seven cores, wherein the center of the seven-core fiber has one core, the six surrounding cores occupy six corners of a regular hexagon, and the core pitch of the seven-core fiber is 42 μm; the core cloth of the multi-core multi-clad fiber 10 used in the fiber coupler 1 is identical to that of a seven-core fiber, and the core pitch is 125 μm. In the scene, the reference tapering ratio is 3 times, and the tapering length is 5-10 cm.
Further, in order to enable the optical signal of each core in the multi-core optical fiber 2 to be guided into one single-mode optical fiber 3 and ensure that the cores of the multi-core optical fiber 2 and the cores 11 of the multi-core multi-clad optical fiber 10 are distributed in the same manner, in a preferred embodiment of the present embodiment, the number of the cores 11 in the multi-core multi-clad optical fiber 10 is the same as the number of the cores of the multi-core optical fiber 2 to be coupled, so as to avoid that the cores cannot be aligned completely. In some special scenarios, the number of cores 11 in the multi-core multi-clad fiber 10 may not be the same as the number of cores of the multi-core fiber 2 to be coupled, as long as the cores to be signal-conducted can be aligned after tapering at the second end of the multi-core multi-clad fiber 10.
In order to ensure that the multi-core multi-clad fiber 10 is matched with the mode field of the multi-core fiber 2 after being tapered, when the multi-core multi-clad fiber 10 is tapered, the process parameters during tapering need to be adjusted so as to achieve the following process standards: the core 11, the inner cladding 12, the depressed inner cladding 13 and the annular cladding 14 before the second end of the multi-core multi-clad fiber 10 is tapered form a tapered core, and the outer cladding 15, the depressed outer cladding 16 and the mechanical cladding 17 before the second end of the multi-core multi-clad fiber 10 is tapered form a tapered cladding. According to the schematic diagram of relative refractive index of each cladding shown in fig. 5, and the predetermined radius range and the predetermined relative refractive index difference range provided in example 1, the depressed inner cladding 13 has a refractive index smaller than that of the core 11, the inner cladding 12, and the annular cladding 14. Therefore, the depressed inner cladding 13 can be used as a channel, the coverage range of a field can be limited when the optical fiber is bent, and the field is prevented from leaking to the annular cladding, so that the coupled optical fiber has small macrobending loss.
After the multi-core multi-clad fiber 10 is tapered, the diameter and the core pitch of the tapered second end of the multi-core multi-clad fiber 10 are consistent with the diameter and the core pitch of the multi-core fiber 2, and at this time, all fiber cores 11 at the tapered second end of the multi-core multi-clad fiber 10 are aligned with all fiber cores in the multi-core fiber 2, which need to be subjected to optical signal conduction, one by one, so that the coupling of the fiber coupler 1 and the multi-core fiber 2 can be completed.
After the fiber coupler 1 is aligned with the core of the multicore fiber 2, a fixed connection is also required. In specific implementation, a suitable connection mode can be selected according to actual needs, for example, various mechanical, chemical, electrical discharge and other methods are used for fixed connection. Preferably, in order to reduce signal attenuation after the fixed connection and to increase the strength of the fixed connection, the fixed connection is performed by a fusion splicing method, the second end of the drawn fiber of the multi-core multi-clad fiber 10 is cut, and the cut end surface is fused to the multi-core fiber 2.
Step 103: single-mode optical fibers 3 are inserted into the ferrules 20 of the optical fiber couplers 1, and each single-mode optical fiber 3 is aligned with and fixed to one core 11 of the multi-core multi-clad optical fiber 10.
When the fiber coupler 1 is coupled with the single-mode fibers 3, the number of the single-mode fibers 3 used is generally the same as the number of the cores 11 of the multi-core multi-clad fiber 10, or the number of the multi-core fibers 2 to be coupled, so as to ensure that the optical signal in each core of the multi-core fibers 2 is guided into one corresponding single-mode fiber 3. However, in some special scenarios, the number of single-mode fibers 3 smaller than the number of cores 11 of the multi-core multi-clad fiber 10 may be used as needed, and only the optical signals of a part of cores in the multi-core fiber 2 may be guided into the single-mode fibers 3.
Since a plurality of single-mode optical fibers 3 are used for coupling, a sleeve 20 may be used for auxiliary fixing in order to facilitate fixing and alignment. Each single mode fiber 3 is sequentially inserted into the ferrule 20, aligned with the core 11 of one multi-core multi-clad fiber 10, and fixed. In a specific implementation, as shown in fig. 8, the following steps may be used to align and fix each single mode fiber 3 with one core 11 of the multicore multi-clad fiber 10.
Step 201: a single mode optical fiber 3 is passed through a ferrule 20 coupled and fixed to the multi-core multi-clad optical fiber 10.
Since the sleeve 20 is sleeved outside the multi-core multi-clad fiber 10 and is coupled and fixed with the multi-core multi-clad fiber 10, the auxiliary positioning and the primary fixing of the single-mode fiber 3 can be performed by means of the sleeve 20. The single mode fiber 3 is inserted into the sleeve 20 to complete the initial positioning, and then the fiber core of the single mode fiber 3 is aligned to any fiber core 11 through the precise positioning, so that the coupling of the single mode fiber 3 and one fiber core 11 of the multi-core multi-clad fiber 10 can be completed. Specifically, in order to facilitate fine adjustment of the alignment of the single-mode optical fibers 3 and the fiber core 11, each single-mode optical fiber 3 may be preliminarily fixed and positioned by using a six-dimensional adjusting frame or other position fine-adjusting device.
Step 202: the single-mode optical fiber 3 is aligned with one core 11 of the multi-core multi-clad optical fiber 10, and then fixed after alignment.
After the alignment of each single-mode fiber 3 is completed, the single-mode fibers 3 need to be fixed, and a specific fixing method can be selected according to process requirements and performance requirements after coupling. Since the single-mode optical fiber 3 has been inserted into the sleeve 20 and other single-mode optical fibers 3 are present around the single-mode optical fiber, the single-mode optical fiber is preferably fixed by using a glue dispensing method in order to simplify the process and reduce the influence on other surrounding single-mode optical fibers 3.
Through steps 201 to 202, the alignment and fixation of one single-mode optical fiber 3 can be completed, and the coupling of the single-mode optical fiber 3 and one fiber core 11 is realized. And step 201 and step 202 are sequentially completed for each single-mode fiber 3 to be coupled, so that alignment and fixation of all the single-mode fibers 3 and each fiber core 11 of the multi-core multi-clad fiber 10 can be completed. After all the single-mode fibers 3 are sequentially stacked, penetrated and fixed in the sleeve, the fiber core mode field and the fiber core position of each single-mode fiber 3 are matched with the fiber core mode field and the fiber core position of the multi-core multi-cladding fiber 10.
Further, in order to improve the alignment efficiency, the alignment procedure of the optical fiber fusion splicer itself may be adopted to simultaneously align the plurality of single-mode optical fibers 3, and align the corresponding cores of the multi-core multi-clad optical fiber 10 and the single-mode optical fibers 3, so that the alignment loss of each core is minimized.
Since some multi-core fibers 2 or single-mode fibers 3 are coated with a coating layer, in order to facilitate cutting and to facilitate matching the diameter of the multi-core fibers 2 or single-mode fibers 3 with the core pitch of the multi-core multi-clad fiber 10, before aligning and fixing the multi-core fibers 2 and the single-mode fibers 3 with each of the cores 11 of the multi-core multi-clad fiber 10, it is necessary to peel off the coating layer of each of the multi-core fibers 2 and the single-mode fibers 3 and complete fiber cleaning. In the specific implementation, in order to avoid the damage to the surface of the optical fiber caused by the stripping and cleaning processes as much as possible and to weaken the strength of the optical fiber and influence the subsequent steps, the coating layer can be stripped by using a commercial optical fiber stripping device.
On the other hand, in order to reduce the signal attenuation after coupling and improve the coupling accuracy, in some scenarios, the multi-core multi-clad fiber 10, the multi-core fiber 2, or the single-mode fiber 3 needs to be cut appropriately to obtain a flat end face. In implementations where there may be large-sized fiber cleaving, the fiber end faces may be cleaved using commercially available large cladding diameter fiber cleavers or fiber cleavers.
Through steps 101 to 103, the optical fiber coupler provided in embodiment 1 is used to simply complete low-loss fusion with a single-mode optical fiber, and the low-loss fusion with a multi-core optical fiber is completed through a micro-tapering method. After the coupling is completed, the specific connection structure of the fiber coupler 1, the multi-core fiber 2 and the single-mode fiber 3 is shown in fig. 9. By using the optical fiber coupling method provided by the embodiment, the process difficulty of the steps of cutting, aligning, fixing and the like in optical fiber coupling is low, the loss of the optical fiber coupler is small, and the attenuation of coupled signals is reduced.
Further, in order to verify the connection accuracy and ensure the coupled signal quality, after aligning the fiber core of the multi-core fiber 2 or the fiber core of each single-mode fiber 3 with the fiber core 11 of the multi-core multi-clad fiber 10 in steps 102 and 103, a signal attenuation test procedure may be performed, or an alignment accuracy test may be performed in other manners, a more precise position adjustment may be performed on the multi-core fiber 2 or the single-mode fiber 3 according to the test result, and after finding the optimal alignment position, the fixation may be performed to ensure that the coupled fiber performance reaches the optimal one.
In steps 102 and 103, the specific welding mode may be electrode discharge welding, graphite heating welding, or other welding modes meeting the requirements of process and material. In the specific implementation process, the parameters of the optical fiber fusion splicer with the lowest fusion loss can be found by testing the variation condition of the fusion loss under different fusion parameters, and the fusion coupling of the optical fibers is carried out according to the parameters.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (10)
1. An optical fiber coupler, characterized by:
comprises a multi-core multi-clad fiber (10) and a sleeve (20);
a first end of the multi-core multi-clad fiber (10) is coupled to the ferrule (20);
the multicore multi-clad fiber (10) comprises at least two cores (11), and the cladding outside each core (11) sequentially comprises from inside to outside: an inner cladding (12), a depressed inner cladding (13), an annular cladding (14), an outer cladding (15), a depressed outer cladding (16) and a mechanical cladding (17);
the radius of the outer surface of the multi-core multi-cladding optical fiber (10) is larger than the preset minimum radius, and the core distance between any two fiber cores (11) is larger than the preset minimum core distance.
2. The fiber optic coupler of claim 1, wherein: the depressed inner cladding (13) has a refractive index less than that of the core (11), the depressed inner cladding (13) has a refractive index less than that of the inner cladding (12), and the depressed outer cladding (16) has a refractive index less than that of the outer cladding (15).
3. The fiber optic coupler of claim 1, wherein: the cladding outside each core (11) of the multi-core multi-cladding fiber (10) is of a step-index profile.
4. The fiber optic coupler of claim 1, wherein: the radius of each cladding is within a predetermined radius of the cladding, and the relative refractive index difference of each cladding is within a predetermined relative refractive index difference of the cladding.
5. The fiber optic coupler of claim 1, wherein: the performance of each core (11) of the multi-core multi-cladding optical fiber (10) is the same.
6. A method of optical fiber coupling, comprising:
obtaining a fiber coupler (1) as provided in claims 1-5;
tapering a second end of the multi-core multi-clad fiber (10) of the fiber coupler (1) to enable the core spacing of the second end of the multi-core multi-clad fiber (10) to reach a preset core spacing threshold value, and fixing the second end of the multi-core multi-clad fiber (10) and the multi-core fiber (2);
single mode fibers (3) are inserted into a sleeve (20) of the optical fiber coupler (1), and each single mode fiber (3) is aligned with and fixed to one fiber core (11) of the multi-core multi-cladding fiber (10).
7. The method according to claim 6, wherein tapering the second end of the multicore multi-clad fiber (10) of the fiber coupler (1) comprises: the fiber core (11), the inner cladding (12), the sunken inner cladding (13) and the annular cladding (14) of the multi-core multi-cladding fiber (10) before tapering the second end form the fiber core after tapering, and the outer cladding (15), the sunken outer cladding (16) and the mechanical cladding (17) of the multi-core multi-cladding fiber (10) before tapering the second end form the cladding after tapering.
8. The method according to claim 6, wherein the fixing the second end of the multi-core multi-clad fiber (10) to the multi-core fiber (2) comprises: and cutting the second end of the multi-core multi-cladding optical fiber (10), and welding the cut end face with the multi-core optical fiber (2).
9. The method of claim 6, wherein before aligning and fixing each single mode fiber (3) with one core (11) of the multi-core multi-clad fiber (10), further comprising: stripping off the coating layer of each single mode optical fiber (3) and cutting the single mode optical fiber (3).
10. The method of optical fiber coupling according to claim 6, wherein each single mode fiber (3) is aligned and fixed with one core (11) of the multicore multi-clad fiber (10), specifically comprising:
a single-mode optical fiber (3) is inserted into the sleeve (20);
aligning the single-mode optical fiber (3) with one fiber core (11) of the multi-core multi-cladding optical fiber (10), and fixing after aligning;
and sequentially finishing the alignment and fixation of all the single-mode optical fibers (3) and each fiber core (11) of the multi-core multi-cladding optical fiber (10).
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