CN116990908A - Multi-core fiber-to-core exchange coupler based on self-focusing optical fiber reflector - Google Patents
Multi-core fiber-to-core exchange coupler based on self-focusing optical fiber reflector Download PDFInfo
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- CN116990908A CN116990908A CN202310820917.5A CN202310820917A CN116990908A CN 116990908 A CN116990908 A CN 116990908A CN 202310820917 A CN202310820917 A CN 202310820917A CN 116990908 A CN116990908 A CN 116990908A
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- 239000013307 optical fiber Substances 0.000 title claims abstract description 85
- 239000000835 fiber Substances 0.000 claims abstract description 115
- 230000008878 coupling Effects 0.000 claims abstract description 32
- 238000010168 coupling process Methods 0.000 claims abstract description 32
- 238000005859 coupling reaction Methods 0.000 claims abstract description 32
- 238000003466 welding Methods 0.000 claims abstract description 7
- 238000007747 plating Methods 0.000 claims abstract description 3
- 230000007704 transition Effects 0.000 claims description 14
- 238000009826 distribution Methods 0.000 claims description 13
- 230000003287 optical effect Effects 0.000 description 8
- 230000005540 biological transmission Effects 0.000 description 7
- 230000005855 radiation Effects 0.000 description 6
- 238000004088 simulation Methods 0.000 description 6
- 230000000694 effects Effects 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 238000005253 cladding Methods 0.000 description 3
- 238000004519 manufacturing process Methods 0.000 description 3
- 238000004891 communication Methods 0.000 description 2
- 230000001808 coupling effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 239000010931 gold Substances 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000004927 fusion Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
Classifications
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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
- G02B6/262—Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
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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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Abstract
The invention discloses a multi-core fiber-core exchange coupler based on a self-focusing optical fiber type reflector, which comprises a multi-core fiber 1, a graded-index multi-mode fiber (self-focusing fiber) 2, a coreless fiber 3 and a total reflection film 4; the multi-core fiber-core exchange coupler is formed by welding a section of graded-index multimode fiber and a section of coreless fiber with multi-core fibers, and then plating a layer of total reflection film on the end face of the flattened coreless fiber; the invention discloses a multi-core fiber-core exchange coupler based on a self-focusing optical fiber reflector, which realizes low-loss coupling among multi-core fiber cores and can be used for multi-core fiber sensors and the like.
Description
Technical Field
The invention relates to a multi-core fiber-core exchange coupler based on a self-focusing optical fiber reflector, which reduces the connection loss between cores and improves the coupling efficiency, can be used for multi-core fiber sensors and the like, and relates to the field of fiber integrated devices.
Technical Field
In the decades of development of optical fiber communication, in order to increase the communication capacity and improve the quality of a data transmission system, the space division multiplexing multi-core optical fiber plays a very important role, and by utilizing the special optical fiber property of the multi-core optical fiber, the multi-core optical fiber is also designed in an optical device, and a module system is formed by combining different optical fibers, so that the space division multiplexing multi-core optical fiber can be applied to different occasions to meet requirements.
The multi-core optical fiber coupler is one of many optical devices, which is a device for connecting optical fibers, so that the optical energy output by the transmitting optical fiber can be coupled into the receiving optical fiber to the maximum extent, and the optical energy can be inserted into an optical link, thereby minimizing the influence on a system.
Most multi-core fiber couplers adopt a fusion tapering method to enable the coupled fiber cores to be close, and the tapering area forms a coupling area, so that the mode has higher requirements on experimental equipment, the loss is not easy to grasp, and the coupling efficiency is relatively unstable. The patent "arc cone fiber end total reflector based on multi-core optical fiber and its preparation method" based on multi-core optical fiber, CN 113671632A, discloses an arc cone fiber end total reflector based on multi-core optical fiber, the fiber end of symmetrical multi-core optical fiber has parabolic arc reflection cone truncated cone, the light wave in the peripheral fiber core of multi-core optical fiber is reflected by the arc cone truncated cone to the symmetrical fiber core for reverse transmission with low loss, the coupling efficiency of the method is obviously improved, but the preparation mode requires higher precision.
The invention welds the graded-index multimode fiber (self-focusing fiber) after the multi-core fiber, uses the optical characteristics to control the beam expansion and collimation effects, and then reflects the multi-core fiber back to the symmetrical fiber core so as to achieve the optimal coupling efficiency.
Disclosure of Invention
The invention aims to provide the multi-core optical fiber inter-core exchange coupler which has high integration level, small device size and relatively low manufacturing cost, realizes low-loss connection among multi-core optical fiber cores, and has large coupling tolerance and relatively high coupling efficiency.
The purpose of the invention is realized in the following way:
the exchange coupler between the cores of the multi-core optical fibers is formed by welding the output end of the multi-core optical fibers with the input end of the graded-index multimode optical fibers, welding the output end of the graded-index multimode optical fibers with the input end of the transition optical fibers, and plating a total reflection film on the output end face of the cut-flat transition optical fibers.
The fiber cores of the multi-core optical fiber are distributed into single-mode fiber cores which are symmetrically distributed. Fig. 1 shows two typical symmetric core distribution multicore fibers, namely a symmetric twin core fiber (a) and a square quad core fiber (b).
The refractive index distribution of the fiber core of the graded-index multimode fiber is raised in the center, the refractive index is gradually reduced along the radial direction, the fiber core beam of the multi-core fiber is approximately parabolic, after entering the graded-index multimode fiber, the off-axis Gaussian mode field output by the fiber core is subjected to beam expansion collimation, and the emergent beam at the emergent end is a section of inclined parallel beam.
The refractive index of the transition optical fiber is 1.4-1.5, and the transition optical fiber has the function of finely adjusting the light fields of the incident light beam and the emergent light beam reflected back to the symmetrical optical fiber, so that the coupling efficiency of the device is improved; the output end face of the transition optical fiber is plated with a layer of total reflection film, so that the light beam at the input end is totally reflected back to the symmetrical multi-core optical fiber core.
The invention has the advantages that:
(1) The input and output are realized in one multi-core optical fiber, so that the connection loss between the optical fibers can be reduced, the coupling efficiency can be improved, and the coupling tolerance is large.
(2) The structure is simple and compact, the manufacturing method is easy, the coupling efficiency is high, and the cost is low.
Drawings
Fig. 1 shows two typical symmetric core distribution multicore fibers, namely a symmetric twin core fiber (a) and a square core distribution quad core fiber (b).
Fig. 2 (a) is a schematic structural view of a dual-core optical fiber inter-core exchange coupler, and fig. 2 (b) is a schematic structural view of an optical path section of the dual-core optical fiber inter-core exchange coupler.
Fig. 3 (a) is a core refractive index profile of a graded-index multimode fiber, and fig. 3 (b) is a schematic cross-sectional view of the refractive index profile of the graded-index fiber.
Fig. 4 is a graph of ray trace simulation results of an exchange coupler between cores of a multicore fiber in a graded-index fiber.
Fig. 5 is a graph of the simulation results of the probability scan of radiation transmission in a graded index fiber.
Fig. 6 (a) is a graph showing a refractive index distribution of a step-index optical fiber, and fig. 6 (b) is a graph showing a simulation result of a radiation transmission probability scan of a change in the length of the step-index optical fiber.
FIG. 7 is a graph of the misalignment error between the x-axis and y-axis of a multicore fiber.
FIG. 8 is a graph of normalized coupling efficiency for x, y axial alignment errors of a multi-core fiber end-to-core coupler.
Fig. 9 is a schematic diagram of a total reflection end face tilt angle profile of a multi-core fiber-optic end-core coupler.
Fig. 10 is a graph of tilt angle normalized coupling efficiency for a multi-core fiber end-to-core coupler.
Detailed Description
Specific examples are given below in conjunction with the drawings to further illustrate how the present invention may be practiced.
The multi-core fiber end-core coupler provided by the invention is suitable for any multi-core fiber structure with symmetrical fiber core distribution. Taking a symmetrical dual-core optical fiber as shown in fig. 1 (a) as an example, the cross-section structure of the inter-core exchange coupler is shown in fig. 2, and the coupling connection between the cores is realized by welding the graded-index multimode optical fiber, the transition optical fiber and the plated total reflection film to enable the outgoing light beam of the a core to return to the symmetrical b core.
Similarly, the square four-core optical fiber of fig. 1 (b) can also realize the coupling connection among the four fiber cores of a core and b core, a core and c core, b core and d core, c core and d core through the structure, and the coupling mode can customize the incident fiber core and the emergent fiber core according to the requirement.
The following describes embodiments and significant effects of the present invention using a symmetrical twin-core optical fiber as an example.
Fig. 2 is a schematic structural diagram of a double-core fiber-core exchange coupler, which consists of a double-core fiber 1, a graded-index multimode fiber 2, a transition fiber 3 and a total reflection film 4.
Example 1: the distance between the core and the center of the dual-core optical fiber 1 is d0=46 μm, the core diameter is 9 μm, the refractive index of the core is n1=1.462, and the refractive index of the cladding is n2=1.457.
A graded-index multimode fiber 2 is welded after the dual-core fiber 1, the fiber core diameter of the graded-index multimode fiber 2 is 105 μm, the fiber core refractive index is raised at the center, the refractive index gradually decreases along the radial direction, the distribution is approximately parabolic, the fiber core central refractive index is n0=1.475, the cladding refractive index is n2=1.457, and the refractive index distribution is shown in fig. 3; the graded-index multimode fiber has a pitch for focusing the light beam, and when the Gaussian light beam deviating from the axis enters the graded-index multimode fiber, the emergent light beam is a parallel light beam deflected by a certain angle at the position with a pitch of 1/4, and the optimized efficiency is achieved at the moment, and the length is L1=360 mu m.
The transition optical fiber 3 is a coreless optical fiber, and is welded at the exit end of the graded-index multimode optical fiber 2, and has a refractive index n2=1.457 and a length l2=10 μm.
A layer of total reflection film 4 is plated at the output end of the cut transition optical fiber 3, and a gold film is plated.
As shown in the simulation result figure 4, an incident beam is arranged at the incident position of the a core of the dual-core optical fiber, is collimated and propagated to the total reflection gold film in the coreless optical fiber and then returns to the graded-index multi-mode optical fiber after being expanded and collimated by the graded-index multi-mode optical fiber core, and the reflected beam is converged into the position of the b core of the symmetrical dual-core optical fiber to achieve the coupling purpose, so that the feasibility of the inter-core exchange coupling is seen.
Wherein the refractive index distribution expression of the graded-index multimode fiber follows a square distribution law:
where r is the distance of the light ray from the radial center axis, n0 is the refractive index of the core center axis, a is the focusing factor, and n0=1.475 and a= 0.000017 are set.
The graded-index multimode fiber has periodicity (pitch) on focusing action of light beams, the pitch is only related to refractive index distribution, namely only related to focusing coefficient, and when the length of the fiber is at a position of 1/4 pitch, the graded-index multimode fiber has good focusing effect, so that when the length of the graded-index multimode fiber is set, the length of the fiber is L1=360 mu m, at the moment, incident light of an incident end fiber core can be reflected back to a symmetrical emergent end fiber core with maximum efficiency, and the minimum loss and the optimal coupling efficiency are realized. The simulation parameter scanning result of fig. 5 shows that when the length of the graded-index optical fiber is 360 μm after the length of the fixed coreless optical fiber is l2=10μm, the radiation transmission probability is maximum, and meanwhile, the length tolerance of the graded-index optical fiber can be seen to be better.
Example 2: a graded-index multimode fiber 2 was fusion-spliced after the twin-core fiber 1, and the graded-index multimode fiber 2 was the same as in example 1. A transition fiber 3 is fused to the exit end of the graded-index fiber 2 to form a step-index fiber, the refractive index distribution of which is shown in fig. 6 (a), the core diameter of which is 50 μm, the core refractive index of which is n3=1.463, and the cladding refractive index of which is n2=1.457.
The optimal transmission coupling efficiency is obtained by adjusting the length of the optical fiber through length scanning, and in the simulation parameter scanning result, as shown in fig. 6 (b), when the length of the graded-index optical fiber is l1=340 μm and the length of the step-index optical fiber is l2=8 μm, the radiation transmission probability can reach 80%.
The coupling tolerance characteristic analysis of the multi-core fiber end-core coupler is performed below.
In the multi-core fiber end-core coupler, the paths of light beam coupling are all completed in the same graded-index multi-mode fiber, namely that the overlapped coupling areas in the fiber cores of the graded-index multi-mode fiber are identical, and under the condition of fixing the focusing coefficient of the graded-index fiber, the axial offset of the single-mode fiber core of the graded-index multi-mode fiber needs to be considered. The multi-core optical fiber used in the multi-core optical fiber end-core coupler is formed by combining single-mode optical fibers, the diameter of the single-mode optical fibers is 9 mu m, the alignment error existing between the optical fibers is necessary to generate the connection coupling loss of optical power, the general alignment tolerance is required to be within 1 mu m, and otherwise, the mismatching of the radiation cone of the incident optical fiber and the receiving radiation cone of the receiving optical fiber can occur. The magnitude of the connection loss and the coupling efficiency depend on the degree of misalignment of the cores of the two fibers.
In the process of manufacturing the symmetrical multi-core optical fiber, the problem of eccentricity of the fiber core is always unavoidable, that is, the symmetrical fiber core is not completely symmetrical, and as shown in fig. 7, for example, the distance between the core of the theoretically symmetrical multi-core optical fiber and the center of the fiber core of the double-core optical fiber is offset by Δx of the x-axis or by Δy of the y-axis.
Fig. 8 is a graph of normalized x, y axial alignment error coupling efficiency, where the core radius of the multicore fiber, m=4.5 μm, the x axial alignment error may be expressed as s=Δx/m, the y axial alignment error may be expressed as t=Δy/m, and t indicates that there is an axial offset in the end-core coupler of the multicore fiber. From this curve, it is found that the coupling efficiency can be 83% or more when the x-axis offset Δx does not exceed 1 μm, and 87% or more when the y-axis offset Δy does not exceed 1 μm, and a remarkable effect can be seen.
As can be seen from fig. 8, the inter-core coupler of the multi-core fiber has a better tolerance characteristic for the core offset, and the tolerance coupling effect is better.
And the optical fibers of the multi-core optical fiber end-core coupler are formed by welding after being cut and flattened, and if the reflecting end surface is cut and not flattened, the reflecting end surface is inclined, so that the coupling efficiency is reduced. As shown in fig. 9, after the graded-index multimode fiber 2 and the transition fiber 3 are welded, the cut end face is uneven, and after the end face is coated with the total reflection film, the inclination angle Θ appears, however, the inclination angle may be inclined to the x-axis direction or may be inclined to the y-axis direction, and fig. 10 is a normalized graph of the influence of the inclination angle Θ of the end face total reflection mirror on the coupling efficiency, it can be obviously seen that the inclination angle has a larger influence on the coupling effect, so that in the remanufacturing process, the smooth cutting of the end face should be ensured as much as possible, and the coupling loss is within 1dB when the inclination angle Θ is less than 0.5 °.
In the description and drawings, there have been disclosed typical embodiments of the invention. The present invention is not limited to these exemplary embodiments. The specific terms are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being protected.
Claims (4)
1. A multi-core fiber-to-core exchange coupler based on a self-focusing optical fiber reflector is characterized in that: the exchange coupler between the cores of the multi-core optical fibers is formed by welding the output end of the multi-core optical fibers with the input end of a graded-index multimode optical fiber (self-focusing optical fiber), welding the output end of the graded-index multimode optical fiber with the input end of a transition optical fiber, and plating a total reflection film on the output end face of the cut-flat transition optical fiber; one end fiber core of the multi-core fiber is used as an incident fiber core, an incident light beam enters the graded-index multimode fiber, enters the coreless fiber and is transmitted to the end face, enters the graded-index multimode fiber again after being reflected by the total reflection film, and enters the other symmetrical end fiber of the multi-core fiber as an emergent fiber core after passing through a symmetrical light path, so that exchange coupling among the cores of the multi-core fiber is realized.
2. The self-focusing fiber mirror-based multi-core fiber-to-core exchange coupler of claim 1, wherein: the fiber cores of the multi-core optical fiber are distributed into single-mode fiber cores which are symmetrically distributed.
3. The self-focusing fiber mirror-based multi-core fiber-to-core exchange coupler of claim 1, wherein: the refractive index distribution of the fiber core of the graded-index multimode fiber is raised in the center, the refractive index is gradually reduced along the radial direction, the fiber core beam of the multi-core fiber is approximately parabolic, after entering the graded-index multimode fiber, the off-axis Gaussian mode field output by the fiber core is subjected to beam expansion collimation, and the emergent beam at the emergent end is a section of inclined parallel beam.
4. The self-focusing fiber mirror-based multi-core fiber-to-core exchange coupler of claim 1, wherein: the refractive index of the transition optical fiber is 1.4-1.5, and the output end face of the optical fiber is plated with a layer of total reflection film.
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| CN202310820917.5A CN116990908A (en) | 2023-07-06 | 2023-07-06 | Multi-core fiber-to-core exchange coupler based on self-focusing optical fiber reflector |
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| CN202310820917.5A CN116990908A (en) | 2023-07-06 | 2023-07-06 | Multi-core fiber-to-core exchange coupler based on self-focusing optical fiber reflector |
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- 2023-07-06 CN CN202310820917.5A patent/CN116990908A/en active Pending
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