EuroWire January 2022

Technical Article

From the refractive index distribution profile and the microscopic graph of MCF ( Figure 2 ), 19 cores are evenly distributed in the cladding. The refractive index of each core region is perfectly coherent with our original design. Conclusion In this paper, we prepare the 19-core MCF with trench-assisted structure. The core diameter and the inter-core distance in MCF are 7.6μm and 35μm, respectively. The geometric position control contributes to the proper separation between different cores in MCF, which therefore lowers the inter- core crosstalk in the MCF.

Figure 2 : 19-core MCF refractive index distribution profile

It should be noted that PCVD is commonly used in preparing complex and fine refractive index structure. The fluorine doping in PCVD guarantees a high concentration of fluorosilicate so that the refractive index of trench structure is able to confine the light power from escaping to the cladding. The core preforms were elongated to the expected diameter to fit in the MCF tube, using oxyhydrogen flame or induction furnace. For the assembly of the MCF preform, careful manipulation is required to avoid component collision or any misplacement. Firstly, both the tube and the core preforms were cleaned with a mixture of hydrofluoric acid and nitric acid for two to three hours. Secondly, the preforms and tube were dried in a clean room at 60~80°C. Thirdly, the MCF tube was vertically fixed and the core preforms were placed in separated holes of MCF tube. Finally, the MCF tube was carefully sealed with Teflon packing in case of any contamination. The drawing of MCF was realised by the online drawing technique, in which the core preforms and the MCF tube were directly drawn to obtain MCF. The formation of the drawing cone in the furnace contributed to the fusion of core preforms and MCF tube. Thus, a low-pressure environment was necessary inside the MCF tube. The coating and curing processing of MCF is similar to commercial optical fibre. The drawing speed and drawing tension are 250m/ min and 170g, respectively. A proper set of drawing parameters can positively stabilise the RI structure of the core preform. Multi-core fibre characterisation The 19-core MCF characterisation mainly focuses on the fibre structural test. The core diameter is identical to each of the 19 cores, of which the average value observed is 7.6μm. The diameter of the trench structure surrounding the core region is 27μm. From the refractive index distribution profile of 19-core MCF, the refractive index difference of the core and the trench are 0.39 per cent and -0.33 per cent, respectively. The inter-core distance of the 19-core MCF is 35μm. Though the claddingdiameter of 19-coreMCF is 250μm, the tapering sample of the MCF with a diameter of 178μm is demonstrated in the distribution profile. The coating material is acrylate-based polymer and the diameter of the outer coating of MCF is 345μm.

References

[1] Miyamoto Y, Shibahara K, Mizuno T, et al. Mode-Division Multiplexing Systems for High-Capacity Optical Transport Network[C]//2019 Optical Fiber Communications Conference and Exhibition (OFC). IEEE, 2019: 1-3. [2] Hayashi T, Taru T, Shimakawa O, et al. Design and fabrication of ultra- low crosstalk and low-loss multi core fiber. Optics Express, 2011, 19(17): 16576~16592.

Courtesy of IWCS Cable & Connectivity Symposium, Charlotte, North Carolina, USA

FiberHome Telecommunication Technologies Co, Ltd No 6, Gaoxinsilu, East Lake, High-Tech Development Zone Wuhan, Hubei Province, China www.fiberhome.com Wuhan Research Institute of Posts and Telecommunications Wuhan University, Hubei, China https://en.whu.edu.cn

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January 2022