Simulation Design And Polarization Filtering Characteristics Of Hollow-core Anti-resonant Fiber

With the continuous development of science and technology,human beings have en-tered the information age based on the Internet,the Internet of Things and artificial intelli-gence.Optical fiber has become a research hotspot in the information age due to its advan-tages of fast transmission speed and large information capacity.Optical fiber can not only transmit information but also perceive changes in information.Optical devices based on opti-cal fiber have developed rapidly due to their advantages of anti-electromagnetic interference and electrical insulation.Compared with traditional optical fibers,hollow-core anti-resonant fibers（HC-ARFs）have attracted extensive attention due to their low loss transmission,large effective mode field area and infinite cut-off single-mode transmission characteristics.With the deepening of research,HC-ARF has been widely used in optical fiber communication,optical fiber sensing and optical fiber filtering due to its excellent optical properties.How-ever,the preparation of optical fiber is still a key factor hindering its further development.Therefore,how to design a HC-ARF with simple structure,easy preparation and good trans-mission characteristics has become a difficult problem for researchers to overcome.In this paper,HC-ARF with simple structure and low loss transmission based on chalcogenide glass is designed by using COMSOL Multiphysics software and full vector finite element method（FV-FEM）.At the same time,a chalcogenide HC-ARF filter with excellent filtering charac-teristics is proposed based on the principle of surface plasmon resonance（SPR）.The specific arrangements are as follows:Firstly,a HC-ARF based on chalcogenide glass is proposed.In order to reduce the difficulty of preparation,six non-contact capillaries with the same structural parameters are set in the inner cladding of the fiber structure.Low loss performance and large effective mode area characteristics are achieved by optimizing the fiber structure parameters.The fiber can maintain low loss transmission in the range of 0.6～6μm,especially at 4.3μm,the confinement loss is reduced to 2.98×10^-8d B/m;the fiber maintains a large effective mode field area at 0.6～6μm,especially when the wavelength is 2.9μm,the effective mode area reaches the order of 10⁴μm²,which is beneficial to high power laser transmission.Secondly,based on the optimization parameters in the previous section,a HC-ARF composed of elliptical capillaries is designed.The simulation results show that the ellip-tical sleeve fiber structure is easier to promote the single-mode performance of the fiber than the circular sleeve fiber structure.The simulated elliptical capillary fiber structure can achieve single-mode transmission at 3～5μm.At 4.3μm,the high-order mode extinction ratio（HOMER）reaches 19032.26,while the circular capillary fiber structure only achieves single-mode transmission within 3.8～4μm and 4.5～4.9μm,and the highest HOMER is6229.45.Numerical results show that the HC-ARF studied in this paper can greatly ensure the purity of the mode.Thirdly,an infrared HC-ARF filter based on chalcogenide glass with low loss single-mode single-polarization transmission near 4μm is proposed and studied.Its performance is numerically simulated by FV-FEM.The results show that the fiber has good single-mode single-polarization characteristics in the wavelength range of 3.99～4μm.Especially at the wavelength of 4μm,the polarization extinction ratio（PER）and HOMER reach 491 and649,respectively,indicating that its polarization performance has good stability.At the same time,it has low loss transmission characteristics.In the range of 3.92～4.01μm,the x-polarized fundamental mode（FM）can be maintained in a flat and low loss anti-resonant region for transmission.Especially at the wavelength of 4μm,the loss of the x-polarized FM is only 1.8×10^-4d B/m;the fiber also has good bending resistance,and the bending loss is always less than 10^-3d B/m under single-mode single-polarization transmission.The infrared HC-ARF not only has broad application prospects in mid-infrared communication and medical systems,but also provides a potential choice of pure light source for quantum cascade detectors operating in the 4μm band.Finally,a broadband wide-band HC-ARF based on SPR effect is designed.The sub-strate material is As₄₀S₆₀,which is developed by Xi’an Institute of Optics and Precision Mechanics.The glass has low intrinsic loss and good chemical stability in the mid-infrared band,which is conducive to the realization of low loss performance of optical fiber.At the same time,the advantages of large mode field area,flexible structure and high design freedom make it more convenient for HC-ARF to be coated and filled.By continuously optimizing the structural parameters,the confinement loss of the x-polarized FM reaches1917.24 d B/m,while the confinement loss of the y-polarized FM is 23.11 d B/m.When the transmission length is 8 mm,the extinction ratio（ER）reaches 131.6174 dB.