| Terahertz technology has been recognized as one of the most emerging scientific and technological fields in the 21st century.Photonic crystal fibers have attracted widespread attention due to their unique advantages,such as high birefringence,large mode area,low loss and controllable chromatic dispersion.In this paper,based on the theory of effective element method,perfect matching layer theory and equivalent refractive index principles,novel photonic crystal fibers with cyclic-olefin copolymer?COC?matrix material and cladding of circular air holes in hexagonal lattice structure are designed.Reasonable parameters and structure are optimized according to the method of optical fiber manufacturing.The influence of these optical photonic fibers on the transmission characteristics in the terahertz band is analyzed in detail.The research results provide reference for designing novel Thz photonic crystal fibers.The main contents are as follows:1.High birefringence was achieved by the diamond-shaped air holes in the core region.The effects of the number of cladding layers,the air filling rate and the ratio of the diagonal lengths of the diamonds on birefringence,confinement loss and absorption loss were investigated.When the ratio of the diamond diagonal was 2.5with the number of claddings is 5 and the air-filling ratio of the cladding is 0.75,the available birefringence value would be up to 9.59×10-3 with the operating frequency of 1.0 THz.Meanwhile,the confinement loss is at a minimum of 2.28×10-4 dB/m with the balance between confinement loss and birefringence.The change of dispersion with frequency is also studied.The results show that the dispersion is flat at the frequency of 1.2-1.6 THz,which provides a theoretical basis on single-polarization single-mode photonic crystal fiber.2.The new photonic crystal fiber with two different sizes of diamond air holes in core region are investigated,while the cladding are still in regular hexagonal lattice structure.As shown in simulation,the single-polarization single-mode transmission in the terahertz band can be achieved in the designed photonic crystal fibers.When the ratio of the diamond in the core decreases,the single-polarization single-mode transmission range will shift to the high frequency band.The single-polarization single-mode transmission can be achieved in the 0.73-1.5 THz frequency ranges with bandwidth of 0.67 THz.At this time the confinement loss is a minimum of 4.537×10-5 dB/m at 0.73 THz.Besides,the effective mode area is at the peak of 6.025um2at frequency of 1.4 THz,and the variation of the effective mode area is small.This achievement has great significance for the future research of the design of single-polarization single-mode photonic crystal fiber.It also provides a reference for the application of single-polarization single-mode photonic crystal fiber in optical communications. |
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