Designs And Applications Of Novel Hollow-core Anti-resonant Fiber

Hollow-core anti-resonant fiber provides a new solution for solving the bottleneck problems in the systems of fiber communication,fiber sensing,high-power laser delivery,and terahertz wave transmission,owing to its unique advantages brought by hollow-core guidance and structure characteristics,such as low delay,high capacity,low dispersion,low nonlinearity,high damage threshold,low scattering noise,and easy to fabricate,large core size,low energy overlap between mode field and material.Supported by the National Nature Science Foundation Program"Single-polarization hollow-core microstructured fiber and its application in high-precision miniaturized resonant fiber optic gyroscope"and Innovation Foundation for Excellent Postgraduates of Beijing Jiaotong University,this dissertation carries out theoretical and experimental research on various high-performance hollow-core anti-resonant fibers applied in near-infrared,mid-infrared and terahertz bands,focusing on the requirements of the development of high-performance hollow-core anti-resonant fibers which are needed in near-infrared,mid-infrared and terahertz applications.The main innovative achievements of this dissertation are listed as below:1.An approximate analytical expression for the mode effective refractive indices in the non-resonant regions of hollow-core anti-resonant fibers is proposed.This approximate analytical expression which can be used to calculate the effective refractive indices of different modes in the non-resonant regions of hollow-core anti-resonant fibers is derived from the Helmholtz equation which is the basic theory of optical waveguides,with the hollow tube with infinite wall thickness used as an alternative model.This result has enriched the theory of hollow-core anti-resonant fiber and lay a solid theoretical foundation for the research and development of novel hollow-core anti-resonant fibers.2.A double-ring mid-infrared single-mode hollow-core anti-resonant fiber is proposed.The all-circular-tube cladding structure is adopted to reduce fabrication difficulty.The excellent low-loss single-mode performance is achieved that the fundamental mode loss is lower than 4×10^-3d B/m and the high order mode extinction ratio is higher than 1000 in the ultra-broad wavelength region from 2.5?m to 3.3?m.The highest high order mode extinction ratio is up to 16600,and the effective mode area is up to 2314?m² at the wavelength of 2.8?m.Compared with single-ring structure,the high order mode extinction ratio is improved by one to two orders of magnitude.This research result provides a superior transmission medium for high-power mid-infrared laser delivery.3.A single-polarization single-mode mid-infrared hollow-core anti-resonant fiber is proposed with the combination of refractive index modulation and geometrical size control.The single-mode performance is guaranteed by introducing cladding tubes with two sizes for suppressing LP₁₁ modes and LP₂₁ modes at the same time.Then the high-index cladding tube is introduced for obtaining the asymmetry of refractive index distribution and y-polarization fundamental mode is suppressed to achieve single-polarization guidance.At the wavelength of 3.0?m,x-polarization fundamental mode loss is 0.048 d B/m,while polarization extinction ratio and high order mode extinction ratio are 5085 and 495 respectively.Moreover,this structure can be expanded in the wavelength region of 2.0?m to 4.0?m to achieve single-polarization single-mode guidance at any desired wavelength,by adjusting structure size.4.A single-polarization single-mode hollow-core anti-resonant fiber with different wall thicknesses is proposed.The single-mode guidance is guaranteed by double-ring cladding structure and different wall thicknesses are introduced to break structure symmetry.The couple between the cladding mode on the thickened tube and specific polarization state is used to suppress this polarization state.At the wavelength of 1550 nm,the excellent single-polarization single-mode performance that polarization extinction ratio and high order mode extinction ratio are 17762 and 393 respectively is achieved.This polarization extinction ratio achieves the highest level in the related researches.5.A design to achieve single polarization guidance is proposed that introducing a high-index clad layer in a single-mode double-ring alternant-tube hollow-core anti-resonant fiber.The structure symmetry of double-ring alternant-tube hollow-core anti-resonant fiber is broken by introducing a silicon-coated cladding tube.The y-polarization fundamental mode couples with the cladding mode on the silicon-coated tube and thus single-polarization single-mode guidance is achieved.At the wavelength of 1550 nm,polarization extinction ratio and high order mode extinction ratio are 5085 and 495 respectively,and x-polarization fundamental mode loss is 0.11 d B/m,and the total single-polarization bandwidth is up to 45 nm.Moreover,this design is also used in different kinds of hollow-core anti-resonant fibers to achieve single-polarization guidance.Compared with different thicknesses design,this design can improve single-polarization bandwidth from several nanometers to tens of nanometers.6.A high birefringence THz hollow-core anti-resonant fiber with asymmetric cladding structure and a slotted-wall THz hollow-core anti-resonant fiber are proposed.The ellipse-like core region is established by different size cladding tubes to obtain high geometric birefringence.High birefringence above 7×10^-4in the frequency range from 1.0-1.24 THz is obtained.The highest birefringence is up to 8.7×10^-4 at the frequency of 1.04 THz.Furthermore,the design of slotted wall is used to achieve the transmission characteristics close to those of thin-wall hollow-core anti-resonant fiber.This design can mediate the conflict between the needed minimum wall thickness in 3D printing technology and the thin wall thickness needed in THz hollow-core anti-resonant fiber to achieve low loss and broad bandwidth.Moreover,the influence of slotted wall on the transmission characteristics is analyzed detailedly.The measured results of the practical THz hollow-core anti-resonantfibers fabricated by 3D printing technology confirm the validity of this design.