Research On The Fabrication And Performance Of Low Loss All-solid Infrared Microstructure Fiber

The infrared spectrum of 2.5-16μm contains the fundamental frequency absorption band of most material molecules,and it has an extremely important position and application in many industries such as spectroscopy,aerospace,biomedicine,and military confrontation.Supercontinuum（SC）source generated by laser nonlinear spectral transformation in this wavelength range has become a new research hotspot with high stability,high coherence and high brightness.The chalcogenide microstructure fiber（MOF）has the advantages of wide transmission window,high nonlinearity,and large mode field area,and become an ideal nonlinear medium for all-infrared SC sources.Compared with the traditional hollow MOF,the all-solid MOF composed of high and low refractive index glass has the advantages of flexible structure design and less deformation.However,the refractive index difference of infrared glass with matching spectral range and temperature characteristics is generally small.At the same time,it faces the problems such as material impurity absorption and optical fiber structure deformation.Firstly,to solve the problem of impurity absorption of chalcogenide materials and reduce the glass matrix loss of all-solid MOF,this paper explores the purification methods of various raw materials and glasses for Te-based chalcogenide glass with difficult purification and poor thermal stability.According to the principle of different vapor pressures of different materials in vacuum,the raw material Ge and Te are purified by dynamic distillation,and two groups of Ge-Ga-Te glasses with high purity and high refractive index are successfully prepared.The test results show that the spectral transmission range of the glass is extended to 22μm,and the absorption peaks of Ga-O and Ge-O in the 14-22μm band are successfully eliminated.The refractive index of the glass is higher than 3.3,and the zero dispersion wavelength（ZDW）is around 10μm.Secondly,to solve the problem of mismatch between the spectral range of Se-based glass with high refractive index and S-based glass with low refractive index,halogen I is used to optimize Se-based chalcogenide glass,and a new type of Ge-As-Se-I glass with consistent spectral range and low refractive index is obtained in this paper.The technology of preparing high-purity chalcogenide glass by doping halogen with high-purity chalcogenide glass as matrix is proposed for the first time.And the Ge-As-Se-I glass with spectral width ranging from visible light（around 750 nm）to long-wave infrared（up to 18μm）is successfully prepared by this technology.The ZDW of(Ge_0.33As_0.12Se_0.55)₇₀I₃₀ is as low as 4.32μm and the direct optical band gap is 1.986.At the same time,the refractive index of this glass is as low as 2.16 at 1.7μm（about 2.8 for traditional Se-based chalcogenide glass）.The preparation of high purity chalcohalide glass with ultra-low refractive index has laid a solid material foundation for the subsequent development of all-solid infrared MOF.Thirdly,to verify the matching degree of thermal and optical properties between Te glass with high refractive index and Ge-As-Se-I glass with low refractive index,a W-type double-cladding MOF with ultra-large numerical aperture（NA）is designed and fabricated.First of all,Ge₂₀As₂₀Se₁₅Te₄₅、(Ge_0.25As_0.1Se_0.65)₈₀I₂₀ and Ge₁₀As₂₂Se₆₈ glasses with matching performance are optimized as the matrix of fiber core,inner cladding and outer cladding of optical fiber.A new type of chalcohalide/chalcogenide glass with low impurity content is obtained by using the above glass purification technology.Second,the structure design and performance simulation of double-cladding MOF is carried out by using COMSOL software and the intrinsic relationship between confinement ability of fiber and core diameter,numerical aperture and transmission wavelength is verified.Finally,This W-type double-cladding MOF with ultra-high NA is successfully prepared by the isolation extrusion method.The experimental results show that the fiber has a large NA（≥2.17）at 2-16μm,and the minimum fiber loss is only 1.7 d B/m（at 6.1μm）.When the pump wavelength is 5μm,SC covering 1.6μm to 10.85μm can be obtained.The successful preparation of W-type double-cladding MOF with ultra-high NA provides experimental feasibility to fabricate all-solid MOF using chalcogenide glass with high refractive index difference in the next step.Fourthly,in terms of design and fabrication technology of all-solid chalcogenide MOF,the all-solid leakage channel fiber（LCF）with more complex structure is designed in the first.The effects of material,core diameter,wavelength,bending radius and other parameters on leakage loss,bending loss and effective mode field area are numerically simulated.Second,this all-solid LCF with six cores is prepared by the extrusion method.The materials of the core and cladding are(Ge_0.25As_0.1Se_0.65)₈₀I₂₀ and Ge₁₀As₂₂Se₆₈.The fiber has a large effective mode field area of 4630μm²at 4μm,and the lowest loss is as low as 1.3 d B/m at 5.6μm.Finally,an ultrabroad SC spectrum covering 1.1-13.0μm is obtained by pumping a 20 cm long fiber.This kind of optical fiber provides some scientific and experimental basis for the subsequent development of the high-energy mid infrared laser.