Design And Preparation Of Fluorotellurite Glass Fibers And Their Application In Mid-infrared Supercontinuum Generation

All-fiber supercontinuum（SC）light sources at 2-5μm have attracted much attention owing to their numerous applications in many fields such as atmospheric remote sensing,infrared imaging,infrared distance measurement,laser guidance,optoelectronic countermeasure,biomedical and trace molecular detection.Up to now,mid-infrared SC source with high output power（>10 W）are mainly generated in ZBLAN fiber which is a kind of heavy metal fluoride fiber with the composition of53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF.However,ZBLAN fiber presented some drawbacks such as poor chemical stability which would do harm to high power SC light source,low glass transition temperature（Tg=265 ^oC）.To promote the stability of the mid-infrared SC light source,it is still necessary to explore new kinds of fiber and investigated their application in mid-infrared SC generation.During the doctoral years,the author has worked on the exploration of fluorotellurite glass,designing and preparation of fluorotellurite glass fibers and obtaining the high power,broadband,coherent mid-infrared supercontinuum light sources from fluorotellurite glass fibers.The author achieved a series of research results as follows:（1）Fluorotellurite glasses with excellent chemical and thermal stability and high glass transition temperature（Tg=425 ^oC）based on the composition of TeO₂-BaF₂-Y₂O₃（TBY）have been explored.To meet some applications,we have designed and fabricated kinds of fluorotellurite glass fibers by using rod-in-tube and bundling methods.（2）Ultra-high NA fluorotellurite fiber with the core and cladding materials of TeO₂-BaF₂-Y₂O₃ and AlF₃–BaF₂–CaF₂–YF₃–SrF₂–MgF₂–TeO₂（ABCYSMT）glasses was fabricated by using rod-in-tube method.The numerical aperture（NA）was calculated to be¹.1 in the range of 400-6000nm.By using 60 cm long fluorotellurite fiber as the nonlinear medium and a high power 1980 nm femtosecond fiber laser as the pump source,we demonstrated the mid-infrared SC generation from 947 to 3934nm with the maximum output power of 10.4 W.The optical-to-optical conversion efficiency was as high as⁶5%.The results indicated that fluorotellurite fiber can be used in the high power mid-infrared SC laser source.（3）Based on the ultra-high NA fluorotellurite fiber,we further designed and fabricated the dispersion-decreasing fluorotellurite glass fibers with the core diameter decreasing from 7 to 1.4μm.By using a 1980 nm femtosecond fiber laser as the pump source,broadband SC from 600 to 5200 nm was obtained from the dispersion-decreasing fluorotellurite glass fiber,the maximum output power is 380mW,and the optical-to-optical conversion efficiency was³0%.Which indicated that wide broadband SC source can be generated in tapered fluorotellurite fiber by controlling the dispersion and loss profiles.（4）The birefringent fluorotellurite microstructured fibers based on TBY glass were fabricated by using the rod-in-tube method,the birefringence is 3.5×10^-2.And we demonstrated tunable mid-infrared dispersive waves from 2680 to 2725 nm（or from 2260 to 2400 nm）in the birefringent fluorotellurite microstructured fibers by varying the polarization state of the 1560 nm femtosecond fiber laser,the corresponding conversion efficiencies were 0.9%and 2.97%.In addition,the simulation shows the operating wavelength of tunable dispersive waves covering 2-5μm can be obtained by using the birefringent fluorotellurite microstructured fibers as the nonlinear medium.（5）We have designed and fabricated the Tm³⁺-doped fluorotellurite microstructured fiber.And by using 1560 nm femtosecond fiber laser and 1570 nm continuum wave laser as the pump source,we demonstrate amplification of wavelength-shifting soliton in the Tm³⁺-doped fluorotellurite microstructured fiber.When a redshifting soliton experiences optical gain at a certain spectral range in the Tm³⁺-doped fluorotellurite microstructured fiber,in addition to its amplification,the redshifting speed of the soliton is increased dramatically and the corresponding pulse width of the soliton can also be reduced down dramatically.Our experimental results showed that optical gain can control the soliton self-frequency shifting effect,and obtained tunable short duration Ramon soliton laser.（6）We have designed and fabricated a kind of fluorotellurite microstructure fiber with two zero dispersion wavelength.By using this fiber as the nonlinear fiber,third harmonic generation is observed and enhanced via soliton self-frequency shifting cancelling in a fluorotellurite microstructured fiber pumped by a 1560 nm femtosecond fiber laser.Such an enhancement is due to the unchanged operating wavelength of Raman soliton with an increase in the pump power when SSFSC occurs and the resulting increase in the interaction length between the Raman soliton and third harmonic.