| Optical fibers have been an extremely successful platform for optical research and photonic devices,including optical communication,fiber lasers,nonlinear optics,bio-medicine,sensing,laser radar,and so on.With the extension of the applications of optical fibers,there are growing needs for specialized optical fibers which can provide greater or enhanced functionality,for example: optical fibers for mid-and far-infrared light transmission and laser generation,all-fiber sensors which can perceive a variety of physical parameter,highly nonlinear optical fiber for all-optical signal processing,optical fibers with low nonlinear optical coefficients for high-energy laser systems,in-fiber solar cells or thermoelectric devices,and wearable optoelectronic fibers.However,traditional silica fibers,which have simple function,cannot be used in mid-and far-infrared wavelength((29)2.5 μm).The way to solve this problem is to incorporate new kinds of materials with different physical and chemical properties and functional microstructures into the fiber geometry,which paving the way to a new generation of multimaterial fibers endowed with optical,electronic,thermal,magnetic,acoustic and dielectric properties.However,there are some difficulties should be overcome to fabricate multimaterial fibers,such as the mismatch of physical parameters between different materials,the chemical stability at high temperature processing,and the structure of the fiber is not easy to be controlled.Thus the motivation of the present work is to provide specialized optical fibers with greater and enhanced functionality for new areas of application.From the composition of glass fibers perspective,the fabrication technology and the properties of multimaterial optical fibers were studied in this dissertation.Detailed research contents and results are as follows:(1)The general rules and technologies of the fabrication of multimaterial optical fibers were researched.The matching rules of core and cladding materials include the relationship between viscosity and melting point,high temperature wettability,the refractive index,the coefficient of thermal expansion,elements diffusion,and so on.The molten core method,reactive molten core approach,and post-drawing thermal treatment were studied to fabricate multimaterial optical fibers.(2)Glass-clad unary semiconductor Se and Te core mulitmaterial glass fibers have been fabricated by using molten core method,respectively.The Se core was found to be amorphous,while the Te core was found to be crystalline.Crystalline Se core fiber can be obtained by using post-drawing heat treatment.There exhibits a three times change in conductivity between dark and illuminated states in the crystalline Se core fiber,showing promising utility in optical switch and photodetector.However,there is no photocurrent in Te core fiber.Te semiconductor core has large Raman gain and high transparency at infrared wavelength,which suggests Te core fiber could be a promising material for Raman-shifted infrared light sources and light transmission in the infrared region.(3)Glass-clad compound semiconductor Se0.8Te0.2 and Sb2Se3 core multiamterial optical fibers have been fabricated,respectively.There exhibits a 100 times change in conductivity between dark and illuminated states in the crystalline Se0.8Te0.2 core fiber,indicating by fine-tuning the initial core composition of Se and Te,it is possible to tune the photoconductivity of the SexTe1-x semiconductor core multimaterial fibers.There exhibits a four orders of magnitude change in conductivity after the whole Sb2Se3 semiconductor core multiamterial fiber was heated from 25 to 195 °C.In addition,the fiber also has photocurrent and relative large Seebeck coefficient(1180 μV k-1).These results have demonstrated the promising potential of Sb2Se3 semiconductor core multiamterial optical fibers in photodetector,optical switch,temperature sensing and thermoelectric devices.(4)Metal Bi and highly rare earth doped phosphate glass have been integrated into fibers,respectively,by using the molten core method.Bi has a high magnetoresistance effect,which means Bi core fiber has promising utility in magnetic fiber sensors.It is well-known that high rare earth ions doping levels of optical fibers make it possible to obtain high gain per unit length.However,the rear earth ions doping concentration were limited by concentration quenching and crystallization during the fiber drawing in typical rod-in-tube technique,as the core glass will go through twice heat drawing process.Silicate glass-clad highly Er3+/Yb3+ co-doped phosphate core multimaterial fibers were fabricated by using molten core method.The combination of core and cladding is very well,and the core-cladding structure of fiber is preserved completely.The propagation loss at 1310 nm was measured to be 7.5 dB/m.An intense 1.53 μm emission was obtained from the multimaterial fiber,indicating its promising application in high efficiency,high power,and ultra compact fiber laser operating at 1.5 μm region.(5)High gain per unit length of Tm3+ doped germanate glass single-mode optical fibers were fabricated.Firstly,the luminescence properties of Er3+/Ho3+ co-doped germanate glass have been studied under 980 and 1550 nm excitations,respectively.The 2.0 μm emission lifetime of the present glass is as high as 5.67 ms with the corresponding energy transfer efficiency of 70.0 % from Er3+: 4I13/2 to Ho3+: 5I7 when pumped by a 980 nm LD.The absorption cross section at 4I13/2 level of Er3+ is larger than that at 4I11/2 level,indicating that the 2.0 μm fluorescence emission is more effectively at 1550 nm excitation compared with 980 nm.Secondly,enhanced 2.85 μm and 2.0 μm emission from Er3+/Yb3+/Ho3+ triple doped germanate glass have been obtained under 980 nm LD excitation.The 2.0 μm emission lifetime of is as high as 7.58 ms.These results suggest that the rare earth doped germanate glasses are the promising 2 ~ 3 μm mid-infrared laser materials.Finally,highly Tm3+ doped germanate glass single mode fibers have been fabricated by optimizing the component,dehydration method,and the fiber drawing technique.Its gain was measured to be 3.6 dB/cm,which is the reported highest gain per unit length of Tm3+ doped germanate fiber.Single-frequency laser at 1.95 μm was realized in a 1.3-cm-long as-drawn active fiber when pumped by a 1568 nm fiber laser.The laser output power was 101.6 mW with slope efficiency of 6.3 %. |
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