Investigation Of Single Crystal Growth Of Core In Multimaterial Glass Fiber

Based on the unique properties of semiconductor materials and the waveguide structure of optical fiber,semiconductor core multimaterial fiber has important application prospects in sensing,nonlinear optics,energy conversion and other fields.The post-processing technology of multimaterial fiber,which can improve its performance by regulating the core structure,has attracted more and more attention.Laser annealing post-processing has realized the preparation of different single crystalline semiconductor core multimaterial fiber and improved various properties of the fiber,such as reducing the optical loss and promoting the photoelectric response.However,the main defects of laser annealing are uneven distribution of residual stress in fiber core and relative short length of fiber.In this thesis,we chose tellurium semiconductor core glass-clad fiber as the research object and realized the transition from polycrystalline state to single crystalline state in fiber core by laser annealing and Bridgman-type fiber post-processing.The performances of photoconductivity and pressure sensing in single crystalline core fiber were improved.The main research contents and results are as follows:?1?The synthesis of Te core borosilicate glass-clad fiber precursors was studied.The fiber with outer diameter of 800?m and inner diameter of 123?m was prepared by molten core method.According to the element analysis,the fiber core kept high purity,existing no obvious diffused Si and O elements.?2?The preparation of single crystalline Te core fiber by the Bridgman-type fiber post-processing technology was studied.We constructed Bridgman-type fiber post-processing technology and device for fiber precursor post-processing based on Bridgman method.The major parameters of fiber precursor post-processing are lowering speed of 5 mm/h and temperature of 460?500?in high temperature zone.Polycrystalline Te core in fiber precursor transformed to single crystalline Te core with c-axis orientation parallel to fiber axis after post-processing,which was confirmed by several measurement results.It can be observed that fiber precursor has no photoelectric response in illuminated states?532 nm laser?while single crystalline Te core fiber shows obvious photoconductivity.Compared with fiber precursor,The conductivity of the single crystalline Te core fiber is 23%higher than that in dark state and 32%higher than that in illuminated state.The single crystalline Te core fiber showed stress sensitivity.When the two ends of single crystalline Te core are under compressive stress,the conductivity is about 4×10^-3?^-1cm^-1,which is one order of magnitude higher than that without the stress.?3?The preparation of single crystalline core from polycrystalline Te core fiber precursor by the 532 nm laser annealing was studied.The laser annealing was carried out with laser power of 200 m W and laser moving speed of 5 mm/h.The single crystal X-ray diffraction result shows that the core of fiber after laser annealing is tellurium single crystal.Raman spectrum indicates that there is a geometric elimination process in the growth of tellurium crystal in laser annealing.After the removing crystals with other orientation of at least 3 mm length,the core can grow along the crystal c-axis completely.