Effects of annealing on the residual stresses distribution and the structural properties of Si core fiber

Effects of annealing on the residual stresses distribution and structural properties of Si core fiber cross-section are mainly investigated using Raman spectra map, scanning electron microscope (SEM) and X-ray diffraction. The annealing was carried out at 800 °C, 1000 °C, and 1200 °C, respectively by muffle furnace. The experimental results show that defects distribution has more obvious effects than the different characters between core and cladding on the residual stresses at the inner area of Si core cross-section. The defects distribution relate to the temperature field distribution during the process of drawing fiber. Annealing could decrease the residual stresses and make the distribution of residual stresses uniform effectively. For all samples, the Si core annealed at 1200 °C has the smallest residual stresses and the most uniform residual stresses distribution. The residual stresses of 155-437.5 MPa mainly caused by different characters between Si core and SiO2 cladding distribute at the narrow ring area near the inner surface of cladding. This area is very likely to be composed by grains which is smaller than grains in the inner, and has looser microstructure than the inner. It exists like a buffer layer. Annealing could also improve the crystal quality of Si core. After annealed at 1200 °C, the high intensity diffraction peak of the (3 1 1) plane is generated in the X-ray diffraction spectra.