Fig. 1. Annealing device

Fig. 2. The schematic diagram of Raman apparatus

Fig. 3. Microscope image of the cross-section of as-drawn Ge core optical fibers with different ODs

Fig. 4. As-drawn fibers and Ge bulk crystal

Fig. 5. Raman peak frequency mapping with an OD of 188 μm fiber

Fig. 6. Raman peak frequency mapping with an OD of 251 μm fiber

Fig. 7. Raman peak frequency mapping with an OD of 270 μm fiber

Fig. 8. Fibers with different ODs

Fig. 9. Simulation diagram of laser annealing of Ge core fiber

Fig. 10. Simulation of temperature variation of the sample with 188 μm OD at different scanning velocities

Fig. 11. Simulation of temperature variation of the sample with 251 μm OD at different scanning velocities

Fig. 12. Simulation of temperature variation of the sample with 270 μm OD at different scanning velocities