Experimental study on passively-mode locked fiber lasers

• Main Author: Koh, Mabel Tengji
• Other Authors: Tang Dingyuan
• Format: Final Year Project
• Language: English
• Published: 2017
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/71562
• Institution: Nanyang Technological University

This report includes the principles of laser, theories of fiber optics, rare earth doped fiber laser and mode locking so that they may be understood by anyone. An experimental study of a thulium doped fiber laser was used as the gain medium of the laser, it was then mode locked by using the Nonlinear Polarization Rotation (NPR) technique. This technique had been successfully used to obtain short pulse generation in the thulium doped fiber laser. The cavity design uses a unidirectional fiber ring cavity containing a polarizer and polarization controller (PC). The polarization state evolves nonlinearly in the fiber as a result of the optical Kerr effect. By tuning the PC waveplate and pump power, the polarizer lets pass the central intense part of a pulse while it blocks the low intensity wings. Through the experiment, stable self-starting mode locking pulses had been generated in a ring cavity laser with the output spectrum centered at 1859.6nm and ∆λ=11.6nm at 3dBm bandwidth. The pulse separation time obtained was approximately 5.5ns, and the repetition rate was 181MHz. The mode locking of the ring cavity was sustained at the threshold pump power of 1412.54mW(31.5dBm).