High Power Photonic Crystal Fiber Laser And Coherent Beam Combining Techniques

High power fiber lasers have many advantages such as better high stable process, low energy consumption, high surface-area/volume ratio for easy heat dissipation and so on. Now they have been widely applied to a variety of practical and commercial applications such as machining industry, medical treatment, science research, etc. Photonic crystal fiber (PCF) has many unique properties such as endlessly single-mode guiding, large mode area, freedom dispersion characteristics, high cladding numerical aperture, etc. These characters make PCF lasers have the potential to obtain higher power laser with better beam quality and realize better beam combination compared to the traditional double-clad fiber lasers.In this paper, the influences of the fiber thermal with different pump absorption coefficients have been researched for high power Yb³⁺-doped PCF lasers. An Yb³⁺-doped PCF with the pump absorption coefficient of 1.45dB/m is used for the fiber laser in the experiment. 428.5W single-mode continuous-wave output power is achieved. The slope efficiency of the system is 76.5% and beam quality is M²<1.2. At the part of the coherent beam combining of fiber lasers, the phase-locking of two PCF Lasers is studied experimentally by using Michelson cavity technique, and 47W coherent output power is obtained. The phenomenon of interference-enhance and interference-loss on the two arms of the Michelson cavity is theoretically explained by analyzing the optical path differences. The coherent beam combining of two PCF lasers has been realized by using self-imaging resonator technique, and the coherent output power 95.8W and the combination efficiency of 90.2% are obtained. Two PCF lasers are mutually injected by direct transmission coupling of the fiber lasers, and 39W coherent output power is obtained with combining efficiency of 97.2%. Another simple and compact scheme for phase-locking of two PCF lasers is presented and studied experimentally by using back transmission coupling technique., and 153W coherent output power is obtained with combining efficiency of 80%.