Applications Of Ultra-high Q Microcavities In Pulsed Fiber Lasers

Microcavities with the whispering gallery mode(WGM)and the ultra-high quality(Q)factor have been widely used in ultra-high sensitivity sensing,ultra-low threshold lasers and nonlinear optics.The research enthusiasm on pulsed fiber lasers have been maintained for several decades in laser processing,military projects,medical equipment and many other fields.Pulsed lasers have been developing towards high energy,high repetition rate and narrow pulse width.Therefore,new Q-switching and mode-locking elements have being discovered constantly.In the thesis,the application of silica microspheres as Q-switching and mode-locking elements in erbium-doped fiber lasers is introduced.The main contents are as follows:1.Based on the theory of classical electromagnetic wave,the eigenmode and electric field distribution in the microspheres were calculated and analyzed by the Maxwell’s equations,and the main parameters of the silica microspheres were introduced.Also,the thermal dynamics in the silica microsphere were modeled and simulated,and a real-time monitoring system for the thermal dynamics in the microsphere was established by the time-domain dispersion stretching technology.The time resolution of the system was 50 ns,and the test results agreed well with the simulation results.At the same time,the thermal dynamics of the microsphere under different pump powers and different scan rates were compared and analyzed.2.Based on the thermal dynamics in silica microspheres,a stable Q-switched pulse output in the fiber laser was realized.The output pulse repetition frequency was 29.09 k Hz,the pulse width was about 3.26 μs,and the single pulse energy was about 78.08 n J.The relationships between different parameters of the laser pulses and different pump powers were analyzed with the experimental results.3.On the premise of the comb filtering characteristics and the nonlinear effect of four-wave mixing,the feasibility of the mode-locking fiber laser based on the silica microsphere was analyzed.In the experiment,the output of the mode-locking fiber laser was a comb-like spectrum,which accorded with the characteristics of mode-locked pulses.Finally,the possible reasons for the undetected mode-locking pulses on the autocorrelator were analyzed.