"Figure-8" Mode-locked Fiber Laser Based On Nonliner Optical Loop Mirror

Passive mode-locked fiber laser has been widely used in optical communication,optical sensing,biomedicine,aerospace and optical measurement due to the characteristics of small size,compact structure,low manufacturing cost and so on.In this paper,the theoretical and experimental researches of “figure-8” mode-locked fiber laser which based on nonlinear optical ring mirror(NOLM)are carried out.In theory,the effects of laser cavity length,2×2 coupler beam splitting ratio and filter bandwidth on output pulse characteristics are discussed.In experiment,the NOLM-based “figure-8” mode-locked fiber laser is built and various types of pulses are obtained.Based on NOLM,a new structured fiber laser with two output ports is designed,the laser could deliver different type of pulses simultaneously from the two ports and the characteristics of the pulses have been discussed.This thesis includes the following contents:1.The background and significance of the topic are investigated.The research progress of passive mode-locked and dual mode-locked state fiber laser are summarize.The structure of ytterbium ion,absorption and emission spectra are introduced.Due to the characteristics of high environmental stability and low background noise,the "8" cavity clamping technology is introduced in detail.2.The formation mechanism and dynamic evolution of dissipated soliton resonance in NOLM-based "8" cavity laser is theoretically simulated.By numerical simulations,the effects of splitting ratio of 2×2 coupler,filter bandwidth and cavity length on the characteristics of output pulse have been discussed.These results could be benefited to the experiments.3.The experiment of NOLM-based “figure-8” mode-locked fiber laser was executed and the effect of NOLM length on output pulse characteristics was investigated.By changing the positions of polarization controller(PC)and cavity length,various types of pulses were obtained include double-spike broadband spectrum pulses,wavelength-tunable dissipative-soliton-resonance(DSR)pulses,2-6th harmonic mode-locked pulses,chair-like pulses,dual nanosecond pulses.The characteristics of these pulses are analyzed and discussed.4.Based on NOLM mode-locking technique,the dual mode-locked fiber laser has been bulit,and the output pulses are discussed.At the pump power of 640 m W,the DSR pulse and the noise-like pulse(NLP)could be simultaneously delivered fromdifferent output couplers by adjusting the PCs carefully.In addition,the center wavelengths at 1056 nm both of the two pulses,the spectra ranges of DSR and NLP are 0.5 nm and 21.5 nm,respectively.Compared to single mode-locking states,the intracavity powers of DSR and NLP are increased 24% and 41% in this dual mode-locking state,respectively.