Self-mode-locked Pulse Suppression Of Erbium-doped (Yb) Fiber Continuous Lasers

Fiber lasers operating in continuous wave mode often suffer from an instability problem which may generate periodic pulses,caused by the named self-mode-locking(SML)phenomenon.SML pulses originated from mode competition,relaxation oscillation and nonlinear effects in fiber laser,which reduce the quality of fiber lasers' output and influence the stability of the lasers output,so that restricting the applications of fiber lasers on engineering project and the field of technology.Here,we introduce a brand new technique to suppress the SML pulses,as well as improve the stability of laser output power.Two fiber optic amplifiers were cascaded connected to fiber laser,with attenuator placed before each amplifier to adjust the input power so that achieving appropriate gain saturation characteristic to suppressing the SML pulses.Firstly,the construction and characteristic of continuous mode fiber lasers and the SML phenomenon were introduced and theoretically researched detailed.After researching on suppression of SML pulses,here we introduce some ways to suppress the SML pulses,for example:double-ending pumping,inserting a section of passive fiber,feedback from the outside cavity.However,each method has its restriction on technique or application.After deeply research and analysis,we propose a simple and effective technique to suppress the SML pulses,that's cascaded fiber optic amplifiers.Which maximize the cost performance with the minimize cost of hardware,in the situation that ensuring the best suppression result of SML pulses.After researching and analysis on the mechanism of the formation of SML pulses,we found that in those articles on SML pulses,the reasons of the origination of SML pulses are different,after researching and analysis on numerous articles,we conclude that:the saturable absorption of lasing signal of the weak-pumped or unpumped section of active fiber,the mode competition in the cavity and the relaxation oscillation of ions are the main reasons leading to SML pulses.The nonlinear effects intensify the formation of SML pulses such as:self-phase modulation,stimulated Raman scattering and stimulated Brillouin scattering.Therefore,SML phenomenon is a complexity process about interaction between lasing light and fiber material.We simulated the suppression to SML pulse of fiber amplifiers by numerical simulation.The SML pulse was suppressed by 40%after once amplification,and the suppression ratio exceeds 75%after twice amplification.Last,we introduce the design and construction of Ytterbium-doped fiber laser,the construction of cascaded Ytterbium-doped fiber amplifiers and the design of the system of the suppression to SML pulses by cascaded optical fiber amplifiers.Besides,we tested the characteristic of the fiber laser and amplifiers.Finally,we analyze and compare the experimental results.During the experiment,we adjust the variable attenuator to change the input power to amplifier so that changing the gain characteristic,resulting in the SML pulses receiving amplification much less than that of lasing signal.The results of experiment indicated that:this method results in 10 times suppression of the self-ML pulses' amplitude,and the overall spectral amplitudes of SML pulses were suppressed by about 15dB,as well as the stability improvement of spectrum about 4times.