Research On 2-3?M Mid-infrared All-fiber Ultrashort Pulsed Lasers

2-20 ?m mid-infrared lasers have attracted considerable attention,due to their potential applications,for example,communications,sensing,military,medical surgery,and scientific research.Among the methods of producing mid-infrared lasers,midinfrared fiber lasers could be more attractive because of their significant advantages such as compactness,maintenance-free operation,good stability and high conversion efficiency.In particular,mid-infrared ultrashort pulsed fiber lasers not only possess the inherent advantages of fiber laser,but also have high peak power,low energy consumption and ultra-fast time-domain characteristics.Therefore,it is of great significance and urgency to develop the mid-infrared ultrafast fiber laser sources.However,so far the research on mid-infrared ultrafast fiber lasers are faced with the following problems:1)requiring bulk optical components and complex coupling systems,and precluding compact mid-infrared all-fiber integration;2)The wavelength of mode-locked fiber laser relying on the rare-earth ions(Er3+,Ho3+,Dy3+,etc.)was astricted and caused a series of spectrum gaps(such as 2.1-2.7 ?m).Therefore,the purpose of this thesis is to develop a compact,all-fiber,high-performance,mid-infrared ultra-short pulsed laser source covering the spectral gap caused by the energy level limitation of rare earth ions mode-locked fiber lasers.The research works presented in this thesis focused on the hotspot of realizing high quality 2-3 ?m all-fiber ultrafast pulsed laser,and a series of innovative results have been achieved on the theoretical and experimental studies:1)based on the nonlinear optical loop mirror(NOLM)constructed by asymmetry coupler and the advantages of high-gain double-clad rare-earth fiber,a series of 2 ?m dissipative soliton resonance(DSR)short pulsed lasers research were carried out,and realizing a peak power up to 84 W and a longest wavelength of 2080 nm;2)a 2166 nm sub-nanosecond pulse has been realized using a 97 mol.%GeO2-doped germania fiber based on high tolerance synchronous pumping technology;3)the generation and evolution of 2-3 ?m midinfrared ultrashort pulse has been numerically simulated using 64 mol.%GeO2-doped germania fiber based on nonlinear schrodinger equation;4)2-3 ?m continuously adjustable Raman soliton has been realized using Raman soliton self-frequency shift.The research results may pave a path towards compact and high-performance midinfrared femtosecond fiber laser sources.The major achievements of this thesis are summarized as follows:?)A systematical investigate of high power,large energy dissipative soliton resonance mode-locked fiber laser based on the NOLM technique.Firstly,a stable dumbbellshaped Er:Yb co-doped double-clad fiber laser has been demonstrated which can stably emit DSR pulses with an average output power of 1.176 W.In particular,the peak power is significantly increased up to?700 W.Secondly,the same technique has been extended to 2 ?m waveband,and a DSR pulse with an average power of 1.4 W,a maximum pulse energy of 353 nJ,and a maximum peak power of 84 W is obtained.Furthermore,the effect of the loop length in the fiber loop mirror on the output performance of the DSR pulses is investigated comparatively.Finally,in order to further extend the wavelength of DSR pulse to longer wavelength,a wide-band mirror is used to replace the 2 ?m fiber Bragg grating(FBG)in the cavity.A wavelength of 2080 nm DSR pulse is obtained in the laser state of free-oscillating.?)A detailed study on 2166 nm Raman fiber laser based on high tolerance synchronous pumping technology.The mid-infrared Raman laser consists of two highreflectivity FBGs and a 22 m germania-core Raman fiber pumped by a 1981 nm homemade noise-like pulse mode-locked fiber laser.By adjusting the lengths of matching fiber in the two lasers,the cavity repetition frequency of the Raman laser cavity is consistent with the repetition frequency of noise-like pulse(NLP),thus achieving the condition of synchronous pumping.The Raman laser can deliver a center wavelength of 2166 nm,a maximum output power of 52.65 mW,and a pulse duration adjusted from 900 ps to 4.4 ns.?)A systematical investigate of the 2-3 ?m tunable mid-infrared all-fiber Raman soliton generation based on Raman soliton self-frequency shift.Firstly,the generation and evolution of the Raman soliton,which is generated by 1965 nm 240 fs ultrashort pulse transmissing in the 64 mol.%GeO2-doped Germania fiber,are systematically simulated based on the generalized schrodinger equation.Secondly,related experimental setup has been designed under the guidance of the simulations.The power of a home-made 1965 nm mode-locked fiber laser is amplified by two-stage amplifiers,and then injecting into a 10 m 64 mol.%GeO2doped germania fiber to generate Raman soliton.Stable Raman solitons are therefore obtained with a continuous wavelength tunability from 2.01 to 2.42 ?m.The maximum average output power is about 27.3 mW,corresponding to a maximum pulse energy of 0.94 nJ and a peak power of 3.6 kW.Finally,the midinfrared Raman soliton self-frequency shift system has been optimized,and successfully realizing the primary and secondary Raman soliton self-frequency shift in the thulium-doped double-clad amplifier and the germania core fiber doped with 94 mol.%GeO2.The wavelength of first-order Raman soliton system can be tuned from 1957 to 2153 nm,and in the second-order soliton system the wavelength can be further redshifted from 2157 up to 2690 nm.