Numerical Simulation Of 1.7 Micron Fiber Laser Based On PbSe Quantum Dot Gain Medium

The light endowed with high stability,excellent beam quality and high photoelectric conversion efficient when it transmits by total reflection in fiber lasers.Fiber lasers are crucial in many fields,laser processing,optical communication and laser measurement,to name a few.However,it is difficult to emit several particular wavelengths from the present fiber lasers owing to the limitation of emission wavelengths from rare-earth-doped gain media in fiber lasers.For instance,rare-earth ions can radiate wavelengths of 1 μm,1.5 μm,2 μm,etc.Yet there is no emission cross-section or extremely low emission cross-section at a number of particular wavelengths,such as the important biomedical wavelength of 1.7 μm.This fact leads to a difficulty of obtaining 1.7 μm from a mode-locked rare-earth-doped fiber laser directly.Quantum dots(QDs),a quasi-zero-dimensional semiconductor nanocrystal,is a promising candidate as a gain medium in fiber lasers for obtaining particular wavelengths;they are not included in rare-earth ion-doped fiber lasers.Because the emission wavelengths of quantum dots can be shifted continuously by only changing the quantum dots size,a QDs doped fiber laser(QDFL)can easily achieve a particular wavelength.To date,IV-VI PbSe QDs,which have large emission cross sections,high quantum yields,broad adjustable spectra,and can be easily embedded in fiber,are an interesting material for obtaining efficient particular-wavelength output from fiber lasers.Herein,a series of numerical models of PbSe QDFL were built and investigated,which mainly include the following parts:(1)The numerical model of CW linear cavity PbSe QDFL and CW ring cavity PbSe QDFL were established.In the linear cavity,the effect of fiber bragg grating(FBG)reflectivity and the superiority of double-sided pumping on output laser were discussed.In the ring cavity,the effect of the PbSe quantum dot fiber(QDF)length,the doping concentration of QDs and the pump power on output laser were explored.(2)To meet the practical senario,variable gain coeffiecient was adopted,as well as the rate equation and the Ginzurg-Landau equation were combined in the numerical model of mode-locked PbSe QDFL.After the resonator parameters were optimized,it was indicated that mode-locked PbSe QDFL was a feasible scheme to obtain ultra-short pulses at 1.7 μm.(3)Based on the numerical model of the mode-locked PbSe QDFL,it was discovered that different initial signals resulted in different buildup dynamics but the same output property at the steady state.The peak power and pulse duration with respect to the QDF length under different PbSe QD doping concentrations were investigated.An optimum QDF length under a fixed pump power and doping concentration was determined.Then the different values of dispersion,nonlinear coefficient and the modulation depth of the saturable absorber were set to contrast the effect on soliton.Finally the evolution of soliton in the time and spectrum domain were given respectively.The results presented herein will facilitate the understanding of the operating principle of this novel laser,which further facilitates the optimization of resonator design and the development of the mode-locked fiber laser at particular wavelength.