Numerical Analysis On The Performance Of The Solitons In A Passively Mode-locked Erbium-doped Fiber Laser

Erbium-doped mode-locked fiber laser has many features,such as tunable broad wavelength,high output energy,tight structure and high transfer efficiency.It is widely used in medicine,spectroscopy,laser radar detection,military and other fields.Optical fiber laser could produce various kinds of pulses,mainly are dissipative solitons and traditional solitons based on the cavity dispersion distribution.Our report gives a specific theoretical analysis on the revolution of the pulse duration,spectrum width,mode-locked threshold and single pulse energy under different cavity dispersions.Previously researchers put their effort on the traditional lasers,but the single pulse energy is generally low under this condition.Recently,in order to improve the mode-locked laser output pulse energy,researchers put forward normal dispersion mode-locked fiber lasers.There exists large normal dispersion compensating optical fibers for the 1.55?m wavelength,which brings much convenient to our experiment and numerical analysis.Our paper systematically discusses the output pulses performance of the 1.55?m mode-locked laser under different cavity dispersions and is arranged as follows:Firstly,based on the 1.55?m normal dispersion mode-locked fiber laser,we theoretically study how the modulation depth affects the single pulse energy of the output pulse,laser mode-locking threshold,the variation of the pulse duration and spectrum width.Our numerical analysis shows that by properly adjusting the modulation depth and pump energy,we could still get excellent solitons under high modulation depth,besides,the higher of the modulation depth,the narrower of the pulse duration,the wider of the spectrum and the higher of the mode-locking energy and single pulse energy.Our results provide important guiding significance for further applications of the saturable absorbers with high modulation depth.Secondly,based on traditional anomalous lasers,we demonstrate how the dispersion affects the output optical pulse,we find that when the dispersion is approaching to zero,the pulse becomes much narrower and the output pulse energy is much higher.The spectrum is becoming broader under this circumstance,which is consistent to the optical transmission theory.The soliton propagating in the cavity follows the non-linear Schrodinger equation.Meanwhile,we obtain second-order solitons after analysis on the generation of the high-order solitons.Besides,we systematically study the effect of high modulation depth on the traditional solitons and find that the performance of the output pulse is much more superb and stable compared with low modulation depths.we improve the code and process to simulate the dispative soliton in the normal dispersion erbium-doped fiber laser,our theoretical results will guide us to devise better lasers to obtain superb output optical solitons with better quality.