| Soliton mode-locked fiber lasers hold significant value in both applied and fundamental research domains,making them a focal point in laser research in recent years.On one hand,they offer advantages such as narrow pulse width,excellent beam quality,compact structure,and relatively low cost,leading to widespread applications in fields like optical communications,precision machining,and biomedicine.On the other hand,the soliton mode-locked fiber laser involves a delicate balance among gain,loss,dispersion,and nonlinear effects,rendering it an ideal platform for studying nonlinear dynamics.Systematically studying the formation and evolution of soliton in mode-locked fiber lasers contributes to a profound understanding of the dynamical laws governing nonlinear systems.Resonant sideband generation stands as one of the intriguing phenomena widely observed in soliton mode-locked fiber lasers.As soliton pulses circulate within the cavity,they undergo periodic variations in system parameters such as gain and dispersion,at certain wavelengths where the dispersive waves are phase-matched to the soliton,resonant sidebands are formed.These resonant sidebands exert significant influences on soliton propagation and interactions between solitons,such as the formation of soliton molecules.Previous studies have primarily focused on low-order resonant sidebands located near the center wavelength of the soliton,leaving gaps in understanding the properties of high-order resonant sidebands.This is mainly due to the weaker intensity typically observed in high-order sidebands during experiments,lacking effective means to generate enhancement high-order resonant sidebands.However,research on high-order resonant sidebands is crucial for comprehending soliton transmission and interactions,precise dispersion measurements,and the synchronized multicolor pulse lasers.This paper primarily revolves around the systematic investigation of the effective generation of high-order resonant sidebands and the mechanism and characteristic underlying the generation of sub-sidebands in soliton mode-locked fiber lasers.The specific innovative achievements are as follows:1.Study on enhancement mechanism of high-order resonant sidebands.By combining experiments with numerical simulations,we thoroughly investigated the phenomenon of high-order resonant sideband enhancement in soliton fiber lasers based on the nonlinear polarization evolution mechanism for modelocking.Theoretically,simulations based on the nonlinear Schr?dinger equation revealed that finely tuning wavelength-dependent saturable absorption curves and gain spectral induced by birefringence are crucial for achieving enhancement of multiple resonant sidebands.Experimentally,a soliton mode-locked fiber laser with a ring cavity structure was constructed.By adjusting the waveplate angles of the polarization controller and the pump power,we changed the saturable absorption curves and gain spectral,leading to the generation of soliton mode-locked pulses with over 30 orders of resonant sidebands under certain conditions.Significantly enhanced resonant sidebands were observed,with the enhanced resonant sidebands is 32 d B higher than that of the soliton,which is the highest yet reported.Long-term monitoring of the mode-locked spectral confirmed the excellent stability of the soliton fiber laser with enhanced resonant sidebands.This work opens possibilities for constructing multi-wavelength laser sources.2.Study on the temporal and spectral characteristics of high-order resonant sidebands.Experimentally,multiple high-order resonant sidebands were filtered using a1 nm bandwidth filter,and their temporal features were observed using a high-speed oscilloscope.Combining experiments with numerical simulations revealed the phenomenon of exponentially decaying leading edges of high-order resonant sidebands,with the decay rate decreases as the sideband order increases.This is attributed to the larger frequency difference between the central frequency of the higher-order resonant sideband and the soliton’s central frequency,resulting in a larger group velocity mismatch and the soliton.Furthermore,it was observed that when the order of the sidebands is high,the commonly used resonant sideband wavelength formula,which only considers second-order dispersion effects,exhibits significant prediction errors.This is because the influence of third-order dispersion effects on high-order resonant sidebands is particularly pronounced,which is overlooked by traditional sideband formulas.Therefore,this study derived and for the first time presented a resonant sideband formula that includes third-order dispersion effects.Utilizing this analytical formula enables accurate prediction of the positions of highorder resonant sidebands.This research holds significant value for precise measurement of fiber dispersion.3.Study on generation mechanism of high-order resonant sub-sidebands.In experiments,by continuously adjusting the waveplate angles of the polarization controller or the pump power,we observed the generation of high-order resonant(second,fourth,and eighth-order)sub-sidebands.Using dispersion Fourier transform real-time measurement techniques and numerical simulation systems,we investigated the generation mechanism of high-order resonant sub-sidebands,revealing that the generation of sub-sidebands is primarily induced by the soliton’s period-N evolution caused by changes in cavity parameters.Considering the soliton’s period-N evolution,setting the cavity length in the resonant sideband wavelength formula derived in this paper to the period-N cavity length,accurately predicted the positions of the resonant sub-bands.This indicates that the generation of subsidebands shares the same mechanism as that of resonant sidebands,both arising from the phase-matched between dispersive waves and solitons.Additionally,using dispersion Fourier transform real-time measurement techniques,we experimentally observed the formation dynamics of soliton lasers with enhanced resonant sidebands,revealing a correlation between the formation of soliton molecules and resonant sidebands.The presence of high-order resonant sidebands leads to an increase in the separation among solitons in the bound state.This research holds significant importance for a deeper understanding of dynamic phenomena in nonlinear science and the generation mechanism of high-order resonant sub-sidebands.4.Research on dual-comb spectroscopy system based on dual-wavelength mode-locked soliton fiber laser.Experimentally,we constructed an all-fiber dual-wavelength mode-locked laser based on the Lyot filtering effect,generating low-coherent-noise dual-wavelength asynchronous mode-locked pulse sequences with central wavelengths of 1534.45 nm and 1561.85 nm.The spectral characteristics and repetition rates of these two pulse sequences exhibited significant differences,making them suitable as seed for the dualcomb spectroscopy system,with a repetition rate difference of 1.6 k Hz between the pulses.Using fiber collimators and gratings,we split the dual-wavelength modelocked pulses into two single-wavelength mode-locked beams with different central wavelengths.After amplification,nonlinear spectral broadening,combination,and filtering,we constructed a dual-comb spectroscopy system capable of applications such as molecular characteristic absorption measurements. |
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