Research On Optical Microfiber Based Broadband Ultrafast Fiber Laser

Optical fiber ring lasers have been widely applied in scientific research,production and liv-ing as the property of low optical loss,free of alignment,compact structure,high beam quality,etc.Such lasers are convenient experimental platforms subject to periodic boundary condi-tions and dissipation,and could work in mode-locking,conventional soliton,soliton molecules,noise-like pulses(NLPs)and other nonlinear dynamic regimes.These series of ultrashort output optical pulses are still under poor understanding in neither original mechanism,regulation nor pulse parameter optimization.As far as the optical fiber lasers are concerned,there exists a basic consensus that intra-cavity dispersion,operating power,intracavity fiber nonlinear parameters and cavity length could boost the mentioned nonlinear dynamic phenomena above by giving impact on intracav-ity nonlinear interaction.Furthermore,as a special highly nonlinear fiber,microfiber showing advantages of enhanced nonlinear interaction induced by tight optical confinement,low optical loss,diameter-dependent dispersion and related full compatibility,has the potential to improve the output performance of fiber lasers.This study achieves noise-like pulses with broadband spectrum range from below 1000 nm to beyond 1600 nm when inserting microfibers in ultrashort pulse fiber lasers,the experimental results show that there is rogue wave in this kind of noise-like pulses,and numerical simu-lations verifies the dispersion and nonlinearity management of microfibers in broad-spectrum generation.The details are as follows:1)Based on the dispersion-and nonlinear management of microfibers with different di-ameters,this study prepared microfibers with diameters of 1,1.2 and 1.5 μm for nonlinear polarization rotation based passive mode-locked fiber lasers.The microfiber with diameter of 1.2 μm and length of～30 cm could assist in a broadband output NLPs spectrum spanning from below 1000 nm to beyond 1600 nm with a 3dB-bandwidth of pedestal more than 100 nm and the averaged power of NLPs greater than 30 mW typically;2)Temporal statistic analysis over millions of pulses demonstrated that these Q-switched NLPs also provided transient rogue wave with extremely high amplitude.It is worth noting that under the pump power level of～600 mW other nonlinear dynamic phenomena such as dissipative soliton,soliton molecules and continuous-wave mode-locking can be observed only by adjusting the intracavity pulse polarization configuration;3)A related simulation model was established with the generalized nonlinear Schrodinger equation.The excellent fitting results between simulation and experiment explained that the microfiber played a great important role in the generation of the ultrabroad spectrum especially in spectral broadening.And dispersion-/nonlinear management was aslo demonstrated as there was obvious differences in corresponding output spectra when utilizing microfibers with differ-ent diameters.Combining the experiment and simulation,this article reveals the basic principles of mi-crofiber enabled dispersion-and nonlinear management for improving the performance of fiber lasers.We believe that this broadband NLPs behaving as low-spectral-coherence sources or su-percontinuum seed sources has the potential for optical coherence tomography,micro-machining,supercontinuum generation,etc.