| Ultrafast laser technology has helped achieve many breakthroughs in fields such as chemistry,biology,and medicine.In the past twenty years,ultrafast fiber lasers have received increasing attention and gradually occupied some of the ultrafast laser market.Passively mode-locked technology is a fundamental means to achieve ultrafast laser output in fiber lasers.This article mainly studies and compares the application and performance of three passively mode-locked technologies,namely nonlinear polarization rotation technology,Kerr-lens self-mode-locking technology based on single-mode fibers,and two-dimensional cylindrite saturable absorption devices,in ultrafast fiber lasers,as well as the rich soliton phenomena among them.(1)First of all,the development status of ultrafast laser technology and the basic principle of mode-locked laser are introduced;Then,the principle of passively mode-locking of semiconductor saturable absorption mirrors,nonlinear polarization rotation,nonlinear optical loop mirror,nonlinear amplifying loop mirror,Kerr-lens self-mode-locking and low-dimensional material saturable absorption devices and their research status in ultra-fast fiber lasers are introduced in detail;In addition,traditional soliton,bound state soliton,noise-like soliton,and dissipative soliton are briefly introduced.(2)Based on NPR technology,traditional soliton,bound state soliton,rectangular noise-like soliton,and dissipative soliton mode-locked fiber laser are built respectively.Among them,the rectangular noise-like soliton fiber laser can realize self-starting,the optical-to-optical conversion efficiency is up to 4.64%,the maximum output power is 49.7m W;By adjusting the intracavity net dispersion,the spectral evolution of dissipative solitons in a normal dispersion resonator is studied.The maximum spectral width is 21.11 nm.(3)The Kerr-lens self-mode locking model in single-mode fiber is innovatively proposed,and the Kerr-lens self-mode-locked fiber laser based on single-mode fiber is successfully realized.This laser can achieve free switching of five different modes: traditional soliton with fundamental frequency(3.93 MHz),bright-dark soliton with fundamental frequency,the third-order harmonic(11.79 MHz)mode-locking,the 81st-order harmonic(318.4 MHz)mode-locking,and the 81st-order harmonic dual-wavelength mode-locking.(4)The working performance of cylindrite used as a 1.5 μm-band laser modulation device is studied.Firstly,the basic properties and research status of cylindrite are introduced;Then 2D cylindrite was prepared and its saturable absorption characteristics at 1.5 μm band are tested;The 2D-cylindrite SA is integrated into the fiber laser using the sandwich structure,and the mode-locked pulse output under different net dispersion is realized through the dispersion management technology.In addition,4.84 MHz stable mode-locked pulse output is realized based on the dual-end pump structure.The above work reveals that fiber lasers based on NPR technology are good platforms for studying various soliton phenomena and nonlinear dynamics;Compared to saturable absorption devices based on two-dimensional cylindrite and Kerr-lens self-mode-locking technology based on single-mode fiber,NPR technology has more advantages in achieving self-starting mode locking,fs pulse output,high-repetition rate,high-power,and high-energy pulse output;Kerr-lens self-mode-locked fiber laser based on single-mode fiber shows obvious polarization-dependent pulse output characteristics;Two-dimensional cylindrite has excellent saturable absorption characteristics,and has great research value and application prospects in passively mode-locked fiber lasers. |
