The Research On Pulsed Fiber Laser Based On Two-dimensional Atomic Crystal

Pulsed fiber lasers mainly contain two technologies:Q-switching and mode-locking.Actively Q-switching or mode-locking is limited in practical applications because of extra modulation devices,what is not necessary in passive Q-switching and mode-locking lasers.Passively Q-switched and mode-locked fiber lasers have widely applications in optical communications,optical sensing,industrial processing,and optical confrontation owing to their simple and compact structures,high beam quality,low cost of maintenance.For passive Q-switching or mode-locking fiber lasers,saturable absorber is the key components.Initially,the dye as the first generation of saturable absorbers has been successfully used for the passive mode-locked neodymium glass laser.As the technology of semiconductor improved,semiconductor saturable absorber mirrors have been successfully applied in pulsed fiber lasers,which largely fostered the development of ultrafast lasers towards the goals of high-power,low cost,compactness,and high-efficiency.However,the preparation of semiconductor saturable absorber mirror is extremely complex and high cost.Most importantly,it has narrow operation bandwidth.Researchers have been looking for superior performance saturable absorbers.As the development of new materials,nano-materials saturable absorbers have obtained extensive attentions.Among them,the most representative material is carbon nanotube,which has excellent non-linear absorption characteristics.However,carbon nanotube has low modulation depth and damage threshold,the response spectral range of carbon nanotube sensitively depends on the diameter and chirality,restricting its practical applications in fiber lasers.Recently,two-dimensional atomic crystal materials,such as graphene,topological insulator,have obtained much of attentions from researchers of ultrafast lasers because of their unique optical and nonlinear optical properties.Based on two-dimensional atomic crystal materials:graphene and topological insulator,this thesis systematically studies the preparation,transfer and the application in Q-switching and mode-locking fiber lasers of graphene and topological insulator.Specific research results are summarized as following:?1?We propose a simple and high quality method to transfer graphene and verify it experimentally though material characterization and application in fiber laser.We experimentally find that the transfer quality of CVD-grown graphene could be improved by ultrasonic processing of target substrates.Atomic force micrograph and Raman spectroscopy reveales that the graphene films transferred onto the target substrate with ultrasonic processing possess less wrinkles and defects than that of the sample without ultrasonic processing.By integrating a fiber pigtailed graphene?treatedby UP?device into a fiber laser cavity,we can obtain stable mode-locking pulse with better characteristics.We anticipate that this transfer technique may be applicable to boost the performance of other graphene photonics devices,such as optical modulator,detector,polarizer,etc.Then,we propose a simple method to study the effects of the number of graphene layers on pulse parameters under the same fiber laser cavity with similar condition,which is introducing space coupling devices.We experimentally find that the pulse parameters?pulse energy,pulse duration and central wavelength?sensitively depend on the characteristics of saturable absorber.?2?For the first time,we achieve passive mode-locking fiber laser with topological insulator.For topological insulator:Bi₂Te₃,we first experimentally study its nonlinear absorber and obtain the parameters of saturation absorption.And then,we achieve mode-locking pulses at communication band.For another topological insulator:Bi₂Se₃,though Z-scan technology,we experimentally verify that Bi₂Se₃ has obvious saturable absorption.And then,we obtain tunable wavelength picosecond mode-locking pulse with Bi₂Se₃.This contribution unambiguously shows that apart from its fantastic electronic property,topological insulator may also possess attractive optoelectronic property,especially for ultrafast fiber laser.?3?For the first time,we achieve passive Q-switching fiber laser with topological insulator.For topological insulator:Bi₂Se₃,by the drop-cast/evaporation approach,we fabricate a self-assembled membrane.The balanced twin-detector technique at communication band is used to characterize the saturation absorption parameters of the device,by deploying this device into a fiber laser,we had achieved stable Q-switched pulses.Through fine tuning the cavity birefringence,we can achieve wavelength tunable,even dual-wavelength passive Q-switching operation.For topological insulator:Bi₂Te₃,through optical depositing method,we fabricate the saturable absorber.And then we demonstrated a passively Q-switched Er-doped all fiber laser based on it in a linear cavity.The results indicate that topological insulator is also suitable for the generation of Q-switch pulses.?4?Based on a topological insulator saturable absorber,we experimentally achieve large energy,widely wavelength tunable passively Q-switched pulses in an erbium-doped fiber laser.The saturable absorber is prepared through an optical deposition method.Its saturating intensity and modulation depth are measured to be about 57 MW/cm² and 22%,respectively.We show that the high modulation depth of TI-SA allows the generation of stable Q-switched pulses with per-pulse energy up to1.5?J and its broadband saturable absorption favors the tunable Q-switching operation from 1510.9 nm to 1589.1 nm.Our study suggests that topological insulator could be a promising saturable absorber for both the high energy and broadband optical applications.?5?We experimentally investigate the soliton dynamics in a topological insulator based mode-locking fiber laser.With the increase of pump power,various multi-soliton operation states:ordered,chaotic and bunched multiple-soliton,are subsequently obtained.Once the pump power exceeds 401 mW,noise-like pulse state emerged,with a maximum 3 dB bandwidth of about 9.3 nm.Though carefully adjusting the polarization controller,we obtain another noise-like state,which can be self-started and maintained even up to the maximum pump power.This systematic study clearly demonstrated that topological insulator could be an effective saturable absorber for studying the formation mechanism of various soliton states.