The Research On Ultrashort Pulse Fiber Laser Based On Noval Two-dimensional Materials

Ultrafast fiber lasers with picosecond or femtosecond pulses generation have exhibited good beam quality,excellent flexibility,designability,and ease integration.In the past decade,it has received extensive attention in optical communications,optical sensing,laser medical treatment,industrial processing,and basic disciplinary research.One of the main methods to obtain ultra-short pulses is passive mode-locked technique,where the key device is the saturable absorber.The most widely used saturable absorber is SESAM,both experimentally and commercially.However,SESAMs have the drawbacks of high cost,complex fabrication and limited range of optical response.These limitations motivate researchers and technologists to search for novel saturable absorbers with broadband response,large modulation depth,low loss,high thermal damage threshold and high stability.Two-dimensional materials,such as BP,have been widely used in mode-locked fiber lasers,due to the excellent saturable absorption properties.However,the instability of BP seriously hinders its practical application.In this dissertation,we make a systematic research on two-dimensional materials based mode-locked fiber lasers and put forward some countermeasures and solutions to this bottleneck problem.We introduce the preparation,characterization,transfer,nonlinear optical properties of the two-dimensional materials and study the two-dimensional material based ultrafast fiber lasers.Firstly,we designed the black phosphorus nanosheets and BPQDs/PMMA based SA mode-locked fiber lasers.The BP nanosheets were obtained by using liquid phase separation method.With the BP SA,fiber laser could generate mode locking pulses at communication band.To overcome the BP oxidation,we present a new method to enhance the stability of BP by making uniform BPQDs/PMMA composite nanofiber film using electrospinning technology.By employing the BPQDs/PMMA SA,the mode locking fiber laser could work well within 3 months,with a pulse duration of about 1.07 ps,cantered at a wavelength of1567 nm.Our experiments can prove that BPQDs/PMMA shows high stability and excellent nonlinear SA characteristics.Secondly,we reported on the synthesis of high quality bulk selenium?Se?-doped BP crystals using a mineralizer assisted gas-phase transformation in a mild growth condition and employed a liquid phase exfoliation approach to obtain few-layer?FL?Se-doped BP nano-sheets with 4 nm thickness from the bulk counterpart.We experimentally obtained FL Se-doped BP optical saturable absorption parameters by using Z-scan system at 800 nm wavelength.Taking advantage of its nonlinear optical property,we set up the negative dispersion and near-zero dispersion mode-locked fiber laser,which can generate femtosecond pulse train.Our results not only provide a new strategy in tailoring the nonlinear optical response of BP through element doping,but also suggest that FL Se-doped BP is an excellent candidate for ultrafast photonics.Finally,we systematic studied the TiS₂ nonlinear optical effect and ultrafast photonics application.Uniform and high purity single-crystal TiS₂ nano-sheets were prepared via a typical colloidal chemistry method.Verified by Z-scan system TiS₂ nano-sheets were found to be have strong nonlinear absorption properties from visible to infrared?IR?region.Here,we fabricate the TiS₂ nano-sheets based SA device.By using the SA,we obtained pulse train with pulse duration of about 1.04 ps centered at 1569.5 nm in the fiber laser.Furthermore,as a stable all-optical thresholding component,the device can effectively attenuate noise and boost the signal-to-noise ratio of the pulse from 1.90 to 10.68 dB.The findings indicate that TiS₂-based SA devices can be developed as excellent highly nonlinear photonic devices,which may advance the development of TiS₂-based optical communication technologies in the future.