Research On The Pulse Characteristics Of Black Phosphorous Fiber Laser

Ultrashort pulse fiber lasers are widely used in the field of industry,medical,defense and communication owing to the advantages of narrow pulse width,high peak power and high energy.We know that there are many ways to implement short pulses,but,with the advancement of disciplines and the continuous development of new nanomaterials,two-dimensional materials are developing rapidly,and their types are becoming more and more abundant,which constantly attracts the attention of researchers in the ultrafast field.Due to the excellent nonlinear absorption coefficient,ultra-fast recovery time and easy fabrication,some two-dimensional nanomaterials are continuously applied to ultrashort pulse fiber lasers,following by graphene materials,like transition metal sulfides(WS2,new saturable absorbing materials such as MoS2,etc.),topological insulators(Bi2Se3,Bi2Te3,etc.)and black phosphorus have been successively applied in passive mode-locked,fiber lasers.Utilizing the saturable absorption of materials and applying them to passive mode-locked fiber lasers to achieve ultrashort pulses is an important research direction in the current and future laser fields,and has broad prospects.This paper mainly focuses on the preparation of black phosphorus materials and the performance of saturable absorber devices.This paper mainly uses a new two-dimensional black phosphorus material as a saturable absorber,and proposes an erbium-doped fiber laser cavity which is combined with black phosphorus material and D-shaped fiber.The performance of the saturable absorption device and the pulse characteristics of the fiber laser output based on black phosphorus nanomaterials are studied experimentally.The black phosphorus material is used for the erbium-doped fiber laser cavity.The output of the dark soliton is implemented.The main research work of this paper is as follows:1.The energy band structure and crystal structure of black phosphorus nanomaterials are introduced.The reason why black phosphorus nanomaterials can be used as saturated absorbers is described and the process of saturated absorption is theoretically analyzed.The samples of black phosphorus nanoparticles were prepared by liquid phase stripping method.The prepared samples were characterized by scanning electron microscopy,Raman spectroscopy and Fourier transform infrared spectroscopy.Under the scanning electron microscope,the black phosphorus nanoparticles were observed to have obvious layered structure and flake structure.The elemental analysis by energy dispersive spectroscopy showed that the proportion of phosphorus atom was 62.2%.The black phosphorus nanoparticles were characterized by Raman spectroscopy.The film has three distinct characteristic peaks in the range of 300-500 wavenumbers.The positions of the three characteristic peaks are 358.2 cm-1,432.9 cm-1,and 463.0 cm-1,respectively.The corresponding vibration modes are Al(out-of-plane modes),B2g and Ag2(in-plane modes);The transmittance in the range of 1300 nm to 1000 nm was measured by Fourier transform infrared spectrometer,and the prepared black phosphorus nanoparticles were observed.The linear transmission spectrum of the dispersion near 1590 nm is about 80%.2.The prepared black phosphorus nanoparticles dispersion is deposited into the active region of the D-shaped fiber by light pulse deposition.Under the action of the pump light,the material is deposited and adsorbed on the surface of the D-shaped fiber to form a saturable absorber device.In the experiment,we used the double-arm bridge method to measure the nonlinear characteristics of the black phosphorus saturable absorber device based on D-shaped fiber.The experimental results show that the modulation depth of the saturable absorber device is about 5.7%,and the saturation intensity is about 11.7 MW/cm2 and the unsaturated loss is about 13%.It can be inferred that we have prepared a good saturable absorber device.Then,an erbium-doped fiber laser based on D-shaped fiber and black phosphorus saturable absorber was built.The dark soliton pulse of the black phosphorus saturable absorber material was realized in the erbium-doped fiber laser by the action of the evanescent field in the D-shaped fiber.The soliton pulse has a center wavelength of 1597.7 nm,a spectral bandwidth of 0.52 nm,a fundamental repetition rate of 14.93 MHz,and a dark soliton pulse width of 951 ps.