Study Of The Nonlinear Optical Property Of Low Dimensional Nano-material And Its Application In Passively Pulsed Fiber Laser

In recent years,low dimensional nano-materials become a research foucs in the area of condensed matter physics.The excellent nonlinear property of graphene has been widely applied in pulsed fiber laser,which not only excites people to find out the optical property of low dimensional nano-materials,but also make people relize that the zero-band gap nature of graphene bring low switch ratio.Besides,the graphene is not compatible with sicilion,which urges people to find out some measures to make good use of the excellent property of graphene.Other than opening up the bandgap of graphene,the effort to find new substitute low dimensional nano-materials is more briefness.The remarkable properties of graphene have renewed interest in inorganic,two-dimensional materials with unique electronic and optical attributes.Transition metal dichalcogenides(TMDCs)are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into two-dimensional layers of single unit cell thickness.Although TMDCs have been studied for decades,recent advances in nanoscale materials characterization and device fabrication have opened up new opportunities for two-dimensional layers of thin TMDCs in nanoelectronics and optoelectronics.TMDCs such as Mo S2 and WS2 have sizable bandgaps that change from indirect to direct in single layers,allowing applications such as transistors,photodetectors and electroluminescent devices.Black phosphorus is a high mobility layered semiconductor with bandgap sensitively dependent on the number of layers,which can fill the space between zero-gap graphene and large gap TMDCs,making it an ideal low dimensional material for near and mid-infrared optoelectronics.Most importantly,the unique anisotropic nature may make black phosphorus attractive in the application of optoelectronic and electronic devices.In this work,the nonlinear optical perperty of two kinds of low dimensional nano-materials is investigate under multi-wavelength.We experimentally study the absorption property of low dimensional nano-materials,such as monolayer WS2,multilayer WS2,black phosphorus nanaoplate and black phosphorus quantum dots,and obtain the parameters of the nonolinear absorption.The absorption process and the absorption mechanism is quanlitatively explain.The nonlinear refractive index of monolayer WS2 and black phosphorus nanaoplate is measured.The advantage of low dimensional nano-materials used as saturable absorber is discussed and the mode-lock pulsed fiber laser which operate at 2?m has been successfully achieved along with Q-switch pulsed fiber laser based on black phosphorus nanaoplate saturable absorber.The results are as follows.1.The broadband saaturable absorption property of monolayer WS2 is investigated.With Z-scan technical,the nonlinear absorption perperty of monolayer WS2 and multilayer WS2 is studied comparably under 800 nm ? 1550 nm and 2?m.The experimental results show that monolayer WS2 has a wider absoption band than multilayer WS2,which induce by the coexistence of semiconducting and metallic states brought by impurity or defect.2.The nonlinear absorption perperty of black phosphorus nanaoplate and black phosphorus quantum dots is studied comparably under 800nm?1550nm and 2?m.The paraments,such as the saturable intensity and normalized modulation depth,are obtained by fitting data with theory model.The results show that the saturable intensity is close to the reverse saturable intensity of black phosphorus nanaoplate and black phosphorus quantum dots under 1550 nm and 2?m,which makes black phosphorus nanaoplate and black phosphorus quantum dots not easy to modulate high power pulsed laser but easy to achieve harmonic mode-lock.3.The nonlinear refractive index of monolayer WS2 and black phosphorus nanaoplate is measured with Z-scan technical for the first time,which is 10–13m2/W,larger than common material by 4 or 5 orders.4.The mode-lock and Q-switch pulsed fiber laser operate at 2?m has been successfully achieved based on black phosphorus nanaoplate saturable absorber.The results are as follows.By coupling black phosphorus nanoplatelets with fiber-taper evanescent light field,a new type of black phosphorus nanoplatelets based saturable absorber had been successfully fabricated and used with a thulium/holmium-doped fiber ring laser as a mode locker.A ~970 fs pulse centered at 1898 nm wavelength with a repetition rate of 19.2 MHz had been achieved with proper cavity dispersion.By increasing the pump power,the harmonically mode-locked solitons with harmonic order up to 37 was obtained.what's more,stable Q-switched operation centered at 1912 nm wavelength is achieved and pulse repetition rates varying from 240 to 600 k Hz.Our results suggest that black phosphorus nanoplatelets based saturable absorber is potential for pulsed laser operation in the eye-safe region of 2 ?m.