Research Of Mode-locked Fiber Laser Based On Low Dimension Materials Coupling With Evanescent Field

Ultra-fast fiber lasers have the advantages of high peak power,high beam quality,high stability,and compact structure,and have important application prospects in fields such as optical communication,optical sensing,material processing,and national defense.Ultrafast fiber lasers can be achieved either by active or passive modulation methods.Compared with active modulation,passive mode-locked laser technology can provide a simple and cost-effective solution.In a passively mode-locked fiber laser,a saturable absorber is the core device that achieves its mode-locking operation.Semiconductor saturable absorber mirror?SESAM?is the first generation of saturable absorbers,its most widely used.However,it has the disadvantages of complicated preparation,limited working bandwidth and easy damage.With the increasing demand for stable,wide-band operation,cost-effective,and short-pulse lasers,researchers have been exploring saturable absorbers with better performance,and at the same time looking for more efficient and compact laser resonator designs.At present,based on different low-dimensional materials,such as zero-dimensional quantum dots,one-dimensional gold nanowires,and two-dimensional materials?graphene,black phosphorus,transition metal sulfides,etc.?,researchers have obtained different low-dimensional materials.Linear optical properties and ultra-fast fiber laser output based on low-dimensional materials.However,due to the immature material preparation methods and the relatively low damage threshold of low-dimensional materials,the conventional low-dimensional material saturable absorbing devices still cannot meet the application requirements of high-power,high-integration fiber laser devices.This paper is based on the defects of low-dimensional material damage,low efficiency of conventional saturable absorbing devices,and low efficiency of light and materials.At the same time,the nonlinear optical properties of two-dimensional metal carbide Ti₃C₂ and one-dimensional gold nanorods are studied for broadband applications.And explored its application potential for ultra-fast laser generation.The main work is as follows:?1?The nonlinear optical properties of Ti₃C₂ were experimentally studied.Based on the evanescent wave coupling mechanism,the mode-locked laser output of the optical communication band was realized.Based on the Z-scan measurement method,the saturated absorption of Ti₃C₂was measured at 1560 nm.At the same time,Ti₃C₂ was transferred to D-shaped fiber,and it was introduced into the resonator as a saturable absorber.The ytterbium-doped high-doped fiber was used as the gain medium to obtain a ytterbium-doped fiber laser?EDFL?pumped by a 980 run laser diode.When thepump power reaches a threshold power of 65 mW,the laser produces a stable dissipative soliton pulse.When the pump power reaches 150 mW,the mode-locked pulse center wavelength of the mode-locked laser is 1572 nm,the pulse width is 210 ps,the repetition frequency is 8.2 MHz and the output power is 0.492 mW.At a pump power of 200 mW,a maximum output power of 2.76 mW can be achieved.The experimental results show that the Ti₃C₂ saturable absorber coupled with the evanescent wave can be used to provide stable mode-locked pulse sequence in the all-fiber EDFL.?2?Gold nanorods were prepared by seed-mediated growth method.The nonlinear material properties of gold nanorods were studied and put into a Z-scan measurement platform.The saturation absorption at 1064 nm was obtained.A gold nanomaterial D-shaped fiber saturable absorber that is compatible with a fiber laser resonator is prepared and introduced into the fiber resonator.Using ytterbium ion highly doped fiber as the gain medium,a ytterbium-doped fiber laser?YDFL?pumped by a 980 nm laser diode was obtained.When the pump power reaches 150 mW,YDFL generates stable dissipative soliton pulses.When the pump power reaches 220 mW,the mode-locked pulse center wavelength of the mode-locked laser is 1041 nm,the pulse width is 162.3 ps,the repetition frequency is 6.649 MHz and the output power is 1.31 mW.It can be seen from the above experimental results that the gold nanorod saturable absorber coupled with the evanescent wave can be applied to the all-fiber YDFL and output a stable dissipative soliton pulses.