Study On Q-switched And Mode-locked Fiber Lasers Based On Sulfur Compounds

Pulse fiber lasers have been widely used in the fields of fiber communication and sensing due to their advantages of compact structure,low manufacturin g cost,mature technology and high electro-optical efficiency.As the simplest and most effective methods to produce pulsed laser,Q-switched and mode-locked technology have attracted extensive attention from scientists all over the world.At present,Q-switched technology can obtain high energy pulse laser.And femtosecond and picosecond orders of ultra-narrow pulse laser can be obtained by mode-locked technology.Among them,the technique of passively Q-switched and mode-locked using saturable absorber?SA?is the most widely used method to obtain pulse laser output.A mature saturable absorber for pulsed laser systems is semiconductor saturable absorption mirror?SESAM?.Stable performance is one of the biggest advantages of semiconductor saturable absorption mirror,but at the same time,it also has some disadvantages,such as low damage threshold,narrow working wavelength and so on.In recent years,with the continuous research and development of saturable absorbers by researchers,materials with the characteristics of saturable absorbers have been gradually discovered,including topological insulators,black scales,two-dimensional transition metal carbonitride,graphene,carbon nanotubes and transition metal sulfides.Although these materials have been used in pulsed fiber lasers,such as the high cost of topological insulators in the manufacturing process,the black scale is very easy to be oxidized in the air,the poor absorption and modulation of graphene,and the long recovery time of excitons due to the transition metal sulfides.Therefore,in order to obtain more stable and comprehensive saturable absorber,it is urgent to study new saturable absorber materials.This paper studies the application of three new two-dimensional metal sulfides,rhenium disselenide?ReSe₂?,germanium sulfide?GeS?and niobium distelluride?NbTe₂?,in pulsed lasers.The specific research contents are as follows:Firstly,rhenium powder and selenium powder were used as raw materials to prepare ReSe₂ powder.Then,liquid phase ultrasonic stripping and high speed centrifugation were carried out to obtain the dispersive liquid with few layers of ReSe₂ nanometer tablets.And stable Q-switched pulse output was obtained in ytterbium-doped fiber laser by using a single ReSe₂-PVA film.The central wavelength of the Q-switched pulse output is 1065.0 nm,the minimum pulse width is 2.27?s,the maximum output power is1.21 m W,the maximum pulse energy is 30.4 n J,and the repet ition frequency is17.89-39.86 k Hz.Secondly,GeS nanocrystals were prepared by liquid phase stripping method and their structure and morphology were characterized.The 1550 nm and 1064 nm passively mode-locked fiber lasers based on the GeS saturable absorber were built and stable mode-locked pulses were obtained.In the 1550 nm mode-locked fiber laser,GeS-SA realized stable mode-locked pulse output with a central wavelength of 1556.92 nm,a spectral width of 3.8 nm,a pulse width of 854 fs and a repetition frequency of 9.05 MHz.Stable pulse output with central wavelength of 1036.88 nm,spectral width of 0.02 nm,pulse width of 560 ps and repetition frequency of 11.40 MHz was achieved in the 1064nm mode-locked fiber laser.In addition,taking a picosecond laser with a wavelength of1550 nm as the test source,the nonlinear saturable absorption characteristics of GeS-SA were tested through the balanced dual-detector test system,and the modulation depth and saturation intensity were measured at 39%and 0.99 m W/cm².Finally,the passively mode-locked laser output characteristics of NbTe₂ nanometer tablets were studied.In the 1064 nm mode-locked fiber laser based on the NbTe₂saturable absorber,stable pulse output was achieved with a central wavelength of1061.31 nm,a spectral width of 1.01 nm,a pulse width of 469.9 ps,a repetition frequency of 9.02 MHz and a maximum monopulse energy of 64.2 p J.