Pulsed Fiber Laser Based On Novel Transition Metal Disulfides

Pulsed fiber lasers have been widely used in numerous scientific research fields such as optical communication,machining,lidar,fiber sensing,biology,medicine,nonlinear optics etc Pulsed fiber lasers have a range of advantages,e.g.simple structure,compact,stability,resilient to harsh environments etc.,which allow it to meet the different demands in many application fields.Mode-locked fiber lasers consists of active mode locking and passive mode locking method,separately.For the active mode-locking method,it usually needs acoustic-optic or electro-optics modulator,which makes the entire laser system complex.Compared with the active method,passive mode-locking technique has many more benefits,such as all-fiber scheme,low cost,high quality of pulse and ease of integration for an all optical fiber application So far two dimensional(2D)materials have been widely investigated because of the high nonlinear reflectivity and high modulation depths.2D materials also have the advantages of low mode locking threshold,wide wavelength range,fast recovery and ease of fabrication,which make it a key device for the passively mode-locked fiber lasers.Systematic discovery of functional 2D materials has been the focus of many studies,to date a number of 2D materials including graphene,topological insulators transition metal disulfides(TMDs)and black phosphorus have been widely used as saturable absorber in mode-locked fiber laser.However,research on 2D materials is still in initials stage.It is very meaningful to study the existing 2D materials for further and explore new type of 2D materials with high performanceIn this work,the existing TMDs(WS2 and SnS2)have been studied comprehensively to generate multi-wavelength pulsed and dissipative soliton.Furthermore,NiS2 has been used in the proposed mode-locked fiber lasers as a new type of TMDs.The mechanism of mode-locked pulse is studied theoretically and the theoretical model of mode-locking based on this saturable absorber has been demonstrated the effects of dispersion and fiber nonlinearity have been also discussed.To study the multi-wavelength fiber laser based on WS2,the WS2 nanosheets were transferred onto the microfiber knot resonator(MKR)to achieve the novel saturable absorber,namely,WS2-MKR SA.Seven-wavelength pulsed fiber laser has been obtained in Er-doped fiber laser using WS2-MKR SA for the first time.Furthermore,the number of the wavelength can be adjusted by changing the diameter of the microfiber knot resonatorIn order to explore the more laser applications for SnS2,the SnS2-PVA film SA was successfully placed into the laser cavity to achieve the dual-wavelength pulse and dissipative soliton.For dual-wavelength soliton,the central wavelength of dual-wavelength pulse were 1536.7 nm and 1562.6 nm,the pulse width was 5.3 ps.For dissipative soliton,the high single pulse energy was obtained by optimizing the dispersion of the laser cavity.The optical spectra of the dissipative soliton were widened from 21.7 nm to 32 nm with the pumping power increasing from 85 mW to 187 mW.The pulse width was 152 fs by using a standard single-mode fiber as pulse compressor.Finally,the novel NiS2 was firstly used in different fiber lasers to achieve Q-switched and mode-locked pulse.The nanosecond pulses in Yb-,Er-and Tm-doped fiber laser were obtained using NiS2-PVA film as saturable absorber.The central wavelengths were 1064.5 nm,1562.86 nm and 1915.5 nm,the corresponding pulse widths were 978 ns,237 ns and 505 ns Subsequently,the NiS2 nanosheets were deposited on the microfiber and inserted into the laser cavity for achieving the ultrafast pulse laser.The central wavelength were 1064.5 nm,1560.2 nm and 1960 nm in Yb-,Er-and Tm-doped fiber laser,the corresponding pulse widths were 11.7 ps,524 fs and 1.2 ps.In this work,the novel transition metal disulfides(TMDs)based mode-locked fiber lasers have been investigated theoretically and experimentally.The research objectives consist of WS2,SnS2 and NiS2.The physical properties of WS2 and SnS2 and their applications in mode locked fiber lasers are demonstrated.Multi-wavelength pulse and dissipative soliton have been obtained based on WS2 and SnS2,which is the strong evidence of their excellent optical nonlinearity.Then,the nonlinear optical properties of the new 2D material-NiS2 has been investigated and used in the fiber laser to achieve Q-switched and mode-locked pulses for the first time.Nanosecond Q-switched pulse and femtosecond mode-locked pulse have been generated based on NiS2 S A as a saturable absorber.This work makes an in-depth study on the physical properties and laser applications of the novel TMDs,which plays an important role in promoting the applications of 2D materials.These results also pave the way for the further interdisciplinary research between 2D materials and nonlinear optics.