Study On Ultrashort Fiber Laser With Novel Two-dimensional Material Saturable Absorber

Ultrashort-pulse fiber laser has the advantages of miniaturization,high efficiency,good environmental stability,convenient heat management,no light path alignment and industrialization.The femtosecond fiber laser has a very wide range of applications and needs in many fields such as industry,commerce,research and military.At present,the main method to achieve ultrashort pulse is passive mode-locked technology based on the semiconductor saturable absorption mirror?SESAM?.However,the preparation of the SESAM requires complicated epitaxial growth techniques and complicated post-processing,the preparation is expensive,and it is not convenient in the fiber.People have been committed to exploring new saturable absorbers to replace SESAM.Exploring new saturable absorbers is an important part of laser physics and laser technology.The dissertation mainly focuses on some common problems and difficult problems that femtosecond fiber lasers currently face,and we mainly researching the nonlinear optical properties of the new two-dimensional material saturable absorbers,and using them to study ultrashort pulse fiber lasers.The main research results of the article are as follows:1.Graphene/phosphorus nanoheterojunction was obtained by using graphene and black phosphorus.From the comparison of Raman spectra of black phosphorus in nanoheterostructures and pure black phosphorus,the nanoheterojunction significantly enhanced the stability of black phosphorus.This method provides a new technology to protect blak phosphorus.And we set up erbium-doped passive Q-switched fiber lasers based on the SA.When the pump power is increased from 67 mW to 607 mW,the repetition frequency of Q-switched pulse is increased from 22.45 kHz to 76.63 kHz,the corresponding pulse width is reduced from 5.99?s to 3.28?s,and the maximum single-pulse energy is up to 267.5 nJ.2.We also studied an erbium-doped passively mode-locked fiber laser based on the SA.The results show that when the pump power is 72 mW,a stable continuous wave mode locked?CWML?was obtained.The laser output power is 2 mW,the pulse width is 820 fs,the repetition frequency is 7.43 MHz,the optical spectrum of mode-locked pulses is centered at 1529.92 nm and 3 dB spectral width is 3.4 nm.In the experiments,increasing the pump power and slightly adjusting the orientation of the polarization controller,the harmonic mode-locking is achieved.The maximum repetition frequency is 295.6 MHz and the corresponding pulse width is 865 fs.The optical spectrum of harmonic mode-locking is centered at 1529 nm and 3 dB spectral width is 4 nm.By adjusting the concentration of Graphene/phosphorus nanoheterojunction saturable absorbers,a mode-locked pulse with a pulse width of 148 fs was realized in an erbium-doped passively fiber laser with a corresponding repetition frequency of 7.5 MHz and a center wavelength of 1531 nm,and a 3 dB bandwidth of 19.4 nm.3.We investigated the optical nonlinearity of MXene Ti₃C₂T_x in four excitation sources with wavelengths centered at 800 nm,1064 nm,1550 nm and 1800 nm by using the widely employed z-scan measurement technique.An erbium-doped mode-locked fiber laser based on MXene Ti₃C₂T_x was built.When the pump power is 238 mW,a stable continuous wave mode-locked laser pulse with an output power of 3 mW.The inter pulse time difference is 137.4 ns and the pulse width is 159 fs.The optical spectrum of mode-locking is centered at 1555.01 nm and 3 dB spectral width is 22.2nm.4.We applied to an ytterbium-doped fiber laser and obtain a stable picosecond pulse output.When the pump power is 482 mW and output power is 9 mW.The repetition frequency is 18.96 MHz and the mode-locking pulse duration is 480 ps.The wavelength center is located at 1065.89 nm with 4.4 nm bandwidth at 3 dB.