Pulsed Fiber Lasers By Using Two-dimensional Materials As Saturable Absorbers

Pulsed fiber laser sources exhibit lots of advantages,such as compactness,cost-effectiveness,robustness,good heat dissipation,freedom from misalignment,and the unique pulse characteristics,which can meet the various requirements in different application fields.They are widely used in high-speed optical fiber communications,surgery,biological detection,laser micromachining of materials and terahertz wave generation and so on.Passively mode locking technique with saturable absorbers?SAs?is one of the simplest and most effective methods to achieve short pulses.The SA plays a key role in shaping the pulses in the time domain.Therefore,there is always a strong incentive in hunting for high-performance SAs.Two-dimensional?2D?materials,thanks to their broadband absorption and high nonlinearity optical properties,are excellent candidates as saturable absorbers.Additionally,they are low cost,easy manufacture,function,and all-fiber integration.Therefore the technology of using the 2D material as a SA has become a current international hot and important frontier.In this thesis,we studied the Q-switched and mode-locked fiber lasers based on 2D materials,which includ the topological insulators and transition metal sulfides experimentally and theoretically.The main contents of the thesis are as follows:1.The formation mechanism and dynamic evolution of conventional solitons and dissipative solitons from passively mode locked fiber lasers with saturable absorbers were investigated by solving the Ginzburg-Landau equation.In order to optimize the fabrication process of the SA,the characteristics of the output pulses of mode locked fiber lasers by using a SA,different parameters were discussed in detail by keeping the pump and cavity conditions unchanged The evolution of the pulse width and the peak power evolution depending on the modulation depth and saturation power were demonstrated.2.The pulsed fiber lasers based on topological insulator of Bi₂Se₃ were receached.The topological insulator?Bi₂Se₃?was synthesized by chemical method and the Bi₂Se₃-PVA film was prepared through mixing it with polyvinyl alcohol?PVA?.The mode-locked pulses of the Er-and Yb-doped fiber lasers were achieved with Bi₂Se₃-PVA film SAs by optimizing the cavity parameters.The wavelength of the conventional soliton was 1600 nm and the shortest pulse width was 360 fs.The wavelength of dissipative solitons could be tuned from 1032 to 1037 nm,and the output pulse width was about 210 ps with pulse energy of 0.83 nJ.By utilizing three pieces of Bi₂Se₃-PVA film,wavelength switchable operation from 1532 nm to 1557nm could be achieved just by adjusting the pump power,and the dual-wavelength solitons and bound state solitons were observed.However,the dual-wavelength soliton operation could not be stable for a long time.The numerical results demonstrated that the separations of bound pulses had small variation and the different phase of the bound pulses appeared jumping change of?.3.The application of the transition metal sulfides as a SA in the pulsed fiber lasers was disscussed.The transition metal sulfides were made into different types of SAs.The high energy Q switched pulse in nanosecond domain was realized in a ring fiber laser with a WS₂-PVA film-type SA.Combining WS₂-PVA film with the nonlinear polarization rotation effect,the dissipative soliton pulse with a pulse width of 17.7 ps was realized in an erbium-doped fiber laser.By depositing the MoS₂ nanosheet onto the tapered fiber,the conventional soliton with a pulse width of 1.2 ps was achieved.A theoretical simulation for optimizing the stretched pulse laser was investigated.The corresponding experimental results of a fiber laser with the WS₂ saturable absorber,were in good agreement with the numerical results.The maxium 3 dB spectral bandwidth of 40 nm was reached.The characteristics of the stretched pulse laser need to be well-discussed by further experiment.4.The nonlinear polarization rotation mode-locking technique in a long fiber oscillator was discussed.The narrowband noise-like pulses,dissipative soliton resonance pulses,square noise-like pulses and nanosecond dual-pulses were observed respectively.All of these pulses have the same property of high energy.The noise-like pulses with narrow spectrum?1-2 nm?have larger pulse duration and lower peak power,and the intra-cavity maximum energy of noise-like pulses is up to 560 nJ without pulse breaking.For dissipative soliton resonance pulses,the spectral width is independent of the pump power,so that it intrinsically gets over the limit of bandwidth of gain fibers.The experimental and simulated results shows that the maximum energy of the rectangular-shape noise-like pulses is restricted by the number density of noise pulses within the envelope.The nanosecond dual-pulses with controlled tunable pulse width and energy,which could improve the efficiency and quality of the material removal,have potential applications in micromachining and material processing.