Theoretical Simulation And Characteristic Analysis Of Passively Mode-locked Fiber Laser

Passively mode-locked laser can generate ultrashort pluses and haveadvantages of the low threshold value, wide wavelength range, the simple structureand easy to initiate, which makes it become not only a new technology of laser field,but also one of the hot research topics. Especially in recent years, passivelymode-locked fiber laser based on the saturable absorber has become a researchhotspot. At the same time, the emergence of carbon nanotubes and graphenespromotes the development of the passive mode-locked fiber laser.Due to the excellent nonlinear optical properties, carbon nanotubes have beennoticed quickly and applied to the passive mode-locked fiber lasers. Researchershave devoted to the integration of these two new materials and fibers for the modelocked device, such as the D-type optical fiber coated with carbon nanotubes,hollow fibers filled with carbon nanotubes, photonic crystal fiber filled graphenes,etc. They sought to make the device fabrication process simple and low cost andmake the device easier to integrate into a fiber laser to achieve the output ofultrashort pulses.In this paper, we simulate the evolution process of passively mode-locked fiberlaser pulse based on the master equation. Then a multimode semiconductor laserand double-clad ytterbium-doped fibers are adopted as pump source and gain mediaand by the use of mode-locked device which combines single-walled carbonnanotubes (SWCNTs) with optical fiber. We fabricate a passively mode locked fiberlaser with a ring cavity and then its output pulses are studied. The main researchwork of this paper is as follows:1. We summarize classifications and characteristics of a passively mode-lockedfiber laser, discuss the domestic and overseas research status of the passivelymode-locked fiber laser and describe the domestic and overseas research status ofthe mode locked fiber laser based on the mode locker with SWCNTs.2. We establish the theoretical model of passively mode-locked fiber laser withthe saturable absorber based on the master equation, analyze the impact of thetunable parameters of the cavity on the output pulse, analyze in detail the influenceof the lengths of ytterbium-doped fiber, single-mode fiber and the absorptioncoefficient of the saturable absorber on pulse width and energy of the output pulse.3. We state the development history of SWCNTs and graphenes as saturableabsorber and their fabrication process and characteristics. Then we introduce thefabrication method of microchannels using femtosecond laser induced water breakdown and fabricate mode locker device combined SWCNTs with optical fiber.4. We build the setup of ring cavity based double clad fiber laser which couldoutput cw laser. On the basis of this laser, we fabricate a passively mode lockedfiber laser with microchannels and test and analyze the characteristics of the outputpulses of the fiber laser.