Research On Erbium-doped Fiber Lasers In The C And L Band Based On Nonlinear Polarization Rotation

Owing to the unique advantages of the small size,ultra-wide bandwidth direction and good compatibility,passively mode-locked erbium-doped fiber lasers have extensive application prospects in optical communication,biomedical,laser processing and others field.Generally,Nonlinear Polarization Rotation(NPR)possesses artificial saturable absorption is regarded a more efficient way to generate mode-locked pulse.At present,erbium-doped fiber lasers with different central wavelength have attracted significant attention,such as C band(1530~1565 nm)and L band(1565~1625 nm).The L band mode-locked fiber laser can extend the communication wavelength from C band to L band.Thus,it greatly improves the communication capacity.In this thesis,characteristics of bound states,dissipative soliton resonance,multiple pulses and other pulses in the C and L band erbium-doped fiber laser with NPR are studied.The main work of this thesis is as follows:1.The research background and development history of fiber lasers are introduced.Several mode-locking technologies in mode-locked fiber lasers are analyzed.Finally,the development process of NPR mode-locked fiber lasers is described.2.The mode locked mechanism based on NPR is analyzed theoretically.In addition,the generation of solitary pulses is simulated by the coupled Ginzburg-Landau equation and the build-up of the mode locking is also analyzed in the time and spectral domains.In the numerical simulation,by adjusting the parameters in the cavity,multiple pulses and pulse switching are obtained.This simulation phenomenon is in good agreement with the experimental phenomenon.Simultaneously,the results help to deepen the understanding of soliton mode locking dynamics.3.Various structures of bound states in a fiber laser mode-locked by NPR are observed.Experimentally,the mode-locking operation is generated at 1564 nm with the 3 dB spectral bandwidth of 11.6 nm.With the alteration of cavity parameters,diverse structural bound-state patterns are obtained in the fiber laser.In particular,the bound states with fixed soliton separation are observed,where the soliton number inside the bound states increases from two solitons to fourteen solitons with boosting the pump power.Apart from the aforementioned bound states with regular triangular envelope of the autocorrelator,the bound states with compound soliton structure are also obtained,typically including the(2+2)-type,(2+2+2)-type,(2+1)-type,and(3+1)-type bound states.Additionally,numerical simulations are also implemented to confirm fine structure of the bound states.The results contribute to further understanding the complex nonlinear dynamics of these multi-soliton optical patterns.4.The wavelength-switchable operation of multiple pulse and dissipative soliton resonance in an L-band fiber laser with NPR are investigated.By properly adjusting polarization controller(PC),the fiber laser is apt to achieve mode locking operation at 1565 nm and 1604 nm waveband,respectively.Moreover,through appropriately controlling the filtering effect induced by NPR,continuously tunable operations have been observed from 1563.7 nm to 1574.6 nm with a spectral tuning range of around 10.9 nm and from 1600.3 nm to 1605.7 nm with a tuning range of around 5.4 nm.Interestingly,by manipulating the cavity parameters,the fiber laser operated at 1565 nm waveband tended to generate multiple solitons,whereas one operated at 1604 nm waveband tended to generate rectangular dissipative soliton resonance whose temporal widths increased with pump power.Our investigations may not only be treated as a multi-functional optical source for further applications,but also benefit the insight into pulse dynamics in fiber laser system.