Research On Dual-Wavelength Ultrashort Pulse Fiber Laser

Ultrashort pulse fiber lasers have been widely used in many applications such as fiber optic communications and material processing due to their advantages such as simple structure and high peak power.Passive mode-locking technology based on saturable absorbers has been considered one of the most effective ways to obtain ultrashort pulse laser due to its compactness,simplified operation,and cost-effectiveness,and has aroused great research interest.On the other hand,dual-wavelength ultrashort pulsed fiber lasers have gained much attention due to their feasibility in many applications,including Raman imaging,difference frequency generation and optical communication system.In this thesis,we fabricated a single-walled carbon nanotube saturable absorber and characterized its properties,and obtained the singlewavelength ultrashort pulse laser output using this saturable absorber.In addition,we demonstrated a dual-wavelength ultrashort pulsed fiber laser system based on dual-resonator cavity,that can obtain C-band dual-wavelength synchronous and asynchronous ultrashort pulses.The main research contents of this thesis are as follows:First,preparation and characterization of single-walled carbon nanotube saturable absorber.In this thesis,the single-walled carbon nanotube saturable absorber thin films with different concentrations were fabricated by liquid-phase exfoliation method.And the microstructure,Xray diffraction,Raman spectrum,and nonlinear absorption characteristic of the single-walled carbon nanotube saturable absorber films were characterized.The characterization results showed that we obtained a stable and reliable single-walled carbon nanotube saturable absorber.Second,single-wavelength ultrashort pulse laser output based on single-walled carbon nanotube saturable absorber.First,the conventional solitons were obtained by applying the low concentration single-walled carbon nanotube saturable absorber to erbium-doped fiber lasers with maximum peak power of 3.12 W and pulse width of 2.3 ps,and the pulse is split into harmonic mode-locked solitons by increasing the pump power.Further,different concentrations of saturable absorbers are placed in the laser,and the influence of the concentration on the pulse characteristics is obtained.The results show that the high-concentration saturable absorber can narrow the pulse and increase the peak power due to the deeper modulation depth.Third,we demonstrate a c-band dual-wavelength mode-locked fiber laser based on a dualcavity,which can obtain stable dual-wavelength synchronous and asynchronous pulses.When the laser has no saturable absorber,the dual-wavelength continuous laser output with center wavelengths of 1532 nm and 1561 nm is obtained.When a saturable absorber is added and the cavity length is not adjusted,the laser system can also work in a stable dual-wavelength asynchronous mode-locked state,with the center wavelengths being 1531 nm and 1556 nm,respectively.Selecting high-concentration saturable absorber as the mode-locking device,and finely adjusting the cavity length difference to less than 830 μm,synchronous mode-locked pulses at two wavelengths of 1533 nm and 1562 nm are obtained.The proposed system has high long-term stability in both asynchronous and synchronous mode-locked states,which provides a novel approach to achieving a dual-wavelength ultrashort pulse laser generation system that is more dependable and consistent.