Pulsed Fiber Laser Actively And Passively Modulated With Low Dimensional Nanomaterials

Pulsed lasers with high peak power,high pulse energy,high repetition rate and broad spectral bandwidth are important sources in optical communications,sensing,materials processing and medicine.Fiber laser is one of the most promising platforms for optical pulse generation because of their compact structure,effective heat dissipation,high beam quality and good compatibility.However,the current pulsed lasers suffer bottleneck due to the limited operation bandwidth,complicated fabrication technology and fiber incompatibility of the traditionally used optical modulation devices for pulse generation.As a result,the most effective solution is to develop novel optical modulators with sophisticated performances,easy fabrication and low cost based on new materials and technologies.In this thesis,we first investigate the optical response and optical modulation properties of black phosphorus(BP),single wall carbon nanotubes(SWNTs)based saturable absorbers and graphene based electro-optic modulator.The as-fabricated saturable absorbers and graphene electro-optic modulator were integrated with fiber lasers to generate tunable laser pulse via active and passive Q-switching and mode-locking.We then studied the pulse formation dynamics in time and frequency domains by theoretical simulation of the mode-locked laser.The research can be summarized as follows:(1)Preparation and characterization of BP and SWNTs based saturable absorbers.The BP based saturable absorbers are fabricated by mechanical exfoliation and liquid phase exfoliation methods,respectively.We then transferred the mechanically exfoliated BP flakes to fiber end to form all-fiber integrated saturable absorber.The liquid phase exfoliated BP was functionalized with polycarbonate polymer to form polycarbonate/BP polymer composite with enhanced stability.The mechanically exfoliated BP flakes were identified to show strong linear and nonlinear anisotropic optical absorption.SWNTs with tube diameters distribution between 1.0 and 1.3 nm were dispersed to sodium-carboxymethycellulose(CMC)solution and ultra-sonicated.The dispersion was extracted and evaporated to form SWNT-CMC polymer composite.The optical absorption measurement shows that the SWNT-CMC has peak absorption at 1.5 ?m communication band.(2)Passively Q-switched and mode-locked laser with BP First,the mechanically exfoliated BP flakes and liquid phase exfoliated BP polymer composite were used as saturable absorbers to generate large energy Q-switched pulses in Erbium doped fiber lasers.The pulse evolution dynamics was analyzed.Mode-locked pulses were obtained after modifying the laser cavity previously used for the mechanically exfoliated BP saturable absorber.The BP mode-locked pulse dynamics was investigated theoretically by the solution of the Ginzburg-Landau equation,which describes the pulse evolution in fiber cavity.Distributed Fourier method was used to solve the equation.(3)Tunable pulsed laser mode-locked with SWNT-CMC saturable absorber SWNTs based saturable absorber has broadband optical response.We integrated the SWNTs-CMC saturable absorber to Erbium doped fiber laser to investigate the central wavelength,spectral bandwidth and pulse duration tunability by introducing spectral filtering effect.By simulating the pulse circulation model in the laser cavity,the influence of the intracavity filtering effect was demonstrated the key reason for the laser spectrum and pulse shape evolution.(4)Design and investigation of graphene electro-optic modulator The graphene optical modulation principle was theoretically analyzed by considering the graphene energy band structure.Based on the merits and demerits of the investigated graphene electro-optic modualtors,for the first time,to the best of our knowledge,we propose a parallel plate capacitive graphene electro-optic modulator.The proposed modulator was then fabricated and demonstrated to be a broadband device(between 1.5 and 2 ?m).The optical response rate and modulation depth were also characterized.(5)Graphene actively Q-switched and synchronously Q-switched lasers.Graphene actively Q-switched lasers were firstly obtained experimentally by using our electro-optic modulator in 1.5?m Erbium doped fiber laser and 2?m Thulium/Holmium co-doped fiber laser.Synchronized Q-switching was also observed by integrating the very same device in a composite fiber cavity consists of 1.5?m Erbium doped fiber laser and 2?m Thulium/Holmium co-doped fiber laser.We demonstrated that the output pulse duration,pulse energy and repetition rate are tunable by adjusting the modulation frequency of the voltage.The relation between the graphene actively Q-switched pulses and the electrical signal was discussed by taking the experiment results into account.