Studies On The Fabrication And Application Of Novel Carbon-based Nanomaterial Saturable Absorber

Ultrafast pulses maintain significant applications,such as transient imaging,optical communications,spectroscopy,medicine,and material processing.Passively mode-locked fiber lasers have been widely utilized to generate ultrashort pulses,which is regarded as the next-generation laser source that can replace the solid state laser.In recent years,single-walled carbon nanotube(SWNT)and graphene have been used to fabricate saturable absorber(SA).By comparison with the conventional mode-locking technique,carbon-based mode locker displays great advantages on saturable intensity,damage threshold,integrated method and cost.The novel SAs provide the foundation for the development of passively mode-locked fiber laser.Additionally,inspired by the investigation of graphene,the nonlinear optics of other two-dimensional material attracted much attention.In our works,the efficient SAs are fabricated with the carbon-based nanomaterial and transition metal dichalcogenides(TMDs),which are used to construct several new-types of passively mode-locked fiber laser,such as ultrafast distributed fiber laser,flexible pulse-controlled fiber laser,bidirectional mode-locked fiber laser.Pulses with distinct features are achieved from theses laser.The pulse evolution dynamics and output characteristics are studied experimentally.The main research contents of this dissertation are as follows:1.It is found that the wavelength can be switched between 1530 and 1560 nm by the intracavity loss in the SWNT-mode-locked fiber laser.By balancing the loss and gain in the oscillator,dual-wavelength mode locking can be observed,and the wavelength-switched phase-locked bound state pulses were studied.A compact pulse-controlled all-fiber laser is proposed based on SWNT,by exploiting a flexible filter system that is composed of an intracavity fiber Bragg grating(FBG).The pulse width of the laser can be tuned from ~7 to ~150 ps flexibly and the wavelength of pulse can be tuned with the range of ~20 nm precisely.2.A distributed ultrafast fiber laser(DUFL)is proposed and demonstrated with a linearly chirped fiber Bragg grating(CFBG).The total cavity length is linearly changeable as a function of the pulse wavelength,which is different from the traditional ultrafast fiber laser having a constant cavity length.The spectral sidebands of pulses emitted from DUFL are greatly enhanced,which exhibits the pulse features.The sidebands of the pulse at different wavelengths experience the same repetition rate,although they have different round-trip lengths.The pulse-shaping of DUFL is dominated by the dissipative processes in addition to the phase modulations of SWNT and fiber nonlinearity.3.The mixture of SWNT and graphene was fabricated via the self-assembly during the liquid-phase fabrication process.Two carbon metamaterials can separate each other giving a benefit of preventing the agglomeration.The optical response of the mixture was measured that it possesses the dual-scale saturable absorption which can used to achieve the self-started mode-locked fiber laser with high pulse energy,high signal-to-noise ratio and the ability to resist disturbance.4.Based on the prepared carbon-based mixture mode locker,passively mode-locked fiber laser with distinctive structure is implemented.Several types of pulses are generated,for instance,conventional solitons(CSs),dissipative solitons(DSs)and noise-like pulses.Firstly,two paths with opposite dispersions and propagation directions were formed with 50/50 couplers in bidirectional fiber laser.CSs and DSs were obtained from two directions of mode-locked fiber laser,respectively.Secondly,a tandem fiber laser connected with a CFBG is proposed.The CFBG can provide the dispersion with the same value and opposite sign for two laser cavity.CSs and DSs were simultaneously achieved from the fiber laser system,which demonstrated the different output features.Finally,a dispersion-free filter was implemented by directly inserting a CFBG in a fiber laser cavity.Bandwidth-tunable DS and noise-like pulses were obtained.Meanwhile,the spectral filtering in DS fiber laser and the degeneration of noise-like pulses were investigated.5.The nonlinear optcal responses of two TMDs,i.e.molybdenum disulfide(Mo S2)and rhenium disulphide(Re S2),were investigated,and they were applied in fiber laser to generate pulses.Firstly,Mo S2 was covered onto a microfiber which could greatly enhance the interaction between light and Mo S2,and overcome the low damage threshold of Mo S2.With the Mo S2-cover microfiber(MCM)SA,conventional,dispersion-managed,and dissipative solitons were generated around 1600 nm in Er-doped fibre lasers with anomalous,near-zero,and normal cavity dispersions,respectively.Secondly,it is found that the Re S2-covered D-shaped fiber(RDF)displayed the remarkable polarization-induced absorption,which indicates the different responses for TE and TM polarizations relative to Re S2 plane.Nonlinear saturable absorption of RDF exhibied the similar saturable fluence and modulation depth for ultrafast pulses with two orthogonal polarizations.RDF was utilized as a saturable absorber to achieve self-started mode-locking operation in an Er-doped fiber laser.