Study Of The Supercontinuum Generation In Liquid-core Photonic Crystal Fiber With High Nonlinearity And Flat Dispersion

Supercontinuum（SC）has the properties of wide bandwidth,high coherence,strong stability and high reliability.The SC properties of high flatness,wide bandwidth and high coherence are very important in the fields of optical imaging,spectroscopy,optical frequency metrology,optical communication and national defense.Therefore,the research on SC is of great significance.Photonic crystal fiber（PCF）has excellent properties such as endless single-mode propagation guidance,enhanced mode confinement,high nonlinearity and its flexible design freedom,so PCF is considered to be an ideal medium for SC generation.In order to generate high-quality SC,filling a variety of highly nonlinear solid,gas and liquid materials in the PCF core has attracted widespread attention,and some organic liquid materials are considered as ideal materials for filling the PCF core due to their good transmission properties and high nonlinear coefficient.The generation of SC is due to the combination of nonlinear effect and dispersion effect when ultra-short pulse propagates in PCF,which leads to greatly broadened optical pulse spectrum.The generation process of SC can be simulated by numerical solution of the generalized nonlinear Schr（?）dinger equation（GNLSE）.In this dissertation,the high nonlinearity and good transmission characteristics of nitrobenzene liquid are utilized to simulate the generation of SC in the highly nonlinear flat dispersion nitrobenzene liquid-core PCF,the coherence properties of SC generation in the nitrobenzene liquid core PCF based on the adaptive step algorithm are analyzed numerically,and the generation of ultra-short pulses in the erbium-doped mode-locked fiber laser is studied experimentally.The main research work is in the following three aspects:1.The SC generation in highly nonlinear flat dispersive nitrobenzene liquid-core PCF is studied.A nitrobenzene liquid-core PCF with eight elliptical air-holes in the innermost ring of the cladding is proposed.By adjusting the structural parameters of this fiber,it has three zero dispersion wavelengths（ZDWs）and a flat dispersion profile with a dispersion fluctuation of less than 40 ps nm^-1km^-1.The split-step Fourier method（SSFM）is used to solve the GNLSE to numerically simulate the generation and evolution of SC in this fiber.When the ultra-short pulse with a center wavelength of 1810 nm,a peak pump power of 1000 W,and a pump pulse width of 50 fs is transmitted in the fiber with a length of 5 cm,a highly coherent supercontinuum of 1.3～2.8μm is obtained.Finally,the influence of different pump pulse parameters on SC and the influence of SC and its coherence in normal dispersion region and abnormal dispersion region are studied and analyzed.2.The influence of different adaptive step size algorithms on the coherence of SC in nitrobenzene liquid-core PCF is analyzed.The GNLSE is numerically solved using a more optimized method,the adaptive step-size method,which includes the local error method（LEM）and the conservation quantity error method（CQEM）.The evolution and generation of SC in nitrobenzene liquid-core PCF are numerically simulated by LEM and CQEM.In a 5 cm liquid-core PCF with a pump wavelength of 1.55μm,a pump pulse width of 50 fs,and a pump pulse peak power of 1000 W,a highly coherent SC with a span of about 1300-2800 nm is numerically generated.The SC and its coherence based on LEM and CQEM under different pump pulse parameters are studied in time domain and frequency domain,respectively.3.Ultrashort pulse generation in erbium-doped mode-locked fiber lasers is experimentally studied.The mode-locking principle of mode-locked fiber laser and the theory of mode-locked device semiconductor saturable absorber mirror（SESAM）are introduced.In the experiment,an erbium-doped mode-locked fiber laser was built with SESAM as the mode-locked device.The center wavelength of the output spectrum of the laser was measured to be1562 nm,the spectral width was 5 nm,the repetition frequency was 12 MHz,and the pulse width was 54 ps.And its output power can reach 4.3 m W when the pump pulse power is 45mW.