The Fundamental Research On Mid-infrared Supercontinuum Sources Based On All-normal Dispersion Photonic Crystal Fiber

Laser in the mid-infrared?MIR?region has numerous applications.Supercontinuum?SC?is a physical phenomenon which can generate a broadband spectrum.Using fiber to generate MIR-SC can combine merits of MIR and SC,which attracts much attention.Besides,the wavelength-tunable MIR fiber laser is significant for scientific and engineering applications.Soliton self-frequency shift?SSFS?is promising due to its large frequency shift.The thesis mainly includes the work mentioned below:1.The pulse propagation equations in the time domain and frequency domain are introduced.The equation in the frequency domain considers frequency-dependent effective mode area and loss naturally,which can precisely describe the SC generation in the nonlinear medium.Besides,several physical effects related to SC are discussed.The spectrogram,noise model and the modulus of the complex degree of first-order coherence are introduced.By using these tools,the properties of SCs can be analyzed.2.A novel Ae₂Se₃-As₂S₅ photonics crystal fiber?PCF?is proposed.When the hole pitch and hole diameter are fixed at 3.2?m and 1.6?m,respectively,the PCF has near-zero flatted all-normal dispersion characteristics.By solving the GNLSE based on the obtained dispersion curve,influences of the pump pulse parameters and the fiber length on the SCs are investigated.When 3-cm-long proposed PCF is pumped at 3?m with 16.8kW femtosecond pulses,the SC covering 1.4-10?m with perfect coherence is generated.3.The characteristics of SSFS in the fluoride step-index fiber?SIF?and tellurite SIF when pumped at 3.5?m with femtosecond pulses are numerically investigated.For these two fibers,the wavelength can be tuned in the region of 3.5-5?m by varying the pump power.For tellurite fiber,the required pump power to shift the most redshifted soliton to5?m is much lower than that of fluoride fiber,and the ratios of the energies of the most redshifted solitons to the input energies are higher.When the length of the tellurite fiber is optimized to 22 cm,the wavelength of the most redshifted soliton can be tuned in the region of 3.5-5?m by changing the pump peak power from 10 kW to 120 kW,and the ratios of the energies of the most redshifted solitons to the input energies are beyond 50%in the tuning range.By increasing the pump power,the wavelength can be shifted to longer wavelength,but the energy efficiency decreases due to the larger anomalous dispersion and higher loss at longer wavelength.