Theoretical Study Of The Ultrashort Laser Pulse Propagation In Photonic Crystal Fiber

Photonic crystal fibre (PCF for short) is a recent proposed optical fibre, in which there exists a periodic dielectric structure in the cross-section of the fibre. PCFs have found many applications in the field of nonlinearity optics, pulse compression, supercontinuum generation and fibre sensors etc. because of its unique properties which can hardly be realized in conventional optical fibres. In this dissertation, we focus on the theoretical and numerical investigation of ultra-short (pico-second and femtosecond) optical pulse propagation in photonic crystal fibres. The main content of the dissertation is organized as follows,1. The concept of a photonic crystal fibre is introduced, the history and development of photonic crystal fibre are reviewed, followed by an analysis of its unique properties and applications.2. The generalized nonlinear Schr?dinger equation (GNLSE) describing the pico-second and femtosecond pulse propagation in fibres is reviewed. Finally, a numerical approach called the split-step Fourier method for solving the GNLSE is studied, and based on this arithmetic, a computer code for the modeling of femtosecond pulse propagation in fibres is developed by us.3. In this chapter, firstly, the principle of adiabatic soliton compression in nonuniform optical fibres is studied. Based on this principle, a scheme for pico-second soliton compression using nonlinearity increasing fibres is proposed and investigated in detail. Secondly, the influence on soliton compression by several different nonlinearity increasing profiles is analyzed. Thirdly, the pico-second soliton compression in dispersion decreasing fibres with different nonlinearity increasing rates is studied and it is found that a nonlinearity increasing fibre with a constant dispersion coefficient along the fibre is the most efficient way for adiabatic soliton compression by using nonuniform fibres. At last, an explanation for the enhanced compression in nonlinearity increasing fibres has been given.4. Soliton compression by nonlinearity increasing scheme is expanded to the femtosecond case and investigated numerically in detail. A comparison with the traditional dispersion decreasing scheme is made.5. Supercontinuum generation and its polarization properties by femtosecond pump in birefringence PCF are studied numerically through solving the coupled nonlinear Schr?dinger equation (CNLSE). By using different pump wavelength, the underlying physics on different dispersion area in the birefringence PCF and the polarization properties of output SC spectra are analyzed. The numerical results suggest that using a highly birefringence PCF with pump polarization closed to its slow axis, SC outputs with linear polarization state across the spectrum can be achieved.