Pulse Compression In Hollow-core Photonic Bandgap Fibers

High-energy ultrashort pulses are widely used in many fields such as light measurement, communication, molecular structure measurement, spectral analysis, super fast process research, etc. Q-switching and mode-locking can be used to generate ultrashort optical pulse, but in general, the width of the pulses are always more than several hundred femtosecond, in order to get more shorter pulses, pulse compression have became a very important research subject. The pulses always split because of the inevitable nonlinear effect in conventional fiberswhen compressed in this fiber. The appearance of hollow-core photonic bandgap fiber with very low nonlinear coefficient and controllable dispersion has made it to be possible that gets high-energy ultrashort pulse. This thesis theoretically makes a relatively deep research into high-energy pulse compression in hollow-core photonic bandgap fiber, and the main contents as follows:1. Starting from maxwell's equations, we deduced the light propagation equation in the fiber-generalized nonlinear schrodinger equation and introduced a numerical simulation method-split step Fourer method.2. We numerically investigated the generation and compression of parabolic similariton pulses, and pointed a novel method of generating high-energy femtosecond pulses, the results show that the high-energy parabolic pulses with linear chirp can be obtained by propagating of pulses inside the Erbium-doped fibers. Combining the linear compression with hollow core photonic bandgap fibers in the first stage and the nonlinear compression with highly nonlinear fiber in the second stage, the parabolic similariton pulse can be compressed into a femtosecond pulse with high peak power. There is an optimum fiber length for the pulse compression. The Raman self-frequency shift and the self-steepening effects are disadvantageous for pulse compression.3. Compression of chirped free femtosecond pulses in hollow-core photonic bandgap fibers is investigated numerically. The results show that intrapulse stimulated Raman scattering can improve the quality of the compressed pulse. Positive third-order dispersion is the main limitation on the compression of the femtosecond pulse. However, the combined effect of the intrapulse stimulated Raman scattering and the negative third-order dispersion can form still shorter pulses than is possible with intrapulse stimulated Raman scattering alone. We also investigate the influence of width and peak power of input pulse on pulse compression. 4. Compression of self-similar pulse in hollow-core photonic bandgap fibers is investigated numerically. A new method for obtain high-energy and ultrashort pulse was found. The peak power, pulse width, chirp of the input pulses and third-order dispersion in hollow-core photonic bandgap fibers effects on pulse compression were all detailed studied.