The Study Of Nonlinear Interaction Between Ultrashort Laser Pulses And Photonic Crystal Fibers

Photonic crystal fibers that occur in several years ago are a new kind of optical fiber with a microstructure cladding. The especially design of the microstructure cladding has made the photonic crystal fiber having obtained many new characteristics which differ remarkably from those of traditional optical fibers. These new characteristics mainly include:endlessly single mode characteristic, Flexible Controllable chromatic dispersion characteristic, enhanced nonlinear characteristic and so on. These outstanding characteristics have made photonic crystal fibers to be a promising medium in the study of nonlinear interaction between ultrashort laser pulses and photonic crystal fibers, which also have made photonic crystal fibers obtain successful application in supercontinuum source, pulse compression, biosensing, soliton switch, communication and so on. Therefore, the study of nonlinear interaction between ultrashort laser pulses and photonic crystal fibers has great academic significance and practical application value.This dissertation conducts a series research in the study of nonlinear interaction between ultrashort laser pulses and photonic crystal fibers. The principal results are as follows.Firstly, the generations of high coherent supercontinuum and its pulse compression in an all-normal dispersion photonic crystal fiber have been studied in detail. It is found the weaker the dispersion effects is, the more advantage to the high coherent supercontinuum generation. A high coherent supercontinuum with band width of587nm and flatness of less7dB can be obtained by pumping the fiber under which the dispersion effect is low. It is also found the higher the coherence properties of supercontinuum is, the more advantage to the compression of the supercontinuum pulse. An ultrashort pulse with pulse duration of8.4fs and compression quality factor of88.88%can be obtained by using a grating pair compressor to compress the high coherent supercontinuum pulse. Therefore, the high coherent supercontinuum and high qulity pulse compression can be obtained by using the effect of self phase modulation and suppressing the dispersion effect.Secondly, a theoretical investigation on the negatively chirped parabolic pulse nonlinear propagation and spectral compression in all-normal dispersion photonic crystal fibers is presented. It is found that the weaker the dispersion effects and the self-phsae modulaton plays the more important role are, the more advantage to obtain the higher quality Fourier transform-limited spectrally compressed pulses, which generation mechanism is the precision balance betwween the negative chirp and the positive chirp generated by self-phase modulation. In addition, the longer the pulse width is, the more advantage to obtain the higher quality transform-limited spectrally compressed pulses. A nearly Fourier transform-limited spectrally compressed pulses with spectral width less than4nm and compression ratio of more than32can be obtained by using a negatively chirped parabolic pulse with pulse width of500fs pumping the fiber at the optimal compression distance ZC=4cm.Thirdly, a theoretical investigation on the red-shifted radiation generation and its generation mechanism in a photonic crystal fiber with two zero-dispersion wavelengths are presented. It is found the intensity of the red-shifted radiation components can be enhanced when the fiber is pumped with two pulses and the pulse trapping occurs than pumped by single pulse when other conditions keep unchanged. The further studies have shown the generation mechanism of the enhanced red-shifted radiation is the energy transfer from the Raman soliton to the red-shifted radiation components due to the effect of pulse trapping and the effect of higher-order dispersion.Fourthly, a theoretical investigation on the single and dual pulses nonlinear propagation and the soliton switching generation in a dual-core photonic crystal fiber are presented. It is found the soliton switching is stable and high conversion efficiency is obtained when the fiber is pumper by a single pulse at the lower input peak power. At a higher input peak power, the soliton splitting appears and multi-frequencies are generated and thus the soliton switching disappears gradually. It is also found the soliton switching still exists and high conversion efficiency is also obtained when the fiber is pumped by dual pulses and its input peak power between the dual cores is largely different. However, the conversion efficiency is reduced rapidly and the soliton switching even disappears when the input peak power is near equal. The energy exchange between the dual cores appears when the delay between the dual pulses is changed and the energy coupling between the dual cores becomes stronger as the delay increases.