Research On The Generation And Propagation Of Ultra-short Pulses In Photonic Crystal Fibers

Photonic crystal fibers(PCFs), demonstrated in recent years, have some unique characteristics such as endlessly single mode, controllable dispersion and rich optical nonlinearity compared with the conventional fibers. PCFs have exhibited wider application potentials in all-optical communication, and have become a hot research topic in optical communication. The unique properties of PCFs make them quite different from conventional fibers in many aspects. In this thesis, we study modulation instability (MI) in PCFs analytically and numerically, and prove a new way to generate an ultra-short pulse sequence based on MI. Furthermore, the propagation properties of ultra-short pulses and supercontinuum generation in PCFs are analyzed. The main research results are listed below:Firstly, the propagation of ultra-short optical pulses in PCFs is limited by many physical factors, and the theoretical analysis is very complicated, so numerical simulation becomes crucial research methods. Based on the physical model of optical pulses propagation in PCFs, we have independently developed the computer program which can simulate the process of linear and nonlinear propagation of optical pulses. Compared with the experimental and theoretical results reported in literatures, the validity of the computation results of our program is confirmed.Secondly, we use the standard linear stability analysis to study MI in PCFs. An generic expression for MI gain spectrum which includes the influence of higher-order effects such as higher-order dispersion (HOD), self-steepening (SS), stimulated Raman scattering (SRS) etc. on MI has been obtained. The theoretical results show that only even-order dispersions influence gain spectrum and they lead to the appearance of new MI regions, whereas odd-order dispersions contribute nothing to MI. SRS can generate an additional MI region and the new region is gradually screened from the conventional MI region as the initial power increases. SS exerts little influence on MI gain spectrum. Numerical simulation confirms the theoretical results and proves that an ultra-short pulse sequence can be generated by MI in the anomalous dispersion region in optical fibers.Thirdly, the characteristics of ultra-short pulses propagation in three kinds of PCFs which have typical dispersion profiles are analyzed. Numerical simulations show that group velocity dispersion and self-phase modulation take main effects in the...