The propagation of light in the linear and nonlinear regimes in multicore photonic crystal fibers

In this project, we systematically investigate the propagation of light in multicore photonic crystal fibers (PCFs) both theoretically and experimentally.;We first study the general light propagation in three-core PCFs. Fresnel and Fraunhofer diffraction patterns are observed and analyzed.;We develop a coupled-mode theory in the linear regime for three-core PCFs and fully describe inter-core coupling in terms of eigenmodes. We have also written a code to calculate the inter-core coupling coefficients using the intensity distribution at the output.;On the experimental front, the coupling coefficients and the coupling lengths are determined. An accuracy of 99.0% is achieved when compared with theory. The inter-core coupling in the three-core PCFs is found to be asymmetric.;We also present the polarization dependence of light propagation. The coupled-mode equations are developed taking into account the input polarization of the light. The states of polarization of the beams in all three cores can be obtained at any propagation distance. In the experiments, the inter-core coupling of three-core PCF is found to be strongly dependent on the state of polarization of the input light. Combining both theory and the experimental results, we are able to identify the birefringent characteristic of the three-core PCF and calculate the ordinary and extraordinary components of the coupling coefficients and the orientations of the principle axes with respect to the fiber microstructure.;We have also studied the wavelength dependence of light propagation in three-core PCFs. The essential factor of this dependence is the overlap integral of the guided cores, which is analyzed by computation. Linear coupling over a wide range of operating wavelengths is simulated. In the experiments, the inter-core coupling of the three-core PCF is found to be wavelength dependent, as predicted by calculations based on theory and simulations.;Finally, we extend the coupled-mode theory to the nonlinear regime for three-core PCFs. Nonlinear coupling for both symmetric and asymmetric fibers with different coupling coefficients and nonlinear parameters is modeled numerically. We also demonstrate experimentally nonlinear optical switching around 300W. The nonlinear coupling is realized with infrared picosecond pulses. The experimental results agree well with the nonlinear coupled-mode theory.