Nonlinear propagation in periodic microstructures

The main objectives of this research project related to the observation of ultrafast, all-optical switching within AlGaAs structures operated in the half-band gap spectral region. The switching configurations investigated were based on nonlinear periodic structures and included nonlinear waveguide arrays and Bragg gratings. Theoretical simulations of the switching characteristics of various nonlinear coupled arrays were carried out using both a fourth order Runge-Kutta algorithm and a split step Fast Fourier Transform code. The effects of linear absorption, dispersion and multi-photon absorption on the efficiency of the switch were taken into consideration. All-optical switching was demonstrated for the first time in uniformly and non-uniformly spaced three, four and eight core couplers. The experimental transmission characteristics compared well to the theoretical simulations. First and second order grating filters were fabricated using both a two step holographic process and a single-step electron beam writing process. Gratings with a 70% reflection efficiency and stopband width of 0.9 nm were fabricated. The linear losses of the filters were measured using a Fabry-Perot technique. The electron beam defined gratings were found to have no significant scattering losses associated with them. In contrast the holographically fabricated gratings were found to increase the losses of the waveguides considerably. Finally the nonlinear response of the grating filters were investigated.