Self-trapping threshold in disordered nonlinear photonic lattices.

We investigate numerically and experimentally the influence of coupling disorder on the self-trapping dynamics in nonlinear one-dimensional optical waveguide arrays. The existence of a lower and upper bound of the effective average propagation constant allows for a generalized definition of the threshold power for the onset of soliton localization. When compared to perfectly ordered systems, this threshold is found to decrease in the presence of coupling disorder.

Observation of a localization transition in quasiperiodic photonic lattices.

We report the observation of the signature of a localization phase transition for light in one-dimensional quasiperiodic photonic lattices, by directly measuring wave transport inside the lattice. Below the predicted transition point an initially narrow wave packet expands as it propagates, while above the transition expansion is fully suppressed. In addition, we measure the effect of focusing nonlinear interaction on the propagation and find it increases the width of the localized wave packets.

Effect of nonlinearity on adiabatic evolution of light.

We investigate the effect of nonlinearity in a system described by an adiabatically evolving Hamiltonian. Experiments are conducted in a three-core waveguide structure that is adiabatically varying with distance, in analogy to the stimulated Raman adiabatic passage process in atomic physics. In the linear regime, the system exhibits an adiabatic power transfer between two waveguides which are not directly coupled, with negligible power recorded in the intermediate coupling waveguide. In the presence of nonlinearity the adiabatic light passage is found to critically depend on the excitation power. We show how this effect is related to the destruction of the dark state formed in this configuration.

Nonlinearly induced relaxation to the ground state in a two-level system.

We report the experimental demonstration of a nonlinear process in a two-level system, in which the amplitude of the excited state decays, transferring irreversibly a large fraction of its energy to the ground state, while shedding a part of it into radiation states. The experiments where preformed in a nonlinear optical waveguide, supporting two or three modes. The process is general, and is expected to occur in other nonlinear few level systems such as nonlinear quantum wells and Bose-Einstein condensates.