Optical spatial solitons, light beams free of diverging, have been demonstrated to exhibit fascinating particle-like behavior, including fusion, fission, annihilation, stable orbiting and clustering. These solitons are promising for applications in controlling light by light and all-optical switching. We focus on novel phenomena from soliton interaction and modulation instability, especially when such solitons are made with partially incoherent light.

Optical waveguide arrays are of particular interest because of their potential applications as well as their collective behavior of nonlinear wave propagation that exhibits many intriguing phenomena. Yet, it has always been a challenge to create or fabricate two-dimensional waveguide arrays in bulk media. We demonstrate the formation of 2Dnonlinear waveguide lattices induced by pixel-like partially coherent spatial solitons in a photorefractive crystal. Such reconfigurable solitonic lattices may find applications in information encoding and optical communication.

Discrete systems are abundant in nature. In optics, a typical example is a closely-spaced waveguide array in which light experiences discrete diffraction. When the waveguide array is embedded in a nonlinear medium, a balance between discrete diffraction and nonlinear self-focusing gives rise to the so-called "discrete solitons" or "lattice solitons".  We study various localized soliton states (dipoles, vortices, vectors, etc.) in two-dimensional light-induced photonic lattices. Understanding the fascinating behavior of light in such periodic photonic structures may provide an insight for study of similar phenomena in other relevant discrete nonlinear systems.

Photorefractive organic materials have been investigated widely for applications in optical phase conjugation and holographic data storage, owning to their low cost, structure flexibility, large beam-coupling gain and ease of fabrication. We focus on a new type of organic photorefractive glass based on DCDHF chromophores.  In particular, we investigate soliton formation, auto-waveguiding, and focusing-to-defocusing switching in such organic photorefractive glasses.