27 November 2007 PhD Thesis Defense
\'All optical-soliton control in photonic lattices\'

Zhiyong Xu

PhD Thesis Defense, November 27th, 12:00.
IN3\'s Auditorium
Optical solitons are light packets (beams and/or pulses) that do not broaden because of the proper balance between diffraction/dispersion and nonlinearity. They propagate and interact with one another while displaying properties that are normally associated with real particles. The main objective of this thesis is the investigation of new techniques for soliton control in nonlinear media with/without an imprinted optical lattice, which might be used for all-optical signal processing and routing devices.

Chapter 2 focuses on properties of optical solitons in quadratic nonlinear media. The first section presents in detail the properties of two-dimensional spatiotemporal solitons in quadratic nonlinear waveguide arrays. The other section reports on the existence and stability of multicolor lattice vortex solitons and their dynamical generation from Gaussian-type input beams with nested vortices.

The technique of optical lattice induction opens a wealth of opportunities for creation of waveguiding configurations with various nondiffracting light beams. Chapter 3 puts forward the concept of reconfigurable structures optically induced by mutually incoherent nondiffracting Bessel beams in Kerr-type nonlinear media. In particular, the properties of two-core and multi-core directional couplers, two-dimensional networks and X-junctions are studied.

Nonlocal response of nonlinear media can play an important role in properties of solitons. Chapter 4 treats the impact of nonlocality in the physical features exhibited by solitons supported by Kerr-type nonlinear media with an imprinted optical lattice. The chapter investigates properties of different families of lattice solitons in nonlocal nonlinear media. It is shown that the nonlocality of the nonlinear response can profoundly affect the soliton mobility. The properties of gap solitons are also discussed for photorefractive crystals with an asymmetric nonlocal diffusion response and in the presence of an imprinted optical lattice.

Chapter 5 is devoted to the impact of nonlocality on the stability of soliton complexes in uniform nonlocal Kerr-type nonlinear media. First, it is shown that the different nonlocal response of materials has different influence on the stability of soliton complexes in scalar case. Second, experimental work is reported on scalar multi-pole solitons in 2D highly nonlocal nonlinear media, including dipole, tripole, and necklace-type solitons, organized as arrays of out-of-phase bright spots. Finally, the chapter addresses the interplay between nonlocal nonlinearity and vectoral coupling, specially emphasizing the stabilization of vector effects on soliton complexes in nonlocal nonlinear media.

Finally, Chapter 6 summarizes the main results obtained in the thesis and discusses some open prospects.

PhD Thesis Defense, 27th of November, 12:00h. IN3\'s Auditorium

Thesis Advisor: Prof. Lluís Torner