טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentOr Peleg
SubjectLinear and Nonlinear Optics in Complex Structures
DepartmentDepartment of Physics
Supervisor ? 18? Segev Mordechai
Full Thesis textFull thesis text - English Version


Abstract

In my doctoral thesis, I study both linear and nonlinear effects in optical structures, including conical diffraction in honeycomb lattices, lattice solitons, nano-scale optical structures, evanescently-originated solitons (phoenix soliton), leaky spatial solitons and anomalous Rabi oscillations. My thesis comprises of both experimental work, which was done mostly on photonic lattices, and theoretical work, which included both numerics and analytics. I attempted to show general phenomena which are relevant to many fields in physics, such as the behavior near singular points, conical diffraction (first predicted 200 year ago) in honeycomb structures, showing a singularity in the spectrum, and divergence behavior near singular points arising from coalescence of forward and backwards traveling waves.

The main subjects I have dealt with in my Ph.D. research are:

Soleakons - Self trapped leaky waves. We propose the combination of two separate fields in optics: linear dynamics of leaky waveguides on one hand, and nonlinear spatial solitons on the other. We have theoretically demonstrated nonlinear self-trapped leaky modes displaying particlelike features, and named these creatures "soleakons". A “soleakon” forms when a wave function induces a potential barrier, whose resonant state (leaky mode) corresponds to the wave function itself. We have shown that soleakons are robust and propagate while maintaining their envelope unchanged almost indefinitely. However, they eventually disintegrate abruptly. These entities exhibit particlelike interactions behavior, which is nevertheless profoundly different from soliton collisions.

Nonlinear waves in subwavelength waveguide arrays. We formulated wave propagation in arrays of subwavelength waveguides with sharp index contrasts and demonstrated the collapse of bands into evanescent modes and lattice solitons with superluminal phase velocity. We find a self-reviving soliton (‘‘phoenix soliton’’) originating solely from evanescent bands. In the linear regime, all Bloch waves comprising this beam decay, whereas a proper nonlinearity assembles them into a propagating selftrapped beam.

Conical diffraction in honeycomb lattices. We studied wave dynamics in a honeycomb photonic lattice ("optical graphene"), and demonstrated the unique phenomenon of conical diffraction around the singular diabolical points connecting the first and second bands. This has constituted the prediction and first experimental observation of conical diffraction arising solely from a periodic potential. It is also the first study on k space singularities in photonic lattices. In addition, we demonstrated ‘‘honeycomb gap solitons’’ residing in the gap between the second and the third bands, reflecting the special properties of these lattices.