טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentRotschild Carmel
SubjectSolitons in Non-Local Nonlinear Media
DepartmentDepartment of Physics
Supervisor ? 18? Mordechai Segev
Full Thesis textFull thesis text - English Version


Abstract

Solitons are self-localized wave-packets arising from a robust balance between dispersion and nonlinearity. They are a universal phenomenon, displaying properties typically associated with particles. Until recently, the vast majority of soliton-research was focused on solitons in nonlinear media with a local response. As such, the interactions between solitons were limited to “nearest neighbors” at close proximity. This feature poses an upper limit to the complexity of a system constructed from solitons as building blocks, for example, a soliton-based computing scheme. In addition, for scalar (single-field) solitons, in almost all nonlinearities with a local response, only the simplest solitons are stable: those possessing a bell-shape structure. The picture changes drastically when the response of the nonlinear material is spatially-nonlocal. In contrast to “local nonlinearities”, the nonlinear response in nonlocal media is carried to regions beyond the range of the localized wave-packet. That is, the nonlinear effect at a given location is a function of the field at some nonlocality-range surrounding that location. Nonlocal optical nonlinearities are inherent in many physical systems. Naturally, their tendency is generally to distribute the nonlinear effect. Interestingly, in spite of this widening effect of nonlocality, even highly-nonlocal nonlinearities can support solitons. Here, I present my research work describing experimental studies on solitons in highly-nonlocal nonlinear media. I demonstrate attraction between solitons propagating in different samples, where their optical fields never overlap, and the interaction is mediated by metal (non-optical) wire. These experiments break the close-proximity and the nearest-neighbor limitations on soliton interactions, and could be used in the construction of novel model systems for studying the behavior of complex nonlinear networks. In addition, I demonstrate solitons spiraling about one another from afar, with their tangential velocity independent from the separation between the interacting solitons. Naturally, solitons in such high-nonlocal nonlinear media can interact with the physical boundaries of the sample in which the solitons are propagating, even if the boundaries are very far away. Utilizing this feature, we demonstrated surface-wave solitons, which have unique properties in nonlocal nonlinearities. In addition, I also show how nonlocality gives rise to the formation of high-order scalar solitons, exhibiting complex, multi-hump, structures, as well as vortex and elliptical solitons. Finally, I demonstrate a new kind of incoherent (random-phase) spatial solitons, which form in effectively-instantaneous nonlocal nonlinear media. These “instantaneous incoherent solitons” exhibit new features that are profoundly different than those of all other incoherent solitons ever observed.