Ph.D Student | Yaakov Lumer |
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Subject | Photonic Systems with Unconventional Symmetries |

Department | Department of Physics |

Supervisor | ? 18? Segev Mordechai |

Full Thesis text |

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This PhD thesis presents unconventional photonic systems, where light propagates in unusual ways. Conventionally, wavepackets of light are considered to propagate along straight lines. Also, in standard optical systems, in order for power to be conserved there has to be no losses and no gain in the system. In my work, I studied systems where these very common assumptions fail. In all of the cases presented here, careful design of special symmetries has to be employed for the emergence of the unique properties that stray away from those of conventional optics. The study of optical systems having special symmetries has flourished in the past few years, yielding an ever increasing body of knowledge, alongside with special applications that stem from such unique properties of light propagation. I have focused on three systems employing different types of special symmetries.

First, I studied PT-symmetric systems. This new type of symmetry allows for a system to conserve power despite having gain and loss. One of the key features of such systems is the existence of a distinct transition from a system with power-conserving modes to a system where the modes have diverging power. The second class of systems I studied was photonic topological insulators. These are systems in which light travels on the edges of the system, in a unidirectional and robust way. The robust propagation is characterized by immunity to scattering from defects, both into the bulk of the system, and more importantly - immunity to back-scattering. In our group we published the first experimental photonic topological insulator - a research project I played a major role in.

In both those types of systems, most of the research and analysis prior to my work was done in a linear context. In my work I made novel theoretical analysis on nonlinear dynamics both in PT-symmetric systems and in photonic topological insulators. In PT-symmetric systems, I predicted a new kind of nonlinear dynamical transition. In photonic topological insulators I predicted the existence of a new type of solitons and studied the nonlinear stability properties of topological edge states.

The third system I studied was accelerating beams. These are beams which appear to propagate in free space along a curved trajectory - instead of going in a straight line. This special property is a diffraction effect, arising from a specially designed interference pattern. In my work I generalized accelerating beams in two ways. First, I showed theoretically and experimentally how accelerating beams can be obtained when using incoherent light. Then, using concepts from accelerating beams I generalized the phenomena of self-imaging to include curved trajectories instead of strictly straight ones.

In summary, my PhD thesis deals with optical systems with unique symmetries, which then leads to systems where light propagates in unconventional ways. I provided several novel theoretical predictions relating to nonlinear properties of such systems, and also conducted experiments demonstrating how light beams propagate in such unusual ways.