With the proliferation of high-speed communications and energy-aware electronic systems worldwide, efficient electromagnetic (EM) radiation sources remain amongst the most critical components. The desired properties of EM oscillators include a precise oscillation frequency, high output power, and high power-generation efficiency to preserve energy and battery life, besides low phase noise and small form factors. Boosting the performance of microwave and optical sources in terms of enhanced efficiency and coherence is a fundamental goal and a very active research area. This dissertation focuses on a new class of EM devices and sources, whose architecture relies on dispersion engineering principles exploiting a new operational condition: the so-called exceptional points of degeneracy (EPD).
An exceptional point of degeneracy (EPD) in the state space of a dynamical system refers to condition at which two, or more, physical eigenstates coalesce into one, and bifurcate as a parameter is varied. In this dissertation, a comprehensive investigation of the use of EPDs in microwaves and optics is undertaken, stimulated by their remarkable physical properties.
First, a coupled transmission line theory is established which provides access to novel dispersion engineering concepts at radio frequencies. Moreover, experimental observation of the degenerate band edge (DBE), which is a fourth order EPD, is also demonstrated in metallic waveguides as well as microstrip lines at microwaves even in the presence of loss and tolerances. Furthermore, new paradigms for coherent light-matter interaction are proposed, resulting in a low-threshold degenerate band edge lasers. Such lasers eliminate the need of cavity mirrors for light confinement, and possess a mode-selection scheme that ensures a single frequency lasing.
We further harness the notions of EPDs to conceive highly-efficient electron-beam-driven oscillators. In traveling wave tubes and oscillators, an electron beam is synchronized with the EM radiation in a slow-wave structure causing amplification. A super synchronous regime is established when the electron beam transfers energy to multiple degenerate waves supported by the structure causing strong amplification. As a result, we demonstrate a design of an electron-beam-driven degenerate band edge oscillator capable of generating mega-watts of microwave power with efficiency up to 60% and compatible with realistic experimental setup.