Tailoring light-matter interactions in waveguide networks for computing applications

Abstract

Computing with electromagnetic waves has, in recent years, emerged as an interesting alternative computing paradigm. This is due to the inherent high-speed (computing at the speed of light in the medium) and the potential for parallelization of electromagnetic wave-based computing systems. Multiple examples of electromagnetic wave-based structures, such as metamaterials, metasurfaces and gratings, have been proposed and demonstrated to perform computing operations. This includes the emulation of digital logic gates and the calculation of operations such as differentiation, integration and convolution. In this PhD thesis, interconnected networks of parallel plate waveguides are exploited to enable high-speed electromagnetic wave-based computing processes. To begin with an introduction to electromagnetism, waveguides and transmission line theory is presented in chapter 1. This is followed in chapter 2 by the outline of an algorithm developed to assist in the characterisation of waveguide networks. In chapter 3, we then explore how waveguide networks may be exploited to emulate conventional computing techniques. Here, we demonstrate how by tailoring the splitting and superposition of transverse electromagnetic pulses at waveguide junctions one can compute the outputs of decision-making processes (i.e., if… then… else… statements). We also exploit the linear superposition of monochromatic waves within waveguide networks to emulate logic operations such as AND and OR logic gates. In chapter 4, transmission line filtering techniques will be exploited to perform 𝑚th order differentiation in the time domain using the Greens function approach. This includes the calculation of fractional derivatives in which 𝑚 may be a positive non-integer value. In chapter 5, it is shown how periodic networks of waveguide-based metatronic circuits may be used to calculate the solutions partial differential equations. This is done with a focus on partial differential equations in the form of the Helmholtz wave equation. Finally, chapter 6 presents a list of the main conclusions of this thesis and potential future work.