Design of all-optical logic gates implemented with nanorod-based photonic crystals

Abstract

The progress in the development of electronic computers has the possibility of being slowed down due to the physical constraints of atomic size and power con- sumption. All optical computing systems hold the promise of an alternative with lower power requirements, higher processing speed, lower crosstalk, and parallel computation facilities. All optical logic gates being the building blocks of all optical computers have become a topic of great interest among researchers. Al- though many different realizations have been proposed for these gates, a clear, general methodology is absent, by referring to which, one can design any such gate with ease. In this thesis, we present a methodology for all optical logic gates based on photonic crystals. Photonic crystal based gates have unique properties of possessing photonic bands and guiding electromagnetic waves efficiently at 900 bends, which are necessary for simple, compact and easily integrable pho- tonic devices. Applying our proposed methodology, we have designed seven basic logic gates and evaluated their performance using the performance metrics: con- trast ratio and footprint. These have been compared with some existing gates proposed by other researchers. It is shown that our proposed gates are smaller in size and provide good contrast ratios. Another important aspect that has been explored in this thesis is the effect on the performance of all optical logic gates due to process variations. Photonic crystals consist of either nanorods or nanoholes; the photonic crystals discussed in this thesis are nanorod based. These nanorods are fabricated using MBE/MOCVD machines, which are prone to some inevitable errors giving rise to some structural irregularities, which we have termed as ’process variation’. We have considered two types of process variation: displacement of nanorods’ positions and diameter inhomogeneity of nanorods. For both our own gates and the gates proposed by others, we investi- gate how process variations affect the performance of optical logic gates. Except for a few anomalies, process variation has been seen to adversely impact the contrast ratio of the logic gates.