Lanterna Rally

Author: Ragip Pala

Publisher: Stanford University

Published: 2010

Total Pages: 95

ISBN-13:

The development of integrated electronic and photonic circuits has led to remarkable data processing and transport capabilities that permeate almost every facet of our daily lives. Scaling these devices to smaller and smaller dimensions has enabled faster, more power efficient and inexpensive components but has also brought about a myriad of new challenges. One very important challenge is the growing size mismatch between electronic and photonic components. To overcome this challenge, we will need to develop radically new device technologies that can facilitate information transport between nanoscale components at optical frequencies and form a bridge between the world of nano-electronic and micro-photonics. Plasmonics is an exciting new field of science and technology that aims to exploit the unique optical properties of metallic nanostructures to gain a new level of control over light-matter interactions. The use of nanometallic (plasmonic) structures may help bridge the size gap between the two technologies and enable an increased synergy between chip-scale electronics and photonics. In the first part of this dissertation we analyze the performance of a surface plasmon-polariton all-optical switch that combines the unique physical properties of small molecules and metallic (plasmonic) nanostructures. The switch consists of a pair of gratings defined on an aluminum film coated with a thin layer of photochromic (PC) molecules. The first grating couples a signal beam consisting of free space photons to SPPs that interact effectively with the PC molecules. These molecules can reversibly be switched between transparent and absorbing states using a free space optical pump. In the transparent (signal "on") state, the SPPs freely propagate through the molecular layer, and in the absorbing (signal "off") state, the SPPs are strongly attenuated. The second grating serves to decouple the SPPs back into a free space optical beam, enabling measurement of the modulated signal with a far-field detector. We confirm and quantify the switching behavior of the PC molecules by using a surface plasmon resonance spectroscopy. The quantitative experimental and theoretical analysis of the nonvolatile switching behavior guides the design of future nanoscale optically or electrically pumped optical switches. In the second part of the dissertation we provide a critical assessment of the opportunities for use of plasmonic nanostructures in thin film solar cell technology. Thin-film solar cells have attracted significant attention as they provide a viable pathway towards reduced materials and processing costs. Unfortunately, the materials quality and resulting energy conversion efficiencies of such cells is still limiting their rapid large-scale implementation. The low efficiencies are a direct result of the large mismatch between electronic and photonic length scales in these devices; the absorption depth of light in popular PV semiconductors tends to be longer than the electronic (minority carrier) diffusion length in deposited thin-film materials. As a result, charge extraction from optically thick cells is challenging due to carrier recombination in the bulk of the semiconductor. We discuss how light absorption could be improved in ultra-thin layers of active material making use of large scattering cross sections of plasmonic structures. We present a combined computational-experimental study aimed at optimizing plasmon-enhanced absorption using periodic and non-periodic metal nanostructure arrays.