Author : Philip Wing-Chun Hon
Publisher :
ISBN 13 :
Total Pages : 199 pages
Book Rating : 4.:/5 (868 download)
Book Synopsis Beam Pattern Engineering of Metamaterial Terahertz Quantum-cascade Devices by : Philip Wing-Chun Hon
Download or read book Beam Pattern Engineering of Metamaterial Terahertz Quantum-cascade Devices written by Philip Wing-Chun Hon and published by . This book was released on 2013 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: Generation and detection of microwave radiation is done with electronic systems where the underyling processes involve oscillating free charges (such as on an antenna or within a transistor or diode). On the higher energy side of the spectrum, generation and detection of near infrared and visible radiation is achieved via quantum transitions with emission wavelengths that are dictated by the material. Solutions moving up towards the THz regime using microwave based solutions are limited by carrier transit time and RC time-constant limitations. Techniques and solutions moving down toward the THz regime using photonic techniques have emission wavelengths naturally limited by the band gap of the material. However, THz quantum-cascade (QC) lasers, which are an extension of photonic concepts to lower energies, have artificially engineered energy levels and hence emission wavelengths. THz QC-lasers have been demonstrated to operate at frequencies between 1.2 and 5.0 THz and the best high-temperature operation is based upon the metal-metal (MM) waveguide configuration, in which the multiple-quantum well active region is sandwiched between two metal cladding layers, typically separated by 2-10 [mu]m. Soon after the demonstration of MM waveguide QC-lasers, it was recognized that the beam pattern from a conventional cleaved-facet Fabry Pérot (FP) ridge cavity produced a highly divergent beam pattern, characterized by concentric rings in the far field. This thesis presents work on a new approach to tailor the beam pattern of THz MM waveguide QC-devices. Namely, dispersion engineering using metamaterials based on the composite right/left-handed (CRLH) transmission line formalism is adapted to the MM waveguide configuration to realize an entirely new class of devices. Dispersion, radiative loss, and radiation patterns are presented for many newly designed 1-D and 2-D THz QC transmission line metamaterial designs. The first ever active 1-D THz QC transmisison line metamaterial is experimentally characterized and its radiation pattern and polarization closely match theoretical and full-wave finite element method (FEM) simulated predictions. Proven microwave techniques such as circuit, antenna cavity modeling and array factor theory are used to understand the radiative properties of conventional THz QC-lasers. We predict far-field beam patterns and polarizations, approximate cavity quality factors, and associate these properties with individual surfaces or structures of the device. The analysis technique is also applied to the project's 1-D and 2-D THz CRLH QC-devices yielding qualitative agreement with experiments. The first THz design, analysis and experimental verification of a metasur face comprised of an array of passive THz QC transmission lines is presented. By using the cavity model, array factor, circuit and electromagnetic theory a surface impedance model is developed to characterize the metasurface. The surface impedance model reveals waveguide mode dependent radiative coupling with the light line and capacitve/inductive surface impedance. Polarization dependent angle-resolved Fourier transform infrared reflection spectroscopy measurements match the model and full-wave FEM predictions, further assisting the understanding of such devices. To address the broader goal of a directive and scalable THz QC-device, thefeasibility of a 2-D metamaterial inspired QC-laser and an active reflectarray is considered. Finally, preliminary work on a technology enabling active metasurface reflector for a QC vertical external cavity surface emitting laser is discussed.
