High efficiency and high frequency resonant tunneling diode sources

Terahertz (THz) technology has been generating a lot of interest due to the numerous potential applications for systems working in this previously unexplored frequency range. THz radiation has unique properties suited for high capacity communication systems and non-invasive, non-ionizing properties that when coupled with a fairly good spatial resolution are unparalleled in its sensing capabilities for use in biomedical, industrial and security fields. However, in order to achieve this potential, effective and efficient ways of generating THz radiation are required. Devices which exhibit negative differential resistance (NDR) in their current-voltage (I – V) characteristics can be used for the generation of these radio frequency (RF) signals. Among them, the resonant tunnelling diode (RTD) is considered to be one of the most promising solid-state sources for millimeter and submillimeter wave radiation, which can operate at room temperature. However, the main limitations of RTD oscillators are producing high output power and increasing the DC-to-RF conversion efficiency. Although oscillation frequencies of up to 1.98 THz have been already reported, the output power is in the range of micro-Watts and conversion efficiencies are under 1 %. This thesis describes the systematic work done on the design, fabrication, and characterization of RTD-based oscillators in monolithic microwave/millimeter-wave integrated circuits (MMIC) that can produce high output power and have a high conversion efficiency at the same time. At the device level, parasitic oscillations caused by the biasing line inductance when the diode is biased in the NDR region prevents accurate characterization and compromises the maximum RF power output. In order to stabilise the NDR devices, a common method is the use of a suitable resistor connected across the device, to make the differential resistance in the NDR region positive. However, this approach severely hinders the diode’s performance in terms of DC-to-RF conversion efficiency. In this work, a new DC bias decoupling circuit topology has been developed to enable accurate, direct measurements of the device’s NDR characteristic and when implemented in an oscillator design provides over a 10-fold improvement in DC-to-RF conversion efficiency. The proposed method can be adapted for higher frequency and higher power devices and could have a major impact with regards to the adoption of RTD technology, especially for portable devices where power consumption must be taken into consideration. RF and DC characterization of the device were used in the realization on an accurate large-signal model of the RTD. S-parameter measurements were used to determine an accurate small-signal model for the device’s capacitance and inductance, while the extracted DC characteristics where used to replicate the I-V characteristics. The model is able to replicate the non-stable behavior of RTD devices when biased in the NDR region and the RF characteristics seen in oscillator circuits. It is expected that the developed model will serve in future optimization processes of RTD devices in millimeter and submillimeter wave applications. Finally, a wireless data transmission link operating in the Ka-band (26.5 GHz – – 40 GHz) using two RTDs operating as a transmitter and receiver is presented in this thesis. Wireless error-free data transfer of up to 2 gigabits per second (Gbit/s) was achieved at a transmission distance of 15 cm. In summary, this work makes important contributions to the accurate characterization, and modeling of RTDs and demonstrates the feasibility of this technology for use in future portable wireless communication systems and imaging setups

Improving the capabilities from the antenna point of view at THZ and SUB-THZ frequencies

Mención Internacional en el título de doctorThe main objective of this Ph.D. dissertation is to improve the capabilities of devices (emitters and detectors) and wireless systems (focusing system) at terahertz and sub-terahertz frequencies from the antenna point of view. It has been proved that only acting over the antenna side, devices with better capabilities can be obtained (increased emitted power in emitters and improved responsivity in detectors). This thesis is focused on the analysis and design of planar antennas, so their behaviour at terahertz and sub-terahertz frequencies has been studied. While obtaining the radiation pattern of planar antennas lying on semi-infinite substrate, an anomaly which appears in the radiation pattern is observed. This anomaly does not have a physical meaning but appears in all the published papers. The origin of such anomaly is explained in this thesis. In addition a program capable to obtain in an accurate way the radiation pattern of planar antennas lying on dielectric hyperhemispherical lenses has been designed. Regarding terahertz and sub-terahertz sub-systems a continuous-wave photomixer based power emitter working at 1.05 terahertz has been designed in such a way that maximum power is transferred from the active device to the antenna. The main contribution is that the design has been simplified in such a way that no external elements (filters, etc.) are needed. This emitter is intended to be the local oscillator of a heterodyne detector for radioastronomy applications. In addition, an equivalent circuit based on Hertzian dipoles to obtain the radiation pattern of the so-called “Large Are Emitters" has been derived. Such devices are photomixer based emitters with the main characteristic of not needing an antenna to emit terahertz power. Other important contributions to this Ph.D. dissertation are the complete design of Quasi-Optical Schottky based receiver working within the E-Band (60 - 90 gigahertz) where the power transferred from the antenna to the diode is maximized. This receiver will be part of a complete very high speed wireless communications system. Also in the detectors section, a CMOS FET based receiver working at 300 gigahertz has been designed. Finally, work over a focusing system for a 300 gigahertz radar for security purposes has been done. The main contribution regarding this aspect is that the focusing system, based on two elliptical mirror and a plane one, has been designed in such a way that the beam is capable to scan over a very large area without distortion. To do so it has been imposed that the target distance is always places at the focus of the output mirror.El objetivo de la presente tesis es mejorar las prestaciones de subsistemas (emisores y detectores) y sistemas (sistema de enfoque) en el rango de terahercios y sub-terahercios desde el punto de vista de antena. Se ha demostrado que actuando únicamente sobre la antena se pueden obtener dispositivos con un mejor rendimiento (potencia emitida incrementada en emisores y responsividad mejorada en detectores). La presente tesis se ha centrado en el análisis y diseño de antenas planas y para ello se ha estudiado su comportamiento a frecuencias de terahercios y sub-terahercios. Obteniendo los diagramas de radiación de antenas planas sobre sustrato semi-infinito se ha observado una anomalía en el diagrama de radiación que no tiene significado físico, pero que aparece en todas las publicaciones. El origen de esta anomalía se explica en el presente trabajo. Asimismo se ha diseñado un programa capaz de obtener de una manera rápida y precisa el diagrama de radiación de antenas planas que tienen como substrato una lente dieléctrica hiperhemiesférica. Con respecto a sub-sistemas de terahercios y sub-terahercios se ha diseñado un emisor para generar señales de onda continua basado en “photomixers" a 1.05 terahercios de tal manera que la potencia transferida de éste a la antena sea maximizada. La mayor aportación es que se ha simplificado el diseño del mismo de tal manera que no hacen falta elementos externos (filtros, etc.). Este emisor está previsto que sirva como oscilador local para un receptor heterodino en aplicaciones de radioastronomía. Con respecto a emisores de terahercios también se ha obtenido un circuito equivalente para obtener el diagrama de radiación basado en dipolos Hertzianos de los conocidos como “Large Area Emitters", que son dispositivos basados también en “photomixers" pero que no necesitan ningún tipo de antena para radiar potencia de terahercios. Otras contribuciones importantes en esta tesis han sido el diseño de un receptor completo Quasi-Óptico basado en diodo Schottky trabajando en la banda E (60 - 90 gigahercios) donde se ha maximizado la potencia entregada al diodo desde la antena. Este receptor está pensado para formar parte de un sistema de comunicaciones inalámbrico de muy alta velocidad. Dentro del apartado de receptores se ha diseñado también un receptor basado en tecnologíaa CMOS y FET trabajando a 300 gigahercios. Finalmente se ha actuado sobre un sistema completo de enfoque para un radar a 300 gigahercios para aplicaciones de seguridad. La mayor contribución en este aspecto es que el sistema de enfoque, basado en dos espejos elípticos y uno plano, se ha diseñado de tal manera que el haz es capaz de escanear en un amplio rango sin apenas distorsión. Para ello se ha forzado que la distancia de escaneo se encuentre siempre en el foco del espejo de salida.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Jordi Romeu Robert.- Secretario: Luis Emilio García Castillo.- Vocal: Yi Huan

The Third International Symposium on Space Terahertz Technology: Symposium proceedings

Papers from the symposium are presented that are relevant to the generation, detection, and use of the terahertz spectral region for space astronomy and remote sensing of the Earth's upper atmosphere. The program included thirteen sessions covering a wide variety of topics including solid-state oscillators, power-combining techniques, mixers, harmonic multipliers, antennas and antenna arrays, submillimeter receivers, and measurement techniques

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

Cumulative index to NASA Tech Briefs, 1970-1975

Tech briefs of technology derived from the research and development activities of the National Aeronautics and Space Administration are presented. Abstracts and indexes of subject, personal author, originating center, and tech brief number for the 1970-1975 tech briefs are presented

Monolithic 1.3 μm InAs/GaAs Quantum Dot Lasers on Silicon: Simulation and Experiment

1.3 μm quantum dot (QD) lasers epitaxially grown on silicon have attracted great interest as light source for silicon photonics and other optical communication applications. This work focuses on improving the understanding of the physical mechanisms limiting the performance of these devices, and on studying the laser dynamics with respect to data transmission potential through simulation and experiment. Dislocation-induced carrier loss is a major concern for the performance of QD lasers on silicon. Part of this work aims, therefore, at identifying the processes degrading the laser characteristics as well as on understanding the performance disparity between silicon-based QD and quantum well (QW) devices. By using two specially extended types of rate equation travelling-wave models it is found that enhanced carrier loss at higher dislocation densities leads to a much larger laser threshold increase in QW than in QD lasers. The QD laser’s increased tolerance to dislocations can be explained based on efficient and ultrafast carrier capture into the QDs, where high energy barriers prevent them from migrating into defects. The carrier density reduction in the higher energy continuum layers is eventually reflected in a lower current injection efficiency and thus reduced light-current slope, confirming experimentally observed trends of 1.3 μm QD lasers on silicon. In particular, a large minority carrier diffusion length is identified as a key parameter inhibiting laser operation in QW-based devices. The other part of this work focuses on investigating the QD lasers’ dynamics by means of gain switching, small-signal and large-signal modulation. 150 ps short gain-switched pulses, modulation bandwidths of 1.6 GHz to 2.3 GHz, and optical eyes at 1.5 Gb/s are obtained from 2.5 mm long ridge-waveguide lasers grown and fabricated at University College London. Numerical simulations reveal that the observed high-speed limitations are a result of limited gain and a long photon lifetime, whereas suitability for 10 Gb/s operation is predicted in an optimised laser design. It was, furthermore, found that neither dislocation-induced carrier loss nor optical loss limit the modulation characteristics fundamentally. The reduced carrier lifetime is, however, reflected in stronger damping of the small-signal modulation curves. Apart from that, the overall device dynamics remain governed by the QD physics.Qualcomm Inc. School of Technology PhD scholarshi

NASA Tech Briefs, May 1996

Topics include: Video and Imaging;Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Report

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis