Multilayer optical learning networks

A new approach to learning in a multilayer optical neural network based on holographically interconnected nonlinear devices is presented. The proposed network can learn the interconnections that form a distributed representation of a desired pattern transformation operation. The interconnections are formed in an adaptive and self-aligning fashioias volume holographic gratings in photorefractive crystals. Parallel arrays of globally space-integrated inner products diffracted by the interconnecting hologram illuminate arrays of nonlinear Fabry-Perot etalons for fast thresholding of the transformed patterns. A phase conjugated reference wave interferes with a backward propagating error signal to form holographic interference patterns which are time integrated in the volume of a photorefractive crystal to modify slowly and learn the appropriate self-aligning interconnections. This multilayer system performs an approximate implementation of the backpropagation learning procedure in a massively parallel high-speed nonlinear optical network

Nanomechanical single-photon routing

The merger between integrated photonics and quantum optics promises new opportunities within photonic quantum technology with the very significant progress on excellent photon-emitter interfaces and advanced optical circuits. A key missing functionality is rapid circuitry reconfigurability that ultimately does not introduce loss or emitter decoherence, and operating at a speed matching the photon generation and quantum memory storage time of the on-chip quantum emitter. This ambitious goal requires entirely new active quantum-photonic devices by extending the traditional approaches to reconfigurability. Here, by merging nano-optomechanics and deterministic photon-emitter interfaces we demonstrate on-chip single-photon routing with low loss, small device footprint, and an intrinsic time response approaching the spin coherence time of solid-state quantum emitters. The device is an essential building block for constructing advanced quantum photonic architectures on-chip, towards, e.g., coherent multi-photon sources, deterministic photon-photon quantum gates, quantum repeater nodes, or scalable quantum networks.Comment: 7 pages, 3 figures, supplementary informatio

Stacking of IGBT devices for fast high-voltage high-current applications

The development of solid-state switches for pulsed power applications has been of considerable interest since high-power semiconductor devices became available. However, the use of solid-state devices in the pulsed power environment has usually been restricted by device limitations in either their voltage/current ratings or their switching speed. The stacking of fast medium-voltage devices, such as IGBTs, to improve the voltage rating, makes solid-state switches a potential substitute for conventional switches such as hard glass tubes, thyratrons and spark gaps. Previous studies into stacking IGBTs have been concerned with specific devices, designed or modified particularly for a specific application. The present study is concerned with stacking fast and commercially available IGBTs and their application to the generation of pulsed electric field and the switching of a high intensity Xenon flashlamp. The aim of the first section of the present study was to investigate different solid-state switching devices with a stacking capability and this led to the choice of the Insulated Gate Bipolar Transistor (IGBT). It was found that the collector-emitter voltage decreases in two stages in most of the available IGBTs. Experiments and simulation showed that a reason for this behaviour could be fast variations in device parasitic parameters particularly gate-collector capacitance. Choosing the proper IGBT, as well as dealing with problems such as unbalanced voltage and current sharing, are important aspects of stacking and these were reported in this study. Dynamic and steady state voltage imbalances caused by gate driver delay was controlled using an array of synchronised pulses, isolated with magnetic and optical coupling. The design procedure for pulse transformers, optical modules, the drive circuits required to minimise possible jitter and time delays, and over-voltage protection of IGBT modules are also important aspects of stacking, and were reported in this study. The second purpose of this study was to investigate the switching performance of both magnetically coupled and optically coupled stacks, in pulse power applications such as Pulse Electric Field (PEF) inactivation of microorganisms and UV light inactivation of food-related pathogenic bacteria. The stack, consisting of 50 1.2 kV IGBTs with the voltage and current capabilities of 10 kV, 400 A, was incorporated into a coaxial cable Blumlein type pulse - generator and its performance was successfully tested with both magnetic and optical coupling. As a second application of the switch, a fully integrated solid-state Marx generator was designed and assembled to drive a UV flashlamp for the purpose of microbiological inactivation. The generator has an output voltage rating of 3 kV and a peak current rating of 2 kA, although the modular approach taken allows for a number of voltage and current ratings to be achieved. The performance of the switch was successfully tested over a period of more than 10⁶ pulses when it was applied to pulse a xenon flashlamp.The development of solid-state switches for pulsed power applications has been of considerable interest since high-power semiconductor devices became available. However, the use of solid-state devices in the pulsed power environment has usually been restricted by device limitations in either their voltage/current ratings or their switching speed. The stacking of fast medium-voltage devices, such as IGBTs, to improve the voltage rating, makes solid-state switches a potential substitute for conventional switches such as hard glass tubes, thyratrons and spark gaps. Previous studies into stacking IGBTs have been concerned with specific devices, designed or modified particularly for a specific application. The present study is concerned with stacking fast and commercially available IGBTs and their application to the generation of pulsed electric field and the switching of a high intensity Xenon flashlamp. The aim of the first section of the present study was to investigate different solid-state switching devices with a stacking capability and this led to the choice of the Insulated Gate Bipolar Transistor (IGBT). It was found that the collector-emitter voltage decreases in two stages in most of the available IGBTs. Experiments and simulation showed that a reason for this behaviour could be fast variations in device parasitic parameters particularly gate-collector capacitance. Choosing the proper IGBT, as well as dealing with problems such as unbalanced voltage and current sharing, are important aspects of stacking and these were reported in this study. Dynamic and steady state voltage imbalances caused by gate driver delay was controlled using an array of synchronised pulses, isolated with magnetic and optical coupling. The design procedure for pulse transformers, optical modules, the drive circuits required to minimise possible jitter and time delays, and over-voltage protection of IGBT modules are also important aspects of stacking, and were reported in this study. The second purpose of this study was to investigate the switching performance of both magnetically coupled and optically coupled stacks, in pulse power applications such as Pulse Electric Field (PEF) inactivation of microorganisms and UV light inactivation of food-related pathogenic bacteria. The stack, consisting of 50 1.2 kV IGBTs with the voltage and current capabilities of 10 kV, 400 A, was incorporated into a coaxial cable Blumlein type pulse - generator and its performance was successfully tested with both magnetic and optical coupling. As a second application of the switch, a fully integrated solid-state Marx generator was designed and assembled to drive a UV flashlamp for the purpose of microbiological inactivation. The generator has an output voltage rating of 3 kV and a peak current rating of 2 kA, although the modular approach taken allows for a number of voltage and current ratings to be achieved. The performance of the switch was successfully tested over a period of more than 10⁶ pulses when it was applied to pulse a xenon flashlamp

Architectural Considerations for Photonic Switching Networks

Photonic technologies are reviewed that could become important components of future telecommunication systems. Photonic devices and systems are divided into two classes according to the function they perform. The first class, relational, refers to devices, that map the input channels to the output channels under external control. The second class, logic, perform some type or combination of Boolean logic functions. Some of the strengths and weaknesses of operating in the photonic domain are presented. Relational devices and their applications are discussed. Optical logic devices and their potential applications are reviewed

Coherent Differential Absorption Lidar for Combined Measurement of Wind and Trace Atmospheric Gases

A lidar system was developed for making combined range-resolved measurements of wind speed and direction, water vapor concentration, and carbon dioxide concentration in the atmosphere. This lidar combines the coherent Doppler technique for wind detection and the differential absorption lidar (DIAL) technique to provide a multifunctional capability. DIAL and coherent lidars have traditionally been thought of and implemented as separate instruments, but the research reported here has shown a demonstration of combining the coherent and DIAL techniques into a single instrument using solid-state lasers. The lasers used are of Ho:Tm:YLF, which operates at a wavelength of 2 μm. This wavelength is a further advantage to the lidar, as this wavelength offers a much higher level of eyesafety than shorter wavelengths conventionally used for DIAL. Two generations are lidars are described, with the first design making combined measurement of wind and water vapor. Wind speed measurements are shown of a precision better than 1 m/s, making it useful for many meteorological applications. Water vapor concentration measurements were of 86% accuracy, requiring improvement for scientific applications. This preliminary experiment revealed the largest source of error in concentration measurement to be a lack of stability in the wavelength of the laser. This problem was solved by implementing a means to precisely control the continuous-wave laser that injection seeds a pulsed laser. The finely tunable Ho:Tm:YLF laser was stabilized to absorption lines of both carbon dioxide and water vapor using a wavelength modulation technique. Long-term stabilization to within 13.5 MHz of absorption line center is shown, representing the first frequency-stabilized laser at or within 500 run of 2μm wavelength. Results are presented on injection seeding a pulsed Ho:Tm:YLF laser to impart the tunability and stabilization to the pulsed laser output. The stabilized laser system was incorporated into a second-generation coherent DIAL to make a combined measurement of wind and carbon dioxide concentration. The DIAL measurement accuracy of concentration was improved to 29%, and designs are suggested for a further reduction in error. The absorption lines around 2-μm have recently become of great interest for a high-accuracy measurements of carbon dioxide for studies in the global carbon cycle, and the lidar demonstration and laser technology presented here are enabling first steps to meet scientific needs for carbon dioxide profiling

Advanced Fluorescence Microscopy Techniques-FRAP, FLIP, FLAP, FRET and FLIM

Fluorescence microscopy provides an efficient and unique approach to study fixed and living cells because of its versatility, specificity, and high sensitivity. Fluorescence microscopes can both detect the fluorescence emitted from labeled molecules in biological samples as images or photometric data from which intensities and emission spectra can be deduced. By exploiting the characteristics of fluorescence, various techniques have been developed that enable the visualization and analysis of complex dynamic events in cells, organelles, and sub-organelle components within the biological specimen. The techniques described here are fluorescence recovery after photobleaching (FRAP), the related fluorescence loss in photobleaching (FLIP), fluorescence localization after photobleaching (FLAP), Forster or fluorescence resonance energy transfer (FRET) and the different ways how to measure FRET, such as acceptor bleaching, sensitized emission, polarization anisotropy, and fluorescence lifetime imaging microscopy (FLIM). First, a brief introduction into the mechanisms underlying fluorescence as a physical phenomenon and fluorescence, confocal, and multiphoton microscopy is given. Subsequently, these advanced microscopy techniques are introduced in more detail, with a description of how these techniques are performed, what needs to be considered, and what practical advantages they can bring to cell biological research

Study of optoelectronic switch for satellite-switched time-division multiple access

The use of optoelectronic switching for satellite switched time division multiple access will improve the isolation and reduce the crosstalk of an IF switch matrix. The results are presented of a study on optoelectronic switching. Tasks include literature search, system requirements study, candidate switching architecture analysis, and switch model optimization. The results show that the power divided and crossbar switching architectures are good candidates for an IF switch matrix

Fiber-based Terahertz Time-Domain Spectroscopy Systems Operated in the Telecom Band

The aim of the doctoral thesis is the study of Terahertz time domain spectrometers relying on telecommunication fiber technology. Optical fiber offers low losses, high stability and compactness, features that ease the deployment of this kind of sensing instruments in industrial scenarios. The development of terahertz signal sources working at telecom wavelengths has enabled the employment of mature, telecom-related photonic components that allowed a transition within THz research from being mainly object of scientific interest to an application-oriented technology. In this thesis, fiber terahertz systems utilizing ultrafast photoconductors with integrated antenna structures have been investigated at different levels, including the control of the photoconductor structure, as well as at instrument and system levels. The carrier transport in InGaAs-InAlAs multilayer hetero-structures, present in the employed photoconductive antennas, has been investigated under the additional injection of a continuous optical wave. By varying the amplitude level of the respective optical signal injected into either the emitter or the receiver, it has been shown that the amplitude of the detected photocurrent could be controlled without affecting its bandwidth. Unlike increasing the optical power of the pulsed signal, raising the continuous optical power results in a reduction of the measured photocurrent. This lowering of the conductivity is related to changes in the instantaneous carrier momentum relaxation time in the photoactive material, rather than to variations of the free carrier density level. This behavior affects systems including continuous-wave optical components, as, for instance, optical amplifiers. The effect has been further exploited to modulate the operation conditions of photoconductive antennas, enabling an all-optical control of the THz amplitude. This represents a method to implement a signal modulation, necessary, for instance, for lock-in signal detection. Different industrial applications and THz imaging systems require fast data acquisition. Slow, stepwise working mechanical optical delay lines are about to be replaced by faster schemes. A fast THz-time-domain spectroscopy system using a coil-based rapid mechanic delay line has been set up and analyzed. A convenience of usage of optical fibers is the simplicity of signal multiplication and distribution. It can be exploited to allow centralized operation of a set of parallel terahertz sensing units. A centralized architecture with optical source sharing simplifies the implementation as well as the cost of nondestructive inspection platforms, where several sensing units would have to work in the same facility, for example at quality control in factories or security checkpoints. The cost of such a distribution system is evaluated, its feasibility experimentally demonstrated, and key features relevant to the system performance are discussed. The present document is formally structured in a brief introduction, Chapter 2, which review common terahertz technology as a whole, with the focus on optoelectronic schemes and respective technology in the telecom band. Chapter 3 includes work carried out dealing with the carrier dynamics under continuous optical wave irradiation of the photoconductive antenna modules and the application of the effect as modulation method. Chapter 4 deals with the implementation of the fast delay in the system and Chapter 5 describes and analyses architecture for parallel, remotely controlled sensing. Finally, Chapter 6 provides conclusion and future work perspectives.El objetivo de la presente Tesis Doctoral es el estudio de espectroscopios temporales de Terahercios basados en tecnología de fibra óptica para telecomunicaciones. La fibra óptica ofrece bajas pérdidas de propagación, alta estabilidad y la capacidad de implementar sistemas robustos y compactos, características que facilitan el despliegue de este tipo de instrumentos de sensado en escenarios industriales. El desarrollo de fuentes de THz que operan en la banda infrarroja empleada en telecomunicaciones permite el uso de componentes maduros de la industria de las comunicaciones ópticas, lo que a su vez se ha traducido en una transición desde el uso de la banda de THz básicamente para intereses científicos al desarrollo de sistemas para aplicaciones industriales. En la presente tesis se investigan sistemas de THz basados en antenas fotoconductivas y fibra óptica a distintos niveles: control de la estructura fotoconductiva, instrumento y sistema. El transporte de portadores en heteroestructuras multicapa InGaAs-InAlAs, empleadas actualmente en antenas fotoconductivas, se ha investigado bajo la inyección de una onda óptica continua. Se ha observado que variando el nivel de amplitud de esta onda continua tanto en el emisor como en el receptor es posible controlar la fotocorriente detectada sin afectar a su ancho de banda. A diferencia de un incremento en la potencia óptica de la señal pulsada, elevar el nivel de continua resulta en una reducción de la fotocorriente medida. Esta reducción de la conductividad se relaciona con cambios en el tiempo de relajación del momento de los portadores en el material fotoactivo en lugar de variaciones de la densidad de portadores libres. Este comportamiento puede tener un efecto en sistemas que introduzcan componentes ópticos continuos como por ejemplo sistemas de sensado que empleen amplificadores ópticos. Este efecto puede ser usado para modular las condiciones de operación de las antenas fotoconductivas permitiendo el control todo-óptico del sistema. Este método permite modular la señal, lo que resulta necesario por ejemplo para realizar detección lock-in. Tanto diferentes aplicaciones industriales como los sistemas de imagen en THz requieren sistemas rápidos de captura. Para ello es necesario sustituir las líneas de retardo ópticas tradicionales basadas en motores paso-a-paso por otros sistemas de mayor velocidad. Se ha implementado y caracterizado un sistema THz-TDS usando una línea de retardo rápida basada en bobinas de voz. Una característica fundamental de la fibra óptica es su extraordinaria simplicidad para realizar la distribución de señales ópticas. Esta característica puede ser explotada para permitir la operación centralizada de un conjunto paralelo de sensores de THz. Una arquitectura centralizada en la que la fuente óptica se comparte entre muchos sensores simplifica la implementación y reduce el coste de sistemas de inspección no destructiva que requieran de múltiples sensores en paralelo, como, por ejemplo, en control de calidad industrial o en controles de seguridad. Se ha evaluado el coste de estos sistemas distribuidos, se ha validado experimentalmente su viabilidad y se han identificado y estudiado sus prestaciones. El documento de la tesis doctoral se estructura formalmente en una breve introducción, el capítulo 2, en el que se revisa la tecnología de THz en su conjunto, los esquemas optoelectrónicos y el uso de tecnologías ópticas basadas en la banda de las telecomunicaciones. El capítulo 3 incluye el estudio realizado sobre la dinámica de los portadores bajo la irradiación dela antena fotoconductiva con una onda óptica continua y su uso como técnica de modulación. El capítulo 4 trata con la implementación de un sistema THz-TDS rápido mientras que el capítulo 5 describe y analiza una arquitectura de sensado paralela para reducir costes. Finalmente el capítulo 6 recoge las conclusiones y futuras líneas de actuación.L'objectiu de la present Tesi Doctoral és l'estudi d'espectroscopis temporals de terahertzs basats en tecnologia de fibra òptica per a telecomunicacions. La fibra òptica ofereix baixes pèrdues de propagació, alta estabilitat i la capacitat d'implementar sistemes robustos i compactes, característiques que faciliten el desplegament d'aquest tipus d'instruments de sensat en escenaris industrials. El desenvolupament de fonts de THz que operen a la banda infraroja emprada en telecomunicacions permet l'ús de components madurs de la indústria de les comunicacions òptiques, el que al seu torn s'ha traduït en una transició des de l'ús de la banda de THz bàsicament per interessos científics al desenvolupament de sistemes per a aplicacions industrials. En la present tesi s'investiguen sistemes de THz basats en antenes fotoconductivas i fibra òptica a diferents nivells: control de l'estructura fotoconductiva, instrument i sistema. El transport de portadors en heteroestructures multicapa InGaAs-InAlAs, emprades actualment en antenes fotoconductivas, s'ha investigat sota la injecció d'una ona òptica contínua. S'ha observat que variant el nivell d'amplitud d'aquesta ona contínua tant en l'emissor com en el receptor és possible controlar la fotocorriente detectada sense afectar el seu ample de banda. A diferència d'un increment en la potència òptica del senyal polsada, elevar el nivell de contínua resulta en una reducció de la fotocorrent mesurada. Aquesta reducció de la conductivitat es relaciona amb canvis en el temps de relaxació del moment dels portadors en el material fotoactiu en lloc de variacions de la densitat de portadors lliures. Aquest comportament pot tenir un efecte en sistemes que introdueixin components òptics continus com ara sistemes de sensat que utilitzen amplificadors òptics. Aquest efecte pot ser usat per modular les condicions d'operació de les antenes fotoconductivas permetent el control tot-òptic del sistema. Aquest mètode permet modular el senyal, el que resulta necessari per exemple per realitzar detecció lock-in. Tant diferents aplicacions industrials com els sistemes d'imatge en THz requereixen sistemes ràpids de captura. Per a això és necessari substituir les línies de retard òptiques tradicionals basades en motors pas-a-pas per altres sistemes de major velocitat. S'ha implementat i caracteritzat un sistema THz-TDS usant una línia de retard ràpida basada en bobines de veu. Una característica fonamental de la fibra òptica és la seua extraordinària simplicitat per realitzar la distribució de senyals òptiques. Aquesta característica pot ser explotada per a permetre l'operació centralitzada d'un conjunt paral·lel de sensors de THz. Una arquitectura centralitzada en la qual la font òptica es comparteix entre molts sensors simplifica la implementació i redueix el cost de sistemes d'inspecció no destructiva que requereixin de múltiples sensors en paral·lel, com, per exemple, en control de qualitat industrial o en controls de seguretat . S'ha avaluat el cost d'aquests sistemes distribuïts, s'ha validat experimentalment la seua viabilitat i s'han identificat i estudiat les seues prestacions. El document de la tesi doctoral s'estructura formalment en una breu introducció, capítol 2, en el qual es revisa la tecnologia de THz en el seu conjunt, els esquemes optoelectrònics i l'ús de tecnologies òptiques basades en la banda de les telecomunicacions. El capítol 4 inclou l'estudi realitzat sobre la dinàmica dels portadors sota la irradiació de la antena fotoconductiva amb una ona òptica contínua i el seu ús com a tècnica de modulació. El capítol 5 tracta la implementació d'un sistema THz-TDS ràpid mentre que el capítol 6 descriu i analitza una arquitectura de sensat paral·lela per reduir costos. Finalment, el capítol 7 recull les conclusions i futures línies d'actuació.Bockelt, AS. (2017). Fiber-based Terahertz Time-Domain Spectroscopy Systems Operated in the Telecom Band [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86148TESI

A 160-Gb/s OTDM demultiplexer based on parametric wavelength exchange

Parametric wavelength exchange (PWE) has been demonstrated as a versatile device in providing different functionalities. In this paper, we will concentrate, numerically and experimentally, on one of these functionalities, namely, all-optical time demultiplexing of 160-Gb/s return-to-zero (RZ) signals based on a pulsed-pump PWE in a 400 m highly nonlinear dispersion-shifted fiber. Experimental results show power penalties < 2.7 dB at bit-error rate of 10-9 for all demultiplexed 10-Gb/s RZ signals. We also derive theoretical expressions for the conversion/residual efficiencies and investigate the impact of pump pulse width and phase mismatch on these efficiencies. Furthermore, the impacts of pulsed-pump wavelength and power level on the characteristics of the switching window are investigated numerically. As a result, the demultiplexer can be easily upgraded to an add-drop multiplexer because of the complete exchange nature of PWE, which is justified by the surviving channels' waveform performance. © 2009 IEEE.published_or_final_versio