Roadmap on optical security

Postprint (author's final draft

Roadmap on holography

From its inception holography has proven an extremely productive and attractive area of research. While specific technical applications give rise to 'hot topics', and three-dimensional (3D) visualisation comes in and out of fashion, the core principals involved continue to lead to exciting innovations in a wide range of areas. We humbly submit that it is impossible, in any journal document of this type, to fully reflect current and potential activity; however, our valiant contributors have produced a series of documents that go no small way to neatly capture progress across a wide range of core activities. As editors we have attempted to spread our net wide in order to illustrate the breadth of international activity. In relation to this we believe we have been at least partially successful.This work was supported by Ministerio de Economía, Industria y Competitividad (Spain) under projects FIS2017-82919-R (MINECO/AEI/FEDER, UE) and FIS2015-66570-P (MINECO/FEDER), and by Generalitat Valenciana (Spain) under project PROMETEO II/2015/015

Liquid Crystal on Silicon Devices: Modeling and Advanced Spatial Light Modulation Applications

Liquid Crystal on Silicon (LCoS) has become one of the most widespread technologies for spatial light modulation in optics and photonics applications. These reflective microdisplays are composed of a high-performance silicon complementary metal oxide semiconductor (CMOS) backplane, which controls the light-modulating properties of the liquid crystal layer. State-of-the-art LCoS microdisplays may exhibit a very small pixel pitch (below 4 ?m), a very large number of pixels (resolutions larger than 4K), and high fill factors (larger than 90%). They modulate illumination sources covering the UV, visible, and far IR. LCoS are used not only as displays but also as polarization, amplitude, and phase-only spatial light modulators, where they achieve full phase modulation. Due to their excellent modulating properties and high degree of flexibility, they are found in all sorts of spatial light modulation applications, such as in LCOS-based display systems for augmented and virtual reality, true holographic displays, digital holography, diffractive optical elements, superresolution optical systems, beam-steering devices, holographic optical traps, and quantum optical computing. In order to fulfil the requirements in this extensive range of applications, specific models and characterization techniques are proposed. These devices may exhibit a number of degradation effects such as interpixel cross-talk and fringing field, and time flicker, which may also depend on the analog or digital backplane of the corresponding LCoS device. The use of appropriate characterization and compensation techniques is then necessary

Holographic optical interconnects in dichromated gelatin

Abstract unavailable please refer to PD

Analysis of the oscillations induced by a supersonic jet applied to produce nanofibers

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUGHigh-performance fibers are key components for enhancing the mechanical properties of composite materials. The development of high strength nanofibers augurs the production of new nano-composites with outstanding features. However, the robust production of continuous glass nanofibers that can be feasible processed for efficiently manufacturing nanocomposites is still challenging. Recently, Cofiblas (Continuous Fiberizing by Laser melting and Supersonic dragging) was demonstrated as a technique capable of producing continuous glass nanofibers with unlimited length. Cofiblas process has some similarities with the widely known melt blowing technique for the production of polymeric fibers. In both techniques, the design of the gas nozzle is key to ensure the feasibility of the process since the turbulences of the gas jet may induce strong whipping of the filament. This paper gives novel experimental evidences on the correlation of the supersonic gas jet instabilities with the oscillation of the filament in the melt-blowing and Cofiblas processes, relating these oscillations with the presence of shock waves and unsteadiness in the flow, and gives valuable insight into the use of supersonic jets in the melt blowing process as an effective approach for the formation of nanofibers. A thin 3D-axisymmetric model in OpenFOAM® was put to test by comparing the performance of different solvers which were validated by flow visualization of the exit jet using digital holography (DH). In order to perform a realistic and thorough validation, we simulated the optical measurements of the flow from the CFD simulations of the mass density by Abel transform and numerical differentiation. The application of digital holography as the flow visualization technique makes possible both a precise validation of the density maps obtained from the Abel transformation of the 2D-alike results, and the analysis of the shockwave pattern in the air jet. Conversely, the numerical reconstruction of time-averaged holograms is employed to detect unsteadiness in the flow and to analyze the fiber oscillation, which is essential to assess the stability of the process. Lastly, the analysis and comparison of the vibration of the filament using the basic design and the optimized nozzle demonstrates a clear influence of the shock waves and flow unsteadiness in the stability of the filament.Agencia Estatal de Investigación | Ref. PGC2018-094900-B-I00Xunta de Galicia | Ref. ED431C 2019/23Ministerio de Universidades | Ref. FPU20/0311

Electro optical system to measure strains at high temperature

The measurement of strains at temperatures of the order of 1000 C has become a very important field of research. Technological advances in areas such as the analysis of high speed aircraft structures and high efficiency thermal engines require operational temperatures of this order of magnitude. Current techniques for the measurement of strains, such as electrical strain gages, are at the limit of their useful range and new methods need to be developed. Optical techniques are very attractive in this type of application because of their noncontacting nature. Holography is of particular interest because a minimal preparation of the surfaces is required. Optoelectronics holography is specially suited for this type of application, from the point of view of industrial use. There are a number of technical problems that need to be overcome to measure strains using holographic interferometry at high temperatures. Some of these problems are discussed, and solutions are given. A specimen instrumented with high temperature strains gages is used to compare the results of both technologies

Contributions to the design of Fourier-optical modulation systems based on micro-opto-electro-mechanical tilt-mirror arrays

Spatial Light Modulators (SLMs) based on Micro-Opto-Electro-Mechanical Systems (MOEMS) are increasingly being used in various fields of optics and enable novel functionalities. The technology features frame rates from a few kHz to the MHz range as well as resolutions in the megapixel range. The field continues to make rapid progress, but technological advancements are always associated with high expenditure. Against this background, this dissertation addresses the question: What contribution can optical system design make to the further development of MOEMS-SLM-based modulation? A lens is a simple example of an optical system. This dissertation deals with system design based on Fourier optics in which the wave properties of light are exploited. On this basis, arrays of micromirrors can modulate light properties in a spatially resolved manner. For example, tilt-mirrors can control the intensity distribution in an image plane. In this dissertation variations of the aperture required for this are investigated. In addition to known absorbing apertures, phase filters in particular are investigated, which apply a spatially distributed delay effect to the light wave. This dissertation proposes the combination of MOEMS-SLMs with static, pixelated elements in the same system. These may be pixelated phase masks, also known as diffractive optical elements (DOEs). Analogously, pixelated polarizer arrays and absorbing photomasks exist. The combination of SLMs and static elements allows new degrees of freedom in system design. This thesis proposes new modulation systems based on MOEMS tilt-mirror SLMs. These systems use analog tilt-mirror arrays for the simultaneous modulation of intensity and phase as well as intensity and polarization. The proposed systems thus open up new possibilities for MOEMS-based spatial light modulation. Their properties are validated and investigated by numerical simulations. System properties and limitations are derived from these near and far field simulations. This dissertation shows that the modulation of different MOEMS-SLM types can be fundamentally changed by system design. Piston mirror arrays are classically used for phase modulation and tilt-mirror arrays for intensity modulation. This thesis proposes the use of subpixel phase structures. Their use approximately provides tilt-mirrors with the phase-modulating effect of piston-mirrors. In order to achieve this, a new optimization method is presented. Piston-mirror arrays are available only to a limited extent. By contrast, tilt-mirror arrays are well established. In combination with subpixel phase features, tilt-mirrors may replace piston-mirrors in some applications. These and other challenges of MOEMS-SLM technology can be adequately addressed on the basis of system design.Räumliche Lichtmodulatoren (Spatial Light Modulators, SLMs) auf Basis von Mikro-Opto-Elektro-Mechanischen Systemen (MOEMS) finden zunehmend Anwendung in verschiedensten Teilgebieten der Optik und ermöglichen neuartige Funktionalitäten. Die Technik ermöglicht Frameraten von einigen kHz bis in den MHz-Bereich sowie Auflösungen bis in den Megapixelbereich. Der Fachbereich macht nach wie vor rasche Fortschritte, technologische Weiterentwicklungen sind aber stets mit hohem Aufwand verbunden. Vor diesem Hintergrund widmet sich diese Arbeit der Frage: Welchen Beitrag kann optisches Systemdesign zur Weiterentwicklung der MOEMS-SLM-basierten Modulation leisten? Bereits eine Linse stellt ein Beispiel für ein optisches System dar. Diese Dissertation beschäftigt sich mit Systemdesign auf Basis der Fourier-Optik, bei der die Welleneigenschaften des Lichts genutzt werden. Auf dieser Basis können Arrays von Mikrospiegeln die flächige Verteilung von Licht einstellen. Beispielsweise können Kippspiegel die Intensitätsverteilung in einer Bildebene steuern. In dieser Dissertation werden Variationen der dafür nötigen Apertur untersucht. Neben bekannten absorbierenden Blenden werden insbesondere Phasenfilter untersucht, welche eine flächig verteilte Verzögerungswirkung auf die Lichtwelle aufbringen. Diese Dissertation schlägt die Kombination von MOEMS-SLMs mit statischen, pixelierten Elementen im selben System vor. Hierbei kann es sich um pixelierte Phasenmasken handeln, auch bekannt als diffraktive optische Elemente (DOEs). Analog existieren pixelierte Polarisatorarrays und absorbierende Fotomasken. Die Kombination von SLMs und statischen Elementen ermöglicht neue Freiheiten im Systemdesign. Diese Arbeit schlägt neue Modulationssysteme auf Basis von MOEMS-Kippspiegel-SLMs vor. Diese Systeme nutzen analoge Kippspiegelarrays für die simultane Modulation von Intensität und Phase sowie von Intensität und Polarisation. Die vorgeschlagenen Systeme eröffnen damit neue Möglichkeiten für die MOEMS-basierte Flächenlichtmodulation. Ihre Eigenschaften werden mithilfe von numerischen Simulationen validiert und untersucht. Aus diesen Nah- und Fernfeldsimulationen werden Systemeigenschaften und Limitierungen abgeleitet. Es wird in dieser Arbeit gezeigt, dass die Modulation verschiedener MOEMS-SLM-Typen auf Basis des Systementwurfs fundamental verändert werden kann. Senkspiegelarrays werden klassischerweise zur Modulation der Phase eingesetzt und Kippspiegelarrays zur Modulation der Intensität. Diese Arbeit schlägt die Nutzung von Subpixel-Phasenstrukturen vor. Diese verleihen Kippspiegeln näherungsweise die phasenmodulierende Wirkung von Senkspiegeln. Um dies zu erreichen, wird ein neuartiges Optimierungsverfahren vorgestellt. Senkspiegelarrays sind nur in geringem Umfang verfügbar. Im Gegensatz dazu sind Kippspiegelarrays gut etabliert. In Kombination mit Subpixel-Phasenstrukturen könnten Kippspiegel in einigen Anwendungen Senkspiegel ersetzen. Diese und andere Herausforderungen der MOEMS-SLM-Technologie lassen sich auf der Grundlage des Systemdesigns adäquat adressieren

The quantitative analysis of transonic flows by holographic interferometry

This thesis explores the feasibility of routine transonic flow analysis by holographic interferometry. Holography is potentially an important quantitative flow diagnostic, because whole-field data is acquired non-intrusively without the use of particle seeding. Holographic recording geometries are assessed and an image plane specular illumination configuration is shown to reduce speckle noise and maximise the depth-of-field of the reconstructed images. Initially, a NACA 0012 aerofoil is wind tunnel tested to investigate the analysis of two-dimensional flows. A method is developed for extracting whole-field density data from the reconstructed interferograms. Fringe analysis errors axe quantified using a combination of experimental and computer generated imagery. The results are compared quantitatively with a laminar boundary layer Navier-Stokes computational fluid dynamics (CFD) prediction. Agreement of the data is excellent, except in the separated wake where the experimental boundary layer has undergone turbulent transition. A second wind tunnel test, on a cone-cylinder model, demonstrates the feasibility of recording multi-directional interferometric projections using holographic optical elements (HOE’s). The prototype system is highly compact and combines the versatility of diffractive elements with the efficiency of refractive components. The processed interferograms are compared to an integrated Euler CFD prediction and it is shown that the experimental shock cone is elliptical due to flow confinement. Tomographic reconstruction algorithms are reviewed for analysing density projections of a three-dimensional flow. Algebraic reconstruction methods are studied in greater detail, because they produce accurate results when the data is ill-posed. The performance of these algorithms is assessed using CFD input data and it is shown that a reconstruction accuracy of approximately 1% may be obtained when sixteen projections are recorded over a viewing angle of ±58°. The effect of noise on the data is also quantified and methods are suggested for visualising and reconstructing obstructed flow regions