Conference on Binary Optics: An Opportunity for Technical Exchange

The papers herein were presented at the Conference on Binary Optics held in Huntsville, AL, February 23-25, 1993. The papers were presented according to subject as follows: modeling and design, fabrication, and applications. Invited papers and tutorial viewgraphs presented on these subjects are included

Micro-optics technology and sensor systems applications

The current generation of electro-optical sensors utilizing refractive and reflective optical elements require sophisticated, complex, and expensive designs. Advanced-technology-based electro-optical sensors of minimum size and weight require miniaturization of optical, electrical, and mechanical devices with an increasing trend toward integration of various components. Micro-optics technology has the potential in a number of areas to simplify optical design with improved performance. This includes internally cooled apertures, hybrid optical design, microlenses, dispersive multicolor microlenses, active dither, electronically controlled optical beam steer, and microscopic integration of micro-optics, detectors, and signal processing layers. This paper describes our approach to the development of micro-optics technology with our main emphasis for sensors applications

Doctor of Philosophy

dissertationOptics is an old topic in physical science and engineering. Historically, bulky materials and components were dominantly used to manipulate light. A new hope arrived when Maxwell unveiled the essence of electromagnetic waves in a micro perspective. On the other side, our world recently embraced a revolutionary technology, metasurface, which modifies the properties of matter-interfaces in subwavelength scale. To complete this story, diffractive optic fills right in the gap. It enables ultrathin flat devices without invoking the concept of nanostructured metasurfaces when only scalar diffraction comes into play. This dissertation contributes to developing a new type of digital diffractive optic, called a polychromat. It consists of uniform pixels and multilevel profile in micrometer scale. Essentially, it modulates the phase of a wavefront to generate certain spatial and spectral responses. Firstly, a complete numerical model based on scalar diffraction theory was developed. In order to functionalize the optic, a nonlinear algorithm was then successfully implemented to optimize its topography. The optic can be patterned in transparent dielectric thin film by single-step grayscale lithography and it is replicable for mass production. The microstructures are 3?m wide and no more than 3?m thick, thus do not require slow and expensive nanopatterning techniques, as opposed to metasurfaces. Polychromat is also less demanding in terms of fabrication and scalability. The next theme is focused on demonstrating unprecedented performances of the diffractive optic when applied to address critical issues in modern society. Photovoltaic efficiency can be significantly enhanced using this optic to split and concentrate the solar spectrum. Focusing through a lens is no news, but we transformed our optic into a flat lens that corrects broadband chromatic aberrations. It can also serve as a phase mask for microlithography on oblique and multiplane surfaces. By introducing the powerful tool of computation, we devised two imaging prototypes, replacing the conventional Bayer filter with the diffractive optic. One system increases light sensitivity by 3 times compared to commercial color sensors. The other one renders the monochrome sensor a new function of high-resolution multispectral video-imaging

Learning Domain Invariant Information to Enhance Presentation Attack Detection in Visible Face Recognition Systems

Face signatures, including size, shape, texture, skin tone, eye color, appearance, and scars/marks, are widely used as discriminative, biometric information for access control. Despite recent advancements in facial recognition systems, presentation attacks on facial recognition systems have become increasingly sophisticated. The ability to detect presentation attacks or spoofing attempts is a pressing concern for the integrity, security, and trust of facial recognition systems. Multi-spectral imaging has been previously introduced as a way to improve presentation attack detection by utilizing sensors that are sensitive to different regions of the electromagnetic spectrum (e.g., visible, near infrared, long-wave infrared). Although multi-spectral presentation attack detection systems may be discriminative, the need for additional sensors and computational resources substantially increases complexity and costs. Instead, we propose a method that exploits information from infrared imagery during training to increase the discriminability of visible-based presentation attack detection systems. We introduce (1) a new cross-domain presentation attack detection framework that increases the separability of bonafide and presentation attacks using only visible spectrum imagery, (2) an inverse domain regularization technique for added training stability when optimizing our cross-domain presentation attack detection framework, and (3) a dense domain adaptation subnetwork to transform representations between visible and non-visible domains. Adviser: Benjamin Rigga

A review of dielectric optical metasurfaces for wavefront control

During the past few years, metasurfaces have been used to demonstrate optical elements and systems with capabilities that surpass those of conventional diffractive optics. Here, we review some of these recent developments, with a focus on dielectric structures for shaping optical wavefronts. We discuss the mechanisms for achieving steep phase gradients with high efficiency, simultaneous polarization and phase control, controlling the chromatic dispersion, and controlling the angular response. Then, we review applications in imaging, conformal optics, tunable devices, and optical systems. We conclude with an outlook on future potentials and challenges that need to be overcome

Resolution enhancement in mask aligner photolithography

Photolithographie ist eine unentbehrliche Technologie in der heutigen Mikrofabrikation integrierter elektronischer Schaltungen und optischer Komponenten auf verschiedenen Größenskalen. Die zugrundeliegende Aufgabe ist die Replikation der gewünschten Struktur, die kodiert ist in einer Photomaske, auf einem photolackbedeckten Wafer. In vergangenen Jahrzehnten gab es eine beeindruckende Weiterentwicklung photolithographischer Anlagen, was Auflösungen weit unterhalb eines Mikrometers ermöglicht. Das einfachste photolithographische Instrument ist der Maskenjustierbelichter, bei dem die Photomaske und der Wafer entweder in Kontakt oder in unmittelbare Nähe gebracht werden (Proximity-Modus), ohne zusätzliche optische Komponenten dazwischen. Vor über 50~Jahren eingeführt bleibt der Maskenjustierbelichter aufgrund seines wirtschaftlichen Betriebs das Instrument der Wahl für die Herstellung unkritischer Schichten, mit einer Auflösung von einigen Mikrometern im bevorzugten Proximity-Modus. Maskenjustierbelichter werden beispielsweise für die Herstellung von Mikrolinsen, lichtemittierende Dioden und mikromechanischen Systemen verwendet. Die erreichbare laterale räumliche Auflösung ist letztlich begrenzt durch die Beugung des Lichts an den Strukturen der Photomaske, was zu Verfälschungen der Abbildung auf dem Photolack führt. In dieser Arbeit entwickeln, präsentieren und diskutieren wir mehrere Technologien zur Auflösungsverbesserung für Maskenjustierbelichter im Proximity-Modus. Dies umfasst Photolithographie mit einer neuartigen Lichtquelle, die im tiefen Ultraviolett-Bereich emittiert, eine rigoros optimierte Phasenschiebermaske für periodische Strukturen, optische Proximity-Korrektur (Nahbereichskorrektur) angewandt auf nichtorthogonale Geometrien, und die Anwendung optischer Metaoberflächen als Photomasken. Eine Reduzierung der Wellenlänge verringert die Auswirkungen der Lichtbrechung und verbessert daher direkt die Auflösung, benötigt aber auch die Entwicklung geeigneter Konzepte für die Strahlformung und Homogenisierung der Beleuchtung. Wir diskutieren die Integration einer neuartigen Lichtquelle, ein frequenzvervierfachter Dauerstrichlaser mit einer Emissionswellenlänge von 193$\,$nm, in einem Maskenjustierbelichter. Damit zeigen wir erfolgreiche Prints von Teststrukturen mit einer Auflösung von bis zu 1,75$\,$µm bei einem Proximity-Abstand von 20$\,$µm. Bei Verwendung des selbstabbildenden Talboteffekts wird sogar eine Auflösung weit unterhalb eines Mikrometers für periodische Strukturen erzielt. Außerdem diskutieren wir die rigorose Simulation und Optimierung der Lichtausbreitung in und hinter Phasenschiebermasken, die unter schrägem Einfall belichtet werden. Mit einem optimierten Photomaskendesign kann dabei die Periode bei Belichtung unter drei diskreten Winkeln verkleinert abgebildet werden. Dies erlaubt es, Strukturen deutlich kleiner als ein Mikrometer abzubilden, wobei die Strukturen auf der Photomaske deutlich größer und damit einfacher herzustellen sind. Zudem betrachten wir eine Simulations- und Optimierungsmethode für die optische Proximity-Korrektur nicht-orthogonaler Strukturen, was deren Formtreue verbessert. die Wirksamkeit beider Konzepte bestätigen wir erfolgreich in experimentellen Prints. Die Verwendung optischer Metaoberflächen erweitert die Fähigkeiten zur Wellenfrontformung von Photomasken gegenüber etablierten Intensitäts- oder Phasenschiebermasken. Wir diskutieren zwei Designs für optische Metaoberflächen, die beide den vollen $2\,\pi$-Phasenbereich abdecken. Ein Design beinhaltet dabei noch einen plasmonischen Absorber, was zusätzliche Möglichkeiten bietet, den Transmissionskoeffizient anzupassen. Desweiteren beschreiben wir einen Algorithmus zur Berechnung des Maskenlayouts für beliebige Strukturen. Eine kontinuierliche Weiterentwicklung von Maskenjustierbelichtern ist unerlässlich, um Schritt zu halten mit der fortschreitenden Miniaturisierung in allen Bereich der Optik, der Mechanik und der Elektronik. Unsere Forschungsergebnisse ermöglichen es, die Auflösung der optischen Lithographie im Proximity-Modus zu verbessern und sich damit den zukünftigen Herausforderungen der optischen Industrie stellen zu können

Space variant guided mode resonant filters

Guided mode resonance filters (GMRF) combine subwavelength gratings and planar slab waveguides to create highly efficient, narrow linewidth spectral filters. Resonances between diffracted orders of the SWG and the waveguide provide the mechanism for spectral filtering. These resonance conditions are dependent on all of the structural and optical parameters of the GMRF structure. Microfabrication technologies are routinely used to fabricate these types of micro-optical structures as well as other types of micro-optical components such as diffractive optical elements. A spatially and spectrally varying optical element can be realized by spatially varying one or more of the structural parameters of a standard GMRF structure. This dissertation will show different methods of achieving a spatially and spectrally varying GMRF. These types devices have applications as beam shaping elements, feedback elements is laser systems, and as an alternate to graded reflectivity mirrors. Unlike graded reflectivity mirrors, the spatial variation in these space variant GMRFs is not limited to axial symmetries. This dissertation will focus on space variant GMRFs through a spatially variation in the fill-fraction of the SWG lattice structure as well as a spatial variation of the waveguiding layer. It will be shown what the effect of each of these variations has on the resonance conditions of a GMRF. Proposed devices for a spatially varying waveguide structure using a silicon oxide SWG with a silicon nitride waveguiding layer and a silicon nitride SWG with a silicon nitride waveguide layer will be discussed

Doctor of Philosophy

dissertationDiffractive optics, an important part of modern optics, involves the control of optical fields by thin microstructured elements via diffraction and interference. Although the basic theoretical understanding of diffractive optics has been known for a long time, many of its applications have not yet been explored. As a result, the field of diffractive optics is old and young at the same time. The interest in diffractive optics originates from the fact that diffractive optical elements are flat and lightweight. This makes their applications into compact optical systems more feasible compared to bulky refractive optics. Although these elements demonstrate excellent diffraction efficiency for monochromatic light, they fail to generate complex intensity profiles under broadband illumination. This is due to the fact that the degrees-of-freedom in these elements are insufficient to overcome their strong chromatic aberration. As a result, despite their so many advantages over refractive optics, their applications are somewhat limited in broadband systems. In this dissertation, a recently developed diffractive optical element, called a polychromat, is demonstrated for several broadband applications. The polychromat is comprised of linear "grooves" or square "pixels" with feature size in the micrometer scale. The grooves or pixels can have multiple height levels. Such grooved or pixelated structures with multilevel topography provide enormous degrees-of-freedom which in turn facilitates generation of complex intensity distributions with high diffraction efficiency under broadband illumination. Furthermore, the super-wavelength feature size and low aspect ratio of this micro-optic make its fabrication process simpler. Also, this diffractive element is not polarization sensitive. As a result, the polychromat holds the potential to be used in numerous technological applications. Throughout this dissertation, the broadband operation of the polychromat is demonstrated in four different areas, namely, photovoltaics, displays, lenses and holograms. Specifically, we have developed a polychromat-photovoltaic system which facilitates better photon-to-electron conversion via spectrum splitting and concentration, a modified liquid crystal display (LCD) that offers higher luminance compared to a standard LCD, a cylindrical lens that demonstrates super-achromatic focusing over the entire visible band, a planar diffractive lens that images over the visible and near-IR spectrum and broadband transmission holograms that project complex full-color images with high efficiency. In each of these applications, a unique figure of merit was defined and the height topography of the polychromat was optimized to maximize the figure of merit. The optimization was achieved with the aid of scalar diffraction theory and a modified version of direct binary search algorithm. Single step grayscale lithography was developed and optimized to fabricate these devices with the smallest possible fabrication errors. Rigorous characterization of these systems demonstrated broadband performance of the polychromat in all of the applications

Three-dimensional scanless holographic optogenetics with temporal focusing (3D-SHOT).

Optical methods capable of manipulating neural activity with cellular resolution and millisecond precision in three dimensions will accelerate the pace of neuroscience research. Existing approaches for targeting individual neurons, however, fall short of these requirements. Here we present a new multiphoton photo-excitation method, termed three-dimensional scanless holographic optogenetics with temporal focusing (3D-SHOT), which allows precise, simultaneous photo-activation of arbitrary sets of neurons anywhere within the addressable volume of a microscope. This technique uses point-cloud holography to place multiple copies of a temporally focused disc matching the dimensions of a neurons cell body. Experiments in cultured cells, brain slices, and in living mice demonstrate single-neuron spatial resolution even when optically targeting randomly distributed groups of neurons in 3D. This approach opens new avenues for mapping and manipulating neural circuits, allowing a real-time, cellular resolution interface to the brain