Perspective and Potential of Smart Optical Materials

The increasing requirements of hyperspectral imaging optics, electro/photo-chromic materials, negative refractive index metamaterial optics, and miniaturized optical components from microscale to quantum-scale optics have all contributed to new features and advancements in optics technology. Development of multifunctional capable optics has pushed the boundaries of optics into new fields that require new disciplines and materials to maximize the potential benefits. The purpose of this study is to understand and show the fundamental materials and fabrication technology for field-controlled spectrally active optics (referred to as smart optics) that are essential for future industrial, scientific, military, and space applications, such as membrane optics, light detection and ranging (LIDAR) filters, windows for sensors and probes, telescopes, spectroscopes, cameras, light valves, light switches, and flat-panel displays. The proposed smart optics are based on the Stark and Zeeman effects in materials tailored with quantum dot arrays and thin films made from readily polarizable materials via ferroelectricity or ferromagnetism. Bound excitonic states of organic crystals are also capable of optical adaptability, tunability, and reconfigurability. To show the benefits of smart optics, this paper reviews spectral characteristics of smart optical materials and device technology. Experiments testing the quantum-confined Stark effect, arising from rare earth element doping effects in semiconductors, and applied electric field effects on spectral and refractive index are discussed. Other bulk and dopant materials were also discovered to have the same aspect of shifts in spectrum and refractive index. Other efforts focus on materials for creating field-controlled spectrally smart active optics (FCSAO) on a selected spectral range. Surface plasmon polariton transmission of light through apertures is also discussed, along with potential applications. New breakthroughs in micro scale multiple zone plate optics as a micro convex lens are reviewed, along with the newly discovered pseudo-focal point not predicted with conventional optics modeling. Micron-sized solid state beam scanner chips for laser waveguides are reviewed as well

Enabling High Performance III-V Thin-Film Photodetectors on Unconventional Surfaces

High performance optoelectronic devices made of III-V compound semiconductors are preferred over elemental semiconductors due to their superior optical and electronic properties. With the development of semiconductor fabrication technology, thin-film optoelectronics on unconventional surfaces have drawn attention due to the benefits of enhanced absorption/reflection, reduced fabrication cost, superior mechanical flexibility, opportunities for integration with dissimilar materials, etc. In this thesis, we demonstrate novel fabrication techniques that transfer the III-V optoelectronic devices, especially high-performance photodetectors focal plane arrays, from their bulky and rigid crystalline substrates, to unconventional lightweight, flexible, conformal, and non-developable surfaces without performance degradation. The demonstrations include a cylindrical and bendable 8×100 thin-film In0.53Ga0.47As p-i-n photodiode array fabricated on a thin flexible plastic foil, and a hemispherical GaAs p-n junction focal plane array that mimics the size, form, and function of the human eye. In addition, we integrate an energy harvesting photodetector comprising an InGaAs-based thin-film thermophotovoltaic (TPV) cell with low index dielectrics and even air for enhanced out-of-band photon recycling. Specifically, an unconventional TPV cell is fabricated over an air cavity, showing 8% (absolute) power conversion efficiency improvement compared to conventional thin-film TPV cells, leading to a record-high TPV power conversion efficiency of > 30% at 1500K emitter temperature. The demonstrated high performance III-V thin-film photodetectors on unconventional surfaces unlock possibilities for future optoelectronics that are beyond current planar and lattice-matched substrates, and provide paths to their ubiquitous applications.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/155088/1/fandejiu_1.pd

Bio-inspired optical components

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references.Guiding electro-magnetic radiation is fundamental to optics. Lenses, mirrors, and photonic crystals all accomplish this task by different routes. Understanding the interaction of light with materials is fundamental to improving and extending optical science and engineering as well as producing novel optical elements. Improvement in this understanding should not only include work to understand the interaction with traditional engineering materials but also should target the understanding of the interaction of electromagnetic radiation with biological structures as millions of years of evolution have sorted out numerous ways to modulate light (e.g. the fish eye or the skin of the octopus). The goal of this thesis work is to fabricate novel optical elements by taking cues from nature and extending the state of the art in light guiding behavior. Here, optical elements are defined as structured materials that guide or direct electromagnetic radiation in a predetermined manner. The work presented in this thesis encompasses biologically inspired tunable multilayer reflectors made from block copolymers and improvements to liquid filled lenses which mimic the human eye.In this thesis a poly(styrene)-poly(2-vinylpyridine) block copolymer was used to create a bio-mimetic, one-dimensional, multilayer reflector. The wavelengths of light reflected from this multilayer reflector or Bragg stack were tuned by the application of stimuli which included temperature, change in the solvent environment, pH, salt concentration in the solvent, and electrochemistry.(cont.) A linear-shear rheometer was also built to investigate the mechanochromic color change brought about through the shearing of a one-dimensional, high molecular-weight, block-copolymer, photonic gel. Biologically inspired lenses were also studied through the construction of a finite element model which simulated the behavior of a liquid-filled lens. Several tunable parameters, such as the modulus, internal residual stress, and thickness of the membrane were studied for their influence on the shape of the lens membrane. Based on these findings, suggestions for the reduction of spherical aberration in a liquid filled lens were made. A gradient in the elastic modulus of the membrane was also investigated for use in the reduction of spherical aberration.by Joseph John Walish.Ph.D

PHOTONIC STRUCTURES AND DEVICES MOLDED ON SOFT POLYMER MATERIALS

Polymer materials are ubiquitous, relatively cheap, easy to process, and functionalize, making them interesting for many applications, in particular for optical systems that are traditionally fabricated from rigid and expensive materials. Polymer properties can be exploited to modulate the optical response of photonic structures. In this dissertation, I will discuss the fabrication and demonstration of several applications of soft polymers in the field of optics. Soft polymers can be used to fabricate structures with optical effects inaccessible using a single optical element created from standard materials. First, I employed a biomimetic approach to produce structural color similar to the bright blue of the Morpho Butterfly. Second, I used shape active polymers to reversibly modulate the height of an optical grating through heat. Lastly, I developed a varifocal polymer lens for an augmented reality system. Structural Color, as opposed to pigmented color, is the result of light interacting with structures with geometrical length scales comparable with the wavelength of visible light. There are many examples of structural color found in nature, from the various colors of the jewel beetles to the vibrant blue of the kingfisher bird. This structural effect can typically be identified by the iridescent nature of the coloration. I will discuss my approach toward biomimicry of the unique photonic structure found on the surface of the Morpho butterfly wings. This sub-micron sized structure is a ridge which in cross-sectional view resembles a tree, with a thin “trunk” and many periodic “branches” that produce a multilayer interference effect, strongly reflecting a brilliant blue color over a wide angular range. Biomimicry of the Morpho butterfly nanostructure has been attempted but the angular insensitivity has never been fully shown in a man-made replica. I will discuss the importance of the inherent randomness found within the Morpho structures that causes light to spread over such a large range. Here in, I will show two different fabrication approaches to integrate microstructure randomness and the consequence of such variations on the angular response. In structures that were fabricated using interference lithography a quasi-randomness (incomplete randomization) is induced through drying. Angular measurements show that a two-lobe reflection, much alike that produced by the true butterfly wing, is produced in angular space and is attributable to this quasi-random nanostructure. However, periodicity needs to be fully destroyed in order to overcome diffraction. To do this a direct-write lithography system was built and used to produce completely non-periodic structures. The results showed a more pronounced a two-lobe reflection at oblique angles. Finite-difference time-domain (FDTD) simulations were employed to understand this reflection signature and to determine effect of other geometric features. From these simulations a photonic structure, capable of spreading light in similar fashion to the butterfly, and that can be fabricated with standard microfabrication techniques is proposed. In connection to the use of polymers in diffractive structures, I will discuss my work with shape active polymers. Shape memory polymers offer a unique approach for application that demand multipurpose parts and have been utilized as heart stents and actuators. The applicability of these shape memory polymers as optical elements is demonstrated by examining the optical response of a shape shifting diffraction grating. As the height of the diffraction grating is reversibly changed the intensity of diffracted light is modulated. This constitutes a simple device realization that nevertheless illustrates the materials and optical issues that arise from the application of shape memory polymer in more complex photonic shapes will lead to the optical systems with versatile components. Finally, the use of elastomeric polymers as shape active lens will be explored. Varifocal lenses have shown the potential to solve an inherent problem in virtual and augmented reality headsets. In augmented and virtual reality headsets, the human eye will focus on the screen several inches from the face but images for both eyes are off set in order cause the users eyes to converge at a certain angle, imitating distance. In the real-world focus and vergence are in sync but these headsets encounter what is known as vergence–accommodation conflict and it is the source of major user discomfort. Vergence–accommodation conflict prevents the wide spread adoption of these potentially impactful technologies. I will present my work in developing a varifocal half silvered mirror for use in an augmented reality system. The system was validated by a perception test that showed users having increased success when the system was properly focusedDoctor of Philosoph

Fabrication and light management of microscale solar cells

Photovoltaic (PV) technology holds great promises to become one of the renewable alternatives that can eventually replace the depleting fossil fuel reserves. Challenges, however, remain in various disciplines to achieve a performance-to-cost ratio that can stay economically competitive against traditional energy sources. This dissertation highlights efforts that tackle such challenges from different perspectives, using lightweight microscale semiconductor membranes with unconventional form factors. We start with the fabrication of second-generation silicon solar microcells, with enhanced processing robustness and energy conversion efficiency by utilizing a thermally grown SiO2 material, which serves as both an etching/doping mask and a passivation/anti-reflection layer. Combined with a backside-reflector and a polymer waveguide, these ribbon-like miniature semiconductor membranes demonstrate performance merits that are comparable to commercial silicon solar cells, albeit with significantly less active material consumption. The inherent low optical absorption of these ultrathin devices can be effectively improved by either creating nanocone structures on the device surface that elongate the photon propagation path within the cell, or converting the polymer waveguide to a luminescent solar concentrator (LSC) with luminophores that actively down-converts incident sunlight and redirects it to the embedded microcells. Strategies explored in this work to improve the performance of such LSC devices include the use of core-shell quantum dots with tunable bandgaps and minimum reabsorption losses, the design of a luminescence-trapping photonic mirror with photon recycling effects and the assembly of a multilayer construct with expanded spectral coverage. The low-cost microcell concept can be extended from Si to III-V PV materials, which have much higher efficiency due to their direct bandgap structure and the ability to form multi-junction architectures that minimize both absorption and carrier thermalization losses. Their high material cost due to the epitaxy growth process is usually compensated by use of concentrating optics, which then leads to performance constraints that include the optical losses from the geometric lenses and the inability to capture diffuse solar radiation. In the last section of this work, novel nanoporous optical materials and hybrid module architectures are created for a commercial concentration photovoltaics (CPV) module that employs triple-junction III-V microcells, with significantly reduced Fresnel losses and added capability of utilizing diffuse sunlight

Study of nanostructured glass surfaces for photovoltaic applications

Ph.DDOCTOR OF PHILOSOPH

Design, Fabrication, and Testing of a Chitosan Based Optical Biosensor

This work presents the design, fabrication, and testing of an original concept for an optical biosensor device intended for use in a microfluidic network. The device uses planar waveguides intersecting a microfludic channel with biofunctionalized patterned sidewalls to detect biomolecules via fluorescent labeling. The optical-biological interface is provided through chitosan, a natural biopolymer. Chitosan is electrodepositable, and this material platform was developed to enable spatially selective and temporally selective assembly of biospecies in the sensor using electrical signals. The unique fabrication process flow integrates waveguides and microfluidic channels which are fabricated in a single step with a thick polymer layer on a Pyrex substrate. Key to the success of the device was the development of a process to pattern indium tin oxide on the sidewalls of deep (130 um) fluid channels. The device was tested in several modes of operation and the proof of concept was shown

Optical Microring Resonators for Photoacoustic Imaging and Detection.

This work is to utilize the superior characteristics of polymer microring resonators in ultrasound detection to push the application of photoacoustic imaging to an entirely new level. We first demonstrated significantly improved imaging quality for photoacoustic tomography (PAT) using microring detectors. For wideband PAT, the microring detectors were able to faithfully detect both the boundaries and the inner structure, while piezoelectric detectors can only preserve one of the two aspects. For high-resolution PAT over a large imaging area, we imaged 50 µm black beads and found that microrings produced high-resolution imaging over a 16-mm-diameter imaging area while the 500 µm piezoelectric detectors only obtained high-resolution imaging over a small area around center. Pure optical photoacoustic microscopy (PAM) has been demonstrated. Microring ultrasonic resonators were applied in in vivo photoacoustic imaging for the first time. Good imaging signal-to-noise ratio and high axial resolution of 8 µm were calibrated. As a comparison, a commercial hydrophone with similar sensitivity produced a low axial resolution of 105 µm. A 5 mm miniaturized probe consisting of a fiber to deliver excitation laser pulses and microring detectors for ultrasound detection has been fabricated for photoacoustic endoscopy. The calibrated high radial resolution of 21 µm was higher than other types of endoscopic photoacoustic probes, around 40 µm or larger. A photoacoustic correlation spectroscopy (PACS) technique was proposed. In a proof-of-concept experiment, we demonstrated low-speed flow measurement of ~15 µm/s by the PACS technique. We also demonstrated in vivo flow speed measurement of red blood cells in capillaries in a chick embryo model by PACS. Other techniques might have difficulties to measure it due to the low signal contrast and/or poor resolutions. We also proposed terahertz electromagnetic pulse detection by photoacoustic method. We used carbon nanotube composites as efficient photoacoustic transmitters and microrings as sensitive detectors. The photoacoustic method provides low-cost and real-time terahertz detection (~µs), which is difficult by conventional terahertz detectors, such as a bolometer or a pyroelectric detector.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91497/1/chensll_1.pd

Development of a microfluidic device for gaseous formaldehyde sensing = Développement d\u27un dispositif microfluidique pour la détection de formaldéhyde à l\u27état gazeux

Formaldehyd (HCHO) ist eine chemische Verbindung, die bei der Herstellung einer großen Zahl von Haushaltsprodukten verwendet wird.Charakteristisch ist seine hohe Flüchtigkeit aufgrund einer niedrigen Siedetemperatur ($T = - 19\ ℃$). Daher ist HCOH fast überall als Luftschadstoff in Innenräumen vorhanden. Die Miniaturisierung analytischer Systeme zu Handheld-Gerät hat das Potenzial, nicht nur effizientere, sondern auch empfindlichere Instrumente für die Echtzeitüberwachung dieses gefährlichen Luftschadstoffs zu ermöglichen. Die vorliegende Doktorarbeit präsentiert die Entwicklung eines Mikrofluidik-Geräts für die Erfassung von HCHO basierend auf der Hantzsch-Reaktion.Hierbei wurde der Schwerpunkt auf die Komponente für Fluoreszenzdetektion gelegt. Es wurde eine umfangreiche Literaturrecherche durchgeführt, die es erlaubt, den Stand der Technik auf dem Gebiet der Miniaturisierung des Fluoreszenzsensors zusammenzufassen. Auf Grund dieser Studie wurde ein modulares Fluoreszenzdetektionskonzept vorgeschlagen, das um einen CMOS-Bildsensor (CIS) herum entwickelt wurde. Zwei dreischichtige Fluidikzellenkonfigurationen (Konfiguration 1: Quarz - SU-8 3050 - Quarz und Konfiguration 2: Silizium - SU-8 3050 - Quarz) wurden in Betracht gezogen und parallel unter den gleichen experimentellen Bedingungen getestet. Die Verfahren der Mikrofabrikation der fluidischen Zellen wurden detailliert beschrieben, einschließlich des Integrationsprozesses der Standardkomponenten und der experimentellen Verfahren. Der CIS-basierte Fluoreszenzdetektor bewies seine Leistungsfähigkeit, eine anfängliche HCHO-Konzentration von 10 µg/L vollständig in 3,5-Diacetyl-1,4-dihydrolutidin (DDL- derivatisiert) sowohl für die Quarz- als auch für die Silizium-Fluidikzellen zu detektieren. Beide Systemewiesenein Abfragevolumen von 3,5 µL auf. Ein offensichtlich höheres Signal-Rausch-Verhältnis (SNR) wurde für die Silizium-Fluidzelle ($\text{SNR}_{\text{silicon}} = 6.1$) im Vergleich zur Quarz-Fluidzelle ($\text{SNR}_{\text{quartz}} = 4.9$) beobachtet. Die Verstärkung der Signalintensität in der Silizium-Fluidzelle ist wahrscheinlich auf den Silizium-Absorptionskoeffizienten bei der Anregungswellenlänge zurückzuführen,$a\left( \lambda_{\text{abs}} = 420\ nm \right) = 5 \bullet 10^{4}\text{cm}^{- 1}$. Dieser Koeffizient ist ungefähr fünfmal höher als der Absorptionskoeffizient bei der Fluoreszenzemissionswellenlänge $a\left(\lambda_{\text{em}} = 515\ nm \right) = 9.25 \bullet 10^{3}\text{cm}^{- 1}$. HCHO wird aufgrund seiner relativ hohen Konstanten für das Henry-Gesetz sehr schnell in ein flüssiges Reagenz aufgenommen. Somit hängt die Auswahl des molekularen Einfangverfahrens (Schwallströmung, Ringströmung oder membranbasierte Strömungswechselwirkung) von derLeistungsfähigkeit des Fluoreszenzdetektors ab. Ein vorläufiges Konzept, das auf der Verwendung einer Gas-Flüssigkeitsmembran-basierten Wechselwirkung zum ständigen Abfangen des gasförmigen HCHO basiert, wurde eingeführt. Hierzu wurden kompatible Materialien und Herstellungsmethoden identifiziert. Darüber hinaus wurden CFD-Simulationen durchgeführt, um die Mikrokanallänge unter verschiedenen hydrodynamischen Bedingungen abzuschätzen, die für eine vollständige HCHO-Derivatisierung erforderlich sind. Eine Verbesserung und Vereinfachung auf der Grundlage von sehrnempfindlichen Fluoreszenzdetektoren mit niedrigen Detektionsgrenzen könnte zukünftig basierend z. B. auf Schwallströmung oder Ringströmung möglich sein

Emerging topics in nanophononics and elastic, acoustic, and mechanical metamaterials: an overview

This broad review summarizes recent advances and “hot” research topics in nanophononics and elastic, acoustic, and mechanical metamaterials based on results presented by the authors at the EUROMECH 610 Colloquium held on April 25–27, 2022 in Benicássim, Spain. The key goal of the colloquium was to highlight important developments in these areas, particularly new results that emerged during the last two years. This work thus presents a “snapshot” of the state-of-the-art of different nanophononics- and metamaterial-related topics rather than a historical view on these subjects, in contrast to a conventional review article. The introduction of basic definitions for each topic is followed by an outline of design strategies for the media under consideration, recently developed analysis and implementation techniques, and discussions of current challenges and promising applications. This review, while not comprehensive, will be helpful especially for early-career researchers, among others, as it offers a broad view of the current state-of-the-art and highlights some unique and flourishing research in the mentioned fields, providing insight into multiple exciting research directions