This talk will introduce some of our recent work on using nanostructures to tailor thermal radiation with applications from solar and thermal energy for electrical generation and storage, to desalination. We fabricated solar photovolatic cells with efficiency >15% using 10 micron-thick crystalline silicon films. We demonstrated that aerogels can be used for concentrated solar thermal power, eliminating the need for vacuum and wavelength selective coatings. Photovoltaic cells can couple to terrestrial heat sources to convert thermal radiation into electricity, at an efficiency higher than photovoltaics. Moving to lower temperature range, we show that fabrics can be made to radiate out human body heat while remain opaque to visible light. We also demonstrate that by localizing solar energy on water surface, we can boil water and even achieve superheated steam under one sun. The talk will end with a discussion of the entropy of light and how we exploit the understanding to design better thermal-to-electrical energy converters.
We report on optical design and applications of hybrid meso-scale devices and materials that combine optical and thermal management functionalities owing to their tailored resonant interaction with light in visible and infrared frequency bands. We outline a general approach to designing such materials, and discuss two specific applications in detail. One example is a hybrid optical-thermal antenna with sub-wavelength light focusing, which simultaneously enables intensity enhancement at the operating wavelength in the visible and reduction of the operating temperature. The enhancement is achieved via light recycling in the form of whispering-gallery modes trapped in an optical microcavity, while cooling functionality is realized via a combination of reduced optical absorption and radiative cooling. The other example is a fabric that is opaque in the visible range yet highly transparent in the infrared, which allows the human body to efficiently shed energy in the form of thermal emission. Such fabrics can find numerous applications for personal thermal management and for buildings energy efficiency improvement.
KEYWORDS: Electrons, Gold, Solar energy, Photons, Metals, Energy efficiency, Semiconductors, Data conversion, P-type semiconductors, Energy conversion efficiency
We evaluate the limiting efficiency of full and partial solar spectrum harvesting via the process of internal photoemission in Au-semiconductor Schottky junctions. Our results based on the ab initio calculations of the electron density of states (e-DOS) reveal that the limiting efficiency of the full-spectrum Au converter based on hot electron injection is below 4%. This value is even lower than previously established limit based on the parabolic approximation of the Au electron energy bands. However, we predict limiting efficiency exceeding 10% for the hot holes collection through the Schottky junction between Au and p-type semiconductor. Furthermore, we demonstrate that such converters have more potential if used as a part of the hybrid system for harvesting high- and low-energy photons of the solar spectrum.
We demonstrated lasing in localized optical resonances of deterministic aperiodic structures
with pseudo-random morphologies. The localized lasing modes in the Rudin-Shapiro arrays of air
nanoholes in GaAs membranes occur at reproducible spatial locations and their frequencies are
only slightly affected by the structural fluctuations in different samples. Numerical study on the
resonances of the passive systems and optical imaging of lasing modes enabled us to interpret the
observed lasing behavior in terms of distinctive localized resonances in the two-dimensional Rudin-
Shapiro structures. The deterministic aperiodic media with controllable structural and optical
properties provide a novel platform, alternative to random lasers and different from photonic crystals
lasers, for the engineering of multi-frequency coherent light sources suitable for technological
integration.
The ability to reproducibly and accurately control light matter interaction on the nanoscale is at the core of the field of
optical biosensing enabled by the engineering of nanophotonic and nanoplasmonic structures. Efficient schemes for
electromagnetic field localization and enhancement over precisely defined sub-wavelength spatial regions is essential to
truly benefit from these emerging technologies. In particular, the engineering of deterministic media without translational
invariance offers an almost unexplored potential for the manipulation of optical states with vastly tunable transport and
localization properties over broadband frequency spectra. In this paper, we discuss deterministic aperiodic plasmonic and
photonic nanostructures for optical biosensing applications based on fingerprinting Surface Enhanced Raman Scattering
(SERS) in metal nanoparticle arrays and engineered light scattering from nanostructured dielectric surfaces with low
refractive index (quartz).
We present a theoretical analysis and numerical design of bent and branched sections of coupled resonator optical waveguides (CROWs) composed of side-coupled whispering-gallery (WG) mode microdisk resonators. Our analysis is based on a rigorous Muller boundary integral equations method that enables accurate treatment of CROWs consisting of both identical and different microdisks as well as studying CROW finite-size effects. Differences in WG modes coupling in the vicinity of bends in CROWs composed of optically-large and wavelength-scale microcavities are revealed and discussed. We propose possible ways of pre- and post-fabrication tuning of bent CROW sections. At the pre-fabrication design stage, adjusting the radius of the microdisk positioned at the CROW bend may yield significant reduction of bend losses for any chosen CROW bend angle. Post-fabrication tuning capability of the designed structures is also discussed.
Photonic molecules, named by analogy with chemical molecules, are clusters of closely located electromagnetically
interacting microcavities or "photonic atoms". As two or several microcavities are brought close together, their optical
modes interact, and a rich spectrum of photonic molecule supermodes emerges, which depends both on geometrical and
material properties of individual cavities and on their mutual interactions. Here, we discuss ways of controllable
manipulation of photonic molecule supermodes, which improve or add new functionalities to microcavity-based optical
components. We present several optimally-tuned photonic molecule designs for lowering thresholds of semiconductor
microlasers, producing directional light emission, enhancing sensitivity of microcavity-based bio(chemical)sensors, and
optimizing electromagnetic energy transfer around bends of coupled-cavity waveguides. Photonic molecules composed
of identical microcavities as well as of microcavities with various degrees of size or material detuning are discussed.
Microwave experiments on scaled photonic molecule structures are currently under way to confirm our theoretical
predictions.
Dielectric resonators promise high functionality components for future optoelectronic integrated circuit applications. Accurate modeling of these components is a prerequisite to their successful deployment in innovative configurations. This paper will compare and contrast a wide variety of simulation techniques, developed by ourselves, that can be used for design. These encompass, (1) ful wave analytical integral equation methods which yield high accuracy and fast computation but are structure specific, (2) direct numerical simulation based upon high performance finite difference schemes which offer significant flexibility at the cost of computational overheads, (3) fast yet accurate semi- analytical approaches which can often provide sufficiently accurate result for the purposes of practical design at a fraction of the effort, in terms of both computational and pre-processing analysis as required by the former methods. The relative merits of the methods will be illustrated through their application to the design of practical components for a variety of systems. These will include examining the resonant frequencies, the quality factors and the field profiles of the lower order modes and the whispering gallery modes of dielectric resonators. Specific applications of interest are in the fields of filters, coupling elements and lasers.
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