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Metamaterial absorbers have been demonstrated across much of the electromagnetic spectrum and exhibit both broad and narrow-band absorption for normally incident radiation. Absorption diminishes for increasing angles of incidence and transverse electric polarization falls off much more rapidly than transverse magnetic. We unambiguously demonstrate that broad-angle TM behavior cannot be associated with periodicity, but rather is due to coupling with a surface electromagnetic mode that is both supported by, and well described via the effective optical constants of the metamaterial where we achieve a resonant wavelength that is 19.1 times larger than the unit cell. Experimental results are supported by simulations and we highlight the potential to modify the angular response of absorbers by tailoring the surface wave.
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At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.
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Endotelina-1/metabolismo , Células Epiteliales/efectos de la radiación , Dolor/metabolismo , Transducción de Señal/efectos de la radiación , Quemadura Solar/metabolismo , Canales Catiónicos TRPV/metabolismo , Rayos Ultravioleta , Análisis de Varianza , Animales , Células Cultivadas , Células Epiteliales/metabolismo , Inmunohistoquímica , Ratones , Ratones Transgénicos , Microscopía Electrónica , Dolor/etiología , Piel/citología , Quemadura Solar/patologíaRESUMEN
We report thin film single crystal silicon photodetectors (PDs), composed of 13- 25 µm thick silicon, heterogeneously bonded to transparent Pyrex® and flexible Kapton® substrates. The measured responsivity and dark current density of the PDs on pyrex is 0.19 A/W - 0.34 A/W (λ = 470 nm - 600 nm) and 0.63 nA/cm(2), respectively, at ~0V bias. The measured responsivity and dark current density of the flexible PDs is 0.16 A/W - 0.26 A/W (λ = 470 nm - 600 nm) and 0.42 nA/cm(2), respectively, at a ~0V bias. The resulting responsivity-to-dark current density ratios for the reported rigid and flexible PDs are 0.3-0.54 cm(2)/nW and 0.38-0.62 cm(2)/nW, respectively. These are the highest reported responsivity-to-dark current density ratios for heterogeneously bonded thin film single crystal Si PDs, to the best of our knowledge. These PDs are customized for applications in biomedical imaging and integrated biochemical sensing.
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Dispositivos Ópticos , Silicio , Ingeniería Biomédica , Diagnóstico por Imagen/instrumentación , Diseño de Equipo , Humanos , Fenómenos Ópticos , Análisis Espectral/instrumentaciónRESUMEN
As a result of advances in nanotechnology and the burgeoning capabilities for fabricating materials with controlled nanoscale geometries, the traditional notion of what constitutes an optical device continues to evolve. The fusion of maturing low-cost lithographic techniques with newer optical design strategies has enabled the introduction of artificially structured metamaterials in place of conventional materials for improving optical components as well as realizing new optical functionality. Here we demonstrate multilayer, lithographically patterned, subwavelength, metal elements, whose distribution forms a computer-generated phase hologram in the infrared region (10.6 µm). Metal inclusions exhibit extremely large scattering and can be implemented in metamaterials that exhibit a wide range of effective medium response, including anomalously large or negative refractive index; optical magnetism; and controlled anisotropy. This large palette of metamaterial responses can be leveraged to achieve greater control over the propagation of light, leading to more compact, efficient and versatile optical components.
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This paper presents an optical element capable of multiplexing two diffraction patterns for two orthogonal linear polarizations, based on the use of non-resonant metamaterial cross elements. The metamaterial cross elements provide unique building blocks for engineering arbitrary birefringence. As a proof-of-concept demonstration, we present the design and experimental characterization of a polarization multiplexed blazed diffraction grating and a polarization multiplexed computer-generated hologram, for the telecommunication wavelength of λ = 1.55 µm. A quantitative study of the polarization multiplexed grating reveals that this approach yields a very large polarization contrast ratio. The results show that metamaterials can form the basis for a versatile and compact platform useful in the design of multi-functional photonic devices.
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Employing artificially structured metamaterials provides a means of circumventing the limits of conventional optical materials. Here, we use transformation optics (TO) combined with nanolithography to produce a planar Luneburg lens with a flat focal surface that operates at telecommunication wavelengths. Whereas previous infrared TO devices have been transformations of free-space, here we implement a transformation of an existing optical element to create a new device with the same optical characteristics but a user-defined geometry.
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Tecnología de Fibra Óptica/instrumentación , Rayos Infrarrojos , Lentes , Materiales Manufacturados , Nanotecnología/instrumentación , Telecomunicaciones/instrumentación , Modelos Teóricos , Silicio/químicaRESUMEN
We demonstrate the design, fabrication and characterization of an artificially structured, gradient index metamaterial with a linear index variation of Δn ~ 3.0. The linear gradient profile is repeated periodically to form the equivalent of a blazed grating, with the gradient occurring across a spatial distance of 61 µm. The grating, which operates at a wavelength of 10.6 µm, is composed of non-resonant, progressively modified "I-beam" metamaterial elements and approximates a linear phase shift gradient using 61 distinguishable phase levels. The grating structure consists of four layers of lithographically patterned metallic I-beam elements separated by dielectric layers of SiO(2). The index gradient is confirmed by comparing the measured magnitudes of the -1, 0 and +1 diffracted orders to those obtained from full wave simulations incorporating all material properties of the metals and dielectrics of the structures. The large index gradient has the potential to enable compact infrared diffractive and gradient index optics, as well as more exotic transformation optical media.
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Materiales Manufacturados , Refractometría/instrumentación , Diseño Asistido por Computadora , Diseño de Equipo , Análisis de Falla de EquipoRESUMEN
In this Letter we demonstrate, for the first time, selective thermal emitters based on metamaterial perfect absorbers. We experimentally realize a narrow band midinfrared (MIR) thermal emitter. Multiple metamaterial sublattices further permit construction of a dual-band MIR emitter. By performing both emissivity and absorptivity measurements, we find that emissivity and absorptivity agree very well as predicted by Kirchhoff's law of thermal radiation. Our results directly demonstrate the great flexibility of metamaterials for tailoring blackbody emission.
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A thin-film InGaAs/GaAs edge-emitting single-quantum-well laser has been integrated with a tapered multimode SU-8 waveguide onto an Si substrate. The SU-8 waveguide is passively aligned to the laser using mask-based photolithography, mimicking electrical interconnection in Si complementary metal-oxide semiconductor, and overlaps one facet of the thin-film laser for coupling power from the laser to the waveguide. Injected threshold current densities of 260A/cm(2) are measured with the reduced reflectivity of the embedded laser facet while improving single mode coupling efficiency, which is theoretically simulated to be 77%.
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Rayos Láser , Silicio/química , Arsenicales/química , Diseño de Equipo , Galio/química , Indio/química , Luz , Óptica y Fotónica , Semiconductores , Dióxido de Silicio/químicaRESUMEN
The integration of fluorescence sensing directly into the fluidic channel in lab-on-a chip systems using thin film Si detectors enables on-chip multi-target medical diagnostics and biochemical analyses. This paper reports on the experimental demonstration and theoretical analysis of a filter-free thin film fluorescence sensor designed for integration into the channel of a fluidic platform. Static tests of this optical sensor show repeatable detection of 6-Hex fluorophore concentrations from 300 nM to 20 µM, with an average signal-to-noise ratio of 26 dB-50 dB, which agrees well with the theoretical model.
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Plasmonic multi-mode interference (MMI) couplers have been investigated both numerically and experimentally at the telecommunication wavelength of 1.55 mum. In this study, the couplers are implemented using thin Au stripes that support long-range surface plasmons. We first detail the operation principle of these devices with numerical simulations and show that useful effects can be obtained despite the high material losses inherent to metallic structures. A series of MMI couplers is subsequently fabricated and experimentally characterized, showing a quantitative agreement with our numerical predictions. We conclude by discussing some of the possible applications for these structures.
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Interferometría/instrumentación , Dispositivos Ópticos , Resonancia por Plasmón de Superficie/instrumentación , Diseño Asistido por Computadora , Diseño de Equipo , Análisis de Falla de Equipo , Reproducibilidad de los Resultados , Sensibilidad y Especificidad , Integración de SistemasRESUMEN
A III-V thin-film single-quantum-well edge-emitting laser is patterned on both sides of the epitaxial layer and bonded to silicon. Injected threshold current densities of 420 A/cm(2) for gain-guided lasers with bottom p-stripes and top n-stripes and 244 A/cm(2) for index-guided bottom p-ridge and top n-stripe lasers are measured with a lasing wavelength of approximately 995 nm. These threshold current densities, among the lowest for thin-film edge-emitting lasers on silicon reported to date (to our knowledge), enable the implementation of integrated applications such as power-efficient portable chip-scale photonic sensing systems.
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Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a promising technique for characterization of colon tissue. Herein, two methods for extracting the reduced scattering and absorption coefficients ( µ s ' ( λ ) and µ a ( λ ) ) from SRDRS data using lookup tables of simulated diffuse reflectance are reported. Experimental measurements of liquid tissue phantoms performed with a custom multi-pixel silicon SRDRS sensor spanning the 450 - 750 nm wavelength range were used to evaluate the extraction methods, demonstrating that the combined use of spatial and spectral data reduces extraction error compared to use of spectral data alone. Additionally, SRDRS measurements of normal and tumor ex-vivo human colon tissue are presented along with µ s ' ( λ ) and µ a ( λ ) extracted from these measurements.
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We present the design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz, as a step towards the development of frequency agile or broadband THz materials and devices. A method of defining the effective thickness of the metamaterial layer is introduced to simplify the material design and characterization. Good agreement between the simulated and measured transmission is obtained for the fabricated sample by treating the sample as multi-layer system, i. e. the effective metamaterial layer plus the rest of the substrate, as well as properly modeling the loss of the substrate. The methods introduced in this paper can be extended to planar metamaterial structures operating in infrared and optical frequency ranges.
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Electrónica/instrumentación , Metales/química , Modelos Teóricos , Óptica y Fotónica/instrumentación , Simulación por Computador , Diseño de Equipo , Análisis de Falla de Equipo , Rayos Infrarrojos , Luz , Ensayo de Materiales , Microondas , Dispersión de RadiaciónRESUMEN
Locally energized particles form the basis for emerging classes of active matter. The design of active particles has led to their controlled locomotion and assembly. The next generation of particles should demonstrate robust control over their active assembly, disassembly, and reconfiguration. Here we introduce a class of semiconductor microparticles that can be comprehensively designed (in size, shape, electric polarizability, and patterned coatings) using standard microfabrication tools. These custom silicon particles draw energy from external electric fields to actively propel, while interacting hydrodynamically, and sequentially assemble and disassemble on demand. We show that a number of electrokinetic effects, such as dielectrophoresis, induced charge electrophoresis, and diode propulsion, can selectively power the microparticle motions and interactions. The ability to achieve on-demand locomotion, tractable fluid flows, synchronized motility, and reversible assembly using engineered silicon microparticles may enable advanced applications that include remotely powered microsensors, artificial muscles, reconfigurable neural networks and computational systems.
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Early detection and surveillance of disease progression in epithelial tissue is key to improving long term patient outcomes for colon and esophageal cancers, which account for nearly a quarter of cancer related mortalities worldwide. Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a non-invasive optical technique to sense biological changes at the cellular and sub-cellular level that occur when normal tissue becomes diseased, and has the potential to significantly improve the current standard of care for endoscopic gastrointestinal (GI) screening. Herein the design, fabrication, and characterization of the first custom SRDRS device to enable endoscopic SRDRS GI tissue characterization using a custom silicon (Si) thin film multi-pixel endoscopic optical sensor (MEOS) is described.
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The revolution in integrated circuits over the past 50 yr has produced inexpensive computing and communications systems that are powerful and portable. The technologies for these integrated chip-scale sensing systems, which will be miniature, lightweight, and portable, are emerging with the integration of sensors with electronics, optical systems, micromachines, microfluidics, and the integration of chemical and biological materials (soft/wet material integration with traditional dry/hard semiconductor materials). Hence, we stand at a threshold for health monitoring technology that promises to provide wearable biochemical sensing systems that are comfortable, inauspicious, wireless, and battery-operated, yet that continuously monitor health status, and can transmit compressed data signals at regular intervals, or alarm conditions immediately. In this paper, we explore recent results in chip-scale sensor integration technology for health monitoring. The development of inexpensive chip-scale biochemical optical sensors, such as microresonators, that are customizable for high sensitivity coupled with rapid prototyping will be discussed. Ground-breaking work in the integration of chip-scale optical systems to support these optical sensors will be highlighted, and the development of inexpensive Si complementary metal-oxide semiconductor circuitry (which makes up the vast majority of computational systems today) for signal processing and wireless communication with local receivers that lie directly on the chip-scale sensor head itself will be examined.
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Técnicas Biosensibles/instrumentación , Procedimientos Analíticos en Microchip , Monitoreo Ambulatorio/instrumentación , Nanotecnología , Procesamiento de Señales Asistido por Computador , Integración de Sistemas , Diseño de Equipo , Humanos , Óptica y Fotónica , Oximetría/instrumentación , Telemetría/instrumentación , TransductoresRESUMEN
Diffuse reflectance spectroscopy (DRS) is being used in exploratory clinical applications such as cancer margin assessment on excised tissue. However, when interrogating nonplanar tissue anomalies can arise from non-uniform pressure. Herein is reported the design, fabrication, and test of flexible, thin film silicon photodetectors (PDs) bonded to a flexible substrate designed for use in conformal DRS. The PDs have dark currents and responsivities comparable to conventional Si PDs, and were characterized while flat and while flexed at multiple radii of curvature using liquid phantoms mimicking adipose and malignant breast tissue. The DRS and nearest neighbor crosstalk results were compared with Monte Carlo simulations, showing good agreement between simulation and experiment.
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We have developed a portable, breast margin assessment probe leveraging diffuse optical spectroscopy to quantify the morphological landscape of breast tumor margins during breast conserving surgery. The approach presented here leverages a custom-made 16-channel annular photodiode imaging array (arranged in a 4 × 4 grid), a raster-scanning imaging platform with precision pressure control, and compressive sensing with an optimized set of eight wavelengths in the visible spectral range. A scalable Monte-Carlo-based inverse model is used to generate optical property [ ? s ? ( ? ) and ? a ( ? ) ] measures for each of the 16 simultaneously captured diffuse reflectance spectra. Subpixel sampling (0.75 mm) is achieved through incremental x , y raster scanning of the imaging probe, providing detailed optical parameter maps of breast margins over a 2 × 2 ?? cm 2 area in ? 9 ?? min . The morphological landscape of a tumor margin is characterized using optical surrogates for the fat to fibroglandular content ratio, which has demonstrated diagnostic utility in delineating tissue subtypes in the breast.
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Neoplasias de la Mama/diagnóstico por imagen , Análisis Espectral/instrumentación , Femenino , Humanos , Mastectomía Segmentaria/instrumentación , Miniaturización , Método de MontecarloRESUMEN
A wavelength selection method that combines an inverse Monte Carlo model of reflectance and a genetic algorithm for global optimization was developed for the application of spectral imaging of breast tumor margins. The selection of wavelengths impacts system design in cost, size, and accuracy of tissue quantitation. The minimum number of wavelengths required for the accurate quantitation of tissue optical properties is 8, with diminishing gains for additional wavelengths. The resulting wavelength choices for the specific probe geometry used for the breast tumor margin spectral imaging application were tested in an independent pathology-confirmed ex vivo breast tissue data set and in tissue-mimicking phantoms. In breast tissue, the optical endpoints (hemoglobin, ß-carotene, and scattering) that provide the contrast between normal and malignant tissue specimens are extracted with the optimized 8-wavelength set with <9% error compared to the full spectrum (450-600 nm). A multi-absorber liquid phantom study was also performed to show the improved extraction accuracy with optimization and without optimization. This technique for selecting wavelengths can be used for designing spectral imaging systems for other clinical applications.