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Optogenetics has transformed studies of neural circuit function, but remains challenging to apply in large brains, such as those of non-human primates (NHPs). A major challenge is delivering intense, spatiotemporally precise, patterned photostimulation across large volumes in deep tissue. Such stimulation is critical, for example, to modulate selectively deep-layer corticocortical feedback projections. To address this unmet need, we have developed the Utah Optrode Array (UOA), a 10×10 glass needle waveguide array fabricated atop a novel opaque optical interposer then bonded to an electrically addressable μLED array.In vivoexperiments with the UOA demonstrated large-scale, spatiotemporally precise, activation of deep circuits in monkey cortex. Specifically, the UOA permitted both focal (confined to single layers/columns), and widespread (multiple layers/columns) optogenetic activation of deep layer neurons, simply by varying the number of activated μLEDs and/or the irradiance. Thus, the UOA represents a powerful optoelectronic device for targeted manipulation of deep-layer circuits in NHP models.

The need for high-performance Data Mining (DM) algorithms is being driven by the exponentially increasing data availability such as images, audio and video from a variety of domains, including social networks and the Internet of Things (IoT). Deep learning is an emerging field of pattern recognition and Machine Learning (ML) study right now. It offers computer simulations of numerous nonlinear processing layers of neurons that may be used to learn and interpret data at higher degrees of abstractions. Deep learning models, which may be used in cloud technology and huge computational systems, can inherently capture complex structures of large data sets. Heterogeneousness is one of the most prominent characteristics of large data sets, and Heterogeneous Computing (HC) causes issues with system integration and Advanced Analytics. This article presents HC processing techniques, Big Data Analytics (BDA), large dataset instruments, and some classic ML and DM methodologies. The use of deep learning to Data Analytics is investigated. The benefits of integrating BDA, deep learning, HPC (High Performance Computing), and HC are highlighted. Data Analytics and coping with a wide range of data are discussed.

An aluminum-based deep-ultraviolet surface plasmon resonance (DUV-SPR) sensor is promising for biological applications. Design aspects of a DUV-SPR sensor are here considered by using Fresnel multilayer model. Angular and wavelength interrogation modes are used, where fused silica, sapphire, and acrylic solacryl ultraviolet transmittance (acrylic SUVT) are used as optical substrates. Aluminum at its oxidized state (alumina) is also considered as an aluminum overlayer. Our 4-layer Kretschmann-Raether-based SPR sensor is applied for gaseous and aqueous solutions, where some figures of merit are used to analyze the sensor performance. Values for sensitivity, linewidth (FWHM, full width at half maximum), and FOM (figure of merit or quality factor) are calculated. Resolution is also found and compared with other devices by using a known formulation. The results indicate that our sensor has a higher sensitivity for both gaseous and aqueous solutions when compared with the visible light-based sensor. For aqueous solutions, analyte is simulated as a bulk or a monolayer. Therefore, DUV-SPR sensors are a good alternative to the conventional visible-based SPR devices, where the performance is similar or higher for some conditions, having a higher affinity for some proteins.

Plasmonic metasurfaces have been widely used for image and color representation using nanoscale structures. By designing the size or shape of nanostructures, the phase or amplitude of transmitted or reflected electromagnetic spectrum can be manipulated via control of resonant wavelength, which results in multiple colors and can be used for color and/or image generation. Instead of color printing, we introduce a new approach from which images with multiple gray scales can be generated and hidden under light with specific wavelengths. In this work, plasmonic structures of nanorods with identical geometries are fabricated in arrays on a glass substrate, but the nanorods comprise binary alloys of aluminum and titanium; therefore, grayscale image information is encoded with the material composition. Under white light illumination with polarization along the long axis of a nanorod, the response of the nanorods has essentially the same resonant frequency, but with varying magnitudes of transmission. Based on this, using nanorods with four different compositions, four gray level imaging has been achieved. Since nanorods are sensitive to the polarization and spectral composition of the incident light, under unpolarized white light illumination, the image disappears. Therefore, this technique is promising in image encryption. We also show that the manipulation of light at the resonant wavelength by this method occurs in amplitude, not phase.

We characterize three commercial resins suitable for three-dimensional two-photon printing of mm3 volume micro-optical components for visible light –IP-S, IP-n162, and IP-Visio– under different print modes and post-processing conditions. Due to the combination of cured resin absorption and bulk scattering, we find a maximum total printed thickness of 4 mm (or greater) for at least 50% transmittance of red light, up to 2 mm for green light, and large maximum thickness variation for blue light (0.1 to 1 mm).

High-resolution microscopy of deep tissue with large field-of-view (FOV) is critical for elucidating organization of cellular structures in plant biology. Microscopy with an implanted probe offers an effective solution. However, there exists a fundamental trade-off between the FOV and probe diameter arising from aberrations inherent in conventional imaging optics (typically, FOV

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with their linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd3As2 has shown ultrahigh mobility and large Fermi velocity and has been hypothesized to support plasmons at terahertz frequencies. In this work, we experimentally demonstrate synthesis of high-quality large-area Cd3As2 thin films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of Cd3As2 stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality factors ( Q) as high as ∼3.7 (at 0.82 THz). Such spectrally narrow resonances can be understood on the basis of a long momentum scattering time, which in our films can approach ∼1 ps at room temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photoinduced carriers in optical pump/terahertz probe experiments. Our results evidence that the intrinsic 3D nature of Cd3As2 might provide for a very robust platform for terahertz plasmonic applications. Moreover, the long momentum scattering time as well as large kinetic inductance in Cd3As2 also holds enormous potential for the redesign of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits.

Solution-processable two-dimensional (2D) organic-inorganic hybrid perovskite (OIHP) quantum wells naturally self-assemble through weak van der Waals forces. In this study, we investigate the structural and optoelectronic properties of 2D-layered butylammonium (C4H9NH3+, BA+) methylammonium (CH3NH3+, MA) lead iodide, (BA)2(MA)n-1PbnI3n+1 quantum wells with varying n from 1 to 4. Through conventional structural characterization, (BA)2(MA)n-1PbnI3n+1 thin films showcase high-quality phase (n) purity. However, while investigating the optoelectronic properties, it is clear that these van der Waals heterostructures consist of multiple quantum well thicknesses coexisting within a single thin film. We utilized electroabsorption spectroscopy and Liptay theory to develop an analytical tool capable of deconvoluting the excitonic features that arise from different quantum well thicknesses (n) in (BA)2(MA)n-1PbnI3n+1 thin films. To obtain a quantitative assessment of exciton heterogeneities within a thin film comprising multiple quantum well structures, exciton resonances quantified by absorption spectroscopy were modeled as Gaussian features to yield various theory-generated electroabsorption spectra, which were then fit to our experimental electroabsorption features. In addition to identifying the quantum well heterostructures present within a thin film, this novel analytical tool provides powerful insights into the exact exciton composition and can be utilized to analyze the optoelectronic properties of many other mixed-phase quantum well heterostructures beyond those formed by OIHPs. Our findings may help in designing more efficient and reproducible light-emitting diodes based on 2D mixed-phase metal-organic multiple quantum wells.

We report on the anisotropy of the terahertz permittivity of β-Ga 2 O 3 through terahertz transmission measurements in single crystals of (010) and (-201) orientation. The electromagnetic wave propagation in this anisotropic crystal is best described with an orthogonal set of eigenmodes, i.e., polarization eigenvectors, wherein each eigenmode possess a distinct refractive index. Polarization-dependent transmission measurements were carried out to ascertain the nature of the eigenmodes and their directions with respect to the crystal axes.

Most of the fiber optic-based surface plasmon resonance (SPR) sensors use gold or silver metal as part of the sensing region. It is known from the literature that silver presents a better performance in terms of sensitivity, although is less stable and strongly affected by oxidation, which in turns reduces its lifetime. To overcome this effect, other materials, such as gold, are proposed as alternatives in combined use with silver, forming bimetallic layers, leading to a higher sensor performance. Furthermore, adding graphene layers over the aforementioned sensors is prominent due to graphene electrical and optical properties. In this work, we propose a sensitivity enhancement of silver-based SPR sensors by adding an ultrathin layer of gold over the silver metal in order to protect against oxidation and also by adding graphene layers over the bimetallic SPR sensor, to increase the evanescent electric field. We also simulate, for comparison, a gold-based SPR sensor with graphene overlay, and it is observed, it is observed a sensitivity increase of over 90% when 13 graphene layers are added. For the silver-based sensor, an increase in sensitivity of approximately 50% (from 3,710 nm/RIU to 5,601.1 nm/RIU) is also achieved, when silver is covered with 13 graphene layers. For the silver and gold bimetallic layer sensor, sensitivity increases from 3,360 nm/RIU to 5,321.1 nm/RIU, using 19 graphene layers, which corresponds to an increase of almost 60%. FWHM and FOM parameters are also improved for all the analyzed configurations, in comparison with the conventional silver-gold bimetallic sensor.

Manipulation of plasmon modes at ultraviolet wavelengths using engineered nanophotonic devices allows for the development of high-sensitivity chiroptical spectroscopy systems. We present here an experimental framework based on aluminum-based crescent-shaped nanostructures that exhibit a strong chiroptical response at ultraviolet wavelengths. Through utilization of higher-order plasmon modes in wavelength-scale nanostructures, we address the inherent fabrication challenges in scaling the response to higher frequencies. Additionally, the distinct far-field spectral response types are analyzed within a coupled-oscillator model framework. We find two competing chiroptical response types that contribute toward potential ambiguity in the interpretation of the circular dichroism spectra. The first, optical activity, originates from the interaction between hybridized eigenmodes, whereas the second manifests as a response superficially similar to optical activity but originating instead from differential near-field absorption modes. The study of the chiroptical response from nanoplasmonic devices presented here is expected to aid the development of next-generation chiroptical spectroscopy systems.

Optogenetics is a powerful tool for neural control that supports perturbation of specific cell types. The Utah Optrode Array, paired with a µLED array, is an optical stimulation device for precise multi-site light delivery in deep cortical layers. We describe recent developments in the evolution of this device, including methods for improved light coupling and device encapsulation.

There is current demand for pattern programmable devices that can deliver light to deep brain structures for use in optogenetic experiments. Here we introduce a microLED optrode device with 181 individually addressable sites, each with the capability to optogenetically excite thousands of neurons in vivo. The device consists of a 10 x 10 glass microneedle array directly integrated with a custom fabricated microLED device. 100 microLEDs couple to the needle tips for intra-cortical light delivery and 81 microLEDs sit at interstitial points for surface illumination. Light delivery and thermal properties are comprehensively evaluated.

We report polarization dependent photoluminescence studies on unintentionally-, Mg-, and Ca-doped β-Ga2O3 bulk crystals grown by the Czochralski method. In particular, we observe a wavelength shift of the highest-energy UV emission which is dependent on the pump photon energy and polarization. For 240 nm (5.17 eV) excitation almost no shift of the UV emission is observed between E||b and E||c, while a shift of the UV emission centroid is clearly observed for 266 nm (4.66 eV), a photon energy lying between the band absorption onsets for the two polarizations. These results are consistent with UV emission originating from transitions between conduction band electrons and two differentially-populated self-trapped hole (STH) states. Calcuations based on hybrid and self-interaction-corrected density functional theories further validate that the polarization dependence is consistent with the relative stability of two STHs. This observation implies that the STHs form primarily at the oxygen atoms involved in the original photon absorption event, thus providing the connection between incident polarization and emission wavelength. The data imposes a lower bound on the energy separation between the self-trapped hole states of ~70–160 meV, which is supported by the calculations.

The study of plasmonic nanostructures in the ultraviolet (UV) is a relatively uncharted field because of the challenges in both engineering and materials science. In this work, two-dimensional peri...

Ciancetta et al suggest ways that students can explore the relationship between areas of "off-the-peg" (OTP) geoboard squares. As they progress through their explorations, students have many opportunities to make sense of the mathematical structure embedded in the context and use it to investigate why the relationship exists. In expanding the exploration of OTP geoboard squares, students can create a rich mathematical environment where geometry, proportional reasoning, and algebra are all used to analyze and generalize interesting results.

We report modification of the ultraviolet (UV) fluorescence decay rate of p-terphenyl dye molecules by magnesium (Mg) nanoapertures in free solution, in comparison with aluminum (Al). Mg nanoapertures exhibit a lifetime reduction of up to ∼7.2×, which to our knowledge is the largest lifetime reduction of a UV fluorescence dye reported so far in the literature. In comparison, Al nanoapertures exhibit a lifetime reduction of ∼5.3×, exceeding the previously reported value ∼3.5× due to smaller aperture size employed here. Simulation results reveal large plasmon resonance frequency shifts between Mg and Al nanoapertures, contributing to different lifetime reductions, where average lifetime reductions of Mg nanoapertures are greater than those of Al nanoapertures with diameters smaller than 40 nm. The dependence of count rate per molecule (CRM) on aperture size and aperture undercut is also reported, revealing that CRM increases with increasing undercut.

The two-dimensional (2D) Ruddlesden−Popper organic-inorganic halide perovskites such as (2D)-phenethylammonium lead iodide (2D-PEPI) have layered structure that resembles multiple quantum wells (MQW). The heavy atoms in 2D-PEPI contribute a large spin-orbit coupling that influences the electronic band structure. Upon breaking the inversion symmetry, a spin splitting (‘Rashba splitting’) occurs in the electronic bands. We have studied the spin splitting in 2D-PEPI single crystals using the circular photogalvanic effect (CPGE). We confirm the existence of Rashba splitting at the electronic band extrema of 35±10 meV, and identify the main inversion symmetry breaking direction perpendicular to the MQW planes. The CPGE action spectrum above the bandgap reveals spin-polarized photocurrent generated by ultrafast relaxation of excited photocarriers separated in momentum space. Whereas the helicity dependent photocurrent with below-gap excitation is due to spin-galvanic effect of the ionized spin-polarized excitons, where spin polarization occurs in the spin-split bands due to asymmetric spin-flip., Hybrid organic-inorganic perovskites (HOIP) have high potential for spintronics applications. Using the circular photogalvanic effect the authors demonstrate the existence of Rashba-splitting in the continuum bands of a 2D layered HOIP that results from inversion symmetry breaking along the growth direction.

Aluminum-based deep-ultraviolet surface plasmon resonance (SPR) sensors have gained much interest in the last years. Multilayer Fresnel-based theoretical investigations were used here to investigate the influence of substrate materials on an aluminum-based SPR sensor. The reflectivity curves were obtained for a wavelength of 266 nm, by considering fused silica, sapphire, calcium fluoride and acrylic solacryl UVT as substrate materials. Performance parameters indicate that sapphire, acrylic solacryl and fused silica may be good alternatives for the design of sensors for gaseous and aqueous solutions. A comparison was also made with a gold-based SPR sensor, and the aluminum-based sensor had better results.

Despite of increasing understandings of UV plasmonic materials, materials that can enable active tuning of UV plasmonic resonance has not been reported. Here, we demonstrate a modification of UV SPR on an aluminum (Al) hole-array by coupling Graphene π plasmon resonance with Al SPR. Graphene monolayer exhibits an abnormal absorption peak in the UV region (270-290nm) due to π plasmon resonance. The location and intensity of the absorption peak depend on the position of Fermi-level, which can be adjusted by electric or chemical doping. Al SPR is shown here to be modified by coupling Graphene π plasmon resonance with Al SPR. FDTD simulation shows the modification of Al hole-array transmission by adding a single layer of Graphene on top. The shifts of transmission dips after adding a Graphene layer shows a distinct transition at around the Graphene π plasmon position. For transmission dips that are located at shorter wavelength compared to Graphene π plasmon, up to 8nm blue shifts occur after adding Graphene. On the other hand, up to 20nm redshifts occur for transmission dips that are at a longer wavelength relative to Graphene π plasmon. This change in the sign of shifts of transmission dips corresponds to the change in the sign of the real permittivity of Graphene. The amount of shifts diminishes as the transmission dip moves further away from Graphene π plasmon resonance into the visible spectrum. Experimentally we have observed redshifts of SPR dips but not blue shifts possibly due to the poor light collection below 250nm.

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with their linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd

We present an electrically addressable optrode array capable of delivering light to 181 sites in the brain, each providing sufficient light to optogenetically excite thousands of neurons in vivo , developed with the aim to allow behavioral studies in large mammals. The device is a glass microneedle array directly integrated with a custom fabricated microLED device, which delivers light to 100 needle tips and 81 interstitial surface sites, giving two-level optogenetic excitation of neurons in vivo . Light delivery and thermal properties are evaluated, with the device capable of peak irradiances >80 mW / mm2 per needle site. The device consists of an array of 181 80 μm × 80 μm2 microLEDs, fabricated on a 150-μm-thick GaN-on-sapphire wafer, coupled to a glass needle array on a 150-μm thick backplane. A pinhole layer is patterned on the sapphire side of the microLED array to reduce stray light. Future designs are explored through optical and thermal modeling and benchmarked against the current device.

Previous evidence suggests optical treatments hold promise for treating migraine and photophobia. We designed an optical notch filter, centered at 480 nm to reduce direct stimulation of intrinsically photosensitive retinal ganglion cells. We used thin-film technology to integrate the filter into spectacle lenses. Our objective was to determine if an optical notch filter, designed to attenuate activity of intrinsically photosensitive retinal ganglion cells, could reduce headache impact in chronic migraine subjects. For this randomized, double-masked study, our primary endpoint was the Headache Impact Test (HIT-6; GlaxoSmithKline, Brentford, Middlesex, UK). We developed two filters: the therapeutic filter blocked visible light at 480 nm; a 620 nm filter was designed as a sham. Participants were asked to wear lenses with one of the filters for 2 weeks; after 2 weeks when no lenses were worn, they wore lenses with the other filter for 2 weeks. Of 48 subjects, 37 completed the study. Wearing either the 480 or 620 nm lenses resulted in clinically and statistically significant HIT-6 reductions. However, there was no significant difference when comparing overall effect of the 480 and 620 nm lenses. Although the 620 nm filter was designed as a sham intervention, research published following the trial indicated that melanopsin, the photopigment in intrinsically photosensitive retinal ganglion cells, is bi-stable. This molecular property may explain the unexpected efficacy of the 620 nm filter. These preliminary findings indicate that lenses outfitted with a thin-film optical notch filter may be useful in treating chronic migraine.

Aluminum plasmonic nanocrescent antennas were fabricated over large substrate areas by incorporating a sacrificial copper layer in nanosphere template lithography (NTL). The addition of the copper mask eliminates the argon ion milling step in the NTL process that is challenging to implement for aluminum nanostructures because of the robust native oxide layer. The aluminum nanocrescents exhibit polarization-dependent localized surface plasmon responses that can be tuned from the near-infrared into the ultraviolet, a region that is difficult to access with more typically used gold and silver. Finite-difference time-domain simulations predict the observed multimodal plasmonic behavior of these aluminum structures. This simple fabrication process will facilitate the implementation of the aluminum nanocrescent antennas in long and short wavelength surface-enhanced spectroscopies, fluorescence lifetime reduction processes, and photocatalysis.

The quasi-static anisotropic permittivity parameters of electrically insulating beta gallium oxide (β-Ga2O3) were determined by terahertz spectroscopy. Polarization-resolved frequency domain spectroscopy in the spectral range from 200 GHz to 1 THz was carried out on bulk crystals along different orientations. Principal directions for permittivity were determined along crystallographic axes c and b and reciprocal lattice direction a *. No significant frequency dispersion in the real part of dielectric permittivity was observed in the measured spectral range. Our results are in excellent agreement with recent radio frequency capacitance measurements as well as with extrapolations from recent infrared measurements of phonon mode and high-frequency contributions and close the knowledge gap for these parameters in the terahertz spectral range. Our results are important for applications of β-Ga2O3 in high-frequency electronic devices.

Aluminum (Al) is a preferred metal for designing deep-ultraviolet (DUV) surface plasmon resonance (SPR)-based sensors. The native oxide layer (alumina), which grows when the Al film is exposed to air, adds an extra layer to the multilayer stack and consequently affects the DUV-SPR sensing performance. To mitigate the performance loss in DUV-SPR-based sensing, new, to the best of our knowledge, approaches are considered here. We first consider chromium, indium (In), nickel, and platinum as alternative plasmonic materials to Al. In-film-based DUV-SPR sensors exhibit the best performance parameters compared to these alternative materials. We next consider the approach of replacing the native oxide layer by an ultrathin gold (Au) layer on top of bare Al or In. With an optimal Au thickness, higher sensitivity as compared to oxidized metals is observed. The next approach adds one or more graphene layers on top of the bare metal film. In this case, the performance depends on the number of graphene layers, but improvement in sensor characteristics in the DUV is also obtained. The use of Au or graphene overlayers increases the refractive index sensing dynamic range, which can be significant for In with these overlayers under certain operating conditions.

We present an electrically addressable optrode array capable of delivering light to 181 sites in the brain, each providing sufficient light to optogenetically excite hundreds of neurons in vivo, developed with the aim to allow behavioural studies in large mammals. The device is a glass microneedle array directly integrated with a custom fabricated microLED device, which delivers light to 100 needle tips and 81 interstitial surface sites, giving 2-level optogenetic excitation of neurons in vivo. Light delivery and thermal properties are evaluated, with the device capable of peak irradiances > 80 mW/mm2 per needle at 50 ms pulse widths with tissue temperature increase less than 1 °C. Future designs are explored through optical and thermal modelling and benchmarked against the current device.

There is growing research interest in UV plasmonics, in part because the UV regime has seen comparatively little activity compared to the visible, NIR/IR, and THz regimes, but also because of application areas such as UV sources and detectors, label-free fluorescence detection of biomolecules, and photocatalysis. There is a rich spectrum of materials that exhibit plasmonic response in the UV. Although no single material can be considered the “best” for all applications, Al is the most often utilized. Our research has focused on Al, Mg, Ga, and their alloys. We have developed deposition methods and top-down and bottom-up patterning methods, and utilized materials analysis methods to gain understanding of the UV plasmonic response of these materials. We have also enabled materials such as Mg and Ga to be used in applications such as enhanced fluorescence. Studies of native fluorescence modification from Al and Mg plasmonic structures show some key differences between the two materials, which I will explain. I will also discuss some plasmonic structures that exhibit very large UV enhancements, some of which can be readily fabricated by nanosphere lithography methods.

Metal nanoarchitectures producing optical responses in the visible and near-infrared form the foundation for most plasmonic studies. In contrast, a relative lack of infrared-active substrates has limited the exploration of plasmonic behavior beyond the near-infrared. In this study, we investigate the polarization-dependent, multimodal localized plasmon resonances of asymmetric nanocrescents for large diameter structures composed of gold and silver. The extended size (0.5–3.0 μm) shifts the plasmon resonances into the mid-infrared (mid-IR) spectral range. Polarization-dependent localized surface plasmon resonance (LSPR) behavior is maintained for nanocrescent diameters up to several microns due to the preservation of nanoscale structural features that result in high aspect ratios. Simulations of the extinction spectra and near-field distributions support experimentally observed plasmonic behavior. Manipulation of nanocrescent plasmon resonances in the mid-IR spectral range through structural-based tuning a...

We report on terahertz characterization of La-doped BaSnO3 (BSO) thin-films. BSO is a transparent complex oxide material, which has attracted substantial interest due to its large electrical conductivity and wide bandgap. The complex refractive index of these films is extracted in the 0.3 to 1.5 THz frequency range, which shows a metal-like response across this broad frequency window. The large optical conductivity found in these films at terahertz wavelengths makes this material an interesting platform for developing electromagnetic structures having a strong response at terahertz wavelengths, i.e. terahertz-functional, while being transparent at visible and near-IR wavelengths. As an example of such application, we demonstrate a visible-transparent terahertz polarizer.

Optogenetics is a powerful tool for neural control, but controlled light delivery beyond the superficial structures of the brain remains a challenge. For this, we have developed an optrode array, which can be used for optogenetic stimulation of the deep layers of the cortex. The device consists of a 10×10 array of penetrating optical waveguides, which are predefined using BOROFLOAT® wafer dicing. A wet etch step is then used to achieve the desired final optrode dimensions, followed by heat treatment to smoothen the edges and the surface. The major challenge that we have addressed is delivering light through individual waveguides in a controlled and efficient fashion. Simply coupling the waveguides in the optrode array to a separately-fabricated μLED array leads to low coupling efficiency and significant light scattering in the optrode backplane and crosstalk to adjacent optrodes due to the large mismatch between the μLED and waveguide numerical aperture and the working distance between them. We mitigate stray light by reducing the thickness of the glass backplane and adding a silicon interposer layer with optical vias connecting the μLEDs to the optrodes. The interposer additionally provides mechanical stability required by very thin backplanes, while restricting the unwanted spread of light. Initial testing of light output from the optrodes confirms intensity levels sufficient for optogenetic neural activation. These results pave the way for future work, which will focus on optimization of light coupling and adding recording electrodes to each optrode shank to create a bidirectional optoelectronic interface.

We fabricated a deep optogenetic cortical stimulation device (10×10 glass waveguide array) using wafer dicing, etching and annealing. A µLED array delivers light through individual shanks. A silicon interposer layer with optical vias prevents crosstalk.

We report on terahertz characterization of La-doped BaSnO3 (BSO) thin-films. BSO is a transparent complex oxide material, which has attracted substantial interest due to its large electrical conductivity and wide bandgap. The complex refractive index of these films is extracted in the 0.3 to 1.5 THz frequency range, which shows a metal-like response across this broad frequency window. The large optical conductivity found in these films at terahertz wavelengths makes this material an interesting platform for developing electromagnetic structures having a strong response at terahertz wavelengths, i.e. terahertz-functional, while being transparent at visible and near-IR wavelengths. As an example of such application, we demonstrate a visible-transparent terahertz polarizer.

Metallic nanostructure can enhance fluorescence through excited surface plasmons which increase the local field as well as improve its quantum efficiency. When coupling to cavity resonance with proper gap dimension, gap hot spots can be generated to interact with fluorescence at their excitation/emission region in UV. A 3D nano-cavity antenna array in Aluminum has been conducted to generate local hot spot resonant at fluorescence emission resonance. Giant field enhancement has been achieved through coupling fundamental resonance modes of nanocavity into surface plasmons polaritons (SPPs). In this work, two distinct plasmonic structure of 3D resonant cavity nanoantenna has been studied and its plasmonic response has been scaled down to the UV regime through finite-difference-time-domain (FDTD) method. Two different strategies for antenna fabrication will be conducted to obtain D-coupled Dots-on-Pillar Antenna array (D2PA) through Focus Ion Beam (FIB) and Cap- Hole Pair Antenna array (CHPA) through nanosphere template lithography (NTL). With proper optimization of the structures, D2PA and CHPA square array with 280nm pitch have achieved distinct enhancement at fluorophore emission wavelength 350nm and excitation wavelength 280nm simultaneously. Maximum field enhancement can reach 20 and 65 fold in the gap of D2PA and CHPA when light incident from substrate, which is expected to greatly enhance fluorescent quantum efficiency that will be confirmed in fluorescence lifetime measurement.

Tunable UV devices can enable enhanced functionalities such as multiplexed sensing, wavelength-tunable light emission and so on. Interestingly, in the UV range, graphene shows a tunable optical absorption due to pi-plasmon resonance. In this work we study the UV transmission through monolayer graphene films transferred on top of aluminum hole-arrays. Transmittance though the hole-array was measured before and after graphene transfer. Interaction of graphene pi-plasmons with surface plasmon resonances leads to strong wavelength shifts, i.e. the surface plasmon resonance at the top-interface red-shifts when graphene is added. Furthermore, it is observed that maximum shift occurs in the 280 to 310 nm wavelength range. This is attributed to an enhanced graphene optical conductivity owed to pi-plasmons.

UV plasmonic nanostructures have applications in label free native fluorescence biosensing. Many aluminum nanostructures have been shown to modify emission properties of UV fluorescence molecules. However, these structures demonstrate small rate enhancement factors (less than 10x). In this paper, we report FDTD simulation results on excitation and emission enhancement factors of a pair of aluminum bowtie antenna in ultraviolet region. Our results show that the optimal geometry is a pair of small bowtie (radius 20nm) with apex angle 60 degrees. The highest radiative enhancement is 25x (~340nm) and highest total decay rate enhancement is 70x, higher than previously studied geometries.

We report excited-state lifetime modification of diffusing molecules by Al nanoapertures in the UV. Lifetime reductions of ∼3.5× have been observed for the high quantum yield laser dye p-terphenyl in a 60 nm diameter aperture. The lifetime reduction is smaller for the low quantum yield molecule tryptophan, for which a maximum reduction of ∼1.7 is observed. Lifetime reduction as a function of aperture size and native quantum yield is accurately predicted by simulation. Simulation further predicts greater net fluorescence enhancement for tryptophan compared to p-terphenyl, which is consistent with the expectation that low quantum yield emitters experience greater enhancement in the effective quantum yield.

Increasing scope and applications of integrated optics necessitates the development of automated techniques for physical design of optical systems. A key area of integrated optic design is waveguide routing, which currently lacks the level of automation found in VLSI design. Unlike VLSI, where signal nets are routed with metal layers and vias, integrated optics is a planar technology and lacks the inherent signal restoration capabilities of static-CMOS. Waveguides suffer signal loss due to planar (perpendicular) waveguide crossings and also from sharp bends. Therefore, in contrast to area or wire length, signal loss minimization—as a function of waveguide crossings and bends—is a primary objective of any routing solution. Our studies show that waveguide routing problems can be suitably formulated as planar channel routing. This paper investigates channel routing for integrated optical waveguides fabricated in a planar substrate. We present routing techniques where crossings, bends, and area are accounted for in an integrated solution. Two distinct channel routing techniques are presented: 1) a new channel router based on net sorting and utilizing non-Manhattan routing grids and 2) a router based on crossing-aware graph-constrained track assignment that also exploits waveguide curves to improve track utilization. Both techniques are crossing-minimal, and are also constrained suitably to reduce bend loss and area. We compare and evaluate the performance of our channel routers on a number of optical design benchmarks.

The optical properties of pure nanostructured magnesium films deposited on glass, Si and GaAs substrates using DC magnetron sputtering are examined in this work to determine the potential of Mg as plasmonic material in the ultraviolet (UV) to near-infrared (NIR) spectral range. Using film thicknesses ranging from 210 to 910 nm, the corresponding optical constants over the wavelength range of 250–1700 nm were measured using a variable angle spectroscopic ellipsometer and these results are compared to reference Al thin films. The optical constants of Mg depend on the film thickness. From the perspective of plasmonics applications, we find that the best values are observed in this work for the 910 nm thick Mg film on glass substrates. The film morphology and structure of the Mg films were characterized using atomic force microscopy, scanning electron microscopy, stylus profilometry and X-ray diffraction. The optical dielectric constants and plasmonic figures of merit are strongly influenced by the film structure. The results show that smooth and [0 0 0 2] textured magnesium films have extremely low loss, superior or comparable to aluminum films in portions of the UV spectrum.

Multiple localized surface plasmon resonance (LSPR) modes induced in gold and silver nanocrescents exhibit anisotropic behavior with respect to polarization of incident light. Extinction spectroscopy with polarization control was used to characterize the optical properties of asymmetric nanocrescents with diameters ranging from 100 to 500 nm. The analysis shows that selective induction of distinct dipole and quadrupole LSPR modes can be accomplished through polarization of incident light. Finite-difference time-domain calculations of the LSPR responses of the nanocrescent corroborate the polarization-dependent optical behavior. Simulations reveal optical near field enhancements with unique spatial patterns associated with the individual resonance modes depending on the polarization and wavelength of incident light. Quantitative analysis of the anisotropic LSPR behavior supports the potential for controlling the near field through selective induction of specific resonance modes with particular near field d...

As the optogenetic field expands its need to target with high specificity only grows more crucial. This work will show a method for customizing soda-lime glass optrode arrays so that fine structures within the brains of small rodents and nonhuman primates can be optically interrogated below the outer cortical layer. An 8 × 6 array is customized for optrode length (400 μm ), optrode width (75 μm ), optrode pitch (400 μm ), backplane thickness (500 μm ), and overall form factor (3.45 mm × 2.65 mm ). The 400 μm long optrode is capable of illuminating the cortical Layer IV of rhesus macaque ( Macaca Fascicularis ) and the motor cortex of small mice ( Mus Musculus ).

Borrowing from the wafer-level fabrication techniques of the Utah Electrode Array, an optical array capable of delivering light for neural optogenetic studies is presented in this paper: the Utah Optrode Array. Utah Optrode Arrays are micromachined out of sheet soda-lime-silica glass using standard backend processes of the semiconductor and microelectronics packaging industries such as precision diamond grinding and wet etching. 9 × 9 arrays with 1100μ m × 100μ m optrodes and a 500μ m back-plane are repeatably reproduced on 2i n wafers 169 arrays at a time. This paper describes the steps and some of the common errors of optrode fabrication.

Extraordinary optical transmission (EOT) is a classic phenomenon in plasmonics. The study of plasmonic nanostructures in the ultraviolet (UV) is a relatively uncharted field due to challenges in both engineering (nanostructure design, optimization, and fabrication) and materials science (detailed composition analysis). Our previous research has been mainly focused on UV field enhancement ofdifferent Al nanostructures. In this work, two-dimensional periodic nanohole arrays in Aluminium (Al) and Magnesium (Mg) films were fabricated using Ga focused ion beam (FIB) lithography. Optical transmission through the arrays was obtained in the UV and visible range, with varying array periodicity. Transmission results showed strong resonance enhancement in the UV and visible region resulting from SPP coupling, with corresponding red-shift as the period increases, while waveguide mode peaks remain in place. Comparing Al and Mg EOT results, Al hole-array enabled larger transmission than that of Mg. Dips in transmission through Al arrays occur at similar spectral positions to those of Mg arrays with same periods. Numerical analysis was carried out through finite-difference-time-domain (FDTD) method, which showed far-field transmission consistent with experiments in general. The model was constructed based on transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) of cross-sectioned samples. The effect of Gallium (Ga) implantation from FIB fabrication was qualitatively studied, which indicated Ga implants inside the hole bottom as well as higher implantation within Mg than that within Al. The model also takes into account sidewall geometry and undercut into the substrate.

Ultra-violet (UV) fluorescence lifetime modification by aluminum (Al) and magnesium (Mg) nanoapertures are reported in this manuscript. Nanoapertures with diameter ranging from 30nm to 90nm are fabricated using focused ion beam (FIB). Largest lifetime reduction are observed for apertures with smallest diameters and undercuts into glass substrate. For Al nanoapertures, largest lifetime reduction is ∼5.30×, larger than perviously reported ∼3.50×.1 For Mg nanoapertures, largest lifetime reduction is ∼6.90×, which is the largest lifetime reduction of UV fluorescence dye reported so far in literature. The dependence of count rate per molecule (CRM) on aperture size and undercut is also investigated, revealing that CRM increases with increasing undercut, however, the CRM is small (less than 2) for the entire range of aperture size and undercut we investigated. FDTD simulation were conducted and in order to favorably compare experimental results with simulated results, it is critical to take into account the exact shape and material properties of the nano aperture. Simulation results revealed the fundamental difference between Al and Mg nano aperture under 266nm illumination-Mg nano aperture presents a waveguide mode in which the maximum field enhancement and Purcell factor is within the nano aperture instead of on the surface which is the case for Al nano aperture.

Interest in label-free detection of biomolecules has given rise to the need for UV plasmonic materials. DNA bases and amino acid residues have electronic resonances in the UV which allow for sensitive detection of these species by surface-enhanced UV fluorescence spectroscopy. Electrochemical roughening has been used extensively to generate plasmonically-active metal surfaces that produce localized enhancement of excitation and emission of electromagnetic radiation from surface-bound molecules. Electrochemically roughened gold and silver surfaces produce enhancement in the visible and near-IR regions, but to the best of our knowledge, application of this technique for producing UV-enhancing substrates has not been reported. Using electropolishing of aluminum, we are able to generate nanostructured surfaces that produce enhanced spectroscopic detection of molecules in the UV. Aluminum is a natural choice for substrate composition as it exhibits a relatively large quality factor in the UV. We have fabricated electropolished aluminum films with nanometer scale roughness and have studied UV-excited fluorescence enhancement from submonolayer coverage of tryptophan on these substrates using a UV-laser based spectrometer. Quantitative dosing by dip-coating was used to deposit known surface concentrations of the aromatic amino acid tryptophan, so that fluorescence enhancement could be evaluated. Compared to a dielectric substrate (surface-oxidized silicon), we observe a 180-fold enhancement in the total fluorescence emitted by tryptophan on electropolished aluminum under photobleaching conditions, allowing detection of sub-monolayer coverages of molecules essential for development of biosensor technologies.

Using the Finite Difference Time Domain method, this paper investigates electromagnetic nanofocusing of ultraviolet light transmitting through V-groove like waveguide in Aluminum via simulation. Parametric study of the field enhancement around the V-groove tip area has been conducted via the change of groove depth, width, and the tip angle. Electric field threshold at the tip of the V-groove in the Ultraviolet wavelength has attracted attention and further effort has been placed to find an origination of this phenomenon. Adiabatic condition and attenuation has been taken into consideration as the possible explanation. Through simplification of the V-groove model into its corresponding Metal-Dielectric-Metal (MDM) waveguide at each distance from the tip, numerical calculations have been taken to figure out the impact of waveguide width on the adiabatic parameter, propagation constant and propagation length. Comparison and analysis for those curves with respect to typical Ultraviolet wavelength is conducted and discussed.

This paper presents optical characterization of a first-generation SiO(2) optrode array as a set of penetrating waveguides for both optogenetic and infrared (IR) neural stimulation. Fused silica and quartz discs of 3-mm thickness and 50-mm diameter were micromachined to yield 10 × 10 arrays of up to 2-mm long optrodes at a 400-μm pitch; array size, length and spacing may be varied along with the width and tip angle. Light delivery and loss mechanisms through these glass optrodes were characterized. Light in-coupling techniques include using optical fibers and collimated beams. Losses involve Fresnel reflection, coupling, scattering and total internal reflection in the tips. Transmission efficiency was constant in the visible and near-IR range, with the highest value measured as 71% using a 50-μm multi-mode in-coupling fiber butt-coupled to the backplane of the device. Transmittance and output beam profiles of optrodes with different geometries was investigated. Length and tip angle do not affect the amount of output power, but optrode width and tip angle influence the beam size and divergence independently. Finally, array insertion in tissue was performed to demonstrate its robustness for optical access in deep tissue.

Multilayer substrates consisting of a glass slide, silver mirror, silica layer, and silver nanoparticles were fabricated using magnetron sputtering. This new geometry of substrates with backplane mirror and dielectric photonic cavity produced large average fluorescence enhancements up to 190-fold. Fluorescence enhancements of five fluorescent probes were measured over the broad spectral range from 470 to 800 nm. Fluorescent probes were streptavidin conjugates attached to the substrate surface through a layer of biotinylated bovine serum albumin. The protein layers represent a common surface modification for surface-based bioassays such as immunoassays or molecular diagnostic assays. We found that optimal enhancement is dependent on the thickness of the dielectric layer separating the silver mirror and the silver nanoparticles and on the spectral range. We performed numerical calculations for enhancement in both the excitation and emission using finite element method (FEM) the results of which were in qualitative agreement with the experimental results. The described method for fabrication multilayered substrates and the results obtained with protein layers demonstrate great potential for the design of simple and ultrasensitive fluorometric bioassays with large optical amplifications compared to the standard approaches of enzyme-based bioassays with dielectric surfaces.