Multi-dimensional data transmission using inverse-designed silicon photonics and microcombs.

The use of optical interconnects has burgeoned as a promising technology that can address the limits of data transfer for future high-performance silicon chips. Recent pushes to enhance optical communication have focused on developing wavelength-division multiplexing technology, and new dimensions of data transfer will be paramount to fulfill the ever-growing need for speed. Here we demonstrate an integrated multi-dimensional communication scheme that combines wavelength- and mode- multiplexing on a silicon photonic circuit. Using foundry-compatible photonic inverse design and spectrally flattened microcombs, we demonstrate a 1.12-Tb/s natively error-free data transmission throughout a silicon nanophotonic waveguide. Furthermore, we implement inverse-designed surface-normal couplers to enable multimode optical transmission between separate silicon chips throughout a multimode-matched fibre. All the inverse-designed devices comply with the process design rules for standard silicon photonic foundries. Our approach is inherently scalable to a multiplicative enhancement over the state of the art silicon photonic transmitters.

Development of a Knowledge-sharing Website for Hypersensitivity Pneumonitis Exposures.

Background: Identification of potential inciting antigens known to be associated with hypersensitivity pneumonitis (HP) is integral to achieving a confident diagnosis, its management, and prognostication. A barrier to achieving diagnostic confidence is that evidence for exposure assessment is not presented in an easily accessible or useful format. Objective: To develop a freely available comprehensive living repository of contemporaneous exposures associated with HP. Methods: Electronic searches were performed through Medline, Embase, and Web of Science from January 1, 2002, to December 31, 2019, using the following broad MeSH headings: ([allerg* or hypersensitiv*], and adj [alveol* or pneumo*]).mp. Articles were included if they described adults or children with a diagnosis of HP (as defined by authors) and a description of the causative exposure. Website development used a structured query language database and was powered by WordPress. Results: HPLung.com is a freely available online searchable repository that lists all exposures and antigens associated with HP and links to their parent studies. Eighty-five unique exposures from 447 citations have been included thus far. The website continues to be updated iteratively. Since its launch in 2019, HPLung.com has been visited over 4,500 times by users from 75 different countries. Conclusion: HPLung.com is a novel knowledge-sharing tool that addresses barriers of accessibility, contemporaneity, efficient evidence synthesis, and making the best use of technological platforms to improve the exposure assessment of those suspected of HP.

Exposures and associations with clinical phenotypes in hypersensitivity pneumonitis: A scoping review.

Antigen identification is important for establishing a confident diagnosis of hypersensitivity pneumonitis (HP). There are no systematically curated lists of HP-associated exposures that inform clinical relevance or disease phenotype. We sought to systematically identify all reported causes of HP in the literature and evaluate their clinical relevance. A scoping review was performed to identify all publications describing HP cases and their associated exposures (even if unknown) from Jan 1990-June 2020. Frequencies of exposures and meta-analysis of proportions for registry-based studies were determined for specific exposure categories, and associations with fibrotic and non-fibrotic HP were assessed. 24,138 publications were identified, with 967 publications included in the final analysis, representing 62 unique exposures associated with HP. Certain exposures were more frequently reported than others, including birds (comprising 32% of HP cases in registry-based studies) and mould (17% registry study HP cases). Antigen-indeterminate HP comprised 15-24% of registry-based studies. Limited data found contaminated metal-working fluids, isocyanate exposure, and hot tub lung were rarely associated with fibrotic features, whereas antigen-indeterminate HP cases were more frequently associated with fibrosis. There was heterogeneity in HP case definition and how causative exposures were identified. We identified 62 unique exposures associated with HP, with specific exposures associated with clinical phenotypes. These data may inform clinical assessment and the development of questionnaires to identify antigens in the diagnostic evaluation of suspected HP. OPEN SCIENCES FRAMEWORK REGISTRATION: osf.io/4aq5m.

Publisher Correction: Data-driven acceleration of photonic simulations.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Data-driven acceleration of photonic simulations.

Designing modern photonic devices often involves traversing a large parameter space via an optimization procedure, gradient based or otherwise, and typically results in the designer performing electromagnetic simulations of a large number of correlated devices. In this paper, we investigate the possibility of accelerating electromagnetic simulations using the data collected from such correlated simulations. In particular, we present an approach to accelerate the Generalized Minimal Residual (GMRES) algorithm for the solution of frequency-domain Maxwell's equations using two machine learning models (principal component analysis and a convolutional neural network). These data-driven models are trained to predict a subspace within which the solution of the frequency-domain Maxwell's equations approximately lies. This subspace is then used for augmenting the Krylov subspace generated during the GMRES iterations, thus effectively reducing the size of the Krylov subspace and hence the number of iterations needed for solving Maxwell's equations. By training the proposed models on a dataset of wavelength-splitting gratings, we show an order of magnitude reduction (~10-50) in the number of GMRES iterations required for solving frequency-domain Maxwell's equations.

Scalable Manufacturing of Solderable and Stretchable Physiologic Sensing Systems.

Methods for microfabrication of solderable and stretchable sensing systems (S4s) and a scaled production of adhesive-integrated active S4s for health monitoring are presented. S4s' excellent solderability is achieved by the sputter-deposited nickel-vanadium and gold pad metal layers and copper interconnection. The donor substrate, which is modified with "PI islands" to become selectively adhesive for the S4s, allows the heterogeneous devices to be integrated with large-area adhesives for packaging. The feasibility for S4-based health monitoring is demonstrated by developing an S4 integrated with a strain gauge and an onboard optical indication circuit. Owing to S4s' compatibility with the standard printed circuit board assembly processes, a variety of commercially available surface mount chip components, such as the wafer level chip scale packages, chip resistors, and light-emitting diodes, can be reflow-soldered onto S4s without modifications, demonstrating the versatile and modular nature of S4s. Tegaderm-integrated S4 respiration sensors are tested for robustness for cyclic deformation, maximum stretchability, durability, and biocompatibility for multiday wear time. The results of the tests and demonstration of the respiration sensing indicate that the adhesive-integrated S4s can provide end users a way for unobtrusive health monitoring.

Inverse design and implementation of a wavelength demultiplexing grating coupler.

Nanophotonics has emerged as a powerful tool for manipulating light on chips. Almost all of today's devices, however, have been designed using slow and ineffective brute-force search methods, leading in many cases to limited device performance. In this article, we provide a complete demonstration of our recently proposed inverse design technique, wherein the user specifies design constraints in the form of target fields rather than a dielectric constant profile, and in particular we use this method to demonstrate a new demultiplexing grating. The novel grating, which has not been developed using conventional techniques, accepts a vertical-incident Gaussian beam from a free-space and separates O-band (1300 nm) and C-band (1550 nm) light into separate waveguides. This inverse design concept is simple and extendable to a broad class of highly compact devices including frequency filters, mode converters, and spatial mode multiplexers.

Nanophotonic computational design.

In contrast to designing nanophotonic devices by tuning a handful of device parameters, we have developed a computational method which utilizes the full parameter space to design linear nanophotonic devices. We show that our method may indeed be capable of designing any linear nanophotonic device by demonstrating designed structures which are fully three-dimensional and multi-modal, exhibit novel functionality, have very compact footprints, exhibit high efficiency, and are manufacturable. In addition, we also demonstrate the ability to produce structures which are strongly robust to wavelength and temperature shift, as well as fabrication error. Critically, we show that our method does not require the user to be a nanophotonic expert or to perform any manual tuning. Instead, we are able to design devices solely based on the user's desired performance specification for the device.

Objective-first design of high-efficiency, small-footprint couplers between arbitrary nanophotonic waveguide modes.

We present an algorithm for designing high efficiency (∼98%), small-footprint (1.5-4 square vacuum wavelengths) couplers between arbitrary nanophotonic waveguide modes in two dimensions. Our "objective-first" method is computationally fast (15 minutes on a single-core personal computer), requires no trial-and-error, and does not require guessing a good starting design. We demonstrate designs for various coupling problems which suggest that our method allows for the design of any single-mode, linear optical device.

Inverse design of a three-dimensional nanophotonic resonator.

The inverse design of a three-dimensional nanophotonic resonator is presented. The design methodology is computationally fast (10 minutes on a standard desktop workstation) and utilizes a 2.5-dimensional approximation of the full three-dimensional structure. As an example, we employ the proposed method to design a resonator which exhibits a mode volume of 0.32(λ/n)3 and a quality factor of 7063.

Laser-synthesized epitaxial graphene.

Owing to its unique electronic properties, graphene has recently attracted wide attention in both the condensed matter physics and microelectronic device communities. Despite intense interest in this material, an industrially scalable graphene synthesis process remains elusive. Here, we demonstrate a high-throughput, low-temperature, spatially controlled and scalable epitaxial graphene (EG) synthesis technique based on laser-induced surface decomposition of the Si-rich face of a SiC single-crystal. We confirm the formation of EG on SiC as a result of excimer laser irradiation by using reflection high-energy electron diffraction (RHEED), Raman spectroscopy, synchrotron-based X-ray diffraction, transmission electron microscopy (TEM), and scanning tunneling microscopy (STM). Laser fluence controls the thickness of the graphene film down to a single monolayer. Laser-synthesized graphene does not display some of the structural characteristics observed in EG grown by conventional thermal decomposition on SiC (0001), such as Bernal stacking and surface reconstruction of the underlying SiC surface.

Loss of LMO4 in the retina leads to reduction of GABAergic amacrine cells and functional deficits.

BACKGROUND: LMO4 is a transcription cofactor expressed during retinal development and in amacrine neurons at birth. A previous study in zebrafish reported that morpholino RNA ablation of one of two related genes, LMO4b, increases the size of eyes in embryos. However, the significance of LMO4 in mammalian eye development and function remained unknown since LMO4 null mice die prior to birth. METHODOLOGY/PRINCIPAL FINDINGS: We observed the presence of a smaller eye and/or coloboma in ∼40% LMO4 null mouse embryos. To investigate the postnatal role of LMO4 in retinal development and function, LMO4 was conditionally ablated in retinal progenitor cells using the Pax6 alpha-enhancer Cre/LMO4flox mice. We found that these mice have fewer Bhlhb5-positive GABAergic amacrine and OFF-cone bipolar cells. The deficit appears to affect the postnatal wave of Bhlhb5+ neurons, suggesting a temporal requirement for LMO4 in retinal neuron development. In contrast, cholinergic and dopaminergic amacrine, rod bipolar and photoreceptor cell numbers were not affected. The selective reduction in these interneurons was accompanied by a functional deficit revealed by electroretinography, with reduced amplitude of b-waves, indicating deficits in the inner nuclear layer of the retina. CONCLUSIONS/SIGNIFICANCE: Inhibitory GABAergic interneurons play a critical function in controlling retinal image processing, and are important for neural networks in the central nervous system. Our finding of an essential postnatal function of LMO4 in the differentiation of Bhlhb5-expressing inhibitory interneurons in the retina may be a general mechanism whereby LMO4 controls the production of inhibitory interneurons in the nervous system.

Tunable-wavelength second harmonic generation from GaP photonic crystal cavities coupled to fiber tapers.

We demonstrate up to 30 nm tuning of gallium phosphide photonic crystal cavities resonances at aproximately 1.5 microm using a tapered optical fiber. The tuning is achieved through a combination of near-field perturbations and mechanical deformation of the membrane, both induced by the fiber probe. By exploiting this effect, we show fiber-coupled second harmonic generation with a tuning range of nearly 10 nm at the second harmonic wavelength of approximately 750 nm. By scaling cavity parameters, the signal could easily be shifted into other parts of the visible spectrum.

Inverse design of nanophotonic structures using complementary convex optimization.

A computationally-fast inverse design method for nanophotonic structures is presented. The method is based on two complementary convex optimization problems which modify the dielectric structure and resonant field respectively. The design of one- and two-dimensional nanophotonic resonators is demonstrated and is shown to require minimal computational resources.

Coupled fiber taper extraction of 1.53 microm photoluminescence from erbium doped silicon nitride photonic crystal cavities.

Optical fiber tapers are used to collect photoluminescence emission at approximately 1.5 microm from photonic crystal cavities fabricated in erbium doped silicon nitride on silicon. In the experiment, photoluminescence collection via one arm of the fiber taper is enhanced 2.5 times relative to free space collection, corresponding to a net collection efficiency of 4%. Theoretically, the collection efficiency into one arm of the fiber-taper with this material system and cavity design can be as high as 12.5%, but the degradation of the experimental coupling efficiency relative to this value mainly comes from scattering loss within the short taper transition regions. By varying the fiber taper offset from the cavity, a broad tuning range of coupling strength and collection efficiency is obtained. This material system combined with fiber taper collection is promising for building on-chip optical amplifiers.

Room temperature 1.6 microm electroluminescence from Ge light emitting diode on Si substrate.

We report the room temperature electroluminescence (EL) at 1.6 microm of a Ge n+/p light emitting diode on a Si substrate. Unlike normal electrically pumped devices, this device shows a super linear luminescence enhancement at high current. By comparing different n type doping concentrations, we observe that a higher concentration is required to achieve better efficiency of the device. Thermal enhancement effects observed in temperature dependent EL spectra show the capability of this device to operate at room temperature or above. These detailed studies show that Ge can be a good candidate for a Si compatible light emitting device.