Integrated Flexible Microscale Mechanical Sensors Based on Cascaded Free Spectral Range-Free Cavities.

Photonic mechanical sensors offer several advantages over their electronic counterparts, including immunity to electromagnetic interference, increased sensitivity, and measurement accuracy. Exploring flexible mechanical sensors on deformable substrates provides new opportunities for strain-optical coupling operations. Nevertheless, existing flexible photonics strategies often require cumbersome signal collection and analysis with bulky setups, limiting their portability and affordability. To address these challenges, we propose a waveguide-integrated flexible mechanical sensor based on cascaded photonic crystal microcavities with inherent deformation and biaxial tensile state analysis. Leveraging the advanced multiplexing capability of the sensor, for the first time, we successfully demonstrate 2D shape reconstruction and quasi-distributed strain sensing with 110 µm spatial resolution. Our microscale mechanical sensor also exhibits exceptional sensitivity with a detected force level as low as 13.6 µN in real-time measurements. This sensing platform has potential applications in various fields, including biomedical sensing, surgical catheters, aircraft and spacecraft engineering, and robotic photonic skin development.

Flexible passive integrated photonic devices with superior optical and mechanical performance.

Flexible integrated photonics is a rapidly emerging technology with a wide range of possible applications in the fields of flexible optical interconnects, conformal multiplexing sensing, health monitoring, and biotechnology. One major challenge in developing mechanically flexible integrated photonics is the functional component within an integrated photonic circuit with superior performance. In this work, several essential flexible passive devices for such a circuit were designed and fabricated based on a multi-neutral-axis mechanical design and a monolithic integration technique. The propagation loss of the waveguide is calculated to be 4.2 dB/cm. In addition, we demonstrate a microring resonator, waveguide crossing, multimode interferometer (MMI), and Mach-Zehnder interferometer (MZI) for use at 1.55 µm, each exhibiting superior optical and mechanical performance. These results represent a significant step towards further exploring a complete flexible photonic integrated circuit.

Deep learning modeling approach for metasurfaces with high degrees of freedom.

Metasurfaces have shown promising potentials in shaping optical wavefronts while remaining compact compared to bulky geometric optics devices. The design of meta-atoms, the fundamental building blocks of metasurfaces, typically relies on trial and error to achieve target electromagnetic responses. This process includes the characterization of an enormous amount of meta-atom designs with varying physical and geometric parameters, which demands huge computational resources. In this paper, a deep learning-based metasurface/meta-atom modeling approach is introduced to significantly reduce the characterization time while maintaining accuracy. Based on a convolutional neural network (CNN) structure, the proposed deep learning network is able to model meta-atoms with nearly freeform 2D patterns and different lattice sizes, material refractive indices and thicknesses. Moreover, the presented approach features the capability of predicting a meta-atom's wide spectrum response in the timescale of milliseconds, attractive for applications necessitating fast on-demand design and optimization of a meta-atom/metasurface.

Broadband couplers for hybrid silicon-chalcogenide glass photonic integrated circuits.

We report on the design, fabrication and testing of three types of coupling structures for hybrid chalcogenide glass Ge23Sb7S70-Silicon (GeSbS-Si) photonic integrated circuit platforms. The first type is a fully etched GeSbS grating coupler defined directly in the GeSbS film. Coupling losses of 5.3 dB and waveguide-to-waveguide back-reflections of 3.4% were measured at a wavelength of 1553 nm. Hybrid GeSbS-to-Si butt couplers and adiabatic couplers transmitting light between GeSbS and Si single-mode waveguides were further developed. The hybrid butt couplers (HBCs) feature coupling losses of 2.7 dB and 9.2% back-reflection. The hybrid adiabatic couplers (HACs) exhibit coupling losses of 0.7 dB and negligible back-reflection. Both HBCs and HACs have passbands exceeding the 100 nm measurement range of the test setup. GeSbS grating couplers and GeSbS-to-Si waveguide couplers can be co-fabricated in the same process flow, providing, for example, a means to first couple high optical power levels required for nonlinear signal processing directly into GeSbS waveguides and to later transition into Si waveguides after attenuation of the pump. Moreover, GeSbS waveguides and HBC transitions have been fabricated on post-processed silicon photonics chips obtained from a commercially available foundry service, with a previously deposited 2 µm thick top waveguide cladding. This fabrication protocol demonstrates the compatibility of the developed integration scheme with standard silicon photonics technology with a complete back-end-of-line process.

Engineering third-order optical nonlinearities in hybrid chalcogenide-on-silicon platform.

We demonstrated a class of highly nonlinear hybrid waveguide structures based on infiltration of As2S3 chalcogenide glass into silicon slot waveguides. The nonlinear properties of the hybrid waveguides were precisely quantified via a bidirectional top-hat D-scan method, enabling a direct comparison between properties measured using different device geometries. We experimentally demonstrate hybrid As2S3-Si slot waveguides with a two-photon absorption (TPA) figure of merit exceeding 2 at near infrared wavelengths. These waveguides largely satisfy the critical criterion for efficient nonlinear integrated photonics (FOMTPAwg>1), allowing phase shifts greater than π with minimal overall losses. These results pave the way for efficient and robust ultrafast all-optical devices and circuits in large-scale silicon photonics technology.

Picojoule-level octave-spanning supercontinuum generation in chalcogenide waveguides.

Low propagation loss Ge23Sb7S70 waveguides (0.56 dB/cm) are fabricated in a wafer scale process. Simulation of a 2 cm long, 1.2 µm wide waveguide with 100 ps/nm/km peak dispersion predicts coherent supercontinuum generation at 1.55 µm pump wavelength. Octave-spanning supercontinuum using a dispersive wave is experimentally demonstrated using picojoule-level energy (26 pJ, 240 fs pulse width, 77 W peak power) pulses.

The Impact of Organic Additives on Copper Trench Microstructure.

Organic additives are typically used in the pulse electrodeposition of copper (Cu) to prevent void formation during the filling of high aspect ratio features. In this work, the role of bath chemistry as modified by organic additives was investigated for its effects on Cu trench microstructure. Polyethylene glycol (PEG), bis(3-sulfopropyl) disulfide (SPS), and Janus green b (JGB) concentrations were varied in the Cu electrodeposition bath. Results indicated a correlation between the JGB/SPS ratio and the surface roughness and residual stresses in the Cu. Electron backscattering diffraction (EBSD) and transmission Kikuchi diffraction (TKD) were used to study the cross-sectional microstructure in the trenches. Finer grain morphologies appeared in trenches filled with organic additives as compared to additive-free structures. Cu trench (111) texture also decreased with increasing organic additive concentrations due to more pronounced influence of sidewall seed layers on trench features. Twin density in the microstructure closely tracked calculated stresses in the Cu trenches. A comprehensive microstructural analysis was conducted in this study, on an area of focus that has garnered little attention from the literature, yet can have a major impact on microelectronic reliability.

The Influence of Pulsed Electroplating Frequency and Duty Cycle on Copper Film Microstructure and Stress State.

In this work we studied the impact of pulse electroplating parameters on the cross-sectional and surface microstructures of blanket copper films using electron backscattering diffraction and x-ray diffraction. The films evaluated were highly (111) textured in the direction perpendicular to the film surface. The degree of preferential orientation was found to decrease with longer pulse on-times, due to strain energy driven growth of other grain orientations. Residual biaxial stresses were also measured in the films and higher pulse frequencies during deposition led to smaller biaxial stresses in the films. Film stress was also found to correlate with the amount of twinning in the copper film cross-sections. This has been attributed to the twins' thermal stability and mechanical properties.

Low-loss photonic device in Ge-Sb-S chalcogenide glass.

Low-loss waveguides constitute an important building block for integrated photonic systems. In this work, we investigated low-loss photonic device fabrication in Ge23Sb7S70 chalcogenide glass using electron beam lithography followed by plasma dry etching. High-index-contrast waveguides with a low propagation loss of 0.5 dB/cm and microdisk resonators with an intrinsic quality factor (Q-factor) of 1.2×106 were demonstrated. Both figures represent, to the best of our knowledge, the best low-loss results reported thus far in submicrometer single-mode chalcogenide glass devices.

Heterogeneous microring and Mach-Zehnder modulators based on lithium niobate and chalcogenide glasses on silicon.

Thin films of lithium niobate are wafer bonded onto silicon substrates and rib-loaded with a chalcogenide glass, Ge(23)Sb(7)S(70), to demonstrate strongly confined single-mode submicron waveguides, microring modulators, and Mach-Zehnder modulators in the telecom C band. The 200 µm radii microring modulators present 1.2 dB/cm waveguide propagation loss, 1.2 × 10(5) quality factor, 0.4 GHz/V tuning rate, and 13 dB extinction ratio. The 6 mm long Mach-Zehnder modulators have a half-wave voltage-length product of 3.8 V.cm and an extinction ratio of 15 dB. The demonstrated work is a key step towards enabling wafer scale dense on-chip integration of high performance lithium niobate electro-optical devices on silicon for short reach optical interconnects and higher order advanced modulation schemes.

Mid-infrared materials and devices on a Si platform for optical sensing.

In this article, we review our recent work on mid-infrared (mid-IR) photonic materials and devices fabricated on silicon for on-chip sensing applications. Pedestal waveguides based on silicon are demonstrated as broadband mid-IR sensors. Our low-loss mid-IR directional couplers demonstrated in SiN x waveguides are useful in differential sensing applications. Photonic crystal cavities and microdisk resonators based on chalcogenide glasses for high sensitivity are also demonstrated as effective mid-IR sensors. Polymer-based functionalization layers, to enhance the sensitivity and selectivity of our sensor devices, are also presented. We discuss the design of mid-IR chalcogenide waveguides integrated with polycrystalline PbTe detectors on a monolithic silicon platform for optical sensing, wherein the use of a low-index spacer layer enables the evanescent coupling of mid-IR light from the waveguides to the detector. Finally, we show the successful fabrication processing of our first prototype mid-IR waveguide-integrated detectors.

Electrically Reconfigurable Phase-Change Transmissive Metasurface.

Programmable and reconfigurable optics hold significant potential for transforming a broad spectrum of applications, spanning space explorations to biomedical imaging, gas sensing, and optical cloaking. The ability to adjust the optical properties of components like filters, lenses, and beam steering devices could result in dramatic reductions in size, weight, and power consumption in future optoelectronic devices. Among the potential candidates for reconfigurable optics, chalcogenide-based phase change materials (PCMs) offer great promise due to their non-volatile and analogue switching characteristics. Although PCM have found widespread use in electronic data storage, these memory devices are deeply sub-micron-sized. To incorporate phase change materials into free-space optical components, it is essential to scale them up to beyond several hundreds of microns while maintaining reliable switching characteristics. This study demonstrated a non-mechanical, non-volatile transmissive filter based on low-loss PCMs with a 200 × 200 µm2 switching area. The device/metafilter can be consistently switched between low- and high-transmission states using electrical pulses with a switching contrast ratio of 5.5 dB. The device was reversibly switched for 1250 cycles before accelerated degradation took place. The work represents an important step toward realizing free-space reconfigurable optics based on PCMs.

Solution-derived Ge-Sb-Se-Te phase-change chalcogenide films.

Ge-Sb-Se-Te chalcogenides, namely Se-substituted Ge-Sb-Te, have been developed as an alternative optical phase change material (PCM) with a high figure-of-merit. A need for the integration of such new PCMs onto a variety of photonic platforms has necessitated the development of fabrication processes compatible with diverse material compositions as well as substrates of varying material types, shapes, and sizes. This study explores the application of chemical solution deposition as a method capable of creating conformally coated layers and delves into the resulting modifications in the structural and optical properties of Ge-Sb-Se-Te PCMs. Specifically, we detail the solution-based deposition of Ge-Sb-Se-Te layers and present a comparative analysis with those deposited via thermal evaporation. We also discuss our ongoing endeavor to improve available choice of processing-material combinations and how to realize solution-derived high figure-of-merit optical PCM layers, which will enable a new era for the development of reconfigurable photonic devices.

Demonstration of mid-infrared waveguide photonic crystal cavities.

We have demonstrated what we believe to be the first waveguide photonic crystal cavity operating in the mid-infrared. The devices were fabricated from Ge23Sb7S70 chalcogenide glass (ChG) on CaF2 substrates by combing photolithographic patterning and focused ion beam milling. The waveguide-coupled cavities were characterized using a fiber end fire coupling method at 5.2 µm wavelength, and a loaded quality factor of ~2000 was measured near the critical coupling regime.

Demonstration of high-Q mid-infrared chalcogenide glass-on-silicon resonators.

We demonstrated high-index-contrast, waveguide-coupled As2Se3 chalcogenide glass resonators monolithically integrated on silicon fabricated using optical lithography and a lift-off process. The resonators exhibited a high intrinsic quality factor of 2×10(5) at 5.2 µm wavelength, which is among the highest values reported in on-chip mid-infrared (mid-IR) photonic devices. The resonator can serve as a key building block for mid-IR planar photonic circuits.

Patient perspectives on pulmonary hypertension in the United States: Burdens, expectations, and goals.

Pulmonary hypertension (PH) is a life-threatening, debilitating disease caused by increased blood pressure in the pulmonary arteries. As patients living in the United States, we have unique insights into the journey from diagnosis and treatment within the US healthcare system and the significant impact that PH has on our quality of life. While there have recently been advances in PH management, there are several areas of PH care which we feel should be reassessed and improved. Commonly, diagnosis is lengthy and convoluted due to the rarity of the disease and limited knowledge of PH in primary care. There are also barriers to obtaining the right treatment and we feel that a more holistic approach to care is needed. Mental health is commonly overlooked and should be an integral part of patient care, as should elements such as nutritional advice, cardiopulmonary rehabilitation, and sexual health. PH patient associations play a key role in providing social, educational, and financial support to patients and caregivers alongside PH research and advocacy. As patients, we feel that we need to advocate for correct diagnosis, timely referral, and optimal treatment, in addition to overcoming the financial and/or administrative hurdles to obtain these. We propose several future goals to help empower patients to play an active, central role in their care and to improve all aspects of PH management. We advocate for further use of the patient voice in research and clinical development programs, including the use of patient-reported outcomes that have been developed with patient input.

The Effectiveness of Utilizing HRV Indices as a Predictor of ACFT Performance Outcomes.

BACKGROUND: The Army Combat Fitness Test (ACFT) is a performance assessment used by the U.S. Army to assess a cadet's strength, endurance, and agility with a series of six events to ensure that cadets are combat ready. Heart rate variability (HRV) is an instrument that measures cardiac autonomic modulation and has been incorporated to predict the performance of athletes in daily training and competition since acute bouts of exercise alter HRV variables. PURPOSE: To assess the applicability of using HRV to predict ACFT score performance outcomes in cadets. METHODS: Fifty army cadets (n = 36 male; n = 14 female; age = 20.60 ± 3.61 years; height = 173.34 ± 10.39 cm; body mass = 76.33 ± 14.68 kg; body fat percentage = 17.58 ± 5.26%) completed the ACFT and reported for HRV assessment. HRV assessment had the participant lay supine for 5 minutes, and traditional time and frequency domain variables were assessed. A Pearson's correlation and multiple linear regressions were run. RESULTS: HRV time and frequency domains were not significantly correlated in linear regression models except the stress index (SI) and the 2-mile run (2MR). The standing power throw and sprint drag carry were significantly correlated with traditional HRV variables. CONCLUSIONS: HRV was not a predictor of ACFT performance for individual events or overall ACFT. The SI presented predictive properties only for 2MR, with no other significant correlations between HRV variables with standing power throw and sprint drag carry. The SI ability to predict 2MR performance outcome via HRV is a promising tool to assess army cadet performance and recovery.

Electrical programmable multilevel nonvolatile photonic random-access memory.

Photonic Random-Access Memories (P-RAM) are an essential component for the on-chip non-von Neumann photonic computing by eliminating optoelectronic conversion losses in data links. Emerging Phase-Change Materials (PCMs) have been showed multilevel memory capability, but demonstrations still yield relatively high optical loss and require cumbersome WRITE-ERASE approaches increasing power consumption and system package challenges. Here we demonstrate a multistate electrically programmed low-loss nonvolatile photonic memory based on a broadband transparent phase-change material (Ge2Sb2Se5, GSSe) with ultralow absorption in the amorphous state. A zero-static-power and electrically programmed multi-bit P-RAM is demonstrated on a silicon-on-insulator platform, featuring efficient amplitude modulation up to 0.2 dB/µm and an ultralow insertion loss of total 0.12 dB for a 4-bit memory showing a 100× improved signal to loss ratio compared to other phase-change-materials based photonic memories. We further optimize the positioning of dual microheaters validating performance tradeoffs. Experimentally we demonstrate a half-a-million cyclability test showcasing the robust approach of this material and device. Low-loss photonic retention-of-state adds a key feature for photonic functional and programmable circuits impacting many applications including neural networks, LiDAR, and sensors for example.

Exploring an Unknown Corner of a Well-Known Topic: HIIE Influence on Renal Health and Filtration in Healthy Individuals Free of Cardiometabolic Diseases.

Aerobic exercise, specifically high-intensity interval exercise (HIIE), and its effects on renal health and filtration (RHF) are not well understood. Several studies support incorporating contemporary biomarkers serum cystatin C (CyC) and urine epidermal growth factor (uEGF) to combat the volatility of serum creatinine (sCr). Using these biomarkers, we examined the acute influences HIIE has on RHF to determine if there is a ceiling effect in healthy populations. The purpose was to determine the influence of an acute bout of HIIE on RHF. Thirty-six participants (n = 22 males; n = 14 females; age 37.6 ± 12.4 years.; BF% 19.2 ± 7.1%; VO2max 41.8 + 7.4 mL/kg/min) completed 30 min of HIIE on a treadmill (80% and 40% of VO2reserve in 3:2 min ratio). Blood and urine samples were obtained under standardized conditions before, 1 h, and 24 h post-exercise. CyC, sCR, uEGF, urine creatinine (uCr), uCr/uEGF ratio, and multiple estimates of glomerular filtration rate (eGFR) Modification of Diet in Renal Disease (MDRD) and CKD-EPI equations were used. The analysis employed paired sample t-tests and repeated measures ANOVAs. CyC, uEGF, uCr, and uCr/uEGF ratio concentrations were not altered between timepoints. sCr increased 1 h post-exercise (p > 0.002) but not at 24 h post-exercise. eGFR decreased in the MDRD and CKD-EPI equations at 1 h (p > 0.012) with no changes at 24 h post-exercise. CyC and sCr/CyC demonstrated no significant changes. CyC and uEGF are not altered by acute HIIE. The results demonstrate a potential ceiling effect in contemporary and traditional biomarkers of RHF, indicating improvements in RHF may be isolated to populations with reduced kidney function.

Roadmap for phase change materials in photonics and beyond.

Phase Change Materials (PCMs) have demonstrated tremendous potential as a platform for achieving diverse functionalities in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum, ranging from terahertz to visible frequencies. This comprehensive roadmap reviews the material and device aspects of PCMs, and their diverse applications in active and reconfigurable micro-nanophotonic devices across the electromagnetic spectrum. It discusses various device configurations and optimization techniques, including deep learning-based metasurface design. The integration of PCMs with Photonic Integrated Circuits and advanced electric-driven PCMs are explored. PCMs hold great promise for multifunctional device development, including applications in non-volatile memory, optical data storage, photonics, energy harvesting, biomedical technology, neuromorphic computing, thermal management, and flexible electronics.