Heterogeneous photodiodes on silicon nitride waveguides.

Heterogeneous integration through low-temperature die bonding is a promising technique to enable high-performance III-V photodetectors on the silicon nitride (Si3N4) photonic platform. Here we demonstrate InGaAs/InP modified uni-traveling carrier photodiodes on Si3N4 waveguides with 20 nA dark current, 20 GHz bandwidth, and record-high external (internal) responsivities of 0.8 A/W (0.94 A/W) and 0.33 A/W (0.83 A/W) at 1550 nm and 1064 nm, respectively. Open eye diagrams at 40 Gbit/s are demonstrated. Balanced photodiodes of this type reach 10 GHz bandwidth with over 40 dB common mode rejection ratio.

Double inverse nanotapers for efficient light coupling to integrated photonic devices.

Efficient light coupling to integrated photonic devices is of key importance to a wide variety of applications. "Inverse nanotapers" are widely used, in which the waveguide width is reduced to match an incident mode. Here, we demonstrate novel "double inverse" tapers, in which we reduce both the waveguide height and width. We demonstrate >45% chip-through coupling efficiency for both the transverse electric and transverse magnetic polarizations in Si3N4 tapers of >500 nm width, in comparison to regular inverse tapers that necessitate <100 nm width. The double inverse tapers show polarization-independent coupling and allow the fabrication using photolithography, relevant for applications at near-infrared and visible wavelengths, e.g., supercontinuum and soliton microcomb generation.

Heterogeneous integration of lithium niobate and silicon nitride waveguides for wafer-scale photonic integrated circuits on silicon.

An ideal photonic integrated circuit for nonlinear photonic applications requires high optical nonlinearities and low loss. This work demonstrates a heterogeneous platform by bonding lithium niobate (LN) thin films onto a silicon nitride (Si3N4) waveguide layer on silicon. It not only provides large second- and third-order nonlinear coefficients, but also shows low propagation loss in both the Si3N4 and the LN-Si3N4 waveguides. The tapers enable low-loss-mode transitions between these two waveguides. This platform is essential for various on-chip applications, e.g., modulators, frequency conversions, and quantum communications.

A Novel Role for Physical Therapists in Infection Prevention and Control in Response to the COVID-19 Pandemic: An Administrative Case Report.

OBJECTIVE: The purpose of this case report is to describe the development, implementation, and sustained use of a Rehabilitation Infection Prevention and Control Team (RIPCT) comprised of physical therapists in response to the COVID-19 pandemic. It also highlights how physical therapists are equipped to serve not only in typical clinical positions but also in nontraditional roles in healthcare. METHODS: The RIPCT served as an extension of the infection prevention and control (IPC) department. The team engaged in self-directed learning and worked alongside a physician mentor to acquire the knowledge and visibility needed to identify, triage, and address pandemic-related questions. Through rounding on units, on-site environmental assessments, and electronic communication, the RIPCT aided in navigating uncertainty, solving problems, and implementing changes for staff and patient safety. RESULTS: The RIPCT addressed safety concerns of 532 rehabilitation professionals, developed rehabilitation IPC policy, facilitated the reopening of 11 ambulatory sites, and created a new pathway to address future rehabilitation IPC needs. A survey of rehabilitation professionals indicated perceived effectiveness of physical therapists filling this role. CONCLUSION: The RIPCT successfully provided clear and consistent education as well as safe practice recommendations to staff and patients across a variety of disciplines and settings. The team quickly incorporated new knowledge and collaborated effectively in a nontraditional role within the healthcare system. The use of a semi-formal learning model with staff level clinicians as champions facilitated translation of IPC-related knowledge in a time of uncertainty throughout the healthcare community. IMPACT: The educational background, professional values, and communication skills of physical therapists allowed for successful integration into the IPC department to ensure staff and patient safety. Healthcare systems should consider utilization of physical therapists in nontraditional multidisciplinary clinical roles.

C- and O-Band Dual-Polarization Fiber-to-Chip Grating Couplers for Silicon Nitride Photonics.

Highly efficient coupling of light from an optical fiber to silicon nitride (SiN) photonic integrated circuits (PICs) is experimentally demonstrated with simple and fabrication-tolerant grating couplers (GC). Fully etched amorphous silicon gratings are formed on top of foundry-produced SiN PICs in a back-end-of-the-line (BEOL) process, which is compatible with 248 nm deep UV lithography. Metallic back reflectors are introduced to enhance the coupling efficiency (CE) from -1.11 to -0.44 dB in simulation and from -2.2 to -1.4 dB in experiments for the TE polarization in the C-band. Furthermore, these gratings can be optimized to couple both TE and TM polarizations with a CE below -3 dB and polarization-dependent losses under 1 dB over a wavelength range of 40 nm in the O-band. This elegant approach offers a simple solution for the realization of compact and, at the same time, highly efficient coupling schemes in SiN PICs.

Towards integrated photonic interposers for processing octave-spanning microresonator frequency combs.

Microcombs-optical frequency combs generated in microresonators-have advanced tremendously in the past decade, and are advantageous for applications in frequency metrology, navigation, spectroscopy, telecommunications, and microwave photonics. Crucially, microcombs promise fully integrated miniaturized optical systems with unprecedented reductions in cost, size, weight, and power. However, the use of bulk free-space and fiber-optic components to process microcombs has restricted form factors to the table-top. Taking microcomb-based optical frequency synthesis around 1550 nm as our target application, here, we address this challenge by proposing an integrated photonics interposer architecture to replace discrete components by collecting, routing, and interfacing octave-wide microcomb-based optical signals between photonic chiplets and heterogeneously integrated devices. Experimentally, we confirm the requisite performance of the individual passive elements of the proposed interposer-octave-wide dichroics, multimode interferometers, and tunable ring filters, and implement the octave-spanning spectral filtering of a microcomb, central to the interposer, using silicon nitride photonics. Moreover, we show that the thick silicon nitride needed for bright dissipative Kerr soliton generation can be integrated with the comparatively thin silicon nitride interposer layer through octave-bandwidth adiabatic evanescent coupling, indicating a path towards future system-level consolidation. Finally, we numerically confirm the feasibility of operating the proposed interposer synthesizer as a fully assembled system. Our interposer architecture addresses the immediate need for on-chip microcomb processing to successfully miniaturize microcomb systems and can be readily adapted to other metrology-grade applications based on optical atomic clocks and high-precision navigation and spectroscopy.

Hybrid integrated photonics using bulk acoustic resonators.

Integrated photonic devices based on Si3N4 waveguides allow for the exploitation of nonlinear frequency conversion, exhibit low propagation loss, and have led to advances in compact atomic clocks, ultrafast ranging, and spectroscopy. Yet, the lack of Pockels effect presents a major challenge to achieve high-speed modulation of Si3N4. Here, microwave-frequency acousto-optic modulation is realized by exciting high-overtone bulk acoustic wave resonances (HBAR) in the photonic stack. Although HBAR is ubiquitously used in modern communication and superconducting circuits, this is the first time it has been incorporated on a photonic integrated chip. The tight vertical acoustic confinement releases the lateral design of freedom, and enables negligible cross-talk and preserving low optical loss. This hybrid HBAR nanophotonic platform can find immediate applications in topological photonics with synthetic dimensions, compact opto-electronic oscillators, and microwave-to-optical converters. As an application, a Si3N4-based optical isolator is demonstrated by spatiotemporal modulation, with over 17 dB isolation achieved.

The Effect of Maximal Strength Training on Strength, Walking, and Balance in People with Multiple Sclerosis: A Pilot Study.

There is little literature examining the use of maximal strength training (MST) in people with multiple sclerosis (pwMS). This pretest-posttest study examined the effects of a MST program on strength, walking, balance, and fatigue in a sample of pwMS. Seven pwMS (median EDSS 3.0, IQR 1.5) participated in a MST program twice weekly for eight weeks. Strength was assessed with 1-repetition maximum (1RM) on each leg. Walking and balance were measured with the 6-Minute Walk Test (6MWT) and Berg Balance Scale (BBS), respectively. Fatigue was measured during each week of the program with the Fatigue Severity Scale (FSS). The program was well tolerated, with an attendance rate of 96.4%. Participants had significant improvements in right leg 1RM (t(6) = -6.032, P = 0.001), left leg 1RM (t(6) = -5.388, P = 0.002), 6MWT distance (t(6) = -2.572, P = 0.042), and BBS score (Z = -2.371, P = 0.018) after the MST intervention. There was no significant change in FSS scores (F(1, 3.312) = 2.411, P = 0.092). Participants in the MST program experienced improved balance and walking without an increase in fatigue. This MST program may be utilized by rehabilitation clinicians to improve lower extremity strength, balance, and mobility in pwMS.

Ultrasound-mediated gastrointestinal drug delivery.

There is a significant clinical need for rapid and efficient delivery of drugs directly to the site of diseased tissues for the treatment of gastrointestinal (GI) pathologies, in particular, Crohn's and ulcerative colitis. However, complex therapeutic molecules cannot easily be delivered through the GI tract because of physiologic and structural barriers. We report the use of ultrasound as a modality for enhanced drug delivery to the GI tract, with an emphasis on rectal delivery. Ultrasound increased the absorption of model therapeutics inulin, hydrocortisone, and mesalamine two- to tenfold in ex vivo tissue, depending on location in the GI tract. In pigs, ultrasound induced transient cavitation with negligible heating, leading to an order of magnitude enhancement in the delivery of mesalamine, as well as successful systemic delivery of a macromolecule, insulin, with the expected hypoglycemic response. In a rodent model of chemically induced acute colitis, the addition of ultrasound to a daily mesalamine enema (compared to enema alone) resulted in superior clinical and histological scores of disease activity. In both animal models, ultrasound treatment was well tolerated and resulted in minimal tissue disruption, and in mice, there was no significant effect on histology, fecal score, or tissue inflammatory cytokine levels. The use of ultrasound to enhance GI drug delivery is safe in animals and could augment the efficacy of GI therapies and broaden the scope of agents that could be delivered locally and systemically through the GI tract for chronic conditions such as inflammatory bowel disease.