High-resolution Si3N4 spectrometer: architecture & virtual channel synthesis and experimental demonstration.

Up-to-date network telemetry is the key enabler for resource optimization by capacity scaling, fault recovery, and network reconfiguration among other means. Reliable optical performance monitoring in general and, specifically, the monitoring of the spectral profile of WDM signals in fixed- and flex- grid architectures across the entire C-band, remains challenging. This article describes a two-stage spectrometer architecture amenable to integration on a single chip that can measure quantitatively the spectrum across the entire C-band with a resolution of ∼ 1.4 GHz. The first stage consists of a ring resonator with intra-ring phase shifter to provide a tuneable fine filter. The second stage makes use of an AWG subsystem and a novel processing algorithm to synthesize a tuneable coarse filter with a flat passband which isolates individual resonances of a multiplicity of ring resonances. The spectrometer is capable of scanning the entire C-band with high resolution using only one dynamic control. Due to its maturity and low loss, CMOS compatible Si3N4 is chosen for fabrication of the ring resonator and two cyclic AWGs. Complete spectrometer operation is demonstrated experimentally over a selected portion of the C-band. A novel virtual channel synthesis algorithm based on the weighted summation of the AWG output port powers relaxes the conventional AWG design requirement of a flat passband and sharp transition to stopband. The operation of the circuit is invariant to the optical path length between individual components and the algorithm corrects to some extent fabrication process variation impairments of the AWG channel spectra substantially improving robustness.

On the performance of optical phased array technology for beam steering: effect of pixel limitations.

Optical phased arrays are of strong interest for beam steering in telecom and LIDAR applications. A phased array ideally requires that the field produced by each element in the array (a pixel) is fully controllable in phase and amplitude (ideally constant). This is needed to realize a phase gradient along a direction in the array, and thus beam steering in that direction. In practice, grating lobes appear if the pixel size is not sub-wavelength, which is an issue for many optical technologies. Furthermore, the phase performance of an optical pixel may not span the required 2π phase range or may not produce a constant amplitude over its phase range. These limitations result in imperfections in the phase gradient, which in turn introduce undesirable secondary lobes. We discuss the effects of non-ideal pixels on beam formation, in a general and technology-agnostic manner. By examining the strength of secondary lobes with respect to the main lobe, we quantify beam steering quality and make recommendations on the pixel performance required for beam steering within prescribed specifications. By applying appropriate compensation strategies, we show that it is possible to realize high-quality beam steering even when the pixel performance is non-ideal, with intensity of the secondary lobes two orders of magnitude smaller than the main lobe.

U-shaped PN junctions for efficient silicon Mach-Zehnder and microring modulators in the O-band: erratum.

We correct two minor errors in the manuscript. The effective diameter of the ring modulator should be 62.5 µm rather than 65 µm. The factor, g, in the FOM for comparing between the O- and C-band results should be 0.83 instead of 0.7.

Tri-layer silicon nitride-on-silicon photonic platform for ultra-low-loss crossings and interlayer transitions.

We present a three-layer silicon nitride on silicon platform for constructing very large photonic integrated circuits. Efficient interlayer transitions are enabled by the close spacing between adjacent layers, while ultra-low-loss crossings are enabled by the large spacing between the topmost and bottommost layers. We demonstrate interlayer taper transitions with losses < 0.15 dB for wavelengths spanning from 1480 nm to 1620 nm. Our overpass waveguide crossings exhibit insertion loss < 2.1 mdB and crosstalk below -56 dB in the wavelength range between 1480 nm and 1620 nm with losses as low as 0.28 mdB. Our platform architecture is suited to meet the demands of large-scale photonic circuits which contain hundreds of crossings.

U-shaped PN junctions for efficient silicon Mach-Zehnder and microring modulators in the O-band.

We demonstrate U-shaped silicon PN junctions for energy efficient Mach-Zehnder modulators and ring modulators in the O-band. This type of junction has an improved modulation efficiency compared to existing PN junction geometries, has low losses, and supports high-speed operation. The U-shaped junctions were fabricated in an 8" silicon photonics platform, and they were incorporated in travelling-wave Mach-Zehnder modulators and microring modulators. For the high-bandwidth Mach-Zehnder modulator, the DC VπL at -0.5 V bias was 4.6 V·mm. It exhibited a 3dB bandwidth of 13 GHz, and eye patterns at up to 24 Gb/s were observed. A VπL as low as ~2.6 V·mm at a -0.5 V bias was measured in another device. The ring modulator tuning efficiency was 40 pm·V-1 between 0 V and -0.5 V bias. It had a 3-dB bandwidth of 13.5 GHz and open eye patterns at up to 13 Gb/s were measured. This type of PN junctions can be easily fabricated without extra masks and can be incorporated into generic silicon photonics platforms.

Inpatient Neurology Deaths and Factors Associated With Discharge to Hospice.

Background and Purpose: The Neurology Mortality Review Committee at our institution identified variability in location of death for patients on our inpatient neurology services. Hospice may increase the number of patients dying in their preferred locations. This study aimed to characterize patients who die on inpatient neurology services and explore barriers to discharge to hospice. Methods: This retrospective study was completed at a single, quaternary care medical center that is a Level I Trauma Center and Comprehensive Stroke Center. Patients discharged by an inpatient neurology service between 6/2019-1/2021 were identified and electronic medical record review was performed on patients who died in the hospital and who were discharged to hospice. Results: 69 inpatient deaths and 74 discharges to hospice occurred during the study period. Of the 69 deaths, 54 occurred following withdrawal of life sustaining treatment (WLST), of which 14 had a referral to hospice placed. There were 88 "hospice-referred" patients and 40 "hospice-eligible" patients. Hospice-referred patients were less likely to require the intensive care unit than hospice-eligible patients. Hospice-referred patients had their code status changed to Do Not Intubate earlier and were more likely to have advanced directives available. Conclusion: Our data highlight opportunities for further research to improve discharge to hospice including interhospital transfers, advanced directives, earlier goals of care discussions, palliative care consultations, and increased hospice bed availability. Importantly, it highlights the limitations of using in-hospital mortality as a quality indicator in this patient population.

Quality Improvement Metrics and Methods for Neurohospitalists.

Measurement of clinical performance is largely driven by the requirements of the Centers for Medicare and Medicaid Services and accrediting bodies like The Joint Commission. Performance measures include length of stay, readmission rate, mortality rate, hospital-acquired complications, and stroke core measures. Hospital rankings also depend heavily on quality and patient safety indicators. Becoming facile with these measures can aid neurohospitalists in understanding their value and garnering resources to support improvement projects. Neurohospitalists can apply a structured A3-based method to define a clinical problem, perform systematic analysis, then design and test solutions to drive improved outcomes for patients with neurologic disease.

Outcomes of a Neurohospitalist Program at an Academic Medical Center.

Background and Purpose: The purpose is to determine the impact of an academic neurohospitalist service on clinical outcomes. Methods: We performed a retrospective, quasi-experimental study of patients discharged from the general neurology service before (August 2010-July 2014) and after implementation of a full-time neurohospitalist service (August 2016-July 2018) compared to a control group of stroke patients. Primary outcomes were length of stay and 30-day readmission. Using the difference-in-difference approach, the impact of introducing a neurohospitalist service compared to controls was assessed with adjustment of patients' characteristics. Secondary outcomes included mortality, in-hospital complications, and cost. Results: There were 2706 neurology admissions (1648 general; 1058 stroke) over the study period. The neurohospitalist service was associated with a trend in reduced 30-day readmissions (ratio of ORs: .52 [.27, .98], P = .088), while length of stay was not incrementally changed in the difference-in-difference model (-.3 [-.7, .1], P = .18). However, descriptive results demonstrated a significant reduction in mean adjusted LOS of .7 days (4.5 to 3.8 days, P < .001) and a trend toward reduced readmissions (8.9% to 7.6%, P = .42) in the post-neurohospitalist cohort despite a significant increase in patient complexity, shift to higher acuity diagnoses, more emergent admissions, and near quadrupling of observation status patients. Mortality and in-hospital complications remained low, patient satisfaction was stable, and cost was not incrementally changed in the post-neurohospitalist cohort. Conclusions: Implementation of a neurohospitalist service at an academic medical center is feasible and associated with a significant increase in patient complexity and acuity and a trend toward reduced readmissions.

A Standardized Checklist Improves the Transfer of Stroke Patients from the Neurocritical Care Unit to Hospital Ward.

BACKGROUND AND PURPOSE: The transfer of patients with ischemic stroke from the intensive care unit (ICU) to noncritical care inpatient wards involves detailed information sharing between care teams. Our local transfer process was not standardized, leading to potential patient risk. We developed and evaluated an "ICU Transfer Checklist" to standardize communication between the neurocritical care team and the stroke ward team. METHODS: Retrospective review of consecutive patients with ischemic stroke admitted to the neurocritical care unit who were transferred to the stroke ward was used to characterize transfer documentation. A multidisciplinary team developed and implemented an ICU Transfer Checklist that contained a synthesis of the patient's clinical course, immediate "to-do" action items, and a system-based review of active medical problems. Postintervention checklist utilization was recorded for 8 months, and quality metrics for the postintervention cohort were compared to the preintervention cohort. Providers were surveyed pre- and postintervention to characterize perceived workflow and quality of care. RESULTS: Patients before (n = 52) and after (n = 81) ICU Transfer Checklist implementation had similar demographic and clinical characteristics. In the postchecklist implementation period, the ICU Transfer Checklist was used in over 85% of patients and median hospital length of stay (LOS) decreased (8.6 days vs 5.4 days, P = .003), while ICU readmission rate remained low. The checklist was associated with improved perceptions of safety and decreased time needed to transfer patients. CONCLUSIONS: Use of the standardized ICU Transfer Checklist was associated with decreased hospital LOS and with improvements in providers' perceptions of patient safety.

Neuroimaging selection for thrombectomy in pediatric stroke: a single-center experience.

BACKGROUND: The extended time window for endovascular therapy in adult stroke represents an opportunity for stroke treatment in children for whom diagnosis may be delayed. However, selection criteria for pediatric thrombectomy has not been defined. METHODS: We performed a retrospective cohort study of patients aged <18 years presenting within 24 hours of acute large vessel occlusion. Patient consent was waived by our institutional IRB. Patient data derived from our institutional stroke database was compared between patients with good and poor outcome using Fisher's exact test, t-test, or Mann-Whitney U-test. RESULTS: Twelve children were included: 8/12 (66.7%) were female, mean age 9.7±5.0 years, median National Institutes of Health Stroke Scale (NIHSS) 11.5 (IQR 10-14). Stroke etiology was cardioembolic in 75%, dissection in 16.7%, and cryptogenic in 8.3%. For 2/5 with perfusion imaging, Tmax >4 s appeared to better correlate with NIHSS. Nine patients (75%) were treated: seven underwent thrombectomy alone; one received IV alteplase and thrombectomy, and one received IV alteplase alone. Favorable outcome was achieved in 78% of treated patients versus 0% of untreated patients (P=0.018). All untreated patients had poor outcome, with death (n=2) or severe disability (n=1) at follow-up. Among treated patients, older children (12.8±2.9 vs 4.2±5.0 years, P=0.014) and children presenting as outpatient (100% vs 0%, P=0.028) appeared to have better outcomes. CONCLUSIONS: Perfusion imaging is feasible in pediatric stroke and may help identify salvageable tissue in extended time windows, though penumbral thresholds may differ from adult values. Further studies are needed to define criteria for thrombectomy in this unique population.

High-performance silicon photonic tri-state switch based on balanced nested Mach-Zehnder interferometer.

ABSATRCT: This work proposes a novel silicon photonic tri-state (cross/bar/blocking) switch, featuring high-speed switching, broadband operation, and crosstalk-free performance. The switch is designed based on a 2 × 2 balanced nested Mach-Zehnder interferometer structure with carrier injection phase tuning. As compared to silicon photonic dual-state (cross/bar) switches based on Mach-Zehnder interferometers with carrier injection phase tuning, the proposed switch not only has better performance in cross/bar switching but also provides an extra blocking state. The unique blocking state has a great advantage in applications of N × N switch fabrics, where idle switching elements in the fabrics can be configured to the blocking state for crosstalk suppression. According to our numerical experiments on a fully loaded 8 × 8 dilated Banyan switch fabric, the worst output crosstalk of the 8 × 8 switch can be dramatically suppressed by more than 50 dB, by assigning the blocking state to idle switching elements in the fabric. The results of this work can extend the functionality of silicon photonic switches and significantly improve the performance of on-chip N × N photonic switching technologies.

Implementation of a compact, four-stage, scalable optical interconnect for photonic backplane applications.

We report on the implementation of a dense 512-beam free-space optical interconnect linking four optoelectronic VLSI chips at the backplane level. The system presented maximizes the positioning tolerances of the components by use of slow f-number (f/16) Gaussian beams and oversized apertures. A beam-clustering scheme whereby a 4 x 4 array of beams is transmitted by each minilens is used to provide a high channel density. A modular approach is used to decrease the number of degrees of freedom in the system and achieve passive alignment of the modules in the final integration phase. A design overview as well as assembly and experimental results are presented.

Design and implementation of a modulator-based free-space optical backplane for multiprocessor applications.

Design and implementation of a free-space optical backplane for multiprocessor applications is presented. The system is designed to interconnect four multiprocessor nodes that communicate by using multiplexed 32-bit packets. Each multiprocessor node is electrically connected to an optoelectronic VLSI chip which implements the hyperplane interconnection architecture. The chips each contain 256 optical transmitters (implemented as dual-rail multiple quantum-well modulators) and 256 optical receivers. A rigid free-space microoptical interconnection system that interconnects the transceiver chips in a 512-channel unidirectional ring is implemented. Full design, implementation, and operational details are provided.