Advancing on-chip Kerr optical parametric oscillation towards coherent applications covering the green gap.

Optical parametric oscillation (OPO) in Kerr microresonators can efficiently transfer near-infrared laser light into the visible spectrum. To date, however, chromatic dispersion has mostly limited output wavelengths to >560 nm, and robust access to the whole green light spectrum has not been demonstrated. In fact, wavelengths between 532 nm and 633 nm, commonly referred to as the "green gap", are especially challenging to produce with conventional laser gain. Hence, there is motivation to extend the Kerr OPO wavelength range and develop reliable device designs. Here, we experimentally show how to robustly access the entire green gap with Kerr OPO in silicon nitride microrings pumped near 780 nm. Our microring geometries are optimized for green-gap emission; in particular, we introduce a dispersion engineering technique, based on partially undercutting the microring, which not only expands wavelength access but also proves robust to variations in resonator dimensions. Using just four devices, we generate >150 wavelengths evenly distributed throughout the green gap, as predicted by our dispersion simulations. Moreover, we establish the usefulness of Kerr OPO to coherent applications by demonstrating continuous frequency tuning (>50 GHz) and narrow optical linewidths (<1 MHz). Our work represents an important step in the quest to bring nonlinear nanophotonics and its advantages to the visible spectrum.

On-chip Kerr parametric oscillation with integrated heating for enhanced frequency tuning and control.

Nonlinear microresonators can convert light from chip-integrated sources into new wavelengths within the visible and near-infrared spectrum. For most applications, such as the interrogation of quantum systems with specific transition wavelengths, tuning the frequency of converted light is critical. Nonetheless, demonstrations of wavelength conversion have mostly overlooked this metric. Here, we apply efficient integrated heaters to tune the idler frequency produced by the Kerr optical parametric oscillation in a silicon nitride microring across a continuous 1.5 terahertz range. Finally, we suppress idler frequency noise between DC and 5 kHz by several orders of magnitude using feedback to the heater drive.

Society for Maternal-Fetal Medicine Position Statement: Extending Medicaid coverage for 12 months postpartum.

Position: The Society for Maternal-Fetal Medicine supports federal and state policies that expand Medicaid eligibility and extend Medicaid coverage through 12 months postpartum to address the maternal morbidity and mortality crisis and improve health equity. Access to coverage is essential to optimize maternal health following pregnancy and childbirth and avoid preventable causes of maternal morbidity and mortality that extend throughout the first year postpartum. The Society opposes policies such as work requirements or limitations on coverage for undocumented individuals that unnecessarily impose restrictions on Medicaid eligibility.

Kerr-induced synchronization of a cavity soliton to an optical reference.

The phase-coherent frequency division of a stabilized optical reference laser to the microwave domain is made possible by optical-frequency combs (OFCs)1,2. OFC-based clockworks3-6 lock one comb tooth to a reference laser, which probes a stable atomic transition, usually through an active servo that increases the complexity of the OFC photonic and electronic integration for fieldable clock applications. Here, we demonstrate that the Kerr nonlinearity enables passive, electronics-free synchronization of a microresonator-based dissipative Kerr soliton (DKS) OFC7 to an externally injected reference laser. We present a theoretical model explaining this Kerr-induced synchronization (KIS), which closely matches experimental results based on a chip-integrated, silicon nitride, micro-ring resonator. Once synchronized, the reference laser captures an OFC tooth, so that tuning its frequency provides direct external control of the OFC repetition rate. We also show that the stability of the repetition rate is linked to that of the reference laser through the expected frequency division factor. Finally, KIS of an octave-spanning DKS exhibits enhancement of the opposite dispersive wave, consistent with the theoretical model, and enables improved self-referencing and access to the OFC carrier-envelope offset frequency. The KIS-mediated enhancements we demonstrate can be directly implemented in integrated optical clocks and chip-scale low-noise microwave generators.

Alternative Payment Models in Pregnancy to Improve Outcomes and Advance Equity.

This Viewpoint reviews the state of alternative payment models (APMs) applied to pregnancy and proposes clinical and policy objectives that could guide model design going forward.

High-performance Kerr microresonator optical parametric oscillator on a silicon chip.

Optical parametric oscillation (OPO) is distinguished by its wavelength access, that is, the ability to flexibly generate coherent light at wavelengths that are dramatically different from the pump laser, and in principle bounded solely by energy conservation between the input pump field and the output signal/idler fields. As society adopts advanced tools in quantum information science, metrology, and sensing, microchip OPO may provide an important path for accessing relevant wavelengths. However, a practical source of coherent light should additionally have high conversion efficiency and high output power. Here, we demonstrate a silicon photonics OPO device with unprecedented performance. Our OPO device, based on the third-order (χ(3)) nonlinearity in a silicon nitride microresonator, produces output signal and idler fields widely separated from each other in frequency ( > 150 THz), and exhibits a pump-to-idler conversion efficiency up to 29 % with a corresponding output idler power of > 18 mW on-chip. This performance is achieved by suppressing competitive processes and by strongly overcoupling the output light. This methodology can be readily applied to existing silicon photonics platforms with heterogeneously-integrated pump lasers, enabling flexible coherent light generation across a broad range of wavelengths with high output power and efficiency.

Fourier Synthesis Dispersion Engineering of Photonic Crystal Microrings for Broadband Frequency Combs.

Dispersion engineering of microring resonators is crucial for optical frequency comb applications, to achieve targeted bandwidths and powers of individual comb teeth. However, conventional microrings only present two geometric degrees of freedom - width and thickness - which limits the degree to which dispersion can be controlled. We present a technique where we tune individual resonance frequencies for arbitrary dispersion tailoring. Using a photonic crystal microring resonator that induces coupling to both directions of propagation within the ring, we investigate an intuitive design based on Fourier synthesis. Here, the desired photonic crystal spatial profile is obtained through a Fourier relationship with the targeted modal frequency shifts, where each modal shift is determined based on the corresponding effective index modulation of the ring. Experimentally, we demonstrate several distinct dispersion profiles over dozens of modes in transverse magnetic polarization. In contrast, we find that the transverse electric polarization requires a more advanced model that accounts for the discontinuity of the field at the modulated interface. Finally, we present simulations showing arbitrary frequency comb spectral envelope tailoring using our Frequency synthesis approach.

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.

Selective Fetoscopic Laser Photocoagulation or Expectant Management for Stage I Twin-Twin Transfusion: A Cost-Effectiveness Analysis.

BACKGROUND: Selective fetoscopic laser photocoagulation (SFLP) is the preferred intervention for stage II-IV twin-twin transfusion syndrome (TTTS); however, there is no consensus on whether SFLP or expectant management (EM) is the preferred strategy to manage Quintero stage I TTTS. OBJECTIVE: The objective of this study is to estimate whether SFLP or EM is the cost-effective strategy for management of Quintero stage I TTTS. STUDY DESIGN: A decision-analysis (DA) model compared SFLP to EM for 1,000 pregnant people with monochorionic-diamniotic twins affected by stage I TTTS. All subjects were assumed to be appropriate candidates for either SFLP or EM. Probabilities, costs, and utilities were derived from the literature. The DA was conducted from a healthcare payor perspective, and the analytic horizon was over the course of an offspring's lifetime, with primary outcomes of survivorship (i.e., no intrauterine fetal demise or neonatal death) and long-term neurodevelopmental impairment. The model incorporated Markov processes with 4-week cycles throughout pregnancy. Incremental cost-effectiveness ratios (ICER) for each strategy were calculated and compared to estimate marginal cost effectiveness. An ICER of USD 100,000 per quality-adjusted life year was used to define the cost-effectiveness threshold. One-way sensitivity and Monte Carlo analyses (MCA), as well as microsimulations, were performed. RESULTS: For base-case estimates, SFLP was found to be cost-effective compared to EM in the management of stage I TTTS. In one-way sensitivity analysis, varying each variable along pre-specified ranges did not result in changes in the conclusion. MCA projects SFLP as the cost-effective strategy in 100% of runs. CONCLUSIONS: With base-case estimates, SFLP is estimated to be the cost-effective strategy for the treatment of Quintero stage I TTTS when compared with EM. This remained true across a wide range of inputs.

Tectonically-driven oxidant production in the hot biosphere.

Genomic reconstructions of the common ancestor to all life have identified genes involved in H2O2 and O2 cycling. Commonly dismissed as an artefact of lateral gene transfer after oxygenic photosynthesis evolved, an alternative is a geological source of H2O2 and O2 on the early Earth. Here, we show that under oxygen-free conditions high concentrations of H2O2 can be released from defects on crushed silicate rocks when water is added and heated to temperatures close to boiling point, but little is released at temperatures <80 °C. This temperature window overlaps the growth ranges of evolutionary ancient heat-loving and oxygen-respiring Bacteria and Archaea near the root of the Universal Tree of Life. We propose that the thermal activation of mineral surface defects during geological fault movements and associated stresses in the Earth's crust was a source of oxidants that helped drive the (bio)geochemistry of hot fractures where life first evolved.

Conversion Efficiency in Kerr-Microresonator Optical Parametric Oscillators: From Three Modes to Many Modes.

Optical parametric oscillation in a Kerr nonlinear microresonator can generate coherent laser light with frequencies that are widely separated from the pump frequency, allowing, for example, visible light to be generated using a near-infrared pump. To be practically useful, the pump-to-signal conversion efficiency must be far higher than what has been demonstrated in microresonator-based oscillators with widely-separated output frequencies. To address this challenge, here we theoretically and numerically study parametric oscillations in Kerr nonlinear microresonators, revealing an intricate solution space that arises from an interplay of nonlinear processes. As a start, we use a three-mode approximation to derive an efficiency-maximizing relation between pump power and frequency mismatch. However, realistic devices, such as integrated microring resonators, support far more than three modes. Hence, a more accurate model that includes the entire modal landscape is necessary to determine potential inefficiencies arising from unwanted competing nonlinear processes. To this end, we numerically simulate the Lugiato-Lefever Equation that accounts for the full spectrum of nonlinearly-coupled resonator modes. We observe and characterize two nonlinear phenomena linked to parametric oscillations in multi-mode resonators: Mode competition and cross phase modulation-induced modulation instability. Both processes may impact conversion efficiency. Finally, we show how to increase the conversion efficiency to ≈ 25 % by tuning the microresonator loss rates. Our analysis will guide microresonator designs that aim for high conversion efficiency and output power.

Efficient chip-based optical parametric oscillators from 590 nm to 1150 nm.

Optical parametric oscillators are widely used to generate coherent light at frequencies not accessible by conventional laser gain. However, chip-based parametric oscillators operating in the visible spectrum have suffered from pump-to-signal conversion efficiencies typically less than 0.1 %. Here, we demonstrate efficient optical parametric oscillators based on silicon nitride photonics that address frequencies between 260 THz (1150 nm) and 510 THz (590 nm). Pumping silicon nitride microrings near 385 THz (780 nm) yields monochromatic signal and idler waves with unprecedented output powers in this wavelength range. We estimate on-chip output powers (separately for the signal and idler) between 1 mW and 5 mW and conversion efficiencies reaching ≈15 %. Underlying this improved performance is our development of pulley waveguides for broadband near-critical coupling, which exploits a fundamental connection between the waveguide-resonator coupling rate and conversion efficiency. Finally, we find that mode competition reduces conversion efficiency at high pump powers, thereby constraining the maximum realizable output power. Our work proves that optical parametric oscillators built with integrated photonics can produce useful amounts of visible laser light with high efficiency.

Priorities and Understanding of Pregnancy Among Women With Congenital Heart Disease: A Mixed-Methods Study.

Background: Many women with congenital heart disease (CHD) desire safe and successful pregnancies, but a significant proportion does not seek prepregnancy counseling. Objectives: This study aims to distinguish the personal priorities and perceptions about pregnancy in this growing population. Methods: Women aged 18 to 50 years with CHD were enrolled from 2 sites. Using a mixed-methods approach (Q-methodology), 179 participants sorted 23 statements representing a collection of views on pregnancy using priority forced ranking along a scale from "strongly agree" to "strongly disagree." Results: Majority of women were between 25 and 29 years of age, had moderate or severely complex CHD, and were married. Five unique group identities were elucidated from patient responses. Group 1 was centered around a strong desire to start a family. Women in group 2 had significant anxiety, and their psychological wellbeing interfered with their decision to start a family. Women in group 3 were concerned about premature death; if they do have kids, they want to be alive to see them grow old. Women in group 4 had strong objections to termination. Group 5 valued health care engagement. Group identities were unrelated to CHD complexity and demographic factors such as age and marital status. Six differentiating statements were identified that help distinguish which group a woman aligns with. Conclusions: Women with CHD have diverse priorities and values relating to pregnancy and heart disease. This study used a mixed-methods approach to provide a framework identifying several domains for targeted prepregnancy counseling in women with CHD.

Ultra-broadband Kerr microcomb through soliton spectral translation.

Broadband and low-noise microresonator frequency combs (microcombs) are critical for deployable optical frequency measurements. Here we expand the bandwidth of a microcomb far beyond its anomalous dispersion region on both sides of its spectrum through spectral translation mediated by mixing of a dissipative Kerr soliton and a secondary pump. We introduce the concept of synthetic dispersion to qualitatively capture the system's key physical behavior, in which the second pump enables spectral translation through four-wave mixing Bragg scattering. Experimentally, we pump a silicon nitride microring at 1063 nm and 1557 nm to enable soliton spectral translation, resulting in a total bandwidth of 1.6 octaves (137-407 THz). We examine the comb's low-noise characteristics, through heterodyne beat note measurements across its spectrum, measurements of the comb tooth spacing in its primary and spectrally translated portions, and their relative noise. These ultra-broadband microcombs provide new opportunities for optical frequency synthesis, optical atomic clocks, and reaching previously unattainable wavelengths.

Harnessing Dispersion in Soliton Microcombs to Mitigate Thermal Noise.

We explore intrinsic thermal noise in soliton microcombs, revealing thermodynamic correlations induced by nonlinearity and group-velocity dispersion. A suitable dispersion design gives rise to control over thermal-noise transduction from the environment to a soliton microcomb. We present simulations with the Lugiato-Lefever equation (LLE), including temperature as a stochastic variable. By systematically tuning the dispersion, we suppress repetition-rate frequency fluctuations by up to 50 decibels for different LLE soliton solutions. In an experiment, we observe a measurement-system-limited 15-decibel reduction in the repetition-rate phase noise for various settings of the pump-laser frequency, and our measurements agree with a thermal-noise model. Finally, we compare two octave-spanning soliton microcombs with similar optical spectra and offset frequencies, but with designed differences in dispersion. Remarkably, their thermal-noise-limited carrier-envelope-offset frequency linewidths are 1 MHz and 100 Hz, which demonstrates an unprecedented potential to mitigate thermal noise. Our results guide future soliton-microcomb design for low-noise applications, and, more generally, they illuminate emergent properties of nonlinear, multimode optical systems subject to intrinsic fluctuations.

Top Ten Tips Palliative Care Clinicians Should Know About Opioid Use Disorder.

Since the prevalence of substance use disorders, and opioid use disorder (OUD) specifically, remains high and represents a public health crisis, it is critical that palliative care (PC) providers have a broad understanding of this class of chronic, yet treatable, diseases. Conceptualizing stigma associated with OUD, treatment modalities available, and educational opportunities are key factors in providing patient-centered care. A solid foundation of knowledge about OUD in the setting of serious illness is also crucial as PC providers often recommend or prescribe opioids for symptom management in patients who also have OUD. Furthermore, the PC interdisciplinary team is particularly well poised to care for patients suffering from OUD due to the inherently holistic approach already present in the specialty of PC. This article offers PC teams a framework for understanding the diagnosis and treatment of OUD, methods for performing risk stratification and monitoring, and an overview of opportunities to enhance our care of PC patients with OUD.

Direct Kerr frequency comb atomic spectroscopy and stabilization.

Microresonator-based soliton frequency combs, microcombs, have recently emerged to offer low-noise, photonic-chip sources for applications, spanning from timekeeping to optical-frequency synthesis and ranging. Broad optical bandwidth, brightness, coherence, and frequency stability have made frequency combs important to directly probe atoms and molecules, especially in trace gas detection, multiphoton light-atom interactions, and spectroscopy in the extreme ultraviolet. Here, we explore direct microcomb atomic spectroscopy, using a cascaded, two-photon 1529-nm atomic transition in a rubidium micromachined cell. Fine and simultaneous repetition rate and carrier-envelope offset frequency control of the soliton enables direct sub-Doppler and hyperfine spectroscopy. Moreover, the entire set of microcomb modes are stabilized to this atomic transition, yielding absolute optical-frequency fluctuations at the kilohertz level over a few seconds and <1-MHz day-to-day accuracy. Our work demonstrates direct atomic spectroscopy with Kerr microcombs and provides an atomic-stabilized microcomb laser source, operating across the telecom band for sensing, dimensional metrology, and communication.

Thermal and Nonlinear Dissipative-Soliton Dynamics in Kerr-Microresonator Frequency Combs.

We explore the dynamical response of dissipative Kerr solitons to changes in pump power and detuning and show how thermal and nonlinear processes couple these parameters to the frequency-comb degrees of freedom. Our experiments are enabled by a Pound-Drever-Hall (PDH) stabilization approach that provides on-demand, radio-frequency control of the frequency comb. PDH locking not only guides Kerr-soliton formation from a cold microresonator but opens a path to decouple the repetition and carrier-envelope-offset frequencies. In particular, we demonstrate phase stabilization of both Kerr-comb degrees of freedom to a fractional frequency precision below 10^{-16}, compatible with optical-time-keeping technology. Moreover, we investigate the fundamental role that residual laser-resonator detuning noise plays in the spectral purity of microwave generation with Kerr combs.

Interlocking Kerr-microresonator frequency combs for microwave to optical synthesis.

We report accurate phase stabilization of an interlocking pair of Kerr-microresonator frequency combs. The two combs, one based on silicon nitride and one on silica, feature nearly harmonic repetition frequencies and can be generated with one laser. The silicon-nitride comb supports an ultrafast-laser regime with three-optical-cycle, 1-picosecond-period soliton pulses and a total dispersive-wave-enhanced bandwidth of 170 THz, while providing a stable phase-link between optical and microwave frequencies. We demonstrate nanofabrication control of the silicon-nitride comb's carrier-envelope offset frequency and spectral profile. The phase-locked combs coherently reproduce their clock with a fractional precision of <6×10-13/τ, a behavior we verified through 2 h of measurement to reach <3×10-16. Our work establishes Kerr combs as a viable technology for applications like optical-atomic timekeeping and optical synchronization.