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The recent advancement in lithium-niobite-on-insulator (LNOI) technology is opening up new opportunities in optoelectronics, as devices with better performance, lower power consumption and a smaller footprint can be realised due to the high optical confinement in the structures. The LNOI platform offers both large χ(2) and χ(3) nonlinearities along with the power of dispersion engineering, enabling brand new nonlinear photonic devices and applications for the next generation of integrated photonic circuits. However, Raman scattering and its interaction with other nonlinear processes have not been extensively studied in dispersion-engineered LNOI nanodevices. In this work, we characterise the Raman radiation spectra in a monolithic lithium niobate (LN) microresonator via selective excitation of Raman-active phonon modes. The dominant mode for the Raman oscillation is observed in the backward direction for a continuous-wave pump threshold power of 20 mW with a high differential quantum efficiency of 46%. We explore the effects of Raman scattering on Kerr optical frequency comb generation. We achieve mode-locked states in an X-cut LNOI chip through sufficient suppression of the Raman effect via cavity geometry control. Our analysis of the Raman effect provides guidance for the development of future chip-based photonic devices on the LNOI platform.Lithium niobate on insulator: the Raman effectBetter understanding, and thus control, of lithium niobate interactions with light could guide the development of an optical device that measures time even more precisely than atomic clocks. Marko Lončar of Harvard University and colleagues studied how light scatters when laser light is pumped into an optical cavity made from lithium niobate, a synthetic crystal widely used in optical materials. Their findings suggested that changing the shape of the lithium niobate cavity could help them suppress ‘Raman scattering’, a type of energy transfer that happens when light interacts with the material’s molecules. When laser light was shone through the specially tuned cavity, it exited in the form of light pulses of extremely short duration. The findings could guide the development of optical devices that can more precisely measure standard units such as distance and time.

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications, including optical atomic clocks 1 , microwave photonics 2 , spectroscopy 3 , optical wave synthesis 4 , frequency conversion 5 , communications 6 , lidar 7 , optical computing 8 and astronomy 9 . The leading approaches for on-chip pulse generation rely on mode-locking inside microresonators with either third-order nonlinearity 10 or with semiconductor gain 11 , 12 . These approaches, however, are limited in noise performance, wavelength and repetition rate tunability  10 , 13 . Alternatively, subpicosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave single-frequency laser using electro-optic modulators 1 , 14 – 17 . Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate photonic platform 18 , using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system 19 . The device is driven by a continuous-wave distributed feedback laser chip and controlled by a single continuous-wave microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520-femtosecond duration) with a 30-gigahertz repetition rate, flat-top optical spectra with a 10-decibel optical bandwidth of 12.6 nanometres, individual comb-line powers above 0.1 milliwatts, and pulse energies of 0.54 picojoules. Our results represent a tunable, robust and low-cost integrated pulsed light source with continuous-wave-to-pulse conversion efficiencies an order of magnitude higher than those achieved with previous integrated sources. Our pulse generator may find applications in fields such as ultrafast optical measurement 19 , 20 or networks of distributed quantum computers 21 , 22 . A femtosecond pulse generator is realized using an electro-optic time-lens system integrated on a lithium niobate photonic chip, capable of tunable repetition rates and wavelengths.

Optical isolators are indispensable components of almost any optical system and are used to protect a laser from unwanted reflections for phase-stable coherent operation. The emergence of chip-scale optical systems, powered by semiconductor lasers that are integrated on the same chip, has generated a demand for a fully integrated optical isolator. Conventional approaches, which rely on the use of magneto-optic materials to break Lorentz reciprocity, present substantial challenges in terms of material integration. Although alternative magnetic-free approaches have been explored, an integrated isolator with a low insertion loss, high isolation ratio, broad bandwidth and low power consumption on a monolithic material platform is yet to be achieved. Here we realize a non-reciprocal travelling-wave-based electro-optic isolator on thin-film lithium niobate. The isolator enables a maximum optical isolation of 48.0 dB with an on-chip insertion loss of 0.5 dB and uses a single-frequency microwave drive power of 21 dBm. The isolation ratio remains larger than 37 dB across a tunable optical wavelength range from 1,510 to 1,630 nm. We realize a hybrid distributed feedback laser–lithium niobate isolator module that successfully protects the single-mode operation and linewidth of the laser from reflection. Our result represents an important step towards a practical high-performance optical isolator on chip.An integrated electro-optic isolator on thin-film lithium niobate enables non-reciprocal isolation by microwave-driven travelling-wave phase modulation. The isolator exhibits a maximum optical isolation of 48.0 dB at around 1,553 nm and an on-chip insertion loss of 0.5 dB.

Mirrors are ubiquitous in optics and are used to control the propagation of optical signals in space. Here we propose and demonstrate frequency domain mirrors that provide reflections of the optical energy in a frequency synthetic dimension, using electro-optic modulation. First, we theoretically explore the concept of frequency mirrors with the investigation of propagation loss, and reflectivity in the frequency domain. Next, we explore the mirror formed through polarization mode-splitting in a thin-film lithium niobate micro-resonator. By exciting the Bloch waves of the synthetic frequency crystal with different wave vectors, we show various states formed by the interference between forward propagating and reflected waves. Finally, we expand on this idea, and generate tunable frequency mirrors as well as demonstrate trapped states formed by these mirrors using coupled lithium niobate micro-resonators. The ability to control the flow of light in the frequency domain could enable a wide range of applications, including the study of random walks, boson sampling, frequency comb sources, optical computation, and topological photonics. Furthermore, demonstration of optical elements such as cavities, lasers, and photonic crystals in the frequency domain, may be possible. We show frequency domain mirrors that provide reflections of optical mode propagation in the frequency domain. We theoretically investigated the mirror properties and experimentally demonstrate it using polarization and coupled-resonator-based coupling on thin film Lithium Niobate.

Resonator-based optical frequency comb generation is an enabling technology for a myriad of applications ranging from communications to precision spectroscopy. These frequency combs can be generated in nonlinear resonators driven using either continuous-wave (CW) light, which requires alignment of the pump frequency with the cavity resonance, or pulsed light, which also mandates that the pulse repetition rate and cavity free spectral range (FSR) are carefully matched. Advancements in nanophotonics have ignited interest in chip-scale optical frequency combs. However, realizing pulse-driven on-chip Kerr combs remains challenging, as microresonator cavities have limited tuning range in their FSR and resonance frequency. Here, we take steps to overcome this limitation and demonstrate broadband frequency comb generation using a χ (3) resonator synchronously pumped by a tunable femtosecond pulse generator with on-chip amplitude and phase modulators. Notably, employing pulsed pumping overcomes limitations in Kerr comb generation typically seen in crystalline resonators from stimulated Raman scattering. Here the authors use on-chip amplitude and phase modulation to synchronously pump a resonator on thin-film lithium niobate for frequency comb generation. They find that pulsed pumping significantly mitigates stimulated Raman scattering and improves the overall efficiency of the device.

The surge in artificial intelligence applications calls for scalable, high-speed, and low-energy computation methods. Computing with photons is promising due to the intrinsic parallelism, high bandwidth, and low latency of photons. However, current photonic computing architectures are limited by the speed and energy consumption associated with electronic-to-optical data transfer, i.e., electro-optic conversion. Here, we demonstrate a thin-film lithium niobate (TFLN) computing circuit that addresses this challenge, leveraging both highly efficient electro-optic modulation and the spatial scalability of TFLN photonics. Our circuit is capable of computing at 43.8 GOPS/channel while consuming 0.0576 pJ/OP, and we demonstrate various inference tasks with high accuracy, including the classification of binary data and complex images. Heightening the integration level, we show another TFLN computing circuit that is combined with a hybrid-integrated distributed-feedback laser and heterogeneous-integrated modified uni-traveling carrier photodiode. Our results show that the TFLN photonic platform holds promise to complement silicon photonics and diffractive optics for photonic computing, with extensions to ultrafast signal processing and ranging. Efficient electro-optic conversion is central to photonic computing, and thin-film lithium niobate (TFLN) offers this capability. Here, the authors demonstrate computing circuits on the TFLN platform, enabling the next generation of photonic computing systems featuring both high-speed and low-power.

Background Team-based primary care (PC) enhances the quality of and access to health care. The Veterans Health Administration (VHA) implements team-based care through Patient Aligned Care Teams (PACTs), consisting of four core members: a primary care provider, registered nurse (RN) care manager, licensed vocational nurse, and scheduling clerk. RNs play a central role: they coordinate patient care, manage operational needs, and serve as a patient point of contact. Currently, it is not known how varying levels of RN staffing on primary care teams impact patient outcomes. Objective This study aims to empirically assess how the stability of RN staffing within team-based primary care affects patient access to care. Methods A retrospective database review using clinical and administrative data from the VHA over 24 months. Participants included 5,897 PC PACTs across 152 VHA healthcare facilities in the United States and its territories. The stability of personnel in the RN role was categorized as: RN continuous churn, RN staffing instability and RN vacancy. All 3 categories were compared to teams with RN stability (i.e., same person in the role for the entire 24-month period). Access measures included: average third-next-available appointment, established patient average wait time in days, urgent care utilization, emergency room utilization, and total inbound-to-outbound PC secure messages ratio. Results RN continuous churn within PACTs had a significant impact on third-next-available appointment (b = 3.70, p  < 0.01). However, RN staffing instability and vacancy had no significant relationship with any of the access measures. Several risk adjustment variables, including team full-time equivalency, team stability, relative team size, and average team size, were significantly associated with access to health care. Conclusions Teams are impacted by churn on the team. Adequate staffing and team stability significantly predict patient access primary care services. Healthcare organizations should focus on personnel retention and strategies to mitigate the impact(s) of continuous RN turnover. Future research should examine the relative impact of turnover and stability of other roles (e.g., clerks) and how team members adapt to personnel changes.

Previous research studies have demonstrated the link between parents’ education and parental stress level. However, these studies have not taken parents’ goal orientation into consideration. Based on the framework of goal orientation theory, we examined how parents’ goals would interact with parents’ education to affect perceived parental stress in face of children’s upsetting school experience. Participants were 189 parents of Hong Kong Chinese children studying in kindergartens. Using an experimental design, parents with various education backgrounds were randomly assigned to mastery or performance goals manipulation. The interaction between parents’ goals and parents’ education on perceived parental stress was investigated. Results from the two-way ANOVA indicated the significant main effect of parents’ goals, while the main effect of parents’ education and the interaction effect between parents’ goals and parents’ education were both nonsignificant. Regardless of parents’ education, parents in the performance goals condition reported significantly higher parental stress than those in the mastery goals condition. The findings highlight the utility of fostering parents’ mastery goal orientation to improve their well-being and capacity to cope with children’s academic setback.

The impact of a rapidly changing climate on the biosphere is an urgent area of research for mitigation policy and management. Plant phenology is a sensitive indicator of climate change and regulates the seasonality of carbon, water, and energy fluxes between the land surface and the climate system, making it an important tool for studying biosphere–atmosphere interactions. To monitor plant phenology at regional and continental scales, automated near-surface cameras are being increasingly used to supplement phenology data derived from satellite imagery and data from ground-based human observers. We used imagery from a network of phenology cameras in a citizen science project called Season Spotter to investigate whether information could be derived from these images beyond standard, color-based vegetation indices. We found that engaging citizen science volunteers resulted in useful science knowledge in three ways: first, volunteers were able to detect some, but not all, reproductive phenology events, connecting landscape-level measures with field-based measures. Second, volunteers successfully demarcated individual trees in landscape imagery, facilitating scaling of vegetation indices from organism to ecosystem. And third, volunteers’ data were used to validate phenology transition dates calculated from vegetation indices and to identify potential improvements to existing algorithms to enable better biological interpretation. As a result, the use of citizen science in combination with near-surface remote sensing of phenology can be used to link ground-based phenology observations to satellite sensor data for scaling and validation. Well-designed citizen science projects targeting improved data processing and validation of remote sensing imagery hold promise for providing the data needed to address grand challenges in environmental science and Earth observation.

This study investigated the moderating effect of gender on the causal relationships between different school play activities (pretend and non-pretend play) and social competence in peer interactions among a sample of Hong Kong children. Participants were 60 Hong Kong preschoolers (mean age = 5.44, 36.67 % female). Children with matched home pretend play time period were randomly assigned to pretend or non-pretend play groups to take part in pretend or non-pretend play activities respectively in the 1-month kindergarten play training. Children’s pre- and post-training social competences were assessed by their teachers. Results revealed a trend that girls who participated in school pretend play tended to be less disruptive during peer interactions after the training than those who participated in non-pretend play, while boys were similarly benefited from the two play activities. The implications for play-related research and children’s social competence development are discussed.