Coprocessed heterogeneous near-infrared lasers on thin-film lithium niobate.

Thin-film lithium niobate (TFLN) is an attractive platform for photonic applications on account of its wide bandgap, its large electro-optic coefficient, and its large nonlinearity. Since these characteristics are used in systems that require a coherent light source, size, weight, power, and cost can be reduced and reliability enhanced by combining TFLN processing and heterogeneous laser fabrication. Here, we report the fabrication of laser devices on a TFLN wafer and also the coprocessing of five different GaAs-based III-V epitaxial structures, including InGaAs quantum wells and InAs quantum dots. Lasing is observed at wavelengths near 930, 1030, and 1180 nm, which, if frequency-doubled using TFLN, would produce blue, green, and orange visible light. A single-sided power over 25 mW is measured with an integrating sphere.

Prolonged Impairment of Short-Chain Fatty Acid and L-Isoleucine Biosynthesis in Gut Microbiome in Patients With COVID-19.

BACKGROUND AND AIMS: Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with altered gut microbiota composition. Phylogenetic groups of gut bacteria involved in the metabolism of short chain fatty acids (SCFAs) were depleted in SARS-CoV-2-infected patients. We aimed to characterize a functional profile of the gut microbiome in patients with COVID-19 before and after disease resolution. METHODS: We performed shotgun metagenomic sequencing on fecal samples from 66 antibiotics-naïve patients with COVID-19 and 70 non-COVID-19 controls. Serial fecal samples were collected (at up to 6 times points) during hospitalization and beyond 1 month after discharge. We assessed gut microbial pathways in association with disease severity and blood inflammatory markers. We also determined changes of microbial functions in fecal samples before and after disease resolution and validated these functions using targeted analysis of fecal metabolites. RESULTS: Compared with non-COVID-19 controls, patients with COVID-19 with severe/critical illness showed significant alterations in gut microbiome functionality (P < .001), characterized by impaired capacity of gut microbiome for SCFA and L-isoleucine biosynthesis and enhanced capacity for urea production. Impaired SCFA and L-isoleucine biosynthesis in gut microbiome persisted beyond 30 days after recovery in patients with COVID-19. Targeted analysis of fecal metabolites showed significantly lower fecal concentrations of SCFAs and L-isoleucine in patients with COVID-19 before and after disease resolution. Lack of SCFA and L-isoleucine biosynthesis significantly correlated with disease severity and increased plasma concentrations of CXCL-10, NT- proB-type natriuretic peptide, and C-reactive protein (all P < .05). CONCLUSIONS: Gut microbiome of patients with COVID-19 displayed impaired capacity for SCFA and L-isoleucine biosynthesis that persisted even after disease resolution. These 2 microbial functions correlated with host immune response underscoring the importance of gut microbial functions in SARS-CoV-2 infection pathogenesis and outcome.

Heterogeneous integration of a III-V quantum dot laser on high thermal conductivity silicon carbide.

Heat accumulation prevents semiconductor lasers from operating at their full potential. This can be addressed through heterogeneous integration of a III-V laser stack onto non-native substrate materials with high thermal conductivity. Here, we demonstrate III-V quantum dot lasers heterogeneously integrated on silicon carbide (SiC) substrates with high temperature stability. A large T0 of 221 K with a relatively temperature-insensitive operation occurs near room temperature, while lasing is sustained up to 105°C. The SiC platform presents a unique and ideal candidate for realizing monolithic integration of optoelectronics, quantum, and nonlinear photonics.

Dye-Encapsulated Metal-Organic Frameworks for the Multi-Parameter Detection of Temperature.

Temperature is an important physical parameter and plays a significant role in scientific research, the detection of which cannot be too crucial to study. In order to reduce the interference of the external environment on the detection of temperature and improve the accuracy of the detection results, a multi-parameter detection method using several optical signals was proposed. Here, a novel porous metal-organic framework (MOF), Zn-CYMPN, was synthesized and structurally characterized. Then, fluorescent organic dyes, either DPEE or DPEM, were encapsulated into the pores of Zn-CYMPN independently. The successful synthesis of the composites Zn-CYMPN⊃DPEE or Zn-CYMPN⊃DPEM could easily introduce other fluorescent centers into the original material and made it more convenient to realize multi-parameter temperature detection. More specifically, when the temperature changed, the maximum fluorescent emission wavelength (W) and the maximum optical intensity (I) of the Zn-CYMPN⊃DPEE/DPEM both showed good linear responses with temperature over a wide range, indicating that the composites were highly sensitive thermometers with multi-parameter temperature readouts. In addition, the quantum efficiency and thermal stability of the organic dyes, which bother every researcher, were improved as well.

Underdevelopment of the gut microbiota and bacteria species as non-invasive markers of prediction in children with autism spectrum disorder.

OBJECTIVE: The gut microbiota has been suggested to play a role in autism spectrum disorder (ASD). We postulate that children with ASD harbour an altered developmental profile of the gut microbiota distinct from that of typically developing (TD) children. Here, we aimed to characterise compositional and functional alterations in gut microbiome in association with age in children with ASD and to identify novel faecal bacterial markers for predicting ASD. DESIGN: We performed deep metagenomic sequencing in faecal samples of 146 Chinese children (72 ASD and 74 TD children). We compared gut microbial composition and functions between children with ASD and TD children. Candidate bacteria markers were identified and validated by metagenomic analysis. Gut microbiota development in relation to chronological age was assessed using random forest model. RESULTS: ASD and chronological age had the most significant and largest impacts on children's faecal microbiome while diet showed no correlation. Children with ASD had significant alterations in faecal microbiome composition compared with TD children characterised by increased bacterial richness (p=0.021) and altered microbiome composition (p<0.05). Five bacterial species were identified to distinguish gut microbes in ASD and TD children, with areas under the receiver operating curve (AUC) of 82.6% and 76.2% in the discovery cohort and validation cohort, respectively. Multiple neurotransmitter biosynthesis related pathways in the gut microbiome were depleted in children with ASD compared with TD children (p<0.05). Developing dynamics of growth-associated gut bacteria (age-discriminatory species) seen in TD children were lost in children with ASD across the early-life age spectrum. CONCLUSIONS: Gut microbiome in Chinese children with ASD was altered in composition, ecological network and functionality compared with TD children. We identified novel bacterial markers for prediction of ASD and demonstrated persistent underdevelopment of the gut microbiota in children with ASD which lagged behind their respective age-matched peers.

Population-Level Configurations of Gut Mycobiome Across 6 Ethnicities in Urban and Rural China.

BACKGROUND & AIMS: Beyond bacteria, the human gastrointestinal tract is host to a vast diversity of fungi, collectively known as the gut mycobiome. Little is known of the impact of geography, ethnicity, and urbanization on the gut mycobiome at a large population level. We aim to delineate the variation of human gut mycobiome and its association with host factors, environmental factors, and diets. METHODS: Using shotgun metagenomic sequencing, we profiled and compared the fecal mycobiome of 942 healthy individuals across different geographic regions in China (Hong Kong and Yunnan), spanning 6 ethnicities: Han, Zang, Bai, Hani, Dai, and Miao (including both urban and rural residents of each ethnicity). In parallel to fecal sampling, we collected participant metadata (environmental exposure, bowel habits, anthropometrics, and medication), diet, and clinical blood measurement results (a total of 118 variables) and investigated their impact on the gut mycobiome variation in humans. RESULTS: The human gut mycobiome was highly variable across populations. Urbanization-related factors had the strongest impact on gut mycobiome variation, followed by geography, dietary habit, and ethnicity. The Hong Kong population (highly urbanized) had a significantly lower fungal richness compared with Yunnan population. Saccharomyces cerevisiae was highly enriched in urban compared with rural populations and showed significant inverse correlations with liver pathology-associated blood parameters, including aspartate transaminase, alanine transaminase, gamma-glutamyltransferase, and direct bilirubin. Candida dubliniensis, which was decreased in urban relative to rural populations, showed correlations with host metabolism-related parameters in blood, including a positive correlation with fasting high-density lipoprotein cholesterol levels and a negative correlation with fasting glucose levels. The fungal-blood parameter correlations were highly geography- and ethnicity-specific. Food choices had differential influences on gut mycobiome and bacterial microbiome, where taxa from the same genus tended to be coregulated by food and thereby cobloom. Ethnicity-specific fungal signatures were associated with distinct habitual foods in each ethnic group. CONCLUSIONS: Our data highlight, for the first time to our knowledge, that geography, urbanization, ethnicity, and habitual diet play an important role in shaping the gut mycobiome composition. Gut fungal configurations in combination with population characteristics (such as residing region, ethnicity, diet, lifestyle) influence host metabolism and health.

Alterations in Gut Microbiota of Patients With COVID-19 During Time of Hospitalization.

BACKGROUND & AIMS: Although severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infects gastrointestinal tissues, little is known about the roles of gut commensal microbes in susceptibility to and severity of infection. We investigated changes in fecal microbiomes of patients with SARS-CoV-2 infection during hospitalization and associations with severity and fecal shedding of virus. METHODS: We performed shotgun metagenomic sequencing analyses of fecal samples from 15 patients with Coronavirus Disease 2019 (COVID-19) in Hong Kong, from February 5 through March 17, 2020. Fecal samples were collected 2 or 3 times per week from time of hospitalization until discharge; disease was categorized as mild (no radiographic evidence of pneumonia), moderate (pneumonia was present), severe (respiratory rate ≥30/min, or oxygen saturation ≤93% when breathing ambient air), or critical (respiratory failure requiring mechanical ventilation, shock, or organ failure requiring intensive care). We compared microbiome data with those from 6 subjects with community-acquired pneumonia and 15 healthy individuals (controls). We assessed gut microbiome profiles in association with disease severity and changes in fecal shedding of SARS-CoV-2. RESULTS: Patients with COVID-19 had significant alterations in fecal microbiomes compared with controls, characterized by enrichment of opportunistic pathogens and depletion of beneficial commensals, at time of hospitalization and at all timepoints during hospitalization. Depleted symbionts and gut dysbiosis persisted even after clearance of SARS-CoV-2 (determined from throat swabs) and resolution of respiratory symptoms. The baseline abundance of Coprobacillus, Clostridium ramosum, and Clostridium hathewayi correlated with COVID-19 severity; there was an inverse correlation between abundance of Faecalibacterium prausnitzii (an anti-inflammatory bacterium) and disease severity. Over the course of hospitalization, Bacteroides dorei, Bacteroides thetaiotaomicron, Bacteroides massiliensis, and Bacteroides ovatus, which downregulate expression of angiotensin-converting enzyme 2 (ACE2) in murine gut, correlated inversely with SARS-CoV-2 load in fecal samples from patients. CONCLUSIONS: In a pilot study of 15 patients with COVID-19, we found persistent alterations in the fecal microbiome during the time of hospitalization, compared with controls. Fecal microbiota alterations were associated with fecal levels of SARS-CoV-2 and COVID-19 severity. Strategies to alter the intestinal microbiota might reduce disease severity.

Series of Luminescent Lanthanide MOFs with Regular SHG Performance.

Second-harmonic generation (SHG) is a kind of nonlinear optical phenomenon which has been widely used in optical devices, and factors influencing its signal are very complex. Here, taking advantage of excellent structural designability and overcoming the limitations of various coordinations of lanthanide metals, for the first time a series of lanthanide metal-organic frameworks (Ln-MOFs) with one particular ligand were synthesized and structurally characterized to study the interference of the SHG signal. The optical performance including single-photon fluorescence and SHG was collected and analyzed. It is found that all 13 kinds of Ln-MOFs can be divided into 2 crystal configurations by their individual space groups and Ln-MOFs with coordinated metal atoms from La to Tb possessing the noncentrosymmetric C2 space group exhibit the SHG property, the intensity of which depends on the type of metal atoms, the pumping wavelength, and the size of the single-crystal particles. This is the first time that the relationship between the nonlinear optical properties and the structure, metal atoms, pumping wavelength, crystal size of the whole series of Ln-MOFs is studied systematically, providing a lot of interesting results and enriching the research scope of nonlinear optics and materials science.

Highly Stable Lanthanide Metal-Organic Framework as an Internal Calibrated Luminescent Sensor for Glutamic Acid, a Neuropathy Biomarker.

Glutamic acid (Glu) is the most abundant excitatory neurotransmitter in the central nervous system, and an elevated level of Glu may indicate some neuropathological diseases. Herein, three isomorphic microporous lanthanide metal-organic frameworks (MOFs) [(CH3)2NH2]2[Ln6(µ3-OH)8(BDC-OH)6(H2O)6]·(solv)x (ZJU-168; ZJU = Zhejiang University, H2BDC-OH = 2-hydroxyterephthalic acid, Ln = Eu, Tb, Gd) were designed for the detection of Glu. ZJU-168(Eu) and ZJU-168(Tb) suspensions simultaneously produce the characteristic emission bands of both lanthanide ions and ligands. When ZJU-168(Eu) and ZJU-168(Tb) suspensions exposed to Glu, the fluorescence intensity of ligands increases while the emission of lanthanide ions is almost unchanged. By utilizing the emission of ligands as the detected signal and the emission of lanthanide ions as the internal reference, an internal calibrated fluorescence sensor for Glu was obtained. There is a good linear relationship between fluorescence intensity ratio and Glu concentration in a wide range with the detection limit of 3.6 µM for ZJU-168(Tb) and 4.3 µM for ZJU-168(Eu). Major compounds present in blood plasma have no interference for the detection of Glu. Furthermore, a convenient analytical device based on a one-to-two logic gate was constructed for monitoring Glu. These establish ZJU-168(Tb) as a potential turn-on, ratiometric, and colorimetric fluorescent sensor for practical detection of Glu.

Directly modulated 1.3 µm quantum dot lasers epitaxially grown on silicon.

We report the first demonstration of direct modulation of InAs/GaAs quantum dot (QD) lasers grown on on-axis (001) Si substrate. A low threading dislocation density GaAs buffer layer enables us to grow a high quality 5-layered QD active region on on-axis Si substrate. The active layer has p-modulation doped GaAs barrier layers with a hole concentration of 5 × 1017 cm-3to suppress gain saturation. Small-signal measurement on a 3 × 580 µm2 Fabry-Perot laser showed a 3dB bandwidth of 6.5 GHz at a bias current of 116 mA. A 12.5 Gbit/s non-return-to-zero signal modulation was achieved by directly probing the chip. Open eyes with an extinction ration of 3.3dB was observed at room temperature. The bit-error-rate (BER) curve showed no error-floor up to BER of 1 × 10-13. 12 km single-mode fiber transmission experiments using the QD laser on Si showed a low power penalty of 1 dB at 5Gbit/s. These results demonstrate the potential for QD lasers epitaxially grown on Si to be used as a low-cost light source for optical communication systems.

Parametric study of high-performance 1.55 µm InAs quantum dot microdisk lasers on Si.

In this paper, we present a parametric study of high performance microdisk lasers at 1.55 µm telecom wavelength, monolithically grown on on-axis (001) Si substrates incorporating quantum dots (QDs) as gain elements. In the optimized structure, seven layers of QDs were adopted to provide a high gain as well as a suppressed inhomogeneous broadening. The same laser structure employing quantum wells (QWs) on Si was concurrently evaluated, showing a higher threshold and more dispersive quantum efficiency than the QDs. Finally, a statistical comparison of these Si-based QD microdisk lasers with those grown on InP native substrates was conducted, revealing somewhat higher thresholds but of the same order. The monolithically grown QD microlasers on Si also demonstrated excellent temperature stability, with a record high characteristic temperature of 277 K. This work thus offers helpful insight towards the optimization of reliable Si-based QD lasers at 1550 nm.

O-band electrically injected quantum dot micro-ring lasers on on-axis (001) GaP/Si and V-groove Si.

We report statistical comparisons of lasing characteristics in InAs quantum dot (QD) micro-rings directly grown on on-axis (001) GaP/Si and V-groove (001) Si substrates. CW thresholds as low as 3 mA and high temperature operation exceeding 80 °C were simultaneously achieved on the GaP/Si template template with an outer-ring radius of 50 µm and a ring width of 4 µm, while a sub-milliamp threshold of 0.6 mA was demonstrated on the V-groove Si template with a smaller cavity size of 5-µm outer-ring radius and 3-µm ring width. Evaluations were also made with devices fabricated simultaneously on native GaAs substrates over a significant sampling analysis. The overall assessment spotlights compelling insights in exploring the optimum epitaxial scheme for low-threshold lasing on industry standard Si substrates.

Electrically pumped continuous wave quantum dot lasers epitaxially grown on patterned, on-axis (001) Si.

High performance III-V lasers at datacom and telecom wavelengths on on-axis (001) Si are needed for scalable datacenter interconnect technologies. We demonstrate electrically injected quantum dot lasers grown on on-axis (001) Si patterned with {111} v-grooves lying in the [110] direction. No additional Ge buffers or substrate miscut was used. The active region consists of five InAs/InGaAs dot-in-a-well layers. We achieve continuous wave lasing with thresholds as low as 36 mA and operation up to 80°C.

Monolithically integrated InAs/InGaAs quantum dot photodetectors on silicon substrates.

We report InAs/InGaAs quantum dot (QD) waveguide photodetectors (PD) monolithically grown on silicon substrates. A high-crystalline quality GaAs-on-Si template was achieved by aspect ratio trapping together with the combined effects of cyclic thermal annealing and strain-balancing layer stacks. An ultra-low dark current of 0.8 nA and an internal responsivity of 0.9 A/W were measured in the O band. We also report, to the best of our knowledge, the first characterization of high-speed performance and the first demonstration of the on-chip photodetection for this QD-on-silicon system. The monolithically integrated waveguide PD shares the same platform as the previously demonstrated micro-ring lasers and can thus be integrated with laser sources for power monitors or amplifiers for pre-amplified receivers.

1.55 µm band low-threshold, continuous-wave lasing from InAs/InAlGaAs quantum dot microdisks.

InAs/InAlGaAs quantum dot active layers within microcavity resonators offer the potential of ultra-low-threshold lasing in the 1.55 µm telecom window. Here, we demonstrate the first quantum dot microdisk laser with single-mode emission around 1.55 µm under continuous-wave optical pumping up to 170 K. The extracted threshold is as low as 32 µW at 77 K. This result lays the foundation of an alternative to quantum-well microlasers for low-threshold and highly compact monolithically integratable light emitting sources in fiber communication.

1.3-µm InAs quantum-dot micro-disk lasers on V-groove patterned and unpatterned (001) silicon.

We report comparison of lasing dynamics in InAs quantum dot (QD) micro-disk lasers (MDLs) monolithically grown on V-groove patterned and planar Si (001) substrates. TEM characterizations reveal abrupt interfaces and reduced threading dislocations in the QD active regions when using the GaAs-on-V-grooved-Si template. The improved crystalline quality translates into lower threshold power in the optically pumped continuous-wave MDLs. Concurrent evaluations were also made with devices fabricated simultaneously on lattice-matched GaAs substrates. Lasing behaviors from 10 K up to room temperature have been studied systematically. The analyses spotlight insights into the optimal epitaxial scheme to achieve low-threshold lasing in telecommunication wavelengths on exact Si (001) substrates.

Optically pumped 1.3 µm room-temperature InAs quantum-dot micro-disk lasers directly grown on (001) silicon.

Direct integration of high-performance laser diodes on silicon will dramatically transform the world of photonics, expediting the progress toward low-cost and compact photonic integrated circuits (PICs) on the mainstream silicon platform. Here, we report, to the best of our knowledge, the first 1.3 µm room-temperature continuous-wave InAs quantum-dot micro-disk lasers epitaxially grown on industrial-compatible Si (001) substrates without offcut. The lasing threshold is as low as hundreds of microwatts, similar to the thresholds of identical lasers grown on a GaAs substrate. The heteroepitaxial structure employed here does not require the use of an absorptive germanium buffer and/or dislocation filter layers, both of which impede the efficient coupling of light from the laser active regions to silicon waveguides. This allows for full compatibility with the extensive silicon-on-insulator (SOI) technology. The large-area virtual GaAs (on Si) substrates can be directly adopted in various mature in-plane laser configurations, both optically and electrically. Thus, this demonstration represents a major advancement toward the commercial success of fully integrated silicon photonics.

Light People: Prof. Kei May Lau, newly elected US NAE member in Hong Kong, talks about future of photonics and women in science.

EDITORIAL: Photonics technology remains a driving force in today's scientific landscape, marked by continuous innovation and cross-disciplinary relevance. In an enlighting conversation with Light: Science & Applications, Prof. Kei May Lau, a pioneer in photonics research, shares her deep insights on the evolution of technologies of LEDs, lasers, challenges of hetero-epitaxy, and the future of micro-LEDs and quantum dot lasers. Recently honored as a member of the US National Academy of Engineering (NAE) for her significant contributions to photonics and electronics using III-V semiconductors on silicon, Prof. Lau stands out as the sole Hong Kong scholar inducted into the NAE this year, joining 114 new and 21 international members. In this exclusive Light People interview, Prof. Lau shares her journey as a pioneering woman in engineering, her commitment to mentorship and academia, and her perspective on advancing female representation in science. The summary provided is distilled from Prof. Lau's thoughtful responses during the interview. For a deeper exploration of Prof. Lau's experiences and advice, the full interview is available in the Supplementary material.

Gradual degradation in InAs quantum dot lasers on Si and GaAs.

Reliable quantum dot lasers on silicon are a key remaining challenge to successful integrated silicon photonics. In this work, quantum dot (QD) lasers on silicon with and without misfit dislocation trapping layers are aged for 12 000 hours and are compared to QD lasers on native GaAs aged for 8400 hours. The non-trapping-layer (TL) laser on silicon degrades heavily during this time, but much more modest gradual degradation is observed for the other two devices. Electroluminescence imaging reveals relatively uniform gradual dimming for the aged TL laser on silicon. At the same time, we find nanoscale dislocation loop defects throughout the quantum dot-based active region of all three aged lasers via electron microscopy. The Burgers vector of these loops is consistent with . We suggest that the primary source of degradation, however, is the generation and migration of point defects that substantially enhance non-radiative recombination in the active region, the visible symptom of which is the formation of dislocation loops. To prevent this, we propose that laser fabrication should be switched from deeply etched to shallow etch ridges where the active region remains intact near the mesa. Additionally, post-growth annealing and altered growth conditions in the active region should be explored to minimize the grown-in point defect density.

Alterations in fecal virome and bacteriome virome interplay in children with autism spectrum disorder.

Emerging evidence suggests autism spectrum disorder (ASD) is associated with altered gut bacteria. However, less is known about the gut viral community and its role in shaping microbiota in neurodevelopmental disorders. Herein, we perform a metagenomic analysis of gut-DNA viruses in 60 children with ASD and 64 age- and gender-matched typically developing children to investigate the effect of the gut virome on host bacteria in children with ASD. ASD is associated with altered gut virome composition accompanied by the enrichment of Clostridium phage, Bacillus phage, and Enterobacteria phage. These ASD-enriched phages are largely associated with disrupted viral ecology in ASD. Importantly, changes in the interplay between the gut bacteriome and virome seen in ASD may influence the encoding capacity of microbial pathways for neuroactive metabolite biosynthesis. These findings suggest an impaired bacteriome-virome ecology in ASD, which sheds light on the importance of bacteriophages in pathogenesis and the development of microbial therapeutics in ASD.