1.5 {\mu}m Epitaxially Regrown Photonic Crystal Surface Emitting Laser Diode

We present an InP-based epitaxially regrown photonic crystal surface emitting laser diode, lasing in quasi- CW conditions at 1523nm.Comment: 4 pages, 5 figures, journal submission for revie

Large-area 2D selective area growth for photonic crystal surface emitting lasers

We report an investigation into large-area selective area growth of InGaAs/GaAs quantum wells by metalorganic vapour phase epitaxy. The emission wavelength tuning range, growth enhancement, and uniformity of material deposited within square masked regions with central square growth windows with widths in the range of 100–300 μm are studied. Micro-photoluminescence measurements at the centre point of each of the growth windows reveals a total wavelength tuning range of 86 nm across all samples, with a typical tuning range of 30 nm for a given window width, dependent upon dielectric mask width. The thickness enhancement in each of features, as determined by white-light interferometric profiling, indicates that centre point growth rate enhancements of between 1.19 and 2.23× are achieved with respect to the nominal epitaxial structure. By comparing the observed emission wavelengths with those simulated using the enhanced quantum well thicknesses, a range of indium concentrations between 12 and 17 % is calculated for the material at the centre of each feature. Two-dimensional analysis of selected features reveals that areas with uniform emission wavelength up to 100 × 100 μm2 in size can be achieved for the mask patterns used, indicating suitability for future applications in the fabrication of monolithically integrated multi-wavelength photonic crystal surface emitting laser arrays

Epitaxially regrown quantum dot photonic crystal surface emitting lasers

Quantum dot-based epitaxially regrown photonic crystal surface emitting lasers are demonstrated at room temperature. The GaAs-based devices, which are monolithically integrated on the same wafer, exhibit ground state lasing at ∼1230 nm and excited state lasing at ∼1140 nm with threshold current densities of 0.69 and 1.05 kA/cm2, respectively

Resonator embedded photonic crystal surface emitting lasers

The finite size of 2D photonic crystals results in them being a lossy resonator, with the normally emitting modes of conventional photonic crystal surface emitting lasers (PCSELs) differing in photon lifetime via their different radiative rates, and the different in-plane losses of higher order spatial modes. As a consequence, the fundamental spatial mode (lowest in-plane loss) with lowest out-of-plane scattering is the primary lasing mode. For electrically driven PCSELs, as current is increased, incomplete gain clamping results in additional spatial (and spectral) modes leading to a reduction in beam quality. A number of approaches have been discussed to enhance the area (power) scalability of epitaxy regrown PCSELs through careful design of the photonic crystal atom1–3. None of these approaches tackle the inflexibility in being unable to independently modify the photon lifetime of the different modes at the Γ2 point. As a method to introduce design flexibility, resonator embedded photonic crystal surface emitting lasers (REPCSELs) are introduced. This device, combining comparatively low coupling strength photonic crystal structures along with perimeter mirrors, allow a Fabry–Pérot resonance effect to be realised that provides wavelength selective modification of the photon lifetime. We show that surface emission of different surface emitting modes may be selectively enhanced, effectively changing the character of the modes at the Γ2 point. This is a consequence of the selective modification of in-plane loss for particular modes, and is dependent upon the alignment of the photonic crystal (PhC) band-structure and distributed Bragg reflectors’ (DBRs) reflectance spectrum. These findings offer new avenues in surface emitting laser diode engineering. The use of DBRs to reduce the lateral size of a PCSEL opens the route to small, low threshold current (Ith), high output efficiency epitaxy regrown PCSELs for high-speed communication and power sensitive sensing applications

Dynamic changes in the epigenomic landscape regulate human organogenesis and link to developmental disorders

From Springer Nature via Jisc Publications RouterHistory: received 2019-10-04, accepted 2020-06-18, registration 2020-06-24, pub-electronic 2020-08-06, online 2020-08-06, collection 2020-12Publication status: PublishedFunder: RCUK | Medical Research Council (MRC); doi: https://doi.org/10.13039/501100000265; Grant(s): CRTF, PhD studentship, MR/J003352/1, MR/L009986/1, MR/L009986/1, MR/S036121/1, MR/000638/1Funder: Academy of Medical Sciences; doi: https://doi.org/10.13039/501100000691; Grant(s): Lecturer starter grantFunder: Wellcome Trust (Wellcome); doi: https://doi.org/10.13039/100004440; Grant(s): 088566, 097820, 105610Abstract: How the genome activates or silences transcriptional programmes governs organ formation. Little is known in human embryos undermining our ability to benchmark the fidelity of stem cell differentiation or cell programming, or interpret the pathogenicity of noncoding variation. Here, we study histone modifications across thirteen tissues during human organogenesis. We integrate the data with transcription to build an overview of how the human genome differentially regulates alternative organ fates including by repression. Promoters from nearly 20,000 genes partition into discrete states. Key developmental gene sets are actively repressed outside of the appropriate organ without obvious bivalency. Candidate enhancers, functional in zebrafish, allow imputation of tissue-specific and shared patterns of transcription factor binding. Overlaying more than 700 noncoding mutations from patients with developmental disorders allows correlation to unanticipated target genes. Taken together, the data provide a comprehensive genomic framework for investigating normal and abnormal human development

Increasing frailty is associated with higher prevalence and reduced recognition of delirium in older hospitalised inpatients: results of a multi-centre study

Purpose: Delirium is a neuropsychiatric disorder delineated by an acute change in cognition, attention, and consciousness. It is common, particularly in older adults, but poorly recognised. Frailty is the accumulation of deficits conferring an increased risk of adverse outcomes. We set out to determine how severity of frailty, as measured using the CFS, affected delirium rates, and recognition in hospitalised older people in the United Kingdom. Methods: Adults over 65 years were included in an observational multi-centre audit across UK hospitals, two prospective rounds, and one retrospective note review. Clinical Frailty Scale (CFS), delirium status, and 30-day outcomes were recorded. Results: The overall prevalence of delirium was 16.3% (483). Patients with delirium were more frail than patients without delirium (median CFS 6 vs 4). The risk of delirium was greater with increasing frailty [OR 2.9 (1.8–4.6) in CFS 4 vs 1–3; OR 12.4 (6.2–24.5) in CFS 8 vs 1–3]. Higher CFS was associated with reduced recognition of delirium (OR of 0.7 (0.3–1.9) in CFS 4 compared to 0.2 (0.1–0.7) in CFS 8). These risks were both independent of age and dementia. Conclusion: We have demonstrated an incremental increase in risk of delirium with increasing frailty. This has important clinical implications, suggesting that frailty may provide a more nuanced measure of vulnerability to delirium and poor outcomes. However, the most frail patients are least likely to have their delirium diagnosed and there is a significant lack of research into the underlying pathophysiology of both of these common geriatric syndromes

Delimiting tropical mountain ecoregions for conservation

Ecological regions aggregate habitats with similar biophysical characteristics within well-defined boundaries, providing spatially consistent platforms for monitoring, managing and forecasting the health of interrelated ecosystems. A major obstacle to the implementation of this approach is imprecise and inconsistent boundary placement. For globally important mountain regions such as the Eastern Arc (Tanzania and Kenya), where qualitative definitions of biophysical affinity are well established, rule-based methods for landform classification provide a straightforward solution to ambiguities in region extent. The method presented in this paper encompasses the majority of both contemporary and estimated preclearance forest cover within strict topographical limits. Many of the species here tentatively considered 'near-endemic' could be reclassified as strictly endemic according to the derived boundaries. LandScan and census data show population density inside the ecoregion to be higher than in rural lowlands, and lowland settlement to be most probable within 30 km. This definition should help to align landscape scale conservation strategies in the Eastern Arc and promote new research in areas of predicted, but as yet undocumented, biological importance. Similar methods could work well in other regions where mountain extent is poorly resolved. Spatial data accompany the online version of this article

Kinetic influences on void formation in epitaxially regrown GaAs-based PCSELs

We report an investigation into the formation of crystallographic voids during the metalorganic vapour phase epitaxial regrowth of GaAs photonic crystal structures. We employ a combination of cross-sectional scanning electron microscopy and scanning transmission electron microscopy to study structures regrown with AlAs, AlGaAs and GaAs. The change in regrowth material allows the effect of adatom diffusion kinetics on the void structure to be assessed. Whilst complete grating infill is observed for GaAs, void formation is promoted for Al-containing materials, with void size increasing with Al mole fraction, in line with reduced adatom mobility. In the case of both AlAs and AlGaAs-regrown structures, a degree of asymmetry is observed in the shape of the voids within the plane of the photonic crystal. These differences are attributed to variations in group-III adatom surface mobility and the polarities of high-index crystal planes along orthogonal crystal directions. Two growth regimes of stable and dynamic faceting are observed in cross-sections containing crystal planes with A- and B-type polarities, respectively