Narrow-line coherently combined tapered laser diodes in a Talbot external cavity with a volume Bragg grating

We present the phase locking of an array of index-guided tapered laser diodes. An external cavity based on the self-imaging Talbot effect has been built. A volume Bragg grating is used as the output coupler to stabilize and narrow the spectrum at 976 nm. A power of 1.7 W is achieved in the in-phase single main lobe mode with a high visibility. We have checked that each emitter is locked to the Bragg wavelength with a 100 pm spectrum linewidth. The experimental results compare well with numerical simulations performed with two-dimensional wide-angle finite difference beam propagation method

Ultra-compact and ultra-broadband hybrid plasmonic-photonic vertical coupler with high coupling efficiency, directivity, and polarisation extinction ratio

An ultra-compact, ultra-broadband vertical coupler for dense photonic integrated circuits is reported with a 1.07×0.62μm2 wavelength-scale footprint. This hybrid plasmonic-photonic coupler uses a unique two-plane plasmonic nanoantenna array on a silicon-on-insulator waveguide. The in- and out-of-plane interference of the multipole moments and dual-feed nanoantennas results in efficient, unidirectional coupling. Finite-element simulations show that, for a 0.8μm diameter Gaussian beam, the maximum coupling efficiency (CE) is −3.4dB across the telecommunication C-, L- and U-bands with a 3-dB bandwidth of 230nm. The CE is>9dB higher than recently reported ultra-compact plasmonic couplers. The maximum directivity and polarisation extinction ratio across the C- to U-bands are 9.2 and 24.1dB, respectively. Finally, as an out-coupler, it has a vertical directivity of >8.5dB, enabling its use for vertical optical interconnects between two vertically separated circuits

Volume Bragg grating external cavities for the passive phase locking of high-brightness diode laser arrays: theoretical and experimental study

We describe the theoretical modeling of the external-cavity operation of a phase-locked array of diode lasers in two configurations, the self-imaging cavity based on the Talbot effect and the angular-filtering cavity. Complex filtering functions, such as the transmission or reflection of a volume Bragg grating (VBG), may be introduced in the external-cavity description. Experiments with high-brightness diode laser arrays were also conducted. The experimental results are carefully analyzed with regard to the numerical simulations, and the beneficial effect of the spectral selectivity of VBGs is demonstrated. (C) 2011 Optical Society of Americ

From the frontline: strengthening surveillance and response capacities of the rural workforce in the Asia-Pacific region. How can grass-roots implementation research help?

Health systems in the Asia-Pacific region are poorly prepared for pandemic threats, particularly in rural/provincial areas. Yet future emerging infectious diseases are highly likely to emerge in these rural/provincial areas, due to high levels of contact between animals and humans (domestically and through agricultural activities), over-stretched and under-resourced health systems, notably within the health workforce, and a diverse array of socio-cultural determinants of health. In order to optimally implement health security measures at the frontline of health services where the people are served, it is vital to build capacity at the local district and facility level to adapt national and global guidelines to local contexts, including health systems, and community and socio-cultural realities. During 2017/18 James Cook University (JCU) facilitated an implementation research training program (funded by Australian Department of Foreign Affairs and Trade) for rural/provincial and regional health and biosecurity workers and managers from Fiji, Indonesia, Papua New Guinea (PNG), Solomon Islands and Timor-Leste. This training was designed so frontline health workers could learn research in their workplace, with no funding other than workplace resources, on topics relevant to health security in their local setting. The program, based upon the WHO-TDR Structured Operational Research and Training IniTiative (SORT-IT) consists of three blocks of teaching and a small, workplace-based research project. Over 50 projects by health workers including surveillance staff, laboratory managers, disease control officers, and border security staff included: analysis and mapping of surveillance data, infection control, IHR readiness, prevention/response and outbreak investigation. Policy briefs written by participants have informed local, provincial and national health managers, policymakers and development partners and provided on-the-ground recommendations for improved practice and training. These policy briefs reflected the socio-cultural, health system and disease-specific realities of each context. The information in the policy briefs can be used collectively to assess and strengthen health workforce capacity in rural/provincial areas. The capacity to use robust but simple research tools for formative and evaluative purposes provides sustainable capacity in the health system, particularly the rural health workforce. This capacity improves responses to infectious diseases threats and builds resilience into fragile health systems

Factors influencing brightness and beam quality of conventional and distributed Bragg reflector tapered laser diodes in absence of self-heating

In this study, the authors examine some of the factors affecting the brightness and the beam quality of high-power tapered lasers. The large volume resonators required to achieve a high-power, high-brightness operation make the beam quality sensitive to carrier lensing and a multimode operation. These cause bleaching of the regions outside the ridge waveguide. The beam quality in the conventional and the distributed Bragg reflector tapered lasers is examined in the absence of the self-heating effects to investigate the effect of the carrier lensing effects. The influence of the front facet reflectivity and the taper angle on the beam quality is investigated. The beam quality was found to degrade with an increase in the front facet reflectivity and for the larger taper angles in the conventional tapered lasers, especially at low ridge waveguide currents. Finally, the performance of the conventional tapered lasers employing a beamspoiler was assessed. The beam quality was found to be comparable with that achieved in the DBR tapered lasers

TEM assessment of As-doped GaN epitaxial layers grown on sapphire

TEM investigations of As-doped GaN layers grown by plasma-assisted molecular beam epitaxy on sapphire substrates reveal the presence of extensive regions of cubic stacking disorder within the hexagonal GaN matrix. Electron energy loss spectroscopy suggests the localization of As within grains immediately below domains containing stacking disorder, and additionally at the layer surface. This suggests that localised strain plays a role in the formation mechanism of the stacking faults