Photonic Integrated Semiconductor Optical Amplifier Switch Circuits

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A Precise Radial Velocity Search for Giant Planets orbiting polluted White Dwarfs

The 21st European Workshop on White Dwarfs was held in Austin, TX from July 23rd to 27th of 2018We present a feasibility study for extending the well-known radial velocity technique to search for planetary companions around white dwarfs. Typically, the spectra of white dwarfs contain only a few pressure-broadened hydrogen and/or helium lines, which do not permit to measure the radial velocity with sufficient precision to detect planets. A small subset of white dwarfs do also show sharp metal lines, presumably from infalling circumstellar material. We suggest to search these “polluted” white dwarfs for possible giant planets using the Doppler reflex motion technique. We show here first results to estimate the Doppler information content from simulated spectra of the metal-polluted WD GD 362.Astronom

Loss mechanisms in dielectric optical micro-bends

Micro-bend waveguides are an important enabler for the interconnection of photonic components in large-scale integrated circuits. There is however limited understanding of how losses scale with bend radii. A detailed analysis is performed using twodimensional finite difference time domain simulations for straight waveguides interconnected by 180° micro-bends. Modal overlap optimization at each straightwaveguide to micro-bend junction is successfully performed to give low losses for radii above 20 mm. However, at reduced radii, simply optimizing the lateral offset between waveguides is insufficient for fabrication tolerance and losses are critically defined by the mode-matching between straight guides and micro-bend structures

Inventory of ammonia emissions from UK agriculture 2009

The National Ammonia Reduction Strategy Evaluation System (NARSES) model (spreadsheet version) was used to estimate ammonia (NH3) emissions from UK agriculture for the year 2009. Year-specific livestock numbers and fertiliser N use were added for 2009 and revised for previous years. The estimate for 2009 was 231.8 kt NH3, representing a 2.3 kt increase from the previously submitted estimate for 2008. Backward and forward projections using the 2009 model structure gave estimates of 317, 245 and 244 kt NH3 for the years 1990, 2010 and 2020, respectively. This inventory reports emission from livestock agriculture and from nitrogen fertilisers applied to agricultural land. There are a number of other minor sources reported as ‘agriculture’ in the total UK emission inventory, including horses not kept on agricultural holdings, emissions from composting and domestic fertiliser use

Integrated extended-cavity 1.5-μm semiconductor laser switchable between self- and anti-colliding pulse passive mode-locking configuration

We present the first integrated linear extended-cavity passively mode-locked (PML) semiconductor laser in which the operating mode can be switched electrically between two configurations. The first configuration is where the saturable absorber (SA) is located next to the output coupler, the so-called anti-colliding pulse mode-locking (ACPML) scheme. The second is where the SA is next to the high reflectance mirror, the self-colliding pulse mode-locking (SCPML) scheme. The 7.5-GHz PML was used to demonstrate experimentally the theoretical prediction that placing the SA next to the output coupler leads to a significant improvement in the laser stability and quality of the optical pulses. The experimental results show that the ACPML scheme allows for more deeply saturated SA due to the increase of optical power in the SA. The measurements of the RF spectra and autocorrelation traces confirm the superiority of the ACPML design in terms of pulse stability and width over the SCPML design for a wide range of operating conditions. The linewidth of the beat tone at the repetition rate was reduced by more than 60 times, the measured minimal autocorrelation width improved from 22 to 7.5 ps and a 3 dB increase in average output power was achieved

Experimental comparison of extended-cavity passively mode-locked 1.5 µm quantum well lasers with anti-colliding design and self-colliding design

In this paper we present an experimental verification of a prediction of significantly improved performance of an integrated passive mode-locked laser (PMLL) through the use of an anti-colliding (AC) design comparing with a self-colliding (SC) scheme. The most commonly used design is the linear SC cavity. In this scheme a saturable absorber (SA) is placed close to the high reflectivity facet, which allows the pulse to interact with itself within the SA. However in [1] it was shown theoretically that an AC design where the SA is placed next to the low reflectivity output coupler is advantageous. It leads to a higher stability, an increase of optical output power and shorter pulses due to the weaker saturation of the gain and enhanced modulation of the SA in comparison with symmetrical mode-locking (SML) and SC scheme. A marked improvement in the performance of two-section cleaved facet PMLLs was achieved by the introduction of a low-reflectance coating at the SA facet and a high-reflectance coating on the other facet in comparison with a non-coated device (SML configuration) in [2]. However, the deposition of the coatings may lead to changes in the reflection spectrum

The Role of Coral Reefs in Coastal Protection: Analysis of Beach Morphology

This paper evaluates the effect of a fringing reef on the morphodynamic behaviour of adjacent beaches in terms of profile stability and cross-shore sediment exchange. Variations in subaerial beach morphology along 39 cross-shore profiles at Pontal do Cupe beach (Northeastern Brazil) were analysed, using modelled wave data and monthly beach topography acquired from November 2014 to September 2016. Pontal do Cupe has a reef to the south but is exposed to waves in the north, making this an ideal location to assess the sheltering effect of the reef. Beach volume and beach width data were used to compare the reef-fronted profiles with those of the exposed adjacent beach. Seven groups of profiles were identified by applying Principal Component Analys is to the topography dataset. A simple numerical model was used to quantify the role of the reef in dissipating wave energy, showing a reduction of approximately 50% in incoming wave energy to the shore. The reef-fronted beach is significantly more stable than the exposed beach. Total beach volume is similar for both the exposed and the reef-fronted beach. The results of this survey can be used as a proxy for the ecosystem service of coastal protection provided by reefs