Fast tuneable InGaAsP DBR laser using quantum-confined stark-effect-induced refractive index change

We report a monolithically integrated InGaAsP DBR ridge waveguide laser that uses the quantum-confined Stark effect (QCSE) to achieve fast tuning response. The laser incorporates three sections: a forward-biased gain section, a reverse-biased phase section, and a reverse-biased DBR tuning section. The laser behavior is modeled using transmission matrix equations and tuning over similar to 8 nm is predicted. Devices were fabricated using post-growth shallow ion implantation to reduce the loss in the phase and DBR sections by quantum well intermixing. The lasing wavelength was measured while varying the reverse bias of the phase and DBR sections in the range 0 V to < - 2.5 V. Timing was noncontinuous over a similar to 7-nm-wavelength range, with a side-mode suppression ratio of similar to 20 dB. Coupled cavity effects due to the fabrication method used introduced discontinuities in tuning. The frequency modulation (FM) response was measured to be uniform within 2 dB over the frequency range 10 MHz to 10 GHz, indicating that tuning times of 100 ps are possible

In situ non-invasive Raman spectroscopic characterisation of succinic acid polymorphism during segmented flow crystallisation

The kinetically regulated automated input crystalliser for Raman spectroscopy (KRAIC-R) combines highly controlled crystallisation environments, via tri segmented flow, with non-invasive confocal Raman spectroscopy. Taking advantage of the highly reproducible crystallisation environment within a segmented flow crystalliser and the non-invasive nature of confocal spectroscopy, we are able to shine light on the nucleation and growth of Raman active polymorphic materials without inducing unrepresentative crystallisation events through our analysis technique. Using the KRAIC-R we have probed the nucleation and subsequent growth of succinic acid. Succinic acid typically crystallises as β-SA from solution-based crystallisation although some examples of a small proportion of α-SA have been reported in the β-SA product. Here we show that α-SA and β-SA nucleate concomitantly but undergo Ostwald ripening to a predominantly β-SA product

Near-Field Analysis of Terahertz Pulse Generation From Photo-Excited Charge Density Gradients

Excitation of photo-current transients at semiconductor surfaces by subpicosecond optical pulses gives rise to emission of electromagnetic pulses of terahertz (THz) frequency radiation. To correlate the THz emission with the photo-excited charge density distribution and the photo-current direction, we mapped near-field and far-field distributions of the generated THz waves from GaAs and Fe-doped InGaAs surfaces. The experimental results show that the charge dynamics in the plane of the surface can radiate substantially stronger THz pulses than the charge dynamics in the direction normal to the surface, which is generally regarded as the dominant origin of the emission

Photonically enabled communication systems beyond 1000 GHz

This paper presents a review of the recent development and research work on InP devices and their associated systems to generate and detect signal beyond 1 THz. The potential of the technology and the remaining challenges are also discussed. The paper will present recent results on laser sources that could be used as the basis of the THz sources as well as a set of potential THz emitters such as the UTC photodiode which has already permitted up to 25 muW to be emitted at 1 THz

Combining work and child care: The experiences of mothers in Accra, Ghana

Work-family research has focused predominantly on Western women. Yet the forms of economic labour in which women are typically involved and the meaning of motherhood are context-specific. This paper aims to explore the experience of combining economic activity and child care of mothers with young children using urban Ghana as a case study. Semi-structured interviews (n=24) were conducted in three locations in the Accra Metropolitan Area. Transcripts were analysed using the general inductive approach. The results found women’s experience of role conflict to be bi-directional. With regard to role enhancement, economic activity allowed women to provide materially for their children. The combination of work and child care had negative consequences for women’s wellbeing. This research questions policy makers’ strategy of frequently targeting women in their roles either as generators of income, or as the primary care-takers of children by highlighting the reality of women’s simultaneous performance of these roles

High Output Power at 110 GHz with a Waveguide Uni-Travelling Carrier photodiode

We present a waveguide uni-travelling carrier photodetector with a bandwidth greater than 110 GHz and record breaking power of 10 dBm extracted at 110 GHz

Traveling-wave Uni-Traveling Carrier Photodiodes for continuous wave THz generation

The design, experimental evaluation and performance of a Traveling-Wave Uni-Traveling Carrier photodiode for Terahertz generation are described and its advantages in terms of frequency response are demonstrated. The device delivered 148 mu W at 457 GHz, 24 mu W at 914 GHz when integrated with resonant antennas and 105 mu W at 255 GHz, 30 mu W at 408 GHz, 16 mu W at 510 GHz and 10 mu W at 612 GHz. Record levels of Terahertz figure of merit (P-THz/P-opt(2) in W-1) were achieved ranging from 1 W-1 at 110 GHz to 0.0024 W-1 at 914 GHz. (C) 2010 Optical Society of Americ

Measuring the unmeasurable? A method to quantify adoption of integrated pest management practices in temperate arable farming systems

BACKGROUND: The impetus to adopt integrated pest management (IPM) practices has re-emerged in the last decade, mainly as a result of legislative and environmental drivers. However a significant deficit exists in the ability to practically monitor and measure IPM adoption across arable farms; therefore the aim of the project reported here was to establish a universal metric for quantifying adoption of IPM in temperate arable farming. This was achieved by: (a) identifying a set of key activities that contribute to IPM; (b) weighting these in terms of their importance to the achievement of IPM using panels of expert stakeholders in order to create the metric (scoring system from 0-100 indicating level of IPM practiced); (c) surveying arable farmers in the UK and Ireland about their pest management practices; and (d) measuring level of farmer adoption of IPM using the new metric. RESULTS. This new metric was found to be based on a consistent conception of IPM between countries and professional groups. The survey results showed that, while level of adoption of IPM practices varied over the sample, all farmers had adopted IPM to some extent (minimum 27.2 points, mean score of 65.1), but only 13 of 225 farmers (5.8%) had adopted more than 85% of what is theoretically possible, as measured by the new metric. CONCLUSION. We believe that this new metric would be a viable and cost-effective system to use to facilitate the benchmarking and monitoring of national IPM programmes in temperate zone countries with large scale arable farming systems

International Perspectives: Birth-Associated Neonatal Encephalopathy: Postresuscitation Care in West African Newborns

The West African subregion has the highest burden of neonatal mortality globally and the neonatal mortality rate is decreasing very slowly. A high proportion of newborn deaths are preventable and improved quality of care can reduce long-term morbidity in survivors. Perinatal asphyxia is the major cause of death and disability in term infants in the subregion. Neonatal resuscitation training programs have reduced stillbirths and early neonatal mortality but the overall effect on survival to discharge, population-based perinatal mortality, and long-term impairment is uncertain. Gaps in the health system and quality of postresuscitation care for affected newborns may defeat gains from global efforts to improve care around the time of birth. The aim of this review is to discuss the current situation of postresuscitation care of term infants with presumed birth-associated neonatal encephalopathy in West Africa. Limitations in diagnosing and treating affected infants and feasible interventions to improve acute and postdischarge care are discussed