Phase shift keyed systems based on a gain switched laser transmitter

Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ) Differential Phase Shift Keyed (DPSK) systems require cheap and optimal transmitters for widespread implementation. The authors report on a gain switched Discrete Mode (DM) laser that can be employed as a cost efficient transmitter in a 10.7 Gb/s RZ DPSK system and compare its performance to that of a gain switched Distributed Feed-Back (DFB) laser. Experimental results show that the gain switched DM laser readily provides error free performance and a receiver sensitivity of -33.1 dBm in the 10.7 Gbit/s RZ DPSK system. The standard DFB laser on the other hand displays an error floor at 10(-1) in the same RZ DPSK system. The difference in performance, between the two types of gain switched transmitters, is analysed by investigating their linewidths. We also demonstrate, for the first time, the generation of a highly coherent gain switched pulse train which displays a spectral comb of approximately 13 sidebands spaced by the 10.7 GHz modulation frequency. The filtered side-bands are then employed as narrow linewidth Continuous Wave (CW) sources in a 10.7 Gb/s NRZ DPSK system.

Experimental investigation of inter-modal cross-gain modulation and transient effects in a two mode group erbium doped fiber amplifier

We report what we believe to be the first experimental study of inter-modal cross-gain modulation and associated transient effects as different spatial modes and wavelength channels are added and dropped within a two-mode amplifier for SDM transmission.

Widely tunable gain-switched operation of external cavity grating-coupled surface emitting laser

Widely tunable gain switching of a grating-coupled surface-emitting laser (GCSEL) has been demonstrated in a simple external cavity configuration for the first time. Pulse duration in range of 40-100ps and wavelength tuning over 100nm have been achieved. High power, tail-free optical pulses have been observed at 980nm.

Self-seeded gain-switched operation of an InGaN MQW laser diode

Self-seeded, gain-switched operation of an InGaN multi-quantum-well laser diode has been demonstrated for the first time. An external cavity comprising Littrow geometry was implemented for spectral control of pulsed operation. The feedback was optimized by adjusting the external cavity length and the driving frequency of the laser. The generated pulses had a peak power in excess of 400mW, a pulse duration of 60ps, a spectral linewidth of 0.14nm and maximum side band suppression ratio of 20dB. It was tunable within the range of 3.6nm centered at a wavelength of 403nm.

Utilising fiction to promote english language acquisition

Towards the end of the university stage, students residing in the United Arab Emirates and specialising in subjects other than English are expected- amongst other university requirements- to have acquired adequate communicative competence as well as a repertoire of critical thinking skills. Despite the efforts made within the field of teaching English to EFL university students in the country, the output gained in terms of acquired skills and competencies is still below expectations. The main concerns of the current thesis are, therefore, a) to investigate the factors which inhibit EFL university students’ progress in the areas of acquiring adequate communicative competence as well as critical thinking skills, and b) to propose a course book and pedagogic methods to improve students’ progress in the areas of acquiring adequate communicative competence as well as critical thinking skills. Believing in the essential role literature plays in enhancing critical thinking and promoting communicative competence on the part of EFL learners, the current study introduces a course, designed and implemented by the researcher: LEARN AND GAIN. The proposed course is fiction-based language teaching, adopting the view that literature is a resource rather than an object, thus advocating the use of literature as one of the main resources in foreign/second language acquisition. Investigating whether or not the proposed course was effective in promoting EFL university students’ communicative competence as well as enhancing their critical thinking skills, a study sample taken from the study population was selected. Adopting an experimental design, the research project involved two groups: experimental and control. The experimental group students were exposed to the proposed course whilst the control group students were exposed to a general English language course. To examine treatment effectiveness, the researcher set and administered a pre-post test. Divided into two main parts, communicative critical reading competence and communicative critical writing competence, the pre-post test measured subjects’ communicative critical reading competence and subjects’ communicative critical writing competence. In addition, a pre-post questionnaire was administered and a semi-structured interview was conducted involving the experimental group students, to gain an awareness of students’ attitudes towards learning literary texts in general, and the proposed course in particular. To examine issues of interest and relevance, gender differences: male vs. female, and university major: science vs. non-science, were also examined for enrichment purposes. For the purpose of gathering sufficient data about subjects’ achievements on the pre-post, the following statistical tests were conducted: Mann-Whitney test, and paired data t-test. Based on the statistical findings, the experimental group students’ performance on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test was significantly better than their counterparts of the control group students. Speaking of gender differences in relation to language performance on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test, no significant differences were cited. Neither did the researcher cite any significant performance differences between science/non-science students on the communicative critical reading competence pre-post test and the communicative critical writing competence pre-post test. As far as the questionnaire’s findings are concerned, the experimental group students’ responses to the post-questionnaire’s items were more positive than those of their responses to the pre-questionnaire’s, thus indicating some positive attitudes towards literature, which students possibly gained throughout the course of implementation. Relating the discussion to the interview’s results, students conveyed their satisfaction with the proposed course, emphasising that promoting English language skills through the use of literary texts was rewarding. In the light of findings and conclusions, a number of recommendations as well as implications have been proposed. The current study aimed to arrive at some appropriate suggestions to a number of enquiries, yet concluding with some areas of enquiry to be explored for further research.

Q-switched induced gain switching of a twotransition cascade laser

A gain-switched laser transition, of a two-laser-transition cascade laser, that is driven by the adjacent laser transition which is Q-switched is demonstrated using a Ho3+ -doped fluoride fiber laser. Q-switching the 5|6 ? 5|7 transition at 3.002 µm produces stable gain-switched pulses from the 5|7 ? 5|8 transition at 2.074 µm; however, Q-switching the 5|7 ? 5|8 transition produced multiple gain switched pulses from the 5|6 ? 5|7 transition. The gain-switched pulses were measured to be of a similar duration to the Q-switched pulses suggesting that much shorter pulses of closer duration could be generated at pump power higher levels.

Experimental investigation of inter-modal cross-gain modulation and transient effects in a two mode group erbium doped fiber amplifier

We report what we believe to be the first experimental study of inter-modal cross-gain modulation and associated transient effects as different spatial modes and wavelength channels are added and dropped within a two-mode amplifier for SDM transmission.

22-km distributed temperature sensor using Brillouin gain in an optical fiber

We describe an experimental distributed temperature sensor that uses the temperature dependence of the Brillouin frequency shift. When a 22.2-km sensing length is used, we have observed a temperature resolution of 1°C and have obtained a spatial resolution of 10 m.

Characteristics of Brillouin gain based distributed temperature sensors

A Brillouin-gain based distributed temperature sensor has been investigated experimentally and theoretically. The relation between Brillouin gain, input probe power and sensing length have been studied. The study shows that there is an optimum probe power providing a maximum Brillouin gain signal for a given sensing length.

Physicians' perceptions, attitudes and expectations regarding the role of hospital-based pharmacists in the West Bank, Palestine

Objective - To evaluate the perceptions, expectations and experiences of physicians with regard to hospital-based pharmacists in the West Bank, Palestine. Methods - A self-administered questionnaire was distributed to 250 physicians practising in four general hospitals in the West Bank, Palestine. The main sections of the questionnaire comprised a series of statements pertaining to physicians' perceptions, expectations and experiences with pharmacists. Key findings - One hundred and fifty seven questionnaires were completed and returned (response rate, 62.8%). The majority of respondents were most comfortable with pharmacists detecting and preventing prescription errors (76.4%; 95% confidence interval (CI) 69.5–81.2%) and patient education (57.9%; CI 51.2–63.4%) but they were not comfortable with pharmacists suggesting the use of prescription medications to patients (56.7%; CI 49.8–62.4%). Most physicians (62.4%; CI 56.8–69.1%) expected the pharmacist to educate their patients about the safe and appropriate use of their medication. However, approximately one-third (31.7%; CI 26.0–39.6%) did not expect pharmacists to be available for consultation during rounds. Physicians' experiences with pharmacists were less favourable; whereas 77% (CI 70.2–81.5%) of the physicians agreed that pharmacists were always a reliable source of information, only 11.5% (CI 6.2–16.4%) agreed that pharmacists appeared to be willing to take responsibility for solving any drug-related problems. Conclusion -The present study showed that hospital physicians are more likely to accept traditional pharmacy services than newer clinical services for hospital-based pharmacists in the West Bank, Palestine. Pharmacists should therefore interact more positively and more frequently with physicians. This will close the gap between the physicians' commonly held perceptions of what they expect pharmacists to do and what pharmacists can actually do, and gain support for an extended role of hospital-based pharmacists in future patient therapy management.

Noise and gain optimisation in bi-directionally pumped dispersion compensating amplifier modules

We perform optimisation of bi-directionally pumped dispersion compensating Raman amplifier modules. Optimal forward and backward pump powers for basic configurations using different commercially available fibers are presented for both single- and multi-channel systems. Optical signal-to-noise ratio improvement of up to 8 dB is achieved as a result of optimisation. © 2003 Published by Elsevier B.V.

Does maternal control during feeding moderate early infant weight gain?

OBJECTIVE. Our objective with this study was to examine whether observed maternal control during feeding at 6 months of age moderates the development of early infant weight gain during the first year of life. METHODS. Sixty-nine women were observed feeding their 6-month-old infants during a standard meal. Mealtimes were coded for maternal use of controlling feeding behavior. All infants were weighed at birth and at 6 and 12 months of age, and weight gain was calculated from birth to 6 months and from 6 to 12 months. Weight scores and weight gain scores were standardized for prematurity, age, and gender. RESULTS. Infant weight gain between 6 and 12 months of age was predicted by an interaction between early infant weight gain (birth to 6 months) and observed maternal control during feeding at 6 months. When maternal control was moderate or low, there was a significant interaction with weight gain from birth to 6 months in the prediction of later infant weight gain from 6 to 12 months, such that infants who showed slow early weight gain accelerated in their subsequent weight gain, and those with greater early weight gain decelerated. Conversely, when maternal control was high, infant weight gain followed the opposite pattern. CONCLUSION. Maternal control of solid feeding can moderate infant weight gain.

Tunable and multiple-wavelengths/temporal output from gain-switched diode laser and a four Bragg-grating fiber

The spectral narrowing and selective tuning of picosecond pulse outputs from gain-switched diode laser and a four Bragg-grating fiber, were investigated. The fiber used under investigation was designed to provide spectral narrowing and multiple wavelength/temporal output. The maximum transmission out of each of the four output fibers was ∼7.5 mW, for a current of 180 mA. The results show that an output of any combination of multiple wavelengths is only produced at modulation frequencies which satisfy resonant conditions for all cavity arms simultaneously.

Hybrid gain-flattened and reduced power excursion scheme for distributed Raman amplification

We propose and evaluate through extensive numerical modelling a novel distributed hybrid amplification scheme combining first and second-order Raman pumping which gives reduced signal power excursion over a wide spatial-spectral range of 60 km × 80 nm in C + L-bands. © 2013 Optical Society of America.

Gain switched multi-carrier transmitter and pilot tone based receiver for long reach access networks

A novel and cost effective long reach PON downlink scenario is proposed employing a multi-carrier transmitter and pilot tone aided direct detection at the receiver. Error free performance with QPSK and 50km transmission is presented. © 2012 OSA.