1,720,973 research outputs found
Gouy phase compensated quasi phase matching (GQPM)
No full textUsing an appropriately designed quasi-phase matched structure it is theoretically possible to compensate for the deleterious effects of Gouy phase shift allowing a symmetric frequency response and tighter focussing for higher conversion efficiencies
Direct UV writing at the University of Southampton - substrates, structures and sensors
No full textWe present our recent developments on direct-UV-written planar lightwave circuits (PLCs) based on applications in telecommunications, material characterisation and optical sensing. Interfering two focussed UV spots provides us with an unique capability to simultaneously define channel waveguides and Bragg gratings [1] in a multifunctional silica-on-silicon PLC chip (Figure 1a). This opens new device and application opportunities for laser-based processing. In particular, we have created a range of refractive index sensors and modulators by accessing the evanescent field of our planar Bragg gratings, incorporating functionalised surface chemistry to demonstrate chemical [2] and biological sensing capabilities [3], or liquid crystals to provide electrical wavelength tuning and selectivity [4]
Period adapted Bragg mirror multimode interference device
Full text linkA direct UV-written multimode interference device is constructed with a pair of Bragg mirrors that have adaptively manipulated period to minimise excess loss. Excess loss achieved is comparable to that of a regular MMI device
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Demonstration of 100 GHz electrically tunable liquid-crystal Bragg gratings for application in dynamic optical networks
No full textWe demonstrate liquid crystal-based integrated optical devices with >140GHz electrical tuning for potential applications in dynamic optical networks. Bragg wavelength tuning covering five 25GHz WDM channel spacings has been achieved with 170V (peak-to-peak) sinusoidal voltages applied across electro-patterned ITO-covered glass electrodes placed 60µm apart. This tunability range was limited only by the initial grating strength and supply voltage level. We also observed two distinct threshold behaviors that manifest during increase of supply voltage, resulting in a hysteresis in the tuning curve for both TE and TM input light
UV written waveguide devices - Bragg gratings and applications in sensors
No full textUV direct writing provides a powerful route for the fabrication of integrated optical devices. It has significant benefits in terms of simplicity, flexibility and cost which make it attractive for applying integrated optical concepts to other areas of science and technology. Within our group, we have developed a novel approach for creating Bragg gratings in a planar format, with great flexibility in terms of centre wavelength, bandwidth and position within chip. These planar Bragg grating devices are ideally suited for use in sensors in etched window is created that allows access of the evanescent field of the optical mode to a liquid measurand. The effective index of the mode is altered by the presence of the liquid, and this, in turn, alters the Bragg wavelength of the grating. By measuring the Bragg grating wavelength shift we can resolve refractive index changes of as small 1 part in 10 In this talk, we will present results on sensors for applications in chemical, phase change and biological sensing. Further recent results will show how this sensor configuration may be used with nematic liquid crystals to achieve tunable grating operation with tuning exceeding 100GHz
Recent developments in direct-UV-written planar waveguides, gratings, sensors and substrates
No full textWe present our recent developments in direct-UV-written integrated optical devices, based on applications in telecommunications, material characterisation, and optical sensing. The inherent advantages of this channel definition technique over traditional etching based approaches are reiterated and demonstrated in the production of small angle, low loss X-couplers with negligible polarisation dependence. Interfering two focussed UV spots also provides us with the capability to simultaneously define a channel waveguide and Bragg grating, opening new device and application opportunities. Such structures provide a method to quantify the photosensitivity effects observed in conventional multilayer substrates, and assess the core uniformity of a novel 'flat-fibre' format recently developed within the ORC. We will also discuss electrically tuned Bragg gratings via liquid crystal overlayers, displaying a dynamic range in excess of 100GHz for use in dynamic optical networks
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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