1,721,062 research outputs found
Inverse scattering designs of optical waveguides and fibres
No full textOptical fibres and waveguides have become vital components in communication systems ranging from on-chip interconnects in datacentres, to trans-oceanic submarine communication cables. Typically, they are designed in a trial-and-error manner and the objective of this thesis was to investigate their inverse design using a method known as inverse-scattering. In contrast to methods of design optimisation where an initial refractive form of index profile of some kind must be chosen, inverse-scattering makes no such assumptions other than that of which modes are carried by the structure and what their respective propagation constants are.Initially, the control over group-velocity dispersion in a single-mode planar waveguide with fixed propagation constant was investigated by considering the form of the transverse reflection response by which the modal properties of the waveguide may be specified, as discussed in the literature. It was demonstrated that common features of dispersion-engineered waveguides were obtained corroborating their use in the existing literature and further understanding of these features was developed.Extending the study to multimode planar waveguides through the application of an inverse-scattering method rooted in the quantum mechanical community, the properties of multiple guided modes, such as their group-velocities and modal gain were controlled. The realisation that both gain and loss are required in a refractive index profile to have exact equalisation of modal gain across multiple modes was novel and differed from existing approaches using genetic algorithms. In addition to this, the design of waveguide couplers by which power can be transferred from one waveguide to another was considered by an approach differing from that of the increasingly popular supersymmetric (SUSY) approach in the literature.Attention turned to the design of few-mode optical fibres which are at the forefront of technology. Since the planar waveguide designs above were found to contain ‘depressions’ and ‘rings’, similar such features were investigated in an optical fibre based upon the knowledge that there were similarities in the modal intensity profiles of the first few linearly polarised (LP) modes in a fibre, and that of the TE modes in planar waveguides. Core depressions and ‘rod-like’ refractive index perturbations were implemented and found to increase the spacing between mode groups.Following on from the above successes, inverse-scattering techniques were applied directly to the cylindrical symmetry of optical fibres and their associated LP modes. A particular feature of this work was the realisation that the propagation constants of such modes can only be specified at the start of the design process for a fixed value of the azimuthal symmetry of the fibre mode. A finding by other researchers using the SUSY technique had been that the modes in coupled fibres (trunk-partner pairs) could only be ‘matched’ when the azimuthal symmetry of the trunk and partner modes differed. The inverse-scattering method in this thesis, on the other hand, does not have this limitation
Doris May Alexander Calder
No full textDoris May Alexander Calder is the wife of Wallace S. Calder. She is the daughter of T.G. Alexander
Inverse scattering designs of active multimode waveguides with tailored modal gain
No full textDarboux inverse scattering transforms are used to design active waveguides with individually tailored modal gain, introducing areas of distributed gain and loss inside the waveguide. Potential applications of such devices include multimode optical amplifiers for which mode-dependent loss and its associated deleterious effects on channel capacity have been compensated. We also show that the commonly used ring-doping approach to modal gain equalization in fibers is a subset of the design approach utilizing gain and loss that derives from the inverse scattering theory
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Inverse scattering designs of dispersion-engineered planar waveguides
No full textWe have introduced a semi-analytical IS technique suitable for multipole, rational function reflection coefficients, and used it for the design of dispersion-engineered planar waveguides. The technique is used to derive extensive dispersion maps, including higher dispersion coefficients, corresponding to three-, five- and seven-pole reflection coefficients. It is shown that common features of dispersion-engineered waveguides such as refractive-index trenches, rings and oscillations come naturally from this approach when the magnitude of leaky poles in increased. Increasing the number of poles is shown to offer a small but measureable change in higher order dispersion with designs dominated by a three pole design with a leaky pole pair of the smallest modulus
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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