1,720,959 research outputs found
Multi-mode hollow-core anti-resonant optical fibres
No full textThe demonstration, during the course of this doctoral project, of an effectively single-mode hollow-core anti-resonant optical fibre with loss rivalling that of single-mode silica fibre represents a huge milestone in the development of hollow-core fibre technology that has the potential to transform the field of fibre optics and its many applications. As attention increasingly turns to a focus on deploying hollow-core fibre in real world applications, one largely unexplored topic is that of multi-mode hollow-core anti-resonant optical fibres. Unlike in solid-core fibre where multiple modes can be guided with virtually the same attenuation, multi-mode guidance in hollow-core fibres presents a unique challenge in the form of large differential loss - and in general optical properties - between modes. Nevertheless, multi-mode guidance in a hollow core presents opportunities in many application areas, including high-power laser delivery, short-haul telecommunication systems and light-gas interaction systems, whilst offering lower loss, nonlinearity and latency across larger bandwidths than solid-core fibres. This thesis presents research concerning the nature of multi-mode guidance in anti-resonant optical fibres, their characteristics and their design for practical applications. Numerical simulation is applied extensively to study in detail the origins of the differential modal properties of these fibres, including attenuation and dispersion, leading to a new understanding of the processes involved. This facilitated the development of methods to engineer the differential properties of the anti-resonant fibres in order to achieve multi-mode guidance in fibres with a variety of micro-structure designs. Methods based on structural design and deployment conditions are explored. Design techniques are presented for multi-mode anti-resonant fibres targeting specific requirements in several application areas: short-haul telecommunications, delivery of high-power laser light and finally, fibre based gas sensors
Designing multi-mode anti-resonant hollow-core fibers for industrial laser power delivery
No full textWe investigate the design of hollow-core fibers for the delivery of 10s of kilowatt average power from multi-mode laser sources. For such lasers, delivery through solid-core fibers is typically limited by nonlinear optical effects to 10s of meters of distance. Techniques are presented here for the design of multi-mode anti-resonant fibers that can efficiently couple and transmit light from these lasers. By numerical simulation we analyze the performance of two anti-resonant fibers targeting continuous-wave lasers with M
2 up to 13 and find they are capable of delivering MW-level power over several kilometers with low leakage loss, and at bend radii as small as 35 cm. Pulsed lasers are also investigated and numerical simulations indicate that optimized fibers could in principle deliver nanosecond pulses with greater than 100 mJ pulse energy over distances up to 1 km. This would be orders of magnitude higher power and longer distances than in typical machining applications using the best available solid core fibers.
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Designing hollow-core multi-mode anti-resonant fibers for industrial high-power laser delivery
No full textWe investigate the design of hollow-core fibers for the delivery of 10s of kilowatt average power from multi-mode laser sources where delivery through solid-core fibers is typically limited by nonlinear optical effects to 10s of metres of distance. A technique is presented for the design of multi-mode anti-resonant fibers that can efficiently capture and deliver light from these lasers. We analyze, by numerical simulation, the performance of two anti-resonant fibers designed using this technique to target lasers with M2 up to 13 and find they are capable of delivering MW-level power over multi-kilometres distances with low leakage loss, and at bend radii as small as 35 cm. Pulsed lasers are also investigated and numerical simulations indicate that optimized fibers could in principle deliver nanosecond pulses with pulse energy greater than 100 mJ over more than 1 km. This would be orders of magnitude higher power and longer distances than in typical machining applications using state-of-the-art solid core fibers
Dataset for the journal paper "Designing multi-mode anti-resonant hollow-core fibers for industrial laser power delivery"
No full textResults of finite-element simulation data used for the preparation of figures for journal article submitted to "Optics Express".</span
Design rules for multi-mode anti-resonant hollow-core fibres
No full textHollow-core fibres typically guide a single low-loss, degenerate spatial mode. Here we present techniques to design HCFs guiding multiple modes with low loss that could be employed in short-haul datacoms or in power delivery
Understanding the impact of cladding modes in multi-mode hollow-core anti-resonant fibres
No full textMulti-moded, anti-resonant hollow-core fibre shows great promise for a range of applications from high power laser delivery to novel, non-linear experiments. Anti-resonant fibers typically guide multiple transverse modes due to their large core size, albeit with often large differential modal loss. Understanding the behaviour of higher order modes in these fibres is of crucial importance if we are to exploit the benefits of hollow-core optical guidance in few- and multi-moded applications, or to design more robustly single mode fibres. In this work we conduct thorough numerical investigations into the origins of confinement loss in tubular anti-resonant fibres and its dependence on the fibre’s key structural parameters.We show that away from the resonances in the glass, leakage loss can be interpreted as originating from resonant out-coupling between the core modes of interest and the lossy modes of the cladding tubes, and is highest when these are phase-matched. Using this insight, we show that the loss can be estimated a posteriori from knowledge of the fields of the core-guided and cladding tube modes and their propagation constants. Such a quantitative estimate is satisfactory by considering only the three lowest mode groups of the cladding tube. This deeper understanding paves the way to a more informed approach to designing few and multi-moded hollow-core fibers for various applications
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
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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