1,720,965 research outputs found
Multipoint-to-point data aggregation using a single receiver and frequency-multiplexed intensity-modulated ONUs
No full textWe demonstrate 2.5-GHz-spaced frequency multiplexing capable of aggregating 64 intensity-modulated end-users using low-speed electronic and optoelectronic components. All optical network units (ONUs) achieved high per-user capacity with dedicated optical bands, enabling future low latency applications
All-fibre heterogeneously-integrated frequency comb generation using silicon core fibre
Full text linkOriginally developed for metrology, optical frequency combs are becoming increasingly pervasive in a wider range of research topics including optical communications, spectroscopy, and radio or microwave signal processing. However, application demands in these fields can be more challenging as they require compact sources with a high tolerance to temperature variations that are capable of delivering flat comb spectra, high power per tone, narrow linewidth and high optical signal-to-noise ratio. This work reports the generation of a flat, high power frequency comb in the telecom band using a 17 mm fully-integrated silicon core fibre as a parametric mixer. Our all-fibre, cavity-free source combines the material benefits of planar waveguide structures with the advantageous properties of fibre platforms to achieve a 30 nm bandwidth comb source containing 143 tones with 30 dB OSNR over the entire spectral region
Parametric frequency comb generation using silicon core fiber
Full text linkWe demonstrate all-fiber frequency comb generation using a 10-mm-length silicon core fiber as the parametric mixer. We achieved 8 dB spectral flatness over 20 nm bandwidth, generating 90 lines at 26 GHz line spacing.</p
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Dual optical frequency comb analog to digital conversion
Full text linkAnalog to digital converters (ADCs) are the fundamental technology that allows the capture and analysis of signals across all scientific and engineering disciplines and underpin the digital links that connect our analog world. Modern communications systems demand high bandwidth, high resolution ADC in order to detect higher order modulation formats at high baud rates and maximise the spectral efficiency of the channel. However, the resolution of high speed (i.e. 1 GHz) electronic ADCs is typically limited by clock jitter and, at especially high frequencies, the speed of the component transistors that results in comparator ambiguity. This presents a trade-off between the frequency of the detected signal and accuracy, defined by the SINAD or ENOB. In a jitter limited ADC, the SINAD decreases quadratically with increasing frequency, giving a 6 dB SINAD penalty for every doubling of the input frequency.
This thesis proposes a frequency interleaving photonic front end for analog to digital converters, based on dual optical frequency combs, in order to meet this challenge of high speed, high resolution signal digitisation. Firstly, the dual frequency comb technique is described and modelled, both analytically and through simulations, to establish the potential performance of the dual comb approach in analog to digital conversion and other radio frequency signal processing applications. Secondly, a dual frequency comb prototype is experimentally demonstrated based on phase coherent electro-optic combs. The phase noise characteristics of the architecture are established and the prototype is evaluated using the IEEE ADC testing standard, outperforming any reported electronic ADC. Finally, arbitrary signal detection using the dual comb technique is demonstrated using a novel phase locking approach that efficiently utilises the comb bandwidth, and the impact of possible implementation errors is investigated
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