1,720,971 research outputs found
High-speed optical signal processing systems based on the switching of broadband frequency-chirped pulses
No full textFuture optical communication networks are likely to require a range of advanced OTDM channel processing functions if the full potential of the fibre transmission bandwidth is to be exploited. Critical processing functions include amongst others time-division demultiplexing, signal regeneration, channel add/drop, signal format conversion and packet compression. Ideally, these processes will be performed directly in the optical domain since this removes any bandwidth constraints associated with the use of electrical signals. In this presentation we describe various optical processing systems that exploit time-to-wavelength signal conversion. All of our systems are based on the nonlinear optical sampling of a linearly chirped pulse that is shaped and synchronised to temporally overlap with a given number of (relatively high-power) OTDM tributary channels in a fibre based switch. The individual tributary OTDM channels are mapped directly onto distinct WDM channels at the switch output by the nonlinear sampling process. Further processing of the OTDM channels can then be performed simply by passive filtering of the resulting WDM channels. If required, the filtered WDM signal can then be mapped back into the time domain onto an OTDM signal in a second nonlinear fibre switch. To highlight the power of the approach we shall present experimental demonstrations of simultaneous demultiplexing of each of the constituent tributary channels of an OTDM signal, tributary channel aggregation into compressed packets, and 10Gbit/s multi-channel add/drop from a 40 Gbit/s TDM signal
All-optical packet compression based on time-to-wavelength conversion
No full textWe experimentally demonstrate a novel optical packet compression scheme based on linearly chirping the packets followed by dispersive compression and multiwavelength conversion back onto a single wavelength. In particular, four-bit packets at 10 Gb/s were compressed into four-bit packets at 40 Gb/s. Error-free performance was achieved for the final compressed packet
OTDM add-drop multiplexer based on time-frequency signal processing
No full textA time-division add-drop multiplexer capable of high-extinction-ratio operation is presented both theoretically and experimentally. The approach used is based on time-to-frequency domain conversion of optical signals and relies upon the switching of linearly chirped optical pulses. By converting a 40-Gb/s optical time-division multiplexing (OTDM) signal to 4 × 10-Gb/s wavelength-division multiplexing (WDM) channels and using fiber Bragg gratings for frequency-domain add-drop multiplexing, a timeslot suppression ratio in excess of 30 dB and error-free operation for the dropped, through, and added channels were achieved. A further stage of WDM-to-TDM signal conversion was used to map the resulting signal back into the time domain. Moreover, it is shown that it is straightforward to simultaneously operate on multiple channels by simply cascading gratings to make more complex filtering functions without the requirement for any further synchronization of the tributary channels
Reduced repetition rate Yb<sup>3+</sup> mode-locked picosecond fiber laser with hollow core fiber
No full textAnti-resonant guiding negative curvature hollow core fiber operating at a
wavelength of 1064 nm is used in the cavity of an ytterbium (Yb3+)
mode-locked fiber laser to increase cavity length without increasing
the nonlinear phase shift. Repetition rates from 37 to 5.4 MHz are
demonstrated using lengths of hollow core fiber up to 48 m in length.
Each constructed cavity produced coherent 4-ps 1/e2 duration
soliton-like pulses, with no degradation of the pulse peak power or
pulse shape at lower repetition rates. Both the spectral distributions
and the autocorrelations of output pulses are compared along with the
mode-locking and multi-pulse power thresholds
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
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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