1,720,959 research outputs found
Picosecond pulse dispersion in cladded glass fibres
No full textPicosecond pulse dispersion measurements have been made on short lengths of multimode glass fibre. With a narrow input beam rapid mode conversion occurs initially, but an equilibrium is reached after ~10 m and the transmitted pulse then broadens at a linear rate of ~10 ps/m
Pulse dispersion in glass fibres
No full textMeasurements indicate that pulses incident normally on the end of a cladded multimode fibre are broadened by less than 0.1 ns over a length of 20 m. The measured dispersions in lengths of 20 m and 35 m do not exceed 5 ps/m. However, with an angle of incidence of 17°, or with a defocused input beam, the pulses are broadened by 0.6 ns
Launching into glass-fibre optical waveguide
No full textSeveral novel and simple launching (and collection) mounts for use in the assessment of single-mode and multi-mode glass-fibre waveguides are described. The transmission efficiency for Gaussian beams of 96% is limited only by Fresnel reflection loss at the entry face. Techniques for preparing the end of the fibre are outlined, a list of some suitable index-matching liquids and their properties is provided and two parameters, namely a smoothing factor S and a ray deviation theta, are proposed for assessing the optical quality of the launching system
Accurate tuning of a laser mode-locking device
No full textTwo simple methods are described for accurately tuning a mode-locking device for a laser. The first is suitable for an acoustic diffraction cell and involves a simple measurement of the diffracted light. The second can be used with any type of active mode locking and requires only a photodiode and a simple low-frequency spectrum analyser
Novel mode filter for use with cladded-glass and liquid-core optical waveguides
No full textTwo methods of filtering off high-order modes in multimode fibres are proposed. One uses a periodic sequence of apertures and the other involves continuous coupling. In this way, it may he possible to achieve bandwidths approaching 100 MHz over kilometre lengths
Propagation model for multimode optical-fibre waveguide
Full text linkPulse dispersions of 5 ps/m have been measured in cladded-glass and liquid-core multimode fibres. A theoretical model is proposed which gives excellent agreement with measured propagation delay and pulse dispersion. In the fibres used, there is little light scattering either in the core or at the core-cladding interface
Theory of dispersion in lossless multimode optical fibres
No full textUsing the ray propagation model generalized expressions for the impulse response of multimode fibres have been derived. The analysis has been applied to lossless fibres for pulses having both Gaussian and Lambertian spatial distributions as well as impulse and Gaussian temporal distributions. Detailed results are given for output pulse shapes and fibre dispersions for various configurations
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
- …
