1,720,966 research outputs found
UV-induced refractive index changes in germanosilicate fibres
No full textPhoto-induced guided index changes approaching at both 633nm and 1.55µm, measured using a simple interferometric technique, are reported in germanosilicate single-mode optical fibres exposed to 266nm from the side
UV-induced refractive index changes in Ce<sup>3+</sup>-doped fibres
No full textAn optically-induced index change of 1.4 x 10-4 has been observed when Ce3+-doped fibres were subjected to UV light at 266nm. The effect is comparable with that observed in Ge-doped fibres with the potential of being improved with higher dopant-level
Generation of permanent second-order susceptibility in lead- silicate glass fibres
No full textThe creation of a permanent second-order susceptibility (χ(2)) for second-harmonic generation (SHG) in Ge-doped silica fiber has been reported by several authors using various techniques (exposure to IR, seeding with IR and its second harmonic, dc-field poling with blue light, and dc field only). Although the microscopic mechanism governing this interesting phenomenon is still not fully understood, it has been suggested that the alignment of defect centers plays an essential role. Defect centers, however, are known to exist or can be induced in many amorphous materials, including a variety of compound glasses that are commercially available. These commercially available compound glasses provide a wide range of options for the fiber core and cladding materials. Moreover, the effect observed to date in Ge-doped silica fibers may be present in a different and stronger form in fibers fabricated from compound glasses. It is therefore interesting to study fibers fabricated from various compound glasses. In this paper we report the first results, to our knowledge, for the dc-field poling effect in lead-silicate glass fibers
Photon-injection polarisation-switching in fibre lasers
No full textA novel photonic switching device based on polarisation switching by optical injection in fibre lasers is investigated. An all-optical switching device with an extremely low threshold (0.1µW) has been demonstrated. The mechanism of operation, experimental realisation and device characteristics are presented
Electric-field induced permanent second-order susceptibility for second-harmonic generation in optical fibres
No full textSince the discovery of efficient second-harmonic generation (SHG) in Ge/P-doped fibres after exposure to intense light at 1064nm, many research groups have reported the creation of a permanent second order susceptibility (χ(2)) using various techniques based on light excitation. We have discovered that a permanent χ(2) for SHG in silica fibres can be induced by a strong DC electric-field without any light
Phasematched three-wave mixing in poled optical fibres
No full textIt is now well known that high-intensity light may be used to write second-order non-linear gratings into optical fibre. The process is thought to be due to the alignment of defect centres, a view which is supported by the recently demonstrated fibre poling technique. In this, even stronger second-order non-linearities are generated by applying external electric fields to the fibre. Fibre poling has produced second-order non-linearities only ten times lower than in KDP and uniformly poled fibres have been employed as electro-optic modulators. Efficient second-harmonic generation has been demonstrated in poled fibres by employing mode-interference gratings (MIGs) for phase-matching. MIGs can maintain coherent in-phase propagation of the pump and SH-light in up to 10cm of fibre, limited only by fibre non-uniformities. Here, we demonstrate for the first time that MIGs may also be employed for phase-matching general three-wave mixing processes in poled optical fibres. The phase-matching conditions for TWM may easily be estimated from measurements of the wavelengths where phase-matched SHG is obtained
Photosensitivity in Ce<sup>3+</sup>-doped optical fibres
No full textA UV-induced absorption change has been studied in Ce3+-doped preforms and fibers made by a solution-doping modified-chemical-vapor-deposition technique. A reduction in the Ce3+- concentration and the creation of a broad absorption band extending from the UV to the IR were seen on UV exposure. In addition, a peak in the absorption band is created at 245 nm, attributed to Ce4+. The reduction in Ce3+- concentration was observed to remain for at least 3 months, whereas the created broad absorption bands at 632.8 nm recovered by 90% in 2h. Large UV-induced refractive-index changes (10-4) in Ce3+-doped fibers are also demonstrated. A linear dependence on the average UV intensity is found below 4 kW/m2, above which saturation occurs. The index change also increases with increasing Ce3+ concentration, again saturating at high levels. A decrease in magnitude with increasing wavelength is observed, but the index change at 1.33µm is still more than 50% of that at 0.5µm, demonstrating the potential of the technique for producing gratings with optical communication 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
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