1,720,959 research outputs found
Quantitative determination of photosensitivity proximity effects in multi-exposure direct UV writing for high density integrated optics
No full textUV direct writing is used to write planar channel waveguide gratings and simultaneously investigate photosensitivity proximity effects. Increases are seen up to 9µm away from the initial exposure with maximum effective index increase of 8.3 x 10-4
Imaging of single-step UV-laser-written channel waveguides by confocal micro-luminescence
No full textWe report on the observation of confocal micro-luminescence originated by defects created in direct UV written silica-on-silicon waveguides. Spatial and spectral analysis of the visible luminescence bands was performed with 488nm excitation. This has revealed the UV formation of different defects which are related to the different compositions of core and cladding layers
Coupling ratio tuning of direct UV-written X-couplers for cascaded power splitters in WDM networks
Full text linkWe present a study of low polarisation sensitivity 2 degrees X-couplers with 20% coupling ratio tuning via refractive index asymmetry, attaining 50:50 power splitting at 1550nm. The device has less than 5% coupling ratio variation over 30nm in the C-band and <0.7dB polarisation dependent loss
Direct UV written optical waveguides in flexible glass flat fiber chips
No full textA glass based substrate technology that fills the gap between a truly flexible extended length distributed sensor medium and the multi-functionality of optical chips is demonstrated. Flat Fiber chips will open further degrees of freedom to control the behavior of light via mechanical manipulation. A flexible flat format will also allow straightforward incorporation into smart structures. Coupled with low manufacturing costs, these flexi-chips can also be a key enabler to disposable high-end sensing devices or fully distributed point sensors. In this work, Bragg gratings were used to demonstrate the optical flatness of the Flat Fiber core layer. Furthermore, the effective index values obtained from the grating experiment were input into a dynamic model, subsequently proving the influence of the dumbbell shaped Flat Fiber cross section on the resultant UV written waveguides. Evanescent field sensing was also demonstrated by adopting a stepped Bragg approach
Demonstration of 100 GHz electrically tunable liquid-crystal Bragg gratings for application in dynamic optical networks
No full textWe demonstrate liquid crystal-based integrated optical devices with >140GHz electrical tuning for potential applications in dynamic optical networks. Bragg wavelength tuning covering five 25GHz WDM channel spacings has been achieved with 170V (peak-to-peak) sinusoidal voltages applied across electro-patterned ITO-covered glass electrodes placed 60µm apart. This tunability range was limited only by the initial grating strength and supply voltage level. We also observed two distinct threshold behaviors that manifest during increase of supply voltage, resulting in a hysteresis in the tuning curve for both TE and TM input light
100 GHz electrically tunable planar Bragg gratings via liquid crystal overlay
Full text linkWe demonstrate 114GHz electrically tunable liquid crystal Bragg gratings using 170Vpp voltage. The devices were made using direct UV grating writing and use evanescent coupling into an electrically tuned nematic liquid crystal. Reconfigurable integrated optical devices are essential in today's dense and complex telecommunication meshes. A commonly employed component on the silica platform fulfilling the above role is a planar Bragg grating. The ability to tune the reflection peak of these gratings is one of the key enablers in realizing an all optical dynamic network. To date, little has been reported on electrically tunable planar Bragg gratings given their potentially superior response times over temperature tuned devices. Such electrically tunable devices work on the principle of shifting the Bragg wavelength by modifying the effective index of a waveguide in a multilayer substrate. One route to achieve this is by overlaying the grating with a liquid crystal as many liquid crystals display refractive index anisotropy that can be electrically manipulated. Modifying the liquid crystal refractive index subsequently alters the effective index of the waveguide, leading to Bragg wavelength shift. Using this approach, Sparrow et al [1] have previously demonstrated 35GHz tunability at 1560nm using 80Vpp (peak-to-peak) square-wave with 250mm-spaced aluminium electrodes. Here, we report a maximum tunability of 114GHz at 1561.8nm using patterned ITO glass electrodes with 170Vpp voltage at 1kHz. Two distinct threshold behaviors which manifest only during the increase of supply voltage were also observed
Towards high-speed liquid crystal electrically tunable planar Bragg gratings for integrated optical networks
No full textLiquid crystal-based integrated optical devices offer the potential for high speed and dynamically tunable optical switches in modern telecommunications networks. Here, electrically tunable devices have major advantages over their thermal counterparts, with superior response times and low operating voltages (~100V). Our approach to achieving such devices is to fabricate planar optical waveguides with integrated Bragg gratings via direct UV writing1 into silica-on-silicon samples with evanescent field coupling into a liquid crystal overlay through an etched window (Fig. 1(a)). Such electrically tunable devices work on the principle of shifting the Bragg wavelength by modifying the effective index of a waveguide in a multilayer substrate. Electrically controlled liquid crystal birefringence modifies the waveguide effective index, producing a Bragg wavelength shift. In our early samples, Merck 18523 nematic liquid crystal is used as it has a compatible refractive index to silica (n=1.49 at lambda=1550nm). Homeotropic alignment of the liquid crystal is provided by application of a surfactant layer
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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