1,720,974 research outputs found
All-UV-written integrated planar Bragg gratings and channel waveguides with no phase mask
No full textDirect UV writing provides an attractive route towards low-cost integrated optical components in photosensitive silica-on-silicon wafers. Combining closely packed channel waveguides with a Bragg grating tailored spectral response would allow the creation of compact systems for wavelength division multiplexing on a single optical chip. To this end, we present our new technique for simultaneous definition of channel waveguides with integral Bragg gratings based on the interference of two focussed UV-writing beams. This single-step approach promotes optimal use of sample photosensitivity for both the waveguide geometry and Bragg grating structure and allows implementation of many aspects of advanced grating design, such as chirp and apodisation, with no need for a phase mask
All-UV written integrated glass devices including planar Bragg gratings and lasers
No full textOne attractive route to low-cost integrated optical components is the use of direct UV writing. This technique may be applied to a wide range of materials including silica-on-silicon wafers, compound oxide glasses, directly bonded glass composites and GLS. This presentation will focus on the first of these material systems - silica-on-silicon. This has a number of attractive features including fibre compatibility, industrial acceptance, stability and most importantly for our work a photosensitivity depends light intensity and not the thermal effects found in many materials. Recent developments of the UV writing technique at Southampton have allowed the realisation of high quality Bragg gratings in silica-on-silicon by simultaneous writing of the channel waveguides and gratings (the direct grating writing technique). This approach together with wavelength detuning, allows an unprecedented range of wavelengths to be written under software control. Latest results will be presented covering laser operation in Neodymium doped channels, small angle couplers, sensors based on planar gratings and liquid crystal tunable devices
Investigation of thermal stability of UV written planar waveguides using direct grating writing
No full textWe use the Direct Grating Writing technique, based on Direct UV writing, to define planar Bragg channel waveguides and accurately probe the refractive index to characterise thermal waveguide erasure and material properties
All-UV-written integrated planar Bragg gratings and channel waveguides through single-step direct grating writing
No full textWe present a single-step technique for defining 2-dimensional integrated channel waveguide structures with internal Bragg gratings in photosensitive germanosilica-on-silicon substrates using two interfering focussed UV beams. Detailed device analysis of the relationship between the photosensitive properties of the glass, UV writing conditions, and subsequent refractive index change and channel waveguide strength is presented based on grating characterisation. Through software control, 300nm wide grating detuning across the E, S, C, L, and U wavelength bands is demonstrated
Single-mode direct-ultraviolet-written channel waveguide laser in neodymium-doped silica on silicon
No full textA waveguide laser with a neodymium-doped silica core is fabricated on a silicon substrate by a combination of flame hydrolysis deposition, solution doping, and direct UV writing. The neodymium-ion concentration is estimated to be ~8000 parts in 106. The propagation loss around 1.05 µm is < 0.8dB/cm. Lasing in the range 1048-1056 nm and 1356 ± 1 nm is observed. A slope efficiency of 33% for a high-reflectivity output coupler and a threshold of 4 mW of absorbed power for a 25% output coupler are measured for the 4F3/2 <--> 4I11/2 transition
Assessment of waveguide thermal response by interrogation of UV written planar gratings
No full textThe technique of direct grating writing, based on direct ultraviolet writing, is demonstrated as a tool for highly accurate measurement of waveguide and material properties. Silica-on-silicon planar samples are processed using hydrogen loading and thermal locking before Bragg channel waveguides are defined in the photosensitive core layer. The refractive index is accurately probed to compare different thermal locking procedures and characterize waveguide thermal stability
Rapid heat treatment for photosensitivity locking in deuterium-loaded planar optical waveguides
Full text linkPermanent deuterium enhanced photosensitivity is demonstrated-in Ge-doped silica-on-silicon thin film layers by applying a rapid thermal process. The long term photosensitivity locking obtained should enable the development of all UV-written devices limited to date by the rapid deuterium outdiffusion during fabrication
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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