315 research outputs found
UV-Photoinduced Defects In Ge-Doped Optical Fibers
We investigated the effect of continuous-wave (cw) UV laser radiation on
single-mode Ge-doped H2- loaded optical fibers. An innovative technique was
developed to measure the optical absorption (OA) induced in the samples by
irradiation, and to study its dependence from laser fluence. The combined use
of the electron spin resonance (ESR) technique allowed the structural
identification of several radiation-induced point defects, among which the
Ge(1) (GeO4 -) is found to be responsible of induced OA in the investigated
spectral region.Comment: 5 pages, 7 figure
Influence of fluorine on the fiber performance studied through the NBOHC-related 1.9 eV microluminescence
The distribution of Non Bridging Oxygen Hole Centers (NBOHC) in Fluorine doped optical fibers was investigated by confocal microluminescence spectroscopy monitoring the characteristic 1.9 eV luminescence band. The results show that these defects are generated by the fiber drawing and their concentration further increases after \u3b3 irradiation.
The NBOHC profile along the fiber is anticorrelated to the fluorine content. This finding agrees with the role of
fluorine in the fiber toughness and is discussed from the microscopic point of view on the basis of previous works
Radiation hardening of Rare-Earth doped fiber amplifiers
We investigated the radiation hardening of optical fiber amplifiers operating in space environments. Through a
real-time analysis in active configuration, we evaluated the role
of Ce in the improvement of the amplifier performance against
ionizing radiations. Ce-codoping is an efficient hardening solution, acting both in the limitation of defects in the host glass matrix of RE-doped optical fibers and in the stabilization of lasing properties of the Er3+-ions. On the one hand, in the nearinfrared
region, radiation induced attenuation measurements show the absence of radiation induced P-related defect species in host glass matrix of the Ce-codoped active fibers; on the other
hand, in the Ce-free fiber, the higher lifetime variation shows stronger local modifications around the Er3+-ions with the absence of Ce
Small Angle Scattering by Fractal Aggregates: A Numerical Investigation of the Crossover Between the Fractal Regime and the Porod Regime
Fractal aggregates are built on a computer using off-lattice cluster-cluster
aggregation models. The aggregates are made of spherical particles of different
sizes distributed according to a Gaussian-like distribution characterised by a
mean and a standard deviation . The wave vector dependent
scattered intensity is computed in order to study the influence of the
particle polydispersity on the crossover between the fractal regime and the
Porod regime. It is shown that, given , the location of the
crossover decreases as increases. The dependence of on
can be understood from the evolution of the shape of the center-to-center
interparticle-distance distribution function.Comment: RevTex, 4 pages + 6 postscript figures, compressed using "uufiles",
published in Phys. Rev. B 50, 1305 (1994
Kinetics of Blue Emission during Ultraviolet Insolation on Germanosilicate Optical Fiber
The research aimed to study the kinetics of 400 nm blue emission during ultraviolet insolation on germanoslicate optical fiber, hydrogenated, and non-hydrogenataed. The hydrogenation of the fibers was carried out at room temperature under 150 atm for 4 weeks. The focused frequency doubled Argon laser ultraviolet beams were directed to the core of the unsheathed fiber. The light beams emerging from the end of the fiber were directed towards a detector. Kinetics the creation of defects in the hydrogenated fiber followed the power law for low fluency insolation. At high fluency, the formation of defects followed the principle of two photosensitization or serial steps
v-P 2 O 5 micro-clustering in P-doped silica studied by a first-principles Raman investigation
Synthetic vitreous silica is currently the preferred material for the production of optical fibres because of the several excellent properties of this glass, e.g. high transmission in the visible and IR domains, high mechanical strength, chemical durability, and ease of doping with various materials. For instance, fiber lasers and amplifiers exploit the light amplification properties provided by rare-earth ions employed as dopants in the core of silica-based optical fibers. The structure and composition of the nearest neighbor shell surrounding rare-earth ions in silica-based optical fibers and amplifiers have been intensively debated in the last decade. To reduce aggregation effects between rare-earth ions, co-dopants such as phosphorus and aluminium are added as structural modifiers; phosphorus-doping, in particular, has proved to be very efficient in dissolving rare-earth ions. In this work, we provide further insights concerning the embedding of P atoms into the silica network, which may be relevant for explaining the ease of formation of a phosphorus pentoxide nearest-neighbor shell around a rare-earth dopant. In particular, by means of first-principles calculations, we discuss alternative models for an irradiation (UV, x\u2013, \u3b3-rays) induced paramagnetic center, i.e. the so called room-temperature phosphorus-oxygen-hole center, and its precursors. We report that the most likely precursor of a room-temperature phosphorus-oxygen-hole center comprises of a micro-cluster of a few (at least two) neighboring phosphate tetrahedra, and correspondingly that the occurrence of isolated [(O-) 2 P(=O) 2 ] 12 units is unlikely even at low P-doping concentrations. In fact, this work predicts that the symmetric stretching of P=O bonds in isolated [(O-) 2 P(=O) 2 ] 12 units appears as a Raman band at a frequency of ~1110 cm 121 , and only by including at least another corner-sharing phosphate tetrahedron, it is shown to shift to higher frequencies (up to ~40 cm 121 ) due to the shortening of P=O bonds, thereby leading to an improved agreement with the observed Raman band located at ~1145 cm 121
Hydroxyl Properties of Hydrogenated Germanosilicate Optical Fiber Due to Thermal Treatment and Ultraviolet Irradiation
The aim of the research was to examine the formation and destruction of the hydroxyl in optical fibers
by comparing the ambient atmosphere, air, and nitrogen during thermal treatment from room temperature
up to 1100 °C. It has been shown that during the heat treatment, molecular hydrogen dissolved in the fiber
plays no role in the formation of OH while under UV irradiation the formation is dependent on the
presence of dissolved hydrogen. The heat treatment preferentially leads to the formation of Si-OH, while
during irradiation it assists the formation of both Ge-OH and Si-OH
Performance Analysis of a Prototype High-Concentration Photovoltaic System Coupled to Silica Optical Fibers
High-concentration photovoltaic (HCPV) systems are one of the most promising technologies for the generation of renewable energy with high-conversion efficiency. Their development is still at an early stage, but the possibility of integrating high-concentration systems into buildings offers new opportunities to achieve the net-zero-energy building goal. Herein, the optical and energetic performance of a hybrid daylighting−HCPV prototype based on pure- or doped-silica optical fibers (OFs) to guide 2000× concentrated sunlight inside the buildings is evaluated. There, the light can either be used to illuminate interior spaces or projected on solar cells to generate electricity. The system equipped with a single 400 μm core-diameter OF is demonstrated to achieve a total efficiency of 15% and an optical efficiency of 45%
Raman scattering from fractals. Simulation on large structures by the method of moments
We have employed the method of spectral moments to study the density of
vibrational states and the Raman coupling coefficient of large 2- and 3-
dimensional percolators at threshold and at higher concentration. We first
discuss the over-and under-flow problems of the procedure which arise when
-like in the present case- it is necessary to calculate a few thousand moments.
Then we report on the numerical results; these show that different scattering
mechanisms, all {\it a priori} equally probable in real systems, produce
largely different coupling coefficients with different frequency dependence.
Our results are compared with existing scaling theories of Raman scattering.
The situation that emerges is complex; on the one hand, there is indication
that the existing theory is not satisfactory; on the other hand, the
simulations above threshold show that in this case the coupling coefficients
have very little resemblance, if any, with the same quantities at threshold.Comment: 26 pages, RevTex, 8 figures available on reques
Radiation hardening techniques for rare-earth based optical fibers and amplifiers
Er/Yb doped fibers and amplifiers have been shown to be very radiation sensitive, limiting their integration in space. We present an approach including successive hardening techniques to enhance their radiation tolerance. The efficiency of our
approach is demonstrated by comparing the radiation responses of optical amplifiers made with same lengths of different rare-earth doped fibers and exposed to gamma-rays. Previous studies indicated that such amplifiers suffered significant degradation for doses exceeding 10 krad. Applying our techniques significantly enhances the amplifier radiation resistance, resulting in a very limited degradation up to 50 krad. Our optimization techniques concern the fiber composition, some possible pre-treatments and the interest of simulation tools used to harden by design the amplifiers.
We showed that adding cerium inside the fiber phosphosilicate-based core strongly decreases the fiber radiation
sensitivity compared to the standard fiber. For both fibers, a pre-treatment with hydrogen permits to enhance again the fiber resistance. Furthermore, simulations tools can also be used to improve the tolerance of the fiber amplifier by
helping identifying the best amplifier configuration for operation in the radiative environment
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