Modelling an Optical Fiber Bragg Grating

A theoretical investigation of a single mode optical fiber with one and two superimposed Bragg grating is presented. The formulation relies in the determination of an approximate solution in the asymptotic region of one of the fiber parameters. A correction is then applied to the asymptotic solution using the Method of the Successive Approximations also known as the Piccard Method. The approximation was then compared to the numerical solution using the Runge-Kutta method. Assuming that each Bragg grating has modulation frequencies given by Ω1 and Ω2, it has been found that the second Bragg grating shifts the peak reflectivity of the first one by a small amount. The direction of the shift depends on the relative value of Ω1 and Ω2. The fiber Bragg grating solution has been succesfully applied to other fiber devices

Injection efficiency of bound modes

Previous work on efficiency of light injection into the core of a fiber from a thin film and a bulk distribution of sources in the cladding, have made use of the fields of a weakly guiding fiber. This approximation simplifies the analysis of the power efficiency by introducing universal values for the eigenvalues of different fibers with same {dollar}V{dollar}-number, but can not predict accurately the behavior of the injected light into a fiber with arbitrary differences in indices of refraction. We have used the exact field solution in the expressions of the power efficiency, {dollar}P\sb{lcub}\rm eff{rcub}{dollar}, and analyzed its behavior as a function of the remaining parameters. Although more complicated and harder to interpret, our formulas allow us to analyze the power injection efficiency of fibers with arbitrary differences in the indices of refraction. The results obtained are relevant for the design of more efficient optical fiber distributed sensors. The conclusions follow.;We have confirmed weakly guiding results obtained previously. However, we have found that the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} does not always increase with the {dollar}V{dollar}-number but with the difference in the indices of refraction, {dollar}n\sb{lcub}\rm core{rcub} -n\sb{lcub}\rm clad{rcub}{dollar}.;For fixed {dollar}a/\lambda{dollar}, indices of refraction, {dollar}n\sb{lcub}\rm core{rcub}{dollar} and {dollar}n\sb{lcub}\rm clad{rcub}{dollar} and normalized inner and outer radius, {dollar}R\sb{lcub}\rm in{rcub}{dollar} and {dollar}R\sb{lcub}\rm out{rcub}{dollar}, the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} is independent of core radius, {dollar}a{dollar}, and the wavelength, {dollar}\lambda{dollar}. This applies for any uniform cylindrical distribution of cladding sources. This result suggests that {dollar}a/\lambda, R\sb{lcub}\rm in{rcub}{dollar} and {dollar}R\sb{lcub}\rm out{rcub}{dollar} are independent variables.;For the bulk distribution we have found that {dollar}P\sb{lcub}\rm eff{rcub}{dollar} increases with the wavelength, {dollar}\lambda{dollar}, and decreases with the fiber core radius, {dollar}a{dollar}, i.e., it decreases with the {dollar}V{dollar}-number. However, for the thin film, the {dollar}P\sb{lcub}\rm eff{rcub}{dollar} remains almost constant with the wavelength, {dollar}\lambda{dollar}, and fiber core radius, {dollar}a{dollar}

Antimicrobial and cleaning modes of action of peroxide and reactive oxygen species for combating biofilms

Poor denture hygiene is the underlying cause behind several undesirable effects including denture stomatitis, bad breath, staining among others. Dentures are immediately exposed to microbes and quickly become colonized by biofilm. Dentures therefore require regular cleaning and disinfection by a safe and reliable product. With this in view, the effects of reactive oxygen species (ROS) in the removal of biofilms and stains were studied. Furthermore, the kinetics of the reaction and the pH conditions necessary for effective production of reactive oxygen species within a formulation and its antibiofilm properties were also investigated. 1H-NMR was used to kinetically follow ROS production at different pH in the tetraacetylethylenediamine (TAED)/ hydrogen peroxide (H2O2) system within different formulations and complemented with fluorometric detection of ROS. Subsequently the antimicrobial properties of the tested formulations were observed against oral microorganisms in suspension and were supplemented with biofilm studies to visualize the biofilm removal properties of ROS using confocal microscopy and scanning electron microscopy. Quantitative 1H-NMR and fluorimetry proved to be robust and reliable methods to assess the efficacy of a formulation in delivering ROS. At pH 5.5, the reaction progressed more slowly but generated a higher amount of singlet oxygen while at pH 7 the initial reaction occurred slightly faster, but the generation of ROS was slower. ROS were also a key component in the removal of biofilm. When Polident was tested vs a placebo tablet it was observed that Polident not only removed biofilm but also killed nearly all of the remaining cells while placebo only managed to remove some biofilm and left many live cells. At optimal pH with only ROS as a weapon our novel formulations achieved results comparable with the denture cleanser tablet proving the excellent antimicrobial properties of ROS

Optical fiber strain sensor with improved linearity range

A strain sensor is constructed from a two mode optical fiber. When the optical fiber is surface mounted in a straight line and the object to which the optical fiber is mounted is subjected to strain within a predetermined range, the light intensity of any point at the output of the optical fiber will have a linear relationship to strain, provided the intermodal phase difference is less than 0.17 radians

Optical fiber sensor having an active core

An optical fiber is provided. The fiber is comprised of an active fiber core which produces waves of light upon excitation. A factor ka is identified and increased until a desired improvement in power efficiency is obtained. The variable a is the radius of the active fiber core and k is defined as 2 pi/lambda wherein lambda is the wavelength of the light produced by the active fiber core. In one embodiment, the factor ka is increased until the power efficiency stabilizes. In addition to a bare fiber core embodiment, a two-stage fluorescent fiber is provided wherein an active cladding surrounds a portion of the active fiber core having an improved ka factor. The power efficiency of the embodiment is further improved by increasing a difference between the respective indices of refraction of the active cladding and the active fiber core

Transversely polarized source cladding for an optical fiber

An optical fiber comprising a fiber core having a longitudinal symmetry axis is provided. An active cladding surrounds a portion of the fiber core and comprises light-producing sources which emit light in response to chemical or light excitation. The cladding sources are oriented transversely with respect to the longitudinal axis of the fiber core. This polarization results in a superior power efficiency compared to active cladding sources that are randomly polarized or longitudinally polarized parallel with the longitudinal symmetry axis

Strain sensor comprising a strain sensitive, two-mode optical

A strain sensor uses an optical fiber including a strain sensitive portion and at least one strain insensitive portion. The strain sensitive portion is mounted on the surface of a structure at a location where a strain is desired to be measured. The strain insensitive portion(s) may be fused to the strain sensitive portion to transmit light therethrough, so that the resulting pattern may be detected to determine the amount of strain by comparison with a similar fiber not subjected to strain, or with the light pattern produced when the fiber is not under strain

The Use of Deep Learning in Verifying the Functioning of LEDs

This article aims to bring an alternative to carrying out manual tests of devices mounted on a production line. One of the tests done by the operator is to find out if the LEDs are present on the device being turned on and working correctly. Image processing techniques were applied in the elaboration of the dataset and the use of Convolutional Neural Networks for the classification of the colors presented by the LEDs and the recognition of their operation. An accuracy of 99.25% was obtained with a low percentage of false positives and true negatives. There were no difficulties in porting the model built to a small computer

Fósforo, nitrogênio, lignina, celulose e polifenóis em amostras de serrapilheira foliar de Neea macrophylla, Cecropia palmata e Casearia arborea no Nordeste do Estado do Pará.

A necessidade de se conhecer a dinâmica de decomposição da serrapilheira (liteira) foliar de espécies potencialmente acumuladoras de fósforo (P) como Neea macrophylla e Cecropia palmata ao longo do tempo, é fundamental na seleção de mulch para a tecnologia de preparo de área para plantio denominada slash and mulch adotada em alguns sistemas agrícolas a Nordeste do Estado do Pará. Com o intuito de caracterizar quantitativamente e temporalmente as Taxas de Incremento de P e N ao longo do processo inicial de decomposição da liteira foliar das espécies estudadas correlacionando com as concentrações iniciais de lignina, celulose e polifenóis, este experimento foi então desenvolvido alocando-se bolsas de decomposição sobre a serrapilheira de uma floresta secundária no Município de Igarapé-Açú, estado do Pará. Os resultados indicaram uma alta correlação (r=-0,82) entre a concentração de polifenóis iniciais no liteira e a perda de biomassa ao longo de 210 dias; a liberação de fósforo (P) durante o processo de decomposição foi determinada em parte pelas concentrações de lignina iniciais (r=-0,54) mas sobretudo de celulose (r=-0,73) e as concentrações de N-NH4 na liteira foliar ao final do período de observação mostraram dependência da concentração inicial de lignina. Neea macrophylla foi a espécie que perdeu mais rapidamente biomassa para o solo mostrando ser uma espécie importante no processo de ciclagem de fósforo em ambientes com deficiência