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  • Fabrication of electron beam generated, chirped, phase mask (1070 . 11 – 1070 . 66 nm) for fiber Bragg grating dispersion compensator

    Resource Type:
    Article
    Creator:
    Hill, K.O., Johnson, D.C., Mihailov, S.J., McClelland, A.W., Stryckman, D., Bilodeau, F., Albert, Jacques, Carr, D.W., Hugues, B.J., Tiberio, R.C., and Rooks, M.J.
    Abstract:
    We report on the fabrication of a chirped, phase mask that was used to create a fiber Bragg grating(FBG)device for the compensation of chromatic dispersion in longhaul optical transmission networks.Electron beamlithography was used to expose the grating onto a resist-coated quartz plate. After etching, this phase mask was used to holographically expose an index grating into the fiber core [K. O. Hill, F. Bilodeau, D. C. Johnson, and J. Albert, Appl. Phys. Lett.62, 1035 (1993)]. The linear increase in the grating period, “chirp,” is only 0.55 nm over the 10 cm grating. This is too small to be defined by computer aided design and a digital deflection system. Instead, the chirp was incorporated by repeatedly rescaling the analog electronics used for field size calibration. Special attention must be paid to minimize any field stitching and exposure artifacts. This was done by using overlapping fields in a “voting” method. As a result, each grating line is exposed by the accumulation of three overlapping exposures at 1/3 dose. This translates any abrupt stitching error into a small but uniform change in the line-to-space ratio of the grating. The phase mask was used with the double-exposure photoprinting technique [K. O. Hill, F. Bilodeau, B. Malo, T. Kitagawa, S. Thériault, D. C. Johnson, J. Albert, and K. Takiguchi, Opt. Lett. 19, 1314 (1994)]: a KrF excimer laser holographically imprints an apodized chirped Bragg grating in a hydrogen loaded SMF-28 optical fiber. Our experiments have demonstrated a spectral delay of −1311 ps/nm with a linearity of +/−10 ps over the 3 dB bandwidth of the resonant wavelength of the FBG. The reflectance, centered on 1550 nm, shows a side-lobe suppression of −25 dB. Fabrication processes and optical characterization will be discussed.
    Date Created:
    1998-09-16

  • A thin metal sheath lifts the EH to HE degeneracy in the cladding mode refractometric sensitivity of optical fiber sensors

    Resource Type:
    Article
    Creator:
    Albert, Jacques, Berini, P., Chen, Chengkun, Caucheteur, C., and Voisin, V.
    Abstract:
    The effective indices of the cladding modes of optical fibers depend on the refractive index of the medium surrounding the fiber. We show experimentally and theoretically that while cladding modes with similar effective indices normally have similar refractometric sensitivities, the addition of a 50 nm thick gold sheath enhances the sensitivity of some EH modes by more than one order of magnitude while nearly completely suppressing the sensitivity of neighbouring HE modes (by three orders of magnitude, down to insignificant levels). A differential sensitivity of ∼1000 nm/(refractive index unit) is experimentally reported between adjacent EH and HE grating resonances.
    Date Created:
    2011-07-25

  • Four-wave mixing in carbon nanotube-coated optical fiber gratings

    Resource Type:
    Article
    Creator:
    Shao, Li-Yang, Simard, Benoit, Albert, Jacques, Sun, Tingting, and Jakubinek, Michael B.
    Abstract:
    The observation of four-wave mixing (FWM) in single-walled carbon nanotubes (SWCNTs) deposited around a tilted fiber Bragg grating (TFBG) has been demonstrated. A thin, floating SWCNT film is manually wrapped around the outer cladding of the fiber and FWM occurs between two core-guided laser signals by TFBG-induced interaction of the core mode and cladding modes. The effective nonlinear coefficient is calculated to be 1.8 10 3W -1Km -1. The wavelength of generated idlers is tunable with a range of 7.8 nm.
    Date Created:
    2012-02-13

  • Bragg gratings fabricated in monomode photosensitive optical fiber by UV exposure through a phase mask

    Resource Type:
    Article
    Creator:
    Albert, Jacques, Bilodeau, F., Malo, B., Hill, K. O., and Johnson, D. C.
    Abstract:
    A photolithographic method is described for fabricating refractive index Bragg gratings in photosensitive optical fiber by using a special phase mask grating made of silica glass. A KrF excimer laser beam (249 nm) at normal incidence is modulated spatially by the phase mask grating. The diffracted light, which forms a periodic, high-contrast intensity pattern with half the phase mask grating pitch, photoimprints a refractive index modulation into the core of photosensitive fiber placed behind, in proximity, and parallel, to the mask; the phase mask grating striations are oriented normal to the fiber axis. This method of fabricating in-fiber Bragg gratings is flexible, simple to use, results in reduced mechanical sensitivity of the grating writing apparatus and is functional even with low spatial and temporal coherence laser sources.
    Date Created:
    1993-12-01

  • Simultaneous corona poling of multiple glass layers for enhanced effective second-order optical nonlinearities

    Resource Type:
    Article
    Creator:
    Blanchetiere, C., Jacob, S., Callender, C. L., Albert, Jacques, Yadav, Ksenia, and Smelser, Christopher W.
    Abstract:
    Silica-based thin-film multilayers are investigated as a means to enhance the effective second-order nonlinearity induced in silica glass structures by corona poling. Structures consisting of phosphorus-doped and undoped silica glass layers exhibit second harmonic generation (SHG) that is higher by an order of magnitude compared to the SHG in bulk silica glass poled under the same conditions. When the poled structure consists of two multilayered stacks separated in space, the stacks exhibit comparable poling-induced nonlinearities. This result suggests that the poling voltage is divided between the two stacks such that simultaneous poling of multiple regions within the sample is realized.
    Date Created:
    2011-07-18

  • Photosensitivity in phosphorus-doped silica glass and optical waveguides

    Resource Type:
    Article
    Creator:
    Hibino, Y., Hattori, K., Johnson, D. C., Hill, K. O., Kitagawa, T., Albert, Jacques, Bilodeau, F., Malo, B., and Gujrathi, S.
    Date Created:
    1994-12-01

  • 1 W tunable dual-wavelength emission from cascaded distributed feedback fiber lasers

    Resource Type:
    Article
    Creator:
    Zhu, X., Peyghambarian, N., Albert, Jacques, Li, L., Moloney, J. V., and Schülzgen, A.
    Date Created:
    2008-02-15

  • Difference in the behavior of oxygen deficient defects in Ge-doped silica optical fiber preforms under ArF and KrF excimer laser irradiation

    Resource Type:
    Article
    Creator:
    Essid, Mourad, Brebner, J.L., Awazu, K., and Albert, Jacques
    Abstract:
    Photobleaching of optical absorption bands in the 5 eV region and the creation of others at higher and lower energy have been examined in the case of ArF (6.4 eV) and KrF (5 eV) excimer laserirradiation of 3GeO2:97SiO2glasses. We report a difference in the transformation process of the neutral oxygen monovacancy and also of the germanium lone pair center (GLPC) into electron trap centers associated with fourfold coordinated Ge ions and Ge-E′ centers when we use one or the other laser. Correlations between absorption bands and electron spin resonance signals were made after different steps of laser irradiation. It was found that the KrF laser generates twice as many Ge-E′ centers as the ArF laser for the same dose of energy delivered. The main reason for this difference is found to be the more efficient bleaching of the GLPC (5.14 eV) by the KrF laser compared to that by the ArF laser.
    Date Created:
    1998-10-15

  • Si ion implantation-induced damage in fused silica probed by variable-energy positrons

    Resource Type:
    Article
    Creator:
    Simpson, P.J., Ilard, L.B., Brebner, J.L., Knights, A.P., and Albert, Jacques
    Abstract:
    Samples of synthetic fused silica have been implanted at room temperature with silicon ions of energy 1.5 MeV. Fluences ranged from 1011 to 1013 cm−2. Samples were probed using variable‐energy positron annihilation spectroscopy. The Doppler‐broadening S parameter corresponding to the implanted region decreased with increasing fluence and saturated at a fluence of 1013 cm−2. It is shown that the decrease in the S parameter is due to the suppression of positronium (Ps) which is formed in the preimplanted material, due to the competing process of implantation‐induced trapping of positrons. In order to satisfactorily model the positron data it was necessary to account for positron trapping due to defects created by both electronic and nuclear stopping of the implanted ions. Annealing of the 1013 cm−2 sample resulted in measurable recovery of the preimplanted S parameter spectrum at 350 °C and complete recovery to the preimplanted condition at 600 °C. Volume compaction was also observed afterimplantation. Upon annealing, the compaction was seen to decrease by 75%.
    Date Created:
    1996-06-16

  • Comparison of one-photon and two-photon effects in the photosensitivity of germanium-doped silica optical fibers exposed to intense ArF excimer laser pulses

    Resource Type:
    Article
    Creator:
    Johnson, D. C., Malo, B., Hill, K. O., Thériault, S., Bilodeau, F., and Albert, Jacques
    Date Created:
    1995-12-01

  • Route discovery with constant memory in oriented planar geometric networks

    Resource Type:
    Article
    Creator:
    Urrutia, J., Opatrny, J., Chávez, E., Dobrev, S., Stacho, L., and Kranakis, Evangelos
    Abstract:
    We address the problem of discovering routes in strongly connected planar geometric networks with directed links. Motivated by the necessity for establishing communication in wireless ad hoc networks in which the only information available to a vertex is its immediate neighborhood, we are considering routing algorithms that use the neighborhood information of a vertex for routing with constant memory only. We solve the problem for three types of directed planar geometric networks: Eulerian (in which every vertex has the same number of incoming and outgoing edges), Outerplanar (in which a single face contains all vertices of the network), and Strongly Face Connected, a new class of geometric networks that we define in the article, consisting of several faces, each face being a strongly connected outerplanar graph.
    Date Created:
    2006-08-01

  • An identification-robust test for time-varying parameters in the dynamics of energy prices

    Resource Type:
    Article
    Creator:
    Khalaf, Lynda A., Kichian, Maral, Bernard, Jean-Thomas, and Dufour, Jean-Marie
    Abstract:
    We test for the presence of time-varying parameters (TVP) in the long-run dynamics of energy prices for oil, natural gas and coal, within a standard class of mean-reverting models. We also propose residual-based diagnostic tests and examine out-of-sample forecasts. In-sample LR tests support the TVP model for coal and gas but not for oil, though companion diagnostics suggest that the model is too restrictive to conclusively fit the data. Out-of-sample analysis suggests a random-walk specification for oil price, and TVP models for both real-time forecasting in the case of gas and long-run forecasting in the case of coal.
    Date Created:
    2012-06-01

  • Age-at-arrival differences in home-ownership attainment among immigrants and their foreign-born offspring in Canada

    Resource Type:
    Article
    Creator:
    Mendez, Pablo
    Abstract:
    This paper asks whether age at arrival matters when it comes to home-ownership attainment among immigrants, paying particular attention to householders' self-identification as a visible minority. Combining methods that were developed separately in the immigrant housing and the immigrant offspring literatures, this study shows the importance of recognising generational groups based on age at arrival, while also accounting for the interacting effects of current age (or birth cohorts) and arrival cohorts. The paper advocates a (quasi-)longitudinal approach to studying home-ownership attainment among immigrants and their foreign-born offspring. Analysis of data from the Canadian Census reveals that foreign-born householders who immigrated as adults in the 1970s and the 1980s are more likely to be home-owners than their counterparts who immigrated at a younger age when they self-identify as South Asian or White, but not always so when they self-identify as Chinese or as ‘other visible minority’. The same bifurcated pattern recurs between householders who immigrated at secondary-school age and those who were younger upon arrival. Age at arrival therefore emerges as a variable of significance to help explain differences in immigrant housing outcomes, and should be taken into account in future studies of immigrant home-ownership attainment. Copyright © 2009 John Wiley & Sons, Ltd.
    Date Created:
    2009-01-01

  • Subterranean Commodification: Informal Housing and the Legalization of Basement Suites in Vancouver from 1928 to 2009

    Resource Type:
    Article
    Creator:
    Quastel, Noah and Mendez, Pablo
    Abstract:
    This article draws on Margaret Radin's theorization of 'contested commodities' to explore the process whereby informal housing becomes formalized while also being shaped by legal regulation. In seeking to move once-informal housing into the domain of official legality, cities can seldom rely on a simple legal framework of private-law principles of property and contract. Instead, they face complex trade-offs between providing basic needs and affordability and meeting public-law norms around living standards, traditional neighbourhood feel and the environment. This article highlights these issues through an examination of the uneven process of legal formalization of basement apartments in Vancouver, Canada. We chose a lengthy period-from 1928 to 2009-to explore how basement apartments became a vital source of housing often at odds with city planning that has long favoured a low-density residential built form. We suggest that Radin's theoretical account makes it possible to link legalization and official market construction with two questions: whether to permit commodification and how to permit commodification. Real-world commodification processes-including legal sanction-reflect hybridization, pragmatic decision making and regulatory compromise. The resolution of questions concerning how to legalize commodification are also intertwined with processes of market expansion.
    Date Created:
    2015-11-01

  • A geography-based critique of new US biofuels regulations

    Resource Type:
    Article
    Creator:
    Fast, Stewart, Saner, Marc, and Brklacich, Michael
    Abstract:
    The new renewable fuels standard (RFS 2) aims to distinguish corn-ethanol that achieves a 20% reduction in greenhouse gas (GHG) emissions compared with gasoline. Field data from Kim et al. (2009) and from our own study suggest that geographic variability in the GHG emissions arising from corn production casts considerable doubt on the approach used in the RFS 2 to measure compliance with the 20% target. If regulators wish to require compliance of fuels with specific GHG emission reduction thresholds, then data from growing biomass should be disaggregated to a level that captures the level of variability in grain corn production and the application of life cycle assessment to biofuels should be modified to capture this variability.
    Date Created:
    2012-05-01

  • Reframing the history of new religious movements

    Resource Type:
    Article
    Creator:
    Driedger, Michael and Wolfart, Johannes
    Abstract:
    In this special issue of Nova Religio four historians of medieval and early modern Christianities offer perspectives on basic conceptual frameworks widely employed in new religions studies, including modernization and secularization, radicalism/violent radicalization, and diversity/diversification. Together with a response essay by J. Gordon Melton, these articles suggest strong possibilities for renewed and ongoing conversation between scholars of "old" and "new" religions. Unlike some early discussions, ours is not aimed simply at questioning the distinction between old and new religions itself. Rather, we think such conversation between scholarly fields holds the prospect of productive scholarly surprise and perspectival shifts, especially via the disciplinary practice of historiographical criticism.
    Date Created:
    2018-05-01

  • Continuity and change in the home literacy environment as predictors of growth in vocabulary and reading

    Resource Type:
    Article
    Creator:
    LeFevre, Jo-Anne and Sénéchal, Monique
    Abstract:
    One hundred and ten English-speaking children schooled in French were followed from kindergarten to Grade 2 (Mage: T1 = 5;6, T2 = 6;4, T3 = 6;11, T4 = 7;11). The findings provided strong support for the Home Literacy Model (Sénéchal & LeFevre, 2002) because in this sample the home language was independent of the language of instruction. The informal literacy environment at home predicted growth in English receptive vocabulary from kindergarten to Grade 1, whereas parent reports of the formal literacy environment in kindergarten predicted growth in children's English early literacy between kindergarten and Grade 1 and growth in English word reading during Grade 1. Furthermore, 76% of parents adjusted their formal literacy practices according to the reading performance of their child, in support of the presence of a responsive home literacy curriculum among middle-class parents.
    Date Created:
    2014-01-01

  • Polarization-selective grating excitation of plasmons in cylindrical optical fibers

    Resource Type:
    Article
    Creator:
    Albert, Jacques, Dakka, Milad A., Shevchenko, Yanina, and Chen, Chengkun
    Abstract:
    We show that the tilted-grating-assisted excitation of surface plasmon polaritons on gold coated single-mode optical fibers depends strongly on the state of polarization of the core-guided light, even in fibers with cylindrical symmetry. Rotating the linear polarization of the guided light by 90° relative to the grating tilt plane is sufficient to turn the plasmon resonances on and off with more than 17 dB of extinction ratio. By monitoring the amplitude changes of selected individual cladding mode resonances we identify what we believe to be a new refractive index measurement method that is shown to be accurate to better than 5 × 10-5.
    Date Created:
    2010-03-01

  • The role of invented spelling on learning to read in low-phoneme awareness kindergartners: A randomized-control-trial study

    Resource Type:
    Article
    Creator:
    Lever, Rosemary, Ouellette, Gene, Pagan, Stephanie, and Sénéchal, Monique
    Abstract:
    The goal of the present intervention research was to test whether guided invented spelling would facilitate entry into reading for at-risk kindergarten children. The 56 participating children had poor phoneme awareness, and as such, were at risk of having difficulty acquiring reading skills. Children were randomly assigned to one of three training conditions: invented spelling, phoneme segmentation, or storybook reading. All children participated in 16 small group sessions over eight weeks. In addition, children in the three training conditions received letter-knowledge training and worked on the same 40 stimulus words that were created from an array of 14 letters. The findings were clear: on pretest, there were no differences between the three conditions on measures of early literacy and vocabulary, but, after training, invented spelling children learned to read more words than did the other children. As expected, the phoneme-segmentation and invented-spelling children were better on phoneme awareness than were the storybook-reading children. Most interesting, however, both the invented spelling and the phoneme-segmentation children performed similarly on phoneme awareness suggesting that the differential effect on learning to read was not due to phoneme awareness per se. As such, the findings support the view that invented spelling is an exploratory process that involves the integration of phoneme and orthographic representations. With guidance and developmentally appropriate feedback, invented spelling provides a milieu for children to explore the relation between oral language and written symbols that can facilitate their entry in reading.
    Date Created:
    2012-04-01

  • Anomalous permittivity and plasmon resonances of copper nanoparticle conformal coatings on optical fibers

    Resource Type:
    Article
    Creator:
    Shao, Li-Yang, Albert, Jacques, Coyle, Jason P., and Barry, Seán T.
    Abstract:
    The conformal coating of a 50 nm-thick layer of copper nanoparticles deposited with pulse chemical vapor deposition of a copper (I) guanidinate precursor on the cladding of a single mode optical fiber was monitored by using a tilted fiber Bragg grating (TFBG) photo-inscribed in the fiber core. The pulse-per-pulse growth of the copper nanoparticles is readily obtained from the position and amplitudes of resonances in the reflection spectrum of the grating. In particular, we confirm that the real part of the effective complex permittivity of the deposited nano-structured copper layer is an order of magnitude larger than that of a bulk copper film at an optical wavelength of 1550 nm. We further observe a transition in the growth behavior from granular to continuous film (as determined from the complex material permittivity) after approximately 20 pulses (corresponding to an effective thickness of 25 nm). Finally, despite the remaining granularity of the film, the final copper-coated optical fiber is shown to support plasmon waves suitable for sensing, even after the growth of a thin oxide layer on the copper surface.
    Date Created:
    2011-06-01