| Records |
| Author |
Kopp, Victor I.; Churikov, Victor M.; Zhang, Guoyin; Singer, Jonathan; Draper, Christopher W.; Chao, Norman; Neugroschl, Daniel; Genack, Azriel Z. |
| Title |
Chiral fiber gratings: perspectives and challenges for sensing applications |
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Conference Article |
| Year |
2007 |
Publication |
Proceedings of Third european workshop on optical fibre sensors |
Abbreviated Journal |
Proc. 3rd European Workshop on Opt. Fibre Sensors |
| Volume |
6619 |
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66190B-(1-8) |
| Keywords |
optical fiber gratings, chiral fiber gratings applications, chiral gratings applications, from chiralphotonics |
| Abstract |
Chiral fiber gratings are produced in a microforming process in which optical fibers with noncircular or nonconcentric cores are twisted as they pass though a miniature oven. Periodic glass structures as stable as the glass material itself are produced with helical pitch that ranges from under a micron to hundreds of microns. The geometry of the fiber cross section determines the symmetry of the resulting structure which in turn determines its polarization selectivity. Single helix structures are polarization insensitive while double helix gratings interact only with a single optical polarization. Both single and double helix gratings may act as a fiber long period grating, coupling the core and cladding modes. The coupling is manifested in a series of narrow dips in the transmission spectrum. The dip position is sensitive to fiber elongation, twist and temperature, and to the refractive index of the surrounding medium. The suitability of chiral gratings for sensing pressure, temperature and liquid levels is investigated. Polarization insensitive single helix silica glass gratings display excellent stability up to temperatures of 6000C, while a pressure sensor with dynamic range of nearly 40 dB is demonstrated in polarization selective double helix gratings. |
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Khosropanah, P.; Merkel, H.; Yngvesson, S.; Adam, A.; Cherednichenko, S.; Kollberg, E. |
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A distributed device model for phonon-cooled HEB mixers predicting IV characteristics, gain, noise and IF bandwidth |
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Conference Article |
| Year |
2000 |
Publication |
Proc. 11th Int. Symp. Space Terahertz Technol. |
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474-488 |
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HEB mixer numerical model, diffusion cooling channel, diffusion channel, distributed HEB model, distributed model |
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A distributed model for phonon-cooled superconductor hot electron bolometer (HEB) mixers is given, which is based on solving the one-dimensional heat balance equation for the electron temperature profile along the superconductor strip. In this model it is assumed that the LO power is absorbed uniformly along the bridge but the DC power absorption depends on the local resistivity and is thus not uniform. The electron temperature dependence of the resistivity is assumed to be continuous and has a Fermi form. These assumptions are used in setting up the non-linear heat balance equation, which is solved numerically for the electron temperature profile along the bolometer strip. Based on this profile the resistance of the device and the IV curves are calculated. The IV curves are in excellent agreement with measurement results. Using a small signal model the conversion gain of the mixer is obtained. The expressions for Johnson noise and thermal fluctuation noise are derived. The calculated results are in close agreement with measurements, provided that one of the parameters used is adjusted. |
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University of Michigan, Ann Arbor, MI USA |
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893 |
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Ynvesson, K. Sigfrid; Kollberg, Erik L. |
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Optimum receiver noise temperature for NbN HEB mixers according to standard model |
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Conference Article |
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1999 |
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Proc. 10th Int. Symp. Space Terahertz Technol. |
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566-582 |
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HEB mixer model, standard model, electro-thermal feedback, self-heating parameter, heating efficiency |
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895 |
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Vercruyssen, N.; Verhagen, T. G. A.; Flokstra, M. G.; Pekola, J. P.; Klapwijk, T. M. |
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Evanescent states and nonequilibrium in driven superconducting nanowires |
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Journal Article |
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2012 |
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Phys. Rev. B |
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Phys. Rev. B |
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85 |
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224503(1-10) |
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Al HEB, Al superconducting nanowire, global state, bimodal state, quasiclassical kinetic equations, Usadel equation |
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We study the nonlinear response of current transport in a superconducting diffusive nanowire between normal reservoirs. We demonstrate theoretically and experimentally the existence of two different superconducting states appearing when the wire is driven out of equilibrium by an applied bias, called the global and bimodal superconducting states. The different states are identified by using two-probe measurements of the wire, and measurements of the local density of states with tunneling probes. The analysis is performed within the framework of the quasiclassical kinetic equations for diffusive superconductors. |
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898 |
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Bardeen, J.; Cooper, L. N.; Schrieffer, J. R. |
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Microscopic theory of superconductivity |
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Journal Article |
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1957 |
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Phys. Rev. |
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Phys. Rev. |
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106 |
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162-164 |
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BCS |
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