155 research outputs found
Computational studies of light acceptance and propagation in straight and curved multimodal active fibres
A Monte Carlo simulation has been performed to track light rays in
cylindrical multimode fibres by ray optics. The trapping efficiencies for skew
and meridional rays in active fibres and distributions of characteristic
quantities for all trapped light rays have been calculated. The simulation
provides new results for curved fibres, where the analytical expressions are
too complex to be solved. The light losses due to sharp bending of fibres are
presented as a function of the ratio of curvature to fibre radius and bending
angle. It is shown that a radius of curvature to fibre radius ratio of greater
than 65 results in a light loss of less than 10% with the loss occurring in a
transition region at bending angles of pi/8 rad.Comment: 21 pages, 13 figure
Ultra-high speed electro-optical systems employing fiber optics final report
Ultrahigh speed electro-optical systems employing fiber optic
Grating-coupled excitation of multiple surface plasmon-polariton waves
The excitation of multiple surface-plasmon-polariton (SPP) waves of different
linear polarization states and phase speeds by a surface-relief grating formed
by a metal and a rugate filter, both of finite thickness, was studied
theoretically, using rigorous coupled-wave-analysis. The incident plane wave
can be either p or s polarized. The excitation of SPP waves is indicated by the
presence of those peaks in the plots of absorbance vs. the incidence angle that
are independent of the thickness of the rugate filter. The absorbance peaks
representing the excitation of s-polarized SPP waves are narrower than those
representing p-polarized SPP waves. Two incident plane waves propagating in
different directions may excite the same SPP wave. A line source could excite
several SPP waves simultaneously
Guided Modes of Elliptical Metamaterial Waveguides
The propagation of guided electromagnetic waves in open elliptical
metamaterial waveguide structures is investigated. The waveguide contains a
negative-index media core, where the permittivity, and permeability
are negative over a given bandwidth. The allowed mode spectrum for these
structures is numerically calculated by solving a dispersion relation that is
expressed in terms of Mathieu functions. By probing certain regions of
parameter space, we find the possibility exists to have extremely localized
waves that transmit along the surface of the waveguide
Dialysis-assisted fiber optic spectroscopy for in situ biomedical sensing
A miniature fiber optic spectrometer enclosed within a semipermeable (dialysis) membrane is proposed for in vivo interstitial sensing applications. The semipermeable membrane acts as a molecular filter, allowing only small molecules to pass through to the sampling volume. This filtering, in principle, should enable continuous in vivo drug sensing, removing the necessity for complex microdialysis systems. We use a biological phantom to examine the reliable detection of a fluorescence signal from small dye molecules in the presence of large fluorophores and scatterers. We find that spectral artefacts arising from scatterers and large fluorophores are substantially suppressed, simplifying the spectral analysis. In addition, the measured sampling rate of 157 s is superior to existing in vivo tissue assaying techniques such as microdialysis, which can take tens of minutes. (c) 2006 Society of Photo- Optical Instrumentation Engineers
Self-Spin-Controlled Rotation of Spatial States of a Dirac Electron in a Cylindrical Potential via Spin-Orbit Interaction
Solution of the Dirac equation predicts that when an electron with non-zero
orbital angular momentum propagates in a cylindrically symmetric potential, its
spin and orbital degrees of freedom interact, causing the electron's phase
velocity to depend on whether its spin and orbital angular momenta vectors are
oriented parallel or anti-parallel with respect to each other. This spin-orbit
splitting of the electronic dispersion curves can result in a rotation of the
electron's spatial state in a manner controlled by the electron's own spin
z-component value. These effects persist at non-relativistic velocities. To
clarify the physical origin of this effect, we compare solutions of the Dirac
equation to perturbative predictions of the Schrodinger-Pauli equation with a
spin-orbit term, using the standard Foldy-Wouthuysen Hamiltonian. This clearly
shows that the origin of the effect is the familiar relativistic spin-orbit
interaction.Comment: 14 pages, 5 figures, 2 appendices, final versio
Real time micro-fiberoptic monitoring of endogenous fluorescence in the rat conceptus during hypoxia
A micro-fiberoptic methodology has been developed for noninvasive, real time measurement of endogenous pyridine nucleotide fluorescence from the surface of the visceral yolk sac (VYS) in intact, viable rat conceptuses. Gestational day (GD) 10–12 conceptuses are maintained in a customized perifusion system, which allows for control of oxygenation, as well as the continuous measurement of pH and oxygen concentration in the effluent perifusate. Miniaturized light guides were constructed by drawing 250 Μm ESKA acrylic optical fibers through a stainless steel sheath with a high strength epoxy polymer. A single fiber supplied the excitation signal from a mercury arc lamp at a wavelength of 366 nm. The emission signal was returned via three additional fibers, electronically amplified, processed, and recorded, using a dual channel lamp-compensated fluorometer, optimized for detection of reduced pyridine nucleotides at 455 nm. Endogenous fluorescence in the conceptus was monitored by placing the polished tip of the sensor directly on the surface of the VYS. Oxygen-equilibrated conceptuses, exposed to 100% nitrogen, produced a reproducible biphasic surface fluorescence peak, which returned to baseline levels upon reoxygenation of the perifusate. This biphasic response consisted of an initial rapid rise in fluorescence (phase I), followed by an attenuated rate in fluorescence signal increase (phase II). The hypoxia produced age-dependent rates of fluorescence change during phase I, while phase II remained relatively unchanged throughout GD 10–12. These results demonstrate the ability to monitor endogenous fluorescence, non-invasively and in real time, during the period of organogenesis in the intact rat conceptus and will provide valuable information in studies of embryonic metabolism and response to chemical embryotoxicants. © 1993 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/38167/1/1420480408_ftp.pd
Quantum Transport in Semiconductor Nanostructures
I. Introduction (Preface, Nanostructures in Si Inversion Layers,
Nanostructures in GaAs-AlGaAs Heterostructures, Basic Properties).
II. Diffusive and Quasi-Ballistic Transport (Classical Size Effects, Weak
Localization, Conductance Fluctuations, Aharonov-Bohm Effect, Electron-Electron
Interactions, Quantum Size Effects, Periodic Potential).
III. Ballistic Transport (Conduction as a Transmission Problem, Quantum Point
Contacts, Coherent Electron Focusing, Collimation, Junction Scattering,
Tunneling).
IV. Adiabatic Transport (Edge Channels and the Quantum Hall Effect, Selective
Population and Detection of Edge Channels, Fractional Quantum Hall Effect,
Aharonov-Bohm Effect in Strong Magnetic Fields, Magnetically Induced Band
Structure).Comment: 111 pages including 109 figures; this review from 1991 has retained
much of its usefulness, but it was not yet available electronicall
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