Higher order Pancharatnam-Berry phase and the angular momentum of light.

The first experimental demonstration of a new Pancharatnam-Berry phase for light beams with spatially inhomogeneous, or vector, states of polarization referred to as the higher-order Pancharatnam-Berry phase is presented. This new geometric phase is proportional to light's total angular momentum, a sum of spin and higher dimensional orbital angular momentum, sharply contrasting the well-known Pancharatnam-Berry phase associated with the plane wave state of polarization of a spatially homogeneous light beam. The higher-order Pancharatnam-Berry phase is directly related to the rotational symmetry of a vortex-bearing electromagnetic field, associated with the rotational frequency shift of a light beam, and has implications in quantum information science as well as other physical systems such as electron vortex beams.

Higher-order Poincaré sphere, stokes parameters, and the angular momentum of light.

A higher-order Poincaré sphere and Stokes parameter representation of the higher-order states of polarization of vector vortex beams that includes radial and azimuthal polarized cylindrical vector beams is presented. The higher-order Poincaré sphere is constructed by naturally extending the Jones vector basis of plane wave polarization in terms of optical spin angular momentum to the total optical angular momentum that includes higher dimensional orbital angular momentum. The salient properties of this representation are illustrated by its ability to describe the higher-order modes of optical fiber waveguides, more exotic vector beams, and a higher-order Pancharatnam-Berry geometric phase.

Properties of polarization evolution in spun fibers.

We study the properties of polarization evolution in sinusoidally spun fibers. It is found that, similar to linear birefringent fibers, the evolution of the state of polarization exhibits periodicity, which can be measured by distributed measurement, such as those made with a polarization optical time domain reflectometer. The spatial period is linked with the spin parameters and fiber beat length in a simple equation. In combination with a previous finding, it is shown that the spatial period is uniquely related to spun-fiber polarization mode dispersion. This suggests that distributed fiber polarization mode dispersion can be determined throughthe measurement of the spatial period obtained in a distributed measurement.

Polarization mode dispersion of spun fibers: an analytical solution.

A simple analytical solution is derived from coupled-mode theory to describe the evolution of polarization mode dispersion (PMD) in spun fibers. For practical fibers with a beat length greater than a few meters, the solution is valid for a whole category of periodic spin profiles. We find that the PMD change factor is independent of the intrinsic birefringence of the fiber and the fiber PMD scales linearly with the fiber length in the short length regime. This solution allows us to determine phase-matching conditions for spun fibers, in which the PMD evolves periodically along the fiber. An example of determining the phase-matching conditions of sinusoidal-type spin profiles is given.

Scaling properties of polarization mode dispersion of spun fibers in the presence of random mode coupling.

The scaling properties of polarization mode dispersion (PMD) in spun fibers are studied. Simple equations have been obtained to describe the scaling properties of spun fibers as a function of intrinsic fiber birefringence, spin parameters, and mode-coupling length under both optimal and nonoptimal spin conditions. In particular, a counterintuitive result is found for fibers with perfect spin optimization, in which case the fiber PMD increases as the mode-coupling length is shortened. The results are verified with direct numerical modeling.

Polarization-insensitive nonlinear optical loop mirror demultiplexer with twisted fiber.

We experimentally demonstrate reduction of the polarization sensitivity of a nonlinear optical loop mirror (NOLM) from 5 to 0.5 dB by use of 550 m of twisted dispersion-shifted fiber with a twist rate of 8 turns/m (24 turns/beat length). The twisting of the fiber induces circular birefringence and equates the parallel-and the orthogonal-polarization nonlinear phase-shift terms. Experimental results show that the polarization sensitivity monotonically decreases from 5 dB for nontwisted fiber to 0.5 dB for fiber that is twisted at a rate of 8 turns/m, and the twist rate should be more than 4 turns/m (>10 turns/beat length) for emulation of circularly polarized fiber. The minimum polarization sensitivity occurs when the control-pulse polarization is aligned with one of the eigenmodes of the twisted fiber. With the fiber twisted at a rate of 8 turns/m in the NOLM, the nonlinear transmission is 23% at a switching energy of 4 pJ/pulse. Simulations confirm the observed behavior and show that the remaining polarization sensitivity results from energy transfer between orthogonal modes of the signal pulse.

Effects of lateral load and external twist on polarization-mode dispersion of spun and unspun fibers.

Using the coupled-mode theory, we have developed a theoretical model to analyze the effects of lateral load and external twist on polarization-mode dispersion (PMD) of spun and unspun fibers. Modeling results show that spun and unspun fibers have very different PMD responses to lateral load and external twist. Experimental results show good agreement with the theory.

Fiber spin-profile designs for producing fibers with low polarization mode dispersion.

Using coupled-mode theory, we develop a theoretical model to analyze the effects of fiber spin profiles on polarization mode dispersion (PMD). Constant, sinusoidal, and frequency-modulated spin profiles are examined, and phase-matching conditions are analyzed. Our analysis shows that PMD can be reduced effectively by use of frequency-modulated spin profiles.

Spurious discharges due to late insulation break in endocardial sensing leads for cardioverter defibrillators.

Despite their similarity to permanent pacemaker leads, endocardial sensing leads for cardioverter defibrillators have a relatively high failure rate. We describe four patients with endocardial rate sensing leads who developed inappropriate discharges 10-30 months after implantation due to small breaks in the lead insulation. This problem may become increasingly common as the number of cardioverter defibrillator implants with transvenous leads continues to grow and should be considered in the differential diagnosis of late sensing failure or inappropriate device discharges.

Perturbation model for computing optical fiber birefringence from a two-dimensional refractive-index profile.

A vector perturbation model for computing optical fiber birefringence for an arbitrary two-dimensional index profile is developed. The vector wave equation is solved to yield the unperturbed vector f ields for an azimuthally symmetric refractive index. These f ields are used as the basis for the degenerate perturbation analysis. Unlike with the scalar perturbation theory, only f irst-order perturbation analysis suff ices for the computation of birefringence. Computed birefringence for various perturbations are reported.

Minimal water activity levels for growth and survival of Listeria monocytogenes and Listeria innocua.

Following initial range-finding experiments, total count determinations were used to determine minimal water activity (aW) levels for the growth and survival of Listeria monocytogenes (L.m.) and L. innocua (L.i.). Media containing three different humectants; NaCl, sucrose or glycerol were used to determine minimal aW levels for growth in the above media which were 0.92, 0.92 and 0.90 respectively. The growth minima for L.i. were similar, or slightly higher than for L.m. in these media. Survival rates were generally lower in NaCl-adjusted media than in systems adjusted with sucrose or glycerol. Survival of L.m. and L.i. in these experiments was similar.

Effects of synthetic atrial natriuretic peptides on sodium-potassium transport in human erythrocytes.

The effects of synthetic human and rat atrial peptides on sodium and potassium ion transport has been investigated in intact human erythrocytes. The effects of these peptides have been tested on the active, sodium pump-dependent (ouabain-sensitive) and on the sodium-potassium cotransport system (bumetanide-sensitive) with 86Rb used as a tracer. Human (alpha-ANP, 28 amino acids) or rat (atriopeptin III) atrial peptides, over a wide range of concentrations, did not influence the uptake of 86Rb in either the ouabain-sensitive or the bumetanide-sensitive transport system. These results suggest that the natriuretic effect of the atrial peptides is not mediated through inhibition of the sodium pump or the loop-diuretic-sensitive Na-K cotransport.

Mode dependent attenuation in parabolic optical fibers.

A previous study of excess attenuation caused by slowly varying perturbations is extended to optical fibers with parabolic index profiles. For random diameter variations, total losses are found to be essentially the same in step and parabolic fibers.

Mode-dependent attenuation of optical fibers: excess loss.

A theory is presented for calculating the excess loss produced by random perturbations of optical fibers. The theory is applicable to perturbations whose longitudinal spatial frequencies are below the range required for mode coupling. To illustrate the method, losses due to diameter variations are calculated for the case of a step-index optical fiber. The diameter variations are found to produce a strong attenuation of the higher order modes. The total excess loss is approximately wavelength independent.