fabrication-characterization-disordered-polymer-optical-fibers-for

Fabrication and Characterization of Disordered Polymer Optical Fibers for Transverse Anderson Localization of Light

We develop and characterize a disordered polymer optical fiber that uses transverse Anderson localization as a novel waveguiding mechanism. The developed ...

By studying the effects of the shape moduli associated with toroidal compactifications, we demonstrate that Planck-sized extra dimensions can cast significant "shadows" over low-energy physics. These shadows distort our perceptions of the compactification geometry associated with large extra dimensions and place a fundamental limit on our ability to probe the geometry of compactification by measuring Kaluza-Klein states. We also find that compactification geometry is effectively renormalized as a function of energy scale, with "renormalization group equations" describing the "flow" of geometric parameters such as compactification radii and shape angles as functions of energy.

Shadows of the planck scale: scale dependence of compactification geometry.

Closed strings in extra compactified dimensions give rise to both Kaluza-Klein states and winding states. Since the masses of these states play a reciprocal role, it is often believed that either the lightest Kaluza-Klein states or the lightest winding states must be at or below the string scale. In this Letter, we demonstrate the contrary, showing that there exist toroidal compactifications for which all Kaluza-Klein states as well as all winding states are heavier than the string scale. Within the context of low-scale string theories, this implies that it may be possible to cross the string scale without detecting any states associated with spacetime compactification.

Kaluza-Klein states versus winding states: can both be above the string scale?

We present a detailed description of a computationally efficient, semi-analytical method (SAM) to calculate the electomagnetic field distribution in a 1D-periodic, subwavelength-structured metal film placed between dielectric substrates. The method is roughly three orders of magnitude faster than the finite-element method (FEM). SAM is used to study the resonant transmission of light through nanoplasmonic structures, and to analyze the role of fundamental and higher-order Bloch surface plasmons in transmission enhancement. The method is also suitable for solving the eigenvalue problem and finding modes of the structure. Results obtained with SAM, FEM, and the finite-difference time-domain method show very good agreement for various parameters of the structure.

Semi-analytical method for light interaction with 1D-periodic nanoplasmonic structures.

We relate local cell gap variations to visible defects in LCD panels using psychophysical methods of human eye perception of intensity variations. Our analysis is applicable to general shape of cell gap variation for any LCD mode. We use our method in an explicit example to determine the visible cell gap variation threshold for TN LCD panels.

A study of visible defects caused by local cell gap variations in LCD panels.

Convergence problems in modal methods for TM polarized fields are often attributed to the inaccuracies in computing the modes of a grating. We report that even in the absence of these inaccuracies convergence problems persist. These arise because of the truncation of the infinite set of linear equations resulting from matching the fields at the grating-substrate and grating-superstrate interfaces with a square matrix. We show that dramatic improvement in convergence can be achieved if the infinite set of linear equations is truncated with a rectangular matrix and by seeking a solution with minimum least squared error.

Reliable computation of scattering from metallic binary gratings using Fourier-based modal methods.

In a recent article [J. Opt. Soc. Am. A27, 1694 (2010)], we proposed a rectangular truncation method to mitigate the convergence problems arising from the boundary matching conditions of a binary metallic grating. The proposed method may underestimate the total power in the scattered field for certain grating parameters. In this article, we extend this method to preserve the total power by introducing appropriate constraints and solving the resulting problem as a constrained least squares minimization problem. We provide examples to show that the new method provides a convergent solution for both lossy and lossless binary metallic gratings while preserving the total power.

Constrained least squares Fourier modal method for computing scattering from metallic binary gratings.

The beam-quality factor M(2) for the fundamental LP01 mode of a step-index fiber is calculated in the presence of gain, in a closed form, as a function of the complex generalized V number. It is shown that the M(2) value of a single-mode gain-guided fiber laser can be arbitrarily large. The results are important for the interpretation of the beam-quality measurements in recent experiments on single-mode gain-guided fiber lasers.

Beam-quality factor of single-mode gain-guided fiber lasers.

We present a method for ultra-low-loss coupling between two single-mode optical fibers with different mode-field diameters using multimode interference in a graded-index multimode optical fiber. We perform a detailed analysis of the interference effects and show that the graded-index fiber can also be used as a beam expander or condenser. The results are important for devices in which optical fibers with different mode-field diameters are coupled in series, such as in ultra-short-pulse fiber ring lasers, or in optical fiber communication links.

Low-loss coupling between two single-mode optical fibers with different mode-field diameters using a graded-index multimode optical fiber.

We utilize transverse Anderson localization as the waveguiding mechanism in optical fibers with random transverse refractive index profiles. Using experiments and numerical simulations, we show that the transverse localization results in an effective propagating beam diameter that is comparable to that of a typical index-guiding optical fiber.

Observation of transverse Anderson localization in an optical fiber.

We recently reported the observation of transverse Anderson localization as the waveguiding mechanism in optical fibers with random transverse refractive index profiles [Opt. Lett. 37, 2304 (2012)]. Here, we explore the impact of the design parameters of the disordered fiber on the beam radius of the propagating transverse localized beam. We show that the optimum value of the fill-fraction of the disorder is 50% and a lower value results in a larger beam radius. We also explore the impact of the average size of the individual random features on the value of the localized beam radius and show how the boundary of the fiber can impact the observed localization radius. A larger refractive index contrast between the host medium and the disorder sites results in smaller value of the beam radius.

Detailed investigation of the impact of the fiber design parameters on the transverse Anderson localization of light in disordered optical fibers.

We investigate the simultaneous propagation of multiple beams in a disordered Anderson localized optical fiber. The profiles of each beam fall off exponentially, enabling multiple channels at high-density. We examine the influence of fiber bends on the movement of the beam positions, which we refer to as drift. We investigate the extent of the drift of localized beams induced by macro-bending and show that it is possible to design Anderson localized optical fibers that can be used for practical beam-multiplexing applications.

Article	Year
Shadows of the planck scale: scale dependence of compactification geometry. Physical review letters\| PubMed ID: 11909392	2002
Kaluza-Klein states versus winding states: can both be above the string scale? Physical review letters\| PubMed ID: 12398657	2002
Semi-analytical method for light interaction with 1D-periodic nanoplasmonic structures. Optics express\| PubMed ID: 18545606	2008
A study of visible defects caused by local cell gap variations in LCD panels. Optics express\| PubMed ID: 19532387	2007
Reliable computation of scattering from metallic binary gratings using Fourier-based modal methods. Journal of the Optical Society of America. A, Optics, image science, and vision\| PubMed ID: 20596158	2010
Constrained least squares Fourier modal method for computing scattering from metallic binary gratings. Journal of the Optical Society of America. A, Optics, image science, and vision\| PubMed ID: 21045901	2010
Beam-quality factor of single-mode gain-guided fiber lasers. Optics letters\| PubMed ID: 21165111	2010
Low-loss coupling between two single-mode optical fibers with different mode-field diameters using a graded-index multimode optical fiber. Optics letters\| PubMed ID: 21931402	2011
Observation of transverse Anderson localization in an optical fiber. Optics letters\| PubMed ID: 22739889	2012
Detailed investigation of the impact of the fiber design parameters on the transverse Anderson localization of light in disordered optical fibers. Optics express\| PubMed ID: 23038510	2012
Multiple-beam propagation in an Anderson localized optical fiber. Optics express\| PubMed ID: 23388924	2013

Arash Mafi

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