Transverse Anderson Localization in Disordered Optical Fibers

Abstract

In any wave-guiding system, disorder and randomness in the wave propagation medium are considered as annoyances that result in wave scattering and inefficient wave transport. In contrast, in this work, the disorder is utilized in the transverse directions of an optical fiber for an effective light transport. The transversely disordered refractive index profile is invariant along the direction of propagation that results in transverse Anderson localization of light. A launched beam of light into the disordered fiber initially expands until it reaches the localization regime then propagates without further expansion in the transverse directions. A disordered polymer optical fiber composed of poly methyl methacrylate (PMMA) and poly styrene (PS) is designed using numerical simulations. The disordered polymer fiber is fabricated by drawing a preform of randomly mixed PMMA and PS strands. The light propagation in the disordered polymer fiber results in a localized beam radius that is comparable to the ones in the conventional optical fibers. The location of the transported beam at the output follows the location of the scanning beam at the input. In order to show the origin of transverse Anderson localization, the full vectorial modes of the disordered polymer optical fiber are calculated. The impacts of different design parameters on the light propagation in the disordered optical fibers are investigated. It is shown that the ultimate practical design is a disordered optical fiber that consists of glass and air sites with equal probability. The light propagation in a disordered glass optical fiber fabricated from porous glass with disordered air voids is studied as the first investigation of transverse Anderson localization in silica optical fibers. The non-uniform distribution of air voids in the glass host results in the wave localization in the regions with high fill-fraction of air voids. The possibility of simultaneous multiple-beam propagation in the disordered polymer optical fiber is examined numerically and experimentally. The impact of macro-bending on drifting the center of a propagating beam in the disordered polymer fiber is inspected. The macro-bending locally increases the refractive index difference between the disordered sites that results in a bend-insensitive wave propagation. The spatial multiplexing property of the disordered polymer fiber is utilized for high quality image transport. The quality of the transported images in the disordered polymer optical fiber is numerically and experimentally compared with the ones in the commercially available imaging fibers. The quality of the transported images is assessed using an effective objective evaluation technique. The impact of disorder on improving the image quality is specifically investigated by randomizing the radii of the cores in a periodic multicore fiber.