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IRG-I Nugget

Total external reflection from photonic bandgap mirror fibers

Parallel fiber array made from 200 mm OD fibers used to obtain reflectivity data in the experiments. Although As2Se3 is highly absorbing in the visible regime, some iridescent colors are visible to the naked eye.

Polymer fibers are ubiquitous in applications such as textile fabrics due to their excellent mechanical properties and the availability of low-cost, high-volume processing techniques. However, the control over their optical properties has so far remained very limited. Conversely, dielectric mirrors are used to precisely control and manipulate light in high performance optical applications, but the fabrication of these typically fragile mirrors has been restricted to planar geometries and remains costly.

In a recent article [Hart et al., Science 296, 510 (2002)], members of IRG-I disclosed that they have successfully combined some of the advantages of each of these seemingly dissimilar products in order to draw polymeric fibers possessing an exterior multilayer dielectric mirror. In particular, they report on the design and fabrication of a multi-layered macroscopic fiber preform and the subsequent drawing and optical characterization of extended lengths of omnidirectional dielectric mirror fiber. This fiber consists of a tough polymer core and 21 coaxial dielectric layers that reflect external light from all incident angles and polarizations in the mid-IR range. The individual layers in these kilometer length scale fibers have submicron layer thickness, thus spanning 10 orders of dimensional magnitude in a single fabrication step. A critical aspect of this work was the identification of a pair of glassy materials with substantially different indices of refraction yet similar thermo-mechanical properties, resulting in high index contrast layers that do not delaminate even when subjected to large temperature variations. Large directional photonic gaps and high reflection efficiencies that surpass standard metallic reflectors (e.g. gold) were measured. Indeed, an editorial in Science [Science 296, 425 (2002)] has referred to these fibers as the new "Gold Standard." High performance optical control, previously limited to telecommunications devices, was thus achieved in these thermally processed dielectric mirror fibers. Potential applications include woven fabrics for radiation barriers, spectral authentication of cloth, and filters for telecommunications.

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