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We have fabricated microstructured polymer optical fibers that guide light in a hollow core using the photonic bandgap mechanism. The hollow core allows the use of polymer fibers to be extended to wavelength ranges where material absorption typically prohibits their use, with attenuation lower than the material loss observed in the infrared. The fabrication method is similar to other microstructured polymer optical fibers, which has favorable implications for the feasibility of manufacturing such bandgap fibers.

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We show how to design a round optical fiber so that it is effectively single moded, with no polarization degeneracy. Such fibers would be free from the consequences of polarization degeneracy or near degeneracy - phenomena such as polarization fading in interferometry, and polarization mode dispersion - and so may offer an alternative to polarization maintaining fibers for the avoidance of these phenomena. The design presented builds on an earlier observation of polarization selective refection in Bragg fibers.

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Recent developments in polymer microstructured optical fibres allow for the realisation of microstructures in fibres that would be problematic to fabricate using glass-based capillary stacking. We present one class of such structures, where the holes lie on circular rings. A fibre of this type is fabricated and shown to be single moded for relatively long lengths of fibre, whereas shorter lengths are multimoded. An average index model for these fibres is developed. Comparison of its predictions to the calculated properties of the exact structure indicates that the ring structures emulate homogeneous rings of lower refractive index resulting in the ring structured fibres behaving approximately as cylindrically layered fibres.

One of the classical statements of the second law of thermodynamics is derived from an assumption about the behavior of an isolated heat reservoir, together with a further assumption, which seems to be a rather weak one, about initial states. The derivation is otherwise based on the unitary property of time evolution in quantum mechanics. An analogous derivation, within the framework of classical mechanics, is also given; in this case Liouville's theorem substitutes for unitarity.

An air-core microstructured fiber design that supports a single-polarization, circularly symmetric nondegenerate mode is presented. The fiber design is modeled directly, and the microstructured cladding is analyzed by use of band diagrams to elucidate the mechanism through which polarization nondegeneracy is achieved.