Double-helix chiral fibers.
ABSTRACT A polarization-selective photonic stop band is demonstrated in a new chiral fiber structure with double-helix symmetry. The stop band exists for only circularly polarized radiation with the same handedness as the structure and is centered at a wavelength in the fiber equal to the fiber pitch. When one part of the chiral fiber is twisted about its axis, a localized mode is produced, which can be tuned across the gap by changing the twist angle. Observations in single-mode fibers are in good agreement with one-dimensional simulations of a dispersive cholesteric material. At higher frequencies, however, we find a sharp onset of a broad polarization-selective scattering band, which is not present in one-dimensional simulations.
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ABSTRACT: Our measurements of the frequency and spatial variation of the microwave field in ensembles of random samples have revealed the underlying structure of wave correlation and photon localization. The intensity correlation was found in terms of displacement and polarization shift of the source and detector can be expressed in terms of the square of the corresponding field correlation function. Nonexponential decay of pulsed transmission through disordered media was found in nominally diffusive media, in which the level width exceeds the spacing between levels. This departure from diffusion theory is interpreted in terms of the decay rate statistics of electromagnetic quasi-normal modes. The influence of these modes of the electromagnetic field is an indication of the breakdown of the particle diffusion theory. Measurements of spatial and polarization correlation as a function of time delay from an exciting pulse show that the structure of the intensity correlation function is the same as found in steady state propagation, being a function only of the corresponding field correlation functions. The degree of correlation in the speckle pattern is seen to be the key parameter in dynamics and hence in steady state propagation. We have discovered a localization laser in random one dimensional systems.12/2003;