Wide-band optical field concentrator for low-index core propagation
  We propose a novel chirped structure consisting of a low index polymer core bounded by modulated multilayer claddings, to realize an optical field concentrator with virtually zero propagation losses in a wide spectral range, independent of wave polarization. In spite of the absence of the total internal reflection mechanism, properly designed multilayer claddings ensure the achievement of unitary transmittance in a wide spectral range, including the widely used wavelengths for optical communications. Several cladding geometries obtained by varying the thicknesses of the cladding layers are reported and discussed. 
D. de Ceglia, M. De Sario, A. D'Orazio, V. Petruzzelli, M. A.   Vincenti, F. Prudenzano, M. Scalora