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Proceedings Paper

Anisotropic photonic-bandgap structures
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Paper Abstract

We show that introducing anisotropy into periodic dielectric structures leads to new optical phenomena as well as to a new approach to a variety of applications. One-dimensional anisotropic structures allow a new type of chiral twist defect resulting in a localized photonic mode with unusual properties. Unlike isotropic layers of alternating index of refraction, where the periodicity can be destroyed only by changing the refractive index or thickness of a layer, a defect can be created in anisotropic media by introducing an additional rotation between consecutive layers. Computer simulations show that introducing an additional rotation in the middle of a sample with cholesteric ordering produces a localized state whose frequency can be tuned from one edge of the photonic stop band to the other by varying the angle of rotation from 0 to 180 degrees. Most of the energy of this mode exists as a circularly polarized standing wave with the same handedness as the structure, independent of the polarization of the exciting wave. This localized mode gives rise to a crossover in the nature of propagation. Below a crossover thickness, the localized mode is excited only by a wave with the same handedness as the structure and exhibits a peak in transmission at the defect frequency. Above the crossover, however, the defect mode can be excited only by the oppositely polarized wave and a resonant peak appears in reflection. Simulations for lengths below the crossover are in agreement with measurements of microwave transmission through stacks of overhead transparencies, ordered in the same way as the molecular layers of a cholesteric liquid crystal. Three types of defect are introduced: (1) an additional 90 degrees rotation, (2) an additional 45 degrees rotation, and (3) a combination of a 45 degrees rotation and a quarter-wavelength separation.

Paper Details

Date Published: 25 April 2002
PDF: 9 pages
Proc. SPIE 4655, Photonic Bandgap Materials and Devices, (25 April 2002); doi: 10.1117/12.463868
Show Author Affiliations
Victor I. Kopp, Chiral Photonics, Inc. (United States)
Peter V. Shibaev, Chiral Photonics, Inc. (United States)
Ranojoy Bose, CUNY/Queens College (United States)
Azriel Z. Genack, Chiral Photonics Inc. and CUNY/Queens College (United States)

Published in SPIE Proceedings Vol. 4655:
Photonic Bandgap Materials and Devices
Ali Adibi; Axel Scherer; Shawn-Yu Lin, Editor(s)

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