We studied a nematic liquid crystal (LC) cylinder under the action of an axial electric field E(0). Elaborate modeling of the free energy leads to the conclusion that the configuration of the molecules is "escaped radial" for low E(0); a phase transition, however, occurs for a critical value E(c), the configuration becoming axial for E(0) >E(c). From these results, the position-dependent dielectric tensor is determined and the photonic band (PB) structure is calculated for a photonic crystal of LC cylinders. It is shown that by varying E(0) a PB gap can be fully tuned from open to closed. Also, switching to a supercritical field can give rise to interesting polarization and directional effects in the propagation of light.

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