Physical origins and general dielectric tensor of photoinduced anisotropy in optical fibers and bulk glasses

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Abstract
The microscopic physical origins of photoinduced anisotropy in optical fibers are discussed, and the perturbations to the dielectric tensor resulting from interference of two arbitrarily polarized waves are derived. Both single- and two-photon absorption processes are treated, making the formulation valid for filter formation both by UV side writing and by axial exposure to copropagating or counterpropagating blue-green guided modes. In addition to elucidating the dielectric tensor for various types of known polarization convertor, the treatment predicts the formation of a number of unusual polarization convertors and filters. These predictions underline the universal result that unusual and complicated periodic forms of dielectric tensor—unlike anything encountered in crystals—can arise in amorphous media such as glass and polymers on exposure to light.