Unlocked evanescent waves in periodic structures

This paper was published in Optics Letters and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://dx.doi.org/10.1364/OL.38.001890. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.We predict the existence of evanescent modes with unlocked phases in two-dimensional (2D) dielectric periodic structures. Contrary to what is known for one-dimensional structures, where evanescent fields lock to the host modulation, we show that in 2D systems a new class of evanescent modes exists with an unlocked real part of the wave vector. Hence, beams constructed from such unlocked evanescent waves can exhibit spatial effects. A significant focalization of a beam propagating within the band gap of a flat photonic crystal slab is also shown. The predicted phenomenon is expected to be generic for spatially modulated materials.We acknowledge financial support by Spanish Ministerio de Ciencia e Innovacion and European Union FEDER through project FIS2011-29731-C02-01 and -02. V. R. G. is grateful for the contract UPV CEI-01-11.Botey, M.; Cheng, Y.; Romero García, V.; Picó Vila, R.; Herrero, R.; Sánchez Morcillo, VJ.; Staliünas, K. (2013). Unlocked evanescent waves in periodic structures. Optics Letters. 38(11):1890-1892. doi:10.1364/OL.38.001890189018923811Yablonovitch, E. (1987). Inhibited Spontaneous Emission in Solid-State Physics and Electronics. Physical Review Letters, 58(20), 2059-2062. doi:10.1103/physrevlett.58.2059John, S. (1987). Strong localization of photons in certain disordered dielectric superlattices. Physical Review Letters, 58(23), 2486-2489. doi:10.1103/physrevlett.58.2486Notomi, M. (2000). 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