Squeezing and expanding light without reflections via transformation optics

This paper was published in OPTICS EXPRESS 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/OE.19.003562. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law [EN] We study the reflection properties of squeezing devices based on transformation optics. An analytical expression for the angle-dependent reflection coefficient of a generic three-dimensional squeezer is derived. In contrast with previous studies, we find that there exist several conditions that guarantee no reflections so it is possible to build transformation-optics-based reflectionless squeezers. Moreover, it is shown that the design of antireflective coatings for the non-reflectionless case can be reduced to matching the impedance between two dielectrics. We illustrate the potential of these devices by proposing two applications in which a reflectionless squeezer is the key element: an ultra-short perfect coupler for high-index nanophotonic waveguides and a completely flat reflectionless hyperlens. We also apply our theory to the coupling of two metallic waveguides with different cross-section. Finally, we show how the studied devices can be implemented with non-magnetic isotropic materials by using a quasi-conformal mapping technique. © 2011 Optical Society of America. Financial support by the Spanish MICINN under contract CONSOLIDER EMET (CSD2008-00066) and PROMETEO-2010-087 R&D Excellency Program (NANOMET) is gratefully acknowledged. C. G.-M., R. O. and F.J. R.-F. acknowledge financial support from grants FPU of MICINN, FPI of U.P.V. and FPI of Generalitat Valenciana, respectively. García Meca, C.; Tung, MM.; Galán Conejos, JV.; Ortuño Molinero, R.; Rodríguez Fortuño, FJ.; Martí Sendra, J.; Martínez Abietar, AJ. (2011). Squeezing and expanding light without reflections via transformation optics. Optics Express. 19(4):3562-3575. https://doi.org/10.1364/OE.19.003562 Yang, R., Abushagur, M. A., & Lu, Z. (2008). Efficiently squeezing near infrared light into a 21nm-by-24nm nanospot. Optics Express, 16(24), 20142. doi:10.1364/oe.16.020142 Vivien, L., Laval, S., Cassan, E., Le Roux, X., & Pascal, D. (2003). 2-d taper for low-loss coupling between polarization-insensitive microwaveguides and single-mode optical fibers. Journal of Lightwave Technology, 21(10), 2429-2433. doi:10.1109