Vera Smolyaninova

Transformation optics (TO) has recently become a useful methodology in the design of unusual optical devices, such as novel metamaterial lenses and invisibility cloaks. Birefringence typically viewed as an obstacle in optical design. We have reported the first experimental realization of birefringent TO devices, which perform different functions for mutually orthogonal polarization states of light. Our designs are based on lithographically defined metal/dielectric waveguides. Adiabatic variations of the waveguide shape enable control of the effective refractive indices experienced by the TE and TM modes propagating inside the waveguides. Using effective birefringence of a lithographically formed dielectric waveguide on a metal substrate, we have created a Luneburg lens for TM polarized light, which behaves as a spatial (directional) filter for TE polarized light. In the second design a Luneburg lens for TM light exhibits an approximate semi-classical cloaking potential for TE polarized light inside the device. Our technique opens up an additional degree of freedom in optical design and considerably improves our ability to manipulate light on submicrometer scale.

Luneburg lens: focusing	Tapered waveguide	effective refractive index
	experiment	COMSOL simulations
TM Luneburg lens
TE Spatial (directional) filter

Vera N. Smolyaninova, H. Kurt Ermer, Alex Piazza, David Schaefer, and Igor I. Smolyaninov, Phys. Rev. B 87, 075406 (2013)

Experimental demonstration of Luneburg waveguides

Here we report the first experimental realization of TO Luneburg lens waveguides and other novel TO devices. The individual Luneburg lenses in the fabricated waveguides are based on lithographically defined metal/dielectric waveguides. We have studied wavelength and polarization dependent performance of the waveguides. Adiabatic variations of the waveguide shape enable control of the effective refractive index experienced by the TM light propagating inside the waveguide. Our experimental designs appear to be broadband, which has been verified in the 480-633 nm range.

Theoretical simulations of a Luneburg waveguide using COMSOL Multiphysics (a-c) and ray optics (d). Panel (a) shows effective refractive index distribution for TM light in a straight Luneburg waveguide, while panel (b) shows calculated energy density within the waveguide. Numerically calculated TM light propagation through a curved Luneburg waveguide (c) illustrates that double periodicity is typically broken within such a waveguide.

TM light propagation through experimentally fabricated straight Luneburg waveguide: (a,c) Microscopic images of the fabricated Luneburg waveguide taken at different magnifications. (b,d) Microscopic images of the same waveguide regions taken while 488 nm light was coupled into the waveguide. Double periodicity of light distribution in the waveguide is indicated by arrows in frames (c) and (d).

Vera N. Smolyaninova, David Lahneman, Todd Adams, Thomas Gresock, Kathryn Zander, Christopher Jensen, and Igor I. Smolyaninov, “Experimental demonstration of Luneburg waveguides,” Photonics 2, 440 (2015), special issue New Frontiers in Plasmonics and Metamaterials

Supported in part by NSF grant DMR-1104676