In modern transformation optics, one explores metamaterials with properties
that vary from point to point in space and time, suitable for applications in
devices such as an "optical invisibility cloak" and an "optical black hole". We
propose an approach to construct spatially varying and switchable metamaterials
that are based on colloidal dispersions of metal nano-rods (NRs) in dielectric
fluids, in which dielectrophoretic forces, originating in the electric field
gradients, create spatially varying configurations of aligned NRs. The electric
field controls orientation and concentration of NRs and thus modulates the
optical properties of the medium. Using gold (Au) NRs dispersed in toluene, we
demonstrate electrically induced change in refractive index on the order of
0.1.Comment: 27 pages, 23 figure
