Materials that can bend light in the opposite direction to normal ('left-handed' materials) reverse the way in which refraction usually works — this negative refractive index is due to simultaneously negative permeability and permittivity^1,2,3. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permittivity and a permeability of unity^4,5,6. This experimental verification of negative refraction is a step towards the realization of a 'superlens' that will be able to focus features smaller than the wavelength of light.

Engineering metamaterials with tunable resonances from mid-infrared to near-infrared wavelengths could have far-reaching consequences for chip based optical devices, active filters, modulators, and sensors. Utilizing the metal-insulator phase transition in vanadium oxide (VO₂), we demonstrate frequency-tunable metamaterials in the near-IR range, from 1.5 - 5 microns. Arrays of Ag split ring resonators (SRRs) are patterned with e-beam lithography onto planar VO₂ and etched via reactive ion etching to yield Ag/VO₂ hybrid SRRs. FTIR reflection data and FDTD simulation results show the resonant peak position red shifts upon heating above the phase transition temperature. We also show that, by including coupling elements in the design of these hybrid Ag/VO₂ bi-layer structures, we can achieve resonant peak position tuning of up to 110 nm.