Optical properties of metal-dielectric based epsilon near zero metamaterials

We demonstrate epsilon near zero (ENZ) metamaterials operating at visible wavelengths near 660 nm. The structure consists of a multilayer stack composite of alternating layers of Ag and TiO2, 16 nm and 54 nm thick, respectively. We found that a high refractive index material like TiO2 (n similar to 2.3) is preferable to a lower index material to achieve good "mixing" resulting in a composite that better approximates a homogenous effective medium. Optical spectroscopy shows that transmission and absorption responses are consistent with ENZ behavior and match well with simulations. The transmission reduces with increasing number of multilayer pairs due to metal absorption. We have proposed an ENZ grating structure to boost the optical transmission at the ENZ frequencies. The grating structures have openings that enable potential introduction of gain media to combat losses or nanoscale emitters for light emission control. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4770517]