OPTICAL METAMATERIALS AND SUPER-RESOLUTION IMAGING

Metamaterials are specially designed periodic structures (a ) that give rise to extraordinary optical properties that no natural materials can possess. It can have extremely large refractive index or a negative refractive index over a frequency band. The refractive index, n, determines how light travels in a medium and is related to the permittivity, ", and permeability, , by the relation n 1⁄4 ð" Þ1=2. It was ̄rst pointed out by Veselago that if " < 0 and < 0, then n becomes negative. Nevertheless, there are no natural materials that possess negative permeability, though metals possess negative permittivity at subplasma frequency. However it was Pendry's suggestion that negative refraction would make a perfect lens that drawn worldwide interests in this ̄eld. 5 Besides subwavelength di®raction limited imaging, metamaterials have also found applications in areas such as wideband directive antennas, band-stop ̄lters, radar absorbers, broadband phase shifters, cloaking and far̄eld optical microscopy. These can be achieved by engineering the propagation of light in the structure. This list of potential applications is non-exhaustive asmore concentrated e®orts are currently ongoing all over the world to design new structures and improve on old ones. The beauty of using metamaterial structures in devices is that the design can be made much smaller with improved performances, or at least comparable performances with conventionally established techniques. Ernest Abbe (184