Long pulse delays in thin metamaterial slabs

We provide experimental evidence that an electromagnetic pulse can be significantly delayed with minimum loss and distortion, while propagating through a new type of planar meta-materials that supports modes weakly coupled to free-space radiation ("dark modes"). Although changes in the velocity and shape of light pulses propagating through bulk dispersive media have been studied extensively in the past [1], these effects have recently drawn considerable attention, since the ability to accurately control the velocity of light is essential for the development of optical communication technologies. We show that the pulse velocity can be controlled through appropriate subwavelength patterning of a thin metal film, namely a planar metamaterial. As typical examples of such structures, we consider two metamaterial arrays with a 15x15 mm unit cell lithographically etched on a 1.5 mm thick PCB dielectric substrate. The first structure is a bi-layered "fish-scale" [2] consisting of an array of continuous wavy metallic strips residing on both faces of the substrate (see inset to Fig. 1a), while the second is an array of split ring resonators with asymmetric arc lengths (see inset to Fig. 1b). As it can be seen from the experimental spectra of Fig. 1a and Fig. 1b, both planar metamaterials exhibit strong normal dispersion in a transmission window (~5.5 GHz) as a result of "dark mode" excitation.