The positive-negative index coupled waveguide systems: Couplers, arrays and bundles

The coupled electromagnetic waves propagating in a waveguide array, which consists of alternating waveguides of positive and negative refraction indexes, are discussed. The pair of positive-negative waveguides acts as oppositely directional coupler. The stop band in the spectrum of linear waves occurs. When pairs of these waveguides are collected in array or bundle the spectral properties of the resulted device are modified. We study spectral gaps in these waveguide systems and demonstrate that the number of waveguides and helical spatial twist of the array can be used to control the size of the gap.