Photonic band gap of loop structure containing negative-index materials

We predict the existence of a special photonic band gap in a quasi-one-dimensional loop structure containing negative-index materials in the subwavelength regime. The mechanism of the formation for this special band gap is quite different from the so-called zero-average-index gaps in the one-dimensional structures, due to the parallel action of the loop. The parallel action enhances the impedance contrast between the two parts on either side of the interface in each unit cell, thus resulting in strong reflection which increases the width of the band gap. In addition, we show that even large band gaps could be obtained in multichannel structures.