Band-gap structure for periodic chiral media

We study electromagnetic wave interactions in periodic chiral media through an examination of the band-gap structure derived from a coupled-mode solution. For oblique incidence the singly periodic chiral medium possesses three separate fundamental Bragg conditions, which lead to a richer band-gap structure than that observed for its achiral counterpart. We examine these fundamental Bragg conditions in three characteristic domains defined as the subchiral, chiral, and superchiral regions. The conditions defining each region and the band-gap characteristics are presented. The chiral band-gap structure suggests that periodic chiral media may be useful as filters, polarization mode converters, mode discriminators, and multiplexers for circularly polarized waves. It also demonstrates the increased degrees of freedom for the design of distributed-feedback or Bragg-reflection devices. (C) 1996 Optical Society of America