Polarization-dependent narrowband spectral filtering by chiral sculptured thin films

We analyse theoretically transmission through two layers of different thin-film helicoidal bianisotropic mediums (TFHBMs), wherein the pitch of each layer bears a precisely determined relation to the overall thickness of the bi-layer. A spectral hole emerges from the interaction of the circular Bragg regimes of both TFHBM layers. Our results generalize a recently discovered scheme for producing spectral holes in fibre-Bragg gratings, with which comparison is made. The proposed TFHBM bi-layers may be useful for the simultaneous production of oppositely polarized beams with narrow bandwidths and a specific amplitude splitting ratio.