Tunable photonic defect modes in a cholesteric liquid crystal induced by optical deformation of helix.

We have demonstrated, based on numerical analyses, that the introduction and tuning of photonic defect modes in a cholesteric liquid crystal (CLC) can be realized by the local deformation of its one-dimensional periodic helical structure. The defect modes appear in transmission spectra only when incident circularly polarized light has the same handedness as CLC's. The tuning of defect modes position can be performed upon both local elongation and shortening of the helix; however, the direction of the shift of the defect mode wavelength is opposite. By controlling the degree of the deformation of helix, a continuous shift of the defect modes can be realized. Our results will open the way for the optical introduction and tuning of defect modes in CLC's.