Mechanically tuned defect-mode multiplet for cholesteric photonic elastomers

The multiplet structure of the optical defect modes generated within the bandgap are analyzed by a finite number of identical equispaced twist defects in axially elongated cholesteric elastomers. It is shown that n(0) defect modes induced by n(0) twist defects can be mechanically tuned. The transfer matrix is obtained and the defect frequencies when n(0) = 1,2 are expressed in terms of twist angle, fractional shape anisotropy, and longitudinal deformation. For n(0) = 2, the coupling between modes is analytically studied and it is shown that when the separation between defects is much larger than the line width, the defect modes do not interact and become degenerated.