Cholesteric ring resonators

Cholesteric liquid crystals (CLCs) show a polarization-sensitive photonic band gap (selective reflection band), the band edges exhibiting resonant optical modes for circularly polarized light. In a theoretical treatment, we discuss the optics of cholesteric ring resonators, where the light is confined to a closed path along the cholesteric helix, which is bent into a circle. Apart from the well-known cavity and band-edge resonances, introduction of an artificial defect (defect layer and/or discontinuity of the director orientation) gives rise to additional resonant modes inside the photonic band gap (defect modes). Such systems show a unique combination of ring cavity, band edge, and defect mode resonances.