Photocontrolled chiral-nematic Fabry-Pérot cavity

The spectral and polarisation characteristics of a Fabry–Pérot cavity filled with photo-controlled chiral nematic are investigated. The chiral nematic under planar-tangential boundary conditions is used, enabling the structure to change in the twist angle continuously under the action of the controlling blue or UV light. An increase in the structure twist angle leads to a rise in the geometric phase of the eigenmodes accompanied by a red spectral shift of $re$-modes and a blue spectral shift of $ro$-modes. The spectral shift of the modes is studied experimentally, through numerical simulation and by analytical treatment. A generalised resonance diagram of the chiral nematic cavity is obtained. Measurements of the geometric phase values as a function of the structure twist angle are made. The proposed chiral nematic cavity with a variable geometric phase can be promising to develop photonic devices with photo-controlled features.