Fabry–Perot enhancement of liquid crystals birefringence effects in terahertz range

Abstract THz technology is a rapidly advancing field in both fundamental and applied research, integrating novel approaches from optical and microwave ranges. Despite the wide applications of liquid crystals (LCs) in the visible range, their efficiency in the THz range is limited due to the low optical path length of existing anisotropic LC materials. In this work, we propose and explore the advantages of incorporating a LC core layer into the Fabry–Perot resonator as a simple strategy to enhance the observed birefringence effects. This enhancement is achieved through multiple wave passes through the LC layer, effectively increasing the effective optical path length. In particular, we demonstrate a more than tenfold improvement in the efficiency of wave transformation within a plane-parallel LC layer. Our findings are well correlated with the THz response of an LC cell composed of two parallel thick quartz substrates infiltrated with commercially available E48 liquid crystal, as observed in our experiments. The low switching voltage for cells with pyrocarbon-based electrodes is also demonstrated.