Tuneable Fabry–Perot etalon for terahertz radiation

An indium tin oxide-clad liquid crystal filled Fabry–Perot etalon structure has been shown to act as an effective narrow-band filter at terahertz frequencies. An applied voltage, which controls the alignment of the nematic liquid crystal allows the refractive index of the core to be tuned. Transmission spectra show well-defined resonant peaks which shift in position when the alignment is changed from planar to homeotropic. The measured transmission spectra agree well with the results of a multilayer optics model and the birefringence of the liquid crystals over this frequency range are determined as Δ n = 0.15(± 0.01) and Δ n = 0.08(± 0.01) for E7 and ZLI 2293, respectively.