Low threshold optical attenuator based on electrically tunable liquid crystal cladding waveguide

We propose a multimode planar waveguide with polymer core of negative photoresist AZ15nXT with an upper cladding of electrically tunable 4-cyano-4'-pentylbiphenyl (5CB) nematic liquid crystal. The waveguide is realized on indium tin oxide (ITO) coated glass substrates using a simple, cost-effective photolithography fabrication technique. The refractive index of LC cladding changes with the applied voltage, which affects the propagation of transverse magnetic (TM) modes of light in the core. We experimentally achieved a relatively low threshold voltage of 1.08 V and the maximum required operating voltage of 4 V-pp (peak to peak) at 633 nm wavelength. An extinction ratio of 12 dB for TM modes is obtained at an applied voltage of 4 V-pp. A theoretical and experimental analysis is done to present the device as a low threshold electro-optic switch and optical attenuator for TM polarization.