Liquid Crystal Based Rib Waveguide

Abstract

We report electrically controlled liquid-crystal-core rib waveguide on fused silica substrate, in which the modal characteristics of waveguide can be tuned over a wide range of wavelengths. The coplanar electrode structure is proposed for controlling the LC molecules direction in the waveguide. Electrically controlled refractive index contrast and profile of waveguide is used for single and dual mode operations of the waveguide. We experimentally demonstrate transition from single mode to dual mode operation by externally applied voltage. In single mode regime the externally applied voltage has been used to tune the mode field diameter of the modes from 11.6 to 9.2 μm along the horizontal direction and 7.8 to 6.4 μm along the vertical direction. In the dual mode regime, long period waveguide grating (LPWG) based mode converter has been numerically demonstrated, and more than 99.9% power conversion from TE00 mode to TE01 mode has been obtained. Further, we show electrically tunable wavelength filters using LPWG in an LC core rib waveguide. We have obtained a tuning range of 140 nm for such electrically tunable wavelength filters. The proposed liquid crystal based rib waveguide has the possibility of on-chip low-cost fabrication.