100 GHz electrically tunable planar Bragg gratings via liquid crystal overlay

We demonstrate 114GHz electrically tunable liquid crystal Bragg gratings using 170Vpp voltage. The devices were made using direct UV grating writing and use evanescent coupling into an electrically tuned nematic liquid crystal. Reconfigurable integrated optical devices are essential in today's dense and complex telecommunication meshes. A commonly employed component on the silica platform fulfilling the above role is a planar Bragg grating. The ability to tune the reflection peak of these gratings is one of the key enablers in realizing an all optical dynamic network. To date, little has been reported on electrically tunable planar Bragg gratings given their potentially superior response times over temperature tuned devices. Such electrically tunable devices work on the principle of shifting the Bragg wavelength by modifying the effective index of a waveguide in a multilayer substrate. One route to achieve this is by overlaying the grating with a liquid crystal as many liquid crystals display refractive index anisotropy that can be electrically manipulated. Modifying the liquid crystal refractive index subsequently alters the effective index of the waveguide, leading to Bragg wavelength shift. Using this approach, Sparrow et al [1] have previously demonstrated 35GHz tunability at 1560nm using 80Vpp (peak-to-peak) square-wave with 250mm-spaced aluminium electrodes. Here, we report a maximum tunability of 114GHz at 1561.8nm using patterned ITO glass electrodes with 170Vpp voltage at 1kHz. Two distinct threshold behaviors which manifest only during the increase of supply voltage were also observed