Optical tracking of the director axis in liquid crystal sensors

In this paper, a new approach in tracking the director axis of uniaxial nematic liquid crystal (LC) for sensing applications is developed. This approach utilizes measuring critical angles for total internal reflection (TIR) at the interface of isotropic and LC film. The proposed optical transduction requires measuring two critical angles in orthogonal directions, which lead to a uniquely tracked director axis in well ordered uniaxial LC films. These critical angles are related to the director axis orientation which is treated as an arbitrary vector. An example of tracking the director is provided and the sensitivity of this approach is also discussed.