Evaluation of Kerr constant of blue-phase liquid crystals by measuring off-axis retardation in vertical electric field cells

Because of the nonuniform electric field of the in-plane-switching cell in the thickness direction, an accurate and efficient way for evaluating the Kerr constant of blue-phase liquid crystal (BPLC) needs to be developed. This study demonstrates a method for evaluating the Kerr constant by measuring the off-axisinduced retardation (R_th) change in normal vertical field cells using a commercial polarimeter. The angledependent behavior of the R _th change is observed as an electric-tunable positive C retarder. In this paper, a sigmoid fitting model has been chosen for calculating the Kerr constant for considering the very small intrinsic birefringence of the BPLC.