External pressure induced liquid crystal defects for optical vortex generation

Simple and arbitrary creation of liquid crystal (LC) defects can be highly useful, in particular, for the creation of optical vortex. We report a novel method to create an isolated and stable +1 type concentric LC defect by combing an external pressure on a vertically aligned liquid crystal cell (VALC) and the application of electric fields. The method does not require special material in alignment layer, nor patterned electrodes such as in spatial light modulator, but it can produce stable and rewritable defects in a LC cell. We show that the created +1 defect can be used to generate optical vortices with ±2ℏ orbital angular momentum. The simple and cost-effective process and its tunability for the position of defect make the method useful in various applications such as advanced optical communication and quantum computation using tunable optical vortices.