LCD pretilt angle measurement using QHQ compensation method

We would like to propose a new, simple method to evaluate the pretilt angle of a transmissive or reflective LCD cell. The compensator is consisted of two quarter-wave plates (QWP) and one half-wave plate (HWP). By proper adjusting the orientation of quarter wave plate and half wave plate, the phase value of the compensator which corresponding to the minimum transmission can be obtained. We can make use such value for calculating the actual pretilt angle.