15.4: Reflective LCD Cell Gap Measurement by QHQ Compensation Method

A phase compensation method is presented for measuring the cell gap of reflective LCD. We use the so-called QHQ compensator that is made up of two quarter-wave plates (Q) and one half-wave plate (H). This method is different from other compensation methods in that we can change both the orientation angle and retardation value of the compensator by rotating the quarterwave and halfwave retarders. As a result, the QHQ compensation method has a higher accuracy and a simpler procedure.