Method for measuring the twist angle of an optically compensation bend by using the heterodyne interferometry

A new measuring method based on the common-path heterodyne interferometry is used to determine the twist angle, pre-tilt angle, and cell gap of an optically compensation bend (OCB) liquid crystal (LC) cell. In this paper, the twist angle of an OCB LC cell can be determined by measurement the phase difference instead of the reflectance difference. Because the measuring system is based on the common-path heterodyne interferometry, it can provide the most sensitive way to measure the twist angle of an OCB LC cell against the air turbulence and environmental vibrations. The method has some merits, e.g., a simple setup, in real-time test and reliability, etc.