Novel fast measurement method of twist angle and optical retardation of liquid crystal display

A novel method is proposed to measure twist angle and optical retardation of liquid crystal display in this paper. The new method which is one of single-wavelength methods has three characteristics: using circularly and homogeneously aligned LC cell (CH-LC) as a unique polarization-converting device; using variable sector diaphragm and photodetector to detect the total intensity of transmitted light whose original polarization direction is continuously changed from 0 degrees to arbitrary angle; introducting a method of measuring the total intensity ratio of the transmitted light to eliminate the influence of absorption by the polarizer, analyzer, CH-LC, liquid crystal display and so on. The twist angle (phi) and optical retardation (Delta nd) can be derived by using Jones matrix analysis and a curve fitting where phi and Delta nd are fitting parameters. Experiment proved the results are accurate, the process of operation is fast, the devices are economical.