Characterization of some wide viewing angle liquid crystal devices.

摘要

It is well known that a standard twisted nematic (TN) display, which is most commonly used in flat panel displays, has inherently narrow and non-uniform viewing angle characteristics. Normally black TN (NBTN) displays suffer from problems with chromaticity and contrast for normal and poor grayscale at wide viewing angles. Ideal compensation of the dark state for a NBTN requires a negative birefringence film with a uniformly twisted optical axis distribution. However, such films have not been fabricated to date. In our work we approximate the twisted structure of compensation film for NBTN displays by stacking several layers of polymer film having in-plane negative retardation. Using only 4 layers of film we obtain much wider viewing cone and higher contrast compare to uncompensated NBTN. The chromaticity is also greatly improved over the uncompensated cell.; Modeling of liquid crystal displays is an efficient and economical way to LCD characterization and optimization without assembling a large number of test cells. It has become a useful tool for the development of new display modes. In the past, optical simulation of LCDs has mainly relied on one-dimensional models. As the liquid crystal technology advances, multidimensional modeling is required for better understanding of optical behavior at smaller feature sizes. In our work, a generalized geometrical optics approach (GOA) has been applied to liquid crystal devices with multiple dimensions. It is faster than other approaches (e.g. FDTD) and proved to be a useful design tool for optimization of liquid crystal devices in more than one-dimension.; We performed detailed characterization of the electrically-induced optical compensation (EOC) mode for information display applications. This mode shows very wide viewing angle and excellent grayscale performance when a negative birefringent compensation film is added. Using GOA, we investigated the detailed transmission profile and the viewing angle properties of EOC mode. The model agrees with the experiment data quite well when diffraction from the cell is taken into account.; To further study the diffraction of EOC and verify the model, we performed detailed measurements of the diffraction profile. For simulations, far field diffraction is obtained using GOA coupled with Kirchoff diffraction theory. Attempts were also made to test the limit of the model by using smaller feature EOC cell. The comparison of simulation and measurement clearly shows the accuracy of the model. The GOA appears to be a promising tool for investigating the optical performance of a range of devices with director fields that vary in multiple dimensions.