Research On High Luminance And Flattening For LED Backlight In LCD Imaging Engine

Liquid Crystal Display(LCD)has been used more and more widely in various kinds of applications and becomes the mainstream technique in image engine.With the environment becoming harsher and harsher,the requirements on luminance,weight,and volume are getting stricter.As a key part of a LCD,the backlight plays an important role on display quality and total weight.It is therefore very necessary to put a detailed study on how to get high luminance and flatten the backlight module.In this thesis,a secondary-optics-based design is firstly proposed.The equations are established based on Snell's law and the law of conservation of energy to get the profiles of the double-free-form surface lens.Then the optimization is performed according to the theory of edge-ray to improve the uniformity for planar source.Based on the vector information of the incident light at each point on the freeform surfaces,the algorithm of flattening is then proposed.It's used to flatten two free-form surfaces of the initial lens respectively so as to obtain the double-layered high-luminance films.However,there is the difficulty on how to align the double-layered films.So a single-free-form surface lens is designed and then flattened to get a single-layered high-luminance film.According to the design results,the two kinds of high-luminance optical films are prepared by directly-writing lithography after a series of optimization on the lithography process.The films are installed in a backlight unit for measurement.To guarantee the viewing angle and improve the display quality,two diffuser films are also employed.The practical measurement results show that the luminance increases by 21.13% than the traditional backlight and the non-uniformity decreases to 13.35% when the double-layered high-luminance film is applied.The luminance improvement becomes 17.53% and the non-uniformity is 16.08% when the single-layered high-luminance film is applied.The optical films designed present high possibility to achieve high luminance as well as small volume.