The Study Of Fabricating Light Guide Plate With Sub-micron Gratings

Light guide plate is the key device in LCD backlight module. At present, the design of Light guide plate in and abroad is based on geometrical optics principle. In this dissertation, a novel Light guide plate fabricated by gratings is proposed, including its designing and fabricating method.Firstly, the diffraction properties of sub-micron gratings is analyzed using rigorous coupled-wave theory, including the relationship of the direction of diffraction light in each grade and grating period, and the relationship between diffraction efficiency and groove depth. By analyzing the diffraction properties of sub-micron gratings, it is summarized that sub-micron gratings can realize the function of light-guiding by controlling the period of gratings and the angle of incident light. The properties are the theory base of the designing light guide plate.The light guide plate is rectangular. The light guiding unit on the surface is composed of sub-micron gratings whose transmission wavelengths are red, green and blue in order. The light source are red,green,blue LED or semiconductor laser array. To enhance the light utilization, the surfaces of Light guide plate except the incident and transmitted surfaces are coated with metallic film. The transmission angle is controlled by grating frequency and the diffraction efficiency is controlled by groove depth of sub-micro gratings to get uniformity of transmission filed.The arrangement of light guide units is the research emphases. Firstly, the dimensions of light guiding unit are calculated by Rayleigh criterion.Then, the parameters of sub-micron gratings are designed: the grating period is calculated by the grating equation according to the incident and transmitted angles; Finally, the groove depths of the gratings are arranged to satisfy the uniformity request.The relationship between diffraction efficiency and groove depth, and the light-guiding properties of sub-micron gratings are verified by experiments. At last, the feasibility of fabricating light guide plate by double beam laser direct writing system is confirmed.