Research On Lens Design For Large-pitch Sparse-array LED Backlight

As a mainstream flat panel display technology,liquid crystal display(LCD)has been widely used in various display fields.As a key component in a LCD,a backlight unit presents an important influence on the performances,including luminance,chromaticity,uniformity,viewing angle and thickness.Direct-lit backlight unit had the advantage of high efficiency as well as the disadvantages of large thickness and low uniformity in the case of large pitch and sparse array.Second optics lens design therefore becomes the research topic,which can improve the uniformity of a ultra-thin backlight unit.Based on the theory of non-imaging optics,the thesis designs two kinds of free-form surface lenses.The lens with a non-rotationally symmetric structure can form a rectangular spot and becomes easier to achieve higher uniformity.The thesis takes use of the traditional grid-based uniform sampling algorithm and the more advanced bipolar coordinate system based non-uniform sampling algorithm to design a non-rotationally symmetric structure lens.With the first traditional algorithm,the lens profile is not continuous due to the deviation of the surface,which makes it not easy to manufacture and the light spot is seriously degraded.The second algorithm has been greatly improved on the basis of the traditional algorithm.The curved surface of the lens is continuous and the illumination distribution of the rectangular spot is uniform.It performs well in the ultra-thin backlight unit,which fully verifies the feasibility of such lens in a direct-lit backlight.For the lens with rotationally symmetric structure,this paper mainly focuses on the problem of the spot degradation caused by the extended light source in a refractive lens design and the problem of applying reflective lens in a large-pitch sparse-array backlight unit.For the extended light source problem,this paper proposes a new surface-based feedback optimization algorithm of energy mapping,which does not need the data interaction and feedback of the optical simulation software.With several-round iterations,the lens profile has been optimized and can achieve good results.For the problem of the backlight unit with large pitch and sparse arrays,the design method of a reflective lens is proposed and further optimized based on Solid Works series part design table,which can reach large DHR at a small OD,satisfying the design requirements.Base on the proposed design algorithm and optimization method,the reflective lens with rotationally symmetrical structure is successfully designed,which can be used inthe case of OD is 10 mm and the pitch is 60 mm,and achieved ultra-thin backlight.