Optical Design Of Freeform Surface In LED Illumination Systems

With the tightening supplies of energy and deterioration of environmentpollution in the global, the new generation of light sources, LEDs, with theiradvantages of lower power consumption and environmental friendly, are becomingmore generally preferred in illumination systems. One of the questions needed to besolved is that how to design the secondary optics of LED to meet the requirements ofspecific applications. Freeform optical surface is an emerging optical technologywith advantages of being high design freedom and being precise light irradiationcontrol. It can simplify the system construction and realize complicated illuminationpattern. As a result, more and more illumination systems adopt the freeform surfaceas the secondary optics. In order to realize the redistribution of the LED light withhigh efficiency according to the applications, this paper researched on the opticaldesign of freeform surface in LED illumination systems. The specific contentsinclude the following work:The design method of the initial freeform surface based on the energy mappingmethod was researched. The energy grid patterns were constructed and analyzedbased on the integrability condition for both symmetric and non-symmetric systems.In order to solve the problem of the traditional calculation of the discrete points onthe surface, which is the real normal vectors deviating from the desired normalvectors, the improved method based on the point position modification was proposed and verified for both symmetric and non-symmetric systems. The improved methodcan almost eliminate the entire deviation for the symmetric system and decrease thatfor the non-symmetric system. The simulation results showed that the illuminationpatterns obtained from the improved method were more close to the design targets.The optimization method was researched. Since the reason why the simulationresult deviated from the desired one was different for the symmetric systems andnon-symmetric systems, different optimization processes were adopted. For thesymmetric system which had no deviation in normal vectors, the parametric modelbased on the quadratic B spline was constructed and the optimization based on thenon-sequential ray tracing was directly carried out. For the non-symmetric systems,the parametric model was constructed based on the bi-cubic B spline. The meritfunction was first constructed from the deviation between the real normal vectorsand the desired normal vectors. The initial optimization was carried out based on thepatternsearch algorithm. Then, the optimization to improve the illuminationuniformity and optical efficiency was carried out. Combining the initial freeformsurface design method with the optimization method, an effective optical designmethod of freeform surface in illumination system was formed and verified by thesimulation and the experiment.