Design Of Freeform Optical Devices And Their Applications In Illumination Systems

Along with the speeding of the pace of modern life and the energy consume, it is hoped that equipments could become more portable and energy saving. So now both in army and civil applications, the modern optoelectronic equipments are eager to accomplish the miniaturization and raise the utilization rate of energy. And LED source has been widely used in various mini illumination systems, for its merits such as its compact size, long life time and so on. And because its luminous distribution is different from other traditional light sources, in order to improve the performance of the illumination system, a secondary optic design should be applied to the LED source. Then the system could be further miniaturized while the utilization rate of energy still acts well. Considering there's no need to image the source in an illumination system in most cases, and then freeform optical equipment based on non-imaging theory is used for the LED's secondary optic design to accomplish an illumination system with portable size and high efficiency.A new method to design the freeform optical equipment was proposed in this paper.Based on the previous design methods, a set of first-order partial differential equation setshad been deduced according to the snell's law and the energy conservation, when theluminous distribution of the light source and the desired illumination were fixed ahead. Afterthe incidence light on the freeform surface was reflected or refracted, the desired illuminationcould be realized on the target plane. The equation sets were solved using numerical methods,and it would cost about 5-20 seconds to solve them by C language according to thecomplexity of the freeform surface. While try and error and other equation solving methodsalways cost hours or even more to get the results. Then the traditional illumination systemoptical design method mainly based on experience would turn into solving specific equations.The whole design process didn't involve any professional optical design software, and there'sno need to optimize, which improving the work efficiency and the illumination performance.After getting the discrete data of the freeform surface by calculation, Rhinoceros andPro/E were applied for the 3D molding. These two softwares both adopt NURBS moldingtechnique, which could yield freeform optical equipment identical to the calculated one.Multiple sub-freeform surfaces splicing method were applied when molding the non-rotational symmetric freeform surface, in order to minimize the molding error and get the desired non-rotational symmetric illumination, while improving the illumination uniformity. After that ASAP and TracePro were applied to simulate the illumination system, using the molded freeform surface or solid. The simulated results showed that when the size of the source could be neglected comparing with the size of the optical equipment, both the uniformity and the efficiency of the illumination system could reach beyond 90%.According to the theory mentioned above, various freeform illumination systems applying LED as the source were designed, which could solve the low efficiency and other problems caused by the mismatching between the LED source and the subsequent optical system, and get the illumination uniformity which was hard to reach using the traditional optical design. In order to verify the feasibility of freeform optical equipment by experiments, a freeform lens in an LED reading lamp was designed and manufactured, the experiment results was coincident with the software simulated results.The deduced partial differential equations have relationship with the luminous distribution of the source, so theoretically this method could be applicable to all kinds of light sources. And to LED, it could be used in the design of the LED projector, street lamp and headlamp of car, which would mostly extend the application of LED, and lay a good foundation for LED replacing the traditional light sources.