为了克服传统LED准直器在近场难以实现均匀照明的缺陷, 设计了一种双自由曲面均匀照明准直透镜.透镜分为折反两部分, 每部分都利用双自由曲面进行匀光和准直.根据马吕斯定律, 推导了实现光束准直出射的等光程方程, 并将切面迭代法加入等光程条件, 同步计算准直透镜上下自由曲面的面形数据.仿真分析表明: 对1 mm×1 mm的白光LED芯片, 84.55%的能量集中在±2°内, 近场照度均匀性达到94.59%, 远场照度均匀性为89.01%；当LED芯片尺寸不超过2.0 mm×2.0 mm时, ±4°内的能量利用率大于83.5%, 近场照度均匀性在90%以上.该准直透镜能同时实现近场和远场的均匀照明, 公差符合装配要求, 光能利用率高.

A LED collimator with double freeform surfaces was designed for uniform illumination in both near field and far field.The collimator includes refractive part and reflective part,and each part has double freeform surfaces.Based on Malus Law,the constant optical path length equations that realize the rays collimating were derived.Then associating with tangent-plane iterative method,the date both up freeform surface and down freeform surface simultaneously could be calculated.The simulations show that,84.55% of the energy is collected in ±2° for 1 mm×1 mm size white LED after considering the Fresnel loss,reflective surfaces loss and material absorbing.The uniformity in near field is 94.59%, and the uniformity in far field is 89.01%.The uniformity in near field and the optical efficiency in ± 4° are above 90% and 83.5% respectively,while the LED chip sizes are under 2 mm×2 mm.It is illustrated that the LED collimator can realize uniform illumination in both near field and far field with high light efficiency and the tolerance meet the requirements of alignment.