用于LED均匀照明的自由曲面菲涅耳TIR透镜光学设计

为了提高透镜的散热能力，设计了一种新型全内反射（TIR）透镜，该透镜的出射面中央为自由曲面菲涅耳面。采用斯涅尔定律和全反射定律分别求解TIR透镜折射部分和反射部分自由曲面的面形。同时，采用一种菲涅耳透镜的普适设计方法将折射部分自由曲面转变成菲涅耳面。通过蒙特卡洛光线追迹模拟自由曲面菲涅耳TIR透镜的照明效果，结果显示:当光源尺寸为2 mm×2 mm时，其远场照度均匀性为82%，光效为96.6%，透镜质量为21.94 g。与未加菲涅耳面的TIR透镜相比，带自由曲面菲涅耳面的TIR透镜在光效仅下降2%，在照度均匀性未变的情况下，透镜质量减少了约20%。这说明对TIR透镜的自由曲面出射面进行菲涅耳化可明显地缩小透镜的体积和质量，缩短光线在透镜内部的光程，因此可有效提高透镜的散热效率和使用寿命，同时保持良好的照明效果。

Optical design of freeform Fresnel TIR lens for LED uniform illumination

A new design of total internal reflection (TIR) lens was presented which had a freeform Fresnel surface in the central part of the front to improve the heat dissipation capability. Snell's law and the reflection law were applied to construct the freeform refractive surface and the freeform reflective surface for the TIR lens. The freeform refractive surface was transformed into the freeform Fresnel surface with universal design method of Fresnel lens. The simulation result for the freeform Fresnel TIR lens obtained by Monte Carlo ray tracing shows that the far field illumination uniformity of 82.0% and the luminous efficiency of 96.6% are achieved for the light source size of 2 mm×2 mm, in the meanwhile the lens weight is only 21.94 g. The freeform Fresnel TIR lens has nearly 20% reduction in lens weight and volume, only a 2% reduction in luminous efficiency, and no reduction in illumination uniformity compared to the TIR lens without the Fresnel surface. The result indicates that the Fresnelization for freeform surface of TIR lens can significantly reduce the volume and weight of TIR lens and shorten the optical path length, thus effectively improve its heat dissipation efficiency and service life while maintaining a high performance.