白光LED二元光学光束整形及其应用

White light-emitting diode (LED) is used in various illuminating systems. After secondary optical design based on the principle of reflection and refraction, the light field, emitted by the white LDE, will be shaped by the optical system to satisfy different demands in various illuminating systems. As well known, based on the principle of diffraction, binary optical element (BOE) is a promising and mature technique to realize beam shaping. However BOE is generally designed for laser incident, not for white LED source. In this project, based on the mechanism of wavelength compensation and the improvement of the optimization method, the limitation of the size of the diffracted pattern, generated by the BOE for beam shaping, is in proportion to the incident wavelength will be broken through. The construction of the optical system and the simulation of the light propagation will be innovated, the optimization algorithms will be continuously improved, the optimized BOE will be fabricated, several typical diffraction patterns for white LED will be obtained, and the diffraction patterns are distinct for different wavelength. Finally, the applications of such BOEs for white LDE beam shaping will be exploited in various illuminating systems, for example, visible light communication system and car headlamp. The research outcomes of this project will provide a new design theory and technique based on the principle of diffraction to realize white LED illuminating, and expand novel optical functions and practical applications of binary optics.

白光LED广泛应用于各种照明领域。基于折反射原理进行二次光学设计，可以使得光学系统对白光LED发出的光场进行整形，满足不同环境的照明需求。二元光学在实现光束整形上具有独特优势，但尚未应用于白光LED照明系统。本项目从“波长补偿机制”与“优化算法改进”的角度出发，突破二元光学光束整形器件的衍射图案通常与波长成正比的限制；创新系统实现方案和光场传输模拟；改进优化设计算法；研制二元光学器件，获得多种典型的白光照明图案，即对不同波长获得相同的衍射图案和光强分布；在无线光通信发射端、汽车前灯等系统中开展应用研究。项目研究成果将为白光LED照明系统提供新的基于衍射原理的光学设计理论和技术，并拓展二元光学的新功能与应用领域。

改进了二维多波长二元光学器件(BOE: Binary optical element)光束整形的迭代算法，减小了初始相位的影响，并将BOE的相位深度限制在合适范围内。利用改进后的迭代算法优化得到了可实现相同尺寸的红蓝两色圆形衍射光斑，而红绿蓝三色衍射光斑尺寸相差5.6%。深入研究了二次采样算法波长补偿机制，为实现白光或多波长光束整形，首先必须将采样间隔与波长的正比关系消除。突破了使用球面波入射或平面波入射折衍混合器件的限制，采用理想平面波垂直入射BOE，实现了红绿波长相同大小和分布的光束整形并扩大了有效衍射场。在中间面上设置方形光阑低通滤波器，消除了图像混叠，获得了良好的光束整形性能。研制了大角度点阵，并通过对目标衍射场的振幅分布进行预处理，提高了点阵均匀性。对扩大有效夫琅禾费衍射场进行了探索。基于所提出的渐进补零迭代算法，设计了新型特殊功能BOE，包括生成了超分辨点阵并实现了衍射超分辨显微成像，分辨率提升了近一倍；设计了多种轴向焦点光强可控的轴向多焦点分布；实现了散斑抑制的环形光斑。根据GB25991-2010对LED汽车前照灯近光灯的照明要求，利用二次采样算法，进行了BOE的优化设计，计算的红光（660nm），绿光（532nm），蓝光（455nm）以及白光仿真结果，光强分布大体满足要求。为避免球面波因子对光束整形性能的干扰，研制BOE实现了白光LED照明下的大角度规则点阵，有望为近距三维传感提供一种新型结构光照明。利用BOE在多波长/白光照明下实现了光束整形，在系统应用中需要对整形光斑进行分色，为此研制白光LED的BOE滤光片设计。深入分析了亚波长金属光栅的透射特性和机理，提出了用于RGB和RGBA两类白光LED的滤光片设计的简便方法并完成了设计、加工与实验。针对Cree公司的XB-D荧光LED光谱，实现了带宽为30nm左右的宽角度蓝光滤光片，峰值透射率为70%，接收角可达正负20°，偏振不敏感且结构简单。