全介质纳米结构实现LED偏振光辐射准直

Radiation Collimation of Polarized LED with All-Dielectric Nanostructures

为提高偏振出光发光二极管(LED)的光场耦合效率,以一维光子晶体和亚波长介质光栅为基础,设计一种集成式全介质纳米结构组合器件。采用有限差分时域(FDTD)方法建立实现偏振光束准直功能的全介质纳米结构模型。系统研究光子晶体和介质光栅的结构参数对偏振LED出射光场调控的影响,分析光子晶体厚度、光子晶体周期、介质光栅周期、介质光栅高度和介质光栅线宽等参数影响准直特性的物理机制。设计优化的纳米结构,自上而下分别为周期为550 nm、线宽为160 nm、深度为120 nm的TiO_(2)纳米光栅和两对Al_(2)O_(3)/SiO_(2)薄膜组成的光子晶体结构(每层厚度均为80 nm)。计算结果表明,所设计的全介质纳米结构可以将绿光波段偏振LED出光远场辐射角度控制在-6°~6°范围内,可以实现光辐射远场准直,同时出光效率大于77%。在垂直方向(远场辐射角度为0°)所设计的结构的远场辐射强度相较无结构LED辐射强度提高了6.6倍。

In order to improve the light-field coupling efficiency of a polarized light emitting diode(LED),a composite device with an integrated all-dielectric nanostructure is designed based on a one-dimensional photonic crystal and a subwavelength dielectric grating.The all-dielectric nanostructure model for collimating polarized beams is established by using the finite-difference time-domain(FDTD)method.The influence of structure parameters of the photonic crystal and the dielectric grating on the light-field regulation of the polarized LED is studied systematically.The physical mechanism of collimation characteristics affected by photonic crystal thickness,photonic crystal period,dielectric grating period,dielectric grating height and dielectric grating linewidth is analyzed.The optimized nanostructures are composed of TiO_(2)nano-gratings with a period of 550 nm,a linewidth of 160 nm and a depth of 120 nm,and a photonic crystal structure composed of two pairs of Al_(2)O_(3)/SiO_(2)films(the thickness of each layer is 80 nm).Calculation results show that the designed all-dielectric nanostructure can control the divergence angle of the polarized LED within the range of-6°-6°in the green light band,and achieve the far-field collimation of the light radiation,with the light extraction efficiency greater than 77%.The far-field radiation intensity of the designed structure is 6.6 times higher than that of the bare LED in the vertical direction(with a divergence angle of 0°).