基于等效介质膜理论及多层减反膜原理设计了用于超宽带太赫兹吸收体的三层微结构光栅, 光栅基质采用重掺硼硅材料.用有限时域差分法分析了光栅周期、光栅宽度和深度对太赫兹吸收体反射系数的影响.数值分析结果表明, 在低于3 THz波段, 吸收率高于98%的带宽为1.3 THz, 吸收率高于95%的带宽达2.1 THz.用严格耦合波理论对该三层光栅的高吸收现象进行理论分析, 分析结果表明,光栅多级衍射的相互作用减少了入射面的反射率, 增大了该吸收体的吸收率.进一步优化三层光栅微结构的参量, 在0.6~6 THz范围内实现了大于95%的太赫兹吸收.基于光栅结构的吸收体结构简单, 易于设计与分析, 可以应用于太赫兹成像与探测应用领域.

A terahertz absorber composed of three-layer micro-structure gratings was designed based on the effective medium theory and the theory of multi-layer antireflection coating. The absorber was designed on the heavily boron doped silicon. By using the finite-difference time-domain method, the influence of the grating period, width and depth on the reflection coefficient was analyzed. The numerical simulation results show that, in the range of 0~3 THz, more than 98% terahertz absorption can be achieved with a bandwidth of 1.3 THz and over 95% terahertz absorption can be obtained with a bandwidth of 2.1 THz. The high performance of the absorber was explained by the rigorous coupled-wave theory, which suggests that the interaction among the different grating diffraction modes reduces the reflection of the incident wave and increases the absorption rate of the absorber. By structural parameter optimization, the absorber can achieve more than 95% broadband terahertz absorption in the range of 0.6~6 THz. The absorber may be a valuable candidate for use in Terahertz imaging and detecting.