A terahertz photoconductive antenna placed on the back side of a semiconductor slab with and without a compact cylindrical semiconductor microlens on the front side is studied theoretically. The antenna is operated as a photomixer giving narrowband radiation at 1 THz. Radiation patterns and emitted powers are found to oscillate with slab thickness as a consequence of multiple-reflection interference. It is further shown that an antireflection layer on the lens may eliminate these oscillations to a large extent. In the absence of a lens, most of the radiation is trapped inside the semiconductor slab, and the radiation pattern is far from that of a pencil-beam. Both light trapping and radiation patterns are shown to be significantly improved by a very compact lens with a size smaller than a cubic wavelength. The improvements on outcoupling of radiation in a predominantly forward direction versus lens radius and height are mapped out. The calculated outcoupling efficiency of the antenna-lens system takes into account the Purcell effect and radiation trapped in the semiconductor slab. The antenna-lens system is modeled rigorously by using the Green’s function volume integral equation method in a form that exploits cylindrical symmetry.

中文翻译：

---

太赫兹光电导天线紧凑型圆柱微透镜在光混合器中的理论分析

理论上研究了置于半导体平板背面的太赫兹光电导天线，在正面带有和不带有紧凑的圆柱形半导体微透镜。天线用作光混频器，可产生1 THz的窄带辐射。由于多次反射干扰，辐射图和发射功率随平板厚度的变化而振荡。进一步表明，透镜上的抗反射层可以在很大程度上消除这些振动。在没有透镜的情况下，大部分辐射被捕获在半导体平板内部，并且辐射方向图与笔形光束的方向图相距甚远。通过尺寸小于立方波长的非常紧凑的透镜，可以显着改善光捕获和辐射图。提出了辐射在主要向前方向上与透镜半径和高度的输出耦合的改进。天线透镜系统的计算出的外耦合效率考虑了珀塞尔效应和半导体平板中捕获的辐射。使用格林函数体积积分方程法以利用圆柱对称性的形式对天线透镜系统进行了严格建模。