Application of Silicon Micropyramid Structures for Antireflection of Terahertz Waves

Reflection from silicon-based terahertz (THz) components degrades the performance of THz spectroscopy systems by inducing loss and interference. In this paper, we report the design, fabrication, and demonstration of silicon-based devices for reflection reduction and transmission enhancement of broadband THz electromagnetic waves. Antireflection (AR) effect is achieved in the broad frequency range of 0.2-3.15 THz using silicon micropyramid structures as the AR devices. We observe a maximum of 89% reduction in reflectivity of THz power when the sample with 60-¿m-period micropyramids is used, compared with the reflectivity of a planar silicon substrate. By varying the period of the micropyramid devices from 110 to 30 ¿m, the cut-off frequency of enhanced transmission is tuned from 0.74 to 2.93 THz and the bandwidth of enhancement increases from 0.91 to 3.15 THz, respectively. Although the structures have been demonstrated as AR devices for silicon substrate, this design can be also used for other substrate materials. Furthermore, the silicon devices also function as low-pass filters.