High aspect-ratio meta-device for broadband and high-efficiency terahertz wave manipulation

Efficient terahertz (THz) wave manipulation is essential for advancing communications, imaging, and security detection.However, conventional THz devices based on natural materials suffer from the issues of bulky size, low efficiency, and narrow bandwidth.Although dielectric metasurfaces offer a promising alternative, their practical applications still face challenges in high-precision manufacturing, particularly for structures with high aspect-ratio (AR) and deep etching depth.Herein, we experimentally construct high-quality silicon meta-devices for THz wave-controls.Guided by the analysis of the potential structural imperfections, we propose an optimized fabrication method based on the Bosch etching technology to address these challenges and create silicon meta-atoms with high AR and vertical sidewall.As a proof-of-concept, we design and fabricate a half-wave plate (HWP) and a quarter-wave plate (QWP) with a maximum AR of 19.2:1 and broad working bands (0.6-0.8 THz and 0.5-0.8THz).Their polarization conversion ratios (PCRs) can reach 0.915 and 0.99 at approximately 0.73 THz and 0.66 THz, respectively.Furthermore, we experimentally realize a highly efficient and broadband metalens exhibiting the high average focusing efficiency of 85.56% within 0.6-0.8THz.Our fabrication methodology can be extended to fabricate other high-performance metasurfaces, opening new possibilities for broadband THz applications.