Although high-resistivity, low-loss silicon is an excellent material for THz transmission optics, its high refractive index necessitates antireflection treatment. We fabricated a wide-bandwidth, two-layer antireflection treatment by cutting subwavelength structures into the silicon surface using multi-depth deep reactive ion etching (DRIE). A wafer with this treatment on both sides has <-20 dB (<1%) reflectance over 190-310 GHz. We also demonstrated that bonding wafers introduces no reflection features above the -20 dB level, reproducing previous work. Together these developments immediately enable construction of wide-bandwidth silicon vacuum windows and represent two important steps toward gradient-index silicon optics with integral broadband antireflection treatment.
@article{arxiv.1803.05168,
title = {A 1.6:1 Bandwidth Two-Layer Antireflection Structure for Silicon Matched to the 190-310 GHz Atmospheric Window},
author = {Fabien Defrance and Cecile Jung-Kubiak and Jack Sayers and Jake Connors and Clare deYoung and Matthew I. Hollister and Hiroshige Yoshida and Goutam Chattopadhyay and Sunil R. Golwala and Simon J. E. Radford},
journal= {arXiv preprint arXiv:1803.05168},
year = {2018}
}