Broadband Pillar-Type Antireflective Subwavelength Structures for Silicon and Alumina

A broadband antireflective subwavelength structure was developed suitable for large diameter silicon or alumina lenses used in the optical systems of superconducting cameras. In this study, a broadband antireflective subwavelength structure that can be easily fabricated with a dicing blade was designed. The model comprised both a pyramidal section (550 $\mu$ m in depth) and a straight section (150 $\mu$ m in depth) to simplify fabrication with a metal bonded V-shaped blade and a normal straight dicing-blade. The simulated transmittance between 97 and 334 GHz was > $\text{90}\%$ , which is comparable to that with a 700- $\mu$ m-depth tapered structure. The structure was fabricated on a flat surface, and transmittance at cryogenic temperatures was measured using a Fourier transform spectrometer. The measured average transmittance between 186 and 346 GHz was approximately 95 $\%$ , and the experimental result is in good agreement with the simulation results.