Optimizing the Efficiency of Fabry-Perot Interferometers with Silicon-Substrate Mirrors

TL;DR

This paper introduces a novel silicon-substrate based design for Fabry-Perot Interferometers, featuring low-reflectance metamaterial coatings and metallic meshes, to enhance broadband efficiency for IR to sub-mm/mm spectroscopy in various telescopic applications.

Contribution

The paper presents a new microfabricated silicon-based FPI design with metamaterial anti-reflection coatings and metallic meshes, including superconducting options, for improved broadband performance.

Findings

Achieved less than 1% reflectance with double-layer ARC

Demonstrated fabrication of plasma-etched silicon metamaterials

Modeled the performance of silicon-based FPIs

Abstract

We present the novel design of microfabricated, silicon-substrate based mirrors for use in cryogenic Fabry-Perot Interferometers (FPIs) for the mid-IR to sub-mm/mm wavelength regime. One side of the silicon substrate will have a double-layer metamaterial anti-reflection coating (ARC) anisotropically etched into it and the other side will be metalized with a reflective mesh pattern. The double-layer ARC ensures a reflectance of less than 1% at the surface substrate over the FPI bandwidth. This low reflectance is required to achieve broadband capability and to mitigate contaminating resonances from the silicon surface. Two silicon substrates with their metalized surfaces facing each other and held parallel with an adjustable separation will compose the FPI. To create an FPI with nearly uniform finesse over the FPI bandwidth, we use a combination of inductive and capacitive gold meshes evaporated onto the silicon substrate. We also consider the use of niobium as a superconducting reflective mesh for long wavelengths to eliminate ohmic losses at each reflection in the resonating cavity of the FPI and thereby increase overall transmission. We develop these silicon-substrate based FPIs for use in ground (e.g. CCAT-prime), air (e.g. HIRMES), and future space-based telescopes (e.g. the Origins Space Telescope concept). Such FPIs are well suited for spectroscopic imaging with the upcoming large IR/sub-mm/mm TES bolometer detector arrays. Here we present the fabrication and performance of multi-layer, plasma-etched, silicon metamaterial ARC, as well as models of the mirrors and FPIs.