Optimizing the efficiency of Fabry-Perot interferometers with silicon-substrate mirrors

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.

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“…The etalon mirrors will either be stretched metal mesh with high heritage (Sec. 10), and recent demonstrations of R ¼ 100;000, 29 or more modern patterned silicon, 30 which could improve performance for wider band coverage.…”

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“…10, Refs. [110,111,112,113]), and we plan on using silicon substrate based mirrors as reflectors [114]. We chose to use the quad-chroic bolometers so that we can filter the resonant orders of the FPI with the narrow-pass bolometer bands and simultaneously image at the four frequencies selected by the bolometers.…”

Prime-Cam: a first-light instrument for the CCAT-prime telescope

“…To avoid these losses, we will use the silicon substrate based (SSB) mirror designs under development at Cornell. 20,58 The nanofabrication techniques inherent in SSB mirrors enable us to tune the reflective geometry and finesse. We have investigated geometries for our reflectors including pure inductive (screen-like), pure capacitive (isolated metal islands) and mixed combinations of the two for a wide variety of metal fill to open silicon values.…”