Collaborative research: tunable dual-polarization photonic ring resonator filters for OH-suppressed ground-based infrared astronomy

Lowell Observatory received a $414,907 Project Grant from the National Science Foundation's Division of Astronomical Sciences under the Mathematical and Physical Sciences (CFDA 47.049) program, effective October 1, 2025 through September 30, 2027. The project develops tunable dual-polarization photonic ring resonator filters fabricated on silicon wafers to suppress atmospheric OH airglow at near-infrared wavelengths, enabling ground-based astronomers to observe cool stars, proto-planets, and galaxies more effectively. The ring resonators function as narrow-band notch filters designed to block prominent OH emission lines while transmitting astronomical signals, with targeted suppression of 20-40 decibels and an estimated signal-to-noise improvement factor of 5 or greater in the near-infrared spectrum.

The primary deliverable is the engineering solution for efficiently coupling telescope light into ring resonators and back out to conventional astronomical instruments such as spectrographs, culminating in on-sky demonstration of the airglow suppression technology. As a collaborative effort leveraged by U.S. industrial partners, the project addresses a critical limitation in ground-based infrared astronomy by providing a domestically fabricated alternative to imported fiber Bragg gratings. Additionally, in partnership with Lowell Observatory's Marley Foundation Astronomy Discovery Center, the grant supports development of a portable interactive exhibit demonstrating critical thinking and problem-solving methodologies used by scientists and engineers in astronomical instrumentation development.

Abstract

This project will develop novel filters called ring-resonators, imprinted on silicon wafers, to suppress the atmospheric airglow at near-infrared (NIR) wavelengths where cool STARS, proto-planets and galaxies glow most brightly. The airglow, coming from narrow emission-lines produced by OH molecules in the upper atmosphere, prevent astronomers from taking full advantage of this window from ground-based observatories. The ring resonators create narrow-band notch filters (like an uneven picket fence with very narrow pickets), thermally tuned to block the air-glow lines but let most of the light from astronomical objects through. This program focuses on solving the engineering problems associated with coupling light from telescopes efficiently into the ring-resonators, and then back out to feed conventional instruments, such as spectrographs. By the conclusion of this project, leveraged by US industrial partners, the technology will be sufficiently advanced for on-sky demonstration of ring resonator-based air-glow suppression. Working with lowell observatory?s marley foundation astronomy discovery center, this program also will develop a portable, interactive exhibit focused on the critical thinking and the problem-solving tools used by scientists and engineers in the development of astronomical instrumentation. Ring resonator filters currently offer the only viable alternative (potentially in a more compact package) to fiber bragg gratings (not fabricated in the US) for reducing the pernicious airglow that limits ground-based NIR observations. The ring resonators developed here aim to suppress (by 20-40 DB) the most prominent OH lines, yielding an estimated signal to noise (s/n) improvement in the NIR of a factor of 5 or more in a broad-band sense, and dramatically reducing scattered light in astronomical instruments. Laboratory efforts focus on the integration of commercial off-the-shelf photonic lanterns into the source-device-sensor pathway; coupling both TE and TM input modes to photonic devices simultaneously; and leveraging the design, fabrication, and packaging expertise of industry leaders in silicon photonics, all for the purpose of mitigating the coupling losses that have thus far limited device throughput. The wavelength range over which OH suppression can be accomplished will also be expanded. The outreach exhibit will be centered upon existing instruments, some previously flown on sofia, and will be portable, allowing lowell?s instrument transport vehicle to take IT to other sites, such as the schools with which lowell partners. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the foundation's intellectual merit and broader impacts review criteria.- subawards are not planned for this award.