Miniature Photonic Filters, Spectrometers, and Nulling Interferometers for Astrophysics and Space Science

We seek to build on our expertise in astrophotonics - photonics applied to astronomical instrumentation - to develop an exciting new technology for future NASA missions. Under our current APRA grant, we have replaced the bulky optics of conventional near-infrared filters and spectrometers with miniature (~1 cubic-centimeter) photonic devices imprinted using buried silicon nitride ("nano-core") technology, the leading solution for low-loss waveguides at 1 - 1.7 um. We have perfected the design of the waveguides, improved the deposition method of the cladding material (silica), and reduced the scattering losses with the use of a new high-precision (a few nm instead of ~8 nm) electron beam writer, resulting in ultra-low propagation losses of only 0.018 dB/cm at 1.6 um (instead of 0.25 dB/cm before the APRA-funded effort). We have fabricated complex photonic filters with improved and reproducible transmission profiles thanks to a new double-spiral design that results in a compact footprint of only 1.5 mm diameter which reduces non-uniformity in the fabrication of these filters. We have put these photonic filters between two 2 x 2 multi-mode interferometers (MMIs) to make use of both the transmitted and reflected spectra, without dispersing the light, for exoplanet science applications. Finally, we have successfullly fabricated and tested two types of polarization splitters, one that makes use of MMIs and another one based on bent directional couplers, to address the polarization dependence of our devices. Here we wish to apply what we learned over the past four years to fabricate and test (1) a new generation of high-throughput, high-resolving-power (> 50,000), polarization-combining, multi-input on-chip spectrometers based on a three-stigmatic-point design with flat focal surfaces to ease coupling with near-infrared detectors, and (2) new on-chip cascaded nulling interferometers that will make use of up to three thermally- or piezoelectrically-tuned MMIs in series to fine tune both the phase and power balance between the signals to deliver suppression ratios of 50-80 dB (10^5 - 10^8). The performances of these photonic devices will exceed those of conventional instruments. All of these devices will be optimized, fabricated, and tested in-house by our trained graduate students using the state-of-the-art facilities of the Maryland NanoCenter and AstroPhotonics Lab as part of their PhD theses. Up to three undergraduate students will also be involved with this research. This effort directly addresses one of the technology gaps identified in the 2019 Astrophysics Biennial Technology Report, namely the need to develop "high-performance spectral dispersion components / devices." Astrophotonics is also explicitly cited in the Astro2020 report as a "potentially revolutionary strategy for the next generation of astronomical instruments." A wide swath of astrophysical research, from spectroscopic studies of the distant universe to searches for biosignatures in the atmospheres of exoplanets, stands to benefit from these miniature devices on board future NASA-funded balloon, CubeSat, Explorer, Probe-class, and Flagship missions.

The Astrophysics Research and Analysis program (APRA) supports suborbital and suborbital-class investigations, development of detectors and supporting technology, laboratory astrophysics, and limited ground based observing. Basic research proposals in these areas are solicited for investigations that are relevant to NASA's programs in astronomy and astrophysics, including the entire range of photons, gravitational waves, and particle astrophysics. The emphasis of this solicitation is on technologies and investigations that advance NASA astrophysics missions and goals.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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