Large Étendue, High Spectral Resolution Asymmetric Spatial Heterodyne Interferometer for Quantum and Dual-Use Remote Sensing Applications

Quantum communication systems, quantum-enhanced LiDAR, and quantum sensing platforms share a critical and unmet instrumentation need: a spectrometer capable of simultaneously achieving large étendue (high optical throughput) and high spectral resolution. In satellite-based and ground-based quantum key distribution (QKD), ground station receivers must collect single photons from spatially extended fields of view — demanding large étendue — while rejecting broadband background noise, including solar background in daylight operations, through extremely narrow spectral filtering — demanding high spectral resolution. Similarly, quantum-enhanced atmospheric and oceanic remote sensing requires the collection of weak, Doppler-shifted optical returns distributed across large solid angles, while resolving velocity-induced frequency shifts at the sub-pm level. Conventional spectrometer architectures, including grating spectrometers and Fabry-Perot etalons, face a fundamental étendue-resolution tradeoff that prevents simultaneous optimization of both parameters. The Asymmetric Spatial Heterodyne (ASH) interferometer architecture — a derivative of the Doppler Asymmetric Spatial Heterodyne (DASH) interferometer — offers a compelling solution: its field-widened, static, no-moving-parts design provides the Jacquinot throughput advantage inherent to interferometric spectrometers while achieving high spectral resolving power through heterodyne detection of small Doppler and frequency shifts [1, 2], making it uniquely suited to serve the quantum and dual-use sensing communities. In this topic, proposers should develop a fieldable ASH interferometer that simultaneously achieves large étendue and high spectral resolution suitable for the quantum and remote sensing applications described herein. The instrument shall achieve a minimum étendue of 0.1 cm² sr, a spectral resolving power (R = λ/Δλ) greater than 10^5, and shall operate at one or more select wavelengths relevant to quantum sensing or communication (e.g., 486 nm H-β for Fraunhofer line sensing, 780 nm for rubidium-based quantum systems, 1550 nm for telecom-band QKD, or other well-motivated wavelengths between 400 nm and 1600 nm). The design shall be static (no moving parts), compatible with space or airborne deployment environments with simultaneous high étendue and narrow spectral bandpass, and shall demonstrate a convincing path toward operation across multiple wavelengths relevant to both quantum and dual-use applications. Proposers should clearly articulate the design trades between étendue, resolving power, and instrument volume, and should demonstrate that the proposed architecture is scalable and manufacturable beyond the prototype stage.