Metrology-grade mid-infrared spectroscopy for multi-dimensional perception

TL;DR

This paper introduces a high-precision mid-infrared spectroscopic system that combines broad tunability, high power, and accurate frequency control, enabling advanced applications like LiDAR and chemical sensing in complex environments.

Contribution

The authors develop a metrology-grade mid-infrared spectroscopy system with continuous tunability and atomic standard traceability, overcoming previous trade-offs in bandwidth, power, and frequency fidelity.

Findings

Achieved >45 mW power output with 7.2 MHz frequency accuracy.

Identified and eliminated hydrogen absorption in silicon nitride microresonators.

Demonstrated LiDAR and dual-modality sensing in foggy conditions.

Abstract

The mid-infrared spectral window is essential for molecular fingerprinting and atmospheric sensing, yet unlocking its full potential is currently constrained by a fundamental instrumental trade-off: existing systems cannot simultaneously deliver broad bandwidth, high photon flux, and metrological frequency fidelity. Here, we resolve this bottleneck by demonstrating a metrology-grade spectroscopic system based on difference frequency generation, driven by widely tunable, near-infrared diode lasers traceable to atomic standards. Our system achieves continuous tunability across the 3-3.7 $\mu$m atmospheric window and delivers output power exceeding 45 mW with an absolute frequency accuracy of 7.2 MHz. We harness this convergence to overcome a critical barrier in integrated photonics, unambiguously identifying and eliminating hydrogen-induced absorption in silicon nitride microresonators to achieve an 88-fold reduction in optical loss. We further reveal multi-phonon absorption in the silica cladding as the fundamental limit to mid-infrared integrated photonics. Finally, we demonstrate the system's versatility through scattering-resilient LiDAR capable of penetrating optically dense fog, and dual-modality sensing that simultaneously retrieves target distance and chemical composition. By unifying the rigor of frequency metrology with the versatility of broadband sensing, this architecture establishes a new paradigm for multi-dimensional perception in complex environments.