Terahertz photonic heterodyne spectral analysis with (sub-) kHz resolution and 6.5 THz frequency coverage

Benedikt Krause (), Sebastian Müller, Thomas Puppe, Lars Liebermeister, Garrit Schwanke, Milan Deumer, Robert Kohlhaas, Rafal Wilk, Nico Vieweg and Sascha Preu ()
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Benedikt Krause: Technical University of Darmstadt, Department of Electrical Engineering and Information Technology
Sebastian Müller: TOPTICA Photonics AG
Thomas Puppe: TOPTICA Photonics AG
Lars Liebermeister: Heinrich-Hertz-Institute, Fraunhofer Institute for Telecommunications
Garrit Schwanke: Heinrich-Hertz-Institute, Fraunhofer Institute for Telecommunications
Milan Deumer: Heinrich-Hertz-Institute, Fraunhofer Institute for Telecommunications
Robert Kohlhaas: Heinrich-Hertz-Institute, Fraunhofer Institute for Telecommunications
Rafal Wilk: TOPTICA Photonics AG
Nico Vieweg: TOPTICA Photonics AG
Sascha Preu: Technical University of Darmstadt, Department of Electrical Engineering and Information Technology

Nature Communications, 2025, vol. 16, issue 1, 1-12

Abstract: Abstract Spectrum analyzers and spectrometers are essential for designing sources, analyzing material properties, layer structures and fingerprinting substances. We present an ultra-wideband, continuous-wave photonic receiver with kHz-level spectral resolution in the terahertz domain for both heterodyne and homodyne detection. Employed as a spectrum analyzer front end, it records the emitted spectrum of a source under test, assessing spectral purity, spectral shape and undesired frequency components. It outperforms state-of-the-art electronic systems in terms of frequency coverage and system cost with a competitive spectral resolution and noise floor on the few aW/Hz level at room temperature. It covers the important frequencies above 1.5 THz, yet commercially inaccessible, where sources like quantum cascade lasers operate. When combined with a comb-based photonic source, we demonstrate hetero- and homodyne spectroscopy over an unprecedented frequency range from below 100 GHz to 6.5 THz and a very low noise floor. Locking the photonic system to GPS enables tracing back the measured parameters to SI units, being of key importance for metrological applications. The presented setups offer the broadest continuous-wave frequency coverage to date, combined with a sharp spectral resolution, enabling diverse applications ranging from fast non-destructive testing, astronomic high-resolution spectroscopy, to frequency-modulated RADAR.

Date: 2025
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DOI: 10.1038/s41467-025-66457-6

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