Miniaturized Continuous-Wave Terahertz Spectrometer With 3.6 THz Bandwidth Enabled by Photonic Integration and Microelectronics

• Published in: IEEE access Vol. 12; pp. 35246 - 35256
• Main Authors: Nellen, Simon, Schwenson, Lauri, Liebermeister, Lars, Deumer, Milan, Lauck, Sebastian, Schell, Martin, Kohlhaas, Robert B.
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 2024; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Continuous radiation; electronic circuit design; frequency domain; Integrated circuits; miniaturization; Optical amplifiers; Optical attenuators; Optical fibers; Optical modulation; Optical receivers; optoelectronic; Phase modulation; photomixing; photonic integrated circuit; photonic integration; Photonics; Spectrometers; Spectroscopy; Terahertz; Terahertz materials; terahertz spectroscopy
• ISSN: 2169-3536; 2169-3536
• DOI: 10.1109/ACCESS.2024.3368912

Broadband terahertz spectroscopy is a valuable analytical tool in science and a promising technology for industrial non-destructive, non-contact testing, e.g. thickness measurements of thin dielectric layers. Optoelectronic conversion using photomixers is a widespread approach for coherent terahertz spectroscopy. State-of-the-art spectrometers consist of discrete, fiber-based components, leading to complex and costly setups. In cost-sensitive applications, this prevents the use of these spectrometers. We developed a terahertz spectrometer based on a dedicated photonic integrated circuit and commercial electronic integrated circuits to overcome these limitations. The photonic subsystem can be connected to commercial tunable lasers and provides the optical signal processing to drive the photoconductive antennas. The electronic subsystem includes the required drivers, analog signal processing, and data acquisition. Combined, the system measures <inline-formula> <tex-math notation="LaTeX">10 \times 16 \times 7.5 </tex-math></inline-formula> cm3 only. We compare both subsystems individually and as a whole to state-of-the-art lab equipment in terms of spectral performance and measurement speed. Due to the flexibility in measurement modes, the integrated system can be adapted to specific measurement tasks, e.g. 2.8 THz-wide spectra within 0.5 s for high-speed, or 3.6 THz bandwidth with >80 dB dynamic range in less than 3 minutes for high-precision. This is the first realization of a terahertz spectrometer based on photonic and electronic integration rivaling state-of-the-art and non-integrated commercial spectrometers. This approach paves the way for compact and economic terahertz systems, providing access to terahertz technology for cost-sensitive sectors in research and industry.