Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations
Chair of Communication Systems (NTS), Faculty of Engineering, University of Duisburg-Essen (UDE), 47057 Duisburg, Germany
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These authors contributed equally to this work.
Sensors 2020, 20(19), 5568; https://doi.org/10.3390/s20195568
Received: 3 August 2020
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Revised: 23 September 2020
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Accepted: 26 September 2020
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Published: 28 September 2020
(This article belongs to the Section Optical Sensors)
Photonic true time delay beam steering on the transmitter side of terahertz time-domain spectroscopy (THz TDS) systems requires many wideband variable optical delay elements and an array of coherently driven emitters operating over a huge bandwidth. We propose driving the THz TDS system with a monolithic mode-locked laser diode (MLLD). This allows us to use integrated optical ring resonators (ORRs) whose periodic group delay spectra are aligned with the spectrum of the MLLD as variable optical delay elements. We show by simulation that a tuning range equal to one round-trip time of the MLLD is sufficient for beam steering to any elevation angle and that the loss introduced by the ORR is less than 0.1 dB. We find that the free spectral ranges (FSRs) of the ORR and the MLLD need to be matched to 0.01% so that the pulse is not significantly broadened by third-order dispersion. Furthermore, the MLLD needs to be frequency-stabilized to about 100 MHz to prevent significant phase errors in the terahertz signal. We compare different element distributions for the array and show that a distribution according to a Golomb ruler offers both reasonable directivity and no grating lobes from 50 GHz to 1 THz.
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Keywords:
terahertz; photonic beam steering; time-domain spectroscopy; optical ring resonator; mode-locked laser diode
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MDPI and ACS Style
Liu, X.; Kolpatzeck, K.; Häring, L.; Balzer, J.C.; Czylwik, A. Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations. Sensors 2020, 20, 5568. https://doi.org/10.3390/s20195568
AMA Style
Liu X, Kolpatzeck K, Häring L, Balzer JC, Czylwik A. Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations. Sensors. 2020; 20(19):5568. https://doi.org/10.3390/s20195568
Chicago/Turabian StyleLiu, Xuan, Kevin Kolpatzeck, Lars Häring, Jan C. Balzer, and Andreas Czylwik. 2020. "Wideband Beam Steering Concept for Terahertz Time-Domain Spectroscopy: Theoretical Considerations" Sensors 20, no. 19: 5568. https://doi.org/10.3390/s20195568
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