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Realtime coherent cw THz system: Phase modulation without phase modulator

: Liebermeister, L.; Nellen, S.; Kohlhaas, R.B.; Breuer, S.; Schell, M.; Globisch, B.


Institute of Electrical and Electronics Engineers -IEEE-:
Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference, CLEO/Europe-EQEC 2019 : 23-27 June 2019, Munich, Germany
Piscataway, NJ: IEEE, 2019
ISBN: 978-1-7281-0469-0
ISBN: 978-1-7281-0470-6
Conference on Lasers and Electro-Optics Europe (CLEO Europe) <2019, Munich>
European Quantum Electronics Conference (EQEC) <2019, Munich>
Fraunhofer HHI ()

In optoelectronic continuous wave (cw) THz spectroscopy phase measurement is very beneficial, to improve SNR and/or to obtain depth information. Often, the required phase modulation limits the acquisition speed and increases the complexity of existing cw THz systems. Commonly, optical free space delay lines, fibre stretchers [1] or electro optical modulators [2] are used for phase modulation. In this paper we demonstrate that a simple optical fiber delay in combination with a fast sweeping laser source can be used for ultrafast fast phase modulation. With this technique we demonstrate a fully fibre-coupled cw THz spectrometer with 58 Hz update rate covering a bandwidth of 2.5 THz. To the best of our knowledge this is the fastest coherent cw THz system demonstrated so far. This makes cw THz systems competitive to time-domain approaches in terms of acquisition speed and simplifies the system architecture significantly. Therefore, it paves the way for compact, broadband and cost-effective THz systems.