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High-Transmittance 2π Electrically Tunable Terahertz Phase Shifter with CMOS-Compatible Driving Voltage Enabled by Liquid Crystals
Open AccessFeature PaperArticle

Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSS Transparent Conducting Electrodes

1
Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
2
Institute of Electro-Optical Science and Technology, National Taiwan Normal University, Taipei 11677, Taiwan
3
Undergraduate Program of Electro-Optical Engineering, National Taiwan Normal University, Taipei 11677, Taiwan
4
Department of photonics, National Chiao Tung University, Hsinchu 30010, Taiwan
5
Office for Academic and Industrial Innovation (Oacis), Kobe University, Kobe 657-8501, Japan
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Appl. Sci. 2019, 9(4), 761; https://doi.org/10.3390/app9040761
Received: 16 January 2019 / Revised: 10 February 2019 / Accepted: 18 February 2019 / Published: 21 February 2019
(This article belongs to the Special Issue Liquid Crystal THz Photonics: Materials, Devices and Applications)
For this study, we demonstrated three different types of twisted nematic (TN) liquid crystal (LC) terahertz (THz) phase shifters using pristine poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) thin films as transparent conducting electrodes (TCEs). The transmittance of spin-coated pristine PEDOT: PSS thin film was as high as 92% in the frequency range of 0.2–1.2 THz. This is among the highest reported. Several TN-LC cells were constructed in a comparative study, which confirmed the reliability of pristine PEDOT: PSS as a TCE layer for THz phase shifter applications. The highest phase shift, required root-mean-square (RMS) driving voltage, and threshold voltage achieved by devices tested were 95.2° at 1 THz, 7.2 VRMS, and 0.5 VRMS, respectively. The thickness of the LC layer for the phase shifter was 250 µm, approximately half as thick as previous designs. In addition, the pristine PEDOT: PSS-based TN-LC phase shifter exhibited a figure-of-merit (FOM) value of approximately 6.65 degree·dB−1·V−1. This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree·dB−1·V−1. Our results indicated that a twisted nematic LC cell with pristine PEDOT: PSS thin films as electrodes is a good combination for a THz phase shifter and wave plates as well as other LC-based THz devices. View Full-Text
Keywords: liquid crystals; LC; twisted nematic; TN; phase shifter; PEDOT: PSS; transparent conducting electrode; TCE; terahertz; THz liquid crystals; LC; twisted nematic; TN; phase shifter; PEDOT: PSS; transparent conducting electrode; TCE; terahertz; THz
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MDPI and ACS Style

Sahoo, A.K.; Yang, C.-S.; Yen, C.-L.; Lin, H.-C.; Wang, Y.-J.; Lin, Y.-H.; Wada, O.; Pan, C.-L. Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSS Transparent Conducting Electrodes. Appl. Sci. 2019, 9, 761.

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