Browsing by Author "Sahoo, Anup Kumar"

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Liquid Crystal Based Terahertz Phase Shifter with Bi-Layer Structure
(2018-01-01)
Sahoo, Anup Kumar
;
Yang, Chan-Shan
;
Yen, Chun-Ling
;
Lin, Hung Chun
;
Wang, Yu-Jen
We propose and demonstrate a liquid crystal (LC) based terahertz phase shifter with a thick (550 mu m in total) bi-layer LC cell structure incorporating a thin transparent polymeric intermediate layer. The present phase shifter exhibited remarkable performance improvement. The phase shift increased from 94 degrees to 111 degrees; threshold and drive voltages decreased from 2.2 V-RMS to 1 V-RMS and from 10 V-RMS to 8.4 V-RMS, respectively, in comparison with those for single-layer cell structure.
Liquid Crystal Based Terahertz Spatial Light Modulator for Imaging Application
(2018-01-01)
Sahoo, Anup Kumar
;
Yang, Chan-Shan
;
Yen, Chun-Ling
;
Lu, Yuan Chun
;
Lin, Hung Chun
We demonstrate a liquid crystal based THz spatial light modulator (SLM). Indium tin oxide or gold finger type patterns were used for transparent (>70 % at 0.08 to 1.2 THz) conductor and self-cross polarizer. The phase shift and amplitude modulation achieved are greater than 90 degrees and 30 % in broadband in THz frequency. This SLM could become a promising candidate for high speed THz imaging application via compress sensing algorithm
Twisted Nematic Liquid-Crystal-Based Terahertz Phase Shifter using Pristine PEDOT: PSS Transparent Conducting Electrodes
(2019-02-02)
Sahoo, Anup Kumar
;
Yang, Chan-Shan
;
Yen, Chun-Ling
;
Lin, Hung-Chun
;
Wang, Yu-Jen
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 degrees at 1 THz, 7.2 V-RMS, and 0.5 V-RMS, respectively. The thickness of the LC layer for the phase shifter was 250 mu m, 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.