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Characterization and Applications of Liquid Crystals in the THz Frequency Range
(2012-01-01)
Pan, Ci-Ling
;
Pan, Ru-Pin
;
電子物理學系
;
Department of Electrophysics
The applications of liquid-crystal-based devices the sub-millimeter wave or THz (1 THz = 10(12) Hz) frequency range has blossomed recently. In this paper, we review the methodology for determination of the THz optical constants of nematic liquid crystals, using E7 as an example. To demonstrate potential applications, we report an electrically tuned THz Solc filter.
Characterization of Subwavelength Plastic Fiber Utilizing Terahertz Time-Domain Spectroscopy
(2009-01-01)
You, Borwen
;
Liu, Tze-An
;
Peng, Jin-Long
;
Pan, Ci-Ling
;
Lu, Ja-Yu
We present the first characterization of a simple subwavelength-diameter plastic wire by using wideband terahertz time-domain spectroscopy. The propagation characteristics including waveguide dispersion, group velocity, and attenuation constant of various plastic wires with different diameters and refractive indices are studied. The experimental results show the subwavelength plastic wire has extremely low waveguide dispersion and low attenuation constant (<0.01cm(-1)) at its THz transmission band due to much reduced fractional power delivered inside the lossy core, which is consistent with the theoretical calculations. With the large evanescent-fields, the subwavelength plastic wire has capability to integrate with micro-fluid channel for sensitive bio-sensing applications.
Recent progress in liquid crystal THz optics
(2006-01-01)
Pan, Ci-Ling
;
Pan, Ru-Pin
;
電子物理學系
;
光電工程學系
;
光電工程研究所
Recently, there have been increasing interests in the study of liquid-crystal-based devices for application in the submillimeter wave or THz frequency range. In this paper, we present recent progress in liquid crystal THz optics from our group. Using time-domain THz spectroscopy, we have determined the complex indices of refraction of nematic liquid crystals, 5CB, PCH5 and E7 from 0.2 to beyond 1 THz. Significantly, the birefrincrence of 5CB and E7 are found to be as large as 0.2 at THz frequencies, while the absorption is negligible. Electrical-field and magnetic-field-controlled birefringence in LC were also investigated. A tunable room-temperature THz phase shifter using magnetic-field-controlled birefringence in nematic 5CB gives a phase shift as large as 108 degrees at 1.0 THz. Phase shift exceeding 360 degrees at 1 THz, an important milestone, was realized by using a sandwiched LC (E7, Merck) cell as thick as 3 nun. The magnetically tuned LC phase shifter served as key components in a two-element tunable LC Lyot filter. The tuning range of the filter is from 0.388 to 0.564 THz or a fractional tuning range of similar to 40%. Our work clearly demonstrates the potential of liquid crystal devices for THz applications. Finally, we will present initial works on control of enhanced THz transmission through a metallic hole array with nematic liquid crystals. Our work clearly demonstrates the potential of liquid crystal devices for THz applications.
Liquid-crystal-based electrically tunable THz optical devices
(2007-01-01)
Pan, Ci-Ling
;
Pan, Ru-Pin
;
電子物理學系
;
光電工程學系
;
光電工程研究所
In this work, we report recent progress in liquid-crystal-based electrically tunable THz optical devices. Tunable phase shift up to 360 degrees at I THz is demonstrated using electrically controlled birefringence in a vertically aligned nematic liquid crystal (E7) cell, 1.83 nun in thickness. The driving voltage and corresponding field required for a phase shift of 360 degrees at 1 THz are 100 V and 90.5 V/cm, respectively. A sandwiched NLC cell about 2 mm in total thickness is used to increase the interaction length while minimizing Fresnel losses at the interfaces. A phase shift of 367 degrees is demonstrated at 1.05 THz, significantly improving the dynamic response of the device.
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.
Enhancement of CMOS THz Imaging Sensing By Packaging Technology
(2017-01-01)
Kuo, Chien-Nan
;
Chen, Wei-Cheng
;
Chiu, Te-Yen
;
Li, Chun-Hsing
;
電子工程學系及電子研究所
Terahertz imaging sensing provides numerous attractive applications in different areas, for example, biology and medicine. CMOS technology benefits an imaging system in low cost and a small form factor. The technology advance is technically viable for circuit design in such high frequencies. Lossy silicon substrate, however, still degrades system performance. We will discuss the techniques of performance enhancement.
High Transmittance Broadband THz Polarizer Using 3D-IC Technologies
(2017-01-01)
Chi, Nai-Chen
;
Yu, Ting-Yang
;
Tsai, Hsin-Cheng
;
Wang, Shiang-Yu
;
Luo, Chih-Wei
A novel method of fabricating high transmittance and broadband terahertz (THz) polarizers is introduced with several advantages. A polarizer with an approximate 100% transmittance is demonstrated with single central frequency of anti-reflection (AR) layers between 0.5 THz and 2 THz. Broadband polarizer, which has a transmission spectrum of over 70% uniformity, is fabricated by bonding two wafers with different AR layers. The bandwidth of broadband THz polarizer exceeds 1 THz. Extinction ratio of the polarizer is about 30 dB depending on the frequency and Cu wire pitch. The high transmittance and broadband THz polarizer can be achieved through deep reactive-ion etching (DRIE) and wafer bonding. This new fabricating method of THz polarizers has advantages of lower cost, no accurate alignment requirement and robust structure. Therefore, this approach can possibly benefit the mass production of THz optical components in THz applications and even more.
Low-Cost High-Performance CMOS Terahertz Imaging System
(2015)
Li, Chung Hsing
;
Yan, Tzu-Chao
;
Chang, Yuhsin
;
Chen, Chyong
;
Kuo, Chien-Nan
CMOS technology has found its way in THz imaging applications. Utilizing the plasma wave theory, a MOSFET device can detect THz radiation beyond the cutoff frequency. Assisted by the system-on-packaging technique, a CMOS source delivers radiation power more effectively. An imaging system demonstrates that a low-cost CMOS solution is feasible.
A Broadband Interconnect for THz Heterogeneous System Integration
(2013)
Li, Chun-Hsing
;
Wu, Jan-Jr
;
Kuo, Chien-Nan
;
Cheng, Yu-Ting
;
Kuo, Ming-Ching
A broadband interconnect for THz heterogeneous system integration is proposed using a resonator coupling technique. Two resonators, deployed on a chip and a carrier, respectively, are coupled through the electromagnetic field to provide a low-loss interconnect in a broadband manner. Simulation results indicate an insertion loss of 0.32 dB at 170 GHz while covering 3-dB bandwidth from 100 to 344 GHz. Measurement can be conducted to verify its performance only from 140 GHz to 220 GHz, due to equipment limit. The measured minimum insertion loss is 0.47 dB at 164 GHz.
A Low-Cost Broadband Bondwire Interconnect for THz Heterogeneous System Integration
(2015)
Li, Chun-Hsing
;
Lai, Chih-Wei
;
Yan, Tzu-Chao
;
Kuo, Chien-Nan
;
電機工程學系
A low-cost broadband bondwire interconnect is proposed for THz heterogeneous system integration. A transversal path composed of two transmission lines and a bondwire is introduced to effectively reduce the bondwire effect of an original signal path consisted of a single bondwire only. Simulation results indicate that the return loss and insertion loss can be better than 15 dB and 2.3 dB from dc to 456 GHz, respectively. Measured interconnect loss is around 0 dB to 1.5 dB from 320 to 340 GHz.

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