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Author: search.filters.author.Pan, Ru-PinSubject: search.filters.subject.liquid-crystal devices

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Now showing 1 - 6 of 6
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    Item type:Item,
    Liquid crystal terahertz photonics with indium tin oxide nanowhiskers and graphene as functional electrodes
    (2015-01-01)
    Yang, Chan-Shan
    ;
    Pan, Ru-Pin
    ;
    Pan, Ci-Ling
    ;
    電子物理學系
    ;
    Department of Electrophysics
    We have constructed and characterized THz phase shifters based on liquid crystals (LCs) with graphene grown by chemical vapor deposition (CVD) and indium-tin-oxide nanowhiskers (ITO NWhs) as transparent conducting electrodes. A graphene-based phase shifter can achieve a phase shift of pi/2 at 1.0 THz with the operating voltage of similar to 2.2 V (rms) as opposed to similar to 5.6 V (rms) for ITO-NWhs-based phase shifter in previous work. On the other hand, 2 pi phase shift at 1.0 THz was achieved in an ITO-NWhs-based phase shifter with a multi-sandwiched structure by applying similar to 2.6 V (rms). The low operation voltage of both two kinds of phase shifters imply compatibility of both type of devices with thin-film transistor (TFT) and complementary metal-oxide-semiconductor (CMOS) technologies. The experimental results of phase shifters are in good agreement with the theoretical predictions.
  • Thumbnail Image
    Item type:Item,
    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.
  • Thumbnail Image
    Item type:Item,
    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.
  • Thumbnail Image
    Item type:Item,
    Liquid-Crystal Terahertz Quarter-Wave Plate Using Chemical-Vapor-Deposited Graphene Electrodes
    (2015-12-01)
    Yang, Chan-Shan
    ;
    Kuo, Chun
    ;
    Tang, Chiu-Chun
    ;
    Chen, J. C.
    ;
    Pan, Ru-Pin
    Quarter-wave operation or a phase shift of more than pi/2, which is approximately ten times greater than that reported in previous works using liquid crystals (LCs) and graphene electrodes, was demonstrated. The device is transparent to the terahertz (THz) wave, and the driving voltage required was as low as approximately 2.2 V (rms), which is also unprecedented. Experimental results supported a theoretical formalism adapted for LC cells with THz wavelength-scale thickness. The scattering rate, DC mobility, and carrier mean free path of bilayer graphene were also determined using THz spectroscopic techniques; the parameters were inferior to those of monolayer graphene. This observation can be attributed to the higher density of charged impurities in the bilayer graphene. The device performances of LC phase shifters using monolayer and bilayer graphene as electrodes were essentially identical.
  • Thumbnail Image
    Item type:Item,
    Recent progress in liquid crystal THz optics - art. no. 61350D
    (2006)
    Pan, Ci-Ling
    ;
    Pan, Ru-Pin
    ;
    光電工程學系
    ;
    Department of Photonics
    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.
  • Thumbnail Image
    Item type:Item,
    Liquid-crystal-based electrically tunable THz optical devices - art. no. 648709
    (2007)
    Pan, Ci-Ling
    ;
    Pan, Ru-Pin
    ;
    電子物理學系
    ;
    光電工程學系
    ;
    Department of Electrophysics
    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.