Browsing by Author "Pan, Ru-Pin"

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A simple method of determining the pitch of a chiral nematic liquid crystal
(2007)
Tang, Tsung-Ta
;
Wu, Hsin-Ying
;
Lin, Chia-Jen
;
Pan, Ru-Pin
;
電子物理學系
The pitch value P of a chiral nematic liquid crystal is a critical parameter fin. azimuthal anchoring strength measurement. The Grandjean-Cano wedge method is a conventional technique for pitch determination, but the perfect wedge cell with known angle and uniform disclination lines are required. In this work, we have developed an improved Grandjean-Cano method, which is simple and gives accurate pitch value. The sensitivity of this new method is +/-lambda/2 Delta n.
A tunable terahertz filter and its switching properties in terahertz region based on a defect mode of a metallic photonic crystal
(2011-06-15)
Kim, Yong Sung
;
Lin, Shawn-Yu
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Wu, Hsin-Ying
;
Pan, Ru-Pin
;
電子物理學系
We theoretically investigate and discuss an electrically tunable terahertz filter design and its optical switching properties based on the defect mode of a woodpile metallic photonic crystal (MPC). The model filter design is based on a dual use of an MPC as a resonator and as electrodes with a liquid crystal used as a defect layer. The static and the dynamic responses of a realistic liquid crystal are obtained using the Oseen-Frank elastic continuum theory, and the corresponding transmission spectra are calculated using an analytic modal expansion method combined with a transfer-matrix method. The tuning range of f = 1.430 similar to 1.577 THz and the order of milliseconds switching property are observed in our design. (C) 2011 American Institute of Physics. [doi:10.1063/1.3603009]
Achromatic Liquid Crystal Phase Plate for Short Laser Pulses
(2010)
Pan, Ru-Pin
;
Lai, Cheng-Wei
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Lin, Chia-Jen
;
Hsieh, Cho-Fan
;
Pan, Ci-Ling
This work demonstrates the feasibility of reducing pulse broadening by using liquid crystal achromatic half and quarter wave plates for ultrafast pulsed lasers. Each wave plate is made of two and three liquid crystal cells stacked together. Total phase retardation and its broadening reducing of the achromatic half wave plate have been measured. The experimental results are in good agreement with theoretical calculation.
Alignment Control of Rubbed Polyimide Layers by UV-Irradiation
(2009)
Lin, Chia-Jen
;
Hong, Guo-Teng
;
Pan, Ru-Pin
;
電子物理學系
;
Department of Electrophysics
This investigation demonstrates the feasibility of re-aligning the assembled liquid crystal cells based on rubbed substrates with photoalignment treatment. A pre-exposure process is proposed to achieve the photo-reorientation effectively. This study shows that the fine-tuning on the LC alignment after a cell is assembled by adjusting UV irradiation conditions can be obtained easily.
Alignment Properties of Liquid Crystal on Etched Anodic Aluminum Oxide Film
(2011)
Tang, Tsung-Ta
;
Li, Che-Hsuan
;
Pan, Ru-Pin
;
電子物理學系
;
Department of Electrophysics
Anodic aluminum oxide (AAO) is a widely studied material with self-assembled nanochannel which is perpendicular to the substrate with nanometer-scale diameters and high aspect ratios. It is used for protecting the aluminum surface or as dielectric material. In this work, the alignment properties of liquid crystal on the etched AAO thin films were studied. By controlling the etching time, not only the pore sizes but also the thickness of the etched AAO thin films can be modified. Both homeotropic and homogenous alignment properties have been demonstrated on the etched AAO thin films with controlling etching time.
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.
Controllable alignment modes of nematic liquid crystals on argon ion beam bombarded polyimide films
(2007)
Wu, Hsin-Ying
;
Wang, Chih-Chieh
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Pan, Ru-Pin
;
Tang, Tsung-Ta
;
Chang, Shao-Ju
We investigate the alignment properties of nematic liquid crystal on polyimide films bombarded by Ar ion beams with a small diode sputter type ion-beam source. The alignments of nematic liquid crystal 4'-n-pentyl-4-cyanobiphenyl (5CB) on treated polyimide surface are characterized by using polarizing optical microscope and conoscope. The polyimide surfaces are also studied by using atomic force microscope and x-ray photoemission spectroscopy. We have demonstrated that the polyimide surface treated by Ar ion beams can give both homogeneous and homeotropic alignments with the same ion beam apparatus but varying the energy of ion beam and the bombarding time.
Electrically Controlled Liquid Crystal Phase Grating for Terahertz Waves
(2009-05-01)
Lin, Chia-Jen
;
Lin, Chuan-Hsien
;
Li, Yu-Tai
;
Pan, Ru-Pin
;
Pan, Ci-Ling
This work demonstrates the feasibility of electrically controlled liquid-crystal-based phase grating for manipulating the terahertz (THz) waves. This device can be utilized as a THz beam splitter and the beam splitting ratio of the zeroth- to the first-order diffractions can be tuned from 10 : 1 to 1: 1.
Electrically tunable room-temperature 2 pi liquid crystal terahertz phase shifter
(2006-07-01)
Wu, Hsin-Ying
;
Hsieh, Cho-Fan
;
Tang, Tsung-Ta
;
Pan, Ru-Pin
;
Pan, Ci-Ling
Tunable phase shift up to 360 degrees at 1 THz is demonstrated using electrically controlled birefringence in a vertically aligned nematic liquid crystal (E7) cell, 1.83 mm 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.
Experimental investigation of liquid crystals in the millimetre frequency range
(2010)
Meriakri, V. V.
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Nikitin, I. P.
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Pan, Ci-Ling
;
Pan, Ru-Pin
;
Parkhomenko, M. P.
Dielectric properties of n center dot CB (n = 5, 6, 7, 8) liquid crystals (LCs) are investigated in the frequency intervals of 50-80, 120-160 GHz, and at 0.6 THz. The measurements are carried out in the millimetre wave range by the resonance method and with use of a reflectometer designed on the basis of a Michelson interferometer and quasi-optical metal-dielectric waveguides. Of most interest are the room temperature measurements of the birefringence of LCs. These measurements show that LCs can be used as polarisation transformers in the short wavelength region of the millimetre wave band and the long wavelength region of the sub-millimetre wave band.
Fabrication of Terahertz Planar Metamaterials Using a Super-Fine Ink-Jet Printer
(2010)
Takano, Keisuke
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Kawabata, Taku
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Hsieh, Cho-Fan
;
Akiyama, Koichi
;
Miyamaru, Fumiaki
Super-fine ink-jet (SIJ) printing technology is applied to the fabrication of terahertz metamaterials. A silver film is fabricated using an SIJ printer with silver paste ink, and it is confirmed that the film behaves as a good conductor in the terahertz frequency region. Then, basic terahertz metamaterials such as metal wire-grid structures and split-ring resonators are printed on high-resistivity silicon substrates. The terahertz responses of the printed samples agree with those expected from their structures. SIJ printing is one of the ideal methods for fabricating terahertz metamaterials owing to its rapidity, simplicity, flexibility, and sufficient accuracy. (C) 2010 The Japan Society of Applied Physics
High-Transmittance 2 Electrically Tunable Terahertz Phase Shifter with CMOS-Compatible Driving Voltage Enabled by Liquid Crystals
(2019-01-02)
Yang, Chan-Shan
;
Kuo, Chun
;
Chen, Po-Han
;
Wu, Wei-Ta
;
Pan, Ru-Pin
We have investigated tunable terahertz (THz) phase shifters that are based on a sandwiched liquid crystal (LC) cell with indium-tin-oxide (ITO) nanowhiskers (NWhs) as transparent electrodes. More than 360 degrees of phase shift at 1.0 THz was achieved at a driving voltage as low as similar to 2.6 V (rms). This is approximately 40 times smaller than that reported in previous works using an electrically tuned LC device. Significance of the NWhs in reducing the required voltage is demonstrated. Overall transmittance of the device is as high as 30%, which is accountable by absorption losses of ITO NWhs, quartz substrate and LC. Experimental results are in good agreement with a theoretical formulism while taking into account super-thick LC cells (similar to 1 mm) and pretilt angles. We also propose and demonstrate a novel THz technique for measuring pretilt angles of liquid crystals.
Liquid crystal alignment in nanoporous anodic aluminum oxide layer for LCD panel applications
(2010-07-16)
Hong, Chitsung
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Tang, Tsung-Ta
;
Hung, Chi-Yu
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Pan, Ru-Pin
;
Fang, Weileun
This paper reports the implementation and integration of a self-assembled nanoporous anodic aluminum oxide (np-AAO) film and liquid crystal (LC) on an ITO-glass substrate for liquid crystal display (LCD) panel applications. An np-AAO layer with a nanopore array acts as the vertical alignment layer to easily and uniformly align the LC molecules. Moreover, the np-AAO nanoalignment layer provides outstanding material properties, such as being inorganic with good transmittance, and colorless on ITO-glass substrates. In this application, an LCD panel, with the LC on the np-AAO nanoalignment layer, is successfully implemented on an ITO-glass substrate, and its performance is demonstrated. The measurements show that the LCD panel, consisting of an ITO-glass substrate and an np-AAO layer, has a transmittance of 60-80%. In addition, the LCD panel switches from a black state to a bright state at 3 V(rms), with a response time of 62.5 ms. In summary, this paper demonstrates the alignment of LC on an np-AAO layer for LCD applications.
Liquid crystal alignment on the a-C : H films by Ar plasma ion immersion
(2007-07-31)
Chang, S. J.
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Wu, K. Y.
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Yang, Y. H.
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Hwang, J.
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Wu, Hsin-Ying
A plasma ion immersion treatment has been developed to enhance the liquid crystal (LC) alignment on the hydrogenated amorphous carbon (a-C:H) layer in an inductively coupled plasma (ICP) chamber. No LC alignment was observed for the a-C:H layer tilted at an angle of 0 degrees during the bombardment with plasma ions. The LC alignment occurs for the a-C:H layer tilted at an angle of 30 degrees or 60 degrees. Their pretilt angles (similar to 1.4 degrees) are approximately the same. The azimuthal anchoring strength is 1.98 x 10(-6) J/m(2) at a tilted angle of 30 degrees and 1.14 x 10(-4) J/m(2) at a tilted angle of 60 degrees. The mechanism for the LC alignment is attributed to the oblique incidence of ions within the matrix sheath of non-uniform thickness near the a-C: H surface under a negative pulse bias. The matrix sheath of non-uniform thickness is confirmed by the plasma density distribution in the ICP chamber and the X-ray photoemission spectra across the a-C:H layer. (C) 2007 Elsevier B.V. All rights reserved.
Liquid crystal enabled multi-channel power equalizer and stabilizer
(2007-10-15)
Pan, Ru-Pin
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Sheu, Chia-Rong
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Lan, Yu-Ping
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Lai, Yi-Fan
;
Pan, Ci-Ling
Automatic power equalization and stabilization of a liquid crystal enabled channel-selectable optical demultiplexer is demonstrated. The variation among output signals from different channels was reduced from similar to 10 dB to 0.15 dB with feedback control. The minimum ripple level of a single channel is similar to 0.05 dB. As a variable optical attenuator (VOA), the attenuation range of the device is similar to 12.6 dB. (c) 2007 Elsevier B.V. All rights reserved.
Liquid crystal surface alignments by using films composed of magnetic nanoparticles - art. no. 691104
(2008)
Pan, Ru-Pin
;
Wu, Hsin-Ying
;
Hsieh, Cho-Fan
;
電子物理學系
;
Department of Electrophysics
A method for liquid crystal surface alignment by using a one-step, ion beam sputtering on glass substrates is demonstrated. Pre-coating by polyimide is not necessary. We use a diode-type sputter to treat the glass substrates with Ar ion-beam. The homeotropic alignments for nematic liquid crystals are achieved. The alignments are characterized by using the polarizing optical microscope and the conoscope. To find out the alignment mechanism, the studies by using super conducting quantum interference device and scanning probe microscopy are carried out. The surveyed surface morphology reveals that the films are amorphous and composed of nanoparticles with dimensions around 30 nm. The magnetization anisotropy of the sputtered magnetic films is analyzed. The polar anchoring strengths of the coated films with different thicknesses are measured and compared with their saturation magnetization. We deduce that the homeotropic alignment is achieved due to the orientation of the diamagnetic nematogenic molecules in the magnetic field caused by the gamma-Fe2O3 ferrimagnetic thin films. A simple model of alternatively distributed magnetic moments with opposite direction is proposed. The profile of magnetic field strength near the surface is then calculated to compare with the measured alignment strength.
Liquid crystal surface alignments by using ion beam sputtered magnetic thin films
(2007-08-13)
Wu, Hsin-Ying
;
Pan, Ru-Pin
;
電子物理學系
;
Department of Electrophysics
A method for liquid crystal surface alignment by using a one-step, ion beam bombardment of the glass substrates is demonstrated. Precoating by polyimide is not necessary. The authors show that the homeotropic alignment is achieved due to orientation of the diamagnetic nematogenic molecules by the magnetic field from the gamma-Fe2O3 ferrimagnetic thin films created on the substrates by ion beam bombardment. The film exhibits a high Curie temperature well above 300 K and a compensation temperature which is the typical feature of ferrimagnetism. This is a simple, noncontact, and reliable alignment method for liquid crystal devices. (C) 2007 American Institute of Physics.
Liquid crystal terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment
(2014-04-07)
Yang, Chan-Shan
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Tang, Tsung-Ta
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Pan, Ru-Pin
;
Yu, Peichen
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Pan, Ci-Ling
Indium Tin Oxide (ITO) nanowhiskers (NWhs) obliquely evaporated by electron-beam glancing-angle deposition can serve simultaneously as transparent electrodes and alignment layer for liquid crystal (LC) devices in the terahertz (THz) frequency range. To demonstrate, we constructed a THz LC phase shifter with ITO NWhs. Phase shift exceeding pi/2 at 1.0 THz was achieved in a similar to 517 mu m-thick cell. The phase shifter exhibits high transmittance (similar to 78%). The driving voltage required for quarter-wave operation is as low as 5.66 V (rms), compatible with complementary metal-oxide-semiconductor (CMOS) and thin-film transistor (TFT) technologies. (C) 2014 AIP Publishing LLC.
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.
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.