Browsing by Author "Tang, Tsung-Ta"

Now showing 1 - 16 of 16

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.
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.
Controllable alignment modes of nematic liquid crystals on argon ion beam bombarded polyimide films
(2007)
Wu, Hsin-Ying
;
Wang, Chih-Chieh
;
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 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.
Liquid crystal alignment in nanoporous anodic aluminum oxide layer for LCD panel applications
(2010-07-16)
Hong, Chitsung
;
Tang, Tsung-Ta
;
Hung, Chi-Yu
;
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 terahertz phase shifters with functional indium-tin-oxide nanostructures for biasing and alignment
(2014-04-07)
Yang, Chan-Shan
;
Tang, Tsung-Ta
;
Pan, Ru-Pin
;
Yu, Peichen
;
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.
Magnetically tunable metallic photonic crystals immersed in liquid crystal for terahertz wave
(2012)
Pan, Ru-Pin
;
Shih, Chih-Chang
;
Tang, Tsung-Ta
;
Wang, Yow-Gwo
;
Wu, Hsin-Ying
We investigated the phenomena of a metallic photonic crystal (MPC) immersed in liquid crystal. According to our design, the photonic crystal has specific photonic band gap (PBG) and can be utilized as a filter. The device is filled with nematic liquid crystal (NLC), MDA-00-3461. The refractive indices of NLC can be magnetically controlled by reorienting the NLC molecules. Consequently, the corresponding PBG and the filtering performance of the device are tunable. According to our experimental results, the low frequency boundary of PBG at 0.121 THz can be blue shifted by 6.17 GHz, and the high frequency boundary of PBG at 0.175 THz can be shifted to the blue by 11.04 GHz. As a tunable THz filter, the peak transmittance at 0.187 THz can be blue shifted by 3.66 GHz.
Optical method for measuring the azimuthal anchoring strength of liquid crystals using pitch values determined in imperfect samples
(2007-09-15)
Tang, Tsung-Ta
;
Wu, Hsin-Ying
;
Lin, Chia-Jen
;
Pan, Ru-Pin
;
電子物理學系
An improved Grandjean-Cano wedge method for measuring the pitch of a chiral nematic liquid crystal is demonstrated. This method is easy to implement and can yield results of high accuracy when it is used for measuring the liquid crystal surface anchoring strength.(C) 2007 American Institute of Physics.
Optical properties and potential applications of epsilon-GaSe at terahertz frequencies
(2009-09-01)
Chen, Ching-Wei
;
Tang, Tsung-Ta
;
Lin, Sung-Hui
;
Huang, Jung Y.
;
Chang, Chen-Shiung
Ordinary and extraordinary refractive indices of an epsilon-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOM similar to 10(3) at 1 THz), the large birefringence (Delta n similar to 0.76 at 1 THz). and the low absorption coefficient (alpha similar to 0.2 cm(-1) at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed. (C) 2009 Optical Society of America
Pulse Shaper Assisted Characterization of Single-cycle Optical Pulses
(2009)
Hsieh, Zhi-Ming
;
Lai, Chien-Jen
;
Liang, Wei-Hong
;
Tang, Tsung-Ta
;
Chen, Wei-Jan
Shaper-assisted autocorrelation is developed to characterize single-cycle pulses. The correlation signal show significantly improved signal-to-noise ratio and thus accuracy in pulse characterization when compared to cross-correlation obtained by splitting the spectral components of the pulse. (C) 2009 Optical Society of America
Spatial Light Modulator for Pulse-Shaping of Single-Cycle Optical Pulses
(2009)
Liang, Wei-Hong
;
Hsieh, Zhi-Ming
;
Tang, Tsung-Ta
;
Kung, A. H.
;
Pan, Ci-Ling
A liquid crystal spatial light modulator that operates from the ultraviolet (350nm) to the mid-infrared (2400nm) is described The modulator is suitable for shaping the electromagnetic wave form of multioctave optical pulses
Strong Vertical Alignment of Liquid Crystal on Porous Anodic Aluminum Oxide Film
(2009-09-01)
Tang, Tsung-Ta
;
Kuo, Cheng-Ying
;
Pan, Ru-Pin
;
Shieh, Jia-Min
;
Pan, Ci-Ling
Properties of anodic aluminum oxide (AAO) film as a liquid crystal (LC) alignment material is studied. We deposit the transparent porous AAO film on glass with the diameter of the pores controlled between 17-65 nm. The liquid crystal can be aligned vertically against the substrate with the AAO film. The measured polar anchoring strength is about 1.5 x 10(-5) J/m(2), which is comparable to that of N,N-dimethyl-N-octadecyl-3-aminopropyl -trimethoxysilyl chloride (DMOAP) layer. AAO films with smaller pore diameters exhibit higher anchoring strengths. On the other hand, the uniformity of the pore array in the AAO films does not affect the alignment quality significantly.
Sub-single-cycle optical pulse train with constant carrier envelope phase
(2008-04-25)
Chen, Wei-Jan
;
Hsieh, Zhi-Ming
;
Huang, ShuWei
;
Su, Hao-Yu
;
Lai, Chien-Jen
We describe the synthesis of periodic waveforms consisting of a train of pulses that are 0.83 cycles long and have an electric field pulse width of 0.44 fs using 7 Raman sidebands generated by molecular modulation in H(2). We verify by optical correlation that the carrier-envelope phase is constant in these waveforms when they are synthesized from commensurate sidebands. The estimated overall shift of the carrier-envelope phase is less than 0.18 cycles from the first to the last pulse of nearly 10(6) pulses in the pulse train.
THz time-domain spectroscopic studies of a ferroelectric liquid crystal in the SmA* and SmC* phases
(2008)
Tang, Tsung-Ta
;
Pan, Ru-Pin
;
Wang, Yi-Chao
;
Pan, Ci-Ling
;
電子物理學系
We report complex refractive indices of a ferroelectric liquid crystal (FLC) ZLI-4654-000 from 0.3 to 3.0 THz by THz time-domain Spectroscopy. Extraordinary and ordinary refractive indices of this FLC in the SmA* phase (67.9 degrees C) as well as the SmC* phase (58.1 degrees C) are determined. The birefringence of the FLC varies with frequency but is comparable to its value in the visible, 0.13, while the imaginary indices of refraction in both phases are <= 0.06. Absorption bands are found for ordinary waves in both phases and e-waves in SmA* phases.
Vertical Alignment of Liquid Crystal on ITO Glass with Anodic Aluminum Oxide Thin Film
(2011)
Tang, Tsung-Ta
;
Hung, Chi-Yuan
;
Pan, Ru-Pin
;
Hong, Chitsung
;
Fang, Weileun
Anodic Aluminum Oxide (AAO) thin films have been demonstrated as a vertical alignment layer for nematic liquid crystal in recent years. To control the liquid crystal orientation by applying the electric field, the AAO alignment layers need to be fabricated on the transparent electrode. In this work, the liquid crystal cell with the AAO alignment layer on Indium Tin Oxide (ITO) transparent electrode has been demonstrated. The performance of the cell has been studied. The transmittance of AAO-ITO substrate is around 55%. The polar anchoring strength of the AAO-ITO cell with good vertical alignment is 1.32 center dot 10-4J/m2, and the response time is around 90ms.
Voltage-controlled liquid-crystal terahertz phase shifter with indium-tin-oxide nanowhiskers as transparent electrodes
(2014-04-15)
Yang, Chan-Shan
;
Tang, Tsung-Ta
;
Chen, Po-Han
;
Pan, Ru-Pin
;
Yu, Peichen
Indium-tin-oxide nanowhiskers were employed as transparent electrodes in a liquid-crystal terahertz phase shifter. Transmittance of the device was as high as similar to 75%. Phase shift exceeding pi/2 at 1.0 THz is achieved in a similar to 500 mu m-thick cell. The driving voltage required for the device operating as a quarter-wave plate was as low as 17.68 V (rms), an improvement of nearly an order of magnitude over previous work. (C) 2014 Optical Society of America