Browsing by Author "Hsieh, Cho-Fan"

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Achromatic Liquid Crystal Phase Plate for Short Laser Pulses
(2010)
Pan, Ru-Pin
;
Lai, Cheng-Wei
;
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.
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.
Fabrication of Terahertz Planar Metamaterials Using a Super-Fine Ink-Jet Printer
(2010)
Takano, Keisuke
;
Kawabata, Taku
;
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
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-based magnetically tunable terahertz achromatic quarter-wave plate
(2019-04-01)
Hsieh, Cho-Fan
;
Yang, Chan-Shan
;
Shih, Fang-Cih
;
Pan, Ru-Pin
;
Pan, Ci-Ling
Development of the wideband and tunable quasi-optic terahertz (THz) components is in high demand. In this work, we demonstrate a tunable achromatic quarter-wave plate (AQWP) for the THz frequency range. The phase retardation of this device can be set at 90 degrees +/- 9 degrees from 0.20 to 0.50 THz. The operation range from 0.20 to 0.50 THz can be tuned to from 0.30 to 0.70 THz by introducing three nematic liquid crystals phase retarders, of which the birefringence can be magnetically tuned. The frequency-dependent phase retardation is in good agreement with theoretical predictions. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Liquid-crystal-based terahertz tunable Solc filter
(2008-07-01)
Ho, I-Chen
;
Pan, Ci-Ling
;
Hsieh, Cho-Fan
;
Pan, Ru-Pin
;
電子物理學系
A broadly tunable terahertz Solc-type birefringence filter is demonstrated. The first central passband frequency of the filter can be continuously tuned from 0.176 to 0.793THz using magnetically controlled birefringence in nematic liquid crystals. The insertion loss of the present device is about 5 dB. (C) 2008 Optical Society of America.
Manipulating terahertz wave by a magnetically tunable liquid crystal phase grating
(2008-03-03)
Lin, Chia-Jen
;
Li, Yu-Tai
;
Hsieh, Cho-Fan
;
Pan, Ru-Pin
;
Pan, Ci-Ling
This investigation demonstrates the feasibility of a magnetically tunable liquid crystal phase grating for the terahertz wave. The phase grating can be used as a beam splitter. The ratio of the zeroth and first-order diffracted THz-beams (0.3 THz) polarized in a direction perpendicular to that of the grooves of the grating can be tuned from 4:1 to 1:2. When the THz wave is polarized in any other direction, this device can be operated as a polarizing beam splitter.
Polarizing terahertz waves with nematic liquid crystals
(2008-06-01)
Hsieh, Cho-Fan
;
Lai, Yu-Chien
;
Pan, Ru-Pin
;
Pan, Ci-Ling
;
電子物理學系
A Feussner-type terahertz polarizer with a nematic liquid crystal (NLC) layer between two fused-silica prisms is demonstrated. The polarization factor and extinction ratio of the NLC-based terahertz polarizer can exceed 0.99 and 10(-5), respectively. (C) 2008 Optical Society of America.
Some Characteristics of a Liquid-Crystal Phase Grating for THz Waves
(2009)
Lin, Chia-Jen
;
Lin, Chuan-Hsien
;
Hsieh, Cho-Fan
;
Pan, Ru-Pin
;
Li, Yu-Tai
We propose and demonstrate an electrically controlled liquid crystal phase grating for the terahertz wave. The performance of the device was characterized by a terahertz time-domain spectrometer. The experimental results were in a good agreement with the prediction by classic diffraction theory.
STRUCTURE OF POLARIZING TERAHERTZ WAVE DEVICE
(2010-03-04)
CHAO, Ru-Pin
;
Pan, Ci-Ling
;
Hsieh, Cho-Fan
;
Lai, Yu-Chien
The Terahertz Polarizer structure of the present invention comprises of: A pair of parallel quartz layers for forming a rectangular cube with internal space, then a birefringent liquid crystal is placed in the internal space and sealed, and a pair of permanent magnets with reverse polarities are placed at both sides of the pair of fused silica layers.
Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range
(2008-05-01)
Pan, Ru-Pin
;
Hsieh, Cho-Fan
;
Pan, Ci-Ling
;
Chen, Chao-Yuan
;
電子物理學系
We have measured the frequency dependence and temperature dependence of the optical constants of a liquid crystal 4(')-n-pentyl-4-cyanobiphenyl (5CB) in both nematic and isotropic phases by using terahertz time-domain spectroscopy. The extinction coefficient of 5CB is less than 0.02 and without sharp absorption features in the frequency range of 0.2-1.0 THz. The extraordinary and ordinary indices of refraction at 25 degrees C are around 1.77 and 1.58, respectively, giving rise to a birefringence of 0.20 +/- 0.02 in this frequency range. The temperature-dependent order parameter extracted from birefringence agrees with the results from the visible region quite well. (C) 2008 American Institute of Physics.