Browsing by Author "Tsai, TR"

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Electrically controlled room temperature terahertz phase shifter with liquid crystal
(2004-02-01)
Tsai, TR
;
Chen, CY
;
Pan, RP
;
Pan, CL
;
Zhang, XC
We present the use of electrically controlled bire-fringence in a nematic liquid crystal cell for phase shifting of electromagnetic waves up to terahertz frequencies. This device. was operated at room temperature and a maximum phase shift of 4.07degrees was demonstrated at 1.07 THz when the interaction length was 38.6 mum. The driving voltage and corresponding field were 176.8 V (rms) and 589.3 V/cm, respectively.
Optical constants of two typical liquid crystals 5CB and PCH5 in the THz frequency range
(2003)
Pan, RP
;
Tsai, TR
;
Chen, CY
;
Pan, CL
;
電子物理學系
The complex refractive indices of two benchmark nematic liquid crystal, 4'-n-pentyl-4-cyanobiphenyl (5CB) and 4-(trans-4'pentylcyclohexyl)-benzonitrile (PCH5) have been determined in the frequency range from 0.2 to 0.8 THz. The technique of coherent THz time-domain spectroscopy (THz-TDS) was used. We show that the birefringence of 5CB is in the range of 0.15 to 0.21, while that of PCH is from 0.01 to 0.08. Both liquid crystals exhibit relatively small absorption in this frequency range. The large birefringence of 5CB indicates possible applications of liquid-crystal-based devices for modulation and polarization control of electromagnetic radiation in the THz frequency range.
Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals
(2003-12-01)
Chen, CY
;
Tsai, TR
;
Pan, CL
;
Pan, RP
;
電子物理學系
We present the use of magnetically controlled birefringence in a nematic liquid crystal cell for phase shifting of electromagnetic waves in the range of terahertz frequencies. This device can be operated at room temperature. A maximum phase shift of 141degrees has been demonstrated at 1.025 THz and the results are in good agreement with theoretical predictions. (C) 2003 American Institute of Physics.
Terahertz phase shifter with nematic liquid crystal in a magnetic field
(2004)
Pan, RP
;
Chen, CY
;
Tsai, TR
;
Pan, CL
;
電子物理學系
We report the phase shifter for terahertz waves utilizing magnetically controlled birefringence in a nematic liquid crystal cell. This device can be operated at room temperature. Two structures of cells were studied in this work. A maximum phase shift of 278degrees has been demonstrated at 1.0 THz. The results are in good agreement with theoretical predictions.
Terahertz time-domain spectroscopy studies of the optical constants of the nematic liquid crystal 5CB
(2003-05-01)
Tsai, TR
;
Chen, CY
;
Pan, CL
;
Pan, RP
;
Zhang, XC
The optical constants of a nematic liquid crystal, 4'-n-pentyl-4-cyanobiphenyl (5CB), in the frequency range 0.3-1.4 THz were determined by terahertz (THz) time-domain spectroscopy. The real parts of the extraordinary refractive index n(e) and the ordinary refractive index n(o) of 5CB varied from 1.74 to 2.04 and from 1.59 to 1.83, respectively. Liquid-crystal 5CB exhibits a relatively small absorption loss in this frequency range. The birefringence of 5CB was found to be as large as 0.21. The experimental results indicate that liquid-crystal 5CB is potentially useful for device applications in the THz frequency range. (C) 2003 Optical Society of America.
The refractive indices of nematic liquid crystal 4'-n-pentyl-4-cyanobiphenyl in the THz frequency range
(2004)
Pan, RP
;
Tsai, TR
;
Chen, CY
;
Wang, CH
;
Pan, CL
The terahertz (THz) refractive indices of a liquid crystal 4'-n-pentyl-4-cycazobiphenyl (5CB) in both of the nematic and isotropic phases were deters mined by terahertz (THz) time-domain spectroscopy for the first time, to our knowledge. We find that the extinction coefficient of 5CB is negligibly small in this frequency range. The birefringence of 5CB, on the other hand, is as large as 0.2. This is comparable to that of 5CB in. the visible and near M. The experimental results indicate that liquid crystals are potentially useful for device applications in the THz frequency range.