Abstract

Tunable phase shift up to 360° at 1 THz is achieved with a liquid crystal (LC) device. The key to this design is (1) the use of a nematic LC, E7, which exhibits a birefringence of ~0.17 (0.2–1.2 THz); (2) a LC cell (3-mm in thickness) with sandwiched structure to increase the interaction length while minimizing interface Fresnel losses; and (3) the use of magnetic field to align the thick LC cell and achieve continuous tuning of phase from 0 to 360°. This device can be operated over a broad range near room temperature.

© 2004 Optical Society of America

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References

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  1. D. Mittleman, �??Terahertz Imaging,�?? in Sensing with THz radiation, (Spring-Verlag, New York, 2002).
  2. Peter H. Siegel,�?? Terahertz technology,�?? IEEE Trans. Microwave Theory Tech., 50, 910-928 (2002).
    [CrossRef]
  3. B. Ferguson and X.-C. Zhang,�?? Materials for terahertz science and technology,�?? Nature Materials, 1, 26-33 (2002).
    [CrossRef]
  4. I. H. Libon, S. Baumgärtner, M. Hempel, N. E. Hecker, J. Feldmann, M. Koch, and P. Dawson, �??An optically controllable terahertz filter,�?? Appl. Phys. Lett. 76, 2821-2823 (2000).
    [CrossRef]
  5. R. Kersting, G. Strasser, and K. Unterrainer,�?? Terahertz phase modulator,�?? Electron. Lett. 36, 1156-1158 (2000).
    [CrossRef]
  6. T. Kleine Ostmann, M. Koch, and P. Dawson,�?? Modulation THz radiation by semiconductor nanostructures,�?? Microwave Opt. Tech. Lett. 35, 343-345 (2002).
    [CrossRef]
  7. K. C. Lim, J. D. Margerum, and A. M. Lackner,�?? Liquid crystal millimeter wave electronic phase shifter,�?? Appl. Phys. Lett. 62, 1065-1067 (1993).
    [CrossRef]
  8. D. Dolfi, M. Labeyrie, P. Joffre, and J. P. Huignard,�?? Liquid crystal microwave phase shifter,�?? Electron. Lett. 29, 926-928 (1993).
    [CrossRef]
  9. T.-R. Tsai, C.-Y. Chen, C.-L. Pan, R.-P. Pan, and X.-C. Zhang,�?? Terahertz time-domain spectroscopy studies of the optical constants of the nematic liquid crystal 5CB,�?? Appl. Opt. 42, 2372-2376 (2003).
    [CrossRef] [PubMed]
  10. R.-P. Pan, T.-R. Tsai, C.-Y. Chen, C.-H. Wang, and C.-L. Pan,�?? The refractive indices of nematic liquid crystal 4�??-n-pentyl-4-cyanobiphenyl in the THz frequency range,�?? Mol. Cryst. Liq. Cryst. (to be published in May 2004 ).
    [CrossRef]
  11. T.-R Tsai, C.-Y. Chen, R.-P. Pan, C.-L. Pan, and X.-C. Zhang,�?? Electrically controlled room temperature terahertz phase shifter with liquid crystal,�?? IEEE Microwave Wireless Comp. Lett. 14, 77-79 (2004).
    [CrossRef]
  12. C.-Y. Chen, T.-R Tsai, C.-L. Pan, R.-P. Pan,�?? Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals,�?? Appl. Phys. Lett. 83, 4497-4499 (2003).
    [CrossRef]
  13. P. G. de Gennes and J. Prost, The Physics of Liquid Crystals, 2nd ed. (Oxford, New York, 1983), Chap. 3.
  14. D.-D. Huang, X.-J. Yu, H.-C. Huang, and H.-S. Kwok,�?? Design of polarizing color filters with double-liquid-crystal cells,�?? Appl. Opt. 41, 4638-4644 (2002).
    [CrossRef] [PubMed]
  15. K. Komori, T. Sugaya, M. Watanabe, T. Hidaka,�?? Ultrafast coherent control of excitons using pulse-shaping technique,�?? Jan. J. Appl. Phys. 39, 2347-2352 (2000).
  16. F. J. Kahn,�?? Orientation of liquid crystals by surface coupling agents,�?? Appl. Phys. Lett. 22, 386-388 (1973).
    [CrossRef]
  17. Z. Jiang, M. Li, and X. -C. Zhang,�?? Dielectric constant measurement of thin films by differential time-domain spectroscopy,�?? Appl. Phys. Lett. 76, 3221-3223 (2000).
    [CrossRef]
  18. P. Yeh, and C. Gu, Optics of Liquid Crystal Displays, (Wiley Interscience Publication, New York, 1999), Chap. 3.
  19. R.-P. Pan, T.-R. Tsai, C.-Y. Chen, and C.-L. Pan,�?? Optical constants of two typical liquid crystals 5CB and PCH5 in the THz frequency range,�?? J. Bio. Phys. 29, 335-338 (2003).
    [CrossRef]
  20. Eugene Hecht, Optics, 3rd ed. (Addison Wesley Longman, New York, 1998), Chap. 4.

Appl. Opt. (2)

Appl. Phys. Lett. (5)

C.-Y. Chen, T.-R Tsai, C.-L. Pan, R.-P. Pan,�?? Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals,�?? Appl. Phys. Lett. 83, 4497-4499 (2003).
[CrossRef]

F. J. Kahn,�?? Orientation of liquid crystals by surface coupling agents,�?? Appl. Phys. Lett. 22, 386-388 (1973).
[CrossRef]

Z. Jiang, M. Li, and X. -C. Zhang,�?? Dielectric constant measurement of thin films by differential time-domain spectroscopy,�?? Appl. Phys. Lett. 76, 3221-3223 (2000).
[CrossRef]

I. H. Libon, S. Baumgärtner, M. Hempel, N. E. Hecker, J. Feldmann, M. Koch, and P. Dawson, �??An optically controllable terahertz filter,�?? Appl. Phys. Lett. 76, 2821-2823 (2000).
[CrossRef]

K. C. Lim, J. D. Margerum, and A. M. Lackner,�?? Liquid crystal millimeter wave electronic phase shifter,�?? Appl. Phys. Lett. 62, 1065-1067 (1993).
[CrossRef]

Electron. Lett. (2)

D. Dolfi, M. Labeyrie, P. Joffre, and J. P. Huignard,�?? Liquid crystal microwave phase shifter,�?? Electron. Lett. 29, 926-928 (1993).
[CrossRef]

R. Kersting, G. Strasser, and K. Unterrainer,�?? Terahertz phase modulator,�?? Electron. Lett. 36, 1156-1158 (2000).
[CrossRef]

IEEE Microwave Wireless Comp. Lett. (1)

T.-R Tsai, C.-Y. Chen, R.-P. Pan, C.-L. Pan, and X.-C. Zhang,�?? Electrically controlled room temperature terahertz phase shifter with liquid crystal,�?? IEEE Microwave Wireless Comp. Lett. 14, 77-79 (2004).
[CrossRef]

IEEE Trans. Microwave Theory Tech. (1)

Peter H. Siegel,�?? Terahertz technology,�?? IEEE Trans. Microwave Theory Tech., 50, 910-928 (2002).
[CrossRef]

J. Bio. Phys. (1)

R.-P. Pan, T.-R. Tsai, C.-Y. Chen, and C.-L. Pan,�?? Optical constants of two typical liquid crystals 5CB and PCH5 in the THz frequency range,�?? J. Bio. Phys. 29, 335-338 (2003).
[CrossRef]

Jan. J. Appl. Phys. (1)

K. Komori, T. Sugaya, M. Watanabe, T. Hidaka,�?? Ultrafast coherent control of excitons using pulse-shaping technique,�?? Jan. J. Appl. Phys. 39, 2347-2352 (2000).

Microwave Opt. Tech. Lett. (1)

T. Kleine Ostmann, M. Koch, and P. Dawson,�?? Modulation THz radiation by semiconductor nanostructures,�?? Microwave Opt. Tech. Lett. 35, 343-345 (2002).
[CrossRef]

Mol. Cryst. Liq. Cryst. (1)

R.-P. Pan, T.-R. Tsai, C.-Y. Chen, C.-H. Wang, and C.-L. Pan,�?? The refractive indices of nematic liquid crystal 4�??-n-pentyl-4-cyanobiphenyl in the THz frequency range,�?? Mol. Cryst. Liq. Cryst. (to be published in May 2004 ).
[CrossRef]

Nature Materials (1)

B. Ferguson and X.-C. Zhang,�?? Materials for terahertz science and technology,�?? Nature Materials, 1, 26-33 (2002).
[CrossRef]

Other (4)

D. Mittleman, �??Terahertz Imaging,�?? in Sensing with THz radiation, (Spring-Verlag, New York, 2002).

Eugene Hecht, Optics, 3rd ed. (Addison Wesley Longman, New York, 1998), Chap. 4.

P. Yeh, and C. Gu, Optics of Liquid Crystal Displays, (Wiley Interscience Publication, New York, 1999), Chap. 3.

P. G. de Gennes and J. Prost, The Physics of Liquid Crystals, 2nd ed. (Oxford, New York, 1983), Chap. 3.

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Figures (4)

Fig. 1.
Fig. 1.

The schematic diagram of the LC THz phase shifter. The inset shows the sandwiched structures of the LC cells used.

Fig. 2.
Fig. 2.

The room-temperature (a) extraordinary (red circles) and ordinary (blue circles) refractive indices, (b) birefringence, and (c) imaginary extraordinary (blue circles) and ordinary (red circles) refractive indices of E7 are shown as a function of frequency between 0.2 to 1.2 THz.

Fig. 3.
Fig. 3.

. The measured THz waveforms transmitted through the LC phase shifter at various magnetic inclination angles. The inset shows the spectrum of the THz signal.

Fig. 4.
Fig. 4.

The phase shift of the THz waves versus the magnetic inclination angle. The solid curves are theoretical predictions. The red and blue circles are experimentally measured phase shift at 0.49 and 1.025 THz.

Equations (2)

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δ ( θ ) = 0 L 2 π f c Δ n eff ( θ , z ) dz ,
δ ( θ ) = 2 π L f c { [ cos 2 ( θ ) n o 2 + sin 2 ( θ ) n e 2 ] 1 2 n o } ,

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