Abstract

Electrical and thermal modulation of porous silicon microcavities is demonstrated based on a change in the refractive index of liquid crystals infiltrated in the porous silicon matrix. Positive and negative anisotropy liquid crystals are investigated, leading to controllable tuning to both longer and shorter wavelengths. Extinction ratios greater than 10 dB have been demonstrated. Larger attenuation can be achieved by increasing the Q-factor of the microcavities.

© 2005 Optical Society of America

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References

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  1. E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58, 2059-2062 (1987).
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    [CrossRef]
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    [CrossRef]
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    [CrossRef]
  12. Y. Shimoda, M. Ozaki, and K. Yoshino, “Electric field tuning of a stop band in a reflection spectrum of synthetic opal infiltrated with nematic liquid crystal,” Appl. Phys. Lett. 79, 3627-3629 (2001).
    [CrossRef]
  13. K. Robbie, D. J. Broer, and M. J. Brett, “Chiral nematic order in liquid crystals imposed by an engineered inorganic structure,” Nature 399, 764-766 (1999).
    [CrossRef]
  14. S. M. Weiss, M. Haurylau, and P. M. Fauchet, “Tunable photonic bandgap structures for optical interconnects,” Opt. Mat. 27, 740-744 (2005).
    [CrossRef]
  15. H. Ouyang, M. Christophersen, R. Viard, and P. M. Fauchet, Center for Future Health, University of Rochester, Rochester, N.Y. 14627, are preparing a manuscript to be called “Macroporous silicon microcavities for macromolecule detection.”
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    [CrossRef]
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  21. R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective (Morgan Kaufmann Publishers, San Francisco, 1998), pp. 423-462.

Appl. Phys. Lett.

Ch. Schuller, F. Klopf, J. P. Reithmaier, M. Kamp, and A. Forchel, “Tunable photonic crystals fabricated in III-V semiconductor slab waveguides using infiltrated liquid crystals,” Appl. Phys. Lett. 82, 2767-2769 (2003).
[CrossRef]

B. Maune, M. Lonèar, J. Witzens, M. Hochberg, T. B. Jones, D. Psaltis, A. Scherer, and Y. Qiu, “Liquid-crystal electric tuning of a photonic crystal laser,” Appl. Phys. Lett. 85, 360-362 (2004).
[CrossRef]

Ozaki, T. Matsui, M. Ozaki, and K. Yoshino, “Electrically color-tunable defect mode lasing in onedimensional photonic-band-gap system containing liquid crystals,” Appl. Phys. Lett. 82, 3593-3595 (2003).
[CrossRef]

K. Yoshino, Y. Shimoda, Y. Kawagishi, K. Nakayama, and M. Ozaki, “Temperature tuning of the stop band in transmission spectra of liquid-crystal infiltrated synthetic opal as tunable photonic crystal,” Appl. Phys. Lett. 75, 932-934 (1999).
[CrossRef]

F. Du, Y.-Q. Lu, and S.-T. Wu, “Electrically tunable liquid-crystal photonic crystal fiber,” Appl. Phys. Lett. 85, 2181-2183 (2004).
[CrossRef]

Y. Shimoda, M. Ozaki, and K. Yoshino, “Electric field tuning of a stop band in a reflection spectrum of synthetic opal infiltrated with nematic liquid crystal,” Appl. Phys. Lett. 79, 3627-3629 (2001).
[CrossRef]

S. M. Weiss, M. Molinari, and P. M. Fauchet, “Temperature stability for silicon-based photonic band-gap structures,” Appl. Phys. Lett. 83, 1980-1982 (2003).
[CrossRef]

J. Appl. Phys.

G. Pucker, A. Mezzetti, M. Crivellari, P. Bellutti, A. Lui, N. Daldosso, and L. Pavesi, “Silicon-based nearinfrared tunable filters filled with positive or negative dielectric anisotropic liquid crystals,” J. Appl. Phys. 95, 767-769 (2004).
[CrossRef]

Mat. Res. Soc. Proc.

G. Lérondel, P. Reece, A. Bruyant and M. Gal, “Strong light confinement in microporous photonic silicon structures,” in Engineered Porosity for Microphotonics and Plasmonics, R. Wehrspohn, F. Garcial-Vidal, M. Notomi, and A. Scherer, eds., Mat. Res. Soc. Proc. 797, W1.7.1-W1.7.6 (2004).

Nature

K. Robbie, D. J. Broer, and M. J. Brett, “Chiral nematic order in liquid crystals imposed by an engineered inorganic structure,” Nature 399, 764-766 (1999).
[CrossRef]

Opt. Express

Opt. Mat.

S. M. Weiss, M. Haurylau, and P. M. Fauchet, “Tunable photonic bandgap structures for optical interconnects,” Opt. Mat. 27, 740-744 (2005).
[CrossRef]

Phys. Rev. B

S. W. Leonard, J. P. Mondia, H. M. van Driel, O. Toader, S. John, K. Busch, A. Birner, U. Gösele, and V. Lehmann, “Tunable two-dimensional photonic crystals using liquid-crystal infiltration,” Phys. Rev. B 61, R2389-R2392 (2000).
[CrossRef]

Phys. Rev. Lett.

E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and electronics,” Phys. Rev. Lett. 58, 2059-2062 (1987).
[CrossRef] [PubMed]

S. John, “Strong localization of photons in certain disordered dielectric superlattices,” Phys. Rev. Lett. 58, 2486-2489 (1987).
[CrossRef] [PubMed]

K. Busch and S. John, “Liquid-crystal photonic-band-gap materials: the tunable electromagnetic spectrum,” Phys. Rev. Lett. 83, 967-970 (1999).
[CrossRef]

Other

G. P. Crawford and S. Žumer, eds., Liquid Crystals in Complex Geometries Formed by Polymer and Porous Networks (Taylor & Francis Ltd., London, 1996), pp. 21-52.

J. Cognard, Alignment of Nematic Liquid Crystals and Their Mixtures (Gordon and Breach, New York, 1982), p. 59.

R. Ramaswami and K. N. Sivarajan, Optical Networks: A Practical Perspective (Morgan Kaufmann Publishers, San Francisco, 1998), pp. 423-462.

H. Ouyang, M. Christophersen, R. Viard, and P. M. Fauchet, Center for Future Health, University of Rochester, Rochester, N.Y. 14627, are preparing a manuscript to be called “Macroporous silicon microcavities for macromolecule detection.”

G. Meier, E. Sackmann, and J. G. Grabmaier, Applications of Liquid Crystals, (Springer Verlag, Berlin, Germany, 1975), pp. 29-30.

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Figures (5)

Fig. 1.
Fig. 1.

Schematic of porous silicon microcavity (a) and SEM images showing the morphology of (b) mesoporous silicon layers and (c) macroporous silicon layers. In the schematic, the yellow layers are low porosity (high refractive index) and the red layers are high porosity (low refractive index). In the SEM images, the darker regions represent the void space and the bright area is the silicon matrix. Therefore, the brighter layers have lower porosity than the darker ones. The pore openings of the macropores are much larger than those of the mesopores.

Fig. 2.
Fig. 2.

Reflectance spectra, before liquid crystal infiltration, of (a) mesoporous silicon microcavity measured by a spectrophotometer and (b) macroporous silicon microcavity measured by an optical spectrum analyzer with a fiber coupled Xenon arc lamp. Tuning of the resonance wavelength after liquid crystal infiltration enables optical modulation.

Fig. 3.
Fig. 3.

(a) Resonance wavelength red shift as a function of applied voltage for mesoporous and macroporous silicon microcavities with positive anisotropy E7 liquid crystals. The liquid crystals rotate more freely in the macroporous silicon, which leads to the larger wavelength shift. Electrical contact is made to the crystalline silicon and ITO-coated glass on top of the microcavity (inset). (b) Resonance wavelength red shift as a function of applied voltage for mesoporous silicon microcavities with negative anisotropy ZLI-4788 liquid crystals.

Fig. 4.
Fig. 4.

Thermal tuning of mesoporous and macroporous silicon microcavities with liquid crystals. The resonance shift takes place at different temperatures depending on the phase transition temperature of the infiltrated liquid crystal, as shown in (a)-(c). The refractive index increases when liquid crystals change from the ordered nematic phase to disordered isotropic phase (inset (a)). (d) For a resonance with a measured Q-factor of 400, the resonance shift resulting from the E7 phase transition corresponds to a 14 dB extinction ratio.

Fig. 5.
Fig. 5.

The extinction ratio is calculated as the change in transmission at the resonance wavelength (inset). As the Q-factor of the resonance increases, the achievable extinction ratio increases, for a given refractive index change. The magnitude of the refractive index change determines the magnitude of the resonance wavelength shift. When the refractive index change becomes too large, the resonance wavelength begins to shift beyond the stopband, which reduces the extinction ratio. For a microcavity with a Q-factor of 600, the maximum attenuation is achieved for Δn=0.1.

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