Abstract

Photonic Crystal Fibers (PCFs) have appeared as a new class of optical waveguides, which have attracted large scientific and commercial interest during the last years. PCFs are microstructured waveguides, usually in silica, with a large number of air holes located in the cladding region of the fiber. The size and location of these air holes opens up for a large degree of design freedom within optical waveguide design. Further, the existence of air holes in the PCF gives access close to the fiber core and by introducing new materials into the air holes, a high interaction between light and hole material can be obtained, while maintaining the microstructure of the waveguide. In this paper, we describe what we call Liquid Crystal Photonic Bandgap Fibers, which are PCFs infiltrated with Liquid Crystals (LCs) in order to obtain increased fiber functionality. We describe a thermo-optic fiber switch with an extinction ratio of 60dB and tunable PBGs using thermo-optic tuning of the LC. These devices operate by the PBG effect and are therefore highly sensitive to the refractive index distributions in the holes.

© 2003 Optical Society of America

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References

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Appl. Phys. Lett. (1)

D. B. Keck, R. D. Maurer, and P. C. Schultz, �??On the ultimate lower limit of attenuation in glass optical waveguides,�?? Appl. Phys. Lett. 22, 307-309 (1973).
[CrossRef]

CLEO 2003 (1)

J. B. Jensen, et al. �??Photonic Crystal Fibre based evanescent-wave sensor for detection of aqueous solutions,�?? Conference on Lasers and Electro-Optics (Optical Society of America, Washington, D.C., 2003).

IEEE Photonics Technol. Lett. 2000 (1)

P. S. Westbrook, et al., �??Cladding-mode resonances in hybrid polymer-silica microstructured optical fiber gratings,�?? IEEE Photonics Technol. Lett. 12, (2000).
[CrossRef]

J. Appl. Phys (1)

P. Rudquist, M. Buivydas, L. Komitov, and S. T. Lagerwall, �??Linear electro-optic effect based on flexoelectricity in a cholesteric with sign change of dielectric anisotropy,�?? J. Appl. Phys. 76, (1994).
[CrossRef]

Mol. Cryst. Liq. Cryst. (2)

S. K. Lo, L. M. Galarneau, D. J. Rogers, and S. R. Flom, �??Smectic Liquid Crystal Waveguides with cylindrical Geometry,�?? Mol. Cryst. Liq. Cryst. 201, 137-145 (1991).
[CrossRef]

J. T. Mang, K. Sakamoto, and S. Kumar, �??Smectic Layer Orientation in Confined Geometries,�?? Mol. Cryst. Liq. Cryst. 223, 133-142 (1992)
[CrossRef]

Nature (2)

B. Temelkuran, S. D. Hart, G. Benolt, J. D. Joannopoulos, and Y. Fink, �??Wavelength-scalable hollow optical fibres with large photonics bandgaps for CO2 laser transmission,�?? Nature 420, 650-653 (2002).
[CrossRef] [PubMed]

E. Yablonovitch, �??Liquid versus photonics crystals,�?? Nature 401, 539-541 (1999)
[CrossRef]

Nature Materials 1 (1)

C. Wenyi, A. Munoz, P. Palffy-Muhoray, and B. Taheri, �??Lasing in a three-dimensional photonics crystal of the liquid crystal blue phase II,�?? Nature Materials 1, 111-113 (2002).
[CrossRef]

Opt Fiber Communication Conf. 2002 (1)

K. P. Hansen, et al., �??Highly nonlinear photonic crystal fiber with zero-dispersion at 1.55µm,�?? Optical Fiber Communication Conference (Optical Society, of America, Washington, D.C., 2002) PDFA9.

Opt. Express (2)

Optical Fiber Communication 2003 (1)

Jasapara, R. Bise, T. Her, and J. Nicholson, �??Effect of Mode Cut-Off on Dispersion in Photonic Bandgap Fibers,�?? Optical Fiber Communication Conference ThI3 (2003).

Optics Express (1)

B. J. Eggleton, C. Kerbage, P. S. Westbrook, R. S. Windeler, and A. Hale, �??Microstructured optical fiber devices�??, Optics Express 9, 698-713 (2001).
[CrossRef] [PubMed]

Phys. Rev. E (2)

S. Kralj and S. Zumer, �??Smectic-A structures in submicrometer cylindrical cavities,�?? Phys. Rev. E, 54(2) 1610-1617 (1996).
[CrossRef]

H. �??S. Kitzerow, B. Liu, F. Xu, and P. P. Crooker, �??Effect on chirality on liquid crystals in capillary tubes with parallel and perpendicular anchoring,�?? Phys. Rev. E 54, 568-575, (1996).
[CrossRef]

Phys. Rev. Lett (1)

K. Busch and S. John, �??Liquid-Crystal Photonic-Band-Gap Materials: The Tuneable Electromagnetic Vacuum,�?? Phys. Rev. Lett. 83, 967-970 (1999).
[CrossRef]

Phys. Rev. Lett. (1)

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

Science (4)

R.F. Cregan et al., �??Single-mode photonic band gap guidance of light in air,�?? Science 285, 1537-153 (1999).
[CrossRef] [PubMed]

J. C. Knight, J. Broeng, T. A. Birks, and P. St. J. Russell, �??Photonic bandgap guidance in optical fibers, Science 283, 1476-1478 (1998).
[CrossRef]

P. Russell, �??Photonic crystal fibers,�?? Science 299, 358-362 (2003).
[CrossRef] [PubMed]

V. K. Gupta, J. J. Skaife, T. B. Dubrowsky, and N. L. Abbott, �??Optical Amplification of Ligand-Receptor Binding Using Liquid Crystals,�?? Science 278, 2077-2080 (1998)
[CrossRef]

Other (4)

J. D. Joannopoulos, R. D. Meade, and J. N. Winn, Photonic Crystals: Molding the Flow of Light, (Princeton Univ. Press, 1995).

R. Syms and J. Cozens, Optical Guided Waves and Devices, (McGraw-Hill Book Company England 1992).

P. G. de Gennes and J. Prost, J. The Physics of liquid crystals, 2nd edition, (Clarendon Press, Oxford 1993).

S. Chandrasekhar, Liquid crystals, (Cambridge University Press, 1977).

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Figures (5)

Fig. 1.
Fig. 1.

Micrograph of the end facet of a liquid-crystal-filled photonic crystal fibre. The periodic structure, consisting of silica and liquid crystal, gives rise to a cladding with photonic bandgaps, and the fibre supports only guided modes at certain wavelength bands. In this case, a blue mode is supported in the visible region of the spectrum.

Fig. 2.
Fig. 2.

Examples of phases of thermotropic liquid crystals: Nematic, Smectic A and Smectic C phases (non-chiral molecules), appearing in that order upon cooling, if the same material possesses all of these phases. If the molecules are chiral, we instead have N* (=cholesteric), SmA* and SmC*. These phases all lack mirror planes. A helical superstructure due to the molecular chirality appears in the N* and SmC* phases (shown), but not in the SmA* phase (not shown).

Fig. 3.
Fig. 3.

(a) Device principle. The voids of a triangular structured PCF is filled with a liquid crystal and coated with a thin conducting layer, which forms a resistive microheater. Upper left inset shows a polarized micrograph of a liquid crystal inside a PCF void. (b) Mode index simulation of rod-type photonic crystal. At short wavelengths, the individual rods form isolated waveguides, for increasing wavelength the rods become resonant and finally strongly coupled waveguides. A forbidden region with mode index below the low-index background material (blue line) appears for narrow spectral ranges. These spectral ranges are utilized to guide light in the core and they are highly dependent on the exact composition of the rod material. Liquid crystals provide a very high sensitivity to the spectral location of these ‘light-guide’ ranges, thereby opening up the possibilities of low-voltage driven all-optical functional devices. Field distributions of a high-index cladding mode (left), a defect mode guided by the core (middle), and a low-index cladding mode (right) are shown in the top panel.

Fig. 4.
Fig. 4.

Micrographs of the guided modes in a PCF filled with a short-pitch cholesteric LC.(MDA-00-1445). Well below the N* to Isotropic phase transition temperature (Tc=94°C), the bandgap location sensitivity is approximately 1nm/°C and 3 nm/°C in the visible and infrared region, respectively. Closer to Tc, the transmission characteristics changes more rapidly, and the color of the guided modes changes from a) green@T=77°C to b) yellow@T=89°C and then into an c) off state@T=91°C for thereafter to change to d) blue@T=94°C

Fig. 5.
Fig. 5.

(a) Transmission spectrum for a triangular structured PCF filled with a liquid crystal (TM216). Spectrum is shown for 3 temperatures around the SmA* to N* phase transition temperature: 26.1°C, 26.5°C and 26.9°C. (b) Spectrum of a 974nm pump laser beam coupled into the fiber and shows an extinction ratio of 60dB with a switching temperature difference of 0.4°C.

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