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Electrically tunable liquid crystal optical microresonators

Abstract

Because of their small mode volume and high Q-factors, optical microresonators are interesting for applications such as laser sources, active filters and all-optical switches. Especially interesting are tunable resonators, in which the resonance frequency tuning by size, shape, temperature or electric field can be achieved. Here we demonstrate electrically tunable, low-loss whispering-gallery-mode (WGM) resonators made of nematic liquid crystal droplets, embedded in a polymer matrix. The shift in resonant frequencies is achieved via electric field-induced structural distortion of the birefringent liquid crystal resonator medium. Nematic liquid crystal microresonators have a large tuning range of the order of 20 nm at 2.6 V µm−1 for a 600 nm WGM in 17-µm-diameter droplets and high Q-factors up to 12,000 in 33-µm-diameter droplets. The tunability is approximately two orders of magnitude larger than usually achieved in solid-state microresonators.

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Figure 1: Light in liquid-crystal microdroplets.
Figure 2: Spectrum of light circulating in a liquid-crystal droplet.
Figure 3: Resonant frequencies (wavelengths) in a dielectrically anisotropic sphere.
Figure 4: Liquid-crystal microresonator in an external electric field.
Figure 5: Electric-field-induced shift of TM WGM resonances.
Figure 6: Electric tuning of the resonant transfer of external light to the liquid-crystal microcavity.

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Acknowledgements

The authors would like to thank P. Ropret, S. Žumer, M. Škarabot, S. Pečar, J. Pirš and J. Štrancar for their help and suggestions. This work was supported by the Slovenian Research Agency under the contracts P1-0099 and J1-9728.

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Authors and Affiliations

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Contributions

M.H. performed all experiments and analysed the results. M.R. has carried out the theoretical calculations. S.P. synthesized the SPP-106 dye. I.M. initiated the work on WGM resonances in LC droplets, organized and supervised the experiments. M.H., M.R. and I.M. wrote the manuscript.

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Correspondence to I. Muševič.

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Humar, M., Ravnik, M., Pajk, S. et al. Electrically tunable liquid crystal optical microresonators. Nature Photon 3, 595–600 (2009). https://doi.org/10.1038/nphoton.2009.170

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