Electro-thermally tunable reflective colors in a self-organized cholesteric helical superstructure

Po Chang Wu, Guan Wei Wu, Ivan V. Timofeev, Victor Ya Zyryanov, Wei Lee*

*Corresponding author for this work

Research output: Contribution to journalArticle

10 Scopus citations

Abstract

We propose to dynamically control the reflective color of a cholesteric liquid crystal (CLC) by electrically tuning the center wavelength (λ c ) of the bandgap. The CLC, sandwiched in a planar-aligned cell with indium–tin-oxide electrodes, possesses negative dielectric anisotropy and thermo-responsive spectral properties. The helix in the Grandjean planar state, which is subject to vertically applied voltage, should be undisturbed in that the long molecular axis is initially perpendicular to the direction of the electric field. Surprisingly, when the frequency of the applied voltage is higher than a critical value, λ c of the CLC cell varies as a function of the voltage. The underlying mechanism is the voltage-induced temperature change through dielectric heating in the frequency regime of pseudo-dielectric relaxation, attributable to the significant equivalent resistance–capacitance circuit of the cell due to the use of electrode layers with finite conductance. The driving voltage enabling the tuning of λ c in the entire visible spectrum is as low as 12 V rms in a 5 μm thick cell at a frequency of 2 MHz. The proposed CLC cell, exhibiting a broad electrically tunable spectral range from the near-infrared to ultraviolet, holds great promise for developing tunable photonic devices such as multicolor reflectors, filters, and sensors.

Original languageEnglish
Pages (from-to)1094-1100
Number of pages7
JournalPhotonics Research
Volume6
Issue number12
DOIs
StatePublished - 1 Dec 2018

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