  Photonic metamaterials with properties unattainable in base materials are
already beginning to revolutionize optical component design. However, their
exceptional characteristics are often static, as artificially engineered into
the material during the fabrication process. This limits their application for
in-operando adjustable optical devices and active optics in general. Here, for
a hybrid material consisting of a liquid crystal-infused nanoporous solid, we
demonstrate active and dynamic control of its meta-optics by applying
alternating electric fields parallel to the long axes of its cylindrical pores.
First-harmonic Pockels and second-harmonic Kerr birefringence responses,
strongly depending on the excitation frequency- and temperature, are observed
in a frequency range from 50 Hz to 50 kHz. This peculiar behavior is
quantitatively traced by a Landau-De Gennes free energy analysis to an
order-disorder orientational transition of the rod-like mesogens and intimately
related changes in the molecular mobilities and polar anchoring at the solid
walls on the single-pore, meta-atomic scale. Thus, our study evidences that
liquid crystal-infused nanopores exhibit integrated multi-physical couplings
and reversible phase changes that make them particularly promising for the
design of photonic metamaterials with thermo-electrically tunable birefringence
in the emerging field of spacetime metamaterials aiming at a full
spatio-temporal control of light.
