Electrically switchable photonic crystals based on liquid-crystal-infiltrated TiO₂-inverse opals

Electrically switchable photonic crystals are demonstrated based on TiO₂ inverse opals infiltrated with liquid crystals. Macroporous anatase TiO₂ inverse opals are fabricated from polystyrene opal templates through a sandwich vacuum backfilled method and followed by calcination. Upon liquid crystal infiltration, the optical properties of the hybrid organic/inorganic structure are characterized by reflectance measurements of the Bragg peak, the position of which can be switched using an external electric field. The physical mechanism underlying this switchable behavior is the reorientation of the liquid crystal molecules inside the spherical voids by the applied electric field, resulting in a significant change of the refractive index contrast between the liquid crystal and the TiO₂ inverse opal. With advantageous features of cost-effective fabrication, easy integration, and electric control, such TiO₂ inverse opals infiltrated with liquid crystals could play an important role in future development of active photonic devices.