Tunable Photonic Band Gap Crystals Based on a Liquid Crystal-Infiltrated Inverse Opal Structure

TLDR

These LC‑inverse opal composites hold promise for optical devices and fundamental research. The authors fabricated SiO₂ inverse opal films infiltrated with nematic liquid crystals and, by evaluating the effective refractive indices, showed that LC orientation governs the photonic band structure, enabling peak tuning through alignment. The LC‑filled inverse opal displays optical properties distinct from bare films, which can be tuned by LC orientation, temperature, or light‑induced phase transitions, allowing controllable photonic band gaps and reflection peaks.

Abstract

Composite materials comprised of nematic liquid crystals (LCs) and SiO(2) inverse opal films were fabricated. Their optical properties were quite different from those of inverse opal films without the LCs. The optical properties could be controlled by changing the refractive indices of the LCs, which vary with orientation, phase, and temperature. In particular, the optical properties were drastically changed by thermal or photoinduced isothermal phase transitions of the LCs. This means that the photonic band structure could be controlled, and tunable photonic crystals have been achieved, based on the inverse opal structure. The mechanism of this change was investigated by the evaluation of the effective refractive indices. As a result, it was found that the change in optical properties was derived from the orientation of the LC molecules in the voids in the inverse opal film. Furthermore, once the mechanism was understood, it was also possible to control the position of the reflection peak by changing the alignment of the LCs. Such materials have the possibility for practical use in optical devices and fundamental research systems.