Nematic liquid crystals and smectic liquid crystals can be infiltrated into a three-dimensional periodic array of interconnected nanosize voids in opal films prepared by sedimentation of SiO2 spheres of various diameters. The optical stop band in the transmission spectra of opals shifts drastically by the infiltration of liquid crystals. The stop band is also found to shift at the phase transition points with changing temperature. This effect enables the tuning of optical properties of opals as a prototype tunable photonic crystal. This phenomenon can also be used as a measurement method for the refractive index.

Electric field tuning of an optical stop band in a reflection spectrum is demonstrated in a synthetic opal thin film infiltrated with liquid crystal. The reflection peak of the opal shifts upon the application of the electric field, and this is based on the refractive index change caused by molecular reorientation upon application of a field. The dynamic response of the stop band shift was also studied, and fast response of the order of microsecond was observed.

The optical stop band in the transmission spectra and the peak in the reflection spectra of opals with a three-dimensional periodic structure shift drastically upon infiltration with organic materials such as liquids, liquid crystals and conducting polymers. In these infiltrated opals, the stop band and reflection peak have been confirmed to be tunable by adjusting various conditions such as temperature and applied voltage.

A polymer inverse opal with a tunable bandgap is presented. It is shown that, when the opal is infiltrated with a nematic liquid crystal, tuning of the stop band upon the application of an electric field is possible (see Figure for an SEM image of the structure). A discontinuous transition of the λLC shift upon a change in the voltage is observed.

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