Thin film ferroelectric photonic crystals and their application to thermo-optic switches

Two-dimensional photonic crystals (PhC) using epitaxial ferroelectric, barium titanate (BTO) thin films as the dielectric medium were fabricated and their thermo-optical response measured and compared to theory. The nanopatterned PhC consists of a square array of air holes 300 nm deep, a period of 780 nm and area 200 × 200 μm². The large refractive index of BTO leads to a high contrast structure that shows strong optical diffraction. Optical diffraction is analyzed along the 〈1 0〉 and 〈1 1〉 directions from phase grating measurements. The thermal tunability of BTO PhC is characterized from the attenuation of the first order diffraction. There is a 3 dB extinction ratio when the temperature increases by 120 °C, which corresponds to an increase of 0.05 in the BTO refractive index. Finite difference time domain (FDTD) technique is used to calculate the PhC band structure and the temperature dependence of the diffraction efficiency. The large change in the diffraction efficiency indicates that thermally tunable BTO PhCs may be useful as active ultra-compact photonic switches.