One-dimensional alumina photonic crystals (PCs) were fabricated with electrochemical anodic oxidation method. A stop band with the central wavelength of 840 nm was formed, prohibiting the propagation of infrared rays in PCs. Planar defects were introduced in PCs by altering the waveform of periodic voltage in the anodization of aluminum foils, which enabled infrared rays to propagate in the original stop band. This method offers an approach to prepare a pattern which is visible with incident infrared rays while invisible when illuminated by natural or white light. This strategy could be applied as an anti-counterfeiting technique.
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