Different Structural Colors or Patterns on the Front and Back Sides of a Multilayer Photonic Structure

The application of photonic crystals in the field of color display and anticounterfeiting has been widely studied because of their brilliant and angle-dependent structural colors. Most of the research is focused on structural colors on the front side of photonic crystals, and both sides of the crystals usually display the same or similar optical properties. Here, multilayer photonic crystals with different structural colors or different patterns on the front and back sides were designed. In a trilayer photonic structure, an amorphous SiO₂ layer with a thickness of about 10 μm was inserted into two layers of highly ordered photonic crystals with band gaps of 625 and 470 nm. The amorphous SiO₂ layer acts as a gate to prohibit light transmission, and thereby, the structural colors of the two photonic crystals were separated. Hence, the trilayer structure shows red and blue colors on each side. Then, a light window was opened in the disordered layer using a patterned mask; thus, a pattern with a mixed color of both ordered layers was observed on each side in the window field, which was obviously different from the background color. Finally, completely different patterns on each side were also realized by building a multilayer structure. The different structural colors or patterns on each side of the photonic structures provide them with enriched color range and enhanced display or anticounterfeiting ability.