Electrochemically prepared pore arrays for photonic-crystal applications

In the last few years, photonic crystals have gained considerable interest due to their ability to “mold the flow of light.” Photonic crystals are physically based on Bragg reflections of electromagnetic waves. In simple terms, a one-dimensional (1D) photonic crystal is a periodic stack of thin dielectric films with two different refractive indices, ns1 and n 2. The two important geometrical parameters determining the wavelength of the photonic bandgap are the lattice constant, a = d1(n1) + d2(n2), and the ratio of d1 to a (where d1 is the thickness of the layer with refractive index n1, and d2 is the thickness of layer n2). For a simple quarter-wavelength stack, the center wavelength λ of the 1D photonic crystal would be simply λ = 2n1d1 + 2n2d2. In the case of 2D photonic crystals, the concept is extended to either airholes in a dielectric medium or dielectric rods in air. Therefore, ordered porous dielectric materials like porous silicon or porous alumina are intrinsically 2D photonic crystals. © Materials Research Society 2001.