Optical properties of woodpile photonic crystals produced by three-dimensional laser lithography

Photonic crystals having a woodpile lattice structure with the lateral sizes of up to 200 $\times$ 200 $\mu$m and lattice period of 1 to 2 $\mu$m have been produced by additive three-dimensional laser lithography. The sample structure has been analyzed by optical and scanning electron microscopy. The ideal woodpile consists of “logs” with a rectangular cross section but, in the synthesized structures, the angles are rounded. Calculations of the photonic band structure of woodpiles, in which the cross sections of logs are specified by the Lame curves, have made it possible to estimate the influence of the rounding on the optical properties. Due to significant sample sizes, patterns of optical diffraction in white and monochromatic light have been studied experimentally. The experimental results have been interpreted using calculations of diffraction patterns in the Born approximation of scattering theory.