Self-collimation of light in three-dimensional photonic crystals

We calculate three-dimensional (3D) dispersion relations of woodpile and inverse opal photonic crystals. Inspecting the iso-frequency surfaces of the four lowest-order bands at appropriate frequencies we identify regions where self-collimation of light may be expected. These predictions are verified by means of finite-difference time-domain calculations both for high- and low-index photonic crystals.