In this paper the finite difference time domain (FDTD) method is applied to calculate the wave propagation in two dimensional photonic crystal optical waveguides and to determine the energy distribution along the propagation path. The band structure is determined taking into account the frequency dependence of the dielectric permittivity. Two dimensional photonic crystals based on bulk and porous silicon material were investigated and a gradual decrease of the averaged energy was found. (c) 2005 Elsevier B.V. All rights reserved.