Photonic band-gap structures are of interest both from fundamental and practical points of view. They are known to enhance nonlinear, magnetooptical, electrooptical and other effects in the medium when frequency is near photonic band gap [1, 2]. Second harmonic generation is observed when phase-matching conditions are fulfilled,
i.e. phase velocities of first and second harmonics are equal. Homogeneous media have their own material dispersion, so phase mismatch always presents. Anisotropy in some materials can compensate dispersion in specific directions, and such nonlinear crystals are commonly used in lasers and parametric light generators . Photonic crystals are attractive for practical applications because of a large diversity of their dispersion properties comparing to homogeneous media. Varying photonic crystal parameters, such as lattice period, filling factor and refractive indices of media, one can manipulate
its band structure.