Enhanced light amplification due to group-velocity anomaly peculiar to two- and three-dimensional photonic crystals.

An analytical expression was derived for light amplification by stimulated emission in arbitrary photonic crystals, which showed and enhancement due to small group velocity. This enhancement was evaluated quantitatively for a two-dimensional crystal with a finite thickness, and an extremely large enhancement due to group-velocity anomaly peculiar to two- and three-dimensional crystals was found even for quite a thin crystal.