Photonic crystals: Past, present and future

A photonic crystal, an analog of a semiconductor for light waves, is a material in which propagation of certain photon wavelengths is forbidden. It appeared first as a theoretical proposal about 10 years ago, but rapid progress in manufacturing such newly-engineered materials at microwave and then optical wavelengths, has involved the development of a new fundamental physical concepts and ideas. We provide a simple introduction into the field and overview the recent progress, emphasising our results on nonlinear photonic crystals and also making an effort to oversee some future developments.