The control of optical modes in microcavities or in photonic bandgap (PBG) materials is coming of age Although these ideas could have been developed some time ago, it is only recently that they have emerged, due to advances in both atomic physics and in fabrication techniques, be it on the high-quality dielectric mirrors required for high-finesse Fabry- Perot resonators or in semiconductor multilayer deposition methods. Initially the principles of quantum electro-dynamics (QED) were demonstrated in elegant atomic physics experiments. Now solid-state implementations are being investigated,...