INTRODUCTION The physics of microcavities is a flourishing research topic with moreover a huge potential for applications [1-2]. Thanks to, on the one hand, revolutions in the epitaxial techniques allowing for the introduction of micro- and nanostructures in photonic semiconductors devices, and on the other hand, to the development of new artificially structured composite materials (the so-called metamaterials), one is now able to tailor the properties of microcavities and to harness new photonic functionalities. For example, optical semiconductor microcavities allow for tailoring the laser emission process. Both active and passive microcavities are currently being developed to realize low-power, optical nonlinear, integrated components (e.g. all-optical memories). In the case of passive devices, microcavities can store enormous optical intensities in very small volumes making it easier and more realistic to bring nonlinear effects into practice at lower powers.