JWST: A mid-IR coronagraph for imaging extrasolar planets

MIRI, the mid-IR instrument of JWST (JamesWebb Space Telescope), will include a coronagraphic device for which the ultimate goal is the detection and caracterization of extrasolar planets around nearby stars. In this paper, we describe the optical concept of MIRI and the instrumental choices that were made in phase A and B regarding the coronagraphic system. Finally, we will present numerical simulations that we carried out to evaluate the capability for detecting extrasolar giant gazeous planets.