  The mid-infrared region is well suited for exoplanet detection thanks to the
reduced contrast between the planet and its host star with respect to the
visible and near-infrared wavelength regimes. This contrast may be further
improved with Vector Vortex Coronagraphs (VVCs), which allow us to cancel the
starlight. One flavour of the VVC is the AGPM (Annular Groove Phase Mask),
which adds the interesting properties of subwavelength gratings (achromaticity,
robustness) to the already known properties of the VVC. In this paper, we
present the optimized designs, as well as the expected performances of mid-IR
AGPMs etched onto synthetic diamond substrates, which are considered for the
E-ELT/METIS instrument.
