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For direct imaging of exoplanets, a stellar coronagraph helps to remove theimage of an observed bright star by attenuating the diffraction effects causedby the telescope aperture of diameter D. The Dual Zone Phase Mask (DZPM)coronagraph constitutes a promising concept since it theoretically offers asmall inner working angle (IWA \sim \lambda_0/D), good achromaticity and highstarlight rejection, typically reaching a 1e6 contrast at 5 \lambda_0/D fromthe star over a spectral bandwidth \Delta\lambda/\lambda_0 of 25% (similar toH-band). This last value proves to be encouraging for broadband imaging ofyoung and warm Jupiter-like planets. Contrast levels higher than 1e6 arehowever required for the observation of older and/or less massive companionsover a finite spectral bandwidth. An achromatization improvement of the DZPMcoronagraph is therefore mandatory to reach such performance. In its design,the DZPM coronagraph uses a grey (or achromatic) apodization. We propose toreplace it by a colored apodization to increase the performance of thiscoronagraphic system over a large spectral range. This innovative concept,called Colored Apodizer Phase Mask (CAPM) coronagraph, is defined with somedesign parameters optimized to reach the best contrast in the exoplanet searcharea. Once this done, we study the performance of the CAPM coronagraph in thepresence of different errors to evaluate the sensitivity of our concept. A 2.5mag contrast gain is estimated from the performance provided by the CAPMcoronagraph with respect to that of the DZPM coronagraph. A 2.2e-8 intensitylevel at 5 \lambda_0/D separation is then theoretically achieved with the CAPMcoronagraph in the presence of a clear circular aperture and a 25% bandwidth.In addition, our studies show that our concept is less sensitive to low thanhigh-order aberrations for a given value of rms wavefront errors.

Improved achromatization of phase mask coronagraphs using colored apodization