Wide-band six-region phase mask coronagraph

An achromatic six-region phase mask coronagraph, used for the detection of exoplanets, is proposed. The mask has six regions in angular direction and could work in wideband. Furthermore, a six-level phase mask, as an example of the six-region phase mask, is theoretically investigated. According to numerical simulations, this specific mask has a deep elimination of starlight, good performance of achromatism and small inner working angle. As a single phase mask, the ratio of the remaining starlight of the six-level phase mask to the total incident starlight is less than 0.001 when the wavelength is between 500 nm and 600 nm.