The Four Quadrant Phase Mask Coronagraph and its avatars

A renewal of interest into Lyot coronagraphy began about 10 years ago with the advent of the new and very demanding goal of detecting directly extrasolar planets. Among the new ideas, the Four Quadrant Phase Mask (4QPMC) has been rather prolific. The 4QPM coronagraph is based the peculiar design of binary phase mask (0,π0,π) dividing the full field of view at the focal plane in four quadrants. The mutual destructive interferences of the coherent light of a source perfectly centered on the mask, produce a total nulling within the pupil image, as is demonstrated analytically. We first recall the concept and performance of the 4QPMC. We then analyse the different limitations in space or ground-based observations from simulations. We then address the issue of device manufacturing and give the status of the actual performance in laboratory. A section reviews the various instruments under development that are equipped with this component. We conclude with a panorama of the rest of the family of the 4QPMC, which comprises several variants proposed by different teams. More specifically we address the important question of the achromatization by describing the various ideas which are currently explored to solve this problem. Among them, some genuine ones, not yet published, are presented