Contrast improvement with imperfect pre-coronagraph and dark-hole

We are studying a coronagraph system with an imperfect pre-coronagraph in the field of direct detection of exoplanets which can provide additional contrast to a main coronagraph. It is a kind of an unbalanced nulling interferometer (UNI) concept which consists of the first deformable mirror (DM), the pre-coronagraph, the second DM, and a main coronagraph. The pre-coronagraph and the DM1 reduce the star light and the speckle noise to about one-hundreds which would be added to the main coronagraph contrast. The DMs can be controlled by the dark-hole algorithm by changing the masks at the coronagraph foci.