Spectral characterization of exo-planets can be made by nulling interferometers. In this context, several projects
have been proposed such as DARWIN, FKSI, PEGASE and TPF, space-based, and ALADDIN, ground-based. To
stabilize the beams with the required nanometric accuracy, a cophasing system is required, made of piston/tip/tilt
actuators on each arm and piston/tip-tilt sensors. The demonstration of the feasibility of such a cophasing system
is a central issue.
In this goal, a laboratory breadboard named PERSEE is under integration. Main goals of PERSEE are the
demonstration of a polychromatic null from 1.65 μm to 3.3 μm with a 10-4 rejection rate and a 10-5 stability
despite the introduction of realistic perturbations, the study of the interfaces with formation-flying spacecrafts
and the joint operation of the cophasing system with the nuller.
We describe the principle of the cophasing system made by Onera, operating in the [0.8 - 1] μm (tip/tilt)
and [0.8 - 1.5] μm (piston) spectral bands. Emphasis is put on the piston sensor and its close integration with