5. Servo-control

An adaptive optics system can be considered as a multivariable servo system (Multi-Input Multi-Output, or MIMO) aimed at rejecting disturbances (turbulence, noise), involving, like most servo systems, a sensor, a corrector and a real-time computer. Defining the control law of an AO system can become complex, since it is necessary to take into account the disturbance conditions encountered, the characteristics of the sensors and correctors (sometimes non-linear), the performance criterion targeted, the delays and the number of degrees of freedom of the system, all the while considering an operational and therefore robust and, if possible, autonomous system. In what follows, we try to make as few assumptions as possible about the sensors and correctors considered, apart from their linearity. The structure of the servo chain and its chronogram are fixed for the sake of simplicity, without reducing...