Digital control of interferometric metrology lines

In a recent paper principles and digital control of Fabry-Perot interferometers (FPI) have been presented, showing a few on-going and potential applications in the field of precision engineering. Among them, metrology lines were mentioned, aiming to reveal sub-nanometric displacements in view of dimensional stabilization/monitoring of demanding space telescopes. The core is a confocal optical cavity, in vacuum, whose light path is sensible to supporting structure length variations. The latter are tracked and revealed by a frequency actuator which acting on the incident light keeps the FPI signal centered to zero although the optical path is varying. Concept and digital control of metrology lines will be outlined and some experimental results from an on-ground breadboard will be discussed. Due to on-ground and test contingencies, a displacement actuator was also active on the cavity, which asked for actuator coordination