Real-time alignment and co-phasing of multi-aperture systems using phase diversity

The alignment of the subapertures is a major challenge for future segmented telescopes and telescope arrays. We show here that a phase diversity sensor using two near-focus images can fully and efficiently align a multiple aperture system, both for the alignment (large amplitude tip/tilt aberrations correction) and phasing (piston and small amplitude tip/tilt aberrations correction) modes. We derive a new algorithm for the alignment of the subapertures : ELASTIC. We quantify the novel algorithm performance by numerical simulations and we demonstrate it experimentally on a test bench. We also study the performance of LAPD, a recent real-time algorithm for the phasing of the sub-apertures. This work should simplify the design of future multiple aperture systems.