A Mach-Zehnder phasing sensor for extremely large segmented telescopes: Laboratory results and close loop algorithm

Alignment of the segmented telescopes requires an accurate phase measurement at the segment borders using an optical sensor. We develop such a sensor based on the Mach-Zehnder interferometer. The operation of this system was previously demonstrated in computer simulation and through the detailed theoretical analysis. In this paper we show the results of the laboratory experiment, which confirms the main predictions we have made. The close loop control for optical phasing of segmented mirrors, analogous to the one with the use of the edge sensors, is also described and illustrated.