Autonomous tip/tilt alignment and phasing of a distributed aperture imaging testbed

Abstract

Star-9 is an experimental demonstration of distributed aperture imaging built at the Lockheed Martin Advanced Technology Center. White light from a scene generator enters an array of nine actively controlled telescopes, and is combined at a focused image plane. This paper describes the algorithms used to automatically bring each telescope's relative tip/tilt and phasing errors to within the operational range of the control system. The algorithms work with point-sources as well as with extended scenes. Experimental results and software algorithms are presented.

The co-phasing detection method for sparse optical synthetic aperture systems

“…From its theoretical basis, it is seen that this method is new and different compared with some of the methods using far-field interferometry, such as the side-lopes information studied by Chanan et al, [18,19] the interferometric pattern studied by Zhao and Cao, [20] and also the one studied by Ni et al. [17] Furthermore, we build an optical setup to demonstrate the ability of this new method by using a sensitive micro-displacement sensor (SMDS) as the criterion. Experimental results show that the relative differences between the measurements of this method and the criterion are less than 4%, and the residual detecting errors are about 0.01 λ for different piston errors, which means that it may be used to perform co-phasing detection with enough accuracy and a valuable reference for relevant concerns.…”

“…[15−17] Horrobin et al [16] fitted the envelope of the far-field intensity (FFI) of a system using the Gauss function to calculate the piston errors from the envelope-removed fringes. Ni et al [17] proposed a method of combining the variations in the side lobe intensity of the module transfer function (MTF) and the symmetry of the point spread function (PSF) with the aid of a PD algorithm to analyse and detect the piston errors of the Star-9 system.…”

Experimental demonstration of enhanced resolution of a Golay3 sparse-aperture telescope

“…In the present Golay3 system, a manual mode is used in which some commands need to be sent to the actuators, while a research of an automatic closed-loop mode is also proceeding. The phasing approach operates in a two-system mode like STAR-9 [14] . We first close one of the horizontal two subsystems and let the upper one open as a reference.…”

“…With only two telescopes open, the tip-tilt is first corrected by controlling the active FSM to slightly adjust the two Airy disks to be superimposed upon each other. Then we use the symmetry measurement algorithm [14] to quantifiaby characterize the piston error. More details of the algorithm can be seen in reference [14].…”

“…Then we use the symmetry measurement algorithm [14] to quantifiaby characterize the piston error. More details of the algorithm can be seen in reference [14]. By commanding the modules of coarse and precision optical path adjustment the piston error becomes nearly zero, which means the open two subsystems are cophased.…”