The concept of an adaptive receive telescope array (RTA) for coherent optical space communications is presented. The RTA consists of N=2, e.g. 16, subtelescopes, N polarization-maintaining single-mode fibers, N optical phase actuators, a binary tree of N-1 symmetrical polarization-maintaining directional couplers, N-1 optical power sensors, and a digital control unit. The output interface, a polarization-maintaining single-mode fiber, can be efficiently coupled to a subsequent coherent receiver. Within a subtelescope's field-of-view, the control unit adapts the subtelescope phases (pistons) to the direction of the incident wavefront, thus maximizing the strength of the optical output field. The RTA is transparent, i.e. it operates independently of the modulation format employed. The feasibility of the RTA concept was demonstrated in a laboratory experiment. The implemented four-aperture antenna operates at a wavelength of 1064nm. At an optical power level of 1nW per subaperture, the experimental system combines the optical input signals with an efficiency greater than 99%. A step-shaped change of input wavefront direction is automatically compensated within 1ms.
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