Active phase locking of a three-aperture array using a corner cube lateral transfer reflector

We present a novel technique for coherent beam combining of a three-aperture array. In our method, a retroreflector samples the beam from the edge of each aperture and redirects the sampled beams back through the gap in the center. The sampled beams contain both angle and phase information for the three-aperture array, which can be used to lock the phase and tip/tilt. In a proof-of-concept experiment, we phase-lock the three-aperture array by maximizing the power through a pin hole of the far-field pattern of the sampled array via the stochastic parallel gradient descent algorithm. This approach eliminates the need for bulky sampling optics, which is particularly advantageous for the large-diameter arrays required for long distance inter-satellite free-space optical communication.