Multi-aperture digital coherent combining for next-generation optical communication receivers

Space terminals for free-space optical communication systems are under constant pressure to reduce their size, weight, and power profiles. Ground terminals with large collection areas are costly, but provide a means to reduce the aperture-power product on a space platform required to close a given link. We present a ground terminal receiver architecture in which many small apertures are coherently combined while maintaining excellent receiver sensitivity. This is accomplished via coherent detection behind each aperture followed by digitization. The digitized signals are then combined in a digital signal processing chain. Experimental results demonstrate lossless coherent combining of low-flux lasercom signals.