Coherent Combining at Ultra-low Optical Signal Powers based on Optically Amplified Error Feedback

Coherent combining in multi-aperture reception for free-space communication applications requires active phase alignment. Here, using 50/50-fiber-couplers and optically preamplified error feedback, coherent combining of four −80dBm, 10Gbaud QPSK signals is demonstrated with 95.4% efficiency. © 2022 The Author(s)