Multi-aperture fiber coherent combining system in urban horizontal laser link

摘要

Multi-aperture receiver with optical combining architecture is an effective approach to overcome the turbulent atmosphere effect on the performance of the free-space optical (FSO) communications. In this paper, we built a 1 km urban horizontal link, and adopted beam combining system with four apertures at receiver. By analogy with aperture smoothing factor, we proposed the concept of fluctuation suppression ratio to evaluate the mitigation ability of the system on atmospheric fading. The experimental results confirmed that the beam combining system can perform best when the aperture interval is larger than the coherent length, and the performance decreases with the increase of the coherent length. Moreover, we found that the change of phase differences between the input beams is more than 40 pi rad, which provides reference for future system design.