研究目的
To overcome the turbulent atmosphere effect on the performance of the free-space optical (FSO) communications using a multi-aperture receiver with optical combining architecture.
研究成果
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. The change of phase differences between the input beams is more than 40 ??rad, providing reference for future system design.
研究不足
The performance of the beam combining system deteriorates with the increase of the coherent length. The theoretical value deviation of the coherence coefficient is too large when the coherence distance is small.
1：Experimental Design and Method Selection:
A 1 km urban horizontal link was built, and a beam combining system with four apertures at the receiver was adopted. The concept of fluctuation suppression ratio was proposed to evaluate the mitigation ability of the system on atmospheric fading.
2：Sample Selection and Data Sources:
The light intensity of each aperture coupled into the fiber and the final output after the beam combining system were measured. The sampling time was 20 s and the sampling frequency was 1 MHz.
3：List of Experimental Equipment and Materials:
A commercial boundary layer scintillometers (Scintec BLS450) was used for turbulence characterization. The system included four apertures with adjustable positions, fiber phase shifters, and a combining module with distributed cascade architecture.
4：Experimental Procedures and Operational Workflow:
Experiments were repeated over multiple periods of the day at three different aperture array intervals. The whole process was finished in 2–3 min.
5：Data Analysis Methods:
The scintillation index and fluctuation suppression ratio were calculated to evaluate the system's performance.
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