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Based on the multi-beam propagation theory, a mathematic model of log-intensity fluctuation variance under multi-beam propagation in slant path atmospheric turbulence near the ground for free-space optical communication is established. Taking single beam, double beam, three beam, and four beams as examples, the intensity fluctuation characteristics of single beam and multi-beam are obtained, and the relationship between the log-intensity fluctuation and the bit error rate (BER) of the heterodyne detection coherent optical communications based on binary phase shift keying modulation is deduced. The results show that, with the increase of beam number, the variance of signal log-intensity fluctuation is significantly mitigated, and the BER of the system is significantly reduced. It proves that the multi-beam propagation method can be effectively applied to the long-distance coherent optical communications, and improve the performance of the system.

Free-Space Optical (FSO) based data center(DC) wireless links are often out of alignment in conventional FSO-based DC architectures due to DC rack vibrations. In order to overcome this problem, this paper proposes a new method, the method adopts adaptive laser beam divergence angle, which change the receiver beam coverage to reduce the requirements of high precision alignment through the adaptive adjustment of the laser beam divergence angle, and compensates the wireless optical link misalignment. This method does not require complex acquisition, tracing and pointing(ATP) mechanism, and has the advantage of low equipment and management cost and easy implementation.Finally, the effect of divergence angle on the performance of wireless optical communication link is analyzed by numerical simulation, and the relationship between the optimal beam divergence angle and the pointing error angle caused by rack vibrations is obtained.

Flexible and reconfigurable communication networks are an important part of an efficient data center. This paper proposes a reconfigurable wireless optical communication link system based tunable laser suitable for connecting data center communication networks. The link system consists of a tunable laser, an optical system, a reflecting mirror, and a photoelectric detection module. A tunable laser that emits multiple wavelengths of laser beams and the corresponding optical system realizes large-angle coverage of the optical link, and at the receiving end, the optical link between different users is constructed by selecting different wavelengths through a band-pass optical filter, realizing flexible, reconfigurable wireless optical communication link system.

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