Fiber coupling efficiency analysis of free space optical communication systems with holographic modal wave-front sensor

•Holographic modal wave-front sensor (HMWFS) is used in free space optical (FSO) communication systems.•HMWFS has advantages of its fast detecting rates and insensitivity to beam scintillation.•For HMWFS, the phase information can be extracted from the relative intensity of pairs of focal spots, rather than complex calculation.•After aberrations correction, the fiber coupling efficiency of FSO communication systems is increased from nearly 30% to more than 70%.

Degradation of fiber coupling efficiency, caused by atmospheric turbulence, seriously hinders the performance of free space optical (FSO) communication systems. Holographic modal wave-front sensor (HMWFS), noted for its fast detecting rates and insensitivity to beam scintillation, is creatively applied to FSO communication systems in this paper. We analyze the principle of HMWFS and the relationship between fiber coupling efficiency and Strehl rate in theory, then simulate wave-front aberrations detection and correction in FSO communication systems. Additionally, the impact on fiber coupling efficiency of the FSO communication systems before and after aberrations correction based on HMWFS is fully discussed. The results show that HMWFS cater for weak atmospheric turbulence with the root-mean-square (RMS) value of residual aberrations less than 0.04λλ and the peak-to-valley (PV) value less than 0.25λλ, while the fiber coupling efficiency is increased from nearly 30% to more than 70%.