Zernike mode analysis of an adaptive optics system for horizontal free-space laser communication

Abstract

Free-space laser communication (FSLC) has attracted wide attention and developed rapidly due to its high bandwidth and strong capability to resist interception and interference. However, communication performance is severely affected by atmospheric turbulence. In this paper we consider the end face of the coupling fiber and adopted power-in-the-bucket (PIB) as the evaluation criterion instead of the traditionally used coupling efficiency. The relationship between FSLC performance (PIB) and adaptive optics parameters (corrected Zernike modes number) is derived for the first time. We simulated and conducted an 8.9 km horizontal FSLC experiment to analyze the effects of corrected modes on communication performance. The simulation and experiment results consistently show that, for turbulence of r0 = 7.51 cm, it is sufficient to correct the first 30 modes. The bit error rate (BER) and the PIB reached values of about 10−7 and 70%, respectively. For r0 = 4.43 cm correction of the first 22 modes, yielded BER and PIB values of around 10−5 and 55%, respectively. For r0 = 1.7 cm, no matter how many Zernike modes are corrected, the BER and PIB values are about 10−3 and 20% respectively. This experiment and its results provide an important reference for corrected modes on communication performance under different turbulence strengths.