Wavefront Coherent Compensation Technology Under Direct Sunlight in Free Space Optical Communication System

Abstract

The charge-coupled device-based Shaker–Hartmann wavefront sensor has been widely used to compensate for wavefront distortion in coherent optical communication. However, the influence of strong background light causes large errors when restoring the signal light wavefront. This study proposes a wavefront recovery method by combining a detector array with an optical nutation of the local oscillator. By adding a small rotation angle to the local oscillator, the wavefront slope is estimated according to the output of the change law of the mixed signal and the local oscillator light, and the multi-order Zernike mode is used to reconstruct the signal light wavefront. Simulation studies show that the root-mean-square value (RMS) and the coherence efficiency of the signal light wavefront were significantly optimized. Under direct sunlight, the estimation compensation error of the wavefront slope reached 0.008. Under strong turbulence, the mixing efficiency was increased by nearly 97.5 times, and the RMS was reduced to the original value of 0.048 The designed system has good background light compensation and wavefront recovery capabilities and is suitable for coherent optical communication under direct sunlight.

Keywords

• Optical communication
• Atmospheric turbulence
• Shaker–Hartmann wavefront sensor