An experimental study of wavefront correction for a heterodyne detection system for optical communication

Abstract

The turbulence effect is the most significant factor limiting the performance of coherent optical communication systems. In this paper, we report on wavefront correction for a coherent free-space optical communication system comprising a Shack–Hartmann wavefront sensor (SH-WFS), a deformable mirror, and a wavefront controller. With this system, distorted wavefronts of laser beams transmitted through the atmosphere can be corrected in real time. To demonstrate this real-time correction, we simulated atmospheric turbulence using phase screens of different intensities, based on a modified Hill spectrum. These laboratory-based simulations indicate that the peak-to-valley value obtained using the wavefront correction system in a closed-loop configuration can be reduced to less than 0.8 μm, the root-mean-squared error to less than 0.05 μm, and the Strehl ratio can be increased to greater than 0.8. Finally, the adaptive optics system described above was applied to a heterodyne detection system in an experiment investigating optical communication at a distance of 1.3 km, from which we were able to demonstrate real-time video transmission. The results of this experiment verified that a closed AO system can improve signal beam coupling power and increase the amplitude of the intermediate frequency signal, making the waveform of the baseband signal more ideal.