Recently, the laser communication team from the Institute of Optics and Electronics (IOE) of the Chinese Academy of Sciences (CAS) has applied adaptive optics (AO) technology to geosynchronous orbit coherent optical communication experiment.  

For a long time, the atmospheric turbulence effect of the star-ground link has caused signal beam wavefront distortion, spot dispersion and jitter, which affect the reception of ground signal light energy, especially the single-mode fiber reception of coherent laser communication. In order to achieve high-speed, high-reliability satellite-to-ground laser communication, the problem of atmospheric turbulence interference must be solved. 

Fig. 1. Schematic diagram of laser communication AO correction system (Image by IOE) 

In response to the problem of atmospheric turbulence suppression in laser communications, the laser communication team took lead in carrying out research on AO technology for laser communications in China.

They solved the technical problems such as atmospheric dynamic wavefront high-precision correction, high-efficiency space light to single-mode fiber coupling and so on. Since 2012, they have developed multiple sets of large-diameter laser communication AO ground stations. 

Now, the team applies AO technology to geosynchronous orbit coherent optical communication experiment.

Under the medium strong atmospheric turbulence intensity, the wavefront distortion and beam jitter of the satellite downlink signal beam are significantly suppressed after adaptive correction. The tracking accuracy is superior to submicron arc level, and the wavefront accuracy is better than λ / 10, both of them ensure high efficient coupling of space light to single-mode fiber.

After adaptive optics correction, the average receive power of single-mode fiber has increased from 0.2 NW to 4.8 NW, which has significantly improved the SNR of coherent receiver. 

Figure 2. Received power of single-mode fiber before and after AO correction (Image by IOE)