## 4 Experimental Results  
We conducted an in-depth study using the system developed in this research and performed the first-ever ground-based ultra-long-distance atmospheric optical communication experiment over 100 km/100 Gbps in the Qinghai Lake region, China. Prior to this, we also conducted numerous near-field outdoor experiments to verify the effectiveness of our system. Although the Qinghai Lake area is at a high altitude, with atmospheric particle concentrations much lower than at lower altitudes, it is important to note that ultra-long-distance atmospheric optical communication experiments still face severe atmo  
Figure 5: Schematic of scanning trajectory.  
spheric turbulence, which significantly impacts the laser energy coupling efficiency. Our system does not include any turbulence compensation systems, such as adaptive optics. However, to validate our laser scanning capture, we can perform this verification at any time of the day. To demonstrate the 100 Gbps high-speed optical communication, we chose the time window with the lowest atmospheric turbulence intensity during the day for the communication experiment.  
When the signal light spot emitted by the staring terminal is detected on the scanning terminal's CCD camera, an image is recorded, and the position of the spot is tracked in real-time. The position of the spot on the detector is adjusted by manually adjusting the PAT terminal and fine-tracking fast mirrors, so that the spot is positioned at the location with the highest fiber coupling efficiency. Figure 6 shows the images of the light spot received under weak, moderate, and strong turbulence conditions. Under weak turbulence, the laser power coupling efficiency is approximately 10%, whereas under strong turbulence, the laser power coupling efficiency is less than 1%.  
We used a high-speed optical power meter with a sampling frequency of 1 kHz to statistically measure the received laser energy under weak turbulence, and the results are shown in Figure 7. From the figure, it is clear that, under favorable atmospheric link conditions, the maximum optical power coupled to the scanning terminal through the optical system is \(-\)34.24 dBm, the minimum optical power is \(-\)50.23 dBm, and the average optical power, calculated from the statistics, is \(-\)40.31 dBm, which achieved the expected ideal result. Under these power coupling conditions, 112 Gbps atmospheric optical communication was achieved in the Qinghai Lake area, with the optimal bit error rate (BER) of 3E-3.  
Although the current experiment utilized a 10 W transmitter in a controlled, remote environment, practical deployment mandates adherence to international laser safety standards. The beam's narrow divergence (65 \(\upmu\)rad) ensures rapid power density attenuation: at 1 km, the spot diameter expands to \(\sim\)6.5 cm, reducing power density to \(<\)1.5 mW/cm\({}^{2}\) (far below the IEC 60825-1 Class 1 limit of 10 mW/cm\({}^{2}\) for 1550 nm lasers). This inherently safe design eliminates public exposure risks under normal operation. For additional safeguards, we propose integrating real-time LiDAR-based intrusion detection (triggering beam shutdown within 50 ms) and deploying transceivers in restricted-access zones (e.g., rooftop towers) with public hazard signage. Compliance with IEC 60825-1 certification will further ensure operational safety across all scenarios.  
Figure 6: Received spot images under different turbulence intensities. (**a**) Weak turbulence spot image; (**b**) Moderate turbulence spot image; (**c**) Strong turbulence spot image.