10 Gbps free-space laser communication link for ranging: phase measurement sensitivity through turbulent atmosphere

to enhance the measurement performance of satellite laser ranging (SLR) on an active satellite, we suggest utilizing a high-data-rate free-space laser communication (lasercom) link for time/distance measurement. As a demonstrator, a new laser ranging technique based on a 10 Gbps lasercom link is implemented to measure the propagation delay over a folded 2.5 km free-space path. In this document, we describe the measurement principle and the experimental setup to achieve a sensitivity of a few tens of fs from a 10 Gbps on-off keying (OOK) telecom signal generated by commercial telecom components. The high speed and high sensitivity of the ranging system make it possible to precisely characterize the timing jitter/drift caused by the atmosphere over 5.0 km. The sensitivity of the ranging system is validated through independent estimates obtained from turbulence monitoring instruments, including GDIMM (generalized differential image motion monitor) and a SHWFS (Shack-Hartmann wavefront sensor). For short time scales, fluctuations exceeding 350 fs rms were observed over integration times between 5 ms and 5 s, consistent with theoretical predictions derived from the turbulence structure parameter Cn2 and outer scale L₀ measured by GDIMM and the SHWFS. For long time ranges, > 1000 s, the variation of the propagation delay is dominated by the slow drift of the air refractive index and is in agreement with estimates based on the metrological parameters (temperature, humidity, pressure, CO₂ content) measured by two stations at two sites.