Ultra-Stable Atmospheric Short Link for the Optical Frequency Signal Transfer

The 17 m open-air link for coherent transfer of ultrastable optical frequency signal have been demonstrated. The fractional frequency instability caused by air turbulence is suppressed by more than 3 orders of magnitude with the help of active noise compensation system and reaches 1.7∙10
^-19
after averaging time of 1000 s. The link contribution to uncertainty is decreased by more than 400 times and is equal to 5∙10
^-20
.