The two data sets contain time series which were determined in measurements evaluating the performance of an optical frequency transfer via frequency combs.
The experiment and the physical background is discussed in a publication entitled "End-to-end topology for fiber comb based optical frequency transfer at
the $10^{-21}$ level" in Optics Express, which cites these data sets. Furthermore, a preprint can be found at arXiv:1910.04261
There are two data sets, one for the NCP setup and one for the CP setup discussed in this manuscript. The files are UTF-8 encoded text files with
tabulator-separated values in two columns. The first line is a header line, the following lines contain the time series data. The first column is the time
in seconds since the beginning of the measurement. The second column is a fractional frequency ratio difference. These are pre-processed measurement data.
The pre-processing steps consist in processing beat frequency data, which where measured using K&K FXE80 dead-time-free frequency counters in \Lambda-mode
with a report time of 1s. In a first step, invalid data are identified and marked as invalid (e.g. if cycle slips occurred in phase-locked loops in the
experiment). This results in gaps, i.e. the time stamps are in principle on 1s grid, but there can be periods without data longer than 1s.
In the second step, several beat frequency data are processed according to equation (2) in the mentioned publication, yielding the fractional frequency
ratio difference y_{DUT-ref} between the reference and DUT frequency transfer system.
Statistical properties, like e.g. the mean value, linear drift, power spectral density, Allan deviation, modified Allan deviation, etc. can be derived
from the y_{DUT-ref} time series.