Avoiding aliasing in fiber link data analysis

A basic rule in signal analysis is to use an antialiasing filter before data decimation. Surprisingly, this fundamental rule is often missed in time and frequency community and this leads to problems when data are analyzed. They are particularly evident in case of fiber links, especially when the Allan variance is calculated. Here, we show that aliasing can be induced by the measurement instrument and, more subtly, by the variance algorithm itself. By properly setting the anti-aliasing filter, this problem can be eliminated. As an example, we apply this method to the experimental data we obtained on the 1284 km Italian coherent optical link.