Figure 6

Sketch of the experimental setup for the zero distance measurement. The additional 1.1-m-long glass fiber in one of the fiber-based interferometer arms ensures a non-zero beat signal at zero distance. To measure the frequency at zero distance, we placed a mirror directly in front of the collimator, resulting in a measured beat signal of \(f_{\textrm{B}}=60\) MHz at \(t_{\textrm{chirp}}=130\) ns rise time. This corresponds to \(\Delta t=11\) ns time delay.