Figure 5
Stretching and sampling of the 15.55 ps input pulse (60 GHz). The signal copies at the output of the ring resonator (green) are multiplied with a sinc pulse sequence (red) by convolution in the frequency domain with a nine-line frequency comb with Δfs = 12.23 GHz. For better visualisation, the pedestal was removed, the output copies were normalized to the one with the highest amplitude and the sampling pulses were multiplied with the corresponding normalization factor. Since the ring behaves equally for all input signals, this can be done by post-processing of the data. The sampling points (red diamonds) are retrieved by an integration of the sampling pulses over their repetition time. Due to limitations of the PLL, the sampling frequency was not close to the repetition rate of the replicas ΔfR = 18.774 GHz. Consequently, only every third copy could be sampled and every second sampling pulse is in the gap between two copies (small red lines). The stretched pulse is the envelope over the sampling points and has a stretching factor of ΔS = 44.
