Fig. 3: Characterization of the PE-AWG in an electrical back-to-back system, where the PE-AWG output is directly connected to a 100-GHz real-time oscilloscope.
As a performance metric, we use the SNDR estimated from received PAM symbols (SNDRPAM). a SNDRPAM penalty as a function of the LO-to-signal power ratio (LOSPR). The penalty is measured with respect to the optimum LOSPR of 14.5 dB and initially decreases with increasing LOSPR, because the residual signal-signal beat interference (SSBI) decreases. b Peak-to-peak voltage swing measured at the PE-AWG output as a function of the LOSPR. Since the electrical output power grows with decreasing LOSPR, a trade-off between output voltage swing and signal quality needs to be made. The yellow stars in Subfigures (a) and (b) correspond to the levels used in the subsequent measurements shown in Subfigures (d) and (e). c Simulated SNDRPAM penalty for BPD skews between 0 and 2 ps and for different LOSPR levels as indicated by the different colors. We find a SNDRPAM penalty of 0.9 dB for a LOSPR of 8 dB and a skew of 0.7 ps as specified for the BPD used in our experiments. We hence conclude that the skew results mainly from a path-length mismatch between the two fiber pigtails connected to the BPD, such that future integration of the PE-AWG can improve the SNDRPAM. d SNDRPAM levels achieved for generating PAM waveforms at various symbol rates with the PE-AWG and with several other waveform generators, comprising both commercially available AWGs2,4,7 as well as other research-type waveform generators21,60,61,62,63. Square markers refer to results obtained in electrical back-to-back measurements, whereas circular markers represent optical back-to-back experiments. In case of the PE-AWG, we compare the SNDRPAM for the case without and with an adaptive equalizer (L = 100 taps) used to remove residual inter-symbol interference, see the associated square markers with white filling and colored filling, respectively. The PE-AWG relies on Keysight’s AWG model M8194A (red star) and offers a signal quality that is on par with that offered by some commercially available waveform generators such as the Keysight M8199A or the Micram DAC5, while featuring a much higher usable bandwidth than these devices. At symbol rates beyond 140 GBd, the PE-AWG is only outperformed by Keysight’s most recent AWG model M8199B (green markers), which was not available as a signal source for our experiments at the time they were conducted. e Average voltage swing observed at the PE-AWG output for RRC pulses with a spectral roll-off of ρ = 0.05. We achieve decent voltage swings between 250 and 300 mVpp irrespective of the symbol rate.
