Fig. 4: IM/DD fiber-optic transmission experiment using the PE-AWG as an electrical signal source.

a Experimental setup. The broadband electrical waveforms generated with the PE-AWG are used to drive an optically packaged thin-film LiNbO₃ MZM³¹ for intensity modulation of an optical carrier. The optical waveform is transmitted over 10.5-km of standard single-mode fiber (SSMF) followed by a dispersion-compensating fiber (DCF) of appropriate length. A 100-GHz PD is used to detect the received signal, and a 100-GHz oscilloscope records the resulting electrical waveform. EDFAs are used to compensate for optical losses in the setup and to adjust the input power at the receiver. b Illustration of the transfer function of the MZM and of the used operation point (yellow dot). We operate close to the minimum-transmission point (null point) to reduce the carrier-to-sideband ratio of the resulting optical data signal. c Double-sided optical spectrum measured after the DCF for a 190-GBd PAM4 signal with an overall optical bandwidth that essentially corresponds to the full symbol rate. The slight asymmetry of the spectrum is caused by the inclined gain profile of the last EDFA in the fiber link. d BER vs. symbol rate for the IM/DD experiment. For OOK, we measure BER levels below the 7% hard-decision FEC limit even at a symbol rate of 200 GBd. For PAM4, the BER for 190 GBd is still below the BER threshold for soft-decision FEC with a 15% overhead. The inset shows an exemplary eye diagram obtained for a 190-GBd PAM4 waveform, obtained by 20-fold up-sampling of the demodulated signal and by applying an interpolation filter with RC-type spectrum. The inset further shows the histogram evaluated at the center of the eye.