Fig. 4: Experimental setup of our OAWG transmission experiment and exemplary measurement results taken at various points Ⓐ...Ⓕ.

The transmitter comb (Tx comb, Point Ⓐ) is generated by modulating a CW tone emitted by an external-cavity laser (ECL). The resulting Tx comb is amplified by an erbium-doped fiber amplifier (EDFA), and individual tones \(f_{1}, \,f_{2}, \,f_{3},\, f_{4}\) are selected by a wavelength-selective switch (WSS) to serve as carriers for IQ modulation. The drive signals for the IQ modulators (IQM1,..., IQM4) are calculated by offline digital signal processing (DSP) and generated by a DAC array (Keysight M8194A) that is RF-synchronized to the Tx comb generator. A phase-stabilizing signal-combining tree (SCT) combines all tributaries, Point Ⓑ, thus forming the output waveform \({\underline{a}}_{{\rm{S}}}(t)\), Point Ⓒ. The generated waveform is measured by a two-channel non-sliced OAWM receiver—either directly (upper position of switches S1 and S2) or after transmission through an 87 km-long fiber link (lower switch positions). The OAWM system uses two IQ receivers (IQRs) that are fed by the received waveform and by time-delayed copies of the Rx comb, comprising two tones (LO1, LO2, Inset Ⓓ) derived from a dissipative Kerr soliton (DKS) comb. The photocurrents of the IQRs are digitized by an ADC array (Keysight UXR series oscilloscope) and are used to reconstruct the received waveform via the OAWM DSP, Point Ⓔ. The reconstructed waveform is then demodulated (Demod. DSP) to retrieve the transmitted data, Point Ⓕ. Inset Ⓐ: Optical spectrum of Tx comb. Note that the displayed spectral width of the individual comb-tones is dictated by the rather large resolution bandwidth (RBW) of the spectrum analyzer that was used for the measurement (RBW = 2.48 GHz). Inset Ⓑ: High-resolution (RBW = 100 MHz) optical spectra of individual the tributary signals. Inset Ⓒ: High-resolution (RBW = 100 MHz) optical spectrum of 320 GBd 16QAM signal. Inset Ⓓ: Optical spectrum of the Rx comb (RBW = 2.48 GHz) that is used for OAWM. Inset Ⓔ: Spectrum of reconstructed 320 GBd 16QAM waveform obtained from the OAWM receiver in the optical back-to-back configuration (RBW = 100 MHz). Inset Ⓕ: Constellation diagram and constellation signal-to-noise ratio (CSNR) for an exemplary 320 GBd 32QAM signal measured in back-to-back configuration