Fig. 1: Vision of an integrated spectrally-sliced photonic-electronic ADC, relying on a photonic-electronic signal processing engine.

The analogue electrical signal is translated into an optical signal by a front-end ultra-broadband electro-optic Mach-Zehnder modulator (MZM), which is fed by a continuous-wave external-cavity laser (ECL) providing an optical carrier at frequency f₀. The ECL consists of a reflective semiconductor optical amplifier (RSOA) and a Sagnac loop reflector that comprises a Vernier pair of tuneable ring resonators (MRR1, MRR2) and a thermally tuneable output coupler. One portion of the ECL emission is used to pump a Kerr frequency comb generator (FCG), which comprises a high-Q Si₃N₄ micro-ring resonator (MRR3), and which generates a Kerr soliton comb serving as a multi-colour local oscillator (LO). The other portion of the ECL emission is amplified by a semiconductor optical amplifier (SOA) or an erbium-doped waveguide amplifier (EDWA) before being sent to the MZM. The modulated output signal of the MZM is then routed to the photonic-electronic signal-processing engine via single-mode fibres (SMF). At the input of the engine, the optical signal is amplified and sent to a first integrated spectral processor (ISP1), which extracts the upper sideband at frequencies f > f₀, partially compensates the electro-optic response of the MZM, and then decomposes the signal into multiple spectrally sliced signal tributaries. A second integrated spectral processor (ISP2) is used to separate the multi-colour LO into individual phase-locked tones. The spectral slices of the signal are coherently detected using an array of M in-phase/quadrature receivers (IQR1, IQR2, …, IQRM), with the corresponding phase-locked comb tones serving as LO. The in-phase and quadrature components of the resulting electrical signals are digitised by an array of 2M synchronised low-speed electronic ADC that are connected via electric wire bonds (EWB) and then spectrally stitched together by a digital signal processor (DSP). This finally results in a digital representation of the reconstructed analogue input waveform. Inset: Illustration of the spectrally sliced photonic-electronic ADC in the spectral domain: Ⓐ Broadband analogue electrical input signal. Ⓑ The resulting optical signal is generated by modulating the broadband analogue electrical input signal onto an optical carrier prior to slicing into M tributaries by ISP1. Ⓒ Spectrally sliced signal tributaries with small overlap regions (OR) between neighbouring slices, generated at the output of ISP1. Ⓓ Spectrum of the frequency comb prior to slicing by ISP2. The selected tones are colour-coded according to the corresponding signal slices. Ⓔ Reconstructed spectrum of the analogue electrical input signal, obtained by merging the M spectral slices in the digital domain