Fig. 1. (a) Schematic of a single-channel (sub-sampled) PADC. E/O, electro-optical modulation; O/E, optical–electrical conversion; DSP, digital signal processor. (b) The output waveforms with different optical input powers. (c) The decrease of the OEC responsivity.

Fig. 2. Simulated and experimental results with or without time stretching to ultrafast optical pulses before and after photodetection. (a) and (b) are simulated temporal waveforms. (c) and (d) are experimental temporal waveforms.

Fig. 3. Experimental setups of (a) PMLL-based and (b) AMLL-based single-channel (sub-sampled) PADC systems. PMLL, passively mode-locked laser; AMLL, actively mode-locked laser; PC, polarization controller; MZM, Mach–Zehnder modulator; VOA, variable optical attenuator; PD, photodiode; EADC, electronic analog-to-digital converter.

Fig. 4. Measured variations of the digitized output power and RPADC with the increase of the optical input power with or without SMF stretching in (a) PMLL-based and (b) AMLL-based PADC systems.

Fig. 5. Experimental results of the ENOB before and after the time-stretching process in the (a) PMLL-based and (b) AMLL-based PADC systems.