Figure 1. Time-domain synthesis of RF waveforms using a Si photonic chip.

(a) Schematic of the time-domain synthesis method where a femtosecond laser pulse is replicated, delayed and recombined through an eight-channel Si pulse shaper. In the spectrum representation of the input pulse, wavelength components that correspond to different resonances of a replica generation microring are labelled using the same colour, and are downloaded by that same microring from the input waveguide to form a channel replica pulse. The eight pulse replicas experience various tuneable delay and are separated in the time domain. The amplitude of each pulse replica can be adjusted during the recombination process by mismatching the resonance of the recombination microring against that of the replica generation ring. Finally, the properly delayed and scaled replicas are recombined at the common output port of the shaper to form the desired optical waveform. An off-chip photodetector detects the envelope of the output optical waveform, producing the synthesized RF waveform. The inset schematically shows the mechanism of the thermally tuneable optical delay lines. FSR, free spectral range of a microring. (b) An optical image of a fabricated pulse shaper. (c,d) Experimental demonstrations of ~27 ps delay tuning and complete amplitude control of a channel replica pulse without appreciably affecting the pulse from an adjacent channel.