Nonlinear spectral-temporal manipulation for chirp-free pulse synthesis at picosecond resolution

We present a novel, to our knowledge, optical arbitrary waveform generation (OAWG) technique, termed four-wave optical-waveguided chirp-free ultrafast shaping (FOCUS), which utilizes four-wave mixing (FWM)-based spectral transcription. FOCUS enables the generation of chirp-free pulse sequences with independently adjustable duration, intensity, interval, and central wavelength of sub-pulses. Experimental validation demonstrates that the system achieves a 2 ps temporal resolution and a 400 ps record length while maintaining <1 nm spectral bandwidth, >30 dB extinction ratio, ∼1 nJ pulse energy consumption, and 3.5 nm continuous wavelength tunability. Fundamental analysis reveals that three key parameters govern temporal resolution: spectral shaper resolution (the current limiting factor), pump bandwidth (potentially expandable to 30 nm), and engineered group delay dispersion (GDD). Recent advancements in chip-scale mode-locked lasers, dispersion-engineered waveguides, and nonlinear FWM modules position the FOCUS platform as a promising candidate for next-generation ultrafast photonic systems designed for simultaneous sub-picosecond temporal resolution and nanosecond-scale waveform programmability within compact integrated architectures.