Frequency-domain parametric downconversion for efficient broadened idler generation

An opposite-chirped frequency-domain optical parametric amplification（OC-FOPA） design is demonstrated and numerically verified. This scheme combines both an ultrabroad seeding generation and the subsequent effective amplification in one single optical parametric amplification stage. Based on a slightly asymmetrical 4-f optical system, the spectral contents of both pump and signal waves are spectrally dispersed with opposite spatial chirps,to broaden the initial idler seeding. Via a properly designed fan-out periodically poled LiNbO3 chip, nearly perfect quasi phase matching can be realized across the full spectrum, whereby each individual spectral pair precisely maps to its required grating period. Full-dimensional simulations based on commercial 110 fs（FWHM） nearinfrared（near-IR） lasers at 790 and 1030 nm are quantitatively discussed, and few-cycle mid-IR laser pulses（60 fs at 3.4 μm） plus a high conversion efficiency exceeding 50% are theoretically predicted. By means of a high-power pump source, the OC-FOPA scheme can be also applied to directly produce high-intensity carrier-envelope-phase-stabilized mid-IR idler pulses.