Temporal walk-off induced dissipative quadratic solitons

A plethora of applications have recently motivated extensive efforts regarding the generation of Kerr solitons and coherent frequency combs. However, the Kerr (cubic) nonlinearity is inherently weak. By contrast, strong quadratic nonlinearity in optical resonators is expected to provide a promising alternative means for soliton formation. Here we demonstrate dissipative quadratic soliton formation via non-stationary optical parametric amplification in the presence of pronounced temporal walk-off between pump and signal, leading to half-harmonic generation accompanied by a substantial pulse compression (exceeding a factor of 40) supported at low pump pulse energies (~4 pJ). The quadratic soliton forms in a low-finesse cavity in both normal and anomalous dispersion regimes. We present a route to considerably improve the performance of the demonstrated quadratic soliton when extended to an integrated platform to realize highly efficient extreme pulse compression, leading to the formation of few-cycle soliton pulses starting from ultra-low-energy picosecond-scale pump pulses.