Phys. Rev. A 85, 031806(R) (2012)

The effects of nonlinear periodic structures on the temporal behaviour of optical pulses are not well understood, and measurements so far have not taken into account the phase dynamics of the pulse. Now, using frequency-resolved optical gating measurements based on second-harmonic generation, Darren Hudson and co-workers from the USA and Canada have studied the impact of nonlinear waveguide arrays on the full electric field of an ultrashort pulse as a function of both input chirp and average power. They experimentally showed that, at a sufficiently high peak power (24 mW), the chirp and average power of an ultrashort pulse after propagating through a 6-mm-long nonlinear waveguide array can be independent of the input chirp and power. In particular, increasing the average power of the input pulses moves the attraction towards an average fixed output power of 4.55 mW and a chirp of 16,600 fs2, which, interestingly, occurs for both normal and anomalous input chirp. The researchers attribute this effect — which they classify as a phase-space fixed-point attractor involving intensity and chirp — to the interplay between dispersion and temporal reshaping of the pulse. The findings allow a pulse to be shortened and dechirped without detailed knowledge of the input pulse, which may be of use in telecommunications.