Theoretical Analysis of Spectral Broadening Through Saturable Photoexcited-Carrier Refraction in Graphene-Covered Nanowires

We perform a thorough study of the spectral broadening of short and intense pulses propagating in graphene- covered nanowires departing from a saturable photoexcited-carrier refraction (SPCR) model. In particular, we put forth an analytical expression for the instantaneous frequency of the traversing pulse, in a relevant limiting case, which allows to calculate the spectral broadening and frequency shift experienced by the pulse and elucidate the role of its initial chirp. Most interestingly, both the spectral broadening and frequency shift are found to be maximized for an optimal input power. In all cases, results from analytical expressions are found to be in excellent agreement with numerical solutions of the propagation equations.