Negative Kerr nonlinearity of graphene as seen via chirped-pulse-pumped self-phase modulation

TL;DR

This paper experimentally demonstrates that graphene exhibits a negative Kerr nonlinearity at telecom wavelengths, challenging previous assumptions, and introduces a versatile method for characterizing Kerr effects in novel materials.

Contribution

The study reveals the negative sign of graphene's Kerr nonlinearity and presents a new chirped-pulse-pumped self-phase modulation technique for characterizing Kerr effects.

Findings

Graphene's Kerr nonlinear index is approximately -10^(-13) m^2/W.

The negative Kerr nonlinearity contrasts with prior assumptions.

The method can be applied to other novel 2D materials.

Abstract

We experimentally demonstrate a negative Kerr nonlinearity for quasi-undoped graphene. Hereto, we introduce the method of chirped-pulse-pumped self-phase modulation and apply it to graphene-covered silicon waveguides at telecom wavelengths. The extracted Kerr-nonlinear index for graphene equals n2,gr = -10^(-13) m^2/W. Whereas the sign of n2,gr turns out to be negative in contrast to what has been assumed so far, its magnitude is in correspondence with that observed in earlier experiments. Graphene's negative Kerr nonlinearity strongly impacts how graphene should be exploited for enhancing the nonlinear response of photonic (integrated) devices exhibiting a positive nonlinearity. It also opens up the possibility of using graphene to annihilate unwanted nonlinear effects in such devices, to develop unexplored approaches for establishing Kerr processes, and to extend the scope of the "periodic poling" method often used for second-order nonlinearities towards third-order Kerr processes. Because of the generic nature of the chirped-pulse-pumped self-phase modulation method, it will allow fully characterizing the Kerr nonlinearity of essentially any novel (2D) material.