Optical Kerr nonlinearities play an important role in applications such as all-optical switching, ultrafast sensing and quantum computation. Unfortunately, natural optical materials usually possess only small intrinsic nonlinearities; noble metals exhibit fast and large nonlinear optical response but they are strongly absorbing. We propose a method of obtaining large optical nonlinearities using epsilon-near-zero (ENZ) metamaterial structures. We take an advantage of the fact that while the linear part of permittivity vanishes, the effective nonlinearity is dramatically enhanced.
We demonstrate an experimental realization of a ENZ metamaterial, composed on alternating layers of dielectric (silica) and metal (silver), using the electron beam evaporation technique. The thicknesses of the layers (70nm of silica and 5nm of silver) are optimized for obtaining the vanishing value of the real part of the homogenized permittivity at the wavelength of 785 nm.
To characterize the nonlinear response of our ENZ samples we resort to the z-scan technique. The measured Kerr coefficients are one order of magnitude larger then the values given by a simple averaging of nonlinear coefficients of the composition materials. Additionally, the measured value of the Kerr coefficient is found to be of the same order of magnitude as that of a single 40nm-thick silver layer. However, the transmission of such a thick silver layer is ten times smaller than the transmission of our ENZ nanostructure.