Nanoscale Nonlinear Circuit Elements at Optical Frequencies

We extend the concept of circuit elements at optical frequencies to include cubic nonlinearity. Based on the perturbation approach to compute the local field for a nonlinear three-dimensional inclusion embedded in a linear host, we extract the equivalent nonlinear impedance of a nanosphere. The results reveal an enhancement in the nonlinearity of the nanosphere due to the local field enhancement while a similar phenomenon was previously reported for composites with nanoparticle inclusions. We also introduce the nonlinear polarizability for a nanosphere. These results can be used in design of different nonlinear devices for optical applications.