Finite-difference time-domain numerical study of ultrashort pulse propagation across sub-micron scale distances in Al:ZnO/ZnO at the epsilon near-zero spectral point

Abstract

The epsilon-near-zero (ENZ) spectral region in metamaterials has shown unique opportunities for enhancing light-matter interactions, particularly due to the large variation of dielectric permittivity over a small frequency range. In this work, ultrashort pulse propagation at the ENZ point is investigated using both the split-step method approach to solving Nonlinear Schrodinger’s equation (NLSE) and the one-dimensional finite-difference time-domain (FDTD) method. We use an estimation for chromatic dispersion at the ENZ for the NLSE, and low input powers for the initial pulse to minimize nonlinearities for both methods. The permittivity for the AZO/ZnO structure was varied only in the AZO layer, which we estimated using Drude model. We found that the damping frequency, γ, in the Drude model has the most influence on pulse shaping during propagation as it relates to losses within the material. Results from our 1D FDTD simulations have shown soliton-like behavior for incoming ultrashort pulses with duration 100 fs in the ENZ region up to 300 nm lengths for γ = 1x1011 and 1x1012 Hz.