Giant controllable gigahertz to terahertz nonlinearities in superlattices

Optical nonlinearities are of perpetual importance, notably connected with emerging new materials. However, they are difficult to exploit in the gigahertz-terahertz (GHz-THz) range at room temperature and using low excitation power. Here, we present a clear-cut theoretical and experimental demonstration of real time, low power, room temperature control of GHz-THz nonlinearities. The nonlinear susceptibility concept, successful in most materials, cannot be used here and we show in contrast, a complex interplay between applied powers, voltages and asymmetric current flow, delivering giant control and enhancement of the nonlinearities. Semiconductor superlattices are used as nonlinear sources and as mixers for heterodyne detection, unlocking their dual potential as compact, room temperature, controllable sources and detectors. The low input powers and voltages applied are within the range of compact devices, enabling the practical extension of nonlinear optics concepts to the GHz-THz range, under controlled conditions and following a predictive design tool.