High-efficiency real-time waveform modulator for free space waves based on dispersion engineering of spoof surface plasmon polaritons

Limited by causality, strong dispersion is always accompanied by a high loss for natural materials, so it is very hard to obtain strong dispersion simultaneously with low loss in a narrow band. The nonlinear dispersion curve of spoof surface plasmon polaritons (SSPPs) provides rich potential for dispersion engineering. By tailoring the asymptotic region of the SSPP dispersion curve, a good compromise can be made between strong dispersion and low loss to obtain a dispersive group delay time (GDT). With a delicate GDT design, signals in the free space can be modulated intentionally with high efficiency. As an example, we demonstrated a waveform modulator operating in an X band. Both the simulation and experiment show that the modulator can produce time delays that are linearly dependent on frequency in a 50 MHz frequency band. Our finding may have applications in radar invisibility, analog signal processing, etc.