Amplified up-conversion of electromagnetic waves using time-varying metasurfaces

Abstract

Time-varying metamaterials and photonic time crystals offer a powerful route to wave amplification through temporal modulation of material parameters. Here, we experimentally demonstrate amplified up-conversion of free-space electromagnetic waves in the microwave regime, with conversion efficiency exceeding the limits imposed by the Manley-Rowe relations as a result of a cascaded amplification process. Using a time-varying metasurface composed of an array of varactor-loaded coupled split-ring resonators, we investigate parametric amplification, frequency up-conversion and wave generation. Direct measurements in both non-degenerate and degenerate regimes show that the Manley-Rowe limits can be surpassed near integer multiples of the incident wave frequency when the pump frequency is approximately twice that of the incident wave. These results establish time-varying metasurfaces as an efficient platform for amplification, generation, and frequency conversion of electromagnetic waves in the microwave and terahertz bands, with potential extension to optical frequencies via ultrafast modulation techniques.