Single Sideband Suppressed Carrier Modulation With Spatiotemporal Metasurfaces at Near-Infrared Spectral Regime

Single sideband suppressed carrier (SSB-SC) modulation enables high efficiency and dispersion-tolerant shifting of light that is of great interest for many optical systems and applications. Herein, the design procedure of a spatiotemporal reflective metasurface is proposed to realize SSB-SC modulation in near-infrared spectral regime. The metasurface consists of a periodic array of plasmonic nanostrips integrated with indium-tin-oxide (ITO) in metal-insulator-metal configuration, wherein two sets of time-varying biasing signals are independently applied to the metasurface for modulating the permittivity of ITO in space and time. The spatiotemporal metasurface features a sawtooth phase profile with linear span over 2\pi and a constant amplitude in time domain, that can be obtained by judicious adjustment of the biasing waveforms. It is established that such spatiotemporal metasurface allows for spurious-free frequency conversion by transforming the incident signal into the first-order up-modulated sideband and suppressing all the undesired mixing products. The normalized conversion efficiency of more than 99% is achieved for the metasurface, while the peak levels of the largest undesired mixing product and the fundamental frequency are reduced down to -39 dB and -44 dB, respectively. The proposed spatiotemporal metasurface is exploited for multi-channel and multi-beam scanning via pixelated control over the modulation phase delays assigned to the constituent elements of the spatially-interleaved sub-arrays, rendering a shared-aperture metasurface in space-time. In this case, the crosstalk between the channels with identical operating frequencies is substantially reduced. In addition, spatiotemporal redirection of light based on frequency gradient metasurface is demonstrated, which enables ultrafast, all-angle, and continuous beam-scanning as progressing in time.