Electrically tunable space-time metasurfaces for steering of frequency-shifted light

We experimentally realize steering of frequency-shifted light up to +/-20° using gate-tunable space-time metasurfaces. To date, active metasurfaces have been employed to control scattered light properties at a fixed wavelength. Recently, there has been considerable interest in high-frequency temporal modulation to create beams at new output wavelengths from a single excitation wavelength. Our plasmonic indium tin oxide (ITO)-based metasurface operates at 1550 nm and features 32 independently addressable electrodes. By collectively driving the metasurface at frequencies up to 10 MHz, we first frequency-shift the reflected light by multiples of the driving frequency. Real-time optimization of the driving waveform allows the generation of desired spectra despite a nonlinear relationship between applied voltage and reflected light amplitude/phase. We then introduce incremental phase offsets between the driving waveforms applied to each electrode to superimpose a spatial phase gradient. The tangential momentum shift introduced through this configuration results in the steering of frequency-shifted light towards a target angle. Finally, we discuss how the proposed space-time metasurface can be used for multi-channel communication in next-generation optical communication and sensing applications.