Optically controlled dielectric metasurfaces for dynamic dual-mode modulation on terahertz waves

Dynamically controlling terahertz(THz)waves with an ultracompact device is highly desired,but previously realized tunable devices are bulky in size and/or exhibit limited light-tuning functionalities.Here,we experimentally demonstrate dynamic modulation on THz waves with a dielectric metasurface in modeselective or mode-unselective manners through pumping the system at different optical wavelengths.Quasi-normal-mode theory reveals that the physics is governed by the spatial overlap between wave functions of resonant modes and regions inside resonators perturbed by pump laser excitation at different wavelengths.We further design/fabricate a dielectric metasurface and experimentally demonstrate that it can dynamically control the polarization state of incident THz waves,dictated by the strength and wavelength of the pumping light.We finally numerically demonstrate pump wavelength-controlled optical information encryption based on a carefully designed dielectric metasurface.Our studies reveal that pump light wavelength can be a new external knob to dynamically control THz waves,which may inspire many tunable metadevices with diversified functionalities.

Dynamically controlling terahertz wavefronts with cascaded metasurfaces

Dynamically controlling terahertz(THz)wavefronts in a designable fashion is highly desired in practice.However,available methods working at microwave frequencies do not work well in the THz regime due to lacking suitable tunable elements with submicrometer sizes.Here,instead of locally controlling individual meta-atoms in a THz metasurface,we show that rotating different layers(each exhibiting a particular phase profile)in a cascaded metadevice at different speeds can dynamically change the effective Jonesmatrix property of the whole device,thus enabling extraordinary manipulations on the wavefront and polarization characteristics of a THz beam impinging on the device.After illustrating our strategy based on model calculations,we experimentally demonstrate two proof-of-concept metadevices,each consisting of two carefully designed all-silicon transmissive metasurfaces exhibiting different phase profiles.Rotating two metasurfaces inside the fabricated devices at different speeds,we experimentally demonstrate that the first metadevice can efficiently redirect a normally incident THz beam to scan over a wide solid-angle range,while the second one can dynamically manipulate both the wavefront and polarization of a THz beam.Our results pave the way to achieving dynamic control of THz beams,which is useful in many applications,such as THz radar,and bio-and chemical sensing and imaging.