Directional terahertz holography with thermally active Janus metasurface

Abstract

Dynamic manipulation of electromagnetic (EM) waves with multiple degrees of freedom plays an essential role in enhancing information processing. Currently, an enormous challenge is to realize directional terahertz (THz) holography. Recently, it was demonstrated that Janus metasurfaces could produce distinct responses to EM waves from two opposite incident directions, making multiplexed dynamic manipulation of THz waves possible. Herein, we show that thermally activated THz Janus metasurfaces integrating with phase change materials on the meta-atoms can produce asymmetric transmission with the designed phase delays. Such reconfigurable Janus metasurfaces can achieve asymmetric focusing of THz wave and directional THz holography with free-space image projections, and particularly the information can be manipulated via temperature and incident THz wave direction. This work not only offers a common strategy for realizing the reconfigurability of Janus metasurfaces, but also shows possible applications in THz optical information encryption, data storage, and smart windows.

Tunable VO2 cavity enables multispectral manipulation from visible to microwave frequencies

“…1b ). The phase transition leads to high contrast in its optical behaviors from VIS to MW regions, thereby endowing VO 2 with the potential for multispectral manipulation 22 – 27 . In the VIS region, the top VO 2 /HfO 2 /VO 2 /Si F-P cavity (TFP) enables the device to change reflective colors by adjusting resonant wavelengths during the phase transition.…”

Wide-angle camouflage detectors by manipulating emissivity using a non-reciprocal metasurface array

“…For practical purposes, radiation camouflage is more promising because the radiative properties can be modulated based on the surface characteristics, whether they are flattened, curved, smooth, rough or flexible. [19][20][21][22] It is possible to modulate the spectral, spatial, and polarization characteristics of thermal radiation, [23][24][25][26][27][28][29][30][31][32][33][34][35] using nanostructures such as photonic crystals, gratings, multi-layered structures, meta-materials, and metasurfaces. For all proposed nanophotonic camouflage designs, emissivity is required to be near zero in the atmospheric window (8 mm to 14 mm), which is transparent to radiation and prone to detection.…”

An Ultrathin, Fast‐Response, Large‐Scale Liquid‐Crystal‐Facilitated Multi‐Functional Reconfigurable Metasurface for Comprehensive Wavefront Modulation

“…As a viable alternative pathway, materials with tunable optical properties can be merged into passive resonator arrays. [22,23] By exploiting a diverse range of materials, including ferroelectric materials, [24] graphene, [25] semiconductors, [26] vanadium dioxide, [27,28] Ge 3 Sb 2 Te 6 , [28,29] nonlinear materials, [30] and indium-tin oxide (ITO), [31] dynamic phase modulation can be effectively controlled by magnetic fields, [24] bias voltages, [25] optical pumping, [27] or temperature [28] at the terahertz frequencies and optical wavelengths. However, it is imperative to recognize that transitioning of the material-enabled tuning strategy to the millimeter-wave band entails a set of distinct challenges.…”

“…Primarily, metasurfaces built upon optically tunable materials and photonic nanostructure platforms face inherent limitations pertaining to the active frequencies of specific materials as well as processing techniques that hinder their direct adaptation to the lower frequency bands. [26][27][28][29][30] Moreover, for the majority of the tunable materials, the required dedicated fabrication process and external biasing fields make them constrained to small-scale experimental samples [24,28,30,31] or necessitate a bulky control module, [24] limiting their practical usage for large-scale beamforming arrays.…”