Frequency-modulated continuous waves controlled by space-time-coding metasurface with nonlinearly periodic phases

Abstract

The rapid development of space-time-coding metasurfaces (STCMs) offers a new avenue to manipulate spatial electromagnetic beams, waveforms, and frequency spectra simultaneously with high efficiency. To date, most studies are primarily focused on harmonic generations and independent controls of finite-order harmonics and their spatial waves, but the manipulations of continuously temporal waveforms that include much rich frequency spectral components are still limited in both theory and experiment based on STCM. Here, we propose a theoretical framework and method to generate frequency-modulated continuous waves (FMCWs) and control their spatial propagation behaviors simultaneously via a novel STCM with nonlinearly periodic phases. Since the carrier frequency of FMCW changes with time rapidly, we can produce customized time-varying reflection phases at will by the required FMCW under the illumination of a monochromatic wave. More importantly, the propagation directions of the time-varying beams can be controlled by encoding the metasurface with different initial phase gradients. A programmable STCM prototype with a full-phase range is designed and fabricated to realize reprogrammable FMCW functions, and experimental results show good agreement with the theoretical analyses.

Computation at the speed of light: metamaterials for all-optical calculations and neural networks

“…Work on such devices has recently been undertaken in the microwave regime 193 , 194 and programming metasurfaces through the power of touch, 195 as well as examples of spatiotemporal functionality 196 – 201 Limitations related to controlling and aligning metasurfaces down to the meta-atom level at shorter wavelengths hinder the progress of fully optical ONNs working at visible wavelengths. However, the standard working wavelengths of LiDAR lie in the near-infrared region, possibly easing such intricate fabrication and control constraints, as well as opening the door for the inclusion of tunable materials such as ITO and GST.…”

Radar Micro‐Doppler Signature Generation Based on Time‐Domain Digital Coding Metasurface

“…With the rapid advance of digital coding metasurfaces, [ 10 ] it became possible to realize direct information modulations onto the radio‐frequency (RF) signals. As revealed by recent studies, [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ] when the digital coding metasurfaces are further modulated periodically in time, a set of nonlinear harmonics can be generated in the reflected spectrum. Owing to the ability of spectrum manipulations, time‐domain digital coding metasurfaces (TDCMs) have opened up a number of remarkable applications such as nonreciprocal effect, [ 11 , 12 , 13 , 16 ] harmonic controls, [ 14 , 15 ] efficient frequency conversion, [ 17 ] and nonlinear information modulations.…”

“…Owing to the ability of spectrum manipulations, time‐domain digital coding metasurfaces (TDCMs) have opened up a number of remarkable applications such as nonreciprocal effect, [ 11 , 12 , 13 , 16 ] harmonic controls, [ 14 , 15 ] efficient frequency conversion, [ 17 ] and nonlinear information modulations. [ 18 , 19 ] From the radar perspective, the emergence of new frequency components in echoes may represent moving targets with radial velocities. On this basis, the feasibility of generating a controllable Doppler effect was demonstrated with a reconfigurable stationary metasurface.…”

Monolithic Integrated Optical Telescope Based on Cascaded Metasurfaces

“…With the development of modern optical technologies, traditional optical components such as refractive lenses and birefringent crystals, are no longer satisfying the growing requirements for the miniaturization, integration, and intelligentialization. In recent years, metasurfaces that are composed of subwavelength-spaced phase shifters at an interface have attracted a great deal of attention due to their superior ability to manipulate light waves far beyond traditional optical devices. − Metasurfaces can flexibly manipulate the amplitude, phase, polarization, and frequency of light waves and provide an attractive approach for achieving ultrathin flat optical components, such as waveplates, − beam splitters, − metalenses, − optical holography, − and so on. However, the existing metasurfaces are typically designed as a single component that is part of the conventional optical systems.…”