Simultaneous Conversion of Polarization and Frequency via Time‐Division‐Multiplexing Metasurfaces

Abstract

Metasurfaces are artificially engineered two‐dimensional materials composed of sub‐wavelength meta‐atoms, which have shown unprecedented capabilities in manipulating the amplitude, phase, frequency, and polarization states of electromagnetic waves. Specifically, polarization control can be attained via suitable anisotropic, linear, and time‐invariant designs, while frequency conversion is realized via nonlinear or time‐varying platforms. Simultaneous manipulations of polarization and frequency would be of considerable practical interest in many application scenarios, but remain unattainable with current approaches. Here, a time‐division‐multiplexing metasurface is proposed to realize the simultaneous conversion of polarization and frequency. The platform relies on time‐modulated polarization switches and, by varying the duty cycle and time delays of the polarization channels, can arbitrarily rotate the polarization at the central frequency of operation, and synthesize various polarization states at selected harmonic frequencies. Theoretical predictions are validated via measurements on a prototype operating at microwave frequencies, providing the first experimental evidence of simultaneous polarization and frequency conversions via time‐division‐multiplexing metasurfaces. The outcomes open a new pathway in manipulating the electromagnetic waves via time‐varying metasurfaces, and may be of interest for a broad variety of applications in scenarios ranging from polarization imaging to quantum optics.

Recent Advances in Reconfigurable Metasurfaces: Principle and Applications

“…Using metasurfaces, beam focusing in any direction can be achieved by configuring phase gradients and is less expensive than traditional beam focusing techniques. Additionally, metasurfaces shows their great capability in polarization conversion [ 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ]. Metasurfaces provide new degrees of freedom to realize complex EM functionalities.…”

“…By specifically designing symmetrical metasurface unit cells, two orthogonal PIN diodes can be loaded on the unit cells to respond independently to x - or y -polarized waves for independent two-dimensional control [ 69 , 204 , 205 , 206 , 207 ]. Figure 7 b [ 208 ] shows the far-field patterns of a coding metasurface encoded for x -polarization and y -polarization, respectively.…”

A Polarization‐Modulated Information Metasurface for Encryption Wireless Communications

“…In recent years, time‐varying metasurfaces have been proposed by applying a time‐varying periodic bias voltage to active components loaded on metasurfaces, which have shown extraordinary ability in controlling the amplitude and phase distributions of EM waves at different harmonic frequencies. [ 32 , 33 ] Since the amplitude and phase of EM waves can be simultaneously manipulated, time‐varying metasurfaces can achieve more powerful PoM functions, such as editing arbitrarily linear polarizations, [ 34 ] or even the generation of arbitrary polarization, [ 35 ] and linear‐nonlinear polarization syntheses. [ 36 ] However, these time‐varying metasurfaces must be derived by continuously applying a time‐varying periodic bias voltage, and the additional spectrum resources will be inevitably occupied due to the generation of harmonics, which still has limitations in practical applications of PoM.…”

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

“…Different from the previous analog time-domain modulations of EM/circuit characteristic parameters, by elaborately designing the reflection amplitudes/phases in different time slices in a digital-coding way, it is possible to tailor the propagation behaviors of nonlinear harmonics 18 , 26 – 29 . Some unique applications based on STCMs have been reported, including independent control of multiple harmonics, high-efficiency frequency synthesizer, space-time modulation, and nonlinear polarization synthesis 30 – 37 . Direct digital information modulations can also be realized by STCM, which enables us to construct new architecture wireless communication transmitters 26 , 38 – 42 .…”