Dynamic-Metasurface-Based Cavity Structures for Enhanced Absorption and Phase Modulation

Abstract

Metasurface-based optical cavity structures consist of a metallic metasurface realized on top of a dielectric slab backed with a metal plane. Such structures have been employed in the design of optical devices such as flat lenses, wave plates, and holograms at frequencies from microwave to mid-infrared. Recently, such structures with dynamically reconfigurable optical characteristics have been explored for electrically tunable optical absorption and reflection phase modulation. To date, absorption modulation and phase modulation have been realized with large insertion loss. In this work, we employ an analytical approach based on transmission line theory where the metasurface is represented by a surface admittance. We extend the above approach for the design and analysis of under-and overcoupled resonance regimes in the metasurface cavity structure. This enables a mutual design of cavity thickness and individual metasurface for large amplitude or phase modulation. A dynamic-metasurface-based optical cavity is experimentally demonstrated at terahertz frequencies where the dynamic metasurface consists of metallic resonators embedded with thin-film vanadium dioxide patches. By driving an insulator to metal transition in vanadium dioxide, the terahertz optical response of the metasurface-based cavity structure is modulated. The fabricated device exhibits perfect absorption modulation and reflection phase modulation up to 180°. The reported results demonstrate the potential of such structures for realizing novel devices such as tunable holograms, high-efficiency modulators, and frequency-tunable filters at terahertz. The analytical approach presented here can be applied to the analysis and design of metasurface cavity structures based on other material systems at frequencies ranging from terahertz to mid-infrared.

Switchable Metamaterial With Terahertz Buffering and Absorbing Performance

“…Subsequently, the VO2 layer is synthesized on the bottom by magnetron sputtering technique from a pure vanadium target and an Ar/O2 gas mixture. Finally, by applying thermal, electrical or optical stimuli, the insulatormetal transition can be induced and the actively controlled conductivity of the VO2 layer can be realized [51]- [53].…”

Waveguide-Mode-Enhanced Millimeter-Wave Photomodulators

“…However, in the millimeterwave and terahertz spectral regions there is a lack of similarly mature technologies. Some possible candidates include electrical control of gated two-dimensional electron gases [2], including graphene [3], resonant metasurface elements [4][5][6], and LiNbO 3 [7]; thermal control of phase change materials such as VO 2 [8][9][10][11] and chalcogenide glasses [12,13]; and microelectromechanical-based systems [14][15][16].…”

Design of a switchable phase‐modulated metasurface with wide modulation bandwidth in S band

“…A PMM has been applied to control the spectrum of a reflection signal that can produce different harmonic frequencies, but this metasurface only works at 10 GHz 23 . Similar to that case, 23 most PMMs have a relatively narrow phase‐modulation band or may even work at a single frequency 21,22 . This is mainly because the reflection phase is very sensitive to changes in the frequency.…”

“…Many switchable metasurfaces are designed to tune the reflection amplitude, 15 frequency, 16 and polarization 17 of the EM waves. In addition, the demand to modulate the reflection phase has become increasingly important [18][19][20][21][22][23][24] because a phase-modulated metasurface (PMM) can effectively control the scattering beam and its distribution in the time domain. Furthermore, it can then modulate the frequency spectrum of the reflection wave, which can be utilized to reduce Radar Cross Section (RCS) in stealth technology.…”

“…23 Similar to that case, 23 most PMMs have a relatively narrow phase-modulation band or may even work at a single frequency. 21,22 This is mainly because the reflection phase is very sensitive to changes in the frequency. Hence, it is relatively difficult to design a wideband PMM with wide phase-modulation bandwidth.…”