Abstract
Metasurfaces in a metal–semiconductor–metal configuration have been studied in multiple contexts, including perfect absorption and phase modulation. Nevertheless, limit progress has been achieved in independent phase modulation. To study further in this work, a metasurface composed of an Au film/ VO<sub>2</sub> film/ Au patch array with square holes was proposed in this paper. Through simulating and analysing the optical properties, simulated results indicated that an extremely switchable function can be realized by modulating the phase transition of VO<sub>2</sub>, when VO<sub>2</sub> was in the metal (semiconductor) phase, the whole structure represented as ON (OFF) state. Additionally, the efficient modulation depth is approximately 99.6% for the y-polarization at a wavelength of 2.019 µm. What’s more, by modulating symmetry-breaking of the structure or polarization, an extreme reflection phase change can been applied. As for the former, by adjusting the asymmetry degreed, the reflection phase can change from less than 180° to nearly 360°, and for the latter, the adjustment in polarization resulted in a phase change of nearly 180° for the x-polarization and nearly 360° for the y-polarization. While the amplitude remained almost constant at the corresponding wavelength. That is to say, an independent regulation of amplitude and phase was accomplished. And a two-mode one-port temporal coupled mode theory supported by full-wave simulations can explain the underlying physics of the designed independent phase modulation. The research findings mentioned above established the possibility for plasmonic integration as well as the design of multi-functional devices such as gradient metasurfaces and temperature-controlled switches.
Highlights
The semiconductor–metal transition (SMT) of vanadium dioxide (VO2) occurs when external parameters, including electric field, magnetic field, light, temperature and stress, reach critical values
Each Au patch was drilled with a 280 nm × 280 nm air hole with the center displaced from the patch center by symmetry breaking in the metasurface
The results indicated that symmetry-breaking of the structure significantly altered the reflection phase, but the amplitude at the corresponding wavelength remained nearly unaffected
Summary
The semiconductor–metal transition (SMT) of vanadium dioxide (VO2) occurs when external parameters, including electric field, magnetic field, light, temperature and stress, reach critical values. In addition to being applied in other approaches for achieving the phase transition of VO2 [1,2,3,4], VO2 has been combined with surface plasmons to achieve numerous dynamically tunable functions. Xu et al fabricated silver nanoparticles on a VO2 film and observed that the localized surface plasmon resonant band exhibited a temperature dependence ranging from 30°C to 80°C [5]. Metamaterial devices with far-infrared resonance frequencies were dynamically tuned [8]. Huang et al implemented a temperature-controlled switch in the near-infrared band using VO2 [9]. Ooi and colleagues designed an ultra-compact VO2 two-mode plasmon-waveguide electroabsorption regulator with a switching regulation depth of 10 dB, and this high-performance plasmon regulator may be critical to integrating optoelectronic circuits in next-generation chip technology [10].
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