Polarization- and Angle-Insensitive Tunable Metasurface for Electro-Optic Modulation

Tunable metasurfaces provide enormous degrees-of-freedom for dynamic control of light–matter interactions at sub-wavelength scales. However, the realization of polarization- and angle-insensitive active nanophotonic devices with low energy-consumption and high modulation depth remains a challenge. This letter reports gap plasmon resonance based electro-tunable metasurface for optical intensity modulation. The proposed metasurface features a 2D array of Au-nanograting on top of indium-tin-oxide (ITO)–Al
₂
O
₃
–Au stack. The external electrical biasing accumulates the free-carriers of ITO at ITO–Al
₂
O
₃
interface, which results in an electro-tunable resonance response in the reflectance spectrum. With a 2V electrical biasing, we observe the resonance dip shifts to the vicinity of
$1.55~\mu \text{m}$
wavelength. Thus, a modulation depth of ~25 dB at
$1.55~\mu \text{m}$
can be achieved for random polarization-angle of incident light. For the first time, the proposed modulator can operate over a wide range of incidence angle (up to 50 degrees) for both x- and y-polarized light. With ~303 fJ/bit energy-consumption and ~900 Mbps modulation speed, the proposed electro-tunable metasurface could help to realize polarization- and angle-independent active flat optics for nanophotonic systems.