Tunable dual-band amplitude modulation with a double epsilon-near-zero metasurface

In this paper, we demonstrate an electrically tunable double epsilon-near-zero (D-ENZ) metasurface by incorporating an ultra-thin indium-tin-oxide layer (≈ 5 nm) into an array of moderately-doped silicon (Si) nanobars. The D-ENZ phenomenon is achieved by accumulation and depletion of carrier densities in ITO and Si active layers under applying the external bias voltages. An active dual-band amplitude modulator is proposed which can realize the modulation depths of 0.86 and 0.71 at operating channels of λ 1 = 1547 nm and λ 2 = 1564.2 nm, leveraging the D-ENZ mechanism. The reasonably low intrinsic loss in such an optical device gives us the opportunity to have continuous amplitude modulation at both operating wavelengths without the necessity of a complicated multi-resonator unit-cell.