Grating-Assisted Polarization-Insensitive Dual-Mode Spatial Light Modulator Design Using Epsilon-Near-Zero Material

摘要

Electro-tunable metamaterials opened new doors to realize spatial light modulation at nanoscale by engineering meta-atoms at sub-wavelength scale. In this study, we propose a novel design of polarization-insensitive spatial light modulator that can operate in both transmission and reflection modes. We leverage GMR (guided-mode resonance)-effect of grating waveguide and ENZ (epsilon-near-zero) phenomenon of ITO (indium-tin-oxide) to realize an efficient electro-optic modulation. The proposed design consists of a two-dimensional array of silicon-nitride nanograting on top of ITO-integrated silicon-on-insulator platform. Effective medium theory combined with temporal coupled-mode analysis is used to examine the excitation of waveguide mode via coupling of spatial light. Upon applying external bias-voltage when ITO exhibits ENZ-effect by accumulating free-carriers at ITO-Al_2O_3 interface, the resonance feature disappears due to large modal loss. A modulation depth of ～0.96 (～0.85) in reflection (transmission)-mode is achieved for normally incident plane wave with random polarization angle at 1.55 μm wavelength. In addition, the operating wavelength can be shifted by utilizing frequency-scaling property of the proposed design. With ～774 Mbps modulation speed, the proposed scalable design paves the way toward the realization of tunable flat-optical components for integrated nanophotonic systems.