Grating-Assisted Polarization-Insensitive Dual-Mode Spatial Light Modulator Design Using Epsilon-Near-Zero Material
Tanmay Bhowmik, Ashish Kumar Chowdhary, Debabrata Sikdar
Abstract
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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.55 ~\mu \text{m}$ </tex-math></inline-formula> 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.