Optical modulation based on tunable light absorption and amplification in metasurfaces coupled with gain medium

While previous tunable metasurfaces were based mainly on tuning of dielectric permittivity or losses in associated tunable elements, here we propose gain-assisted tunable metasurfaces as optical modulators with high ON-OFF ratio. They consist of a dye-doped film placed within metal-insulator-metal (MIM) cavities. Plasmonic modes with enhanced electric field significantly enhance both absorption and emission of light by dye molecules. As a result, it is possible to achieve the perfect absorption in MIM cavities with zero reflection, as well as to compensate losses thus achieving unit reflection. As a result, the achievable ON/OFF ratio is more than 100.