Amplitude modulation in infrared metamaterial absorbers based on electro-optically tunable conducting oxides

• DOI: 10.1007/s00339-017-1506-0
• Publication Date: 2018-01-10T01:59:53Z
• Authors: D. C. Zografopoulos; G. Sinatkas; E. Lotfi; L. A. Shahada; M. A. Swillam; E. E. Kriezis; R. Beccherelli
• Keywords: Indium tin oxide; Modulation (music); Extinction ratio; Picosecond

A class of electro-optically tunable metamaterial absorbers is designed and theoretically investigated in the infrared regimetowards realizing free-space amplitude modulators. The spacer between a subwavelength metallic stripe grating and a backmetal reflector is occupied by a bilayer of indium tin oxide (ITO) and hafnium oxide ( HfO2 ). The application of a bias voltageacross the bilayer induces free-carrier accumulation at the HfO2/ITO interface that locally modulates the ITO permittivityand drastically modifies the optical response of the absorber owing to the induced epsilon-near-zero (ENZ) effect. The carrierdistribution and dynamics are solved via the drift–diffusion model, which is coupled with optical wave propagation studiesin a common finite-element method platform. Optimized structures are derived that enable the amplitude modulation of thereflected wave with moderate insertion losses, theoretically infinite extinction ratio, sub-picosecond switching times andlow operating voltages.