Nonlinear terahertz devices utilizing semiconducting plasmonic metamaterials

The development of responsive metamaterials has enabled the realization of compact tunable photonic devices capable of manipulating the amplitude, polarization, wave vector and frequency of light. Integration of semiconductors into the active regions of metallic resonators is a proven approach for creating nonlinear metamaterials through optoelectronic control of the semiconductor carrier density. Metal-free subwavelength resonant semiconductor structures offer an alternative approach to create dynamic metamaterials. We present InAs plasmonic disk arrays as a viable resonant metamaterial at terahertz frequencies. Importantly, InAs plasmonic disks exhibit a strong nonlinear response arising from electric field-induced intervalley scattering, resulting in a reduced carrier mobility thereby damping the plasmonic response. We demonstrate nonlinear perfect absorbers configured as either optical limiters or saturable absorbers, including flexible nonlinear absorbers achieved by transferring the disks to polyimide films. Nonlinear plasmonic metamaterials show potential for use in ultrafast terahertz (THz) optics and for passive protection of sensitive electromagnetic devices. Nonlinear plasmonic metamaterials that are resonant in the terahertz spectral range have been made from disks of indium arsenide. Huseyin Seren and co-workers in the USA fabricated these materials and note that nonlinear semiconductor plasmonic disks may be useful as optical limiters or saturable absorbers. The team used dry etching to fabricate hexagonal arrays of indium arsenide disks that are 70 micrometres in diameter. The samples were doped to a level of 1017 cm−3 resulting in a strong plasmonic response at 0.8 terahertz. A key advantage of using semiconductors as the plasmonic medium is that the doping level can be used to control the resonance frequency and other properties of the metamaterial.