Ultrafast Electrically Tunable Polaritonic Metasurfaces

Electrically tunable mid-infrared metasurfaces with nanosecond response time and broad tuning range are reported. Electrical tuning is achieved by employing strong polaritonic coupling of electromagnetic modes in metallic nanoresonators with voltage-tunable inter-subband transitions in semiconductor heterostructures, tailored for a giant quantum-confined Stark effect. Experimentally, a 220-nm-thick multi-quantum-well semiconductor layer is sandwiched between a ground plane and a metal layer patterned with plasmonic nanoresonators. Approximately 300 nm absorption peak tuning and over 30% absorption change are demonstrated at around 7 m wavelength at normal incidence by changing the DC bias voltage from 0 to +5 V. Fast reflectivity modulation of the metasurface is shown with a response time less than approximate to 10 ns using bias voltage modulation between +2 V and +4 V. Since the bias affects the optical response at the individual nanoresonator level, this approach may be used to create metasurfaces for ultrafast electrical wavefront tuning and beam steering.