Electrically Tunable Metasurface Perfect Absorbers for Ultrathin Mid-Infrared Optical Modulators

TLDR

Dynamically reconfigurable metasurfaces promise high‑capacity communications, beam shaping, hyperspectral imaging, and adaptive optics, yet achieving high performance remains difficult because of limited tuning ranges and modulation depths. The study demonstrates that a graphene‑based, widely tunable metasurface integrated into a subwavelength cavity can act as an electrically tunable perfect absorber. The absorber employs graphene‑based optical antennas in a subwavelength cavity, with its wavelength tunable from near‑IR to terahertz by adjusting metasurface and cavity dimensions. The device achieves 100 % modulation depth by electrically tuning critical coupling, enabling ultrathin (<λ0/10) modulators operating up to 20 GHz across 5–7 µm.

Abstract

Dynamically reconfigurable metasurfaces open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping, hyperspectral imaging, and adaptive optics. The realization of high performance metasurface-based devices remains a great challenge due to very limited tuning ranges and modulation depths. Here we show that a widely tunable metasurface composed of optical antennas on graphene can be incorporated into a subwavelength-thick optical cavity to create an electrically tunable perfect absorber. By switching the absorber in and out of the critical coupling condition via the gate voltage applied on graphene, a modulation depth of up to 100% can be achieved. In particular, we demonstrated ultrathin (thickness < λ0/10) high speed (up to 20 GHz) optical modulators over a broad wavelength range (5-7 μm). The operating wavelength can be scaled from the near-infrared to the terahertz by simply tailoring the metasurface and cavity dimensions.