  Metasurfaces have become one of the most prominent research topics in the
field of optics owing to their unprecedented properties and novel applications
on an ultrathin platform. By combining graphene with metasurfaces, electrical
tunable functions can be achieved with fast tuning speed, large modulation
depth and broad tuning range. However, the tuning efficiency of hybrid graphene
metasurfaces within the short-wavelength infrared (SWIR) spectrum is typically
low because of the small resonance wavelength shift in this wavelength range.
In this work, through the integration of graphene and silicon metasurfaces that
support quasi-bound states in the continuum (quasi-BIC), we experimentally
demonstrate significant transmittance tuning even with less than 30 nm
resonance wavelength shift thanks to the high quality-factor of quasi-BIC
metasurfaces. The tunable transmittance spectrum was measured using Fourier
Transform Infrared Spectroscopy (FTIR) with a modified reflective lens to
improve the accuracy, and the electrical tuning was realized utilizing the
cut-and-stick method of ion gel. At the wavelength of 3.0 um, the measured
change of transmittance T_max-T_min and modulation depth (T_max-T_min)/T_max
can reach 22.2% and 28.9%, respectively, under a small bias voltage ranging
from -2 V to +2 V. To the best of our knowledge, this work is the first
experimental demonstration of tunable graphene/quasi-BIC metasurfaces, which
have potential applications in optical modulation, reconfigurable photonic
devices, and optical communications.
