  We study, both theoretically and experimentally, tunable metasurfaces
supporting sharp Fano-resonances inspired by optical bound states in the
continuum. We explore the use of arsenic trisulfide (a photosensitive
chalcogenide glass) having optical properties which can be finely tuned by
light absorption at the post-fabrication stage. We select the resonant
wavelength of the metasurface corresponding to the energy below the arsenic
trisulfide bandgap, and experimentally control the resonance spectral position
via exposure to the light of energies above the bandgap.
