  Bound states in the continuum (BICs) emerge throughout Physics as
leaky/resonant modes that remain however highly localized. They have attracted
much attention in Optics and Photonics, and especially in metasurfaces, i.e.
planar arrays of sub-wavelength meta-atoms. One of their most outstanding
feature is the arbitrarily large Q-factors they induce upon approaching the BIC
condition, which we exploit here to achieve a narrow transparency band. We
first show how to shift a canonical BIC in an all-dielectric metasurface,
consisting of high-refractive disks exhibiting in- and out-of-plane magnetic
dipole (MD) resonances, by tuning the periodicity of the array. By means of our
coupled electric/magnetic dipole formulation, we show analytically that when
the quasi-BIC overlaps with the broad (in-plane MD) resonance, a full
transparency band emerges with diverging Q-factor upon approaching the BIC
condition in parameter space. Finally, our experimental measurements in the
microwave regime with a large array of high-refractive-index disks confirm the
theoretical predictions. Our results reveal a simple mechanism to engineer an
ultra-narrow BIC-induced transparency band that could be exploited throughout
the electromagnetic spectrum with obvious applications in filtering and
sensing.
