  We investigate the strong coupling between the excitons and quasi-bound
states in the continuum (BIC) resonance in a bulk WS$_2$ metasurface. Here we
employ the bulk WS$_2$ to construct an ultrathin nanodisk metasurface,
supporting the symmetry-protected magnetic dipole (MD) quasi-BIC resonance,
which can self-hybridize with the excitons and lead to a strong light-matter
interaction enhancement within the structure without the necessity for an
external cavity. This strong coupling can be charactered by the considerable
Rabi splitting of 159 meV and the clearly anti-crossing behavior appeared in
the absorption spectrum. Furthermore, we analyze such light-matter coupling by
constructing a Hamiltonian model including the surplus excitons, and tune the
interaction from weak coupling to strong coupling regimes via the tunability
radiation loss of the quasi-BIC resonance. Our results have great potential for
manipulating the exciton-polaritons at room temperature, and provide a
promising prospect for photonic devices that exploit strong coupling in
applications.
