  It is proposed and demonstrated that Q-factor of optical resonators can be
significantly enhanced by introducing an extra anisotropic cladding. We study
the optical resonances of all-dielectric core-shell nanoresonators and reveal
that radially anisotropic claddings can be employed to squeeze more energy into
the core area, leading to stronger light confinement and thus significant
Q-factor enhancement. We further show that the required homogenous claddings of
unusual anisotropy parameters can be realized through all-dielectric
multi-layered isotropic structures, which offers realistic extra flexibilities
of resonance manipulations for optical resonators.
