  We present theoretical and numerical analysis of a plasmonic-dielectric
hybrid system for symmetric and asymmetric coupling between silver cut-wire
pairs and silicon grating waveguide with periodic grooves. The results show
that both couplings can induce electromagnetically-induced transparency (EIT)
analogous to the quantum optical phenomenon. The transmission spectrum shows a
single transparency window for the symmetric coupling. The strong normal phase
dispersion in the vicinity of this transparent window results in the slow light
effect. However, the transmission spectrum appears an additional transparency
window for asymmetry coupling due to the double EIT effect, which stems from an
asymmetrically coupled resonance (ACR) between the dark and bright modes. More
importantly, the excitation of ACR is further associated with remarkable
improvement of the group index from less than 40 to more than 2500
corresponding to a high transparent efficiency by comparing with the symmetry
coupling. This scheme provides an alternative way to develop the building
blocks of systems for plasmonic sensing, all optical switching and slow light
applications.
