  We configure and analyze a nanostructured device that hybridizes grating
modes and surface plasmon resonances. The model uses an effective index of
refraction that considers the volume fraction of the involved materials, and
the propagation depth of the plasmon through the structure. Our geometry is an
extruded low-order diffraction grating made of dielectric nano-triangles.
Surface plasmon resonances are excited at a metal/dielectric interface, which
is separated from the analyte by a high-index dielectric layer. The optical
performance of the refractometric sensor is highly competitive in sensitivity
and figure of merit (FOM) because of the the ultra-narrow spectral response
(below 0.1 nm). Moreover, it is operative within a wide range of the index of
refraction (from 1.3 till 1.56), and also works under normal incidence
conditions.
