  In this article, we examine plasmon induced transparency (PIT) effect in a
parallel plate waveguide (PPWG) comprising of two similar pyramidal shaped
grooves. One of the grooves is filled with air, while the other is filled with
a dielectric material whose refractive index can be varied. The resonant
frequencies corresponding to the air and dielectric grooves in the proposed
configuration results in the transparency window which can be modulated with
the refractive index of the dielectric material. The approach provides
flexibility to actively control transparency effect in a waveguide
configuration without changing physical dimensions. We examined field profiles
in the transparency region to clearly depict the PIT effect. We have employed
an analytical model based upon the three-level plasmonic model to validate our
numerical findings. Further, we examined the switching and tunability of
transparency effect by including silicon layers between the grooves whose
conductivity can be varied. Actively tunable response in plasmon induced
transparency effect in terahertz waveguides can be significant in the
construction of terahertz active components.
