  In this paper, we utilize coupled mode theory (CMT) to model the coupling of
surface plasmon polaritons (SPPs) between tri-layered corrugated thin films
(CTF) structure coupler in the terahertz region. Employing the stimulated raman
adiabatic passage (STIRAP) quantum control technique, we propose a novel
directional coupler based on SPPs evolution in tri-layered CTF in some curved
configuration. Our calculated results show that the SPPs can be completely
transferred from the input to the output CTF waveguides, and even we consider
SPPs propagation loss, the transfer rate is still above 70%. The performance of
our coupler is also robust that it is not sensitive to the geometry of device
and wavelength of SPPs. As a result, our device can tolerate defect induced by
fabrication and manipulate THz wave at broadband.
