Efficient Coupling Between Photonic and Dielectric-Loaded Surface Plasmon Polariton Waveguides With the Same Core Material

We theoretically investigate how to efficiently couple a photonic waveguide to a dielectric-loaded surface plasmon polariton (DLSPP) waveguide when they are based on a common core material. The DLSPP waveguide is tapered and butt coupled to the photonic waveguide. First, we propose the use of a dielectric with a higher refractive index than the dielectrics of previous DLSPP waveguides. The photonic and DLSPP waveguides are designed to reduce the loss and tapering region length of the coupling, and the tapering region is optimized. We achieve the coupling between the photonic and DLSPP waveguides based on a dielectric of refractive index of 1.57 with a coupling loss of 2.3 dB through a 3-
$\mu\hbox{m}$
-long coupling region. The coupling loss is further reduced by modifying the DLSPP waveguide into a double-DLSPP
$( \hbox{D}^{2}\hbox{LSPP})$
waveguide. The
$\hbox{D}^{2} \hbox{LSPP}$
waveguide has an additional low-index dielectric between its high-index dielectric and metal layer. Designed appropriately, the
$\hbox{D}^{2}\hbox{LSPP}$
waveguide can be coupled to the photonic waveguide with a coupling loss of 1.1 dB through a 4-
$\mu\hbox{m}$
-long coupling region. Since the photonic and DLSPP or
$\hbox{D}^{2}\hbox{LSPP}$
waveguides investigated in this paper can be simultaneously fabricated, they may constitute an easily realizable hybrid planar lightwave circuit with a relatively low loss.