Several works have already shown that the excitation of plasmonic structures through waveguides enables a strong
light confinement and low propagation losses . This kind of excitation is currently exploited in areas such as
biosensing , nanocircuits and spectroscopy.
The efficient excitation of surface plasmon modes (SPP) with guided modes supported by high-index-contrast
waveguides, such as silicon-on-insulator waveguides, had already been shown [1,5]. However, the use of weakconfined
guided modes of a glass ion exchanged waveguide as a SPP excitation source represents a technological
challenge, because the mismatch between the size of their respective electromagnetic modes is so high that the
resultant coupling loss is unacceptable for practical applications.
In this work, we describe how an adiabatic taper structure formed by an intermediate high-index-contrast layer
placed between a plasmonic structure and an ion-exchanged waveguide decreases the mismatch between effective
indices, size, and shape of the guided modes. This hybrid structure concentrates the electromagnetic energy from the
micrometer to the nanometer scale with low coupling losses to radiative modes. The electromagnetic mode confined
to the high-index-contrast waveguide then works as an efficient source of SPP supported by metallic nanostructures
placed on its surface.
We theoretically studied the modal properties and field distribution along the adiabatic coupler structure. In
addition, we fabricated a high-index-contrast waveguide by electron beam lithography and thermal evaporation on
top of an ion-exchanged waveguide on glass. This structure was characterized with the use of near field scanning
optical microscopy (NSOM). Numerical simulations were compared with the experimental results.
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