Low-Return-Loss Plasmonic Multiplexer With Tapered Structure

We demonstrate a novel wavelength-division multiplexing 1.31- and 1.55-μm-wavelength-band plasmonic multiplexer that employs the multimode interference effect. The multiplexer comprises SiO₂ stripes on a Au film and was fabricated using a process compatible with standard complementary metal-oxide-semiconductor processing techniques. To suppress the return loss, tapered structures were introduced to the multiplexer. Finite-difference time-domain simulations indicate that losses were reduced by 12 dB. The multiplexing operation was confirmed with a scanning near-field optical microscopy. The reflection effect (return loss) appeared as an interference fringe of incident and reflecting surface plasmons in the multimode waveguide. The interference fringe disappeared in the multiplexer employing the taper structure.