Efficient interfacing photonic and long-range dielectric-loaded plasmonic waveguides.

Long-range dielectric-loaded surface plasmon-polariton waveguides (LR-DLSPPWs) operating at telecom wavelengths are efficiently (end-fire) interfaced with photonic waveguides by taking advantage of very similar lateral mode field profiles in these waveguide configurations. The LR-DLSPPWs are formed by 1-μm-high and 1-μm-wide polymer ridges fabricated atop 15-nm-thin and 500-nm-wide gold stripes supported by a 289-nm-thick ormoclear polymer deposited on a low-index (1.34) layer of cytop, whereas gold stripes are absent in the photonic waveguide configuration that is identical to the plasmonic one in all other respects. The coupling efficiency between LR-DLSPPWs and photonic waveguides is numerically estimated to be 97%, decreasing by only a few percents for non-centered gold stripes (as long as a gold stripe is kept inside the polymer ridge). The fabricated LR-DLSPPWs coupled to photonic waveguides are first characterized using amplitude- and phase-resolved near-field imaging of propagating radiation that reveals very similar mode field distributions in these waveguides as well as their efficient interfacing. The coupling efficiency is then experimentally characterized using the cutback approach resulting in an average level of 75% per interface, while the LR-DLSPPW mode propagation length is estimated to be on average 0.3 mm. Possible reasons for differences between experimental and simulation results are discussed, indicating that a 3-nm-thin titanium layer (used for improving adhesion between gold and ormoclear) introduces substantial mode absorption. The results obtained open new perspectives for realization of hybrid photonic-plasmonic components and circuits.