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Straight Long-Range Surface Plasmon Polariton Waveguides with a Gap.

In straight long-range surface plasmon polariton (LR-SPP) waveguides with a gap (G-SPPWs), an excited input SPP propagates, jump overs the gap with low coupling loss, and propagates again, despite a micrometers-long gap. The micrometers long gap can be filled with various materials to control the LR-SPP mode in the G-SPPWs. Here, the optical characteristics of fabricated 20-nm-thick G-SPPWs with a fixed 2 µm gap length are experimentally evaluated at a wavelength of 1.55 µm. The gap coupling losses in the G-SPPWs were determined to be less than ~0.22 dB for various widths of the SPP waveguide (SPPW) up to ~8 µm, and the insertion losses were determined to be less than ~0.89 dB for the same design range. A minimum insertion loss of ~0.45 dB was obtained from the G-SPPW with a fixed 2 µm gap length and a 7 µm SPPW width. In the 2.5-Gbps optical signal transmission experiment, the G-SPPW exhibits excellent eye opening and the G-SPPW transfers the carrier wave as well as the data signal. The G-SPPW has potential to serve as a new plasmonic modulation element offering control of the guided SPP through interaction with an applied force in the gap.