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Efficient optical coupling into ultra-compact plasmonic slot waveguides using dipole nanoantennas

Nanoantenna is used for coupling free space radiation to subwavelength plasmonic waveguide. We provide a theoretical design of ultra-compact dipole nanoantennas --- Yagi-Uda antenna with a reflector in telecom range and experimentally demonstrate efficient optical coupling between lensed fiber and plasmonic slot waveguide by utilizing our designed nanoantenna. We also prove that the couple-in efficiency of 8% from the lensed fiber does not equal to the couple-out efficiency of 50% from the plasmonic slot waveguide using the same nanoantenna design, which is different than many published and experimental results. We also study the relationship between couple in efficiency and the incident light spot size, which is experimentally characterized.