Abstract
An efficient on-chip coupling mechanism is essential for nanoplasmonic circuits and elements. We show theoretically that end-fire coupling is a promising candidate to deliver light into regions with subwavelength dimension on flat metal surfaces. A design and optimization principle is presented for a flat metal surface and further demonstrated in a plasmonic Mach-Zehnder interferometer platform. The physical mechanism is discussed based on reciprocity. By considering the radiation pattern and position of the incidence, the coupling efficiency at the metal/air interface can be enhanced up to 77.6%-95.4%, which is promising to develop energy-efficient applications for on-chip plasmonic waveguide networks and sensors. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4789809]