We propose and theoretically verify an efficient mechanism of broadband coupling between incident light and on-chip dielectric slot waveguide by employing a tapered plasmonic nanoantenna. The nanoantenna receives free space radiation and couples it to a dielectric slot waveguide with the efficiency of up to 20% in a broad spectral range, having a small footprint as compared with the currently used narrowband dielectric grating couplers. We argue that the frequency selective properties of such nanoantennas also allow for using them as ultrasmall on-chip multiplexer/demultiplexer devices.
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