Compact, ultra-broadband plasmonic grating couplers.

We demonstrate all-metallic grating couplers that enable vertical, compact and broadband fiber-coupling. The grating couplers are based on a metal layer and directly convert a vertical fiber mode into surface plasmon polaritons (SPPs). In combination with a focusing arrangement, the grating couplers require only a small footprint of 13.5 x 12 mu m(2). We characterize the grating couplers with both periodic and apodized gratings and experimentally show a 1-dB bandwidth of 115 nm with a coupling efficiency of 2.9 dB. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement