Waveguide-coupled plasmonic nanogap-integrated phase change metasurfaces

Silicon photonics has emerged as the dominant technology platform for short distance, inter-chip communication for a variety of photonic computing and sensing applications due to its efficiency in modulation and confinement of light across telecom frequencies in addition to its inherent CMOS compatibility. The integration of metallic nanogaps within silicon photonic architectures provides a promising route for scaling this platform through the extreme confinement offered by plasmonics while providing an efficient route to interfacing future photonic integrated circuits with electronics. However, fabricating the gap sizes (< λg/10) required of plasmonic resonating nanogaps for efficient operation across telecommunication frequencies is highly challenging. Efficient coupling from waveguides to plasmonic nanogaps also remains a major source of loss. Here, we show that the key to merging these platforms lies in applying metamaterial/metasurface engineering principles to the design of the nanogap. Over the last decade, metamaterials and metasurfaces have emerged as a versatile toolkit for control and enhancement of light-matter interaction at application-driven wavelengths of interest in nanophotonic device platforms. We show that integrating a metagrating within a waveguide-coupled plasmonic nanogap made from Au, can enhance coupling to and from the silicon waveguides. Furthermore, the incorporation of the metasurface within the gap allows resonant response to be maintained at user-specified wavelength of interest with gaps as large as λg/5, drastically easing fabrication. Finally, we show that by incorporating a reconfigurable phase change chalcogenide alloy into the gap, non-volatile signal switching with modulation contrasts of up to 10:1 can be achieved across telecom frequencies.