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The growing maturity of nanofabrication technology has recently enabled the deployment of high-quality subwavelength nanostructures on photonic chips. Combining existing photonic waveguide technology with the paradigms adapted from metamaterials opens new avenues towards unprecedented control of guided light waves. However, developing new functionalities while preserving efficiencies and offering compatibility with current technology remains a major challenge in on-chip nanophotonics. Here, a novel silicon nanophotonic waveguide comprising a chain of resonantly forward scattering nanoparticles empowered by spectrally overlapping electric and magnetic dipolar Mie-type resonances is proposed and demonstrated. The propagation loss of the meta-waveguides in the telecom spectral range is as low as 0.4 dB mm −1 , exceeding the current record for Mie-resonant waveguides by more than an order of magnitude. Furthermore, the meta-waveguides support a negative group index over a broad spectral range of 60 nm and regions of vanishing and anomalous dispersion within the transmission band. Finally, it is shown that meta-waveguide topologies can implement compact resonance-protected waveguide bends and efficient splitters within just 320 nm propagation length. This work addresses the fundamental challenges of miniaturization, dispersion, and scattering control in integrated photonics and opens new opportunities for enhancing light-matter interactions, interfacing nanophotonic components, and developing nonlinear, ultrafast, and quantum optics resonant on-chip devices.

During the past decade, optical metasurfaces consisting of designed nanoresonators arranged in a planar fashion were successfully demonstrated to allow for the realization of a large variety of flat optical components. However, in common implementations of metasurfaces and metasurface-based devices, their flat nature is thwarted by the presence of a substrate of macroscopic thickness, which is needed to mechanically support the individual nanoresonators. Here, we demonstrate that carbon nanomembranes (CNMs) having nanoscale thicknesses can be used as a basis for arranging an array of plasmonic nanoresonators into a metamembrane, allowing for the realization of genuinely flat optical devices. CNMs belong to the family of two-dimensional materials, and their thicknesses and mechanical, chemical, and electrical properties can be tailored by the choice of the molecular precursors used for their fabrication. We experimentally fabricate gold split-ring-resonator (SRR) metasurfaces on top of a free-standing CNM, which has a thickness of only about 1 nm and shows a negligible interaction with the incident light field. For optical characterization of the fabricated SRR CNM metasurfaces, we perform linear-optical transmittance spectroscopy, revealing the typical resonance structure of an SRR metasurface. Furthermore, numerical calculations assuming free-standing SRR arrays are in good overall agreement with corresponding experimental transmittance spectra. We believe that our scheme offers a versatile solution for the realization of ultrathin, ultra lightweight metadevices, and may initiate various future research directions and applications including complex sensor technologies, conformal coating of complex topographies with functional metasurfaces, fast prototyping of multilayer metasurfaces, and studying the optical properties of effectively free-standing nanoparticles without the need for levitation schemes.

The growing maturity of nanofabrication technology has recently enabled the deployment of high-quality subwavelength nanostructures on photonic chips. A combination of existing photonic waveguide technology with nanophotonics and paradigms adapted from the field of optical metamaterials opens new avenues towards photonic integrated circuits providing unprecedented control of guided light waves. However, developing new functionalities while preserving both compatibility with current technology and the efficiencies required by existing and emerging applications remains a major challenge in on-chip nanophotonics. Here, we propose and demonstrate a radically new type of silicon nanophotonic waveguide consisting of a chain of resonantly forward scattering nanoparticles empowered by spectrally overlapping electric and magnetic dipolar Mie-type resonances. The propagation loss of the realized meta-waveguides in the telecom spectral range is as low as 0.4 dB/mm, exceeding the current record for Mie-resonant waveguides by more than an order of magnitude. Furthermore, the meta-waveguides support a negative group index over a broad spectral range of 60 nm and several millimeters of propagation distance, as well as regions of vanishing and anomalous dispersion within the transmission band. Finally, we show that meta-waveguide architectures composed of resonantly forward scattering nanoparticles can implement sharp bends with bending radii below 3 µm, and efficiently split the input signal within just 315 nm propagation length. Our work does not only contribute to addressing the challenges of miniaturization, dispersion and scattering control in on-chip photonics, but furthermore opens up completely new opportunities for enhanced light-matter interactions, interfacing with nanophotonic components, as well as nonlinear, ultrafast and quantum optics in resonant integrated light-guiding architectures.

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