Guided mode meta-optics: Metasurface-dressed nanophotonic waveguides for arbitrary designer mode couplers and on-chip OAM emitters with configurable topological charge

TL;DR

This paper introduces a metasurface-based approach to precisely control and excite high-order waveguide modes, enabling advanced on-chip light manipulation including configurable orbital angular momentum generation.

Contribution

It presents a systematic method to selectively excite arbitrary high-order waveguide modes using silicon metasurfaces, achieving high purity and broad bandwidth, with potential for integrated photonic applications.

Findings

High-purity excitation of high-order modes up to 98%

Broad bandwidth operation demonstrated

On-chip generation of twisted light with configurable topological charge

Abstract

Metasurfaces have achieved fruitful results in tailoring complexing light fields in free space. However, a systematic investigation on applying the concept of meta-optics to completely control waveguide modes is still elusive. Here we present a comprehensive catalog capable of selectively and exclusively excite almost arbitrary high-order waveguide modes of interest, leveraging silicon metasurface-patterned silicon nitride waveguides. By simultaneously engineering the phase-matched gradient of the metasurface and the vectorial spatial modal overlap between the nanoantenna near-field and target waveguide mode for excitation, either single or multiple high-order modes are successfully launched with high purity reaching 98% and broad bandwidth. Moreover, on-chip twisted light generators are also theoretically demonstrated with configurable OAM topological charge \ell from -3 to +2, serving as a comprehensive framework for metasurface-enabled guided mode optics and motivating further applications such as versatile integrated couplers, demultiplexers, and mode-division multiplexing-based communication systems.