Waveguide-integrated spatial mode filters with PtSe₂ nanoribbons

Low-dimensional material-based heterogeneous silicon photonics has attracted significant attention due to their applications in developing integrated optoelectronic devices from the telecommunication band to mid-infrared wavelengths. However, the study of waveguide components integrated with low-dimensional materials for mode-division multiplexing (MDM) applications mostly remains in its infancy. In this paper, we demonstrated waveguide-integrated spatial mode filters by integrating subtly designed ten-layer PtSe₂ nanoribbons on an ultrathin silicon waveguide with a deep-subwavelength thickness to eliminate modal crosstalk. To be specific, the undesirable propagating mode can be filtered out due to its strong interaction with the PtSe₂ nanoribbons on the silicon waveguide surface. Our results show that TE₁-to-TE₀ and TE₂-to-TE₀ modal extinction ratios of 12 dB and 14.5 dB were measured in 100 and 75-μm-long PtSe₂-on-silicon waveguides at 2200-nm wavelengths. Our study paves the intriguing approach to developing waveguide-integrated spatial mode filters for on-chip MDM applications for optical interconnects and optical communications.