Universal Design of Ultra-Broadband and Ultra-Compact High Order Mode Pass Filters Based on Enhanced Absorption in Ultrathin Metal Layers

In hybrid plasmonic Si waveguides integrated with ultrathin Au stripes, mode hybridization effects between quasi-TE modes of different orders and various bound modes are first presented. Enabled by nearly complete mode-selective absorption attributed to the enlarged mode propagation attenuation (MPA) coefficient for lower-order quasi-TE modes under circumstances of mode hybridizations, multi-segment tapered structures are theoretically proposed to constitute high order mode (HOM) pass filters. It is believed that these innovative observations would have potential applications in the ultra-compact on-chip mode division multiplexing (MDM) systems, and provide inspirations for the development of multimode photonics.