Scalable and Compact Silicon Mode Multiplexer Via Tilt Waveguide Junctions With Shallow Etched Slots

The integration density and the system complexity of photonic integrated circuits are scaling significantly, especially for optical computing, signal processing, and other emerging applications. As is such, the quest for information multiplexing is becoming increasingly important. On-chip mode division multiplexing (MDM) is considered to be a promising solution which is capable of processing a large amount of data via intrinsic parallelism. Various device structures have been proposed for on-chip mode multiplexing while most of which either lack the scalability or occupy too much chip area. Here, a scalable and compact silicon photonic mode (de)multiplexer is proposed and experimentally demonstrated based on tilt waveguide junctions assisted with shallow-etched subwavelength slots. The number of channels can be easily scaled by cascading multiple junctions. Compared with conventional cascaded structures, the proposed shallow etched slots enable a new mode evolution scheme which significantly shrinks the device length. For a proof-of-concept demonstration, four-mode (de)multiplexer for TE
₀
–TE
₃
modes is designed, fabricated, and characterized. The measured insertion losses for all four modes are below 1.29 dB, while the crosstalks are all below −14.4 dB.