Subwavelength and broadband on-chip mode splitting with shifted junctions

We design and fabricate a sub-wavelength on-chip mode splitter based on the implementation of a shifted junction between a single-mode waveguide and a multimode waveguide. A proper choice of the device parameters enables to split the input beam into a combination of different guided modes of the multimode waveguide, minimizing radiation and reflection losses that amount to ∼ 0.4 dB in our experiments. Because the splitting mechanism does not rely on phase-matching, we achieve broadband operation that could exceed 200 nm bandwidth (<0.5 dB splitting variation). This approach ensures temporal and phase synchronization among the output modes, with applications spanning from the emergent multimode photonics platform to traditional single-mode photonics operations.