Experimental demonstration of integrated horizontal Cu-Si3N4-Cu plasmonic waveguide and passive components

The Si₃N₄ waveguide offers very low propagation loss and feasibility for three-dimensional photonic integration, but it suffers from large optical mode size (thus low integration density) due to the relatively small refractive index contrast between the Si₃N₄ core and the SiO₂ cladding. On the other hand, the metal-insulator-metal plasmonic waveguide offers very tight light confinement but it suffers from large propagation loss. In this work, we integrate Cu-Si₃N₄-Cu nanoplasmonic waveguides along with various passive components with the conventional Si₃N₄ waveguides. The Cu-Si₃N₄-Cu waveguide exhibits ~0.37-dB/μm propagation loss at telecommunication wavelengths of 1550 nm and ~45% coupling efficiency with the conventional 1-μm-wide S₃N₄ waveguide through a simple 2-μm-long tapered coupler. Ultracompact 1×2 and 1×4 plasmonic power splitters can split light almost equally with an excess loss of ~3.5 dB and ~1 dB, respectively.