Silicon-on-nitride structures for mid-infrared gap-plasmon waveguiding

Silicon-on-nitride (SON) is a convenient, low-loss platform for mid-infrared group IV plasmonics and photonics. We have designed 5-layer SON channel-waveguides and slab-waveguides for the 2.0 to 5.4 μm wavelength range and have simulated the resulting three-dimensional (3D) and two-dimensional (2D) SON gap-plasmon modes. Our simulations show propagation lengths of ∼60 μm for 3D gap-strip modes having a 0.003 λ2 cross-section. Because the ∼50-nm SON (Si3N4) mode region is also a gate insulator between silver (Ag) and n-doped Silicon (Si), metal-oxide-semiconductor accumulation gating is available for electro-optical loss modulation of the gap-confined mode.