Low-loss, broadband and high fabrication tolerant vertically tapered optical couplers for monolithic integration of Si₃N₄ and polymer waveguides

A low-loss, broadband and high fabrication tolerant optical coupler for the monolithic integration of Si₃N₄ and polymer waveguides is designed and experimentally demonstrated. The coupler is based on the adiabatic vertical tapering of the Si₃N₄ waveguides. Low-loss operation is experimentally verified at both 976 and 1460–1635 nm wavelengths. Measured losses per coupler are as low as 0.12 and 0.14 dB at 976 and 1550 nm, respectively, and below 0.2 dB at both wavelengths for lateral misalignments between the Si₃N₄ and polymer waveguides up to 1.0 μm.