Low-loss highly tolerant flip-chip couplers for hybrid integration of Si3N4 and polymer waveguides

In this letter, low-loss and highly fabrication-tolerant flip-chip bonded vertical couplers under single-mode condition are demonstrated for the integration of a polymer waveguide chip onto the Si3N4/SiO2 passive platform. The passively aligned vertical couplers have a lateral misalignment between polymer and Si3N4 waveguide cores of ±1.25 μm. Low-loss operation has been experimentally demonstrated over a wide spectral window of 1480-1560 nm, with measured coupler losses below 0.8 dB for Si3N4 taper angles below 1.2°, in good agreement with the calculated values. Furthermore, thermal shock test results show less than 0.1 dB degradation, indicating a robust coupling performance.