Cleaved fiber-to-nano waveguide mode converter for silicon photonics devices

In this paper, a high efficient fiber-to-waveguide mode converter is demonstrated on the SOI platform, which is composed of a suspended tapered SiO2 waveguide and overlapped Si nano-tapers. The overlapped Si nano-tapers are located in the center of suspended tapered SiO2 waveguide. With a refractive index (<;1.4) matching liquid, the coupling losses between the cleaved optical fiber and this converter are 1.5 dB/facet and 2.1 dB/facet for TE and TM modes, respectively. The 1 dB bandwidths for both TE and TM modes are more than 100 nm. The alignment tolerances for both TE and TM modes are ± 2.5 μm and 2.0 μm for 1 dB excess loss in horizontal direction and vertical direction, respectively.