Highly efficient out-of-plane optical coupler based on tapered hollow waveguide

We proposed a highly efficient out-of-plane optical coupler based on a tapered hollow waveguide. Modeling shows low polarization and wavelength dependences in a 35 nm wavelength window (C-band). The relative lateral displacements per spot size of the vertical output for the entire C-band are less than 0.13 and 0.38 for TE and TM input modes, respectively. At the same time, the polarization-dependent insertion loss is below 1.35 dB for both TE and TM input modes. Our device functions as a spot size converter, via taper angle modification, which can be used for a variety of applications such as out-of-plane coupling of vertical cavity surface emitting lasers (VCSELs), detectors, and so on.