Compact Broadband Taper for Low-Loss Coupling to a Silicon Nitride Photonic Wire

We demonstrate a compact efficient waveguide taper in Silicon Nitride platform. The proposed taper provides a coupling-efficiency of 95% at a length of 19.5 mu m in comparison to the standard linear taper of length 50 mu m that connects a 10 mu m wide waveguide to a 1 mu m wide photonic wire. The taper has a spectral response > 75% spanning over 800 nm (spanning O, C & L band) and robustness to fabrication variations; +/- 200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally report a taper insertion loss of <0.1 dB/transition and reduction in the footprint of the photonic device by 50.8% for the proposed compact taper in comparison to the traditional adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in Silicon Nitride.