Compact broadband low-loss taper for coupling to a silicon nitride photonic wire.

Abstract

We demonstrate an ultra-compact waveguide taper on a silicon nitride platform. The proposed taper provides a coupling efficiency of 95% at a length of 19.5μm in comparison to the standard linear taper of length 50μm, which connects a 10μm wide waveguide to a 1μm wide photonic wire. The taper has a spectral response >75% spanning over 800nm and resilience to fabrication variations; ±200 nm change in taper and end waveguide width varies transmission by <5%. We experimentally demonstrate taper insertion loss of <0.1 dB/transition for a taper as short as 19.5μm, and reduce the footprint of the photonic device by 50.8% compared to the standard adiabatic taper. To the best of our knowledge, the proposed taper is the shortest waveguide taper ever reported in silicon nitride.