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

TL;DR

This paper presents an ultra-compact, high-efficiency silicon nitride waveguide taper with broad spectral response and high fabrication tolerance, significantly reducing device footprint.

Contribution

It introduces the shortest silicon nitride waveguide taper with high coupling efficiency and broad spectral response, outperforming existing designs in size and robustness.

Findings

Achieves 95% coupling efficiency at 19.5 um length

Spectral response >75% over 800 nm

Taper insertion loss <0.1 dB/transition

Abstract

We demonstrate an ultra-compact waveguide taper in Silicon Nitride platform. The proposed taper provides a coupling-efficiency of 95% at a length of 19.5 um in comparison to the standard linear taper of length 50 um that connects a 10 um wide waveguide to a 1 um wide photonic wire. The taper has a spectral response > 75% spanning over 800 nm 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 19.5 um, and reduces 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.