High-performance, adiabatically nanotapered fibre-chip couplers in silicon at 2 microns wavelength

TL;DR

This paper introduces a low-loss, broadband, and planar fibre-chip coupling method using adiabatic nanotapers in silicon photonics at 2 microns, improving integration and manufacturability.

Contribution

The authors demonstrate a novel adiabatic nanotapered fibre-chip coupler in silicon photonics that surpasses traditional grating couplers in bandwidth and ease of fabrication.

Findings

Optimal per-coupler transmission of -0.48 dB

1-dB bandwidth of 295 nm

Tolerance to lateral misalignment within +/- 0.968 micron

Abstract

Fibre optic technology connects the world through the Internet, enables remote sensing, and connects disparate functional optical devices. Highly confined silicon photonics promises extreme scale and functional integration. However, the optical modes of silicon nanowire waveguides and optical fibres are very different, making efficient fibre-chip coupling a challenge. Vertical grating couplers, the dominant coupling method today, have limited optical bandwidth and are naturally out-of-plane. Here we demonstrate a new method that is low-loss, broadband, easily manufacturable, and naturally planar. We adiabatically couple a tapering silicon nanowire waveguide to a conic nanotapered optical fibre, measuring transmission between 2.0 and 2.2 micron wavelength. The silicon chip is fabricated at a commercial foundry and then post-processed to release the tapering nanowires. We estimate an optimal per-coupler transmission of -0.48 dB (maximum; 95% confidence interval [+0.46, -1.68] dB) and a 1-dB bandwidth of 295 nm . With automated measurements, we quantify the device tolerance to lateral misalignment, measuring a flat response within +/- 0.968 micron. This design can enable low-loss modular systems of integrated photonics irrespective of material and waveband.