  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.
