  Silicon photonics is becoming a leading technology in photonics, displacing
traditional fiber optic transceivers in long-haul and intra-data-center links
and enabling new applications such as solid-state LiDAR (Light Detection and
Ranging) and optical machine learning. Further improving the density and
performance of silicon photonics, however, has been challenging, due to the
large size and limited performance of traditional semi-analytically designed
components. Automated optimization of photonic devices using inverse design is
a promising path forward but has until now faced difficulties in producing
designs that can be fabricated reliably at scale. Here we experimentally
demonstrate four inverse-designed devices - a spatial mode multiplexer,
wavelength demultiplexer, 50-50 directional coupler, and 3-way power splitter -
made successfully in a commercial silicon photonics foundry. These devices are
efficient, robust to fabrication variability, and compact, with footprints only
a few micrometers across. They pave the way forward for the widespread
practical use of inverse design.
