  Photonic integration has witnessed tremendous progress over the last years,
and chip-scale transceiver systems with Terabit/s data rates have come into
reach. However, as on-chip integration density increases, efficient off-chip
interfaces are becoming more and more crucial. A technological breakthrough is
considered indispensable to cope with the challenges arising from large-scale
photonic integration, and this particularly applies to short-distance optical
interconnects. In this letter we introduce the concept of photonic wire
bonding, where transparent waveguide wire bonds are used to bridge the gap
between nanophotonic circuits located on different chips. We demonstrate for
the first time the fabrication of three-dimensional freeform photonic wire
bonds (PWB), and we confirm their viability in a multi-Terabit/s data
transmission experiment. First-generation prototypes allow for efficient
broadband coupling with overall losses of only 1.6 dB. Photonic wire bonding
will enable flexible optical multi-chip assemblies, thereby challenging the
current paradigm of highly-complex monolithic integration.
