Photonic welding points for arbitrary on-chip optical interconnects

Photonic integrated circuits (PICs) are an ideal platform for chip-scale computation and communication. To date, the integration density remains an outstanding problem that limits the further development of PIC-based photonic networks. Achieving low-loss waveguide routing with arbitrary configuration is crucial for both classical and quantum photonic applications. To manipulate light flows on a chip, the conventional wisdom relies on waveguide bends of large bending radii and adiabatic mode converters to avoid insertion losses from radiation leakage and modal mismatch, respectively. However, those structures usually occupy large footprints and thus reduce the integration density. To overcome this difficulty, this work presents a fundamentally new approach to turn light flows arbitrarily within an ultracompact footprint. A type of "photonic welding points" joining two waveguides of an arbitrary intersecting angle has been proposed and experimentally demonstrated. These devices with a footprint of less than 4 mu m(2) can operate in the telecommunication band over a bandwidth of at least 140 nm with an insertion loss of less than 0.5 dB. Their fabrication is compatible with photonic foundry processes and does not introduce additional steps beyond those needed for the waveguides. Therefore, they are suitable for the mass production of PICs and will enhance the integration density to the next level.