Laser Structured Optical Interposer for Ultra-dense Vertical Coupling of Multi-core Fibers to Silicon Photonic Chip

Abstract: Femtosecond laser writing in glass was harnessed to fabricate photonic circuits comprised of waveguides, micro-mirrors, and fiber sockets, in an optical interposer chip. The compact design enabled ultra-dense routing of 40 optical channels from six multi-core fibers, in a two-layer array, vertically coupling onto a 2D grid of silicon photonic grating couplers. Various photonic circuit designs were explored and tested, achieving an average single-pass insertion loss of 5.0 dB for the fully packaged system, with a minimum loss of 3.2 dB. The reasonably low loss and low-profile, compact package make such interposers an attractive option for densifying interconnects to address bottlenecks in optical networks, datacenters, and optical computing applications.