Laser Structured Optical Interposer for Ultra-Dense Surface Coupling of Multicore Fibers to Silicon Photonic Chip

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