Direct optical wire bonding through open-to-air polymerization for silicon photonic chips

We developed an inter-chip optical link using direct optical wire (DOW) bonding by open-to-air polymerization. An arch-shaped wire was drawn from a tip in a similar way to a metal wire, but the wire was formed from a polymer solution that solidified in the air during wiring. The DOW bonding was examined for silicon photonic chips where grating couplers are integrated for input/output coupling. Cone-shaped studs were formed at the ends of the wire, and their geometry was optimized using finite-difference time-domain simulation to give a mode conversion function. Although the polymer wire had a multimode scale of 7 µm, the wire bonding between the grating couplers showed a relatively low insertion loss of 5.8 dB at a wavelength of 1590 nm compared to a conventional connection using single-mode fiber blocks. It also showed a larger wavelength tolerance within the range of ∼1520-1590 nm. DOW bonding between a grating coupler and a single-mode fiber were also examined to verify the feasibility of out-of-plane connection with edge-coupling devices. The grating-to-fiber wire link also exhibited a large wavelength tolerance.