Their paper "Hybrid integration of silicon photonics circuits and InP lasers by photonic wire bonding" published in the Optica journal detail how starting from readily processed III–V lasers and photonic circuits assembled side by side on a common heat-sinking carrier substrate, they could connect the dies' optical paths through 3D lithography-designed photonic wire bonds, manufactured in-situ to accommodate for any misalignments.
This hybrid integration allows photonic chip designers to integrate the best characteristics of native III–V light sources together with silicon-based modulators, only using pre-tested chips and conventional pick-and-place equipment, yet achieving very low insertion losses (down to 0.4 dB) compared to 2.3dB optical coupling losses as reported so far in literature.
As the authors explain, the photonic wire bonding (PWB) is fabricated in-situ relying on the additive nanofabrication of freeform polymer waveguides between the pre-positioned photonic chips. That means the optical paths can be freely configured in 3D between the chips for the best fit while relaxing die-placement accuracy.
As a demonstration, the researchers connected indium phosphide (InP)-based horizontal-cavity surface-emitting lasers (HCSEL) to passive silicon photonic circuits. But using the same photonic wire bonding strategy, they had already successfully demonstrated direct SiP chip to SiP chip bonding and connected the individual cores of a multi-core fibre to an array of planar SOI waveguides.