  Photonic integrated circuits utilize various waveguide materials, each
excelling in specific metrics like efficient light emission, low propagation
loss, high electro-optic efficiency, and potential for mass production.
Inherent shortcomings in each platform push exploration of hybrid and
heterogeneous integration, which demands specialized designs and extra
fabrication processes for each material combination. Our work introduces a
novel hybrid integration scheme employing a 3D-nanoprinted interposer for a
photonic chiplet interconnection system. This method represents a generic
solution that can readily couple between chips of any material system, with
each fabricated on its own technology platform with no change in the
established process flow for the individual chips. Mode-size engineering is
enhanced by the off-chip parabolic micro-reflectors. The 3D-nanoprinted
chip-coupling frame and fiber-guiding funnel enable low-loss, fully passive
assembly with a fast-printing process achieving sub-micron accuracy.
Mode-field-dimension conversion ratio of 5:2 from fiber to chip is demonstrated
with <0.5dB excess loss on top of the 1.7dB inherent coupling loss, marking the
largest mode size conversion using non-waveguided components. Additionally, our
system demonstrates a 2.5dB die-to-die coupling loss between silicon and InP
chips over a 140nm wavelength range (1480nm to 1620nm), showcasing the
potential for extensive cross-platform integration by bridging different
waveguide materials.
