  We report single-mode 3D optical couplers leveraging adiabatic power transfer
towards up to 4 output ports. We use the CMOS compatible additive (3+1)D
\emph{flash}-TPP printing for fast and scalable fabrication. Coupling optical
losses of such devices are reduced below $\sim$~0.06~dB by tailoring the
coupling and waveguides geometry, and we demonstrate almost octave-spanning
broadband functionality from 520~nm to 980~nm.

Optics