  Multi-photon lithography has emerged as a powerful tool for photonic
integration, allowing to complement planar photonic circuits by 3D-printed
freeform structures such as waveguides or micro-optical elements. These
structures can be fabricated with high precision on the facets of optical
devices and lend themselves to highly efficient package-level
chip-chip-connections in photonic assemblies. However, plain light transport
and efficient coupling is far from exploiting the full geometrical design
freedom that is offered by 3D laser lithography. Here, we extend the
functionality of 3D-printed optical structures to manipulation of optical
polarization states. We demonstrate compact ultra-broadband polarization beam
splitters (PBS) that can be combined with polarization rotators (PR) and
mode-field adapters into a monolithic 3D-printed structure, fabricated directly
on the facets of optical devices. In a proof-of-concept experiment, we
demonstrate measured polarization extinction ratios beyond 11 dB over a
bandwidth of 350 nm at near-infrared (NIR) telecommunication wavelengths around
1550 nm. We demonstrate the viability of the device by receiving a 640 Gbit/s
dual-polarization data signal using 16-state quadrature amplitude modulation
(16QAM), without any measurable optical-signal-to-noise-ratio (OSNR) penalty
compared to a commercial PBS.
