High-resolution 3D-printed reflective micro-collimators for facet-emitting mid-infrared lasers

Highly divergent and asymmetric beam profiles are an inherent limitation of facet-emitting mid-infrared semiconductor lasers and complicate their use in free-space optical systems. In this work, we demonstrate beam collimation of a facet-emitting interband cascade laser using a gold-coated parabolic mirror fabricated by high-resolution two-photon lithography. A three-dimensional adaptive resolution printing strategy with dynamically adjusted voxel size for shorter print times is employed. The additively manufactured mirror is externally coupled to the laser and redirects the emitted beam by 90°, transforming the strongly divergent facet emission into a collimated free-space beam without modifying the laser cavity. Beam profiles are characterized experimentally over a propagation distance of up to 32 cm and show a substantial reduction in divergence compared to the uncollimated emission. Wave-optical simulations performed in Ansys Zemax OpticStudio reproduce the measured beam evolution and provide insight into the influence of finite mirror geometry and modal asymmetry. The results demonstrate the potential of 3D-printed reflective micro-optics as flexible beam-shaping elements for mid-infrared laser sources and highlight a pathway toward integrated, alignment-free optical systems.