Generation of a high-resolution 3D-printed freeform collimator for VCSEL-based 3D-depth sensing

This Letter discusses the generation of 3D-printed micro-optics to obtain the desired beam profile from a multimode vertical-cavity surface-emitting laser (VCSEL) with a significantly reduced divergence angle via the usage of high-resolution two-photon polymerization. Due to the low cost and compact packaging, the VCSEL array is a novel light source for structured-light projection. Particularly for long-distance 3D sensing applications, a greatly reduced divergence angle ensures that a good signal with a sufficiently large number of photons can be recorded, and the projected illumination spots do not overlap. Therefore, exact laser beam characterization and appropriate physical modeling are required in accurate production of an optimal collimator lens. Furthermore, elliptical beam profiles with different orientations can solve the correspondence problem and improve the post-processing speed and robustness in structured light. To generate this special type of beam profile and verify the optical design process, this Letter describes thoroughly the optical prototyping process starting from the beam characterization, the optical design to the production of the two-photon polymerized optics, and its validation. The test of the beam profile and divergence confirm a good match of the produced optics with the physical optical simulation in Zemax. The collimator transforms the input laser beam divergence angle of 324 mrad to an output angle of 20 mrad only.