3D integrated optics enabled by inverse design and two-photon polymerization

Topology optimization is a powerful technique for inverse design, whose potential in nano and integrated optics is not fully explored yet due to fabrication limitations. In fact, most designs to date are obtained in 2.5D. 3D printing techniques, e.g. two-photon polymerization (2PP), are cost-efficient, provide faster prototyping capabilities than silicon foundries, and allow the manufacturing of free-form devices obtained via inverse design. Here, we explore for the first time the viability of 3D designs and their performance in comparison to 2.5D designs, laying the groundwork for potential integration of multiple functionalities, such as phase and polarization, within a single device instead of multiple discrete components. By overcoming the convergence issues characteristic of the polymer platform via multi-objective and multi-layer strategies, we realize 3D designs that are viable for manufacturing via 2PP for wavelength demultiplexing with better performance than their 2.5D counterpart.