Adjustment-free two-sided 3D direct laser writing for aligned micro-optics on both substrate sides

3D direct laser writing is a powerful and widely used tool to create complex micro-optics. The fabrication method offers two different writing modes. During the immersion mode, an immersion medium is applied between the objective and the substrate while the photoresist is exposed on its back side. Alternatively, when using the dip-in mode, the objective is in direct contact with the photoresist and the structure is fabricated on the objective facing side of the substrate. In this Letter, we demonstrate the combination of dip-in and photoresist immersion printing, by using the photoresist itself as immersion medium. This way, two parts of a doublet objective can be fabricated on the front and back sides of a substrate, using it as a spacer with a lateral registration below 1 mu m and without the need of additional alignment. This approach also enables the alignment free combination of different photoresists on the back and front sides. We use this benefit by printing a black aperture on the back of the substrate, while the objective lens is printed on the front. (c) 2022 Optica Publishing Group

Automated summary

3D direct laser writing is a powerful technique for creating complex micro-optics. It offers two different writing modes: immersion mode, where an immersion medium is used between the objective and substrate, and dip-in mode, where the objective is in direct contact with the photoresist. In this Letter, the combination of dip-in and photoresist immersion printing is demonstrated by using the photoresist as the immersion medium, allowing the fabrication of doublet objectives on both sides of a substrate with high precision.