Precision laser direct writing of polymer optical waveguides and optofluidic systems

We present a flexible fabrication setup for precision Iaser direct writing of µm-sized polymer structures. As a demonstration, multimodal waveguides on printed circuit boards were fabricated. These waveguides play a key role in short-distance communications and medical diagnostics. Laser direct writing is superior to mask based exposure techniques, as it yields smooth sidewalls and offers the flexibility to locally vary the exposure area. Our setup uses standard components and can be extended easily by further degrees of freedom and process feedback. A lower cladding and core layer (EpoClad, SU-8) are fabricated by spin coating at a thickness of 50 µm. Focused UV light (375 nm) exposes the photosensitive core material. A Gaussian intensity profile with a beam waist of 33 µm (M² = 1.08) has been confirmed by beam profiling. A motorized high-precision XY translation stage provides constant velocity motion. Optionally, we perform a second mask-based exposure. The development is followed by a post exposure and a final hard bake. An optical cladding layer is processed as well. We integrate these waveguides with polymer microfluidic systems for biofluid characterization.