Fabrication of flexible PDMS optical waveguides by soft lithography and capillary filling

Flexible optical waveguides are crucial for emerging soft photonic systems, yet their fabrication in elastomeric substrates remains challenging due to difficulties in filling high-aspect-ratio microchannels with viscous materials. To resolve this issue, we present a simple and scalable method for fabricating PDMS-based optical waveguides using soft lithography and capillary-driven filling. This method uses temperature-aided filling which enhances the complete and uniform filling of microchannels without external pressure. To demonstrate this, a droplet of UV-curable photoresist is introduced at the microchannel entrance and fills the structure completely under mild thermal assistance. Optical characterization of the fabricated waveguides at 638 nm reveals low propagation loss (~0.53 dB/cm), validating the approach for use in soft, flexible, and integrated photonic systems such as wearable sensors and lab-on-chip devices.