Design and 3D printing of soft optical waveguides towards monolithic perceptive systems

Integrating sensors into soft systems poses significant challenges in fabrication, assembly, and integration. Optical sensors represent a valuable solution due to their rapid response, minimal wiring, and negligible electromagnetic susceptibility. Still, developing optical soft sensing via additive manufacturing, like stereolithography (SLA), remains underexplored. Indeed, there’s a strong potential to unlock the fabrication of intricate and integrated perceptive structures, eliminating the need for assembly processes or multi-material interfaces that can compromise durability and signal accuracy. This study introduces a novel and versatile approach for developing soft optical bending sensors with enhanced performance by SLA. We systematically investigate the role of printed layers’ orientation for the mechanical and optical properties of the material, focusing on its effect on light attenuation in optical waveguides. The high resolution and design freedom of SLA are leveraged to finely incorporate superficial pattern (or wells) with precisely tunable dimensions, leading to light scattering phenomena. The optical loss and signal linearity trade-off was investigated by Finite Element Method (FEM) simulations, and the experimental results indicate the optimal design for sensors printed at different orientations, e.g. , 1.2 mm × 1 mm × 1.55 mm rectangular wells for waveguides printed orthogonally to the building platform. To demonstrate the potential of this approach for developing fully integrated sensorized architectures, we present a proof-of-concept consisting of three sensors printed monolithically in a lattice structure. The versatility and scalability of our method contributes to the field of additive manufacturing by enabling the creation of smart soft systems with embedded soft sensors, suitable for a wide range of applications that benefit from responsive and flexible sensing capabilities. • Fabricated soft optical bending sensors via SLA 3D printing of elastomeric resin. • Sensing response enhanced by tuning surface structure of deformable waveguides. • Orientation of printed single layer influences sensor’s mechano-optical properties. • Demonstrated a Monolithic Proprioceptive Unit (MPU) integrating three sensors in one print.