Sensing with a Biodegradable, Agar-made Structured Optical Waveguide

Biodegradable optical waveguides are emerging technologies for illumination, actuation, and sensing. Aside from available biopolymer-based optical fibers, flat designs prevail in microfluidics, imaging systems, and tactile interfaces. Therefore, we propose a flat and soft multimode waveguide made of agar, an edible and renewable phycocolloid. While a straightforward molding procedure generates a core/cladding structure with 12 concentric air holes, the glycerol addition improves the mechanical characteristics and reduces the optical loss (2.4 dB/cm). Subsequently, we explored speckle pattern analysis in force magnitude/position and temperature measurements, achieving practical resolutions of 0.05 N, 0.03 mm, and 0.42 °C, respectively. Moreover, pilot experiments demonstrated the sensor's response to surrounding fluids based on the hydrogel's swelling/syneresis behavior. These results motivate forthcoming applications in human-computer interaction, environmental surveillance, and biochemical/biomedical setups.