Abstract:We introduce the concept of mechanically stretchable optical waveguides. The technology to fabricate these waveguides is based on a cost-efficient replication method, employing commercially available polydimethylsiloxane (PDMS) materials. Furthermore, VCSELs (λ = 850 nm) and photodiodes, embedded in a flexible package, were integrated with the waveguides to obtain a truly bendable, stretchable and mechanically deformable optical link. Since these sources and detectors were integrated, it was possible to determine the influence of bending and stretching on the waveguide performance. Appl. Phys. Lett. 85, 3435-3437 (2004). 7. J. A. Rogers, T. Someya, and Y. Huang, "Materials and mechanics for stretchable electronics," Science 327, 1603Science 327, -1607Science 327, (2010. 8. T. Sekitani, Y. Noguchi, K. Hata, T. Fukushima, T. Aida, and T. Someya, "A rubberlike stretchable active matrix using elastic conductors," Science 321, 1468Science 321, -1472Science 321, (2008. 9. D. Pham, H. Subbaraman, M. Chen, X. Xu, and R. Chen, "Self-aligned carbon nanotube thin-film transistors on flexible substrates with novel source -drain contact and multilayer metal interconnection," IEEE Trans. Nanotechnol. 11, 44-50 (2012).

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Tactile shear stresses play an important role in the medical field and robotics. To monitor these stresses in situ, there is a need for unobtrusive flexible sensors that can be wrapped around curved surfaces or moving body parts. The presented sensor is based on changing coupling of optical power between a verticalcavity surface-emitting laser (VCSEL) and a photodiode facing each other and separated by a deformable transducer layer. The required optoelectronic components were embedded in a polymer foil of only 40 m thick, yielding a very thin and flexible total sensor stack of 250 m thick. In the linear part of the range (between 2 and 5.5 N), the sensitivity of the prototype was 350 A/N; the maximum measurable force was 5.5 N. However, by selecting the appropriate deformable sensor transducer material, the sensitivity and range can be tuned for a specific application.

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Thin and flexible photonic sensor foils are proposed, fabricated, and tested as a promising alternative for monitoring composite structures. Sensor foils are implemented using two different optical polymers and as such optimized for multi‐axial sensing and embedding within composite materials, respectively. It is first shown that those sensor foils allow multi‐axial strain sensing by multiplexing a multitude of Bragg grating sensors in a rosette configuration. Secondly, those sensors can be realized in very thin foils (down to 50 µm) making them suitable for embedding in composite materials during their production. This is proven by visually inspecting and by testing the functionality of the embedded sensors. Finally, owing to their low Young's modulus and flexibility, polymer sensor foils can be bent to small curvature radii and withstand large elongations. Herein, the sensors are bent down to a radius of 11 mm, and elongated by 1.4% without losing functionality.

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