Design and Fabrication of Stretchable Photonic Fibers

Optical fibers have reshaped the technological landscape, from optical networks and high-speed data communication to in situ imaging and non-invasive surgery methods. The revolution allowed by these fibers has been made possible by its fabrication method, the thermal drawing process, which combines high scalability and nanoscale fabrication accuracy. Despite tremendous successes, silica step-index and photonic crystal fibers have held intrinsic limitations due to their mechanical rigidity and fragility, limiting their possible applications . There is however an increasing demand for optical fibers that could guide light efficiently while sustaining large deformations in fields like robotics, smart textiles and the automotive world. Other fields in sensing, helath care or advanced textiles could benefit from soft fibers that could display tunable optical effects. Techniques like lithography and molding have proven valuable to fabricate complex elastomeric photonic fibers, but their limited scalability intrinsically limits their use in several fields of application. On the other hand, scalable fabrication techniques like extrusion guarantee the desired throughput but fail to deliver the architectural complexity required to realize softfibers advanced optical properties. In this thesis, we propose to exploit the thermal drawing process to realize different types of soft and highly stretchable optical fibers, from the classic step-index architecture to 1D photonic crystal fibers, liquid core fibers and 2D photonic crystal fibers. To achieve this overall objective, we first establish a theoretical framework to evaluate the material requirements from the rheological, optical and mechanical point of view. After selecting the materials, we develop a step-by-step fabrication process that starts from the material pellets and ends with the fabrication of meters of elastomeric photonic fiber via thermal drawing. We then move on to fully characterize the optical and mechanical properties of the fibers and design several fiber-based devices with specific optical effects. More specifically in Chapter 2, we demonstrate the materials selection, innovative fabrication process, and the optical and mechanical characterizations to realize a soft optical wave-guide based on a step-index design. To highlight its optical and mechanical performance, we demonstrate a strain sensing sport gear that integrates this newly developed fiber. In chapter 3, we go one step further in the control over feature size by going about a similar demonstration for a 1D photonic crystal fibers based on all-elastomeric materials, with feature sizes down to sub-100 nm. We show in particular a mechanochromic fiber that can reversibly change color upon stretching. In Chapter 4, we propose a series of other fiber architectures based on our scientific and technological achievements that include a multicore stretchable step-index fiber that form the basis of an advanced demonstrator of a soft fiber with multiple channels and functionalities found in endoscopes. We also present preliminary results on a liquid-core step index fiber, and a stretchable 2D photonic crystal fiber, that pave the way towards highly complex and high-performance soft optical fiber devices.