Microstructured polymer optical fibres fabricated from 3D printers for sensing applications

Abstract

This research project had focused on the development of a novel optical fibre drawing technique based on a 3D printer to fabricate microstructured polymer optical fibres (MPOFs) in a single step for the sensing applications. The aim of this work is to overcome the drawbacks of the conventional drawing-tower based fabrication techniques, including the time-consuming, incapable of producing more complex non-geometrical structures, and high-cost. The research starts with studying the sensing capabilities of micro/nanofibre devices. A nanofibre coupler (NFC) operating near the cut-off region of the higher order supermodes for thermal and refractive index sensing was proposed and experimentally demonstrated. The microfibre coupler (MFC) was also considered for biological sensing applications due to its large evanescent field. DNA covalent attachment on the coupler surface has been demonstrated through the functionalisation, immobilization and hybridization processes. Covalent attachment and hybridization of the DNA on the MFC surface was confirmed via the fluorescent image that shows successful bonding to the complementary DNA strand that contains a fluorescent label. Then, the research was moved to establish new methods for manufacturing MPOFs sensors with built-in fluidic channels. The research started focusing on fibre preforms, with the design and 3D printing of a structured hollow-core polymer fibre preform. A commercial 3D printer was used to manufacture the preform, which was drawn into a hollow-core MPOF using a conventional fibre drawing tower. Guiding in the mid-IR was observed, with a propagation loss of 0.3 dB/mm at the wavelength of 4.5 µm. Although 3D printed structured polymer fibre preforms can be drawn into MPOF, large deformations in the fibre geometry were observed during the drawing process. Therefore, extrusion of MPOFs directly from a modified structured nozzle of a 3D printer was investigated. 3D printer nozzles, with structures complimentary to those of the MPOFs, were developed and fabricated by two techniques: micromachining and metal 3D printing. Simulations of heat transfer and material flow in the heated nozzle were also studied. Two structures of MPOFs were fabricated using this technique: the suspended-core fibre and the hexagonal hollow-core fibre. The suspendedcore fibre was fabricated for guiding in the optical communication and Terahertz (THz) bands, while the hollow-core fibre for mid-IR and THz. The microstructure inside the MPOFs was maintained, and guiding in near-IR, mid-IR, and THz region was observed. This research was the first successful attempt of direct extrusion of microstructured polymer optical fibres from a 3D printer which reduce the MPOF fabrication time and a step of optical fibre fabrication into a single step