3D Printing for Optical Fibre Applications

Abstract

The objective of this thesis is to combine the technology of silica and polymer fibre Bragg (FBG) gratings with fused deposition modelling (FDM), which is an additive layer manufacturing (3D printing) technique. The research into optimising transparency of the printouts allowed the printing of solid-core and hollow-core preforms of poly(methyl methacrylate) (PMMA) and polycarbonate. The first microstructured polymer optical fibre was then fabricated from the 3D-printed solid-core polycarbonate preform. This was the first fibre drawn from a 3D-printed preform to show single-mode operation (at a wavelength of 870 and 1550 nm). Moreover, the fibre displayed the lowest attenuation of all the fibres drawn from 3D-printed preforms reported so far, with a lowest attenuation figure of ~0.27 dB/cm in a few spectral regions (780-785 nm, 820-825 nm, 953-956 nm, 1070-1090 nm). Also, FBGs were inscribed in the fibre using three different laser systems: a 248-nm nanosecond krypton-fluoride laser, a 517-nm femtosecond laser, and a 325-nm continuous-wave helium-cadmium laser. The temperature sensitivity of the latter FBG was measured to be -21.3±1.9 pm/°C. Finally, the linear coefficient of thermal expansion and the thermo-optic coefficient of the fibre were measured to yield the values as low as 7.34±0.53×10-7 °C-1 and -39.4±3.7×10-6 °C-1, respectively. FDM was also used to embed polymer and silica FBGs into 3D printed protective housings. The printing process was paused midway to introduce the fibre. Such sensing patches were found to provide good mechanical protection while the measured strain sensitivity amounted to 92% of this for the unembedded grating. Furthermore, embedded silica FBGs yielded a temperature sensitivity 103±14 pm/°C. This figure is over 12 times higher compared to unembedded silica gratings and two times higher compared to polymer FBGs of the highest temperature sensitivity. Finally, embedded silica FBGs were capable of gauging humidity, its sensitivity value being measured as 13.8±1.1 pm/%RH.