Femtosecond laser-written integrated components for future all-fibre mid-infrared laser systems

Lasers emitting at mid-infrared (mid-IR) wavelengths in the 2.5-5 µm range are essential for various applications as this spectral region coincides with the vibrational-rotational absorption lines of many important atmospheric gases and liquid water. Fibre lasers are an efficient way to generate light at mid-IR wavelengths. However, mid-IR fibre laser technology is still in its infancy, mainly due to the non-existence of fibre coupled optical components to create all-fibre cavities, which severely limits their practical applications. This thesis investigates the feasibility of using a femtosecond laser to fabricate integrated components such as fibre Bragg gratings (FBGs), couplers and splitters which can add a new perspective for mid-IR all-fibre lasers. We report the development of a widely tunable (37 nm) all-fibre mid-IR laser based on a mechanically robust FBG which was inscribed through the polymer coating of a double clad fluoride fibre by focusing femtosecond laser pulses into the core of the fibre without the use of a phase mask. In a further step, the possibility of using on-chip optical couplers inscribed in fluoride and chalcogenide glasses is also investigated to pave the way for the realization of compact and robust mid-IR fibre laser systems for real-world applications in spectroscopy and medicine.