Focused ion beam milling of optical fiber sensors is a very recent field that first started with the milling of apertures on fiber tips, but it is the assessment of the viability and potential of applying this technology to the creation of optical fiber sensors that is the main goal of this thesis. To achieve this, an initial round-up of instances where focused ion beam was applied to optical fibers, whether as a mere investigative tool or as the core technique of a fabrication procedure, was performed. This allowed a global view of what had been done before and what could still be done and how. In the recent past, focused ion beam has been successfully used to fabricate structures on optical fibers but the question if the technology had further potential or was simply a publication gimmick, remained. This work shows that focused ion beam has a promising future in creating optical fiber structures with a quality and resolution that cannot be replicated with other techniques.

Detailed procedures for preparing optical fibers for focused ion beam milling are described throughout the thesis. Microwire fabrication and dynamic chemical etching of tapered fiber tips are just two of the techniques used to prepare intermediate fiber structures for efficient milling. Taking advantage of suspended microwires, focused ion beam milling was used to cleave said microwires and create a suspended microwire cantilever structure, on a fiber end, for vibration sensing. Such a cleave, due to the abnormal configuration of the microwire structure, is easily achieved with focused ion beam but would be a challenge using conventional techniques.

Further, the milling of Fabry-Perot microcavities on tapered fiber tips came as a need from the field of optogenetics and neural signal recording. Microcavity probes capable of sensing temperature and refractive index simultaneously were milled and characterized. These probes are currently being tested for optical recording of neural activity in rat brains.

Finally, a push towards even smaller details was achieved with the fabrication of fiber Bragg gratings on tapered fiber tips. Such geometric, corrugation-based gratings allow for high-temperature operation in extreme environments and their fabrication led to the limit of the focused ion beam system available in our lab.