The application potential of sub-structured fiber tips in optical sensor technology and photonic microsystems is high. The miniaturization of sensor systems and the technical implementation using optical fibers allow novel sensor designs with improved properties and extended functionality. The post-processing of specifically doped or undoped silica fibers by chemical etching or focused ion beam etching (FIB) are promising methods in order to form complex photonic microstructures at the end or on the inside of glass fibers in the form of tips or cavities. The profiling of fiber tips was achieved through different etching rates that depend on the type of treatment and the doping characteristic of the fiber. Based on etch-structured microcavities with embedded fiber tips high-sensitivity Fabry-Perot temperature sensors were prepared and subjected to temperature variations both in air and water. An ultra-high sensitive strain sensor is proposed, too. The sensing head, based on the post-processing of a fiber Bragg grating, is used to perform passive strain measurements. Both wavelength and full width half maximum dependences with the applied strain. Furthermore, a novel fluid sensor concept consisting of a 5-hole microstructured fiber, FIB-inscribed with microfluidic canals is introduced.