| Fiber sensors are particularly attractive for harsh environment defined by high temperature, high pressure, corrosive/erosive, and strong electromagnetic interference, where conventional electronic sensors do not have a chance to survive. However, the key issue has been the robustness of the sensor probe (not the fiber itself) mostly due to the problems stemmed from the traditional assembly based approaches used to construct fiber optic sensors. For example, at high temperatures (e.g., above 500°C), the thermal expansion coefficient mismatch between different composited parts has a high chance to lead to sensors' malfunction by breaking the sensor as a result of the excessive thermo-stress building up inside the multi-component sensor structure. To survive the high temperature harsh environment, it is thus highly desired that the sensor probes are made assembly-free. We are proposing to fabricate assembly-free fiber sensor probes by manufacturing various microstructures directly on optical fibers.;This dissertation aims to design, develop and demonstrate robust, miniaturized fiber sensor probes for harsh environment applications through assembly-free, laser fabrication. Working towards this objective, the dissertation explored three types of fiber inline microsensors fabricated by two types of laser systems. Using a CO2 laser, long period fiber grating (LPFG) and core-cladding mode interferometer sensors were fabricated. Using a femto-second laser, an extrinsic Fabry-Perot interferometric (EFPI) sensor with an open cavity was fabricated. The scope of the dissertation work consists of device design, device modeling/simulation, laser fabrication system setups, signal processing method development and sensor performance evaluation and demonstration.;This research work provides theoretical and experimental evidences that laser fabrication technique is a valid tool to fabricate previously undoable miniaturized photonic sensor structures, which can avoid complicated assembly processes and, as a result, enhance robustness, functionality and survivability of the sensor for applications in harsh environments. In addition, a number of novel optical fiber sensor platforms are proposed, studied and demonstrated for sensing and monitoring of various physical and chemical parameters in high temperature harsh environments. |
