Optical fiber sensors embedded in metals with distributed sensing can sense temperature at multiple points with single fiber. This is useful for smart manufacturing like structural health monitoring in aerospace industry and smart molds in manufacturing plants. There is a huge difference in thermal coefficient of expansion for fiber and metal. This is the reason for the increase in sensitivity for embedded fiber sensors. However, at high temperatures, the stress on the fiber increases, eventually damaging the sensor. The fiber-metal interface determines the sensor performance. A tight interface results in high sensitivity and a gap in the interface enhances sensing range. There is a dilemma to choose either high sensitivity or high sensing range. The objective of this study is to enhance the interface to have both high sensitivity and high sensing range which can be used for casting application. Extrinsic Fabry-Perot interferometer (EFPI) sensors with a single sensing point and cavity length around 50 μm are embedded into copper substrate using electrodeposition. The embedded sensors are 300 μm deep from the surface. Three different interface: chemical plated, copper painted, and dual-layer interface, were tested. The results show that dual-layer interface can provide both high sensitivity of 45 pm/°C and high sensing range of 700°C at the same time, which overcomes sensitivity-sensing range dilemma. The analysis shows that one layer in the dual-layer interface increases the longitudinal strain for sensitivity and the other layer reduces the radial strain which enhances the sensing range. This new dual-layer interface developed in this research can have high sensitivity and high sensing range at the same time. Aluminum casting was done to test the effectiveness of the dual-layer interface. The cooling curve data from the EFPI sensor is consistent with the thermocouple data --Abstract, page iv
