Multi-point sensing in gas turbines using fiber-based intrinsic Fabry-Perot interferometers

It is well known that using a single-mode lead-in fiber, a multi-mode fiber section as a Fabry-Perot cavity, and an additional single-mode fiber as the tail results in a structure that generates strong interference fringes while remaining robust. Due to their compact size, sensitivity, and ability to be multiplexed, intrinsic Fabry-Perot interferometers (IFPIs) are excellent candidates for almost any multi-point temperature or strain application. Four of these sensors were to be installed on a 2"x2" coupon for installation in a simulated gas turbine environment. Though the basic principles behind these sensors are well known, serious issues associated with geometric constraints resulting from the size of the test coupon, sensor placement, and mechanical reinforcement of the fiber arose; fabricating a sensor chain with appropriate sensor spacing and excellent temperature response characteristics proved a significant challenge. Issues addressed include inter-sensor interference, high-temperature mechanical reinforcement for bare fiber sections, and high bending losses. After overcoming these problems, a final sensor chain was fabricated and characterized. This chain was then subjected to a battery of tests at the National Energy Technology Laboratory (NETL). Final results are presented and analyzed.