Fiber Bragg gratings (FBGs) in the center of multimode microfibers (MM-MF) with 10μm diameter were successfully inscribed with point-by-point method and their reflection spectra show peaks over 10dB signal-to-noise ratio (SNR) and less than 0.5nm bandwidth. FBGs on regular size multimode fiber (~60μm core size) shows nearly continuous reflection spectrum. However, when the diameter of the multimode fiber is reduced to ~10μm, its modal volume significantly decreases so that the remaining optical modes are separated by larger propagation constant difference, resulting distinguishable sharp peaks on FBG reflection spectrum. Therefore, MM-MF based FBGs could be practical sensors for simultaneous multi-parameters with outstanding sensitivity and accuracy.
We proposed a Brillouin optical fiber time domain analysis (BOTDA)-based fully-distributed temperature system as high as 1000°C and spatial resolution to 5 meters. This technique is prominent for high spatial resolution fully distributed high temperature and stress sensing over long distance.
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