Distributed Pressure Sensing Using an Embedded-Core Capillary Fiber and Optical Frequency Domain Reflectometry

In this paper, we describe a distributed pressure sensor using a simplified and high sensitive microstructured optical fiber - the embedded-core fiber - and autocorrelation analysis of the data obtained from an optical frequency domain reflectometer (OFDR). The special fiber consists of a microcapillary, which has a germanium-doped core placed within the capillary wall. When this structure is subjected to pressure variations, an asymmetric stress distribution is induced within the fiber, entailing birefringence variations. Here, we show that the use of a commercial OFDR with submillimeter resolution-together with an autocorrelation data analysis routine in the spectral domain allows mapping the fiber birefringence and performing distributed pressure sensing. In the experiments, the fiber passed through two pressure chambers, which allowed for pressure to be locally and independently applied. No cross-sensitivity between the pressure points was observed. The embedded-core fiber exhibited a birefringence sensitivity to pressure of 3.8×10
^-7
bar
^-1
, which is 21% higher than that measured in commercial photonic crystal fibers using the same setup.