Quasi-static pressure sensitivity characterization of single-mode optical fibers

We present a measurement setup designed to characterize the pressure sensitivity of single-mode optical fibers, whether freestanding or embedded within a structure. The system uses an unbalanced interferometer, with its long arm consisting of the fiber under test. This fiber is placed inside an air-sealed chamber and submerged in water. Pressure is modulated in a sinusoidal pattern at 1 Hz by injecting air above the water bath. Because the fiber is fully immersed in a water bath with large thermal capacitance, we expect the temperature fluctuations to be strongly attenuated at 1 Hz; thus, the fiber primarily experiences the applied pressure modulation rather than temperature-induced phase changes. We also detail the data processing method, which leverages the non-linear response of the interferometer to accurately extract the fiber's pressure sensitivity. Using this setup, we characterize five standard optical fibers with different coatings, jackets, and geometries, obtaining pressure sensitivities ranging from 40 to 530 μrad Pa-1 m-1. The experimental results are in good agreement with predictions from a standard model. In addition, we demonstrate the setup capability to measure the pressure sensitivity of more complex samples, for which the model is no longer valid. As an illustration, we study how the fiber pressure sensitivity depends on the embedding depth for fibers inserted into Plexiglas plates. We believe that this experimental characterization setup can be useful for the development of new smart materials relying on fiber sensing.