Acoustically scanned low-coherence interrogated simultaneous measurement of absolute strain and temperature using highly birefringent fibers

We have utilized a traveling acoustic pulse in a two-mode optical fiber to create a moving beam splitter coupling light from LP₀₁ to LP₁₁ mode. As these optical modes have different group velocities, a variable intermodal delay is generated as a function of acoustic pulse position in the fiber. The device can be used as a receiving interferometer in low-coherence interferometry to scan time delay for carrying out fast extended range absolute measurement using simple analog electronic circuits. With this scanning technique we demonstrate measurement of absolute strain over 1600 με in the temperature range from 20 to 60°C with resolutions of the order of 40 με and 0.7°C, respectively, employing highly birefringent fibers as sensing elements