Low-coherence interferometric fiber sensor with improved resolution using stepper motor assisted optical ruler

Low-coherence interferometric sensing is typically used to detect phase changes without simultaneous optical ruler calibration in order to by-pass light intensity fluctuations and the periodic nature of the interferometric signal. An interferogram from a two-staged optical low-coherence Mach-Zehnder interferometer is proposed to double the sensitivity improvement for fiber strain sensing. A 1310-nm wavelength distributed feedback laser implemented in an optical ruler achieved 655-nm resolved characterization from its high-coherence interferogram, which could further be enhanced to an average of 18.9 nm using a stepper motor assisted optical ruler. A 2.7-nε high strain resolution was then demonstrated on a 3-m long fiber sensing arm in a Mach-Zehnder interferometer. The relative movement distances between the interferograms were utilized to experimentally show the strain and force sensitivity as 6.8 μm/με and 8.5 μm/mN, respectively.