Technique for an interrupt-immune two-mode fiber-optic strain sensor

The concept for an interrupt-immune two-mode sensor based on the absolute variation of the two-mode modulation depth in the single-mode cutoff transition region as a function of strain is developed and demonstrated. While the minimum resolution for absolute measurement greatly depends on the detection electronics, with the experimental apparatus used for the present research a resolution of 400 microstrain, which corresponds to a shift in the cutoff wavelength by 83 pm or a 1.2-dB reduction in the modulation depth, was achieved. The minimum resolution may be improved by optimizing the cutoff transition curve of the fiber.