Strain sensing based on modal interference spectrum in polarization-maintaining fiber

We investigate a simple structure in which a polarization-maintaining fiber (PMF) is sandwiched between two single-mode fibers (SMFs). By injecting broadband light and observing the modal interference spectrum of the transmitted light in the 870 nm range, we identify a clear shift dependent on the strain applied to the PMF. In addition, we demonstrate that in the same wavelength range, the strain applied to the SMFs before and after the PMF does not influence the interference spectrum. This result confirms that only the PMF segment exhibits strain sensitivity.