Ultrasensitive strain sensor based on Mach-Zehnder interferometer with bent structures

In this paper, an all-single-mode fiber strain sensor based on a bent structure Mach-Zehnder interferometer (BS-MZI) is proposed. This sensor consists of two identical bent structures, one of which excites the cladding modes, and the other couples them back to the core. Interference occurs when the cladding and the core modes meet each other. Therefore, the bent structures function as an MZI. The bent structures are fabricated by releasing the pulse of the CO2 laser along the specific designed paths. The fiber shaping method based on CO2 laser polishing is flexible, which is demonstrated in detail. The unique geometrical shape of the bent structures brings high strain sensitivity to the sensor. As a consequence, the sensor with a length of 9.6 mm exhibits an ultrahigh strain sensitivity, which reaches 165 pm/. Experimental results show that the strain responses of the BS-MZIs are highly correlated with their interference lengths and the modulated lengths. Its temperature-strain cross-sensitivity is as low as 0.21 /. Moreover, the sensor exhibits high stability and repeatability in strain measurement, which makes it a promising sensor in strain measurement.