Strain sensor based on sectional crosstalk change in dual-core fibers

Multi-core fibers are recognized as the medium designed to be used in telecommunication for space division multiplexing. At the same time, they can be advantageously used in sensor technology. The most crucial parameter for multi-core fibers is crosstalk, as its presence at a high level is found to be highly undesirable in telecommunication applications. However, this phenomenon can be used advantageously in the construction of new types of fiber optic sensor. For the strain sensor, we used a dual-core microstructured fiber. In the research presented, we take advantage of the technology of fiber post-processing, namely fiber tapering. This treatment, which enables changes in the conditions for interference between supermodes, makes the fiber sensitive to elongation. In the un-tapered section, supermodes do not interfere efficiently (crosstalk <-50 dB), whereas in the tapered section the crosstalk increases significantly (crosstalk = 0 dB meaning all the power from one core can be transferred to the neighboring core), creating a strain sensitive area. The distribution of power between the cores of a multi-core fiber at the output of the sample depends on the elongation of the sample. The strain value can be read off both in the domain of power and wavelength. Research results show that sensor performance can be adjusted by changing the taper length and ratio. The results presented are promising for the construction of a temperature independent strain sensor, whose strain sensitivity (17nm/mε) is far better than optical fiber sensors based on Fiber Bragg Gratings. Meanwhile, the temperature sensitivity is negligible assuring no cross-sensitivity.