Strain sensor based on two concatenated abrupt-tapers in twin-core fiber

In this paper, a novel and high sensitivity optical fiber sensor based on Mach-Zehnder interferometer (MZI) with two concatenated abrupt-tapers in twin-core fiber (TCF) is proposed and experimentally demonstrated. The setup includes two abrupt-tapers with different size in TCF and then spliced with two segment of normal single mode fibers (SMFs). The multiple cladding mode will be excited within the TCF, partly coupled with the core mode while in the first taper. After propagation of these coupled modes, they will be recouped in the second tapers. Through the two abrupt-tapers, we realized twice MZI. It is because of the two abrupt-tapers structure that the interference between modes is strengthened. Maximum interference resonance dips exceeds 19 dB. The interference fringe of this device would shift with the variation of strain. Therefore, we can desire the parameters through monitoring the wavelength shift of the transmission spectrum. The experimental results show that the sensitivity of the strain sensor is 6.39 pm/με when the resonance wavelength is 1466.2 nm. Especially, a higher sensitivity has achieved in this paper compared with other strain sensor, which sensitivity is up to 7.6 pm/με at 1716.5 nm with interferometer extinction ratio of 11 dB. The proposed sensor is easy-fabricated, low-cost and high sensitivity, which is very suitable for physical application of strain measurement.