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A novel optical fiber sensor based on weak coupling twin-core fiber (TCF) is proposed and experimentally demonstrated. The sensing structure consists of two single mode fibers (SMF) and fabricated by program controlled tapering the spliced region between the first SMF and a segment of TCF. During this period the light power was gradually transferred from the SMF into the cladding mode near the waist zone, after the waist zone, the optical power was gradually concentrated from the cladding mode into the cores mode, which could affect the extinction ratio of the interference peaks in the transmission spectrum. In order to obtain better interference spectrum, we adjusted the fusion structure of the tail fiber and the TCF, and the cross sections of the optical fibers are dislocated to a certain extent, so that the interference process of the beam changes. In the process of adjusting the structure, we observed the spectral changes in the spectrometer at the same time until the best interference spectrum appeared, and then we completed the fusion. The interference between different modes can be affected by changes in the external environment, like refractive index (RI) and strain, which also dictates the wavelength shift of the transmission spectrum. In the experiment, we have studied the sensing response of the optical fiber sensor to the RI and strain, and the sensing sensitivity is 131.1nm/RIU and 1.26x10-3 dB/με respectively. All sensors fabricated in this paper show good linearity in terms of the spectral wavelength shift.
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