Optical fiber sensor with a lateral-offset structure assisted by virtual vernier effect for stretching strain measurement

Abstract

This paper proposes an optical fiber sensor based on multimode interference (MMI) with a lateral offset structure to measure tensile strain. The coupling ratio of each higher-order mode in the coreless fiber (NCF) can be controlled by the dislocation distance. The experimental results show that the best interference fringes are obtained when the dislocation is 10μm and the sensitivity in the range of 0–500 μɛ is 28 pm/μɛ. To improve the sensitivity of the sensor further, the measured data were filtered by fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) to obtain a sinusoidal component, superimposed with a simulated signal to form a vernier effect. With the method of virtual vernier effect, the sensitivity is increased to 452.64 pm/μɛ, which is 15.6 times the original sensitivity. Compared with the traditional vernier effect, the virtual vernier effect method does not require cascade or series method, the reference part is not affected by the environment, and the method can be widely used in many types of interferometric fiber optic sensor devices, especially to overcome the problem that MMI is not suitable for vernier effect.