Three-parameter high-precision sensor based on superimposed cladding-reduced coated long-period fiber grating and fiber Bragg grating

摘要

Abstract In this paper, a coated cladding-reduced superimposed long period fiber grating and fiber Bragg grating structure (SLBG) is proposed, which could measure three parameters, strain, temperature and surrounding refractive index (SRI), simultaneously. Firstly, the mode-coupling behaviors in the structure is determined according to the phase matching conditions, and thus the coupled-mode equations of the structure is given by coupled-mode theory. Then, the simulated transmission spectrum shows three attenuation peaks generated by the coupling between forward core mode with forward cladding modes, the backward core mode and backward cladding modes respectively. To make demodulation more convenient and accurate, the structure is optimized. The signal-to-noise ratio is improved by reducing the attenuation peak amplitude based on the corroded cladding, and the sensitivity is enhanced based on mode barrier effect caused by high refractive index film. After the optimization, the simulation results of the response of the three transmission peaks to three parameters show good performance in both sensitivity and linearity (all larger than 0.999). The maximum sensitivities of three transmission peaks to strain, temperature, and SRI are 3.15?pm/με, 817.6?pm/°C, and ??3472?nm/RIU, respectively. Finally, the condition number of the parametric demodulation matrix is 6.0046, indicating the inversion of the resonant wavelength offset has high precision. This paper provides reliable theoretical guidance for the design of superimposed fiber grating structure, and the proposed structure can be applied to submarine communication optical fiber monitoring.