Simultaneous temperature and refractive index sensing using etched few-mode fiber Bragg grating: Cross-sensitivity and mode coupling issues

Abstract

We examine the performance of a few-mode fiber Bragg grating sensor for refractive index and temperature sensing using ${\text{LP}}_{01}$ and ${\text{LP}}_{11}$ modes. We have obtained sensitivities for temperature and refractive index sensing and have examined in detail the role of cross-sensitivity in simultaneous measurement of these two parameters. We have based our simulation study on the available experimental results. Our study shows that the cross sensitivity is very small and is difficult to quantify reliably. Further, since fiber supports several modes when water or a water-based solution is used as cladding in the sensor, coupling to other modes particularly, the LP₀₁-LP₀₂ mode coupling must be minimized. We have obtained the optimum length to minimize this coupling without compromising the reflection characteristics of the LP₀₁ and LP₁₁ modes. Our results match well with the available experimental results.