Temperature-insensitive bending measurement method using optical fiber sensors

Abstract

This paper presents a new and simple method for indirect bending measurements. The main advantage of the proposed method is its immunity from temperature as well as electromagnetic interference. It uses small and simple-to-fabricate transducer-based fiber Bragg gratings tilted in the fiber core at a small angle. In this work, analysis of the characteristic changes in the transmission of tilted Bragg gratings with different bending treatments are presented. It is shown that selected areas of the spectrum are more or less sensitive to different fiber curvatures. Additionally, the sensitivity of the method to changes in the polarization angle is presented for selected examples. The division of the complete transmission spectrum into more or less sensitive areas provides a development of output parameter dynamics by improving the usable range. This paper shows the difference between the curvature-dependent transmission spectrum changes for 2-degree and 4-degree tilted gratings. The contour length changes in selected divided ranges of the spectrum have a quasi-linear character, which is promising for applications. The influence of changes in the input light polarization direction on changes in the calculated contour length is also investigated. In three boundary polarization cases, the greatest difference in the normalized contour length for a constant curvature radius is 0.01028, which is 1,028% of the maximum. The results for bending radius measurements based on contour changes are presented for the range from 30 to 12 mm, but the proposed system allows for bending radius measurements over a wider range.