Axial Strain Measurement Based on Dual-Wavelength Ratio for Helical Long-Period Grating

Abstract

This research involves a novel axial strain measurement of helical long-period grating by dual-wavelength ratio. The single-mode fiber is spirally processed via the commercial welding machine. There are two obvious resonance dips near 1473 and 1517 nm, with the pitch length around 782 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m. The experimental results show that both the transmission of dip1 and dip2 rise along with increasing axial strain. The relationships between axial strain versus transmission of resonance dip and axial strain versus transmission of a fixed wavelength are studied separately. They are all linear change with axial strain. This indicates that the axial strain can be measured by the linear relationship between the transmission and axial strain. Furthermore, to eliminate the influence of light source, the dual-wavelength ratio is studied. The experimental results show that the ratio also changes linearly with axial strain. The fixed wavelength can be selected by a filter or a fiber Bragg grating, and the transmission intensity can be measured by a light intensity detector. This exploits a new way to devise high precision, low cost, and gains great potential application in the axial strain sensor.