Highly sensitive strain sensor based on a long-period fiber grating with chain-shaped structure

Abstract

In this paper, a novel chain-shaped long-period fiber grating (CS-LPFG) for strain measurement is investigated and experimentally demonstrated. This structure is achieved by polishing periodic slant planes on a single-mode fiber with a high-frequency <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">C</mml:mi> <mml:mi mathvariant="normal">O</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> laser. The chain-shaped structures improved the strain sensitivity of the sensor while shortening the length of the sensing unit. Experimental results show that the strain sensitivity of CS-LPFG is 34.8 pm/ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mtext>µ</mml:mtext> <mml:mtext>ε</mml:mtext> </mml:math> in the range of 0–650 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mtext>µ</mml:mtext> <mml:mtext>ε</mml:mtext> </mml:math> , and the total length of the sensing unit is significantly reduced to 7.5 mm. Meanwhile, the temperature-strain cross talk is 1.6 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mtext>µ</mml:mtext> <mml:mtext>ε</mml:mtext> </mml:math> /°C, which is much lower than that of most fiber strain sensors.