Simultaneous Measurement of Strain and Temperature by a Sawtooth Stressor-Assisted Highly Birefringent Fiber Bragg Grating

Abstract

We propose and demonstrate a highly birefringent fiber Bragg grating (Hi-Bi FBG) fabricated for the simultaneous measurement of strain and temperature. A birefringence of up to 2.96 × 10-4 was created in the FBG by inscribing a sawtooth stressor near the fiber core with femtosecond laser irradiation. This provides a method for measuring the strain and temperature simultaneously, using one Hi-Bi FBG with two parameters (i.e., the Bragg wavelength λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> and the birefringence-induced wavelength difference λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> ). Such a sawtooth stressor-assisted Hi-Bi FBG exhibits strain sensitivities of 1.24 pm/με in λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> and 2.14 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> pm/ με in λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> , and temperature sensitivities of 9.52 pm/°C in λB and 0.13 pm/°C in λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> . Moreover, the proposed sawtooth stressor can significantly increase the sensitivities of the birefringence to the applied strain and temperature. The strain and temperature sensitivities in λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> of the proposed sawtooth stressor-assisted Hi-Bi FBG are of several orders of magnitude, higher than those (i.e., 6.07 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> pm/με and 9.42 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> pm/°C in λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> ) of a straight stressor-assisted Hi-Bi FBG. Consequently, the proposed sawtooth stressor-assisted Hi-Bi FBG sensors are promising in many areas, such as smart structures and intelligent robotics.