Research on Temperature and Strain Sensing of Novel Femtosecond Laser-Based Three-Core Optical Fiber Parallel Bragg Grating

A femtosecond laser micromachining technique is used to write optical waveguides directly into the two sides of a three-core fiber from a single-mode fiber. The intermediate fiber core is welded and aligned, with an optical waveguide length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1420~\mu $ </tex-math></inline-formula>m and an angle of 1.15°. This method realizes parallel writing technology for multicore fibers, achieving a fiber Bragg grating (FBG) signal-to-noise ratio (SNR) of 20 dB. The temperature and strain characteristics of the sensor are studied. Through experiments, the average temperature sensitivity is found to be 11.3 pm/°C, and the strain sensitivity is 1.69 pm/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula>. The sensor exhibits good temperature and strain response characteristics and stability. This method provides a novel approach to parallel writing in multicore fibers and lays a foundation for subsequent experiments involving curvature and torsion characteristics. It holds great potential for applications in ocean temperature and depth measurement.