Cladding waveguide fiber Bragg grating accelerometer fabricated in single-mode fiber using femtosecond laser direct writing

Abstract

This paper presents a cladding waveguide fiber Bragg gratings (CWFBGs) two-dimensional (2D) vector accelerometer in a standard single-mode fiber. The cladding waveguides with large eccentricity are inscribed using the femtosecond laser direct writing technique with a multiple-scan method. Subsequently, FBGs are inscribed into cladding straight waveguides. Experiments were conducted to monitor the variation of the central wavelength of the CWFBGs in response to bending and vibration. The results show that the maximum bending sensitivity is 67.38 pm/m⁻¹ and the maximum acceleration sensitivity is 37.78 pm/g at an offset distance of 45 $\mu$m. According to the method described above, orthogonal CWFBGs are inscribed at the same position in the single-mode fiber, which overcomes the limitations of the geometry of multi-core fiber (MCF), achieving higher sensitivity than MCF under the same conditions. Additionally, the demodulation of multiple channels does not require a fan-in/fan-out device, reducing the cost of sensing. The findings of this study illustrate that CWFBGs offer highly sensitive 2D vector vibration measurement in a compact form factor, thus holding promising applications in miniaturized vector fiber sensing.