An FBG-FPI Accelerometer Based on Femtosecond Laser-Written Ultrashort Fiber Bragg Gratings

We demonstrate an improved Fabry-Pérot interferometer (FPI) fiber accelerometer using ultrashort fiber Bragg gratings (FBGs) fabricated with femtosecond laser plane-by-plane direct writing. The length of these ultrashort FBGs ranges from 30 to $100~\mu $ m, with a 3-dB bandwidth spanning 24.25–7.08 nm. Two identical ultrashort FBGs create FP interference along the grating’s Gaussian spectral line, achieving a high extinction ratio (>26 dB). The fabricated ultrashort FBGs and FBG-FP interferometric structures exhibit high-temperature stability in the $25~^{\circ } $ C– $500~^{\circ } $ C range, with the temperature sensitivities of 12.67 pm/°C and 12.75 pm/°C, respectively. The interferometric fiber accelerometers are formed by combining ultrashort FBGs with a spring-mass transducer structure and 5 m of sensing fiber, showcasing the sensitivities of approximately 90 rad/g within the operational frequency band of 10–500 Hz. The linearity is impressively high at 99.98%, and the accelerometers operate reliably in the temperature range of $25~^{\circ } $ C– $300~^{\circ } $ C. The accelerometers are simple to manufacture, compact, and highly temperature-resistant. In addition, this accelerometer can cascade to realize multipoint quasi-distributed detection based on $\varphi $ -OTDR technology, which is expected to play an important role in the seismic exploration of deep oil and gas wells.

I. Introduction

Fiber-optic accelerometers have garnered significant attention in the realm of oil and gas exploration [1], [2], [3], [4]. Compared with electrical accelerometers, fiber-optic accelerometers have many advantages, such as compact structure, high sensitivity, robust resistance to electromagnetic radiation, and elevated temperature tolerance. The electrical accelerometers face challenges in maintaining stable operation above 210 °C. These characteristics render fiber-optic accelerometers well suited for deployment in harsh environments, such as oil and gas wells.