Abstract
We propose a bend-insensitive distributed Brillouin optical fiber sensing by using a singlemode-multimode-singlemode optical fiber structure for the first time to the best of our knowledge. The sensing fiber is a graded-index multimode fiber (GI-MMF) sandwiched by two standard single-mode fibers (SMFs) with central-alignment splicing at the interface between GI-MMF and SMF to excite the fundamental mode in GI-MMF. The sensing system can resist a minimal bend radius of 1.25mm while maintain the measurement performance, with which the measured coefficients of strain and temperature are 421.6MHz/% and 0.826MHz/°C, respectively. We also demonstrate that the higher-order modes excited in GI-MMF can be easily influenced by bending, so that exciting the fundamental mode is essential for bend-insensitive distributed sensing.
Highlights
Recent years, distributed sensing system based on Brillouin scattering in single mode fiber (SMF) has been widely studied in the research field of Structural Health Monitoring (SHM) of civil infrastructures such as buildings, bridges, highway pavements and dams [1]
We propose a configuration of singlemode-multimode-singlemode (SMS) fiber structure to achieve a bend-insensitive distributed sensing in Brillouin optical time-domain analysis (BOTDA) system for the first time to be best of our knowledge, which features low cost, simple structure, and suitable for long distance
We stimulate the practical conditions by purposely introducing a single loop to the graded index multimode fiber (GI-MMF) of SMS structure at the position of ~26m with different radii varying from 1.25mm to 12.5mm with a step of 0.5mm
Summary
Recent years, distributed sensing system based on Brillouin scattering in single mode fiber (SMF) has been widely studied in the research field of Structural Health Monitoring (SHM) of civil infrastructures such as buildings, bridges, highway pavements and dams [1]. Several distributed measurement techniques based on Brillouin scattering in standard single mode optical fibers have been proposed, including Brillouin optical time-, frequency-, and correlationdomain techniques, which can be classified into two categories: “reflectometry” and “analysis.” In reflectometry systems, a relatively weak signal and a low signal noise ratio (SNR) is produced due to spontaneous Brillouin scattering , resulting in a low accuracy and small measurement scale of the distributed sensing system. We propose a configuration of singlemode-multimode-singlemode (SMS) fiber structure to achieve a bend-insensitive distributed sensing in BOTDA system for the first time to be best of our knowledge, which features low cost, simple structure, and suitable for long distance. We demonstrate that higher order modes exciting in the GI-MMF of the SMS structure are influenced by bending, so that fundamental mode exciting is essential for bend-insensitive distributed sensing
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