Characteristics Research and Optimal Shaping of Brillouin Scattering Spectrum in Multimode Fiber
LI Yong-qian1, 2, 3, FAN Hai-jun1, 2, 3*, ZHANG Li-xin1, 2, 3, WANG Lei1, 2, 3, WU Jia-qi1, 2, 3, ZHAO Xu1, 2, 3
1. Department of Electronic and Communication Engineering, North China Electric Power University, Baoding 071003, China
2. Hebei Key Laboratory of Power Internet of Things Technology, North China Electric Power University, Baoding 071003, China
3. Baoding Key Laboratory of Optical Fiber Sensing and Optical Communication Technology, North China Electric Power University, Baoding 071003, China
Abstract：The presence of multiple degrees of freedom in multimode fiber allows high-capacity communication and multi-parameter sensing. However, the presence of high-order modes in multimode fiber is not only unstable, easy to couple and radiate loss but also leads to Brillouin gain spectrum distortion, spectrum width broadening and Brillouin gain peak reduction, which seriously deteriorates the measurement accuracy and sensing reliability of the system. Therefore, studying the characteristics and shaping optimization of Brillouin gain spectrum in multimode fiber is particularly important. Firstly, the Brillouin frequency shift and the multimode fibre gain spectrum characteristics are investigated and compared with few-mode fiber and single-mode fiber. The results show that the Brillouin frequency shift of multimode fiber is related to the mode refractive index and Brillouin scattering angle. When the Brillouin scattering angle is constant, the Brillouin frequency shift is negatively correlated with the mode group number. When the mode group number is constant, the Brillouin frequency shift is positively correlated with the Brillouin scattering angle. Compared with single-mode fiber, few-mode fiber and multimode fiber have lower Brillouin gain peak and Brillouin frequency shift and wider Brillouin gain spectrum due to the influence of high-order modes. Multimode fibers have the most high-order modes, corresponding to the lowest Brillouin gain peak and Brillouin frequency shift and the widest Brillouin gain spectrum. Furthermore, two Brillouin gain spectrum shaping optimization methods of multimode fiber based on single-mode fiber are analyzed and designed. A frequency-shifted local heterodyne Brillouin optical time domain reflectometry system is constructed to evaluate the degree of shaping optimization by measuring the Brillouin scattering spectrum width and bend-tolerant capacity of two. The experimental results show that the proposed two shaping optimization methods reduce the Brillouin gain spectrum width of multimode fiber to varying degrees, and the obtained Brillouin gain spectrums have good Lorenz fitting degrees, which are 0.974 47 and 0.987 89, respectively. Using a single mode optical circulator combined with a single mode fiber alignment fusion to an multimode fiber has better shaping optimization effect and bending tolerance. The minimum bending radius and Brillouin gain spectrum width are 2.25 mm and 53.12 MHz, respectively.
李永倩，范海军，张立欣，王 磊，武佳琪，赵 旭. 多模光纤的布里渊散射谱特性研究及优化整形[J]. 光谱学与光谱分析, 2023, 43(11): 3559-3564.
LI Yong-qian, FAN Hai-jun, ZHANG Li-xin, WANG Lei, WU Jia-qi, ZHAO Xu. Characteristics Research and Optimal Shaping of Brillouin Scattering Spectrum in Multimode Fiber. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2023, 43(11): 3559-3564.
