Guided acoustic waves near cutoff-induced backward double peak Brillouin spectrum in ring-core optical fibers for...

Stimulated Brillouin scattering involved with multiple optoacoustic interactions is of large interest to numerous advanced photonics applications in micro- and nano-waveguides. While the multi-peak Brillouin spectrum has been exploited in various optical fibers, these fibers often present complex and cumbersome structural designs, high costs, and limited interaction lengths. In this paper, we conduct a theoretical analysis and numerical simulation of the dynamic spectral behavior of backward Brillouin scattering in simple ring-core fibers, varying both the core thickness and diameter, applying it to dual-parameter simultaneous sensing. During the evolution of the Brillouin scattering, we find that the Brillouin gain spectrum transitions from a single peak to stable double peak due to the transition of guided acoustic modes to near-cutoff state. Furthermore, the variation in core size can maintain dual-peak characteristic and can manifest dual-peak spectrum in the two types with remarkable frequency jump due to different near-cutoff states. Finally, we employ these two dual-peak Brillouin gain spectra for simultaneous temperature and strain sensing. We believe that our fiber has an integrated advantage, such as very simple structure profile with commercial ring-core shape that is widely used, natural bending loss-resistant capacity, large frequency spacing of about 600 MHz and relatively no so small sensitivities difference. We expect that our theoretical analysis and results will be highly relevant in the study of spectral dynamics of Brillouin scattering and in the context of multi-parameter Brillouin sensors.