Recent progress in emerging directions of Brillouin optical fiber sensing: analyzing, designing, and implementing acoustic waves [Invited]

Brillouin scattering is a cornerstone of optical fiber sensing, enabling distributed measurements of temperature, strain, and birefringence, with expanding use in substance identification, radiation detection, and microwave photonics. Analyzing, designing, and implementing acoustic waves has been pivotal in developing novel Brillouin mechanisms and enhancing sensing performance. This review examines emerging branches of Brillouin sensing, focusing on newly proposed physical mechanisms and their corresponding application progress, including the transient response of Brillouin scattering, coherent forward Brillouin scattering, the quasi-matching condition of forward Brillouin scattering, and some latest advancements on efficient demodulation of forward Brillouin scattering. Furthermore, we explore some prospects and hurdles in this field, along with potentially effective solutions, highlighting a paradigm shift toward tailored acoustic-wave engineering for high-performance and multifunctional sensing.