Zhang Yongsheng, Lu Haifei, Deng Shuo, Wen Xiaoyan, Li Min
Appl Opt. 2022 Jun 10;61(17):5055-5061. doi: 10.1364/AO.456455.
The acousto-optic interaction is strongly modified and different in subwavelength confinement. Here, the optical propagation and acoustic propagation in a subwavelength-diameter fiber (SDF) have been investigated through adopting a two-layer fiber model of air-coated silica rod. Theoretical investigation indicates that SDF with a diameter below 1.2 µm supports the single mode of light propagation, and various Brillouin acoustic modes with well-spaced spectral distribution can be also excited. Due to the light propagation with the outer environment as the cladding layer, the surrounding medium will greatly affect Brillouin scattering of SDFs. Both the simulation and experiment results indicate a relatively good linear relationship between the Brillouin frequency shift of the lower acoustic modes and surrounding environmental refractive index (RI), and the higher RI sensitivity in finer SDFs can be obtained. In addition, hybrid acoustic waves have shown higher sensitivity and stability than surface acoustic modes. A RI sensitivity of about 5.1 GHz/RIU has been achieved in a 1.1 µm SDF, demonstrating its potential application in RI sensing.
声光相互作用在亚波长限制下会被强烈改变且有所不同。在此，通过采用空气包覆石英棒的双层光纤模型，对亚波长直径光纤（SDF）中的光传播和声传播进行了研究。理论研究表明，直径小于1.2 µm的SDF支持光的单模传播，并且还可以激发具有良好间隔光谱分布的各种布里渊声学模式。由于以外界环境作为包层进行光传播，周围介质会极大地影响SDF的布里渊散射。模拟和实验结果均表明，较低声学模式的布里渊频移与周围环境折射率（RI）之间存在相对良好的线性关系，并且在更细的SDF中可以获得更高的RI灵敏度。此外，混合声波已显示出比表面声波模式更高的灵敏度和稳定性。在1.1 µm的SDF中已实现约5.1 GHz/RIU的RI灵敏度，证明了其在RI传感中的潜在应用。
