Kim Jee Myung, Wee Junghyun, Peters Kara
Department of Mechanical and Aerospace Engineering, North Carolina State University, Raleigh, NC 27695, USA.
Sensors (Basel). 2022 May 30;22(11):4163. doi: 10.3390/s22114163.
Optical fibers were previously demonstrated to propagate and detect acoustic modes that were converted from Lamb waves for structural health-monitoring applications; typically, a fiber Bragg grating sensor in the optical fiber is used to detect acoustic modes. Acoustic modes can transfer from one fiber to another through a simple adhesive bond coupler, preserving the waveform of the acoustic mode. This paper experimentally investigates the coherence of acoustic waves through the adhesive coupler, using a fiber ring resonator (FRR) configuration. This configuration was chosen because the wave coupled to the second fiber interferes with the original wave after it encircles the fiber ring. We performed this experiment using different geometries of optical fibers in the ring, including a standard single-mode optical fiber, a hollow silica capillary tube, and a large-diameter multi-mode fiber. The results demonstrate that the acoustic wave, when transferring through an adhesive coupler, interferes coherently even when the main and ring fibers are of different types. Finally, we demonstrate that the FRR can be applied for sensing applications by measuring the mode attenuations in the ring due to a changing external environment (water-level sensing) and measuring the optical-path length change in the ring (temperature sensing).
先前已证明，光纤可传播和检测从兰姆波转换而来的声学模式，用于结构健康监测应用；通常，光纤中的光纤布拉格光栅传感器用于检测声学模式。声学模式可以通过简单的粘合剂耦合器从一根光纤传输到另一根光纤，保持声学模式的波形。本文使用光纤环形谐振器（FRR）配置，通过实验研究了通过粘合剂耦合器的声波相干性。选择这种配置是因为耦合到第二根光纤的波在环绕光纤环后会与原始波发生干涉。我们使用环中不同几何形状的光纤进行了该实验，包括标准单模光纤、空心石英毛细管和大直径多模光纤。结果表明，当声波通过粘合剂耦合器传输时，即使主光纤和环形光纤类型不同，也会发生相干干涉。最后，我们证明了FRR可通过测量由于外部环境变化（水位传感）导致的环中模式衰减以及测量环中的光程长度变化（温度传感）应用于传感应用。
