Development of photothermal vibrating sensor using optical fiber with a built-in Bragg grating

讨论了一种由光纤尖端制成的石英芯悬臂梁，作为一种用于测量各种物理量的实用传感器。它的工作原理是光热振动悬臂梁的共振特性随周围的物理量而变化。在共振频率的测量中，通过光纤从石英芯悬臂梁返回的光来检测振动。然而，该方法在谐振频率的测量范围内存在局限性。首先，利用多模(GI型)光纤制作了直径D-32μm、长2.4 mm的石英芯悬臂梁。虽然检测到了共振点，但其特征与通常的不同。除了共振点外，振动的幅度甚至在频率上也是变化的。此外，在共振点处，振幅也有所降低。其次，利用单模光纤制作了直径D=9μm，长度为1.1 mm的石英芯悬臂梁。虽然不可能测量到谐振的半功率宽度，但检测到了谐振点，因此，如果要用光纤实现非对称截面的石英芯悬臂梁，对提高振动的检测灵敏度是有效的。

A quartz-core cantilever fabricated from an optical fiber tip was discussed as a practical sensor for measurement of various physical quantities. Its operation is based on the principle that the resonance characteristics of the photothermally vibrated cantilever vary with the surrounding physical quantities. In the measurement of resonance frequency, the vibration was detected from light returned from the quartz-core cantilever through an optical fiber. However, the limit existed in the measurement region of resonance frequency on this method. In this study, a quartz-core cantilever was fabricated from an Bragg grating fiber for the purpose of enhancing the detection sensitivity of vibration.First, a quartz-core cantilever (diameter D-32 μm, length L=2.4 mm) was fabricated from multi-mode (GI type) grating fiber. Alhough the resonance point was detected, the characteristics were different from usual one. The amplitude of vibration were varied even at frequency with the exception of a resonance point. Also, the amplitude decreased at the resonance point. Next, a quartz-core cantilever (diameter D=9μm, length L=1.1 mm) was fabricated from single-mode grating fiber. Alhough measuerment of the half power width of the resonance was impossible, the resonance point was detected, As the results, if a quartz-core cantilever with unsymmetrical cross section would be realized using a grating fiber, it must be effective to enhance the detection sensitivity of vibration.