Highly Sensitive Displacement Sensor Using Open Fiber-Optics Air Bubbles

A microfiber-optics interferometer was proposed, and the theoretical analysis and experimental demonstration were characterized in detail. The device comprised a Fabry-Perot interference (FPI) structure with an open-cavity, whereby a hollow core fiber (HCF), spliced to the single mode fiber (SMF), was collapsed and swelled into a thin-wall air bubble by multiple discharge operations. The closed bubble was then partially opened by using a micromachining technology, i.e., the focused femtosecond laser was utilized to ensure that the removed portion of the wall was precisely positioned over the cavity. The remaining wall was acted as a support beam that was easy to deform by external pressure. The smooth inside surfaces of the opened air cavity reflected light backwards to the leading-in SMF, resulting in a well-defined interference spectrum. For exerting the micropressure on the top of the open cavity and making the support beam bend, the proposed sensor shows a high resolution of 0.42 μm for the detection of displacement by simply monitoring the interference wavelength shift.