Highly sensitive fiber force sensor based on cascaded Fabry-Perot cavities and Vernier effect

In this article, we introduce a new concept for an in-line optical fiber force sensor probe, which is based on two cascaded Fabry-Perot (F-P) cavities to generate the Vernier effect and enhance sensitivity. Due to the significantly low Young's modulus of UV-cured adhesive within the sensing cavity, extremely high force sensitivity is obtained. In our initial sample, we achieved an impressive force sensitivity of -61,301 nm/N. To improve that, the optical path difference between the two cavities is further reduced, exhibiting a remarkable increased force sensitivity of -140,813 nm/N. As an application, we conducted an experiment using this highly sensitive force sensor probe to measure the evaporation rate of ethanol, a common solvent, which is 7.79 x 10-5 g/s at room temperature. The proposed sensor features advantages of high sensitivity, simple structure, ease of fabrication, compactness, which is an ideal fiber sensor probe for sensitive force measurement.