Ultra-sensitive strain sensor composed of tapered two-mode fiber micro-cantilever inserted into quartz capillary

An ultra -sensitive strain sensor has been designed using two parallel Fabry-Perot interferometers (FPI) as well as the Vernier effect (VE) and harmonic vernier effect (HVE). This new FPI is formed between tapered two -mode fiber cantilever beam inserted into quartz capillary and single -mode fiber. We prepared two similar cantilever beam structures, namely FPI1 and FPI3. Due to the cantilever beam inserted into the capillary tube increasing the effective length of strain acting on FPI, the strain sensitivities of FPI1 and FPI3 are as high as 167 pm/mu epsilon and 83 pm/mu epsilon, respectively. In order to further improve the strain sensitivity of FPI, based on the principles of optical VE and HVE, we prepared FPI2 and FPI4 with air -cavity using capillaries. FPI1 and FPI2 were matched to form a VE sensor (named S1), while FPI3 and FPI4 were matched to form a first -order HVE sensor (named S2). The strain sensitivities of S1 and S2 are as high as -2.30 nm/mu epsilon and -2.98 nm/mu epsilon respectively. This is currently the highest reported strain sensitivity. Additionally, their temperature cross -sensitivity is only 35 n epsilon/celcius and 23 n epsilon/celcius, respectively. The proposed sensor has excellent repeatability and stability in measuring strain. In short, the proposed strain sensor has a simple structure, cost-effective, easy to manufacture, and has extremely high sensitivity, making it one of the best candidate structures for strain measurement.