High sensitivity Fabry-Perot interferometer based on offset splicing fibers and Vernier effect for strain measurement

An all-fiber Fabry-Perot interferometer (FPI) strain sensor based on offset splicing fibers and Vernier effect is proposed and experimentally demonstrated. The proposed sensor consists of two separated air-cavity FPIs connected by a long section of single mode fiber (SMF) in a fiber link. The two separated FPIs have approximately equal optical paths, so that the Vernier effect can be generated. One FPI is used as the sensing FPI (SFPI) for strain measurement, which is formed by splicing a section of microfiber between two SMFs with large lateral offset. The other FPI is used as the reference FPI (RFPI) to employ the Vernier effect and amplify the sensitivity, which is formed by splicing a section of silica tube between two SMFs. Compared to a single FPI based sensor, the strain sensitivity of the proposed sensor with Vernier effect can be improved by tens of times. The strain sensitivity of our proposed sensor reaches 1.3 nm/μe, which is the highest strain sensitivity of fiber sensor based on FPI and wavelength demodulation mechanism. Since the aircavity SFPI is insensitive to temperature, the proposed sensor also exhibits low temperature sensitivity of 50.2 pm/℃. With the advantages of high strain sensitivity, low temperature cross-sensitivity, compact size and easy fabrication, the proposed sensor has great applications in many fields.