Abstract

The Vernier effect of two cascaded in-fiber Mach–Zehnder interferometers (MZIs) based on a spherical-shaped structure has been investigated. The envelope based on the Vernier effect is actually formed by a frequency component of the superimposed spectrum, and the frequency value is determined by the subtraction between the optical path differences of two cascaded MZIs. A method based on band-pass filtering is put forward to extract the envelope efficiently; strain and curvature measurements are carried out to verify the validity of the method. The results show that the strain and curvature sensitivities are enhanced to $-8.47\mathrm{pm}/\mathrm{\mu \epsilon }$ and $-33.70\mathrm{nm}/{\mathrm{m}}^{-1}$ with magnification factors of 5.4 and $-5.4$, respectively. The detection limit of the sensors with the Vernier effect is also discussed.

© 2019 Optical Society of America

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