Demonstration of Improving the Performance of a Fibre Optic Displacement Sensor Using the Optical Harmonic Vernier Effect by Cascading Tapered Optical Single-Mode Fibres

An experimental demonstration for generating harmonics in the optical Vernier effect (OVE) by cascading tapered single-mode fibres (SMF28) is presented. The tapered optical fibres conformed to a pair of in-series Mach-Zehnder fibre interferometers (MZFI), in which one MZFI was a reference while the other was a sensor. The first-order harmonic was achieved by increasing the distance between tapers of the sensor MZFI by a multiple of (i + 1) times the distance between tapers of the reference MZFI plus a mismatch factor. A series of experiments using an individual MZFI and two MZFIs with traditional and harmonic OVE as displacement sensors were performed to compare their sensitivities and magnification factors and demonstrate the improving the sensitivity. The displacement sensor with the first-order harmonic exhibited a maximum sensitivity of −33.3 nm/mm with an M-factor of 8.53 in the mm range.