3D printing fiber-tip integrated Fabry–Perot interferometers for ultrasensitive RI sensing with an enhanced Vernier effect

An ultrasensitive refractive index (RI) sensing technology based on an enhanced Vernier effect is proposed, which integrates a polymer Fabry-Perot interferometer (FPI) with an open cavity FPI on the tip of a seven-core optical fiber. Interference spectra of the polymer FPI and the open cavity FPI shift to opposite directions as the ambient RI changes, thus leading to the enhanced Vernier effect. Investigations of RI sensitivity and temperature dependence of the proposed fiber sensors are carried out. Taking advantage of the enhanced Vernier effect, we demonstrate a remarkable sensitivity of 19742.86 nm/RIU within the RI range from 1.39 to 1.395. The sensor exhibits substantial advantages such as ease of fabrication, compact structure, high sensitivity, and good repeatability, providing a practical and competitive solution for RI sensing.