Vernier Effect in a Compact Strain Sensor Based on Fiber Loop Mirrors Using a 3 × 3 Coupler

In this letter, a new configuration based on two fiber loop mirrors in series using a $3\times 3$ coupler is demonstrated. This configuration is compact and can explore the Vernier effect. The results obtained were a sensitivity of 74.9 $\pm 0.2~pm/\mu \varepsilon $ for the Vernier envelope and 6.41 $\pm 0.01~pm/\mu \varepsilon $ for the Vernier carrier. These results were compared to the sensitivity of the setup using only one fiber loop mirror interferometer, obtaining 14.41 $\pm 0.01~pm/\mu \varepsilon $ . This means a magnification factor of 5.2 for the Vernier envelope. Theoretical treatment of the system was carried out, using Jones matrix calculus, and the subsequent simulation results are also presented, having obtained good agreement with the experimental data.