Lateral Offset Single-Mode Fiber-Based Fabry–Perot Interferometers with Vernier Effect for Hydrogen Sensing

A high-sensitive optical fiber hydrogen (H 2 ) sensor with Vernier effect by cascading three Fabry–Perot interferometers (FPIs) has been proposed. It is prepared by welding three sections of a single-mode fiber with a lateral offset structure and coating polydimethylsiloxane (PDMS) at the offset part to form three cascaded FPIs and generate a Vernier envelope spectrum. To realize H 2 sensing, the hydrogen-sensitive material Pd/WO 3 is fabricated and coated on the outside of the PDMS. Pd/WO 3 will generate local heat when in contact with H 2, which will cause the thermal expansion and refractive index change of PDMS and finally lead to the Vernier envelope wavelength shifting with the change of H 2 concentration. Due to the Vernier effect, the H 2 sensor can achieve a linear measurement sensitivity of 6.214 nm/% in the concentration range of 0–1%, which is 16.11 times that of a single FPI. The proposed H 2 sensor possesses advantages of high sensitivity, easy preparation, compact structure, low cost, and easy long-distance transmission.