In-situ adjustable fiber-optic piezometer based on parallelly structured external Fabry-Perot interferometers with Vernier effect and its harmonics

Translating interferometric applications into practical field use with the required flexible precision and measurement range, is a recognized challenge. We report an in-situ adjustable fiber-optic piezometer based on parallelly structured external Fabry-Perot interferometers (EFPIs) Vernier effect its harmonics. By accommodating EFPI structure fixed cavity length, EFPIs are utilized as referencing fiber (RFP), sensing (SFP), respectively. The amplified sensitivity formed by connecting RFP SFP in parallel via 3 dB optical coupler. simply tuning length of RFP, magnification factor M continuously adjustable. Using two prototypes SFP1 SFP2, water level performed fundamental (FVE) mode harmonic (HVE) mode. Experimental results demonstrate that FVE mode, can be predictably tuned from ?0.15 nm/cm to ?7.02 =1?48 for SFP1, ?0.31 ?7.22 =1?23 SFP2. In HVE further enhanced high ?9.08 nm/cm, while performance fluctuates during adjusting process. Benefiting merits simplicity composition, robustness, remote capability, proposed scheme applied various applications.