High-resolution and large dynamic range fiber extrinsic Fabry–Perot sensing by multi-extrema-tracing technique

An approach based on the multi-extrema-tracing technique for measuring the cavity length of fiber extrinsic Fabry–Perot sensors is proposed and demonstrated. The wavelength-scanning method is used to get the high-resolution central wavelength of the interference extrema with the calibration of the HCN gas cell. By deriving the interference order number of each interference extremum with little ambiguity through an improved linear fitting algorithm, the cavity length can be retrieved by tracing the wavelength of all extrema in the scanning wavelength range. The experimental results show that the interrogation resolution can reach 1 nm, which is demonstrated for a large dynamic range of cavity lengths from ∼250 to ∼3000  μm.