Highly Sensitive Fabry–Perot Demodulation Based on Coarse Wavelength Sampling and Vernier Effect.

A highly sensitive demodulation method for the low-finesse Fabry–Perot interferometer (FPI) sensor is proposed and experimentally demonstrated. To generate the Vernier effect, the sampling interval of a tunable laser source is set close to the free spectral range of the FPI sensor. In order to improve the demodulation precision, the spline fitting process was applied to the sampling data. The dip wavelength of the fitted curve was chosen to measure the spectral shift. In the strain test experiment, the sensitivity of $0.01836~nm/{\mu \epsilon }$ was obtained. A controllable sensitivity is achieved by changing the sampling interval. It is convenient to balance the sensitivity and the measuring time. The method can be used to enhance the sensitivity of the preexistent low-finesse FPI sensors by changing an optical source in the sensing system. There is no need to make any changes to the FPI sensors and sensing nodes. Furthermore, the method can also be applied for other two-beam interferometry sensors. [ABSTRACT FROM AUTHOR]