The influence of Fabry-Perot tunable filter on dynamic strain sensing system

One of the key issues in establishing an optical fiber sensing system based on fiber Bragg gratings (FBGs) is the selection of a suitable wavelength shift detection scheme in terms of the performance it offers. By use of a compact Fabry-Perot (F-P) tunable filter, the Bragg wavelength variation can be detected with a relatively high speed and satisfying resolution. In this paper, a dynamic strain sensing system based on F-P tunable filter is described, and the F-P tunable filter is demonstrated to have a significant impact on the system. The relationship between the collected spectrum of grating and the 3-dB bandwidth of the F-P tunable filter is discussed. The optimum 3-dB bandwidth of the F-P tunable filter for most FBGs is obtained. It is exhibited in this paper that the demodulation precision and sensitivity of the strain sensing system is influenced by the nonlinearity between the transmission wavelength of the F-P tunable filter and the drive voltage. The drive voltage is rectified using interpolation algorithm. The experimental results illustrate that the average error and the maximum error of the transmission wavelength are decreased by 96.4% and 80.9% respectively. The strain sensitivity of the optimized system is below 3μe. The error between the practical strain value demodulated by the system and theoretical value is below 5%.