Simple wavelength-to-phase mapping FBG interrogation method

ALEJANDRO GIORDANA; ENRIQUE SICRE; RICARDO DUCHOWICZ

Porto

Congreso; RIAO-OPTILAS 2013; 2013

SPIE

In this work an interrogation technique for FBG sensors is presented. The method is based on the employment of a two fixed filters scheme and considering a wavelength-time transformation procedure. Proposed scheme uses a externally modulated broad band source, an optical circulator and three Bragg gratings fixed in three different fiber branches , one acting as sensor (FBG)and other two (FBG1 and FBG2) acting as calibration Standards. Spectral positions of the maximum of these gratings are shifted each other by DFI while the maximum of FBG lies between the maximum of FBG1 and FBG2. Moreover, a relative optical time delay between the reflections of both standard gratings is introduced including a path length DL) in one of the branches. Reflections from both gratings are added by employed a 50/50 coupler. Considering for favorable cases of SNR, a relative phase of tenth of degree can be determined in practice, a 20°/nm sensibility should be equivalent to an error of 5 pm for the wavelength determination, while one with sensitivity of 400°/nm reached an error of 0.25 pm. In the present work, a sensitivity of 600º/nm has been experimentally demonstrated. This system combines low cost and high flexibility to be customized in a particular application