Intermodal interferometer for strain and temperature sensing fabricated in birefringent boron doped microstructured fiber

Abstract

We present a compact in-line fiber interferometric sensor fabricated in a boron doped two-mode highly birefringent microstructured fiber using a CO2 laser. The intermodal interference arises at the fiber output due to coupling between the fundamental and the first order modes occurring at two fiber tapers distant by a few millimeters. The visibility of intermodal interference fringes is modulated by a polarimetric differential signal and varies in response to measurand changes. The proposed interferometer was tested for measurements of the strain and temperature, respectively, in the range of 20-700 °C and 0-17 mstrain. The sensitivity coefficients corresponding to fringe displacement and contrast variations are equal respectively for strain −2:51nm=mstrain and −0:0256 1=mstrain and for temperature 16:7pm=°C and 5:74 × 10−5 1=°C. This allows for simultaneous measurements of the two parameters by interrogation of the visibility and the displacement of interference fringes.