Development of an optical fiber-based interferometer for strain measurements in non-destructive application

In this paper, an extrinsic Fabry-Perot interferometer (EFPI) has been demonstrated for strain measurements. A monochromatic light source with a wavelength of 1310 nm is propagated into a single-mode fiber and then passed through the sensing arm. Approximately, 4 % of the beam is reflected off at the fiber end generating the "reference signal", while the rest is next transmitted to the target and reflected back to the sensing arm as the "sensing beam". The interference signal is, however, generated from the superposition between two beams (reference and sensing signals) in the fiber arm. The number of interference signal also called "fringe" is, normally, directly proportional to the displacement of the target movement. Fringe counting technique is also proposed for demodulating the fringe number to the displacement information. Consequently, the displacement is then converted to the strain value by referring to a basic of strain theory. A cantilever beam fastened to a mechanical wave driver has been utilized as a vibrator for the experimental studies. Two experiments have been investigated for the sensor performance's study. By varying the frequency excitation from 60 to 180 Hz, and also the amplitude excitation from 0.25 to 5 V, the output strain range of 0.082-1.556 and 0.246-2.702 has been apparent, respectively. In addition, a commercial strain sensor has also been used as a reference, leading to an average percentage error of 1.563 %.