Spectral shadowing suppression technique in phase-OTDR sensing based on weak fiber Bragg grating array.

A postprocessing procedure is presented to suppress spectral shadowing in phase-OTDR sensing systems based on a weak fiber Bragg grating array. A complete theoretical analysis of the interfering signals has been carried out to identify a compensation method. The proposed approach has been applied to simulated and experimental phase-OTDR in the context of vibration measurements. Fast Fourier transform has been employed to analyze the obtained results, which has verified the validity of the proposed method to suppress spectral shadowing.

Temperature characteristics of the birefringence properties of filled side-hole fibers.

The temperature characteristics of the birefringence of side-hole fibers filled with liquids or metal are investigated, aiming at providing a basis for on/off temperature sensing. Short pieces of fiber are filled and the change in birefringence is registered using measurements in reflective mode of the transmitted power through a linear polarizer at 1550 nm. The rapid change in the birefringence behavior of the fiber at the temperature of the phase transition of the filler substance is shown, and from the measurement data the phase transition temperatures can be determined as well as an estimation of the birefringence change with temperature. The experimental results are supported by numerical simulations.

Robustness analysis of an intensity modulated fiber-optic position sensor with an image sensor readout system.

An intensity modulated fiber-optic position sensor, based on a fiber-to-bundle coupling and a readout system using a CMOS image camera together with fast routines for position extraction and calibration, is presented and analyzed. The proposed system eliminates alignment issues otherwise associated with coupling-based fiber-optic sensors, still keeping the sensing point free from detector electronics. In this study the robustness of the system is characterized through simulations of the system performance, and the outcome is compared with experimental results. It is shown that knowledge of the shape of the coupled power distribution is the single most important factor for high performance of the system. Further it is experimentally shown that the position extraction error can be improved down to the theoretical limit by employing a modulation function model well fitted to the real coupled power distribution.