Enhancing the performance of Rayleigh backscattering based fiber optic sensors

In this thesis, firstly, an Optical Time Domain Reflectometer (OTDR) system was simulated using OptiSystem which was successful at locating connector positions along a 10 km test fiber. Then the simulated OTDR system is constructed in laboratory to successfully detect connector positions along a 22 km fiber. Furthermore, the effects of laser pulse width and peak to peak voltage of low frequency (LF) trigger signal over the received signal are observed. The detection capabilities of biased and non-biased photo detectors are observed. A MATLAB remote control code is created to fully automate data acquisition process and parameter changes. Standard Commands for Programmable Instruments (SCPI) command protocol is utilized in the remote-control code. Then, the performance of the OTDR system is tried to be improved. The high reflection loss effects of connectors are negated using splices. The effect of an isolator at the end of the test fiber is observed. A GUI is designed to improve OTDR monitoring. Finally, an investigation of different types of fiber for their compatibility in a Rayleigh based optical time domain reflectometer (R-OTDR) temperature sensor setup is conducted. A reference test setup consisting of standard single mode fiber (SMF) is observed to constitute a background for comparison. In this setup, the Rayleigh response of -50.25 dBm and a temperature sensitivity of 0.002 dB/°C is achieved. Then Rayleigh responses for highly nonlinear fiber (HNLF), dispersion shifted fiber (DSF) and polarization maintaining fiber (PMF) are observed. The Rayleigh responses were: HNLF had -39.83 dBm, DSF had -34.03 dBm and PMF had -31.34 dBm. Since PMF showed the best Rayleigh response it was selected to be observed as fiber under test (FUT) in a classical R-OTDR temperature sensor setup. With the PMF used in temperature R-OTDR setup a temperature sensitivity of 0.018 dB/°C was achieved. As a result, it has been determined that PMF fiber has high temperature sensitivity in R-OTDR installations compared to SMF. It has been shown that temperature measurements can be made on shorter lengths of fiber with a much simpler setup using PMF as opposed to the more complex alternatives.