The analysis and comparison of cross-correlation and phase demodulation methods in an OFDR system for strain/temperature sensing

As a kind of distributed optical fiber sensor, Optical Frequency-Domain Reflectometry (OFDR) can realize high spatial resolution distributed strain/temperature measurement. A method of measuring Rayleigh backscatter spectrum shift by cross-correlation calculation is widely adopted in OFDR sensor system. The other approach is based on the phase shift induced by the strain/temperature variation. In this paper, we propose a digital demodulation method to achieve it. Firstly the output of the photon detector is Fourier transformed and the phase information is obtained. The cross-correlation method and phase demodulation method are compared based on the theoretical and numerical analysis. The result shows that the spatial resolution (SR) of strain/temperature sensing is decided by the sweep range of the tunable laser source, while this parameter is much larger in traditional scheme. However, better stability can be achieved in cross-correlation scheme for sharp varying strain/temperature.