The Distributed OTDR Measuring System with UWFBGs based on Correlation Degree Spectrum

Abstract

The distributed OTDR measuring system based on correlation degree spectrum of UWFBGs is proposed. The traditional OTDR system uses a white light source to reduce the noise signal induced by the interference from multiple reflections between UWFBGs (reflectivity of each to be 0.1%), in addition we used the optical pulse with high extinction ratio (>40dB) to reduce the noise floor of OTDR trace, so that the large number (330) of the FBGs can be detected at the end of 850m due to the low noise floor. The spectrums of 330FBGs have been characterized with a high-precision tunable filter at the receiver end. By calculating the correlation degree of adjacent spectrum we improved SNR to 35dB. The wavelength shift accuracy is 3.2pm. The accuracy of measured temperature and strain are respectively 3.2and 0.32°C.