Improving OFDR sensing performance based on SEFR in both reference and measurement stages.

Abstract

In addition to laser frequency sweep nonlinearity, sensing point misalignment caused by a random laser frequency sweep range (LFSR) is a key factor limiting the sensing performance of the optical frequency domain reflectometer (OFDR). Here we propose a synchronous equal frequency resampling (SEFR) method for the first time to our knowledge to simultaneously compensate both the random LFSR and sweep nonlinearity. A new linear frequency sequence has been constructed to perform signal resampling of both the reference and measurement stages, which eliminates the sensing point misalignment and nonlinear frequency interval at the same time. Thus the sensing distance and accuracy of both phase demodulation (PD) and cross-correlation demodulation (CD)-based OFDR have been greatly improved in distributed strain measurement. For PD, with SEFR the sensing distance is extended to 70 m, and the strain root mean square error (RMSE) is reduced by 16 times under the worst LFSR difference of 579.4 MHz. For CD, the sensing distance is extended from 6.8 m to 70 m, and the RMSE is reduced by 41 times when using SEFR under the worst LFSR difference.