Range limitations of optical frequency domain reflectometry with all-grating fiber for distributed strain and temperature sensing

Abstract

In distributed strain or temperature sensing applications such as structural health monitoring, optical frequency domain reflectometry (OFDR) is often used to interrogate all-grating fiber (AGF), which consists of many weak, nominally identical Bragg gratings spatially multiplexed on a single optical fiber. In order to investigate the limits of OFDR-based distributed strain sensing using AGF, we develop a model that considers the critical fact that these Bragg gratings are not identical. We find that while the “auto-correlation term” significantly impacts OFDR measurements of the complex coupling coefficient, it typically does not cause a significant error in distributed strain or temperature measurements. On the other hand, the breakdown of the Born approximation generally limits the sensing range of AGF. Our model is verified by measurements on all-grating fiber using a commercially available OFDR. We propose and verify novel solutions to extend the sensing range of AGF by controlling the properties of the non-identical Bragg gratings.