Distributed high temperature sensing in large-scale plants by LPFG with multiplexed resonant wavelengths

Ten resonant wavelengths could be multiplexed successfully by writing long-period gratings (LPGs) with different pitches. A preliminary distributed temperature monitoring experiment was conducted, and it was estimated that separation between 2 adjacent resonant peaks was 13.2 nm apart, even when the temperature difference between 2 adjacent LPGs was 150°C. The results clarified that this multiplexing approach enables the LPFG to detect a local high temperature caused by an abnormal reaction inside in a large-scale plant.