Multiplexing of LPFG resonant wavelengths for abnormal reaction detection in large-scale plants by distributed high temperature monitoring

Five 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 23.7 nm, even when the temperature difference between 2 adjacent LPGs was 100 °C. This separation is large enough to distinguish the resonant wavelengths individually. 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.