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The High Spatial Resolution Demodulation Method of FBGs Based on the Section Demodulation and OTDR

The section demodulation method that a number of dense gratings are considered as a whole is proposed for distributed weak fiber Bragg Grating (FBG) sensing. This scheme uses the accumulation of the optical time domain reflectometry of all gratings in the section as a section spectrum. The section spectrum can be regarded as the envelope of the spectrum of gratings in this section. The spectrum drifts with the temperature but it's width does not change when all of the gratings in the section under the same temperature. If the temperature of one grating changes, its spectrum will deviate from the section spectrum of all. Therefore, it is possible to calculate the change of temperature of the dense FBGs. The system can be applied to fire alarms, which can effectively detect small-scale fires and greatly reduce the time of fire detection.