A new absorbance sensor based on long-period fiber gratings(LPFGs)is presented,The measurand is coated on the cladding of the LPFG.It is found that the depth of the stop band of the LPFG spectrum will be strongly affected by the absorbance of the measurand if an optimum coating thickness is selected.The analysis showsthat within the optimal thickness range,the cladding modes could transform into the overlay modes and interact with the measurand more effectively.An absorbance sensitivity of 7×10^(3)is available when the sensor structure is optimized.
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