NON-LINEAR BEHAVIOR OF LONG PERIOD GRATING THERMAL SENSITIVITY IN DIFFERENT SURROUNDINGS
Keywords:
Long period grating, optical sensor, non-linear thermal sensitivityAbstract
We report the thermal sensitivity dependence of long period gratings on the surroundings refractive index, with a noticeable non-linear behavior for surrounding media with refractive indexes above 1.404. For refractive indexes ranging from 1.000 to 1.447, the grating thermal sensitivity changes from 0.040 ± 0.001 nm/ºC to 0.393 ± 0.015 nm/ºC. The higher observed non-linearity occurs when the refractive index of the external medium is close to 1.447. For this case, two different average thermal sensitivities are obtained: 0.393 ± 0.014 nm/ºC and 0.213 ± 0.002 nm/ºC. If this non-linear behavior is not properly considered, the error in the measurement of the grating resonance wavelength is 3.16 nm for temperatures about 40 ºC. The presented results indicates that the non-linearity in the thermal sensitivity response is an important behavior that must be considered when a long period grating device is designed to operates as a temperature sensor in the presence of different external media, or as a refractometer working at different temperatures.
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