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Resonant wavelength and amplitude of the long period fiber grating (LPG) is very sensitive to changes in the external environment , the LPG sensor without reflection , sensing and measuring system does not require isolation , light weight , easy fiber coupling , without electromagnetic interference and has a good temperature , bend , twist , concentration , and refractive index sensitivity , so it 's more and more attention , more and more extensive . This article take a combination of theoretical and experimental research is 1650nm band linear characteristics of long period fiber grating for temperature sensing experimental study . On the one hand , in theory , combined piecewise uniform method , the mode coupling theory and fast Fourier transform analog 1650nm band LPG spectral response characteristics , delay and dispersion characteristics of multi-mode coupling characteristics and temperature sensing characteristics ; and the coupling strength are π / 4 and π / 2 when the LPG, cascade LPG and the spectral response characteristics of a plurality of cascaded LPG analyzed; while the the LPG temperature sensing aspects discussed different cladding material thermal light coefficients or a different grating period under the influence of characteristics . On the other hand , from the experiment , the use of cycle pressure the fiber produces microbending principle LPG structure design of the introduction of a stress type and use it writes LPG 1650nm band experimental study of the temperature sensing ; setting a control group experiments to illustrate the temperature stability of the sensor . Draw LPG temperature sensor sensitivity is about 0.4nm / ℃ , with the theory are in good agreement , and for the insertion loss in the experiment , been some analysis of the extinction ratio, temperature sensing , and the refractive index of the impact . This paper for 1650nm at U -band fiber sensing has very important significance .
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