Optical EngineeringTemperature dependence of fiber optic Bragg gratings at low temperatures
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The temperature dependence of the Bragg wavelength of fiber optic gratings was measured at temperatures from 4.2 to 350 K. The measured wavelength dependence at room temperature (293 K) corresponds to a refractive index dependence of dn/dT=9.1×10-6 /°C, which agrees with earlier results for fused silica. However, dn/dT decreases with lower temperatures, declining to 3.5×10-6/°C at liquid nitrogen temperature (77 K), and to approximately zero at liquid helium temperature (4.2 K). The Bragg wavelength of a fiber grating embedded in a composite material displayed the same temperature dependence as a non-embedded grating.