Calibration of temperature-sensitivity coefficient of fiber Bragg grating at ultra-low temperature

In order to address the limitation of poor reliability of temperature-sensitive coefficient calibration of grating in an ultra-low temperature environment, a reference thermometer probe and fiber Bragg grating sensor were encapsulated in a self-designed non-contact liquid-nitrogen-cooled temperature measuring mold, and calibration experiments were conducted at ultra-low temperatures ranging from 93 K to 293 K. The thermal sensitivity coefficient of the bare grating and thermal expansion coefficient of the coating were used to verify the credibility of the experimental design. The experimental results indicate that the maximum initial temperature change rate of the reference thermometer is 1.8 K/min, which effectively reduces the temperature change rate of the temperature measuring mold and improves the temperature consistency between the reference thermometer and labeled grating. The test results are in good agreement with those of comparable studies. The temperature sensitivity of the bare grating decreases from 9.18 pm/K@293 K to 2.19 pm/K@93 K due to its low temperature nonlinearity. The thermal expansion coefficient of organic modified ceramic (ORMOCER) is 3.7×10-6 K-1 at room temperature. The temperature-sensitivity coefficient of one layer of the ORMOCER coating with a thickness of 50 μm is 4.43 pm/K. At 93 K, the temperature-sensitive coefficient is 7.17 pm/K, the temperature-sensitivity coefficient and linearity of the coating grating are significantly improved. © 2022, Chinese Institute of Electronics. All right reserved.