Wide-Range and Sensitivity-Tunable Optical Fiber Microstructures for High-Temperature Detection System

We propose fiber microstructures based on the dispersion-compensated fiber (DCF) for industrial high- temperature detection (1000 °C). The single mode fiber - dispersion compensated fiber - single mode fiber (SDS) sensor achieves a temperature sensitivity of 47.35 pm/°C in the range of 30–110 °C, which is four times greater than that of a typical fiber Bragg grating (10 pm/°C). The single mode fiber - dispersion compensated fiber (SD) sensor based on the Michelson interference (MI) principle is fabricated by splicing a DCF at the end of a single mode fiber (SMF), which effectively suppresses multimode interference and attenuates interference peaks using Fresnel reflection. The sensitivities of the SD fiber sensors with DCF lengths of 7 mm, 8 mm and 9 mm are 62.38 pm/°C, 53.45 pm/°C and 51.25 pm/°C, respectively, in the temperature range of 30–200 °C, and the free spectral range (FSR) of the interference spectra decreases with increasing DCF length. After high-temperature annealing of the fiber microstructures, the internal stress of the DCF can be effectively released, which improves the dispersion compensation performance and reduces the transmission loss. We select SD fiber sensors with a DCF length of 7 mm for high-temperature annealing and then repeat the high-temperature experiments over a wide range of 30–800 °C, and the interference spectra all show consistent redshifts. The temperature sensitivity in the range of 500–800 °C is as high as 106 pm/°C. The refractive index difference between the DCF core and cladding changes as the temperature increases from 800–1000 °C, and the redshift trend of the interference spectrum with increasing temperature is reversed to a blueshift at 920 °C. This sensor, characterized by a wide temperature range, adjustable sensitivity and good repeatability and stability in high-temperature environments, has significant application potential in industrial production.