Hollow Core Fiber Based Interferometer for High-Temperature (1000 °c) Measurement

A simple, cost effective high-temperature sensor (up to 1000 °C) based on a hollow core fiber (HCF) structure is reported. It is configured by fusion splicing a short section of HCF with a length of few millimeters between two standard single mode fibers (SMF-28). Due to multiple beam interference introduced by the cladding of the HCF, periodic transmission dips with high spectral extinction ratio and high-quality (Q) factor are excited. However, theoretical analysis shows that minor variations of the HCF cladding diameter may result in a significant decrease in the Q factor. Experimental results demonstrate that the position of periodic transmission dips are independent of the HCF length, but spectral Q factors and transmission power varies with different HCF lengths. A maximum Q factor of 3.3 × 10⁴ has been demonstrated with large free spectral range of 23 nm and extinction ratio of 26 dB. Furthermore, the structure is proved to be an excellent high-temperature sensor with advantages of high sensitivity (up to 33.4 pm/ °C), wide working temperature range (from room temperature to 1000 °C), high resolution, good stability, repeatability, relatively low strain sensitivity (0.46 pm/μϵ), low cost, and a simple and flexible fabrication process that offers a great potential for practical applications. A thorough theoretic analysis of the HCF-based fiber structure has been proposed. The experimental results are demonstrated to be well matched with our simulation results.