Tip-Packaged High-Temperature Fiber-Optic Sensor Based on Parallel Fabry–Perot Interferometers and the Vernier Effect

Abstract

A high-temperature measurement fiber sensor based on the Vernier effect is proposed and demonstrated. The sensor comprises two parallel Fabry–Perot interferometers (FPIs) constructed by the splicing of the single-mode fiber (SMF) and a micrometer-scale dimensions suspended-core fiber (SCF). These two parallel interferometers possess a high degree of symmetry and both packaged with a hollow core fiber (HCF) to provide resistance against external pollution. The HCF is charged to collapse on the other side, but the length of SCF differs between them. High-temperature tests were conducted on both a single sensing FPI and parallel structures. The impact of the reference units with different free spectrum ranges (FSRs) on the sensitivity of parallel structures was investigated through simulation and experimentation. Leveraging on the Vernier effect and the parallel structures, the sensor exhibited highest temperature sensitivities of −86.11, −99.01, and −112.66 pm/°C across a temperature range from 25 °C to 1000 °C. Furthermore, the parallel structures were subjected to three rounds of heating with a 24-h interval to verify their repeatability and stability. Additionally, a high-temperature stability error test was conducted on these tip-packaged parallel sensors, which exhibit simple fabrication, excellent repeatability, and stability across a wide temperature range. As such, they are expected to be highly practical for use in harsh environments and mass production.