MOF-based fiber-optic iodine vapor vernier sensor with temperature crosstalk reduction by TOC＆TEC

• The polymer waveguide doped with UiO-66-PYDC enables selective detection of iodine vapor. • The optical fiber sensor uses vernier effect to achieve sensitivity amplification, and M = 19.86. • The iodine vapor detection limit of the sensor can reach 10 ppb, and it can be lower theoretically. • Temperature sensitivity as low as −3.35 ppm/°C based on mutual elimination of TEC and TOC. Monitoring of iodine vapor during spent fuel reprocessing plays an important role in nuclear safety and environmental health. In this article, we proposed a temperature insensitive fiber-optic vernier sensor based on dual Fabry-Perot interferometer (FPI) for trace detection of iodine vapor in 0°C-80°C. The sensing structure adopts a single-mode fiber (SMF)-hollow-core fiber (HCF)-polymer waveguide structure, which adjusts the spectrum by controlling the ratio of the air cavity length to the polymer waveguide length. The polymer waveguide uses polycarbonate (PC) and polyamide (PA) as composite matrix, doped with N-functionalized metal–organic frame material UiO-66-PYDC to achieve specific recognition and capture of iodine vapor. The research results indicate that the sensitivity of the sensor for detecting iodine vapor is 77.76 pm/ppb, and the detection accuracy reaches 10 ppb in actual calibration. Meanwhile, due to the matching of thermal optical coefficient (TOC, decrease) and thermal expansion coefficient (TEC, increase) of the mixed matrix, the influence of temperature on the optical path of the polymer waveguide is weakened, and the temperature sensitivity is as low as −3.35 pm/°C. Due to the similar chemical properties of iodine isotopes, this work is not only a pioneering attempt to use optical fiber sensors to detect iodine vapor, but also has a promising application in the monitoring of radioactive iodine waste gas in nuclear industry.