We propose and demonstrate a temperature and humidity sensor based on a fluorinated polyimide film and fiber Bragg grating. Moisture-induced film expansion or contraction causes an extra strain, which is transferred to the fiber Bragg grating and leads to a humidity-dependent wavelength shift. The hydrophobic fluoride doping in the polyimide film helps to restrain its humidity hysteresis and provides a short moisture breathing time less than 2 min. Additionally, another cascaded fiber Bragg grating is used to exclude its thermal crosstalk, with a temperature accuracy of ±0.5 °C. Experimental monitoring over 9000 min revealed a considerable humidity accuracy better than ±3% relative humidity, due to the sensitized separate film-grating structure. The passive and electromagnetic immune sensor proved itself in field tests and could have sensing applications in the electro-sensitive storage of fuel, explosives, and chemicals.

中文翻译：

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光纤布拉格光栅的基于氟化聚酰亚胺薄膜的温湿度传感器

我们提出并演示了基于氟化聚酰亚胺薄膜和光纤布拉格光栅的温度和湿度传感器。水分引起的薄膜膨胀或收缩会引起额外的应变，该应变会传递到布拉格光栅光纤，并导致与湿度有关的波长偏移。聚酰亚胺薄膜中的疏水氟化物掺杂有助于抑制其湿度滞后，并提供短于2分钟的湿气呼吸时间。此外，另一个级联光纤布拉格光栅用于消除其热串扰，温度精度为±0.5°C。超过9000分钟的实验监控表明，由于采用了敏化的独立薄膜光栅结构，其相对湿度的准确度要优于±3％。