Abstract
Fiber Bragg grating (FBG) cascaded with balloon-like sensing structure with up-tapered Mach-Zehnder interferometer (MZI) inner embedded is proposed and experimentally investigated for relative humidity (RH) and temperature measurement. The up-tapered MZI is formed by splicing a section of no-core fiber (NCF) between two sections of single mode fiber (SMF) to inspire cladding mode. The diameter of the balloon-like sensing structure adopted in this letter is 3.0 cm after optimization. RH measurement is carried out at room temperature, and the sensitivity is 6.1 pm/%RH in the range of 9.73–80.37 %RH. Meanwhile, the temperature sensitivity is 11 pm/°C in the range of 15.9–26.2 °C. Compared with transmission sensing structure, the balloon-like sensing structure makes it easier to contact with measurement environment in practical application. In addition, the proposed sensor is simple manufacture technology and low cost.
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