Microfiber Bragg Grating Hydrogen Sensors

In this letter, hydrogen sensors based on microfiber Bragg gratings (mFBGs) with palladium coatings are presented. The reflection peak of a grating with a diameter of 3.3 μm can shift by -1.08 nm when exposed to hydrogen with a concentration of 5%, as a result of the evanescent field interaction with the coated palladium film. The resultant wavelength shift is 26 times higher than its counterpart in the conventional singlemode fiber. Calculated and measured results show that thinner gratings enable higher sensitivities due to the stronger evanescent fields. The temperature sensitivity increases by only 27%, and thus the temperature cross sensitivity is greatly lowered. The response time of the reflection peak shift is ~60 s.