Ultrasensitive Hydrogen Sensor With Vernier Effect by Dual Parallel Structured Fiber-Optic Fabry-Perot Interferometers

A novel dual parallel structured fiber-optic Fabry-Perot interferometers (FPIs) for ultrasensitive hydrogen (
${{\text{H}}_{2}}$
) sensing using the Vernier effect is proposed and demonstrated. Leveraging the high mechanical strength and chemical stability of hexagonal boron nitride (hBN), a nanoscale hydrogen-sensitive thin film of palladium (Pd)-decorated hBN is prepared and integrated with optical fiber to form a probe-type FPI hydrogen sensor. To further enhance the sensitivity, dual FPIs with similar but different cavity lengths are connected in parallel to exploit the Vernier effect, resulting in a significant amplification factor. The sensitivity of dual parallel structured FPIs based on the Vernier effect is
$-$
14.19 nm/%, which is 9.27 times higher than that of the individual FPI within the
${{\text{H}}_{2}}$
concentration range of 0
$ \sim$
1%. Moreover, as the dual FPIs possess similar temperature coefficients, the Vernier effect reduces the impact of ambient temperature on the sensor, yielding a temperature coefficient as low as
$ \sim$
46 pm/
${}^\circ \text{C}$
. Additionally, the sensor offers several advantages, including good repeatability, fast response time (
$ \sim$
31.3 s), compact structure, easy preparation, and low cost, making it a practical solution for detecting trace amounts of hydrogen.